It is fact that evolution still brings to mind the kind of change that happens over millions of years, such as humans evolving from forerunners of apes. Cod fish can also evolve quite quickly, within its lifetimes. It is said that overfishing has made cod fish rare species in New England’s waters because the decades of intense fishing for the largest cod have meant the species has evolved along the lines of the survivors, which is to say, smaller cod.
Researchers analyzed that human harvesting caused changes three times as fast as those observed in natural populations. In 95 percent of the cases, the result was a decrease in size (or size-related traits, like bighorn sheep horns). And the shrinkage was substantial, an average of 20 percent. In nearly all cases the individuals were also reproducing at much younger ages and smaller sizes.
Teri Frady, an NOAA Fisheries representative, said that the decline of New England cod is the result of decades of overfishing that continues to this day. In Canadian waters, cod have not recovered as expected. Douglas Swain, of Fisheries and Oceans Canada, said that this result supports the hypothesis that there have been genetic changes in growth in this population in response to size-selective fishing.
It is found though research on captive fish that selective pressure can cause significant genetic changes in just four years. Researchers admit that catching the large fish in a population selects for smaller, slower-growing fish; catching the small ones selects for large individuals, and results in greater yields. Evolutionary change is the expectation in biology given these sorts of pressures.
