Exporting seabird by-catch: concentration of foraging activity and fisheries interactions around closure areas

SOFIA COPELLO; GABRIELA S. BLANCO; JUAN P. SECO PON; FLAVIO QUINTANA; MARCO FAVERO

Cape Town

Conferencia; 2nd World Seabird Conference; 2015

World Seabird Union and The African Seabird Group

Fisheries are one of the main threats affecting the survival of most albatrosses and petrels species around the globe. Fisheries management (e.g. fishing quotas, closures, regulations) may impact on a range of seabirds? traits such as foraging behavior and the interactions with the vessels. There is an extensive year-round fishing closure in the Patagonian Shelf (area of approximately 120,000 km2) where trawling is banned. The consequent concentration of trawlers? fishing effort in the boundary of this area and the strong overlapping with the distribution of albatrosses triggered the question of a potential exacerbated negative effect of bycatch in such border area. Hence, this study was conducted having as main objectives: (1) the analysis of the effect of fishing closures on the flight patterns of Black-browed Albatrosses (BBAs) and Southern Giant Petrels (SGPs) as case study species known to extensively interact with trawlers, and (2) the analysis in space and time of seabird-fisheries interactions (i.e. contacts with the fishing gear as a proxy of risk of mortality) in relation to the vicinity to fishing closure. For this, 55 satellite transmitters were deployed on BBAs and SGPs between 1999 and 2013. Discrete behavioral mode (foraging vs. transiting) was inferred inside and outside the closure area from satellite movement data using state-space models. Seabird bycatch data were obtained from on-board observers (for 2007-2009 and 2011-2012). The spatial density for each behavioral mode and the seabird bycatch was determined by performing a Kernel density analysis. Foraging in both species was mainly concentrated on the border of the fishing closure where the fishing activity also concentrated. However, the presence of the fishing closure did not influence transiting behavior. Seabird-fishery interactions were significantly concentrated in the external boundary of the fishing closure in relation with other foraging areas in waters distant to the fishing closure. The study highlights that, although by definition seabird bycatch inside closure areas is null, in practice the ?exporting effect? due to the concentration of both fishing effort and seabird foraging in border areas may substantially increase seabird by-catch in the immediate neighboring waters. Hence, the design of conservation management measures for seabird by-catch should contemplate specific regulations to address these negative side effects of concentrating both fishing and seabird activity in border areas.