FAO recently updated a 1994 study which reported a first global estimate of the total quantity of marine life caught by fisheries and subsequently discarded. This new paper provides an update of the quantity of discards in the world’s marine fisheries based on a fishery-by-fishery approach. The weighted discard rate is estimated at 8 percent (proportion of the catch discarded). Based on this discard rate, in the 1992-2001 period, yearly average discards are estimated to be 7.3 million tonnes. Because of the different method used in the current estimate, it is not directly comparable with the previous estimates of 27 million and 20 million tonnes.
Trawl fisheries for shrimp and demersal finfish account for over 50 percent of total estimated discards while representing approximately 22 percent of total landings recorded in the study. Tropical shrimp trawl fisheries have the highest discard rate and account for over 27 percent of total estimated discards. Demersal finfish trawls account for 36 percent of the estimated global discards. Most purse-seine, handline, jig, trap and pot fisheries have low discard rates. Small-scale fisheries generally have lower discard rates than industrial fisheries. The small-scale fisheries account for over 11 percent of the discard database landings and have a weighted discard rate of 3.7 percent.
The study presents evidence for a substantial reduction in discards in recent years. The major reasons for this are a reduction in unwanted bycatch and increased utilization of catches. Bycatch reduction is largely a result of the use of more selective fishing gears, introduction of bycatch and discard regulations, and improved enforcement of regulatory measures. Increased retention of bycatch for human or animal food results from improved processing technologies and expanding market opportunities for lower-value catch.
A number of policy issues are also raised. These include a “no-discards” approach to fisheries management; the need for balance between bycatch reduction and bycatch utilization initiatives; and concerns arising from incidental catches of marine mammals, birds and reptiles. The study advocates the development of more robust methods of estimating discards, allowance for discards in fishery management plans, development of bycatch management plans and promotion of best practices for bycatch reduction and mitigation of incidental catches. Global discard estimates could achieve greater precision through additional studies at national and regional levels.
The 1994 figures showed an estimate of global discards in marine fisheries indicating that 27 million tonnes, or approximately 27 percent of the global catch, were discarded annually. The initial estimate was a major achievement, providing the order of magnitude for the estimate of global discards and illustrating the difficulty in estimating global discards, as indicated by the wide range of the estimate (17.9-39.5 million tonnes). In particular, the Alverson assessment helped to reduce global discards by focusing attention on the potential magnitude of the “discard problem”.
The 1994 estimate was based on data from the 1980s and early 1990s and cannot accurately reflect the changes that have occurred in world fisheries. However, the estimate continues to be cited in support of particular policies and actions. The Alverson assessment was also subject to criticism with respect to aspects of the estimation method, including the assumptions on which the assessment was based and the limited geographical coverage of the available discard information.
The objectives of the current study were to develop an improved and more robust and transparent method for estimating discards at the global level, and to use the method to re-estimate discards in the world’s marine capture fisheries.
The approach used in this study differs substantially from that used in the 1994 assessment, which was based on discard/catch ratios determined by species or species group. These ratios were then applied to FAO’s Fishstat nominal catch statistics for the 1988-1990 period in order to derive the global estimate.
In contrast, the current study compiled an inventory of the world’s fisheries and their respective catches. Information on the quantity of discards or the proportion of discards in the catch was obtained from available discard studies. As discard studies were not available for all fisheries, in some cases the ratio of discards to catch was assumed, based on information from similar fisheries. The total quantity of discards for the fishery was calculated by raising (extrapolating) the results of the discard studies to the total recorded landings for the fishery, as extracted from national fisheries statistics and other sources.
The fishery-by-fishery approach offers the possibility of verification and periodic updating of the discard estimates at the country or regional level in consultation with national fisheries authorities and regional fisheries organizations.
While it is unlikely that a definitive estimate of discards at the global level can be made, the re-estimate is seen as a contribution to an ongoing FAO process to focus attention on the scale of discards, trends in discarding and on fisheries management issues and practices associated with discards.