This Week

3 January 1998

Late bloomers live long and prosper

FISH that grow bigger and take longer to reach sexual maturity are more
vulnerable to overfishing than their smaller, slower-growing cousins, according
to a British study. The finding, which had long been suspected but never proven,
could help poor countries without access to detailed fisheries research to
manage their fisheries cheaply.

A team led by Simon Jennings of the University of East Anglia looked at
different populations of 11 species in the northeast Atlantic, including cod,
herring and haddock. The researchers compared the sizes and growth rates within
each species, which often vary widely according to geography, water temperature
and other factors. They found that stocks that were older and larger when they
reached sexual maturity declined much more quickly under the same fishing
pressure because they could not make up numbers quickly enough to compensate for
overfishing. The team released the results at a meeting of the British
Ecological Society at the University of Warwick last month.

Jennings says that previous studies of overfishing compared unrelated species
where there were too many differences between the fish to tease out which was
the most important. His study is the first to compare different local stocks of
the same or closely related species.

If the relationship between vulnerability, maturation and size is true for
other fish, says Jennings, then threatened fish stocks in poor countries could
be managed cheaply. For example, if officials know how one population of fish
responds to a certain level of fishing, they can predict how another would react
simply by knowing its size and age at maturity—and without carrying out
expensive research.