Big Fish Catches Yield Smaller Fish: Genetic Shift in Marine Populations

Do you like to eat tuna? How about swordfish or marlin? Unfortunately, you may be finding smaller versions of these species at your supermarket in the future--if not already. A new study shows that big fish catches may mean smaller fish that are less fertile.

The study, published in the journal Frontiers in Ecology and the Environment, studied a model tropical fish, the Trinidadian guppy, in the lab. The scientists examined changes in the fish's DNA as the species became both fewer and smaller.

In fact, the researchers found that they proved for the first time that changes in the body size and maturation of the fish is "an evolutionary response to over-fishing," according to BBC News. Their findings could have major repercussions for the fishing industry.

Fish species in the wild are indeed becoming smaller over time. Large adults are sought by the industry, which means that species have to reproduce when they're younger in order to successfully survive. Genes are naturally selected for fish to be generally smaller and reproduce earlier. The selection also predisposes fish to grow more slowly, which means that the industry needs to harvest more individual fish in order to meet the same tonnage.

Yet these particular changes may not be rectified right away if fishing practices were changed. The researchers suggested that it may take as much as five to ten times longer than anticipated for fish stocks to recover from the changes to their DNA--assuming that the DNA change can be reversed.

"This means that current estimates for how quickly commercial fisheries will recover from declines and over-fishing are probably far too optimistic," the researchers stated to BBC News.

The fishing industry has long regulated the size of the fish that can be fished for. In particular, it has favored fishing for larger fish over smaller ones in order to give juveniles a chance to grow to maturity and reproduce. These latest findings, though, suggest that these regulations may be having the opposite effect. Instead of preserving populations, it's driving them further toward being fished unsustainably.

"As well as losing the capacity to produce large sized and productive fish, specific fish populations may also be at risk of losing other specific adaptations by selective fishing, such as adaptations to particular locations characteristics, like colder water or migration routes," said Serinde van Wijk, one of the researchers involved in the study, in an interview with BBC News.