282 



Fishery Bulletin 100(2) 



Daily meal is /• multiplied by 24 h for fish that feed both 

 day and night. Daily ration is daily meal expressed as a 

 percent of body weight. We estimated the body weight of 

 each dolphinfish from the length, according to the rela- 

 tionships of Lasso and Zapata (1999): 



where M  



L ■- 



M = aL\ 



body weight (g); and 

 fork length (cm). 



(2) 



They estimated that a = 0.0406. 0.0420, and 0.0224, and b = 

 2.6588, 2.6328. and 2.78 for males, females, and common 

 dolphinfish of undetermined sex, respectively. We esti- 

 mated daily consumption rates for dolphinfish of six size 

 strata by sex and area. 



The time-course of gastric evacuation has not been ad- 

 equately described for dolphinfishes. This fact prevents a 

 rigorous analysis of consumption rates using stomach-con- 

 tents data. However, we provide preliminary, first-order es- 

 timates of daily rations of common dolphinfish because this 

 information is important for analyses of ecosystem effects 

 of fishing (see "Discussion" section). A preliminary experi- 

 ment indicated that the gastric evacuation rate for squid 

 tissue by juvenile dolphinfish is comparable to that for 

 squid by yellowfin tuna. Five juvenile common dolphinfish 

 passed pellets of moist squid tissue through the digestive 

 tract in 6-8 h at 27"C (Suzuki. 1992). The fastest gastric 

 evacuation times for squid (Loligo opalescens) voluntarily 

 ingested by yellowfin tuna (mean L=36.2 cm) in the labo- 

 ratory were about 8 h at 23.5-25.5"C (Olson and Boggs. 

 1986). We assume, therefore, that gastric evacuation rates 

 measured for yellowfin tuna are adequate for estimating 

 daily rations of dolphinfish. We assigned values of A (Eq. 

 1) for squid (4.48), mackerel iScomber japonicus) (5.29). 

 smelt (Hypomesus pretiosus) (4.12). and nehu iStolepho- 

 rits purpureus) (2.24). and the mean for four experimental 

 food species (3.77) determined by Olson and Boggs (1986) 

 to the various prey taxa of common dolphinfish, as they 



did for yellowfin tuna. We omitted the data for the trace 

 hard parts (cephalopod mandibles and fish otoliths), which 

 apparently accumulate in the stomachs, when calculating 

 consumption rates because of the possibility that these re- 

 mained from predation on previous days. 



Results 



Stomach samples were obtained from 545 dolphinfish: 175 

 males, 323 females, and 47 of undetermined sex. Two 

 hundred and forty-six specimens had fresh or partially 

 digested food remains in their stomachs. 274 had empty 

 stomachs, and 25 had only trace amounts of digestion- 

 resistant hard parts (cephalopod mandibles and fish oto- 

 liths). We present the sample sizes by sex and area in 

 Table 1 and the detailed prey-composition data by area in 

 Tables 2-4. We analyzed the prey composition data by se.x 

 but did not discover important differences or trends. 



Few samples were obtained in the north and west areas. 

 Therefore, we briefly summarize those data here and in 

 Tables 2-4 and do not include them in the detailed treat- 

 ments of diel feeding periodicity, diet measures by area, 

 and size-specific predation. Only four common dolphinfish 

 were sampled in the north area, three from sets on schoolf- 

 ish and one from a set on dolphins. Three of the stomach 

 samples contained food and one was empty A large dol- 

 phinfish ( 1149 mm) had recently eaten a large squid iSthe- 

 noteuthis oualaniensis) in the early morning. Another large 

 fish (1239 mm) had a full stomach containing 7 fresh Cory- 

 phaena equiselis in the late afternoon. Both fish had been 

 collected from schoolfish sets. A smaller dolphinfish (768 

 mm) from a dolphin set in the late afternoon had remains 

 of various taxa. principally C. equiselis, flyingfishes. and 

 galatheid red crabs {Pleuruncodes plampes) in advanced 

 states of digestion. In addition, a 564-mm dolphinfish from 

 a schoolfish set was found to have an empty stomach. 



Thirty-eight common dolphinfish were sampled in the 

 west area from 4 sets on floating objects between 05:40 and 



