Wednesday, February 27, 2008

Survival of the wimps-unnatural selection from fishing

Forget survival of the fittest for fish. Instead, it's survival of the wimpiest because fishing catches the biggest, boldest fish.

A recent study found that even a short period of fishing can select for slower growing and more timid fish. This happens because the biggest, boldest fish are more active as they try to find more food to fuel faster growth rates. All that's left behind for breeding are the smaller, more timid fish...the weaklings and wimps of the fish world.

According to scientist Paul Biro, this may
"slow the rate of recovery for fished populations, and could explain why fisheries tend not to rebound in the manner we expect after we reduce harvest or close a fishery."
In other words, fishing today can undermine the success of fishing tomorrow.

Scientists have long wondered why depleted fish populations often fail to recover. Could it be that survival of the wimpiest fish is part of the problem?

8 comments:

jsobel@oceanconservancy.org said...

Fascinating. Further increases our knowledge about the genetic damage being done to fish populations from fishing. Also, adds yet another compelling reason why marine reserves (areas closed to fishing) are an essential tool for ecosystem protection, fish conservation, and sustainable fisheries.

Aaron said...

I haven't read the paper yet, and I'm not sure if I buy their story.

Presumably in this case the trout are the top predators in the system. What happens in a normal situation where the fish are facing predation from larger predators? Presumably because the bolder fish are more active and more frequently encounter they would be picked off by the predators before the more cautious fish wouldn't they? Additionally, the predators are hunting pretty much everyday and are better at finding fish than we are so wouldn't predation be a bigger threat to large fish over the long term than fishing? Additionally, the vast majority of the mortality to a fish stock seems to happen well before fish recruit to the fishery.

Anonymous said...

Please don't forget that there has been an organization called the International Game Fish Association (IGFA) that has for decades, been promoting and chronicaling the destruction of the biggest individual fish of virtually all game fish species on earth. Natural selection tends to indicates that the biggest individuals of any fish specie have superior genetic qualities compared to that of the average fish of that specie. There is no telling what damage this most narcissistic aspect of sportifshing has caused...

It may have been fun years ago to see who could catch the biggest fish, but due to the state of decline in the last 20 years, that pursuit has turned into a crime against nature.

I have to disagree with aaaron when he says:

"Presumably because the bolder fish are more active and more frequently encounter they would be picked off by the predators before the more cautious fish wouldn't they?"

Fish get big not only because of their predation skills, but equally important to their survival is their ability to perceive danger and avoid it. If you have ever seen an anchovie tail-walk across the surface for 20ft trying to get away from a mackeral, you know what i am talking about.

Brad

Aaron said...

You have to realize that fish are facing at least two sets of selection pressures with respect to feeding behavior/aggressiveness.

If the fish is overly bold, it increases it's risk of predation as the more a fish moves, the greater the probability of encountering a predator.

On the other hand if the fish is overly cautious it ends up growing at a very slow rate and remains vulnerable to high predation for a longer period of time.

It would be interesting to know more about the source populations of the two strains of rainbow trout. If I were to guess, I would guess that the aggressive rainbows are from a system that has very few potential predators while the cautious rainbows are from a system with lots of potential predators.

Mark Powell said...

Aaron assumes that bold fish are more likely to get eaten, and that may or may not be true. Regardless, that's not the most important issue. The important result from this study is that unnatural selection from fishing can change the growth and behavior patterns of fish, and that's a scary possibility for the future of fishing if it makes fish less desirable (smaller) or harder to catch.

The genetic consequences of fishing is a relatively new area of research that could be very important. It's clear that fishing selectively catches larger fish, and that may turn out to be a problem. We might have to change our typical fishing strategies and target the full size range of fish or even small fish. This refers mostly to commercial fishing, but holds true also for trophy fishing as Brad pointed out.

Ilse said...

I would say, the whole problem is all about how much fish we catch. I mean it won't be good to go after the smaller fish too, because then we would catch them, before they are mature. All in all it is important to lessen the pressure on the populations, and catch less fish and, like jsobel said, marine reserves seem to be very important.
Natural predators, like dolphins for example, go after the slower fish. So they tend to feed on the weaker fish, not the bolder ones.
I am kind of remindet on some elephant populations in afrika that tend to have no or small tusks, because formerly the hunters killed only the males with the biggest tusks. So much for manmade evolution.

Anonymous said...

THE best thing for fish populations is for man to stop killing fish--the worst thing for fish populations is man killing fish--PERIOD. Man does more harm to fish populations than ALL natural phenomonon combined. Further, i will assert that commercial fishermen have destroyed more life on this planet than all other industries combined. There may have been a time when fishermen were feeding a hungry world, but with the price of fresh fish, it has turned into a gourmet food industry.

The obvious solution is for people to stop or drastically curtale killing fish, but that isn't going to happen.

On a personal note, i sportfished for 35 years--ALWAYS fishing ethically. For the last 10 years i fished, i kept only 10 fish per year, even though i spent 80-90 days per year on the water.

When the Channel Islands reserves (MPA's) were first proposed around a decade ago, i was thrilled that we would finally get some absolute protection for fish in areas of productive habitat. Eventually the money interests in the sportfishing community intervened and got everyone to jump on their bandwagon by jioning them in their political WAR against the reserves...

The reserves were THE most comprehensive conservation measures EVER proposed for OUR shared waters and the SF community declared war against it!!????

In utter disgust, back in '01 i quit the sport that had consumed virtually my entire life. I destroyed all of my fishing equipment so that it could never kill again, i stripped my skiff of all vestiges of fishing equipment and took up underwater photography in earnest. I am the only person that i know of that quit fishing because of the reserve issue.

i visit fishing sites once in a while and tangle with these self-proclaimed "conservationists" who continue their (futile) WAR against the reserves. But i bring with me a profile of experience on the water that no other boater in the Southern California bight can match. I have watched the decline first-hand for the last 25 years. I've spent too many days and nights on the water and i know too much about what has happened. When i tangle with these fisherman, they resent me, but they cannot refute the eye-witness truth that i bring to the debate.

We ARE going to have a set of reserves in the southern bight in the not-so-distant future and that is going to be a great day for all of us who truly love the sea~!

Brad

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