Effects of time-area closure on tropical tuna purse-seine fleet dynamics through some fishery indicators

Abstract

-Time-area closures have become a frequently used tool to control fishing effort and protect feeding and spawning areas. However, because time-area closure strata are mainly based on biological and ecological considerations, and do not accounts for fishermen's behavior-at-sea, this type of regulation tool may not entirely achieve its objectives. With the aim of comparing the impact of two different time-area regulations: (1) a moratorium on Fish Aggregating Devices (FAD) sets (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005) and (2) a no-take area for surface fleets (2005)(2006)(2007)(2008)(2009)(2010) on the dynamics of the European (EU) tuna purse seine fleet operating in the eastern tropical Atlantic, several fishery indicators were evaluated through a Before-After, Control-Impact (BACI) approach. The results showed that prior to any regulation, the fleet used to be concentrated within the Gulf of Guinea area. During the first years of the moratorium on FAD (from November to January within a large region in the eastern Atlantic) there was a movement towards outside the protected area, increasing the total sets on FAD (restricted fishing activity). In general, this moratorium fulfilled its objectives; however, it was not respected during the last years of this regulation. The no-take time-area closure restricted all tuna catches for the surface fisheries but only in November and within a small area (i.e., the Picolo zone). As a result, there was an increase in activities on free schools outside the no-take area. Our findings suggest the use of some simple fishery indicators to understand fleet dynamics as a complement of ecological information before implementing new time area closures. Furthermore, since tunas are highly mobile species, anticipating the possible re-allocation of effort of purse seiners to adjacent areas in response to the spatial regulation is required to design different candidate time-area closures and to evaluate their effectiveness to protect juvenile tunas.

Adaptive responses of tropical tuna purse-seiners under temporal regulations

“…Our study provides an example of how fishers can respond to the implementation of seasonal regulations. Similar situations have been reported in several fisheries with unintended impacts on fishing resources (Dorn 1998;Arendse et al 2007;Demestre et al 2008;Torres-Irineo et al 2011). For instance, Arendse et al (2007) showed that a closed season during the breeding period did not increase the reproductive output of the population through a per-recruit simulation.…”

“…In another example, Demestre et al (2008) analysed the use of seasonal closures to minimize the benthic communities' degradation by trawling in the Mediterranean; they found that after the closure, the faunal abundance decreased due to the resumption of fishing activity. In the eastern Atlantic Ocean, Torres-Irineo et al (2011) found that purse-seiners increased their fishing sets on FADs after the implementation of a seasonal closure area. In the case of the Pacific Hake, Dorn (1998) showed how the vessels adjusted their response to a ban to fish at night by increasing their catches during the day in order to maximize their profits.…”

Modelling the effect of marine protected areas on the population of skipjack tuna in the Indian Ocean

“…These aspects have proven to be important (Salas and Gaertner 2004;Abbott and Haynie 2012) and could be included by adding a dynamic model of the fleet spatial behaviour, linked to the fishing costs and the prices of the fish. Several models that incorporate these effects are documented in the literature (Wilen et al 2002;Grafton et al 2005;Dowling et al 2011), but in order to better anticipate the possible re-allocation of effort in response the implementation of an MPA, we need first to deepen our understanding of fisher behaviour (Salas and Gaertner 2004;Torres-Irineo et al 2011;Abbott and Haynie 2012).…”

Consequences of fishing moratoria on catch and bycatch: the case of tropical tuna purse-seiners and whale and whale shark associated sets

“…A key issue is the reduction of incidental catches of marine megafauna (e.g., sharks, marine mammals, turtles and seabirds) (Lewison et al 2004a, b). The effect of various conservation or management measures have been assessed on exploited stocks (Nowlis 2000;Torres-Irineo et al 2011;Morris and Green 2014) and, more rarely, on incidental megafauna catches (Grantham et al 2008;Werner et al 2015). These include changes in fishing gear and spatial closures.…”