Sex ratios in reef fish

A new paper appearing in American Naturalist examines the impact of overfishing on reef fish populations, and comes to some interesting and, perhaps, unexpected conclusions.  Australian biologist Stefan Walker and his colleagues observed that, as population sizes declined, many reef fish were producing fewer young per individual.  This in spite of the fact that lower population sizes should mean more available resources.  To get at the cause of this phenomenon, the researchers tagged and followed over 200 cylindrical sandperches (Parapercis cylindrica) on the Great Barrier Reef.  These fish are sequential hermaphrodites, born female with some later changing to males.  Walker and team found that the frequency of sex changes was inversely related to fish density, resulting in a higher percentage of males, and therefore lower egg production, in more heavily impacted populations.  The researchers go on to tout their findings as further evidence that marine protected areas, which do a better job of densities, are a more effective way to conserving populations than fishing quotas.