Minimizing bycatch of sensitive species groups in marine capture fisheries:lessons from tuna fisheries

11.1. INTRODUCTION 11.1.1. Ecological, Economic, and Social Issues Related to Fisheries Bycatch Bycatch in marine capture fisheries is the retained catch of nontargeted but commercially viable species (referred to as incidental catch‚ÄövÑvp) plus all discards (Food and Agriculture Organization of the United Nations [FAO] 2005).1 It is an increasingly prominent international issue, raising ecological concerns, as some bycatch species of cetaceans (whales, dolphins, and porpoises), seabirds, sea turtles, elasmobranchs (sharks, skates, and rays), and other fi sh species are particularly vulnerable to overexploitation and slow to recover from large population declines (FAO 1999a, 1999b, in press; Fowler et al. 2005; Gales 1998; Gilman et al. 2005, 2006a, 2006c, 2008; Lutz and Musick 1997). Bycatch can alter biodiversity and ecosystem functions by removing top predators and prey species at unsustainable levels (Myers et al. 2007). It also alters foraging behavior of species that learn to take advantage of discards. Economic effects of bycatch on fi sheries include loss of bait, reduced availability of baited hooks when they are occupied with unwanted bycatch species, and concomitant reduced catch of marketable species; the imposition of a range of restrictions, closed areas, embargos, and possible closures; allocation among fi sheries, where bycatch in one fi shery reduces target catch in another, and bycatch of juvenile and undersized individuals of a commercial species can adversely affect future catch levels (Brothers et al. 1999; Hall et al. 2000). Discarded bycatch raises a social issue over waste: From 1992 to 2001 an average of 7.3 million metric tons of fi sh were annually discarded, representing 8 percent of the world catch (FAO 2005). Prominent bycatch issues include dolphins and porpoises in purse seine fi sheries and driftnets; fi sh discards in shrimp trawl fi sheries; and seabird, sea turtle, marine mammal, and shark bycatch in longline, purse seine, gillnet, and trawl fi sheries (FAO 1999a, 1999b, 2005, in press; Hall et al. 2000). In commercial tuna fi sheries, the incidental bycatch of sensitive species groups (seabirds, sea turtles, marine mammals, and sharks) and bycatch of juvenile and undersized tunas are allocation and conservation issues. In addition to problematic bycatch, overexploitation and illegal, unreported, and unregulated (IUU) fi shing, which complicates bycatch management, are additional conservation issues facing the management of tuna fi sheries. This chapter employs examples of bycatch in commercial tuna fi sheries to describe (1) the range of options to reduce bycatch, (2) principles and approaches to successfully introduce effective bycatch reduction measures, and (3) initiatives taken by intergovernmental organizations, the fi shing industry, and retailers to address bycatch. Changes needed to improve the sustainability of tuna production are recommended.