Global warming making fish smaller: study
Fish have lost half their average body mass and smaller species are making up a larger proportion of European fish stocks as a result of global warming, a study has found.
"It's huge," said study author Martin Daufresne of the Cemagref Public Agricultural and Environmental Research Institute in Lyon, France.
"Size is a fundamental characteristic that is linked to a number of biological functions, such as fecundity - the capacity to reproduce."
Smaller fish tend to produce fewer eggs. They also provide less sustenance for predators - including humans - which could have significant implications for the food chain and ecosystem.
A similar shrinking effect was recently documented in Scottish sheep and Mr Daufresne said it is possible that global warming could have "a significant impact on organisms in general."
Earlier research has already established that fish have shifted their geographic ranges and their migratory and breeding patters in response to rising water temperatures. It has also been established that warmer regions tend to be inhabited by smaller fish.
Mr Daufresne and his colleagues examined long-term surveys of fish populations in rivers, streams and the Baltic and North Seas and also performed experiments on bacteria and plankton.
They found the individual species lost an average of 50 per cent of their body mass over the past 20 to 30 years while the average size of the overall fishing stock had shrunk by 60 per cent.
This was a result of a decrease in the average size-at-age and an increase in the proportion of juveniles and small-sized species, Mr Daufresne said.
"It was an effect that we observed in a number of organisms and in a number of very different environments - on fish, on plankton, on bacteria, in fresh water, in salt water - and we observed a global shrinking of size for all the organisms in all the environments," he said.
While commercial and recreational fishing did impact some of the fisheries studied, it "cannot be considered as the unique trigger" for the changes in size, the study published in the Proceedings of the National Academy of Sciences found.
"Although not negating the role of other factors, our study provides strong evidence that temperature actually plays a major role in driving changes in the size structure of populations and communities," the study concluded.
Courtesy of the ABC
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saltatrix
Posts: 1081
Date Joined: 30/03/08
Considering warmer water
Considering warmer water makes many species grow faster quicker spawning at a larger size with more eggs you would have thought it actually increases the spawning size.
Fish spawn at specific temperatures so itmeans that the spawning temperature would be reached more often.
This study is a global generalisation so it would be interesting to see how true t is across the board with different species.
Global warming would have occurred without human intervention so it would be interesting to see whether it was destiny with oooor without humans.After all there is more water with the stated ice melt.
Mr Daufresne and his colleagues examined long-term surveys of fish populations in rivers, streams and the Baltic and North Seas and also performed experiments on bacteria and plankton.
This sounds like Northern hemisphere species such as trout which spawn at about 13 degrees water temp and do like colder water. Things like pesticides that kill insects may result in stunted fish if there isnt the food available?
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Colin Hay
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Date Joined: 23/10/07
Nice work saltatrix
Some interesting points you make there.
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saltatrix
Posts: 1081
Date Joined: 30/03/08
Things like pesticides that
Things like pesticides that kill insects may result in stunted fish if there isnt the food available?
Genetically modified food to prevent insect damage on crops? Maybe not for either.
They are talking about Salmonoids the insect eaters. Some "pure" bred animals do get smaller with each generation. This could be said for some dogs.
Then there is the warmer air more often meaning in the northern area more hatches of insects? This should point to more available food?
Smaller fish is normally associated with colder water. For instance Pink Snapper are smaller in the South than their Northern cousins because of the colder water. They start spawning at a smaller size but similar age I think.
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saltatrix
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Date Joined: 30/03/08
There is also the predators
There is also the predators like Northern Pike that keep the balance in a fishery. It was popular prior to about the early 90s to kill Northern Pike in waters as they were seen as the predator that ate all the smaller fish. What was found is that the big female Pike kept the whole fishery in balance in specific areas. Large Pike would eat their own t keep the numbers down. They would eat numbers of say eg: Redfin Perch.
If the big female or a large Pike was killed that population would explode of other Pike not kept in check. It was also that large numbers of smaller Redfin exploded as well.
It was that the smaller Redfin were competing for food in the immediate vicinity which meant more Redfin at smaller sizes.
So now there is a little more respect for the top end predator which eats its own and thins Redfin numbers for them to get bigger keeping the populations in rough balance.
The Pike are also introduced to Trout fisheries to eat injured or poorly handled fishes in the fishery to prevent diseased or dead fish fouling the fishery.
So it is established that without a top end predator you can have explosions of smaller fish competing for the same amount of fish.
For a bit fo trivia it has been discussed that possibly the sticky eggs of the Pike can stick to the feet of water birds and be carried to another waterway. Water keepers have found Pike appear from nowhere in their waters.
It maybe that our own Murray Cod plays a similar role as a scavenger feeder.
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Ewan
Posts: 271
Date Joined: 15/05/06
Predators...
The Pike situation there - same concepts apply with sharks, coral trout, dhufish and any other predatory species...ecology is a complex web of everything having some kind of positive and/or negative impact on something else...
something we will never have a total handle on i think, not within a century or so anyway!!
any of these studies are just another clue to help though. And manage by as required...the suite of information is never going to be complete, or complete enough.
That is pretty cool about the sticky pike eggs...!! Nice one!
temperature effects are always going to have different effects on different species.
For e.g. Turtle eggs are incubated in the sand on beaches. The sex of the hatchlings is determined by the average incubation temperature - as temperatures increase, one sex (i cant remember which) will end up dominating the population, and so it would likely decline, without human intervention (artificial incubation, etc). What if this decrease in available turtles means less turtle food for tiger sharks, which means they switch to eat more large fish species, or alternatively, also decline, meaning they exert less predatory pressure on big fish species, etc, etc, blah, blah...one thing can trigger so many others in unknown, or little known, ways.
The thing about the current global warming situation - pretty widely accepted by pretty much every research organisation in the world as being due to the release of CO2 from fossil fuels - is that it is occurring faster than usual (in the geological timeframe context). So for some (many) species (and whole ecosystems) under all of the other human pressures like loss of habitat, pollution effects, over-exploitation - organisms arent always able to migrate to stay in their optimal temperatures, and cant evolve fast enough to keep up and to sustain themselves in the one place they are stuck with. mass evolution occurs over very long timeframes, but modern global warming has only been around for a few generations, relatively speaking...
How fast can we incorporate science into management change? How fast can we get long-term science monitoring in place so that we can identify any such temperature effects on our precious ecosystems. And, if we find a problem, how fast can we implement any changes required? As a hypothetical - if research into climate change effects on the rock lobster or dhufish fisheries suggested that we have to cut catches by another 50% to ensure the sustainance of these endemic species - how fast could such management changes be implemented? Could they be implemented at all?
Just some thoughts...but potentially topical at the moment. The current proposed regulation changes are designed to address the survival of the species (albeit within a region) due solely to direct human impacts - overfishing. What if climate change adds even more negative impacts to their recruitment and survival?
How would we deal with that?
Ewan
edit/addendum: of course climate change effects could pop up some benefits for some species too!!
a whole bunch of interesting things here:
http://ftp.marine.csiro.au/research/climate.html#marine
Ewan
Posts: 271
Date Joined: 15/05/06
CSIRO report on climate change and marine life
http://www.climatechange.gov.au/impacts/publications/marinelife.html