Monday, May 31, 2010
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.
Sunday, May 30, 2010
Saturday, May 29, 2010
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
Tuesday, May 25, 2010
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!!!!
Saturday, May 15, 2010
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?
Lizard species are already disappearing, and becoming extinct, due to global warming.
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.
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.
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.
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.
Posted by Dan at 6:50 PM
Tuesday, May 11, 2010
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
Monday, May 10, 2010
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.
Tuesday, May 4, 2010
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