For thousands of years, humans and many other species have thrived off of marine life for nourishment and functional materials. However, as our population grows and modern fishing methods make capturing large quantities of sea life more accessible, we pose a threat to their genetic, species, ecosystem, and functional diversity. In the face of environmental change, the loss of genetic diversity hinders a population’s ability to adapt; the loss of species diversity hinders a community’s ability to adapt; the loss of functional diversity hinders an ecosystem’s ability to adapt; and the loss of ecological diversity hinders the whole biosphere’s ability to adapt.
Genes are the driving force behind an organism’s defining characteristics and functions. Overfishing can act as a form of environmental change that selects for and alters certain physical and developmental traits, essentially causing evolution. One example of this selection pressure is the preferential exploitation of larger fish in a population. Obviously, a larger fish provides more nourishment for more people, and it also offers more in terms of marketable profit. However, if these larger fish are removed much more frequently, over time the survival of smaller fish is favored and they gain an evolutionary advantage. Individuals that mature earlier than others in their reproductive lives begin to flourish and do most of the reproducing. These fish are the ones that have a chance to consistently pass their genes on before being caught, and the genetic variability of the population begins to change in favor of the fish that begin reproducing at a younger age and/or smaller size.
One example of this effect has been observed in Pacific pink salmon. Over-fishing placed an uncustomary pressure on their species by catching nearly 80 percent of spawning fish; researchers examined the catch data and identified a steady decrease in the average weight per fish. Even after accounting for outside factors such as environmental woes, they concluded that our human inflicted fishing pressure was the sole cause of this miniaturization of Pacific pink salmon.
In Part 2 of my series on over-fishing, I will be examining the effects we have on species diversity.