Overfishing leads to loss of genetic diversity
Science Centres: Fisheries
Overfishing can harm the genetic diversity of marine fish populations to a much greater extent than was previously thought, according to a paper published recently*.
Genetic diversity in Tasman Bay snapper.
Genetic diversity in a population is critical to a species’ ability to adapt to environmental changes and for the continued productivity of a fish stock.
In theory, genetic diversity begins to decline only when populations decline to very small numbers. Even overexploited stocks consist of several million fish, apparently protecting them from loss of genetic diversity. However, a recent study on New Zealand snapper, involving Peter Smith from NIWA, suggests that genetic variability may be declining in heavily exploited fish stocks.
Changes in DNA variability were measured over time using snapper scale collections from two populations in Tasman Bay and the Hauraki Gulf that had been archived at NIWA. Recent developments in technology allow the extraction of DNA from preserved and dried material. Scale samples, originally collected for routine ageing, provide a rare opportunity to recover genetic data from old populations.
Snapper in Tasman Bay form a small, isolated population that was first exploited commercially in the 1950s; the Hauraki Gulf population is much larger and has been exploited for a longer period. The Tasman Bay population lost variation in several DNA markers between 1950 and 1998, but the Hauraki Gulf population showed no similar decline over the same period.
The results suggest that the number of fish in the population may be many times greater than the number of fish effectively reproducing and contributing to the next generation and maintaining genetic diversity. Heavily overfished marine stocks may have already lost genetic diversity, putting their long-term survival at risk.