Fishing skews sex ratios in fish

POPULATION crashes in many species of reef fish may be linked to an excess of males brought about by fishing - and imposing quotas won't remedy the situation.

In many species, particularly those where individuals can change their sex, each fish produces fewer young as the population density drops. "It's perplexing," says Stefan Walker of James Cook University in Townsville, Queensland, Australia, "because as population density drops, more resources should be available and populations should increase."

To find out why this happens, Walker tagged 232 cylindrical sandperches (Parapercis cylindrica) in a Great Barrier Reef lagoon, and followed their movements and reproductive behaviour. Cylindrical sandperches are born female, but some later change into males, with harems of two to 10 females.

Walker saw more sex changes in regions where fish populations were low. This led to more males holding court to fewer females and a drop in the number of eggs laid per square metre of lagoon (The American Naturalist, DOI: 10.1086/655219).

The finding is likely to apply to at least 70 other sex-changing reef fish, including many commonly caught species, says Walker, and suggests that marine protected areas are a better strategy for conserving populations than fishing quotas. Protected areas maintain the density of populations whereas quotas may still allow populations to decline, increasing the rate of sex change.

An interesting article that can be read in further detail at the New Scientist following this link

http://www.newscientist.com/article/mg20727702.000-fishing-skews-sex-ratios-in-fish.html

Contributed by Tim Hochgrebe added 2010-07-24