OVERFISHING is leading to a massive decline in genetic diversity in some fisheries, potentially robbing them of their best chance of recovery.
A research team in New Zealand has discovered that in one stock of snapper fish, just one in every 10,000 produces a large number of surviving offspring, and that the gene pool has shrunk dramatically in the past 50 years.
Until now scientists thought overfishing posed little threat to genetic diversity, assuming that even small numbers of fish could still produce millions of offspring. Recent research has also revealed that small fractions of each stock produce most offspring, but the genetic implications of this were unclear.
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Now an international team led by Lorenz Hauser from the University of Hull has found a unique way to tackle this question. They took DNA samples from the scales of New Zealand snapper kept in archive collections. They chose fish from two populations 鈥� one huge fishery that has sustained commercial fishing for 100 years, and a smaller stock that began to dwindle about 50 years ago after becoming a commercial target.
They analysed a specific section of the DNA from each scale. For the larger, stable population they found genetic diversity had remained relatively constant. But with the smaller population they made two startling discoveries. First, the number of different alleles in the section of DNA plummeted over the years as the population decreased. Second, using calculations based on this decreasing genetic diversity, they estimated that just one in every 10,000 fish had a large number of offspring that survived (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.172242899).
鈥淭hat was the biggest surprise,鈥� says team member Peter Smith, a fisheries scientist at the University of Melbourne in Victoria. Smith says it is not clear yet exactly why so few fish breed successfully. But in a small population, it becomes more likely that the few effective breeders will also end up in a fishing net, leading to further declines in the genetic diversity of the stock. 鈥淚f we lose diversity,鈥� Smith says, 鈥渢hen it鈥檚 gone for good.鈥�