Otolith Size versus Weight and 

 Body-Length Relationships for 

 Eleven Fish Species of Baja 

 California, Mexico 



David Auriofes Gamboa 



Departamento de Recursos Marinos, Division de Biologia Manna 

 Centra de Investigaciones Biologicas de Baja California Sur 

 Apartado Postal 128. La Paz, Baja California Sur, Mexico 



Identification of otoliths recovered 

 from scats or stomachs of marine 

 mammals has been used in feeding- 

 habit studies in recent years (Fitch 

 and Brownell 1968, Brown and 

 Mate 1982, Antonelis et al. 1984, 

 Aurioles et al. 1984). Because of the 

 relatively large number of pinniped 

 scats available, this method has 

 proven useful for identifying prey. 

 However, the method depends on 

 the laborious collection of otoliths 

 from fish in the study area. The 

 relative frequency of a prey species 

 in the diet is determined by the 

 number of otoliths (either right or 

 left) counted. However, two prey 

 species with the same otolith count 

 may not be of equal importance in 

 the diet because of differences in 

 biomass. Antonelis et al. (1984) ad- 

 dressed this problem by estimating 

 the biomass of fish and one species 

 of squid off California, from regres- 

 sions of weight (biomass) versus the 

 size of otoliths (or squid beaks). The 

 relationship of otolith length to fish 

 size or weight has been reported for 

 other areas (Frost and Lowry 1981, 

 Wyllie Echeverria 1987). 



Eleven known species of Califor- 

 nia sea lion Zalophus californianus 

 prey (Aurioles et al. 1984, Lowry 

 and Oliver 1986) were sampled to 

 obtain weight, body length, and 

 otolith length to estimate regres- 

 sions. These results will be useful 

 for estimating prey size and weight 

 in feeding-habit studies in areas 

 where these fish species occur. 



Methods 



Fish were sampled by bottom trawl- 

 ing with commercial shrimp nets. 

 Trawls were conducted at depths of 

 30-200 m on the continental shelf 

 off the Pacific coast of Baja Califor- 

 nia (23°-27°N lat.) and in the south- 

 ern Gulf of California. Trawling, 

 fish sampling, and fish measure- 

 ments were conducted aboard the 

 Research Vessel El Puma owned by 

 the Universidad Nacional Autono- 

 ma de Mexico during cruises in the 

 summer and fall of 1987 and the 

 summer of 1988. 



Standard length (mm) and weight 

 (g) were recorded for fresh fish spe- 

 cimens. Weight ( ± 0.01 g) was mea- 

 sured using a digital scale (Ohaus). 

 Calipers were used to measure the 

 greatest length (anterior tip to pos- 

 terior projection) of each dissected 

 sagittal otolith. Values were aver- 

 aged for each otolith pair. Linear 

 regressions were used to determine 

 the relationship between standard 

 length or fish weight and otolith 

 length. 



Results and discussion 



Eleven fish species were studied 

 (Table 1 ). Serrano Serranus aequi- 

 dens and yellowbelly lizardfish Sy- 

 nodus jenkinsi were collected in 

 Bahia de La Paz (Golfo de Califor- 

 nia), while the remaining nine spe- 

 cies were typically found off the 

 western coast of Baja California. 



The standard length of fishes 

 sampled in this study fell within 

 lengths reported in the literature 

 (Miller and Lea 1976, Eschmeyer et 

 al. 1983) (Table 1). Linear regres- 

 sion of otolith length (mm) against 

 fish length for all species are given 

 in Table 2. 



A high correlation coefficient was 

 obtained for the longfin sanddab 

 Citharichthys xanthostigma (r 0.974) 

 in spite of the small sample size 

 (Table 2). This was probably due to 

 the relatively large size range of in- 

 dividuals in the sample. Scatter 

 plots of fish length on otolith length 

 for 8 of the 1 1 species are shown in 

 Figures 1-8. The remaining three 

 species had correlation coefficients 

 smaller than r 0.86 and were not 

 plotted. 



The equation for hake (Table 2) 

 was the highest for the sampled 

 species. Antonelis et al. (1984) cal- 

 culated a regression equation for 

 Pacific hake Merluccius productus 

 collected off California. Using an 

 otolith of 6 mm in length in their 

 equation (Y = 26.2 + 19.38x), the 

 predicted fish length would be 142.5 

 mm. Using the equation in Table 2 

 for hake collected in this study 

 yields a length of 113.76mm. A 

 "dwarf" Pacific hake in Baja Cali- 

 fornia waters was reported by 

 Vrooman and Paloma (1977). Inada 

 (1981) in an extensive study of the 

 genus stated that the "dwarf" form 

 is actually Panama hake Merluccius 

 angustimanus. It is probable that 

 our sample specimens were this 

 species, which is limited in range to 

 the area between 24° and 27°N 

 latitude. According to Vrooman and 

 Paloma (1977), and confirmed by 

 several cruises conducted by the 

 Centro de Investigaciones Biolo- 

 gicas de B.C.S (CIB), the southern 

 limit of distribution of the "large" 

 form of Pacific hake is probably 

 near Bahia Sebastian Vizcaino 

 (28°N lat.). 



Manuscript accepted 9 August 1991. 

 Fishery Bulletin. U.S. 89:701-706 (1991). 



701 



