Factors affecting magellanic penguin mortality at coastal trawlers in Patagonia, Argentina

Abstract

Incidental capture at trawlers has been recognized as a significant source of seabird mortality, and is considered one of the main threats to seabirds at sea. The understanding of seabird-fishery interactions and of factors influencing individual mortality is fundamental to develop management actions and help protect seabird populations. We quantified seasonal and annual variability in Magellanic Penguin (Spheniscus magellanicus) incidental captures and explored factors which may be influencing their by-catch at coastal trawlers targeting either Argentine Red Shrimp (Pleoticus muelleri) or Argentine Hake (Merluccius hubbsi) in the Isla Escondida fishing area, Argentina, for the months encompassing most of the penguin's breeding period (October-February) of the 2008, 2009, 2011 and 2012 fishing seasons (n=2336 hauls). A total of 203 penguins were incidentally caught in nets, with rates that varied between months and years. Mean monthly capture rate was 0.087 birds haul-1, and ranged between 0.01 and 2.07 birds per haul. All captured penguins were adult individuals. Incidental capture occurred almost exclusively when targeting Argentine Hake (97.5% of cases) and during 2009. Incidental captures were more likely to occur when vessels operated closer to penguin colonies, with 85% of incidental captures occurring at less than 45km. Vessels targeting hake operated significantly closer to the colonies than those targeting shrimp. Incidental capture of Magellanic Penguins in coastal trawlers in the study area appears to be highly variable and relatively low. Our results suggest that in the event Magellanic Penguin mortality at coastal trawlers becomes a conservation issue, spatial and temporal closures focused on the Argentine hake could be used as potential measures to reduce penguin by-catch, complementing the effective implementation of a marine protected area.