Olson and Galvan Magaha: Food habits and consumption rates of Coryphaena hippuius 



289 



08:34 hours; 1.'^ fish had stomachs with 

 undigested food remains, 23 had stom- 

 achs that were empty, and 2 had stom- 

 achs that contained only trace amounts 

 of hard parts. One of the two dolphin- 

 fish in the fi51-800 mm size group con- 

 tained remains of flyingfishes and the 

 other contained tetraodontid puffers. In 

 the larger group (801-950 mm). 11 dol- 

 phinfish ate mostly triggerfishes (Balis- 

 tidae), boxfish (Ostraciidae), and flying- 

 fishes. In addition, 3 fish <650 mm and 

 2 fish in the 951-1100 mm class had 

 empty stomachs or contained only trace 

 amounts of hard parts. 



Diel feeding periodicity 



Early a m 

 Late am 

 Early p.m. 

 Late p.m 



E 

 84 



4 

 21 



7 



Early a.m. 



Late am 

 Early p.m. 



Late p.m 



Early am 

 Late am. 



Early p.m 

 Late p.m 





-J 



Early a. m 

 Late a.m 



Early p.m 

 Late p.m 



Early am 

 Late am 



Early p m 

 Late p m 



Although common dolphinfish are 

 thought to be visual predators that feed 

 primarily in the daytime (Massutf et al., 

 1998), our data suggest that they also 

 feed at night. In the areas where suffi- 

 cient sample sizes were obtained (east, 

 southwest, and southeast), an average of 

 about IS*/? of the dolphinfish caught in 

 the early morning contained food classi- 

 fied in the "previous-high" category (Fig. 

 3). Many of these prey were flyingfishes, 

 cephalopods, dolphinfishes, wahoo, and 

 snake mackerel in digestion states 3 or 

 4 and were found in stomachs that were 

 over 50% full. Prey of these or similar 

 taxa were found to be completely evacu- 

 ated from the stomachs of yellowfin tuna 

 in about 6-18 h (Olson and Boggs, 1986). 

 If dolphinfish gastric evacuation rates 

 are on the order of those of yellowfin 

 tuna (see "Discussion," and "Consump- 

 tion rates" sections), these prey would 

 have been ingested during the night. 



We examined the time of day that the 

 dolphinfish fed, by area. In the east area, the data indi- 

 cated peak feeding activity in the early morning and ear- 

 ly afternoon, although few samples were obtained in the 

 late morning and late afternoon ( Fig. 3, "recent high"). The 

 most important prey taxa by percent biomass in the early 

 morning were flyingfishes (549t}, snake mackerel (Gem- 

 pylidae, 18'7r), and epipelagic cephalopods ( 10%). The most 

 important prey taxa in the early afternoon were frigate or 

 bullet tunas iAuxis spp., 37%) (or a combination of both), 

 pelagic portunid crabs (27% ), and Thunnus spp. (yellowfin 

 and bigeye tunas, 15%). 



In the southwest area, feeding appears to have occurred 

 throughout the day (Fig. 3). The frequency of observations 

 in the two "recent" categories combined was highest in 

 the early afternoon (4170 and lowest in the late afternoon 

 (22'7r). The highest proportion of empty stomachs and those 

 containing only residual hard parts occurred in the late af- 

 ternoon, followed by the early and late morning. The flving- 



East - RH 



m^ 



East - RL 



a 



East - PH 



-3 



East - PL&E 



SW 



132 



59 



66 



14 



_l_ 



SE 

 81 

 16 

 18 

 



Southwest - RH 





Southwest - RL 



m 



Southwest - PH 



Southwest - PL&E 



^ 



e: 



Southeast - RH 



Southeast - RL 



Southeast - PH 



i 



Southeast - PL&E 



:m 



:m 



25 50 75 too 



75 100 



Percent occurence 



Figure 3 



Percent occurrence of the prey items of common dolphinfish corresponding to 

 four fullness-digestion categories (defined in Fig. 2) in three areas of the east- 

 ern Pacific Ocean (Fig. 1) and by the time of day the sets were made. RH = 

 recent high, RL = recent low, PH = previous high, PL&E = previous low 

 and empty. Early a.m. = 05:12-09:00, Late a.m. = 09:01-12:00, Early p.m. = 

 12:01-1.5:00, Late p.m. = 1.5:01-18:16 hours. Sample sizes for each time-area 

 stratum are shown at the top. Data for the north area are not shown because 

 the sample size was too small, nor for the west area because only one time 

 stratum was represented. 



fishes dominated in the diet between 09:00 and 15:00 hours 

 (64% and 57% by weight), and 71% of the diet of dolphinfish 

 caught in the late afternoon was epipelagic cephalopods. 

 The important prey in the early morning were more varied 

 and comprised frigate and bullet tunas (Au.xis spp., 28%), 

 flyingfishes (18%), epipelagic cephalopods (17%), and meso- 

 pelagic fishes (primarily Vinciguerria lucetia, 15%). 



In the southeast area, although no samples were ob- 

 tained in the late afternoon, the data suggested peak feed- 

 ing activity in the early afternoon (Fig. 3). The frequency 

 of observations in both "recent" categories in the early af- 

 ternoon summed to 42% of the total, compared with only 

 25% in the late morning. Most of the empty stomachs were 

 from fish captured in sets made before noon. The epipelag- 

 ic cephalopod Dosidicus gigas dominated in the diet dur- 

 ing all time periods. Fifteen percent of the stomach con- 

 tents of the common dolphinfish caught before 09:00 hours 

 were small yellowfin tuna. 



