Other media are taking quite a lot of interest in a Nature paper on fish stocks which suggests that a great deal of fishing policy is wrong headed
Using records of fish larvae researchers attempted to discern why fished populations fluctuate more than un-fished populations. Their conclusion: the problem is we take all the big fish.
And current fishing policies often specify a minimum size, below which things must be put back in the ocean.
“That type of regulation, which we see in many sport fisheries, is exactly wrong,” says George Sugihara, of the Scripps Institution of Oceanography. “It’s not the young ones that should be thrown back, but the larger, older fish that should be spared.”
Sugihara and a heavyweight team of researchers investigated three possible reasons for fluctuations in fished fish:
– Variable fishing pressure directly leading to variability;
– Fishing decreasing size and age of a stock, making fish populations more susceptible to environmental changes;
– Younger populations being more unstable.
Their conclusion: “We find no evidence for the first hypothesis, limited evidence for the second and strong evidence for the third.”
For me there’s a problem with the ‘throw the big ones back’ solution though. Fish thrown back for being undersize are quite often dead. A maximum size limit could just mean more big, dead fish in the sea. Surely reducing the overall catch quota and letting fishermen sell everything they catch would be the way forward? Any oceanographers out there please feel free to correct me.
There’s another interesting fact thrown up by this research. In a commentary running alongside Sugihara’s paper, Nils Stenseth and Tristan Rouyer, of the University of Oslo, suggest taking the big ones can increase the evolution of fish:
The higher mortality experienced by older and bigger fish, directly caused by size-selective harvesting, can induce earlier maturation of fish within the stock, and can do so in two ways that are not mutually exclusive. One is ‘phenotypic plasticity’, the ability of the fish to change its characteristics, or phenotype, in response to changes in its environment. This is a reversible response that is primarily an ecological effect. The other is a potentially irreversible evolutionary response due to harvesting.
AFP quotes them as saying, “When the ecological effects of fishing a particular population are observed, the evolutionary consequences may have already set it [sic], and may be irreversible.”
It’s not quite so bleak, they actually caveat that statement. Here’s the full quote: “When the ecological effects of fishing a particular population are observed, the evolutionary consequences may have already set in, and may be irreversible, or at least only slowly reversible, depending on whether sufficient genetic variability remains in the stocks.”
Image top: fishing vessel / NOAA
Image lower: fishing gear / NOAA