Fish Schooled

Porcupinefish

2011-02-05T19:13:00.001-03:30

Porcupine fish are almost cartoon like in their appearance. They belong to the family Diodontidae. They are closely related to pufferfishes, but possess big heavy spines on their body. They are found throughout the world in shallow temperate and tropical seas. They range in size from 7 to 50 cm depending on the species of which there are around 15.

Porcupine fish are slow and as a result are unable to escape very easily from predators. One evolutionary tactic that they have up their sleeve is the ability to blow up their body by gulping in water to their gut. In larger species the spines then become erect whereas small species always have erect spines. They can double their size, and it helps to avoid been eaten since they are then hard to swallow (with the added help of been covered in spines). Here is a good example of how such a tactic works.

If this wasn't enough some species are also poisonous, with the neurotoxin been produced in their organs such as the liver. The tetrodotoxin is 1200 times more potent than cyanide!!! Interestingly, this poisen is likely to be produced by bacteria which are taken in through the animals diet. Evidence for this comes from the fact that porcupine fish in captivity are not poisonous. Despite all these defense mechanisms sometimes they do fall prey to sharks or orcas.

Despite been slow these fish are highly manouverable as is evident when watching them feed. Many come out at night searching for their favourite prey.....mollusks. To our eyes the prey may not be obvious but the porcupine fish will detect their prey, position themselves over the sandy spot, and blow water over the sand exposing their dinner. It could be that porcupine fish detect water jets of their prey that are produced as they breathe out water and this is why they are able to detect them from under the sand.
Porcupine fish have a mouth that in appearance resembles a beak, which is actually made up of fused teeth. This set up is ideal for crushing up the shells of mollusks.

Deep Sea Creatures

2010-11-26T07:20:00.000-03:30

In 2009 I went out on deep sea fishing vessels in New Zealand as a scientific observer. Although the conditions were tough you did get to see fish species that you probably would never encounter under any other conditions. Here are some of these strange sea creatures.

Giant Black Ghost Shark

Electric Ray

Fur Seal

Cape Pigeons

Thresher Shark

Porcupine Fish

Sunset

Elephant Fish

Sunfish

Sealion/Albatross

Prickly Dogfish

Dealfish

Lizardfish

Blobfish

Whale

Elongate Dory

Scaley Stargazer

Postdoctoral Research Begins - Finding Sites

2010-11-23T17:46:00.000-03:30

In the last week I have begun to work on my new postdoctoral research that focuses on how elevated turbidity levels can impact on exotic and native fish populations. This work forms part of a grant that I was awarded earlier in the year, and will continue to fund me for the next few years.

I arrived back in New Zealand this last Saturday and have been looking at sites to initiate field sampling. I will be working in the Waikato River in New Zealand. The Waikato River is the longest river in New Zealand running for 425 km in the North Island. It has a strong turbidity gradient that I aim to sample fish biodiversity along. Some site searching managed to turn up some turbid sites and some clear water sites. Here are some pics.

Whangaparino River Turbid Site

Waikato River Turbid Site

Waikato River Clear Site

Koi Carp Feeding In Turbid Waikato Tributary

Sustainable Seafood

2010-11-02T18:35:00.000-02:30

We are told time and again that we need to eat more seafood for a healthier diet. But how does this work when, globally, fish populations are in massive decline. Barton Seaver, sustainable seafood advocate and chef, gives his opinion in this 10 min video. Enjoy.

Should Fishing Be Protected?

2010-11-02T14:16:00.000-02:30

So here is an interesting topic, which is bound to produce anger and anxieties on both sides of the fence. Today (Nov. 2) voters in Arizona, Arkansas, South Carolina, and Tennessee are going to the polls to decide whether hunting and fishing should be protected under each states constitution. When something is protected then it becomes very difficult for the courts to take that right away from you. So by doing this today it is ensuring that fishermen will have a right to catch fish for future generations.

This has largely come about because recreational fishermen have become fearful of recent attacks by PETA (People For The Ethical Treatment Of Animals) who have campaigns against fishing - viewing it as cruel and unnecessary. PETA are nothing to be ignored, and honestly, if I were a fishermen I would be concerned too. By implementing these laws they protect their 'right' to fish. I think that both hunting and fishing should be allowed if it is undertaken responsibly.

The problem is that PETA have made this into an animal cruelty issue when it should be a conservation issue. With these laws in place it would be very difficult for any government agency to reduce fishing if this action was resulting in a significant reduction in fish populations. It is already difficult for these agencies to enforce current regulations to stop recreational fishers from overfishing, and the last thing we need is to make this job even harder! For example, what if fish stocks were depleted in an area and the government agency wanted to stop fishing in that area to help them recover? Fishermen might argue that it is their constitutional right to fish there. Recreational fishermen tend to be very resistant, maybe even a bit touchy, when it comes to other people telling them what they can do with their fish. This can sometimes be despite mounting evidence that that fish stock may be in trouble. One only needs to remember the arguments commercial fishermen made when the scientists told them the cod stocks were running out.

In the end people need to remember that we all want the same thing. I want to be able to go diving and see fish in their natural environment. Fishermen want to be able to go out and fish. The emphasis should not be on protecting the right of the fishermen, or even PETA's animal cruelty agenda, the focus should be on protecting fish stocks so we can all enjoy them.

X Fish

2010-10-26T16:00:00.002-02:30

Kansas has agreed to designate Xiphactinus or X-fish the states official fossil. This fish was found within a Kansas prairie, which was once covered by water. This was after a petition with over 3000 names on it.

Hmmmm fossils in Kansas how will the creationists feel about that?

Fish vs. Turtle

2010-10-26T00:46:00.000-02:30

Well its high time I did a post. So here is a short one.....but worth it. Bad commentary aside it's worth watching!

Cave Angelfish

2010-08-03T23:22:00.001-02:30

Member of the family Balitoridae (Loaches) belonging to the order Cypriniformes (Carps). This group of fish is known for their non-visual senses and its a good thing since this fish is perhaps one of the most specialised species on earth inhabiting only waterfalls within caves in Thailand. This fish has no eyes and lives out its entire life within the cave. They hang on to rock with microscopic hooks on their flattened fins. Their diet is bacteria. They were filmed for the first time for the BBC documentary Planet Earth.

Would You Eat Fish From The Gulf Of Mexico?

2010-08-02T20:43:00.000-02:30

BP's chief operating officer has said that he would eat fish from the Gulf of Mexico and would let his family eat it, too. This from the Associated Press. His reasoning is that the USA governmental bodies wouldn't allow unsafe fish to be eaten. I find this interesting after all that has gone down in the meat packing industry. But my main question I want to ask is......

Would you?

Gender Bending In The Long Dase Minnow

2010-07-30T12:23:00.001-02:30

An article in the Vancouver Sun today discusses how scientists from the University of Calgary have found that Long Dase Minnow in Southern Alberta are feminising. In fact 90% of fish in two of the provinces rivers are female. This is attributed to man-made contaminants entering the rivers and includes chemicals such as pesticides, flame retardants, steroids, growth hormones and birth control pills. Nearly all locations studied showed that males had elevated levels of a protein that is typically only found in the girls. The two main culprits are agriculture and waste water that has not been treated sufficiently. Sigh.

Socializing Makes Thick-Skinned Fish

2010-07-29T16:17:00.000-02:30

Cyprinid fishes (carps) show fright, or escape behaviour, when smelling alarm signals produced by conspecifics. These chemical alarm signals are found within special club cells and are released when these cells are ruptured. In nature, fish possessing the alarm club cells may become aware of a predator as it becomes labelled with the alarm pheromones when ingesting prey. In cyprinids it has been found that higher club cell densities exist in regions where there is a high abundance of predators. Higher club cell densities means the fish is able to produce a greater volume of alarm pheromones. Important when a predator could be lurking around any corner. The authors in this study hypothesized that club cell density is plastic in regards to predator presence.

For the study they raised crucian carp individually and in groups of four. For both rearing types, fish were exposed to the skin extracts of either conspecifics (alarm signals) or brown trout (without club cells), and provided food in either low or high food rations. Interestingly, they did not find an association with club cell density and the presence of an alarm pheromone or predator chemical cue. However, what they did find was that club cell density increased when fish were living in close quarters with conspecifics (ie group of four fish).

The data from this study suggests that group-raised fish are more chemically on guard than those raised singly. The data shows that club cell density can show a ten-fold increase through an increased feeding regime combined with group rearing. Club cell density is plastic and is likely to be controlled through internal physiological regulators such as blood androgen levels, but also through external regulators such as nutritional status and growth promoting factors via chemical sensing. But in the end it just makes sense to not spend growth energy on lots of alarm substances when there will be no one else around to heed your warning.

Stabell, O., & Vegusdal, A. (2010). Socializing makes thick-skinned individuals: on the density of epidermal alarm substance cells in cyprinid fish, the crucian carp (Carassius carassius) Journal of Comparative Physiology A DOI: 10.1007/s00359-010-0550-4

Fisheries Collapse: When Predator Becomes Prey

2010-07-28T12:48:00.013-02:30

In marine ecosystems overfishing of top predators has led to major changes in ecosystem properties at the most basic level. This is likely to be because a change in the food web directly changes the feedback mechanisms that are inherent within any ecosystem. In marine ecosystems a typical pattern occurs after overfishing, which includes a low abundance of predatory fish and a high abundance of small, pelagic, forage fish. These small fish are themselves predators of the eggs and larvae of marine organisms including the large predatory fish. Thus it is hypothesized that by controlling the numbers of these small forage fish the large predators are ensuring their recruitment for the next generation.

In this study they analysed a 44 year long time series of cod recruitment and herring abundance in the North Sea. In this ecosystem, atlantic cod are the top predators feeding on the small and pelagic herring. Herring have been shown to feed extensively on cod eggs, and therefore may negatively effect cod recruitment when they are found in high numbers. This study showed that abundance of herring in the North Sea was negatively correlated to the recruitment of cod. Other studies have found that this may be due to a reduction in prey for both groups of fish as was found in the Baltic Sea where overall zooplankton biomass was reduced. But this study controlled for larval food and still found a negative relationship. Thus, it would seem that a reduction in atlantic cod leads to an increase in herring. This increase in herring then reduces the recruitment of atlantic cod as their larvae and eggs are consumed by the herring.

Catastrophic shifts in ecosystems has been referred to as 'ecosystem hysteresis'. Ecosystem hysteresis occurs when changes in the state of an ecosystem are path dependent. Ecosystem hysteresis is generated by various forms of reinforcement that keep the ecosystem in a given state. Often there are two ecosystem states that occur under different critical conditions. This predator-prey reversal may keep the North Sea in a herring dominated state. It begs the question of whether it is important to reduce herring numbers in order to restore cod populations. Something that if true will bring a smile to any fisherman's face.
Fauchald, P. (2010). Predator–prey reversal: A possible mechanism for ecosystem hysteresis in the North Sea? Ecology, 91 (8), 2191-2197 DOI: 10.1890/09-1500.1

Episode 1: Birth of an Ocean - Episode Guide - The Series - One Ocean: The Nature of Things with David Suzuki: CBC-TV

2010-07-25T00:23:00.000-02:30

Episode 1: Birth of an Ocean - Episode Guide - The Series - One Ocean: The Nature of Things with David Suzuki: CBC-TV

Toadfish Vocalisations

2010-07-22T22:12:00.000-02:30

My poor neglected blog. I will write a decent post soon but for now here is a video of toadfish vocalisations. Its kind of cool.

The Leaping Blenny: A Fish Out Of Water

2010-06-22T18:48:00.001-02:30

Using high speed video researchers have shown how a leaping blenny, Alticus arnoldorum (a fish), can thrive on land. The blennies use a twisting motion of their tail to spring forward. Essentially these fish curl their bodies into a C-Shape and then let fire. Typically, this is used as an escape response to avoid been eaten by a predator. But these leaping blennies have adjusted their biomechanics a little so they can use it to colonise intertidal areas. Intertidal means that area between low and high tides. In other words, these fish can, and do, live a substantial part of their lives out of water.

Below is a lateral view of a leaping blenny, well, leaping.

Below is a ventral view of the leaping blenny climbing up a upright piece of plexiglass.

The Seahorse: A Perfect Dad

2010-06-21T15:19:00.003-02:30

Here is a video I found over at Deep Sea News (check it out). It shows amazing video of the seahorse, a fish. This fish is probably best known for its odd appearance almost looking like a dragon from a fairy tale. But did you know that the seahorse has a very unique reproduction strategy. The female places her eggs in the males brooding pouch where he then fertilizes the eggs and carries them for about two months until they are ready to be released. The male then cares for the young until they are ready to look after themselves. Ok so no dad is perfect and he may occasionally eat his children every now and then. But when you have a thousand of them who can blame him!!

So for all you fish geeks out there here is the reason why. Females spend twice as much energy generating the eggs than the males do incubating them. Because this is so energetically costly to the females it seems evolution has decided to give them a break, and the males incubate them instead. This means that females have more time to go and get pregnant all over again thus raising reproductive output.

The Burglar Alarm Hypothesis: The Role Of Bioluminescence

2010-06-19T12:46:00.000-02:30

Anyone who has disturbed water at night, especially during a bloom, will have seen the intense bioluminescence produced (see picture above). But why this occurs has long been the subject of scientific query. Dinoflagellates are one planktonic group that bioluminesce, and this occurs due to deformation of their cell membrane caused by shear forces. This is often caused by intense water movement such as breaking waves or a predators swimming movements. One hypothesis is that this is a form of communication. This certainly seems to be the case when you consider that the light emitted by dinoflagellates has a maximum emission of around 475nm (blue-green), which produces light that is visible over long distances.

The authors in this paper propose that bioluminescence from the dinoflagellates serves to attract predators to the grazer. This 'burglar alarm' hypothesis argues that dinoflagellates become less attractive to grazers by increasing the risk of predation for the grazer. In other words, if a planktivore eats these dinoflagellates they will shine big bright lights saying 'food here' for predators within the area. Thus, dinoflagellates would be expected to be eliminated from the grazers diet.

Experiments to test this hypothesis were undertaken in glass jars containing dinoflagellates (those that bioluminesce, and those that don't), copepods (predators of dinoflagellates) and three-spined sticklebacks (predators of copepods). Thus, these experiments were able to directly test the predation rate on grazers, while feeding on dinoflagellates that either bioluminesce or don't. After 3.5 hrs both grazer and prey were removed from the jars, and the number of dinoflagellates remaining were counted. What they found was that the predation rate was almost doubled in the jars containing bioluminescent dinoflagellates. This shows that the mortality rates on copepods feeding on bioluminescent dinoflagellates increased, confirming the burglar alarm hypothesis.

It is important to note that the sticklebacks used in these experiments were never exposed to the experimental conditions. Thus, the light emitted by the dinoflagellates is a cue used in nature. Using signals to attract predators is not unique to dinoflagellates. Fear screams produced by birds and mammals is thought to be used for the same purpose.

Abrahams, M., & Townsend, L. (1993). BIOLUMINESCENCE IN DINOFLAGELLATES: A TEST OF THE BURGLAR ALARM HYPOTHESIS Ecology, 74 (1), 258-260 : 10.2307/1939521

End Of Postdoctoral Stress

2010-06-16T19:37:00.000-02:30

Every graduate student knows that behind any faculty position lies many years as a postdoctoral fellow. The big problem here is getting those postdoctoral positions, which itself is a bottleneck, unfortunately weeding out the unlucky many. This has formed the basis of my anxiety for the last few years since I handed in my PhD. I had a postdoctoral position, but only for a year. The constant worry of where that next job was coming from was hugely stressful. I spent a year as a fisheries scientific observer until I got my next position, and this was for one more year.

Last night I found out that I had finally been awarded a huge grant, which would provide my salary and research costs for the next three years. Obviously the amount of relief I am feeling is huge. I can finally plan my future for the next three years and actually feel settled. A lot of my work will be looking at the above fish. Can you guess what it is?

Saving Estuaries In Sri Lanka

2010-06-14T00:13:00.000-02:30

Don't you just love a good news story. Well here is one. Over the past decade the northeast coastal district of Puttalam (Sri Lanka) has had decreasing fish catches. As a result the livelihood of the people living there is imperiled. The International Conservation Union (IUCN) has tackled this problem by training locals to cultivate aloe vera. This provides between $30-60 US to supplement their incomes.

Conservationists say that the fisheries stocks collapsed because the mangroves were systematically destroyed, and in the process wiped out crucial nursery habitat for juvenile fish, crabs and prawns. IUCN is also educating the locals not to cut down any more mangroves with good results. Once they are engaged they realise the value of the estuary, and voluntarily conserve the ecosystem.

BP Oil Will Kill Baby Fish

2010-06-11T23:14:00.000-02:30

Louisiana's 3.5 million hectares of marshes and estuaries is teeming with life. This area contains far more species than that of the Everglades, Yellowstone Park, or the Rocky Mountains. This region contains major nurseries for juvenile marine animals, and nearly everything that lives in the gulf is linked back to these estuaries. The natural capital of this area has been valued at around $1.3 trillion dollars due to the great contribution it makes to US fisheries.

These marshes are already devastated from hurricanes, canals built for the oil industry, as well as dikes. levees and channels that have altered the natural flow. However, now oil is about to further threaten life within this ecosystem and all the biodiversity it contains. At present huge populations of nesting birds are directly in the path of the incoming oil. This includes 400 pairs of brown pelicans, 8500 royal terns, 30000 sandwich terns, and 200 black skimmers.

Ciscoe die as Minnesota Lakes warm up.

2010-06-01T18:06:00.000-02:30

Ciscoe, a prey species of gamefish such as lake trout, are experiencing die offs more frequently in recent years. This is likely to be caused by raised water lake temperatures and run off from surrounding areas that depletes the water of oxygen. Populations are significantly declining in some lakes.

Some studies have predicted that the climate of Minnesota will become equivalent to Kansas in 85 years. For coldwater fish such as Ciscoe this is bad news since this would increase the die offs even more.

For more on this story goto the StarTribune. Its very interesting reading the comments. Some good examples of ignorance about global warming.

Radioactive Fish

2010-05-31T18:45:00.000-02:30

In January it was announced that the Vermont Yankee nuclear plant leaked radioactive substances into the Connecticut River (see image above). Recently, a yellow perch was caught for miles upstream and tested positive for the radioactive strontium-90. This isotope has been linked with bone cancer and leukemia, and was found 100 times above the federal Environmental Protection Agencies limit for safe drinking water. Despite this health officials say there is no reason for alarm and that people should not limit their fish intake. Hmmmm.

Scorpionfish vs Octopus - who will win?

2010-05-31T18:07:00.002-02:30

Yao Ming: Shark Fin Soup

2010-05-30T00:52:00.000-02:30

Vertical Migration: A Hunting Tactic of the Blue Shark

2010-05-29T19:23:00.012-02:30

The blue shark, Prionace glauca, is a common species found throughout tropical and temperate oceans. This shark is often considered to be a surface dwelling fish of the open sea, but it is also commonly found in the dark waters of the continental shelf, swimming into the sunless depths. In this study acoustic telemetry was used to follow 22 blue sharks over the continental shelf and slope, between George's Bank and Cape Hatteras, in the North Atlantic, between 1979 and 1986.

One of the most interesting points of the paper was the authors explanation for their movement patterns. Sharks exhibited highly predictable vertical migrations over several hundred meters. Most sharks, including the blue shark, have strong chemosensory capabilities. In the ocean olfactory cues would be better distributed along the horizontal plane due to the current shear between layers of differing density. Thus, an olfactory stimulus will spread as a radiating disk. By moving vertically through the ocean the sharks would significantly increase the odds of encountering such an odour trace and this is what was observed.

Carey, F., Scharold, J., & Kalmijn, A. (1990). Movements of blue sharks (Prionace glauca) in depth and course Marine Biology, 106 (3), 329-342 DOI: 10.1007/BF01344309

Beautiful Canada

2010-05-25T21:32:00.006-02:30

One of the perks of fieldwork is driving through a new country and seeing the landscape as you check out field sites. I was lucky enough to do that last week hence the lack of posts lately. So I thought I would share some of the photos of my trip rather than write up a proper post. I was traveling around Newfoundland checking out turbid estuaries, of which there are apparently none!!!!

Weekly Links

2010-05-15T18:50:00.007-02:30

Killing Sharks: Is Ocean Science Compatible With Ocean Conservation

Discusses whether their is room in science for ethics, politics and emotions. Should we be sampling sharks for scientific purposes given the pressure their populations are under worldwide?

The Future Is Now

Lizard species are already disappearing, and becoming extinct, due to global warming.

Black Ghost Knifefish In A Strange Angle

Why does a black ghost knifefish feed at a body angle of 30 degrees? This post explains how this may increase the electric field of the fish giving it a greater search area for detection of prey.

Extreme Conservation: Constructing New Habitat In Ecological Wastelands

Discusses how our approach to remediation of abandoned mines and industrial wastelands should be changed. Using species that naturally occur in difficult environments with analogous conditions.

Baby Corals Swim Home By Following The Sounds Of Reefs

The title pretty much says it all. How to coral larvae find their way to reefs for settlement. This post discusses the role of sound for navigation in these planktonic animals.

Green Light

Over 4 trillion cigarette butts are dumped into our environment each day. This post discusses a useful option for what to do with the cigarette butts.

Senses of the Deep Sea

2010-05-11T18:51:00.015-02:30

The most abundant life on this planet is found deep beneath the waves at depths that sunlight hardly penetrates. Species that live at these depths are impossible to capture for behavioural studies where questions can then be asked about how fish at these depths 'see' the world. Thus, deep sea scientists are restricted to undertaking morphological analysis on these organisms and interpreting the results. One of the long held beliefs is that vision becomes less important for fish the deeper you go, and this is obvious when you look at eye size. Generally, after a certain point, when sunlight can no longer penetrate, the size of fish eyes becomes increasingly smaller and the non-visual senses become elaborate and highly specialised. In this post I discuss two papers that investigate what senses are utilised by mesopelagic and abyssal demersal fish species. For those of you who do not know mesopelagic fish are those that swim in the water column at depths of 500 and 1500m while abyssal demersal fish are those found near the bottom of the sea floor at depths of 2000-6000m.

What the author did was capture fish during deep water trawls in the Atlantic and Pacific oceans, and investigate their brain morphology. He described the brains with special reference to the differentiation of the sensory centres - olfactory bulb (smell), optic tectum (vision), octavolateral region (water motion via lateral line), and gustatory lobes (taste). For those who do not know what the lateral line is it is a hair cell based sensory system that detects local water movements surrounding the fish. Such as the wake of a passing prey. By comparing the size of each brain region for a specific species, with the overall average across all species, the author was able to determine whether the fish was a specialist for that particular sensory system.

Some species were 'specialised' in one particular sensory system (mesopelagic fishes 36%; abyssal demersal fishes 40%). Other species 'dominated' in two sensory systems (mesopelagic fishes 49%; abyssal demersal fishes 46%), while the remaining species were generalists and specialised in three senses (mesopelagic fishes 15%; abyssal demersal fishes 14%). No fish therefore were not specialised in any sense.

For mesopelagic fishes that were specialists 92% were masters of vision. This pattern, although not as strong, continues to hold true when you take into account 'dominated' and 'generalist' species. Sixty one percent of fish had above average volumes of the optic tectum. This would suggest that vision is the most important sense in the mesopelagic environment. This pattern is not as strong for abyssal demersal fish with fish specialising in vision in only 50% of cases both for specialists and when dominated and generalist species are accounted for. Vision therefore seems to play a lesser role in the deeper abyss.

The use of the lateral line shows the reverse trend becoming more important the deeper you go. Mesopelagic fish that specialised in the lateral line (25%) were less than those found in the abyss (49%). However, in both environments the lateral line was the second most important sensory system. This pattern of increasing importance of non-visual senses in deeper waters continues to hold for the other senses also. When shifting from the mesopelagic to the abyss, species with above average gustation areas (taste) increased from 10% to 34% , and from 3% to 37% for olfaction.

This pattern shows that the sensory environment of the abyss is markedly different than the open waters of the deep sea. Vision was clearly dominant in the mesopelagic waters, and this may be due to the abundant sources of bioluminescence found in this environment. This is quite evident when comparing the species between the two depth categories. Bioluminescent species were common in the mesopelagic, but not a single bioluminescent species was found in the abyss. With a lack of any visual cues for feeding or mating it is not surprising that non-visual senses begin to become more dominant at greater depth.

Wagner, H. (2001). Sensory Brain Areas in Mesopelagic Fishes Brain, Behavior and Evolution, 57 (3), 117-133 DOI: 10.1159/000047231
Wagner, H. (2001). Brain Areas in Abyssal Demersal Fishes Brain, Behavior and Evolution, 57 (6), 301-316 DOI: 10.1159/000047249

The Wolffish

2010-05-10T22:03:00.009-02:30

Sometimes you come across some really cool videos that make you feel like a kid again. For me these are some of those videos showing wolffish feeding on prey, and just hanging. I got these videos over at Eclectic Echoes where he gives a great run down of this species - the Atlantic Wolffish (Anarhichas lupu).

Wolffish devouring a crab.

Wolffish eat a sea urchin.

Wolffish pair.

from CLF (credit: Jonathan Bird) on Vimeo.

Turbidity: A Safe Haven For Prey?

2010-05-04T17:44:00.012-02:30

Turbidity is well known for its negative impact on fish feeding ability. As turbidity increases the visual range of the predator decreases, which leads to a reduction in the area searched, and therefore a lowered encounter rate. But what is one fish's garbage maybe another's treasure. The authors of this paper investigated whether turbidity can also provide a cover, or safe haven, for prey fish making them harder to detect.

In the experiment two predators were used, including the yellow perch (Perca flavescens), and the black bullhead (Ameiurus melas). These predators differ significantly in their sensory modes of feeding with the yellow perch relying on vision, and the black bullhead relying on chemosenses. Their unfortunate prey for this experiment were fathead minnows (Pimephales promelas). Fathead minnows were placed into a three chambered aquarium, and in order to feed from artificial feeders, they had to make a choice between two chambers. The authors manipulated the choice chambers with clear or turbid water, and with the predators. The variable measured was either the number of minnows feeding in the treatment chamber, or the number of mortalities.

The predators were active in the apparatus and mortalities did occur. There was no effect of increased turbidity on the mortality of fathead minnow when yellow perch were present. However, higher mortality was observed for the black bullhead, the non-visual predator, when in turbid water. Of course this makes sense since, within turbid water, the non-visual hunter would have the dice loaded in its favour against a prey that is strictly visual. Unfortunately, mortality events were not high enough to show any statistical significance. But the trend was there, and if a greater sample was taken Im sure this would have been found.

The fathead minnow showed significant avoidance behaviour of the clear water chamber when it contained a predator. When no predator was present, in either chambers, a strong preference for the turbid habitat was observed. When a predator was placed into the turbid habitat, fathead minnows preference for turbid water was suppressed, but they nevertheless still showed a slight preference for the turbid water over clear water. This despite the fact that a predator was only present in that chamber!

Thus, fathead minnows still maintained a preference for turbid water even when their was a real risk of been consumed by a predator. There are two possible explanations for this behaviour. The first is that increased turbidity makes it difficult for the prey to know that a predator is in that chamber. However, this is unlikely to be the case. Both predator and prey were constrained to such small areas it would have been highly unlikely the prey did not detect the presence of the predator. Also, their were many instances where the predator chased the prey. Fathead minnows are also known to possess chemical alarm signals, and therefore this also should have alerted other conspecifics of the predators presence. It would seem likely then that the second possibility is true: that increased turbidity makes it so hard for the predator to detect the prey that it becomes worthwhile for the prey to feed under the cover of turbidity where it perceives less threat.

This has rather large ecological implications. Turbidity has, thus far, been considered as a negative abiotic factor for fish. However, this experiment shows that in certain circumstances turbidity could be beneficial for many prey species. The ecological impacts of these safe havens on prey fish communities still needs to be investigated. What I would be interested in is if the benefit of having a reduced predation risk is outweighed, or eliminated, by a reduction in the ability of the prey to also find food. Im sure certain trade offs would exist with the perceived predation threat, and the fish's own ability to find food, driving a fish to choose certain habitats that would have large ramifications on their population dynamics.

Chiu, S., & Abrahams, M. (2010). Effects of turbidity and risk of predation on habitat selection decisions by Fathead Minnow (Pimephales promelas) Environmental Biology of Fishes, 87, 309-316 : 10.1007/s10641-010-9599-8

ResearchBlogCast: Fewer Big Fish In The Sea

2010-04-26T23:04:00.004-02:30

I am quite honoured to have the ResearchBlogCast #4 pick an article that I have covered here on Fish Schooled.

For the post follow this link.

For the podcast follow this link.

Fish of the Day: Flying Fish

2010-04-20T19:03:00.004-02:30

Flying fish are a group of marine species that belong to the family Exocoetidae (order Beloniformes, Class Actinopterygii). There are approximately 64 species from seven to nine genera. Flying fish are found in all the worlds major oceans, particularly the warmer subtropical and tropical regions. Of course their most noticeable feature are their oversized pectoral fins, which they spread out like wings as they glide through the air. The enlarged lower lobe of their tail acts like an outboard motor, the speedy sideways motion of the tail allows the fish to gain height from the surface of the water. This morphology allows the fish to 'fly' out of water for extended periods of time with glides usually lasting for 50m, but upto 100m . This proves to be an effective predator avoidance strategy. Below is an example of a 'flying' flying fish.

Prey populations explode as predators get smaller.

2010-04-15T19:44:00.011-02:30

When top predators are removed from ecosystems their prey and/or competitors increase due to decreased predation and competitive release. However, can changes in behaviour, or body size, of the predators also cause this effect? If true, this would be most evident in heavily exploited marine ecosystems where size selective fishing has lead to rapid reductions in the size of top predators. The authors in this study used a 38 year time series to examine the relationship between predator size and prey biomass within such an ecosystem, the Western Scotian Shelf.

Their analysis showed that since the mid 1990's predator biomass has remained relatively constant. If one species of predatory fish was overfished it tended to be replaced by another species of predatory fish. Yet, despite no changes in predator biomass, prey biomass has increased by a huge 300%. Statistically, what matched this increase most closely was a decrease in the size and body mass of fish at higher trophic levels. The mean lengths of benthivores decreased by 21%, piscivores by 8%, and planktivores by 16%. When translated into body mass large benthivores decreased by 59%, medium benthivores by 48%, piscivores by 45%, and planktivores by 34%. For example, a haddock in the 1970's weighed, on average, 2 kg, but now weighs approximately 0.8 kg.

The empirical results from this study support the hypothesis that reduction of predatory fish size is the dominant factor in the underlying explosion of prey biomass. Why would this occur? Larger predators have been shown to be more successful at capturing prey due to their faster swimming speeds, and greater visual acuity. Thus, larger predators can consume more prey per unit time than smaller predators, and as a result larger predators can regulate their prey populations more effectively. As predators get smaller, a reduction in predation pressure results, leading to large increases in prey populations such as the pattern observed in this study.

Shackell, N., Frank, K., Fisher, J., Petrie, B., & Leggett, W. (2009). Decline in top predator body size and changing climate alter trophic structure in an oceanic ecosystem Proceedings of the Royal Society B: Biological Sciences, 277 (1686), 1353-1360 DOI: 10.1098/rspb.2009.1020

Sensory Plasticity in Changing Environments

2010-04-13T20:17:00.012-02:30

Can environmental conditions during early development shape individuals phenotypes so they become more adaptive to the conditions they are likely to encounter later in life? Such phenotypic plasticity could provide organisms with the potential to respond effectively to environmental change. One area where such plasticity would be important would be in an animals sensory capabilities. Animals extract information from the environment using a number of sensory systems, and this information guides the animal as it locates food and mates, while also avoiding predators. Thus, the ability to compensate for a deficit in one sense, by increasing the acuity in another, is likely to be of critical importance within sensory disparate habitats. This is what is named the 'compensatory plasticity hypotheses'.

In this experiment the authors raised newly born guppies at low and high light intensities, and then tested their ability to locate food using both chemosensory and visual cues. Guppies, Poecilia reticulata, reared at high light intensities responded best to visual cues, while those guppies reared under low light intensity responded the strongest to olfactory cues. These results confirm the 'compensatory plasticity hypothesis' and shows that these fish have remarkable sensory plasticity. They are able to switch from vision to olfaction in environments where light is limiting.

How this switch occurs is unknown. It may be due to increased attention to sensory signals through learning, neurophysiological changes in the hard wiring of the sensory circuits, or structural changes in the morphology of the sensory unit (i.e olfactory epithelium such as increased lamellae folding) or in the brain itself. In rats that have undergone early visual deprivation you find a reduction in the grey matter within the visual cortex, and an increase in neuron density in the auditory cortex.

The ability to switch sensory modes is likely to be of upmost importance in aquatic ecosystems, which are among the most heavily impacted in the world due to human induced changes. These changes can often result in decreased visibility due to increases in turbidity, or change the olfactory environment through the release of pollutants. How fish species can respond to these changes through sensory plasticity is still largely unknown. Research on larvae of the marine striped trumpeter, Latris lineata, showed that individuals reared in clear water had reduced foraging efficiencies in turbid water. In contrast, larvae reared in turbid water were able to maintain their foraging capability. This suggests that fish are capable of doing so, but to what degree is an area that definitely requires further investigation.

Chapman, B., Morrell, L., Tosh, C., & Krause, J. (2010). Behavioural consequences of sensory plasticity in guppies Proceedings of the Royal Society B: Biological Sciences, 277 (1686), 1395-1401 DOI: 10.1098/rspb.2009.2055

How Swimming Can Change The Way You Forage

2010-04-11T14:39:00.008-02:30

This study really excites me as it shows how functional morphology and swimming mode can be reflected in the ecology and evolution of animals. The authors in this study used digital particle image velocimetry (DPIV) to measure the wakes produced by swimming jellyfish. DPIV is a technique where you place neutrally buoyant beads into the water that fluoresce under light. You then shine a plane of light through the water and measure the movement of those beads, which is typically caused by some biological organism such as a moving or feeding animal. For example here is a DPIV of fish suction feeding with shrimp as prey.

So back to the science. In this study two distinct types of wake patterns were formed behind the jellyfish. All jellyfish form vortex rings in their wakes. As the wake vortices grow during the formation process, which occurs during the contraction phase of swimming, the vortices approach a maximal limit for their size. In some jellyfish, within this study, this limit is not met and so their wake consists of a single vortex ring in their wake. In others this limit is passed, and as such can no longer incorporate or entrain the additional fluid, and thus a trailing jet is produced behind the vortex ring.

What they found was that those species that formed vortex rings had less effective propulsion compared to those that produced a trailing jet. However, producing vortex rings for locomotion was more energetically efficient than producing a trailing jet. In short, you either move quickly but for short periods, or you move more slowly but continuously. The cool part was that they found that those species that forage by continuously cruising are the species that produce vortex rings without trailing jets (energy efficient mode), whereas those species that ambush their prey produced trailing jets (speed mode). This of course makes perfect functional sense. This is a trade off and there was no species that could move both quickly and for long periods.

Dabiri, J., Colin, S., Katija, K., & Costello, J. (2010). A wake-based correlate of swimming performance and foraging behavior in seven co-occurring jellyfish species Journal of Experimental Biology, 213 (8), 1217-1225 DOI: 10.1242/jeb.034660

Do fish have six second memories?

2010-04-08T21:10:00.010-02:30

The ability to find food is one of the most important behaviours an animal can undertake, and one of the best advantages an animal can have is to remember where food can commonly be found. Laboratory studies have shown that fish are able to use learning-based strategies to locate food with most studies focusing on the aquatic equivalent of the lab rat - the goldfish. This fish has been shown to typically use visual landmarks to remember a food source within laboratory arenas. In this study the authors used radio tagged common carp to investigate the ability of free ranging fish to undertake similar behaviours. Carp are very closely related to goldfish and share similar feeding habits and sensory cues while feeding. This was undertaken in a highly turbid lake with a water clarity of <>

This study showed that carp could quickly learn and find the location of a food reward in the natural environment. It typically took the carp six days to learn and remember where the food reward was. This matches that found in laboratory trials. Carp were highly nocturnal in their feeding habits and would leave their home range during the night consistently visiting the food reward once the location was known.

What impresses me the most is that they did this at night, in highly turbid conditions, and in a featureless environment. This precludes the use of visual landmarks which is what is typically used by fish in laboratory arenas. It is likely that carp were using olfactory cues to locate the food source rather than vision since carp are known to have an extremely well developed sense of smell. The authors also suggest that the speed with which carp learned to find the food may have been facilitated by social learning as carp and goldfish both learn from shoaling conspecifics in laboratory trials.

This study has some big implications. Firstly, carp are known to undergo extensive movements of 100 km or more. They will often enter areas to spawn that are unstable but predator free, and the ability to remember such locations would significantly improve the survival of their offspring. The ability to remember important sites would therefore be highly adaptive. Another implication is to use this knowledge to reduce the numbers of this fish, which is one of the most invasive species worldwide. By setting up feeding stations you may be able to attract many carp to a specific location within a short time frame and then undertake selective removal.

Bajer, P., Lim, H., Travaline, M., Miller, B., & Sorensen, P. (2010). Cognitive aspects of food searching behavior in free-ranging wild Common Carp Environmental Biology of Fishes DOI: 10.1007/s10641-010-9643-8

The Top Down Effect Of Turbidity Within Marine Ecosystems

2010-04-06T16:17:00.007-02:30

Most studies on turbidity investigate freshwater ecosystems and few studies have focused on the impacts of turbidity on marine ecosystems. Eianne et al. (1999) showed that invertebrate planktivores (jellyfish) replaced planktivorous fish within Norwegian turbid fiords. This was likely to be because increased turbidity levels reduced the possibility of foraging in visually oriented fish, while tactile feeding in jellyfish allowed them to continue to feed under light-limited conditions. A reduction in fish populations was unlikely to be a result of a reduction in plankton abundance. In fiords where fish populations were reduced zooplankton were more numerous and grew to larger sizes. This confirms modeling and experimental studies which show that turbidity is likely to have a top down effect within marine ecosystems by reducing the ability of fish to feed visually and this in turn leads to changes in prey composition.

Eiane, K., Aksnes, D.L., Bagoien, E., & Kaartvedt, S. (1999). Fish or jellies - a question of visibility? Limnology and Oceangraphy, 44 (5), 1352-1357

Arrived in Canada

2010-03-23T18:09:00.007-02:30

I have safely arrived in Canada. Sorry about the delay in posts. I aim to get back into it tomorrow. I have been here for a week and it is a very beautiful country. Going to live in a new country the second time around is certainly easier, but you just can't escape the feeling of been completely alone, homesickness and of course jet lag. But I am handling it a lot better than last time so these anxious feelings hopefully won't hang around for long. The marine lab I am at is amazing and so is the project. I am very much looking forward to this year. Today I spent most of my day trying to write more grants for more money so I can stay longer. Here are some pics of the place to keep you occupied until tomorrow.

Are Dolphins Non-Human People?

2010-02-27T21:35:00.007-03:30

"Are Dolphins Non-Human People" was one of the questions raised by scientists and philosophers at the meeting for the American Association for the Advancement of Science (publisher of Science). Yes this sounds a little 'tree huggy' even for me, but, upon reading this latest brief in Science I can see the arguments made. This debate couldn't be anymore topical right now with the incident that happened with Shamu at Seaworld in Florida. If dolphins are to be considered as non-human persons then should we be making them do shows and keeping them in captivity?

The first argument of course is the extreme intelligence of dolphins. They (1) have larger brains than humans, (2) have a brain to body weight ratio greater than great apes, and (3) they are the second most encephalized beings on the planet. Encephalisation is the folding of the brain and increases volume and surface area, which has been shown to correlate with intelligence. But intelligence is just one part of the argument. The neocortex of dolphins is very advanced and allows them to problem solve and be self aware, and even have a form of intellect or rational thought. They also have spindle neurons that are involved in emotions, social cognition, and the ability to sense what others are thinking.

Thomas White, a philosopher at Loyola Marymount University, argues that these characteristics makes the dolphin a person, but a non-human person. They are alive, aware of their environment, have emotions, have distinct personalities, exhibit self control, and treat others with respect or ethical consideration. White argues that dolphins tick off all the boxes of what it is to be human. Research on intelligence is still in it's infancy with a lot to discover. But, based on these ideas can we justify putting dolphins in places like Seaworld for our own amusement?

Grimm, D. (2010). Is a Dolphin a Person? Science, 327 (5969), 1070-1071 DOI: 10.1126/science.327.5969.1070-c

New Postdoc!!

2010-02-25T17:57:00.005-03:30

Yesterday I finally got VISA approval and so the last hurdle is jumped. On 15 March I leave the shores of New Zealand and set sail (actually flight) for Newfoundland, Canada, where I will start my new postdoctorate. This will be my home for the forseeable future. How do I feel? I am excited at the new adventure and about getting into a fresh new research project, nervous that I will be able to do it, and sad to be leaving my friends.

it has made me realise what a sacrifice and lonely life a scientist can be. As much as I am glad and appreciative to be going, even if I had wanted to stay in New Zealand I couldn't. Research funding is terrible. I imagine it is better, but not much, in other western countries throughout the world. Thus, you are forced to travel to different locations if you want to succeed. I am single and have few ties to NZ (even though I grew up here) and so it would be much easier for me to travel to a new job than someone who is say in a relationship or married with kids!!!

But on the flip side my friend has the opposite problem. He is a medical doctor and thus can't leave the country even though he is desperate too. I guess its the usual story of you miss what you can't have.

What do juvenile mangrove fish want to do when they grow up?

2010-02-24T07:24:00.013-03:30

Worldwide, juvenile fish are highly abundant in mangrove habitats and this is especially true for tropical marine ecosystems. Mangroves can act as nurseries to juvenile fish offering protection from predators and a ready supply of food. It has long been considered in conservation circles that such nursery habitats should be protected in order to increase the replenishment of adult fish populations in nearby coral reefs. However, this last idea has actually never been proven, and it could be argued that mangroves act as a sink rather than a source of potential recruits.

Taking a longitudinal approach of following cohorts over time, we evaluated evidence for mangrove-derived replenishment of 10 coral reef fishes by drawing on data from 2 concurrent fish monitoring efforts conducted in Biscayne National Park, Florida, USA, over the period 1999 to 2007. Annual indices of abundance were calculated for fish estimated to be age-0 to 4+ in both habitats, and correlation analyses, with appropriate temporal lags, were performed. Statistically significant (p < 0.05; r2 = 0.30 to 0.71) correlations between juvenile abundances in mangrove habitats and adult abundances on the reef tract 1 to 2 yr later emerged for 4 species: Abudefduf saxatilis, Lutjanus apodus, L. griseus, and Sphyraena barracuda.

This study is novel in that it uses a long term data set > 2 years. It is also one of the few longitudinal studies that matches juvenile abundance with adult abundance in mangrove habitats. The results clearly illustrate that some species spend time as juveniles in mangroves and later migrate to coral reefs. This mangrove-reef ontogenetic connectivity has potential for conservation issues such as nursery habitat assessment and marine reserve design.

Jones, D., Walter, J., Brooks, E., & Serafy, J. (2010). Connectivity through ontogeny: fish population linkages among mangrove and coral reef habitats Marine Ecology Progress Series, 401, 245-258 DOI: 10.3354/meps08404

Tracking the wakes of prey

2010-02-23T04:32:00.022-03:30

Image: http://www.flower-horn.de

I received a comment yesterday asking about the mechanosensory lateral line. So I thought I would write a post today about one of the really cool behaviours that is mediated by this sensory system. I know this is not a well known sensory system but it is a very important one for fish and aquatic amphibians. The lateral line is a hair cell based sensory system that detects the water movement surrounding the fish. Normally this is to within one or two body lengths. However a recent study has shown that in the European catfish (see picture above) it is involved in the detection of wakes left by potential prey.

Here is the abstract:

Swimming fish leave wakes containing hydrodynamic and chemical traces. These traces mark their swim paths and could guide predators. We now show that nocturnal European catfish (Silurus glanis) locate a piscine prey (guppy, Poecilia reticulata) by accurately tracking its three-dimensional swim path before an attack in the absence of visible light. Wakes that were up to 10 s old were followed over distances up to 55 prey-body lengths in our setup. These results demonstrate that prey wakes remain sufficiently identifiable to guide predators, and to extend considerably the area in which prey is detectable. Moreover, wakes elicit rear attacks, which may be more difficult to detect by prey. Wake tracking may be a common strategy among aquatic predators.

In a later paper the lateral line was ablated and once this was done the fish could no longer track the prey. Thus the lateral line was essential in the tracking behaviour. Although this would have limited functional value in coastal water ecosystems where there is a large degree of water motion, and thus background noise breaking up the wake, this may become more important in still water environments. The catfish in this study is obviously a case in point inhabiting slow flowing or still waters such as lakes.

Image: http://oceanexplorer.noaa.gov

This predation strategy may be even more important in deep sea fish where below 1000m, when vision becomes useless, the lateral line is likely to be the dominant sensory system. In such a hydrodynamically 'noiseless' environment many deep sea fish would be capable of detecting the wakes of prey for up to three minutes since they had passed by. Although this next idea is purely conjecture this may also explain why so many deep sea fishes have rat tails (see pic above). Such a tail would likely result in a much reduced wake!

Hanke W, Brucker C, & Bleckmann H (2000). The ageing of the low-frequency water disturbances caused by swimming goldfish and its possible relevance to prey detection. Journal of Experimental Biology 203(7), 1193-1200
Pohlmann K, Grasso FW, & Breithaupt T (2001). Tracking wakes: the nocturnal predatory strategy of piscivorous catfish. Proceedings of the National Academy of Sciences of the United States of America, 98 (13), 7371-4 PMID: 11390962

Pohlmann K, Atema J, & Breithaupt T (2004). The importance of the lateral line in nocturnal predation of piscivorous catfish. The Journal of Experimental Biology 207, 2971-2978

Big Price For Big Tuna

2010-02-22T17:28:00.007-03:30

A tuna has sold for $175,000 in Tokyo's fish market. This is the highest price paid for a fish in nine years. It was caught off the main island of Honshu, which is famed for its high quality fish. It is most likely to end up as Sushi, is this a good sign of just plain luck?

From the BBC

Asocial fish - Coming to a town near you!

2010-02-19T19:04:00.017-03:30

A recent paper in the journal 'Proceedings of the Royal Society of London' by researchers at UCDavis have shown that asocial tendencies are crucial in the dispersal of biological invaders, and asocial individuals could lead the invasion front. Researchers investigated the mosquitofish, Gambusia affinis, a small freshwater fish that feeds on aquatic larvae and terrestrial insects trapped at the water surface. The Mosquitofish is identfied by the global invasive species database as one of the most invasive species worldwide invading over 40 countries.

In the study they measured the dispersal ability of different individuals within an artificial stream and compared this to the sociability of the individuals. Sociability was measured as the willingness to shoal. This study is unique in that it investigates within species variation in personality traits whereas most studies undertake comparisons between species.

Their results showed that the distance moved during a dispersal assay was strongly correlated with sociability. Asocial individuals were found to disperse further and more often. In addition, when these same trials were undertaken later the same fish showed similar behaviour indicating that these personality traits are consistent over time. This study highlights that differences in personality traits could have large implications in the invasive process.

This idea is not only restricted to fish. Bluebirds found at the invasion front were also shown to be the most aggressive among their peers. More surprisingly humans also show high dispersal characteristics when asocial personality traits are high. This doesn't bode well for our great discoverers such as Captain James Cook or Columbus. Or those people who colonised the British colonies or moved out west in the USA. Maybe thats why cowboys had such a chip on their shoulder. They really were asocial bastards!

Cote J, Fogarty S, Weinersmith K, Brodin T, Sih A (2010) Personality traits and dispersal tendency in the invasive mosquitofish (Gambusia affinis). Proceedings of the royal society of London: February 19.

Jokela M, Elovainio M, Kivima'ki M, Keltikangas-Ja"rvinen L (2008) Temperament and migration patterns in Finland. Psychological Science 19: 831-837

The Eyes Have It

2010-02-18T18:25:00.008-03:30

Image: Christopher Hoffman

African Cichlids are one of the most speciose groups of fish on the planet and have received a lot of attention from evolutionary biologists due to their explosive radiation. These fish produce new species faster than any other vertebrate on the planet with hundreds of species evolving in the last 120,000 years in Lake Victoria. To put this into context this is much less than the amount of time humans have been a species. One of the reasons for this is due to sexual selection. African cichlids are well known for identifying species specific patterns and colour when selecting mates. This indicates that the use of visual sensory systems is important in this group of fish and a recent study by Meadows (2009) shows how visual tuning may boost African cichlid diversity.

Researchers compared visual sensitivity between cichlids from Lake Malawi, where the water is clear, and cichlids from Lake Victoria, where the water is more turbid. They found that Malawi cichlids were divided into those with opsins that were sensitive to short, medium and long wavelengths. Opsins are a protein that forms part of the visual pigment rhodopsin that is released by the action of light. In Malawi cichlids opsin sensitivity was tuned largely by foraging. For example, cichlids that fed on plankton in the water column had more short wavelength opsins. Short wavelength opsins make a fish more sensitive to ultraviolet light and this is known to increase the fishes ability to detect zooplankton. In contrast, none of the Lake Victoria cichlids showed ultraviolet light sensitivity and instead were most sensitive to red light. In turbid water ultraviolet light is rapidly absorbed and thus it would be maladaptive to be sensitive to this spectrum of light. What they did find is that a gradient existed in fish sensitive to violet light with those found in the clearer parts of the lake showing most sensitivity to violet light, which would provide an advantage when feeding in clear water.

http://www.accuracyingenesis.com/cichlids.jpg

The researchers then showed that changes in gene expression generated large scale shifts in opsin sensitivity (30-100 nm), while changes in DNA sequences fine-tuned opsin sensitivity by 5-10 nm at the extreme ends of their visual range. This could provide a basis for the rapid number of species generated in such a short evolutionary time frame. By changing the way these cichlids see each other and their environment, shifts in opsin sensitivity could lead to changes in their mating and feeding behaviour thus driving speciation.

However, my own research has shown that some cichlids make very good non-visual hunters also. During my postdoc I showed that a Lake Malawi Cichlid from the genus Aulonocara was able to feed using the mechanosensory lateral line. This sensory system is a hair cell based system that detects minute water movements surrounding the fish. Species of Aulonocara are unique in that they possess widened membranous canals, a morphology normally found only in deep sea fish. These fish search similar to a metal detector picking up on the respiratory currents of buried invertebrates within the sand. I also observed these species undertaking aggression and courtship displays within complete darkness. I assume that these behaviours were also mediated by the lateral line. This genus of Aulonocara is one of the most speciose of the African cichlids, and therefore vision may not be the only factor to consider in their rapid speciation.

Meadows R (2009) Visual Tuning May Boost African Cichlid Diversity. PLos Biol 7 (12)

How To Assess Fish Populations?

2010-02-17T18:23:00.010-03:30

Source: AIMS - Australia's Tropical Marine Research Agency

Studying fish populations has long been the domain of underwater visual census surveys (UVC). Using this approach is useful in that the technique is straight forward and inexpensive, as it usually involves SCUBA divers or snorkelers counting fish along a transect. This method is a critical part for monitoring environmental changes over time or conservation efforts. The problems with such a method is that it involves a human observer bias, which directly or indirectly affects fish behaviour. Fish tend to be scared off or attracted to the noise and sight of the observers (Willis et al. 2000; Radford et al. 2005). Thus, it has been proposed that such methods bias any results during fish quantification.

Recently, baited underwater video (BUV) has been utilised to assess fish populations and it was found to be far more successful at estimating fish density (Willis et al. 2000; Dearden et al. 2009). This method relies on a camera that typically sits directly above some smelly bait in a container, and records any fish that is attracted to the bait. The advantages of such methods is that the human observer presence effect is eliminated.

Source: Tepapa NZ

However, a recent study comparing BUV with UVC has found the opposite result (Stobart, 2007) . Here is the abstract:

A baited underwater video (BUV) system for the study of reef-associated fish populations on shallow (10–20 m) rocky habitats in the western Mediterranean was assessed at four locations in Spain and two in France. We describe the apparatus and optimal deployment times for video sampling. Different species had different response times to the bait, with four response groups identified. Examination of species accumulation curves and fish abundance estimates over time revealed that a period of approximately 20 min deployment was sufficient to capture most species on video. The technique sampled a wide variety of species, with 51 species belonging to 33 families recorded. Nine species of fish appeared regularly at the bait in relatively high numbers, and consist of six carnivores (Serranus cabrilla, Serranus scriba, Coris julis, Diplodus annularis, Diplodus vulgaris, Thalassoma pavo), two planktivores (Chromis chromis, Boops boops) and one omnivore (Oblada melanura). However, abundance estimates for other species were generally very low (mean b1 per location). Comparison of results from BUV with those obtained by Underwater Visual Census (UVC) at the same locations suggests that although BUV estimates species richness reliably, UVC is the more suitable technique for estimating the abundance of shallow-water reef fish in the Mediterranean. BUV improvements are suggested to optimise its use in deeper waters where UVC using scuba is inoperable.

The author also correctly states that the amount of effort required to undertake a BUV based estimation of fish abundance may not be worth the effort. This requires hundreds of hours (perhaps thousands) of painstakingly slow video analysis. It is also only feasible to have one BUV apparatus deployed at any given time unless you have a large vessel, which would be expensive. Thus, the field work component would also take a much longer time than using SCUBA divers. The advantages of BUV is that it is not biased by human observers (although training can minimise this problem), and data can be continuously checked after the event.

In the end I think it largely comes down to the geographic locality and the fish species involved. Different fish species behave differently, and therefore one method might be better suited to that particular type of fish. For example, nocturnal fish are likely to be deterred by the bright lights produced from torches at night, and may be more attracted to bait due to relying more heavily on non-visual senses such as olfaction. Thus, for nocturnal fish the BUV maybe a more appropriate methodology. Also, no technique is perfect and each would have it's own advantages and disadvantages. As the authors suggest it would be most beneficial to combine the methods so that they are able to cross check one another. Unfortunately, this is likely to not be feasible the majority of the time.

Willis T, Millar R, Babcock R (2000) Detection of the spatial variability in relative density of fishes: comparison of visual census, angling, and baited underwater video. Marine Ecology Progress Series 198: 249-260

Radford C, Jeffs A, Tindle C, Cole R, Montgomery J (2005) Bubbled waters: The noise generated by underwater breathing apparatus. Marine and Freshwater Behaviour and Physiology 38: 313-356

Dearden P, Theberge M, Yasne M (2009) Using underwater cameras to assess the effects of snorkeler and SCUBA diver presence on coral reef fish abundance, family richness, and species composition. Environmental Monitoring and Assessment

Stobart et al. (2007) A baited underwater video technique to assess shallow-water Mediterranean fish assemblages: Methodological evaluation. Journal of Experimental Marine Biology and Ecology 345: 158-174

Pirates Cause Damage to Indian Ocean Fish Stocks

2010-02-16T21:10:00.004-03:30

I was reading the New Scientist today, and came across an interesting article on how Somali pirates could literally be contributing to the demise of fish stocks in the Indian Ocean. A consequence of such piracy has meant that fishing boats now need to carry armed guards. This has resulted in little available room for scientific observers to collect fisheries information relating to fish stocks and bycatch, as well as ensuring boats abide by fishing rules.

Without this data an increase in fishing pressure may result. One example is the use of bamboo rafts with attached nets that capture any fish that shelter beneath it. Such shelters in the open ocean are rare and typically are a boon to fish. Rafts such as these float in the Indian Ocean for weeks on end. Michel Goujon, director of the French tuna-boat owners' assoication, has evidence that such use is on the rise. Unfortunately, there is no good news - piracy looks like it is here to stay.

New Scientist, 13 February 2010, No 2747