Olson and Galvan Magana: Food habits and consumption rates of Coryphaena hippuivs 



291 



100 

 80 

 60 



40 

 20 H 



North 



i 



m 





!• ' • "I Epi. cephalopods [""jj Gempylidae 



I ] Meso. cephalopods fT^^ Auxis spp. 



^^S Crustacea .t-j-j ., ,. . . 



!SS= ^pr'jj Yellowfin tuna 



^ 1 N/leso. fishes " „'„ 



F^ mm Nomeidae 



\f^ Flyingllshes '^^ 



R^^^ /-— ,„t,^„„,H.,« [ 1 Tetraodontilormes 



Lv^ Coryphaentdae I 1 



^SS <^3rangidae | 



IVIisc. fishes 



417-650 801-950 1101-1250 417-650 801-950 1101-1250 



651-eOO 951-1100 1251-1770 651-600 951-1100 1251-1770 



Fork length (mm) 



Figure 5 



Gravimetric composition of prey groups (defined in Table 2), excluding trace quantities of hard 

 parts, in the stomachs of 545 common dolphinfish sampled in five areas of the eastern Pacific Ocean 

 (Fig. 1 ) versus dolphinfish size. Sample sizes for each size-area stratum are given in Table 1. 



In the southwest area, the stomachs of 272 common dol- 

 phinfish were sampleci from 2 dolphin sets, 5 schoolfish 

 sets, and 22 floating-object sets. One hundred and thirty- 

 six of the samples were empty and 14 contained only trace 

 hard parts (60.1'%^ of the females, 47.6% of the males). Fly- 

 ingfishes and epipelagic cephalopods were found in 329?^ 

 and 14''f of the dolphinfish sampled, and also ranked first 

 and second in biomass, respectively (Fig. 4, southwest). 

 The dietary importance of both, as well asAuxis spp., was 

 determined more by weight than by numbers of individu- 

 als, whereas the contrary was true for mesopelagic fishes. 

 All the other prey categories were relatively rare in the 

 diet according to all three measures. 



In the southeast area, the stomachs of 115 dolphinfish 

 were sampled from 1 schoolfish set and 13 floating-object 

 sets. Fifty-two of the stomachs were empty and 7 con- 

 tained only trace hard parts (44. S"^* of the females, 61.5^r 

 of the males). The epipelagic cephalopods were, by far, the 

 dominant component in the diet in this area (Fig. 4, south- 

 east). They were present in 45'7f of the stomachs sampled. 

 Biomass and counts contributed about equally to the over- 

 all importance of epipelagic cephalopods in the diet. Fly- 

 ingfishes also occurred in many of the samples (19%), but 

 their contribution to the diet by weight and numbers was 

 overshadowed by the epipelagic cephalopods. Four other 

 diet categories were rare. 



Size-specific predation 



We present the prey composition in ^W. excluding trace 

 quantities of hard parts (cephalopod mandibles and fish 

 otoliths), by six dolphinfish size strata for five areas (Fig. 5). 

 Sample sizes for each stratum are given in Table 1. 



Considerable variability in the diet was apparent for 

 common dolphinfish of different sizes. However, the statis- 

 tical importance of size could be detected by the regression 

 trees for only two prey groups because of the rarity of the 

 other prey in the diet or because of small sample sizes. The 

 regression tree for flyingfishes indicated that 7% of the ap- 

 parent variation in the % W of these prey was explained 

 by dolphinfish size. Size was also an important predictor 

 of predation on Tetraodontiformes, explaining 9% of the 

 apparent variation in the 9(W of these prey. Although dol- 

 phinfish size was not an important predictor of predation 

 on the other prey categories, we present the feeding data 

 by size strata within each area because we believe this 

 variability is biologically important. 



In the east area, the flyingfishes were the most impor- 

 tant prey gi'oup overall for dolphinfish of the three small- 

 est size classes and of the largest size class. For the two 

 size classes between 951 and 1250 mm, frigate and bullet 

 tuna [Auxis spp.), snake mackerels (Gempylidae), and epi- 

 pelagic cephalopods were dominant (Fig. 5, east). 



