Modifying fishing gear to achieve ecosystem objectives.

Abstract

AbstractRecent developments in navigational aids and instruments for improving the classification of bottom habitats enable the fishing industry to harvest target resources more efficiently and to reduce impacts on benthic habitats and their communities. These changes hold promise for the achievement of broader ecosystem objectives, such as maintaining species and ecosystem diversities. This chapter provides a review of successful developments and applications of selective fishing techniques that have been used to achieve ecosystem objectives. For example, the introduction of turtle excluder devices (TEDs) in shrimp trawls has dramatically reduced mortality of endangered sea turtles; the declines of the by-catches and discards of finfish in many shrimp trawl fisheries has been the result mainly of the sorting grids and square mesh panels introduced in these fisheries; changes in the construction and operation of tuna purse seines have significantly reduced the mortality of dolphins that are captured incidentally; and technical measures to reduce the incidental catch of seabirds in longline fisheries have been developed successfully. By-catch considerations and gear modifications play an important role in the regulation of several major fisheries, and new by-catch reduction devices and other innovative gear modifications continuously are being proposed and tested to mitigate problems. This chapter also reviews the status of the development of gears, instruments and practices that can reduce the impacts of fishing on benthic communities and their habitats. During the last two decades, there has been increasing concerns over the effects of bottom-fishing activities on benthic ecosystems in all major regions where commercial fishing is done. The evidence that fishing gears may injure benthic organisms and at least locally reduce habitat complexity and cause reduced biodiversity has appeared in various media with increasing frequency. Finally, this chapter discusses the most likely future development of commercial fishing practices, including an analysis of the likely consequences that changes to achieve ecosystem objectives might have on the efficiency of fishing. It is unlikely that gear modifications will eliminate all adverse effects completely - progress will take place by modest steps. Therefore, realistic short- and long-term objectives are necessary when attempting to minimize ecosystem impacts of a fishery. Managers should set measurable limits for by-catch levels and benthic disturbances caused by fishing gears. In many cases, a combination of technological improvement, active avoidance of areas and seasons of high by-catch rates (hot spots), and other management actions maybe necessary to achieve the desired outcomes. Some gear modifications may make gears more expensive to construct, and more difficult to operate and maintain. Moreover, catches of marketable fish may be reduced. Measures and techniques that increase costs and reduce earnings are unattractive to fishermen. There is little point in introducing totally unacceptable concepts or modifications - they will probably fail. The fishing effectiveness and practicality of new designs are important because an inefficient gear will not be used or will be 'sabotaged', or may require so much additional fishing effort that overall impacts could actually be increased. Close cooperation between the fishing industry, scientists and other stakeholders will be necessary in the process of developing and introducing environmentally friendly fishing technology. In conclusion, technologies developed in recent years demonstrate that the impact of fishing gears on non-target species and habitats can be significantly reduced without having a major negative effect on the profitability of the fishing operation. Clearly, economic rewards should be offered for the creation of new types of gear and modifications that reduce by-catch and minimize impact on habitats.