Coastal Zone

Impacts of Capture fishing

There is no doubt that humans have severely damaged the Earths's fish resources, although there is no consensus about the true extent of the damage. Determining the number of fish in the oceans, their ability to withstand fishing pressures and ecological damages is extremely difficult. To complicate matters, fishing is not the only factor that affects the marine environment, other factors including pollution, habitat destruction, and environmental changes affect the marine ecosystem.

There are currently over 37,000 industrial trawlers and 12 million small fishing boats fishing the world's oceans in a $70 billion dollar-a-year industry. Over 100 million tons of fish are harvested annually. Unfortunately, most scientists, and even fishermen agree that such levels of production are not sustainable. There are approximately 200 fish stocks being harvested globally and only 75 of those are not being fished at or above sustainable levels. Of those 200 global fish stocks, about 50 are overfished, while about another 75 are fully utilized (Science News June 8, 1996). Maintaining current levels of production is likely to become more and more difficult with an increasing amount of the burden being placed on fish farming. More research is needed on how to manage large fish farming operations and over-exploited stocks.

Almost every expert agrees that the oceans are overfished and many fish stocks are in danger. However, this threat is barely visible to the average consumer. Fish meat still lines the supermarket shelves and prices have not skyrocketed. What most consumers don't know is that most of types of fish on the supermarket shelves are not the same kind of fish that was on those same shelves ten years ago. Today's fish is the "trash" fish of decades past. Often, these "trash" fish were simply thrown overboard to make room for more "valuable" fish. However, much of the "valuable" fish stocks have disappeared, and yesterday's trash fish have become today's goods.

Many of the new fish on the market come from lower trophic levels in the marine food web. The trophic level indicates where the organism is in the food web. Primary producers such as seaweed, and other photosynthetic organisms are on the first trophic level. Organisms that consume the primary consumers belong to the second trophic level; organisms that eat second trophic level organisms are considered to be third trophic level. Each trophic level has approximately 10 times more biomass than the trophic level directly above it. Thus, there are more fish at lower trophic levels than higher ones. However, lower trophic level fish tend to be smaller. Humans tend to prefer fish at higher trophic levels, typically between 3 and 4. The top of the marine food web, the killer whale and shark, belong to the 5th trophic level. In the past several hundred years, human activity has decimated the higher trophic levels of fish, and is now beginning to decimate the lower levels. Human fishing is slowly dismantling the ecological system that has been developing for millions of years.

Attacks on the marine ecosystem have not been limited to the higher trophic levels. Scientists believe that certain fishing techniques are capable of destroying entire ecosystems, starting with the first trophic level. There is still insufficient evidence indicating how widespread the damage is or if it is even significant. One such potentially devastating technique is trawling. The trawl works by dragging along the oceans bottom and scooping up everything in its path, leaving a swath of devastation behind it. Scientists fear that by destroying the ecosystem on the ocean floor fishermen are destroying a vital link in the marine ecosystem, the lower trophic levels along with the habitat for species of higher trophic levels. No one knows how long it takes for the ecosystem to recover, or even if the trawlers have the effect some scientists fear it has, but most experts agree that trawling in shallow waters is less devastating to the local ecosystem as it more easily recovers because of natural disturbances such as tidal flow and storms.

The cause of these problems are, too many fishermen, to great a demand, for not enough fish. At present it appears that the only sustainable option is to drastically reduce fishing to let stocks recover, before resuming at sustainable levels. The sustainable option is not an easy one, because a carrying capacity of each fishery must be determined, and such levels may not be commercially sustainable.

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