WIOMSA-CORDIO spawning book Full Doc 10 oct 13.pdf

Chapter 12: Conservation and fisheries effects ofprotecting species forming spawning aggregations usingno-take marine reservesJan Robinson, Arnaud Grüss and David KaplanIntroductionThe study of reef fish spawning aggregations and their fisheries typically raises concerns forconservation and management. This is due to the fact that many species forming aggregationsfor the purpose of spawning (hereafter referred to collectively as ‘aggregative spawners’) arevulnerable to exploitation and very few aggregation fisheries appear to be sustainable (Sadovyand Domeier 2005; Sadovy de Mitcheson and Erisman 2012). Given widespread decline andcollapse of spawning aggregations and the unsustainable depletion of the populations fromwhich they form, a conservation response is often imperative (Sadovy de Mitcheson et al. 2012).Consequently, no-take reserves (NTRs) combined with temporal catch and market restrictions areoften recommended (Johannes 1998; Domeier et al. 2002; Rhodes and Warren-Rhodes 2005) andapplied for the protection of spawning aggregations (Sadovy de Mitcheson et al. 2008; Russell etel. 2012). However, as is the case with the general application of NTRs for supporting fisheriesmanagement objectives, notably for enhancing yields (Hilborn et al. 2004), critical science andimplementation constraints remain in the use of this tool for protecting aggregative spawners (Saleet al. 2005; Le Quesne 2009).Spawning aggregation-based NTRs differ fundamentally from conventional NTRs models that aimto produce conservation and fisheries benefits. Conventional NTRs aim to confer both persistenceof a proportion of population biomass within their boundaries and a net export of eggs and larvae(‘larval subsidy’) and adults (‘spillover’) to fished areas in order to enhance yield (Gell and Roberts2003; Russ et al. 2004; McClanahan 2010). Small NTRs that only protect the area of reef wherespawning aggregations form typically do not contain a significant resident biomass, since the vastmajority of the population will reside in areas beyond the NTR for much of the year, only migratinginto the protected area during spawning periods (e.g. Hutchinson and Rhodes 2010; Rhodes etal. 2012). Thus, spawning aggregation-based NTRs deviate from conventional models in that theydo not create the conditions for spillover and larval subsidy and will only offer protection to mostparticipating adult fish during a limited part of the year. This distinction may appear obvious, butthe fundamental difference between movement leading to spillover and yield enhancement from aconventional reserve, and mobility associated with migrations to and from a spawning area, is ofteninexplicit in the discourse on NTR effects for highly mobile species (Gaines et al. 2010).A few empirical (e.g. Beets and Friedlander 1998; Rhodes and Sadovy 2002b; Claro and Lindeman2003; Burton et al. 2005; Rhodes and Warren-Rhodes 2005; Nemeth 2005; Rhodes and Tupper2008; Mangubhai et al. 2011) and theoretical studies (Alonzo and Mangel 2004; Heppell et al.2006) have addressed the effects of spawning aggregation-based NTRs. While empirical evidenceof recovery remains scarce and is limited to a single site (e.g. Beets and Friedlander 1998; Nemeth2005), the existing studies do generally concur that NTRs protecting spawning aggregationsites can lead to significant increases in population size, biomass and, in the case of protogynouspopulations, normalization of sex ratio (Beets and Friedlander 1998). The latter effect is thought toimprove egg fertilization rates (Coleman et al. 1996; Rhodes and Warren-Rhodes 2005).The caveat to this concurrence is that such benefits are undermined or lost if fish suffer high fishingmortality as juveniles or as adults when outside of the protected spawning sites. Due to generallylow catchability outside of the spawning season, a few groupers are often fished almost exclusivelywhile aggregating to spawn (e.g. Nassau grouper, Epinephelus striatus: Sadovy and Eklund 1999;113