Big, old fish key to stocks' survival, OSU experts say, THIS IS A MUST READ! For those interested in preservation of species.

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Big, old fish key to stocks' survival, OSU experts say, THIS IS A MUST READ! For those interested in preservation of species. Kurt

 

Date:

Wed, 19 Jan 2005 19:08:42 -0800

Big, old fish key to stocks' survival, OSU experts say

From Bend.com news sources

Posted: Tuesday, January 18, 2005 12:36 PM

Reference Code: PR-20624

January 18 - CORVALLIS – Recent studies have found that large, old and oily

groundfish are significantly more important than their younger counterparts

in maintaining healthy marine fish stocks – the larvae from their eggs

better resist starvation and have a much greater chance of survival.

These same big, old fish are also routinely sought by fisherman, scientists

say, and the age decline in fish populations helps to explain the collapsing

fisheries off the Pacific Northwest coast.

Other research also indicated that many fish populations up and down the

coast are essentially distinct, and fish from one area don’t intermingle as

much as had been assumed with fish from elsewhere.

These combined problems might be most effectively addressed with a diverse

network of marine protected areas, said scientists at Oregon State

University.

The findings were recently summarized in an article in Fisheries, a

professional journal.

“We’ve known for a long time that bigger fish produce more eggs, that we

might need to have numerous smaller females to produce as many eggs as one

larger fish,” said Mark Hixon, an OSU professor of zoology. “Modern fish

management is based on this assumption. But we’ve also assumed that one fish

egg is just as good as another, and the newest studies are showing that’s

just not the case.”

New studies by OSU researcher Steven Berkeley, who is now at the University

of California–Santa Cruz, have shown that eggs from very old fish have much

larger oil globules in their yolk, giving the larvae that develop from these

eggs a chance to grow faster and survive starvation longer. Older fish also

spawn earlier, which sometimes better coordinates larval birth with peak

food availability.

A marine ecosystem routinely has more than 99 percent mortality of fish

larvae due to predation, starvation and fluctuating ocean conditions. So

anything that helps young larvae pass through their most vulnerable

lifestyle stages can significantly increase their chance of survival,

scientists say.

“In some cases, it appears that almost all of the surviving larvae have come

from large, old, fat fish,” Hixon said. “For effective replenishment of our

groundfish stocks, these older fish may be essential. But with the fish

management systems we now have in place, fish of this age range may

represent far less than 5 percent of the total population of a species.”

Black rockfish, for instance, can begin to reproduce at about five years of

age, but need to be about 12 years old with heavier amounts of fat before

they can produce the type of “oily” eggs that may have increased survival

chances. Larvae from the oldest fish can survive starvation 2.5 times as

long as those of the youngest, and grow three times as fast on the same

diet. Similar findings have been made with other species.

For a fish, surviving to adulthood is not easy. But after that, the natural

dangers decline.

In a natural system, old fish actually have an extremely low rate of

mortality compared to their younger counterparts, and a disproportionately

higher level of body lipids – they get fat. Young fish are comparatively

lean. And fishing pressure works exactly to the opposite of most natural

mortality agents.

During a period of intense fishing off the Oregon coast from 1996 to 1999,

the average age of mature female black rockfish declined from 9.5 to 6.5

years – in a fish species that has a maximum lifespan of about 50 years.

Soon after, many fisheries were in serious decline.

Genetic studies by OSU researcher Michael Banks and his graduate students

have also shown that there are many unique fishery stocks up and down the

coast that do not interbreed, meaning that a collapse of a fishery in one

location may not be easily corrected by migrating fish from other areas.

There are few easy remedies to this problem, Hixon said.

Complete closure of fishing or extremely low fishing quotas would be one

approach, but this has economic repercussions and is often not acceptable to

the public, he said. A “catch and release” requirement for large, older fish

is not practical for most groundfish species, because their swim bladder

often ruptures or other trauma occurs when they are brought to the surface,

and they die anyway.

“Given the demand to have a sustainable fishery and the biological

constraints of most marine groundfish species, the option that seems to make

the most sense is marine reserves,” Hixon said.

A well-devised network of marine reserves, Berkeley, Hixon and colleagues

said in their report, would allow a much higher population of large, old

fish within those reserves, a higher level of larvae survival, and provide

the ability of reserves to help replenish other marine areas nearby. If

properly located, reserves might also address the distinct nature of

groundfish populations in different geographic locations, they said.

Exactly that type of “seeding” effect has now been documented with some

populations in the Georges Bank off the East Coast, Hixon said, which had

huge closures in the mid-1990s due to collapsing fisheries.

“As we come to better understand the biology of these fish populations and

what may have led to their dramatic decline, more and more people are

realizing the role that selected reserves could play in addressing some of

these problems,” Hixon said. “They offer some benefits that frankly cannot

be found with any other management option.”

 

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