For many years, folk wisdom about limiting the capture of small fish in order to increase the numbers of breeding fish has guided fishing practices. Unfortunately, this simple strategy of taking the big critters and leaving the little ones does not sustain healthy fisheries or healthy ecosystems. Two elements of natural history—genetics and reproductive capacity and ecosystem integrity—tell us why this practice doesn’t work and what we can do about it.
Genetics and Reproductive Capacity
Unlike mammals and birds, which reach maturity and maximum size simultaneously and then raise a few offspring each year, most fish and shellfish (such as lobsters and clams) grow throughout their lives. This dramatically increases the number of young they are able to produce each season. For example, a young Atlantic cod will produce one million eggs each year, while an older cod will produce nine million eggs. By selectively removing the largest, oldest individuals of a species, we were taking out those fish that grew fastest, matured at larger sizes, and had greater reproductive potential. We inadvertently rewarded those that stayed small, matured quickly, and produced fewer eggs, thus genetically reducing the size at which certain species matured.
Because of the astounding number of offspring a fish can produce, people once assumed, incorrectly, that fish could quickly rebound from depleted stocks. Now we know that a fishery management strategy that removes most of the population’s reproductive potential actually works against our goals of sustaining productive fish populations and fisheries.
If selective fishing is bad for individual species, it’s even worse for marine ecosystems. Taking the biggest species (usually predators and dominant grazers) out of the ocean allows a few ‘weedy’ species to grow uncontrolled and take over. For example, sea urchins and brittle stars can replace towering kelp forests in places where fishing has removed both their predators (lobsters, wrasses, and other fishes), and also their competitors for space and food (abalones and snails). Free to multiply and spread unchecked, the urchins and brittle stars can turn a once diverse ecosystem into a barren environment. Healthy oceans need their top predators as well as a complete complement of grazers to continuously respond and adapt to each other and to the environment.
What is the solution? We need food from the sea, but it can no longer supply us with enough for an increasingly hungry world. Aquaculture, or fish farming, control of disease and parasites, and the education of consumers about smart choices for seafood are all projects underway to try and solve the problems of overfishing.
Fishing in national parks seeks to balance the needs of nature for healthy wildlife with the value of recreation and the connections to nature that visitors experience when fishing. Read more about fishing opportunities in America’s great waters in the ‘Recreation’ section of our website, found under ‘Places – Ocean and Coastal Parks.’
Last updated: May 6, 2016