Marinao and Yorio • SEABIRD MORTALITY AND FISHERY DISCARDS 
717 
110 km north of the colony (Boersma and 
Rebstock 2009). and may spatially overlap with 
vessels operating in the Isla Escondida area. 
Similarly, the distance of operating vessels to 
the Imperial Shag colony at Escondida Island, 
particularly during January 2007, was within the 
foraging range recorded for breeding shags at 
other locations in Chubut (Yorio el al. 2010; F. R. 
Quintana, unpubl. data). The population sizes of 
Magellanic Penguins and Imperial Shags in the 
study area were estimated at 490.000 and 1,000 
individuals, respectively (Yorio et al. 1998b). It is 
unlikely that mortality in nets at coastal shrimp 
trawlers has a significant impact on their popula¬ 
tions, although adult mortality should not be 
underestimated given seabird life-history traits 
(Sifther and Bakke 2000). No interactions with 
cables were recorded at coastal shrimp trawlers in 
the Isla Escondida area in contrast to that 
observed for hake trawlers at Golfo San Jorge, 
where Black-browed Albatrosses and Kelp Gulls 
were killed by warp cables (Gonz&lez-Zevallos et 
al. 2007). This could be the result of differences in 
fishing gear dimension and configuration. Outrig¬ 
gers in coastal shrimp trawlers stretch about 3-4 m 
off the side of the vessel and cables do not reach 
the stern of the vessel where most birds 
concentrate to make use of discards. 
The coastal shrimp fishery at Isla Escondida 
appears to have a small impact on seabirds in 
terms of incidental mortality but provides signif¬ 
icant amounts of supplementary food. This 
resource is more relevant as discard provision 
overlaps with the Kelp Gulfs breeding season, 
although actual use by breeders may depend on 
the spatial and temporal distribution of hauls. The 
fishery in the Isla Escondida area can also target 
Argentine hake, and changes in both net and mesh 
sizes, and in the characteristics of the fishing 
operation may result in differences in composition 
and amounts of discards. These variables can 
affect the composition and abundance of seabirds 
attending vessels, the way and effectiveness at 
which each species uses available dicards, and 
their probability of being killed in fishing gear 
(Arcos and Oro 2002. Furness et id. 2007, Favero 
et al. 2011). Fishing for Argentine red shrimp and 
Argentine hake may often coincide in time and 
space, Thus, the effects of coastal hake trawlers 
on seabirds should be assessed in conjunction with 
those of shrimp trawlers to obtain a more 
integrated view of the interaction between the 
Isla Escondida fishery and seabird populations. 
ACKNOWLEDGMENTS 
We thank Centro Nacional Patagonico (CONICET) for 
institutional support. Secretarfa de Pesca de la Provincia de 
Chuhut for logistical support and for providing data from 
the On-board Observer Program, and the Wildlife Conser¬ 
vation Society for financial support. We especially thank 
M. I-!. Gongora, D. R. Gonzdlez-Zevallos, N. D. Bovcon, P. 
O. Dell’Arcipretc, J. R. C. Saravia. and the captains and 
crews of the coastal shrimp trawlers for their help and 
advice. 
LITERATURE CITED 
ABRAMS. R. W. 1983. Pelagic seabirds and trawl-fisheries 
in the southern Benguela Current region. Marine 
Ecology Progress Series 11:151-156. 
Albarnaz. J. D., J. Toso. A. A. Correa. C. M. O. Simoes, 
and C. R. M. Barardi. 2007. Relationship between 
the contamination of gulls f Lama dominicanus) and 
oysters (Crassostrea gigas) with Salmonella serovar 
Typhimurium by PCR-RFLP. International Journal of 
Environmental Health Research 17:133-140. 
Alverson. D. L.. M. H. Freeberg, S. A. Murawski, and 
J. G. Pope. 1994. A global assessment of fisheries 
bycatch and discards. FAO Fisheries Technical Paper 
339:1-233, 
Annett. C. A. and R. Pierotti. 1999. Long-term 
reproductive output in Western Gulls: consequences 
of alternate tactics in diet choice. Ecology 80:288-297. 
Arcos, J. M. and D. Oro, 2002. Significance of fisheries 
discards for a threatened Mediterranean seabird, the 
Balearic Shearwater Puffiiitts man reran icus. Marine 
Ecology Progress Series 239:209-220. 
BBRTELLOTTl. M. andP. Yorio. 1999. Spatial and temporal 
patterns in the diet of the Kelp Gull in northern 
Chubut, Patagonia. Condor 101:790-798. 
Bertellotti, M. and P. Yorio. 2000a. Age-related 
feeding behaviour and foraging efficiency in Kelp 
Gulls Larus dominicanus attending coastal trawlers in 
Argentina. Ardea 88:207-214. 
Berteu-OTTI. M. and P. Yorio. 2000b. Utilisation of 
fishery waste by Kelp Gulls attending coastal trawl 
and longline vessels in northern Patagonia, Argentina. 
Ornis Fennica 77:105-15. 
Blaber. S. 1. M. and T. J. Wassenberg. 1989. Feeding 
ecology of the piscivorous birds Phalucnu orax varius , 
P. melanoleucus and Siern/i hergii in Moreton Bay, 
Australia: diets and dependence on trawler discards. 
Marine Biology 101:1-10. 
Bo, N. A.. C. A. Darrjeij, and A. R. CAMPERI. 1995. Aves 
Charadriifonnes: Laridae y Rynchopidae. Fauna de 
Agua Dulce de la Republica Argentina 43(4c):l-47. 
PROFADU (CONICET). La Plata, Argetnina. 
Boersma, P. D. and G. A. Rebstock. 2009. Foraging 
distance affects reproductive success in Magellanic 
Penguins. Marine Ecoloev Progress Series 375 263- 
275. 
Boersma, P. D.. D. L. Stokes, and P. M. Yorio. 1990. 
Reproductive variability and historical change of 
Magellanic Penguins (Spheniscus mogelionicus) at 
Punta Tombo, Argentina. Pages 15-43 in Penguin 
