By-catch is bad, most fishing gear incidentally captures animals that are not the target of the fishery. These animals are termed “by-catch” and can include benthic invertebrates, non-commercial fish species, sharks, sea turtles and even seabirds. Most often, by-catch is discarded at sea and most animal do not survive. It is estimated that as much as 25% of the world’s fishery catch is disposed of overboard as by-catch. This amounts to 18 to 40 million tons per year.
Aquaculture operations can supply food to meet part of the demand for certain species, thereby relieving fishing pressure on some wild populations. Herbivorous species (such as tilapia) are preferred for aquaculture because they do not require protein for food. Oysters, clams and mussels are good aquaculture species because they do not require supplemental feeding. Properly implemented, aquaculture also has minimal impacts on the environment. Recirculating water systems in ponds and tanks reduce waste discharge to the environment. These designs will also allow operations to be moved inland away from the vulnerable coastal areas.
Some aspects of aquaculture can reduce sustainability or have adverse environmental impacts. Some operations use many pounds of wild fish protein to produce a few pounds of farmed fish protein with a higher market value. Organic wastes, chemicals and pharmaceuticals discharged from enclosures can be harmful to the environment. Construction of ponds can damage coastal wetlands or disturb natural water flows.
The key issues that are evaluated to determine whether a fishery is being exploited sustainably include:
- The inherent vulnerability of the species to fishing pressure: Is the reproduction and other aspects of the species biology sufficiently robust to allow the harvesting of numerous individuals without impairing the populations ability to continually replace those animals that are removed?
- The status of the species population: Is the population healthy or is it reduced from optimal levels by other factors such as habitat loss or population?
- The nature and extent of by-catch: What are the types and numbers of non-target species that are caught and will not survive using the gear and methods employed by the fishery?
- The effects of the fishing practices on habitats and ecosystems: Does the gear damage the sea bottom or adversely affect, whether directly or indirectly, any other aspect of the ecosystem?
- Effectiveness of the management of the fishery: Is sufficient data being collected and records maintained to allow specialists to determine the status of target species populations and take action to ensure sustainability?
Many marine ecologists think that the biggest single threat to marine ecosystems today is overfishing. Overfishing means catching fish faster than they can reproduce. It is a non sustainable use of our oceans.
Overfishing pushes the fish population lower and lower, until fish are so few that fishermen can't make a living any more. This can occur in any body of water from a pond to the oceans.
Today the modern fishing industry is dominated by fishing vessels that far out-match nature's ability to replenish fish. Giant ships using state-of-the-art fish finding sonar can pinpoint large schools of fish quickly and accurately. The ships are outfitted like giant floating factories with fish processing and packing plants, huge freezing systems and powerful engines to drag enormous fishing gear through the ocean. Put simply: the fish don't stand a chance.
Evidence of overfishing is seen throughout U.S. waters, including the near-disappearance of fish that were once abundant, and the shrinking sizes of average-sized fish. Many fish are caught before they are old enough to reproduce.
Overfishing is causing changes in our oceans’ ecosystem, which may never be reversed, particularly in light of the fact that the world population continues to increase along with increased consumer demand for seafood.