Predation by southern sea lions (Otaria flavescens) on artisanal fishing catches in Uruguay

Abstract

Southern sea lions (Otaria flavescens) forage in coastal fishery grounds in shallow waters, where they interact with coastal fishing activities. The main objective of this research was to evaluate the predation of southern sea lions on artisanal fishery catches and thus determine whether interactions with sea lions affected catches. Between July 1997 and March 1998, we observed 53 fishing events onboard artisanal fishing boats in four localities. The presence and number of sea lions around the boat and the numbers of each fish species consumed by sea lions were recorded by an onboard observer. To estimate the damage caused by sea lions to fishery catches, we considered two scenarios, a conservative scenario and a maximized scenario. Predation on catches was observed in 50.9% of all the fishing events and up to four sea lions were sighted in 67.9% of fishing events. Considering a conservative scenario, predation varied from 0.8 to 9.1% of the catch per unit effort (CPUE) depending on the location. Considering the maximized scenario, predation varied from 3.4 to 46.2%. However, no significant relationship was found between CPUE and the number of sea lions in any locality or with either type of fishing gear. Furthermore, CPUE did not differ in the presence or absence of sea lion interactions and predation per unit effort did not vary between localities or seasons. It was concluded that neither the presence of sea lions nor the damage they cause were responsible for variations in CPUE.

Overlap between pinniped summer diet and artisanal fishery catches in Uruguay

“…During the same month, a quantification of artisanal fisheries catch was recorded directly onboard fishing boats at three localities on the Uruguayan coast (Szteren and Páez, 2002). These three localities, named 'Piriápolis', 'La Paloma' and 'Cabo Polonio', are situated within a maximum distance of 100km from 'Isla de Lobos' ( Figure 1).…”

“…Operational interactions, which include damage to fishing gear or catches, disturbance to the fishing activity and marine mammal incidental catch, and biological interactions which involves predation or competition for resources between both predators (Wickens, 1995). In Uruguay, only one study focused on operational interactions between southern sea lions and artisanal fisheries quantifying damages caused by the animals to the fishing catches (Szteren and Páez, 2002). However, no studies have considered ecological interactions.…”

Composition and seasonal variation in the diet of the South American sea lion (<i>Otaria flavescens</i>) from Quequén, Argentina

“…A direct method is based on travelling on fishing boats and counting the number of fishes damaged or consumed by sea lions directly from the net (operational interaction) (Szteren and Páez, 2002). Such method allows for the estimation of the economic loss in catches (commercial target species) or gear damage by sea lions (Northridge, 1984;.…”

“…The diet of South American sea lions has been studied in south Brazil (Oliveira, 1995), in Chile (GeorgeNascimento et al, 1985, reviewed by Siefield, 1999, in Uruguay (Szteren and Páez, 2002;Steren et al 2004), and in Patagonia, Argentina (Rivero et al, 1999 6 ; Koen Alonso et al, 2000). South American sea lions feed on a wide variety of prey, mainly teleost fish, cephalopods, and crustaceans (Vaz-Ferreira, 1982;George-Nascimento et al, 1985;Koen Alonso et al, 2000, Trites andSoto, 2004 7 ), some of which are important to commercial fisheries (Daneri and Carlini, 1999;Koen Alonso et al, 2000, Naya et al, 2002Soto et al, 2004).…”

Uruguayan Pinnipeds (Arctocephalus australis and Otaria flavescens): Evidence of Influenza Virus and Mycobacterium pinnipedii Infections

“…Sea lions compete directly with small-scale coastal fishing and artisanal fisheries, feeding on species that are part of the fishermen's daily catch by stealing prey trapped in nets and longlines, and sometimes causing important damage or cracks in the gear Lezama & Szteren, 2003;Ponce de León & Pin, 2006;Szteren & Páez, 2002). According to different authors, the sea lions' diet is mainly made up of coastal prey and some pelagic fishes: whitemouth croaker (Micropogonias furnieri), striped weakfish (Cynoscion guatucupa), Brazilian codling (Urophysis brasiliensis), cutlassfish (Trichiurus lepturus), mackerel (Trachurus lathami), Argentinean conger (Conger orbignyanus), carangid (Parona signata), two species of anchovies (Engraulis anchoita and Anchoa marinii), and Argentinean croaker (Umbrina canosai) (Franco-Trecu, 2010;Naya et al, 2000;Pinedo & Barros, 1983;Ponce de León & Pin, 2006;Riet et al, 2011Riet et al, , 2012Vaz Ferreira, 1981).…”