The Wilson Journal of Ornithology 123(4):709-719, 2011 
FISHERY DISCARDS AND INCIDENTAL MORTALITY OF SEABIRDS 
ATTENDING COASTAL SHRIMP TRAWLERS AT ISLA ESCONDIDA, 
PATAGONIA, ARGENTINA 
CRISTIAN JAVIER MARINAO 13 AND PABLO YORIO 2 
ABSTRACT.—We evaluated seabird attendance and incidental mortality ut coastal trawl vessels targeting Argentine red 
shrimp (Pleoticus muelleri) in the Isla Escondida fishing area. Argentina, during 2006-2007 and 2007-2008. Eight seabird 
species attended vessels, and the most frequent and abundant seabird (percent occurrence, mean number per haul) in the two 
seasons was the Kelp Gull (Larus dnminicanus) (100%. 112.3 and 100%. 263.4. respectively), followed by the Black- 
browed Albatross ( Thalassarche melanophris) (85%. 17.6. and 90%. 32 4. respectively). Eleven Magellanic Penguins 
(Spheniscus magellanicus ) and one Imperial Shag ( Uucocarho athceps) were killed in nets with a mean capture rate of 
0.003 and 0.0003 birds per haul, respectively. The estimated total number of birds killed was 53 penguins and five shags 
considering the total number of hauls made by the fishery in the two seasons. No contacts between seabirds and warp cables 
were recorded. Coastal shrimp vessels generally operated between 15 and 20 km offshore, at a mean distance from the main 
Kelp Gull colony (Punta Tombo) of 43.9 km. At least UK) fish and invertebrate species were discarded, mostly Argentine 
hake ( Merluccius hubhsi). Total amount discarded per season by this coastal fishery in the two seasons was estimated at 
3.2S4 and 6.590 tonnes, respectively. The coastal shrimp fishery in the Isla Escondida area appears to have a small impact 
on seabirds in terms of incidental mortality but provides significant amounts of supplementary food during the breeding 
season of the Kelp Gull. Received 27 January 2011. Accepted 22 May 2011. 
Commercial fishing can generate important 
alterations in marine ecosystems and have impor¬ 
tant effects on top predators (Pauly et al. 2(X)5). 
Seabirds are among the top predators which most 
regularly interact with fisheries, and can be 
negatively affected as a result of incidental 
capture and competition for common resources 
(Duffy and Schneider 1994. Tasker et al. 2000. 
Montevecehi 2002). In addition, due to the low 
selectivity of fishing gear, trawl fisheries discard 
large amounts of fish and invertebrates (Alverson 
et al. 1994) which are used by many organisms, 
including seabirds (Garthe et al. 1996, Furness et 
al. 2007). Discard consumption at sea is currently 
an important component of the trophic ecology of 
many seabird species (Camphuysen 1994. Gartlie 
and Hiippop 1994), and many studies show that 
provision of this supplementary food may affect 
at-sea distribution, body condition, individual 
survival, and breeding success (c.g.. Ryan and 
Moloney 1988, Hudson and Furness 1989, Oro 
1999. Hiippop and Wurm 2000, Gremillet et al. 
2008). In addition, it has been argued that discard 
use can contribute to population growth of some 
species of seabirds (Furness 2003), although there 
Universidad Nacional de la Patagonia ‘San Juan Bosco'. 
Trelew, Chubut. Argentina. 
Centro Nacional Patagonico (CONICET) and Wildlife 
Conservation Society. Bv. Brown 2915, U9I20ACD, 
Puerto Madryn, Chubut. Argentina. 
‘Corresponding author; e-mail: 
cristianmarinao@yahoo.com.ar 
is some controversy (Camphuysen and Garthe 
1999. Thompson 2006). Attraction to vessels may 
also result in incidental mortality from drowning 
in fishing gear and/or collisions with warp cables 
(Weimerskirch et al. 2000. Gonzalez-Zevallos and 
Yorio 2006, Sullivan et al. 2006, Watkins et al. 
2008. Favero et al. 2011). 
The use of fishing discards has been evaluated 
in several regions worldwide (Abrams 1983, 
Furness et al. 1988, Blaber and Wassenberg 
1989, Thompson 1992, Oro and Ruiz 1997, 
Branco 2001, Garthe and Scherp 2003, Wickliffe 
and Jodice 2010). Seabird attendance and 
discard use in Argentina has been analyzed for 
several trawl fisheries (Yorio and Caille 1999, 
Bertellotti and Yorio 2000b. Gonzalez-Zevallos 
and Yorio 2006). including the coastal fishery 
that operates in the Isla Escondida area, 
Patagonia. However, information available for 
this fishery includes only identification and 
frequency of occurrence of attending seabirds 
(Yorio and Caille 1999) and further information 
is required to adequately interpret the magnitude 
of the seabird-fishery interaction. One of the 
main species taking advantage of discards at this 
and other Patagonian coastal fisheries is the 
Kelp Gull ( Larus dominlcattus ) (Yorio and 
Caille 1999. Bertellotti and Yorio 2000b. 
Gonzalez-Zevallos and Yorio 2006). Kelp Gull 
populations have increased since the 1980s. and 
it has been suggested that human-derived food 
sources have been an important factor (Yorio et 
709 
