what is now called "Malthusian" overfishing (Pauly et al. 1998), characterized by the widespread use of dynamite and cyanide as cheap ("entry-level") fishing gears.

The effects on coastal ecosystems of the combined fishing pressure of the industrial and small-scale sectors, fishing techniques that destroy reefs, and the downstream effects of nonsustainable agricultural and forestry practices have been devastating, with most of the fringing reefs surrounding the Philippine islands choking under silt and experiencing massive species changes. The slowly declining fish supply is now dominated by small, low-value species.

Bycatch, Discards, and Unobserved Fishing Mortality

Bycatch is the capture of nontarget species in directed fisheries. Discards are animals returned to the sea after being caught. Some bycatch is retained in most fisheries, but most of it is usually discarded and not reported in official landing statistics. Even some retained bycatch is not reported, and sometimes targeted species are discarded if they are too small. It is important to be clear about these terms (Alverson et al. 1994) because they are often used differently by different authors, and it is impossible to evaluate the importance of bycatch and discards if they are not clearly distinguished from each other.

Because a significant portion of the catch (discards) in many fisheries is not reported, the portion that is reported constitutes only a fraction of the actual catch. Discards make stock assessments and fishing mortalities difficult to estimate because they are usually unreported; even when they are, the reports usually lack specific information on the age and size of the animals discarded, which is needed for stock assessment. Thus, inferred patterns of exploitation are significantly underestimated. The situation is made worse by a variety of other unobserved sources of fishing mortality such as illegal fishing, underreporting, deaths of fish that escape from fishing gear, and ghost fishing. Recreational and subsistence fishing are also difficult to monitor and thus can represent a significant source of unobserved fishing mortality, especially for widely sought species such as bluefish (Pomatomus saltatrix), spotted seatrout (Cynoscion nebulosus), and summer flounder (Paralichthys dentatus) in the southern and eastern United States. The magnitude of discard mortality and unobserved fishing mortality could be important factors contributing to global overfishing and undesirable ecological changes.

Alverson et al. (1994) reviewed the literature on worldwide bycatch and discards and concluded that marine discards in the period 1988–1990 amounted to approximately 27 million t per year, roughly one-third as much as the total marine capture fisheries.1 There is great variation in bycatch associated with


Bycatch and discards are extremely difficult to estimate precisely, in part because they often are illegal or unregulated activities. The estimates of bycatch by Alverson et al. (1994) had a low limit of 17.9 million t and a high limit of 39.5 million t; more recent estimates suggest that bycatch has decreased (D.L. Alverson, personal communication, May 1998).

The National Academies of Sciences, Engineering, and Medicine
500 Fifth St. N.W. | Washington, D.C. 20001

Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement