574 



Fishery Bulletin 92(3). 1994 



Table 4 



Percent composition by weight and frequency of occurrence of prey found in stomach contents of dusky dolphins, 

 Lagenorhynchus obscurus, classified by reproductive status. All collection periods are pooled (summers and win- 

 ters of 1985 and 1986). 



Reproductive status' n 



Weight- l '% Frequency of occurrence ) 



M. gayi 



S. sagax 



L. gahl 



D. gigas 



Imm. Fem.'s 14 



Rest. Fem.'s 15 



Preg. Fem.'s 18 



Lact. Fem.'s 22 



Males 59 



7.3 

 (14.31 



0.0 

 (0.0) 



0.9 

 (5.6) 



8.3 

 (13.6) 



5.9 

 (8.5) 



0.0 

 (0.01 

 15.9 

 (6.7) 



3.0 

 (11.1) 



0.6 

 (4.5) 



0.4 

 (1.7) 



' Imm. Fem.'s=immature females; Rest. Fem.'s=resting females; Preg. Fem.'s=pregnant females; Lact. Fem.'s=lactating females, including those 



simultaneously pregnant and lactatmg; Males=all males; individuals of unknown reproductive status omitted. 

 2 May not total 100 in each row due to rounding. 



most common prey species, E. 

 ringens, T. symmetricus, and L. 

 gahi, averaged less than 20 cm and 

 100 g (Table 5). 



The regression-estimated lengths 

 of consumed anchoveta varied sig- 

 nificantly with year, season, and the 

 interaction between year and sea- 

 son (F=416.06, 62.56, and 35.42, 

 respectively; df=l, 67, P<0.0001; 

 Table 6). In comparisons between 

 pairs of means, anchoveta were 

 found to be significantly larger in 

 the summer and the winter of 1986 

 than in either the summer or the 

 winter of 1985 (Table 6). In 1985, 

 otolith lengths were significantly 

 different between summer and 

 winter, but not in 1986 (Table 6). 



Mean total lengths of anchoveta 

 from fishery samples (for each 

 combination of year and season) 

 were positively correlated with 

 mean regression-estimated lengths 

 of anchoveta consumed by dusky 

 dolphins (r=0.98, df=2, P<0.05; Table 6). Mean esti- 

 mates of total length for anchoveta consumed by 

 dusky dolphins were consistently 1.4-2.0 cm smaller 

 than mean total lengths of anchoveta taken by the 

 fishery, however (paired /-test, /=12.4, df=3, P<0.01). 



Discussion 



The prey of the dusky dolphin in Peruvian coastal 



Table 5 



Mean lengths (cm) and weights (g), as estimated from regressions on otolith 

 length/radius and squid beak rostrum length, offish and squid species com- 

 monly found in the stomachs of the dusky dolphin, Lagenorhynchus 

 obscurus, landed along the central Peruvian coast in 1985 and 1986. 



Total length. 



Fork length. 



Mantle length. 



Number of hard parts measured. 



Number of stomachs from which samples were taken 



waters can be characterized as schooling, small to 

 medium size, pelagic or semi-pelagic species (M. gayi 

 is usually demersal but sometimes forms large pe- 

 lagic schools [Mejia and Jordan, 1979]). Anchoveta 

 was typical and was unequivocally the most impor- 

 tant prey species in 1985-86. It was most important 

 by all measures of consumption and constituted al- 

 most 90'/t of the dusky dolphin's diet by percent gross 



