Fish Schooled: February 2010

Saturday, February 27, 2010

Are Dolphins Non-Human People?

"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

Thursday, February 25, 2010

New Postdoc!!

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.

Wednesday, February 24, 2010

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

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

Tuesday, February 23, 2010

Tracking the wakes of prey

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

Monday, February 22, 2010

Big Price For Big Tuna

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

Friday, February 19, 2010

Asocial fish - Coming to a town near you!

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

Thursday, February 18, 2010

The Eyes Have It

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)

Wednesday, February 17, 2010

How To Assess Fish Populations?

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

Tuesday, February 16, 2010

Pirates Cause Damage to Indian Ocean Fish Stocks

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