NOTE Gandini and Frere Bycatch of seabirds in the Argentinian longlme fishery 



483 



S-54- 



Results 



Bycatch of fish and seabirds 



The mean depth for longlining operations 

 was 139 ±11 meters (n=156) and the mean 

 number of hooks per set was 20.474 ±2588 

 U!=156). Effort for the whole fleet during the 

 nine-month sampling period represented a 

 total of 10,088,235 hooks. 



Kingclip represented 80'7f of the fish 

 caught. Additional catch included Patago- 

 nian toothfish (29c). Argentine hake (3%; 

 Merluccius hubbsi). Brazilian codling (8%; 

 Urophycis brasiliensis), blackbelly rose- 

 fish (2'7(\ Helicolenus dactylopterus lahil- 

 lei), skates (5%; Raja spp.) and other fish 

 in proportions below 1% (i.e., Patagonian 

 cod {Salilota australis); hoki (Macrorunus 

 magellanicus); tope shark (Galeorhinus ga- 

 lena). Patagonian smoothhound iMusfelus 

 schmitti), among others). 



Only two species of seabirds were caught 

 during setting of the longline: 12 white- 

 chinned petrels (Procellaria aequinoctialis) 

 and 19 black-browed albatrosses; no sea- 

 birds were caught during hauling. Most fish- 

 ing and bycatch occurred between 48-46°S 

 latitude and 63-61°W longitude (Fig. 1). The 

 observed distribution of genders was not sig- 

 nificantly different from an expected 1:1 sex 

 ratio for albatrosses (x^=0.06, df=l), or pe- 

 trels (x-=0.15, df =1). Fifty-three percent of 

 the albatrosses caught were males and 47% 

 females (?!=17). White-chinned petrel were 

 evenly divided: 50% were males and 50% 

 females (n='l2). Bycatch was not homoge- 

 nous throughout the year. The majority of the petrels 

 were caught during autumn (x^=66.3, df=2, P<0.001), 

 whereas albatrosses were predominantly caught during 

 winter (■)^=bA.l, df=2, P>0.001, Fig. 2). We estimated 

 a mean bycatch rate of 0.034 ±0.009 birds/1000 hooks 

 which, extrapolated to the other vessels, represents a 

 total of 343 birds caught in a nine-month period. Of 

 these birds, 55% would be black-browed albatross and 

 45% white-chinned petrels. 



Factors affecting bycatch rates 



Logistic regression analysis indicated that water depth 

 (/Jq=-0.96) and moon phase (/3q=0.24) explained most 

 of the variability in "capture events"; the probability of 

 a bird getting caught increased with water depth and 

 during brighter nights. Two variables were important 

 in explaining the variation in bycatch rate (F=3.13; 

 df=4, 42; P=0.02): moon phase (/3=-0.327, P=0.03) and 

 water depth (/3=0.335, P=0.02). When we analyzed the 

 variables that explained the incidental capture for both 

 species separately, moonlight was the most important 

 for albatrosses (F=4.637, df=3, 21, /3=-0.52, P<0.01), 



200 m 



■57 W 



Figure 1 



Map showing ports (solid triangles) used by longliners in Argentina. 

 Open triangles indicate set positions where seabird bycatch occurred 

 and circles indicate sets without seabird bycatch. The 200-m isobath 

 indicates the shelf break. 



whereas water depth was the most important for petrels 

 (F=2.4, df=2, 22, /J=0.584, P<0.05). 



Discussion 



This note reports the first estimation of seabird bycatch 

 in the Argentinean EEZ outside of the CCMLAR (Com- 

 mission for the Conservation of Antarctic Marine Living 

 Resources) area for the Atlantic Ocean with data from 

 onboard observers. Pelagic seabird species, such as 

 white-chinned petrels and black-browed albatrosses, 

 actively forage in the highly productive Patagonian shelf 

 waters (Cherel and Klages, 1998; Prince et al., 1998; 

 Weimerskirch et al., 1999; Gremillet et al., 2000); there- 

 fore these species are especially vulnerable to fisheries 

 around coastal shelf-edge habitats (Weimerskirch et 

 al., 1999; Gremillet et al., 2000). These two species are 

 often associated (Veit, 1995) and are similarly affected 

 by longline fishing (Moreno et al., 1996; Berrow et al., 

 2000). We found the average bycatch rate to be 0.034 

 birds/1000 hooks, which is one or two orders of mag- 

 nitude lower than those reported from other longline 



