Fisheries Bycatch and Discards

The capture of non-target species—termed bycatch (or in some cases by-kill)—ranks as one of the major environmental impacts of the global marine fisheries industry. Bycatch, the vast majority of which is “discarded” overboard, includes:

• marketable species that are too small or that are prohibited from landings

• species that are not marketable

• commercial species that are not the target of a species-specific fishery

• species that are not fishery related, such as sea birds, sea turtles and marine mammals.

In a major study done for the FAO (Alverson et al. 1994) it was provisionally and conservatively estimated that 27.0 million tonnes of fish and invertebrate life (thus not including marine mammals, seabirds or turtles) are caught and then discarded—much of it dead or dying—by commercial fishery operations each year. This is equivalent to more than one-third the weight of all reported marine landings in commercial fisheries worldwide, estimated at some 77 million tonnes.

In addition to the ethical issues associated with wastage, there is great public concern about the environmental impacts of discard mortalities, such as potential biodiversity loss and reduced fish stocks. Perhaps as many as 200,000 marine mammals are killed annually in fishing gear (Alverson et al. 1994). Gill net fishing is likely the most serious threat to many porpoise populations; at least one species (the yaquita in the Gulf of California) and several populations of harbour porpoise are nearing extinction due to this fishery type. The inadvertent capture and mortality of sea turtles, notably those associated with shrimp trawls and some long-line fisheries, is an important factor in the continued endangerment of various populations throughout the world’s oceans (Dayton et al. 1995). High numbers of seabirds are also killed in some fisheries; long-line operations kill many tens of thousands of albatross annually and are considered the major threat to the survival of many albatross species and populations (Gales 1993).

The issue of bycatch has been a major factor in the now negative public perception of the commercial marine fisheries. As a consequence, there has been much research in recent years to improve the selectivity of fishing gear and fishing methods. Indeed, the FAO (1995) estimates that a 60% reduction in discards could be achieved by the year 2000 if a major concerted effort is undertaken by governments and industry.

Fish/Seafood Waste and Bycatch Disposal

Fish and seafood wastes can include the internal organs (viscera), heads, tails, blood, scales and wastewater or sludge (e.g., cooker juices, chemical coagulants used in primary treatment systems, oil, grease, suspended solids and so on). In many regions, most seafood-processing material from land-based industry is converted to fishmeal or fertilizer, with any remaining waste either dumped at sea, discharged into coastal waters, applied directly on land or landfilled. Waste from ship-based processing (i.e., fish cleaning) is comprised of fish parts (offal) and is invariably dumped at sea.

The impact of processed fish material on aquatic systems can vary widely according to the type of waste, the rate and amount of discharge, the ecological sensitivity of the receiving environment and physical factors influencing waste mixing and dispersion. The greatest concern involves the discharge of waste by processing companies into coastal environments; here the influx of excessive nutrients can lead to eutrophication and, subsequently, loss of local aquatic plant and animal populations.

The discharge of offal and bycatch from fishing boats can result in oxygen depletion of benthic (i.e., bottom) habitats if sufficient quantities accumulate on the seabed. However, discards and offal are considered factors contributing to the rapid growth of some seabird populations, though this may be to the detriment of less competitive species (Alverson et al. 1994).

Commercial Whaling

Commercial whaling continues to provoke intense public and political focus due (1) to the perceived uniqueness of whales, (2) to concerns about the humaneness of hunting techniques and (3) to the fact that most populations of whales—such as of blues, fins and rights—have been dramatically reduced. The current focus of hunts is the minke whale, which had been spared by the historical whaling fleets because of its small size (7 to 10 m) relative to the much larger “great” whales.

In 1982, the International Whaling Commission (IWC) voted for a global moratorium on commercial whaling. This moratorium came into effect with the 1985/86 whaling season and is scheduled to last for an indefinite period. However, two countries—Norway and Russia—maintain official objections to the moratorium, and Norway uses that objection to continue commercial whaling in the Northeast Atlantic. Although Japan does not maintain an objection to the moratorium, it continues whaling in the North Pacific and the Southern Oceans, taking advantage of an article in the International Convention for the Regulation of Whaling which allows member States to kill whales for purposes of scientific research. Less than 1,000 whales are killed annually by the Japanese and Norwegian fleets; virtually all of the whale meat ends up in the Japanese market for human consumption (Stroud 1996).

Seafood Safety: Pathogens, Chemical Pollutants and Natural Toxins

Human illness can occur from ingestion of contaminated seafood through three main routes:

1. Raw, undercooked or poorly processed fish and shellfish that are contaminated by pathogens that can cause such diseases as hepatitis A, cholera or typhoid. Untreated or inadequately treated domestic sewage is the primary source of microbial pathogens, such as viruses and bacteria, in seafood; some disease-causing organisms can persist for months in or on fish or within the digestive tracts or gills of fish and shellfish. The health risks posed by these pathogens can be virtually eliminated with proper sewage treatment and disposal, monitoring programmes, proper food processing and preparation techniques and, most importantly, through thorough cooking of seafood products (Food and Nutrition Board 1991).
2. Consumption of seafood that has been contaminated by industrial chemicals such as mercury, lead and pesticides. The global nature and pervasiveness of environmental pollution means that a wide variety of industrial chemicals—such as pesticides and heavy metals (e.g., lead and mercury)—are typically found in seafood. However, the extent of contamination varies widely from region to region and between species. Of particular concern are those chemicals that can bioaccumulate in humans, such as PCBs, dioxins and mercury. In these cases, contaminant burdens (from a wide variety of sources, including seafood) increase over time to levels where toxic effects may be exerted. Though much remains to be understood concerning the effects on human health of chronic contaminant exposure, an impressive body of information suggests a clear potential for increased cancer risks, immunosuppression, reproductive impacts and subtle impairment of neurological development in foetuses and children. In a major report on seafood safety, the Institute of Medicine of the US Academy of Sciences (Food and Nutrition Board 1991) recommended—as have numerous environmental and human health organizations—that an active environmental stance aimed at pollution prevention would ultimately be the best means to avoid continuing human health problems and pollution disasters as a result of industrial chemicals.
3. Consumption of seafood contaminated by natural algae-related toxins, such as domoic acid, ciguatoxin and saxitoxin. A wide range of toxins are produced by various algae species, and these can accumulate in a range of seafood products, notably shellfish (the exception being ciguatoxin, which is found only in reef fish). Resulting illnesses include “shellfish poisoning”—either paralytic (PSP), amnesic (ASP), diarrhetic (DSP) or neurotoxic (NSP)—and ciguatera. Mortalities continue to result from PSP and ciguatera; no fatalities have been reported from ASP since its discovery in 1987, when three people died. There has been what appears to be an increase in toxic algal blooms since the 1970s, as well as changes in the distribution and intensity of fish and shellfish toxicity. Though algal blooms are natural events, it is strongly suspected that coastal nutrient pollution—mainly from fertilizers and sewage—is enhancing bloom formation or duration and thereby increasing the likelihood of seafood toxicity episodes (Anderson 1994). It is important to note that, unlike for pathogens, thorough cooking does not reduce the toxicity of seafood contaminated by these natural poisons.

Back