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[tvoivozhd <tvoivozd AT infionline.net>]

Big, old fish, like big, old trees are best seedstock to conserve 
healthy, more productive populations. Present fishing, logging practices 
are selective against, not for healthy populations---like a beef farmer 
selecting the runtiest cattle as breeders for the next generation.



Source: Oregon State University
Date: 2005-01-26
URL: http://www.sciencedaily.com/releases/2005/01/050125085716.htm
Big, Old Fish Key To Restoring Groundfish Stocks

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. Requiring "catch and release" 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."