Lowry et al Food habits of Zaiophus cahfornianus at San Clemente Island, California 



513 



Table 2 (continued) 



Prey 



Scientific name 



Common name 



Unid. Gonatidae 

 Unid. Scombridae 



squid 



mackerel or tuna 



Unid. flatfish 



Unid. cephalopod 



Unid. cartilaginous fish 



Unid. fishes 



'Not previously reported as prey of California sea lions. 

 * * Data impossible to compute in fields marked with a dash I 



: Occur 



PO 



PPC 



1 

 1 

 5 



31 

 2 

 83 



n Ind. 



1 

 2 



6 

 19 



62 



PMN 



<0.5 



<0.5 

 <0.5 

 <0.5 



<0.5 



February), spring (March-May), summer (June- Aug- 

 ust), and autumn (September-November). We also 

 categorized our sample into three groups related to the 

 California El Niiio: (1) pre-El Nino (September 1981- 

 August 1982), (2) El Nino (November 1982-September 

 1984), and (3) post-El Nino (November 1984-September 

 1986). 



We tested for seasonal and yearly differences in 

 presence or absence of each prey taxon using two-way 

 ANOVA (Program YD of BMDP-87; Dixon 1985) in the 

 binomial format. Two data sets were identified with full 

 cells in order to meet the requirements of the test: (1) 

 all seasons for the years 1982-85 (called four-season- 

 four-year data set); and (2) three seasons (spring, sum- 

 mer, and autumn) for 1982-86 (called three-season-five- 

 year data set). We identified prey taxa that showed 

 significant season, year, and season-year interaction dif- 

 ferences in their occurrence through time using Browne- 

 Forsythe analysis of variance for unequal variances. For 

 the pre-El Nino, El Nino, and post-El Nino comparisons, 

 we tested for differences in presence or absence of the 

 same nine prey taxa using two-way Browne-Forsythe 

 ANOVA (Dixon 1985) in the binomial format. 



We also examined temporal differences in the relative 

 number of different prey taxa found per scat (1,2,3,4, 

 5, or >5). Pearson's chi-square test (Dixon 1985) was 

 used to test for differences among numbers of prey 

 occurring per scat. 



Results 



Identification of prey remains 



In the 1476 scats collected (Table 1), we found the follow- 

 ing: (1) 1455 scats (98.5%) contained fish remains (i.e., 

 bones, otoliths, or eye lenses); (2) 525 scats (35.5%) con- 

 tained cephalopod remains (i.e. , beaks or eye lenses); (3) 

 1309 scats (88.6%) contained fish otoliths, cephalopod 

 beaks, or other prey remains that were used to identify 



prey; (4) 1271 scats (86.1%) contained fish otoliths; and 

 (5) 344 scats (23.3%) contained cephalopod beaks. 



We identified 95.4% of 2647 prey occurrences to 

 species, genus, or family (Table 2). Of the 2,647 prey 

 occurrences, 75.2% were bony fishes, 14.1% were 

 cephalopod, 10.5% were Crustacea (99.3% of Crustacea 

 were pelagic red crab), and 0.2% were cartilaginous fish. 

 We identified 44 prey taxa to species level and 8 to genus 

 level. Sevenprey taxa occurred in > 10% of scats: north- 

 ern anchovy Engraulis mordax (51.3%); jack mackerel 

 Trachurus symmetricus (24.6%); pelagic red crahPleu- 

 roncodes planipes (21.2%); Pacific whiting Merhiccius 

 productus (19.6%); rockfishes, Sebastes spp. (19.0%); 

 market squid Loligo opalescens {16.3%); and blacksmith 

 Chromis punctipinnis (10.7%). Two prey taxa occurred 

 in 5.0-10.0% of the scats: Pacific mackerel Scomber 

 japonicus (9.5%) and octopus. Octopus spp. (5.1%). We 

 identified 17 species and two genera of fish, and two 

 species and one genus of cephalopod not reported 

 previously as prey of California sea lions (Table 2). 



Nearly half of the scats (46.1%) contained only one 

 prey taxa (Fig. 2). Northern anchovy constituted 56.2% 

 of 603 scat samples with single prey taxa (Fig. 3). 



Variability in diet through time 



We found differences in distributions of occurrence 

 (occurrence and composition indices) and numbers of 

 individuals (number index) for nine prey taxa examined 

 for temporal variability during the pre-El Nino. El Nino, 

 and post-El Nino periods (Fig. 4). The distributions of 

 occurrence were significantly different for Pacific whit- 

 ing, northern anchovy, jack mackerel, Pacific mackerel, 

 market squid, octopus and pelagic red crab (P<0.01). 

 Northern anchovy occurred frequently and in the highest 

 numbers of any prey taxa in all three periods. During 

 the pre-El Niiio period, jack mackerel occurred in the 

 scat samples more often than the other prey; and jack 

 mackerel and market squid were found in greater indi- 



