279 



Abstract— An ecosystem approach to 

 tisluTR's management requires an un- 

 derstanding of the impact of predatory 

 fishes on the underlying prey resources. 

 Defining trophic connections and mea- 

 suring rates of food consumption by 

 apex predators lays the gi-oundwork for 

 gaining insight into the role of pred- 

 ators and commercial fisheries in influ- 

 encing food web structure and ecosys- 

 tem dynamics. We analyzed the stomach 

 contents of 545 common dolphinfish 

 iCoryphaena hippurus) sampled from 

 74 sets of tuna purse-seine vessels fish- 

 ing in the eastern Pacific Ocean lEPO) 

 over a 22-month period. Stomach full- 

 ness of these dolphinfish and digestion 

 state of the prey indicated that diel 

 feeding periodicity varied by area and 

 may be related to the digestibility and 

 energy content of the prey. Common dol- 

 phinfish in the EPO appear to feed at 

 night, as well as during the da.vtime. We 

 analyzed prey importance by weight, 

 numbers, and frequency of occurrence 

 for five regions of the EPO. Prey impor- 

 tance varied by area. FUnngfishes. epi- 

 pelagic cephalopods. tetraodontiform 

 fishes, several mesopelagic fishes. Aiixis 

 spp., and gempylid fishes predominated 

 in the diet. Ratios of prey length to pred- 

 ator length ranged from 0.014 to 0.720. 

 Consumption-rate estimates averaged 

 5.6''c of body weight per day. Stratified by 

 sex. area, and length class, daily rations 

 ranged up to 9.6'< for large males and 

 up to 19.8'5 for small dolphinfish in the 

 east area (0-15°N. lll°W-coastline). 

 Because common dolphinfish exert sub- 

 stantial predation pressure on several 

 important prey groups, we concluded 

 that their feeding ecology provides im- 

 portant clues to the pelagic food web 

 and ecosystem structure in the EPO. 



Food habits and consumption rates of 

 common dolphinfish (Coryphaena hippurus) 

 in the eastern Pacific Ocean 



Robert J. Olson 



Inter American Tropical Tuna Commission 

 8604 La Jolla Shores Dnve 

 La Jolla, Calilornia 92037-1508 

 E-mail address rolsoniaiattcorg 



Felipe Galvan-Magana 



Centre Interdisciplinario de Ciencias Mannas 



Institute Politecnico Nacional 



Apdo Postal 592 



La Paz, B,C S , Mexico 



Manuscript accepted 3 October 2001. 

 Fish. Bull. 279-298 (2002). 



Dolphinfishes ^Coryphaena hippurus 

 and C. equiselis) are abundant, wide- 

 ranging, epipelagic predators in tropi- 

 cal and subtropical oceans (Palko et al., 

 1982 ). They support important commer- 

 cial, artisanal, and recreational fisher- 

 ies in several regions (Beardsley, 1967: 

 Oxenford and Hunte. 1986; Patterson 

 and Martinez. 1991; Campos et al.. 

 1993; Norton and Crooke. 1994; Lasso 

 and Zapata. 1999). Dolphinfishes are 

 also a large component of the bycatches 

 of the tuna purse-seine and longline 

 fisheries in the Pacific Ocean (Lawson. 

 1997; lATTC. 1999 ). They are commonly 

 found near natural and artificial float- 

 ing objects (Kojima, 1956; Hunter and 

 Mitchell. 1966; Gooding and Magnu- 

 son, 1967; Wickliam et al., 1973 ). a trait 

 which facilitates their capture. 



Calls have been issued for developing 

 an ecological approach to fisheries man- 

 agement, taking greater note of species 

 interactions and underlying ecosystem 

 dynamics (FAO, 1995: Larkin, 1996; 

 Mangel et al., 1996: Botsford et al.. 

 1997). Removal of predator biomass by 

 commercial fishing represents a "top- 

 down" disturbance of the system. Selec- 

 tive exploitation of apex predators can 

 have profound effects on pelagic ecosys- 

 tems because of the removal of preda- 

 tion pressure ( Essington et al.. in press ) 

 and because of top-down, trophic-cas- 

 cade effects (Shiomoto et al.. 1997; Es- 

 tes et al.. 1998; Verheye and Richard- 

 son, 1998). An understanding of how 

 top-down processes infiuence the dy- 



namics of marine communities derives 

 from a basic understanding of the tro- 

 phic connections and rates of food con- 

 sumption of the predators. Although 

 four studies have provided limited da- 

 ta on the food habits of dolphinfishes 

 in coastal areas of the eastern Pacific 

 Ocean (EPO) (Hida, 1973; Campos et 

 al.. 1993; Aguilar-Palomino et al., 1998; 

 Lasso and Zapata. 1999 ). little is known 

 of the predation dynamics of dolphin- 

 fishes over the majority of their oceanic 

 habitat. 



Common dolphinfish (C. hippurus) are 

 renowned for their rapid rates of growth 

 and metabolism. In Hawaiian waters, 

 common dolphinfish have attained av- 

 erage lengths of 120 cm and weights 

 of 12.5 kg at 12 months of age (Uchi- 

 yama et al., 1986). Standard metabolic 

 rates of common dolphinfish are compa- 

 rable to those of yellowfin (Thunnus al- 

 bacares) and skipjack iKatsuwonus pe- 

 kunis) tunas (Benetti et al.. 1995). All 

 three species have large surface areas 

 and thin blood-water interfaces in their 

 gills, morphological features that permit 

 high oxygen diffusion capacity and ele- 

 vated metabolic rates (Brill, 1996). High 

 energy requirements imply that preda- 

 tors like dolphinfish can account for im- 

 poi1;ant amounts of tertiary production 

 removed from an ecosystem (Essington 

 et al., in press), but rates of food con- 

 sumption by dolphinfish in nature have 

 not been measured. 



The objectives of our study were to 

 define the trophic relations of the com- 



