48 



Fishery Bulletin 102(1) 



spp. ), and Pacific whiting (Merluccius spp. ) 

 (Orta-Davila, 1988). 



Some California sea lion prey are important 

 fisheries resources in Mexico. The Pacific sar- 

 dine, for example, is the target of a fishery be- 

 gun in 1967 and which, along with the northern 

 anchovy, contributed to most of the volume of 

 the catch (200,870 t during the 1995-96 season) 

 obtained in the Gulf (Cisneros-Mata et al. 3 ). 

 The central and northern regions of the Gulf 

 of California harbor the greatest abundance of 

 sea lions and schooling fishes, such as the sar- 

 dine and anchovy. Because of this, knowledge of 

 sea lion feeding habits and their temporal and 

 spatial variability is relevant to understanding 

 the potential interaction between sea lions and 

 fisheries in the area (Orta-Davila, 1988; San- 

 chez-Arias, 1992; Bautista-Vega, 2000). 



In this article, we present the results of 

 concurrent diet studies conducted at various 

 rookeries and haulout areas of sea lions in the 

 northern rookeries of the Gulf of California to 

 examine the prey consumed, and spatial and 

 temporal variability in their diet. 



Materials and methods 



32° 



28° 



24° 



20° 



16° 



12° 



Scat samples of California sea lions were 

 collected at Isla San Pedro Martir (SPM, 

 28°24'00"N, 112°25'3"W), Isla San Esteban 

 (EST, 28°42'00"N, 112°36'00"W), Isla Rasito 

 (RAS, 28°49'30"N, 112°59'30"W), Isla Granito 

 (GRA, 29°34'30"N, 113°32'15"W), Isla Lobos 

 (LOB, 30°02'30"N, 114°. 28'30"W), and at two 

 colonies of Isla Angel de la Guarda known as 

 Los Machos (MAC, 29°20'00"N, 113°30'00"W), 

 and Los Cantiles (CAN, 29°32'00"N, 113°29'00"W, Fig. 1). 

 The total number of California sea lions in these seven 

 rookeries was approximately 15,000 animals (that were 

 hauled out) of which about 12.2% inhabit San Pedro Martir. 

 34.7% San Esteban, 2.8% El Rasito, 10.0% Los Machos, 

 8.7%. Los Cantiles, 11.0% Isla Granito, and 20.6% Isla 

 Lobos (Aurioles-Gamboa and Zavala-Gonzalez, 1994). All 

 the animals were spread out along the shoreline of each 

 island, except at Isla Angel de la Guarda, where they were 

 clustered within two areas: Los Cantiles, on the eastern 

 shoreline and Los Machos on the western shoreline. 



Scat samples were obtained at reproductive and non- 

 reproductive haulout areas between June 1995 and May 

 1996. At El Rasito, sampling was done only at one reproduc- 

 tive area; fresh and dried samples were collected (Fig. 2). 

 If for any reason a scat was not collected (because it was 

 found in pieces or in poor condition), it was destroyed and 

 the site was cleared to avoid collection during subsequent 

 trips. All fresh and dried samples collected were pooled to 

 represent each sampling period. We assumed that the diet 

 information corresponded to a time period close to the col- 

 lection trip, but some dried scats could have been deposited 

 shortly after the last collection. 



Pacific 

 Ocean 



122° 



118° 



114° 



110° 



106° 



Figure 1 



Map of Baja California showing location of California sea lion rook- 

 eries that were studied in the Gulf of California. 



Scats were stored in plastic bottles and then dried 

 shortly thereafter to prevent decomposition offish otoliths 

 and other hard parts (which were used in subsequent 

 prey identification) until the scats could be processed at 

 a later date. The samples were processed by soaking in 

 a weak biodegradable detergent solution for 1 to 7 days 

 before being sifted through nested sieves of 2. 00-, 1.18-. 

 and 0.5-mm mesh size. Fish bones and scales, eye lenses of 

 fish and squid, otoliths, cephalopod beaks, and crustacean 

 fragments were extracted from the samples. Cephalopod 

 beaks were stored in 70% ethanol, and the other items were 

 dried and stored in vials. Sagittal otoliths and cephalopod 

 beaks were used to identify teleost fish and cephalopods, re- 

 spectively. Identifications were made by using photographs 

 and diagrams from Clarke (1962), Fitch ( 1966), Fitch and 

 Brownell (1968), and Wolff (1984), as well as voucher 

 specimen material from the 1) Center Interdiseiplinario 

 de Marinas Ciencias (CICIMAR), 2) Instituto Tecnologico 

 y de Estudios Superiores de Monterrey, Guaymas, 3) Los 

 Angeles County Museum of Natural History, California, 

 and 4) Centro de Investigacion Cientifica y de Educacion 

 Superior de Ensenada (CICESE). Baja California, Mexico. 

 Prey species identifed to family level were coded by using 



