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[troutbreath]

Overfished species suffer evolutionary damage: report
'Darwinian debt' may be irreversible
 
Reuters


Friday, November 23, 2007


 
CREDIT: Jeff J Mitchell/Getty Images
Trends show that the North Seas fish stocks are in decline including cod mackerel, and haddock other fish such as bluefin tuna have disappeared completely.
 
VIENNA -- Industrial-scale fisheries have not only sapped the world's fish stocks but also changed the species' evolutionary course, exacerbating the effect of overfishing by producing smaller and less fertile fish.

Scientist Ulf Dieckmann also said overfishing and the practice of throwing lower quality fish back into the sea to raise the value of fishing quotas might explain the massive drop in population.

"Human activity had a possibly irreversible evolutionary effect in just a few generations," said Dieckmann, a member of a group of scientists who wrote a comment in the journal Science on managing fish stocks published Thursday.

"We are running up a Darwinian debt that future generations will have to pay back."

Some 15 years ago, cod stocks on the Grand Banks in the northwest Atlantic collapsed, bringing down the fishing industry in the region. The same species is now under threat in the northeast Atlantic off Norway and Russia, he said.

On the Canadian Grand Banks, fish stocks still show little sign of recovery, Dieckmann said.

Looking at fishery data from the past few decades, the scientists found that increased mortality due to overfishing had favoured fish that matured smaller and earlier, yet also carried far fewer eggs at their first reproduction.

Older data showed a typical cod caught in Norway might have taken 10 years to mature, while the same fish now would only take six years or even less, said Dieckmann.

"The question is not whether such evolution will occur, but how fast fishing practices bring about evolutionary changes and what the consequences will be," the group wrote in Science.

Dieckmann expected that a change coming about in 40 years might take up to 250 years to reverse -- if it happened at all.

"Upsetting the dynamics of predators and prey may cause other changes that block this," he said.

Assessing the evolutionary impact could become an essential tool in managing fish stocks, said Dieckmann.

Fishing policy makers could've helped avoid the collapse of Atlantic cod stocks by taking into account the fishing industry's impact on evolution in the oceans.

Dieckmann said recommendations based on the research include: less fishing overall, avoiding catching small fish by using wider-meshed nets and banning fishing in areas where fish spawn.

"Based on data that were available seven to 10 years before the collapse of the Grand Banks cod fisheries, an evolutionary impact assessment could have been used to send an early warning signal to policy makers," said Dieckmann.

"(Such assessments) applied now can thus help us avoid future catastrophes unfolding elsewhere."

© The Vancouver Sun 2007
 

 

[odesseus]

Just read this article in the sun this morning, very disturbing. Not unlike another clip I came across in a canadian fishing magazine some time ago that highlights the effects of trophy taking on small lakes and rivers. By removing the largest of each species (especially in smaller lakes and streams) the gene pool is forever more deprived of these larger fish. This leads, each season, to smaller and smaller fish, as well as an increase in genetic disorders, illness ect. Not advocating throwing every fish back, but maybe we need to follow the sturgeon success story and keep the little ones and throw the big ones back? Not sure, but some discussion would be good as I would like my grand kids one day to be able to still catch trophies.

[mattcass]

I've always thought there should not only be minimum retention sizes for salmon, but maximum sizes as well. It makes sense that if you only fish from the top half of the bell curve, the bell curve will continuously shift left, and you'll be left with smaller and smaller fish. Years and years ago the larger fish could be taken without consequence, there were just so many. Now, with dwindling numbers of salmon, the priority should be to maintain the strongest genetics in the population.

[SeaRun]

Interesting topic!  Keeping trophy trout from lakes without natural spawning areas should not be a problem since most of these lakes are stocked with hatchery fry or fingerlings.   A lot of shallow Interior lakes with no natural spawning areas that suffer from winterkill are stocked annually to create a fishery that would not previously exist.   However, keeping wild trophy trout could affect the genetic make up if this occurs over a long period of time. For example, the Gerrard strain of rainbows from Kootenay Lake evolved to spawn for the first time at a much older age.   Only the larger, stronger fish are capable of spawning in the faster flowing stream with large gravel.   If these large fish were removed then you may create a fishery with smaller sized trout spawning at a younger age in other areas.   

There has also been an interesting pattern with hatchery coho.   The Chehalis had large coho which entered the river around mid-November.   After hatchery production began, the average size coho was much smaller and entered the river earlier.  This also occurred on the Capilano.   Wild coho are often much larger in size... not many 4 pounders!    Hatcheries can be thought as a form of domestication that can affect the genetic make up and evolutionary change of salmon stocks.   Hatchery fish are spawned artificially where humans determine which fish are used for egg production.   Hatchery fish are raised in very high densities and conditioned to feed near the surface, something which does not occur in nature.   Adult hatchery salmon that swim the fastest upstream without being caught are the ones that survive compared to more aggressive wild fish which are more willing to bite.   B.C.'s salmon fishery is an area of concern when one looks at how there have been major changes in less than 100 years.   Hopefully, our salmon will not go down the same path as the East Coast cod fishery.