572 



Fishery Bulletin 92(3). 1994 



estimate of 0.922 kcalg l was calculated from bomb 

 calorimetric and proximate composition data in 

 Croxall and Prince (1982), Vlieg (1984), and Clarke 

 etal. (1985). 



Statistical analyses 



Seasonal and annual variation in the size of con- 

 sumed anchoveta were analyzed with a two-way 

 AN OVA of the mean estimated lengths of the ancho- 

 veta in each dolphin stomach, weighted by the num- 

 ber of otoliths measured (SAS, 1985 and 1987). Be- 

 cause of the unbalanced design, sums of squares and 

 F-values were calculated by using the "Type III sum 

 of squares" (SAS, 1985). Sidak adjusted <-tests were 

 used for comparisons among pairs of means (Sokal 

 and Rohlf, 1981; SAS, 1987). Log-linear analyses 

 were conducted on frequency of occurrence data, also 

 by using SAS (1987), and the resulting G-statistics 

 were tested for significance following Sokal and Rohlf 

 (1981). 



Data from different locations were pooled for analy- 

 ses of the effects of year and season on dusky dol- 

 phin feeding habits. This was appropriate because 

 the two most distant of the three ports are separated 

 by only about 160 km (Fig. 1 ), and all three ports are 

 found along the central portion of the Peruvian coast. 

 This region is relatively homogeneous and often 

 treated as a single unit in analyses of oceanographic 

 processes and fish populations (e.g. Brainard and 

 McLain, 1987; Pena et al., 1989). It was necessary to 

 pool data from all locations and collection periods to 

 obtain sample sizes sufficient for analyses of prey oc- 

 currence with respect to dolphin reproductive status. 



Results 



One hundred and thirty-six stomach samples con- 

 tained recognizable hard parts and were used in sub- 

 sequent analyses (Table 1). Six additional stomachs 

 were empty, containing no recognizable hard parts 

 at the time of their collection. There were no obvious 

 patterns in the years, seasons, or locations in which 

 the empty stomachs occurred, or the reproductive 

 status of the individuals from which they were ob- 

 tained ( Table 1 ). Eight additional samples contained 

 otoliths at the time of their collection, according to 

 field notes, but lacked otoliths when examined in the 

 laboratory several months later. These otoliths may 

 have dissolved during storage; therefore these 

 samples were not included in analyses. 



Species included in percent weight and percent 

 gross energy calculations — E. ringens, T. symmet- 

 ricus, M. gayi, S. sagax, L. gahi and D. gigcis — repre- 

 sented the vast majority of prey, over 98% of the to- 

 tal number consumed. Other species, anchoa, Anchoa 

 sp., blackruff, Seriolella violacea, a flyingfish, 

 Hirundichthys sp., and deepsea smelt, Leuroglossus 

 urotramus, were found in only trace amounts in stom- 

 ach contents (Table 2). 



Anchoveta was the most important prey species 

 by all measures of relative importance. It accounted 

 for 92.5% of all dusky dolphin prey items by total num- 

 bers and was present in 97.8% of stomachs. By weight, 

 anchoveta accounted for 83.8% of prey, and by gross 

 energy, 87.3% (Table 2). No other prey species accounted 

 for more than 5.1% of prey by weight, 2.5% by total 

 numbers, or 4.0% by gross energy, or was found in more 

 than 26.5% of the stomachs examined (Table 2). 



Table 1 



Distribution of stomach content samples containing otoliths or squid beaks, or both, collected from dusky dolphins, 

 Lagenorhynchus obscurus, by year, season, and dolphin reproductive status. Numbers in parentheses represent 

 number of empty stomachs containing neither otoliths nor squid beaks. 



lmmF's= immature females: RestF*s=resting females; PregF's=pregnant females, LactF's =1 acta ting females (including simultaneously pregnanl 

 and lactating females; two were collected, one at Ancon in the winter of 1985, one at Pucusana in the summer (if 1986); UnknF's= females of 

 unknown reproductive status; Males=all males; Unkn's=individuals of unknown sex 



