Food habits of sailfish Istiophorus platypterus

BULLETIN OF MARINE SCIENCE, 79(3): 777 791, 2006 Food habits of sailfish Istiophorus platypterus off Mazatlán, Sinaloa, MExico Dana Isela Arizmendi-Rodríguez, Leonardo Andres Abitia- Cárdenas, Felipe Galván-Magaña, and Idaly Trejo-Escamilla Abstract We analyzed the stomach contents of 533 sailfish taken between August 2002 and August 2003 by the sport fishing fleet off the coast of Mazatlán, Sinaloa, Mexico. A total of 62 different prey taxa was classified, 53 were identified by species, and according to index of relative importance, the most important prey species were Dosidicus gigas (d Orbigny, 1835) (65%), Argonauta spp. (26%), Balistes polylepis (Steindachner, 1876) (6%), and Auxis spp. (1%). In spite of the apparent high prey diversity, the trophic niche breadth (Levin s index = 0.02) suggests that sailfish close to Mazatlán are specialist predators, feeding mainly on cephalopods (D. gigas and Argonauta spp.). In general, dietary overlap values between size classes ranged from moderate to high and were more evident between sizes of 99.5 119.4 cm than 179.5 199.4 cm postorbital length. There was also a high trophic overlap by sex. The sailfish Istiophorus platypterus (Shaw in Shaw and Nodder, 1792) is a large predator, widely distributed in the tropical and temperate waters of the world. In the eastern Pacific, this highly migratory species ranges from Mexico to Peru (Joseph et al., 1974), and prefers habitats within the 28 C isotherm (Miyabe and Bayliff, 1987). Sailfish is one of the most important sport fishing species in Mexico (Kume and Joseph, 1969; Hoolihan, 2003). The sailfish has high economic and ecological importance in Mazatlán, Mexico, where it is found year-round, with higher abundance in warmer months. Several studies on sailfish feeding habits (Voss, 1953; Williams, 1963; Ovchinnikov, 1970; Evans and Wares, 1972; Eldridge and Wares, 1974; Jolley, 1977; Nakamura, 1985; Post et al., 1997; Galván, 1999), mention that fish of the families Balistidae, Belonidae, Bramidae, Carangidae, Clupeidae, Exocoetidae, Gempylidae, Phosichthyidae, Scombridae, and Stromateidae are the main prey for sailfish. Recently, sailfish from six tourist ports of the Mexican Pacific (La Paz, Cabo San Lucas, Mazatlán, Puerto Vallarta, Barra de Navidad, and Manzanillo) were found to be generalist predators, feeding mainly on epipelagic prey in coastal and oceanic waters, and occasionally diving to feed on demersal prey (Rosas-Alayola et al., 2002). The purpose of our study was to investigate in greater detail the trophic relationships of saifish directly offshore of Mazatlán. Material and Methods Sailfish samples were obtained weekly between August 2002 and August 2003 from the sport fishing fleet that operates off the coast of Mazatlán, Sinaloa, Mexico (22 40 23 38 N, and 105 50 106 45 W) (Fig. 1). Total weight and postorbital length (eye-fork length) of each individual were measured. Stomachs were removed and frozen for later analysis in the laboratory. During gastric content analysis, the different prey species were separated by taxonomic group, and identified to the lowest possible taxon, depending on digestion state of the remains. For complete undigested fish, the keys of Allen and Robertson (1994), Fischer et al. (1995a,b), and Thomson et al. (2000) were used for identification. Vertebral characteristics Bulletin of Marine Science 2006 Rosenstiel School of Marine and Atmospheric Science of the University of Miami 777

778 BULLETIN OF MARINE SCIENCE, VOL. 79, NO. 3, 2006 Figure 1. Location of the study area. Semi-circle around Mazatlán City denotes fishing area. (e.g., number, position) were used to identify fish remains with the help of taxonomic keys of Clothier (1950), Monod (1968), and Miller and Jorgensen (1973). Crustacean prey species were identified from exoskeleton remains with the keys of Garth and Stephenson (1966), Brusca (1980), and Fischer et al. (1995a). We identified cephalopod prey from mandible remains (Clarke 1962, 1986; Iverson and Pinkas, 1971; Wolff, 1982). The fish and cephalopod collections of the Centro Interdisciplinario de Ciencias Marinas (CICIMAR) at La Paz, Mexico, were used to compare and validate prey identifications. The diet was analyzed by calculating three diet indices for each prey taxon. We calculated gravimetric importance of the prey (%W), numerical importance (%N), and frequency of occurrence (%FO). We also combined these methods to calculate the index of relative importance of Pinkas et al. (1971) to represent the most important prey: ] g IRI = % W + % N % FO Five size classes of postorbital length (PL) were selected to compare size changes in the diet: 99.5 119.4 cm, 119.5 139.4 cm, 139.5 159.4 cm, 159.5 179.4 cm, and 179.5 199.4 cm. For seasonal analysis, the 12 mo samples (August 2002 July 2003) were divided into cold and warm seasons, following Alvarez-Borrego and Schwartzlose (1979), and anonymous (2001), considering sea surface temperature records obtained by the Advanced Very High Resolution Radiometer (AVHRR) sensors of the satellites NOAA 14 and NOAA 16. The months of August, September, October, November, and December 2002 were considered to be the warm season (27 31 C), whereas January, February, March, April, May, and June 2003 were considered the cold season (23 26 C). Considering the absolutes values of the numeric method, diet breadth was calculated using Levin s standardized index (Krebs, 1989) according to Labropoulou and Eleftheriou (1997): P 2 Bi = 1 n - 1% `1 / j - 1/ ij where Bi is Levin s index for the predator i; Pij is the proportion of the diet of predator i that is made up of prey j; and n is the number of prey categories.

ARIZMENDI-RODRÍGUEZ ET AL.: FOOD HABITS OF SAILFISH OFF MAZATLÁN, MEXICO 779 This index ranges from 0 to 1. Low values (< 0.6) indicate a diet dominated by few prey species (specialist predator) and high values (> 0.6) indicate a generalist diet (Krebs, 1989; Labropoulou and Eleftheriou, 1997). Diet overlap among different size classes and sexes of sailfish was calculated using Morisita-Horn index (Smith and Zaret, 1982), with the absolutes values of the numeric method: n / 2 ^Pxi ) Pyih i = 1 Cm = n n 2 2 d P + P n / / xi i = 1 i = 1 yi where Cλ is the Morisita-Horn index of predators x and y, P xi is proportion of predator x with prey i; P yi is proportion of predator y with prey i, and n is total prey. Diet overlap ranges between 0 and 1, and values exceeding 0.60 are considered significant (Langton, 1982). We compared our results to those from two studies on sailfish food habits done in Mazatlán (Evans and Wares, 1972 and Rosas-Alayola et al., 2002), to see the possible changes in the diet over the time. We used the prey biomass of prey 1% of volumetric or gravimetric importance (considering the conversion 1 g = 1 ml), because one study used only the volumetric method. Results A total of 533 sailfish had an average postorbital length of 159.5 ± 13.1 cm, and an average weight of 23.40 ± 5.10 kg. Of the stomachs sampled, 463 (87%) had identifiable food, 24 (4%) had empty stomachs, and 46 (9%) had regurgitated. The percentage of fish with stomachs between 1% and 25% fullness was 94.4%. Sixty-two prey taxa were identified in three categories: cephalopods (6 prey taxa), crustaceans (4), and fish (52). There was a total of 38 families, 53 genera, and 53 species (Table 1). The most frequent prey species in the stomach contents were the jumbo squid Dosidicus gigas, occurring in 67% (311) of stomachs, followed by the cephalopod Argonauta spp. in 58% (268), the fish Balistes polylepis at 40% (183), and Auxis spp. at 14 % (63) (Table 1). In total, 11,449 organisms were enumerated, of which 73% (8308) were cephalopods, 26% (2931) were fish, and 1% (142) were crustaceans. The dominant prey by number were Argonauta spp. with 32% (3727), D. gigas with 30% (3407), unidentified cephalopods with 10% (1116), B. polylepis with 10% (1091), and Auxis spp. with 3% (312) (Table 1). The total accumulated weight of prey in the stomachs was 37.7 kg, where cephalopods contributed 26.2 kg (69.6%); fish composed 11.4 kg (30.1%), and crustaceans weighed 0.9 kg (0.2 %). The most important components were cephalopods with D. gigas at 60% (22.5 kg) and Argonauta spp. at 9% (3.5 kg), followed by the fish Opisthonema spp. with 4% (1.6 kg), B. polylepis with 4% (1.5 kg), and Mugil cephalus with 3% (1.2 kg) (Table 1). The IRI calculation placed cephalopods highest with 92.05%, followed by fish with 7.9%, and crustaceans with 0.04%. The most important prey were D. gigas (65%), Argonauta spp. (26%), B. polylepis (6%), and Auxis spp. (1%) (Table 1). The low values of Levin s standardized index of diet breadth (Bi = 0.02) characterize the sailfish as specialist predator, probably dominated by the higher predation on two species of cephalopods (D. gigas and Argonauta spp.). During the warm season of 2002, we analyzed 157 stomachs with 61 prey items. The IRI indicated that D. gigas (56%), B. polylepis (19%), Argonauta spp. (13%), and

780 BULLETIN OF MARINE SCIENCE, VOL. 79, NO. 3, 2006 Table 1. Prey found in sailfish stomach contents from Mazatlán, Sinaloa, Mexico, expressed as percentages of number (N), weight (W), frequency of occurrence (FO), and index of relative importance (IRI). Item prey N % N FO % FO W % W IRI % IRI Mollusca Gastropoda Cephalopoda Loliginidae 1 0.01 1 0.2 0.1 0.0003 0.0019 0.00002 Enoploteuthidae Abraliopsis affinis (Pfeffer, 1912) 12 0.1 7 2 144.1 0.38 0.7349 0.00792 Ommastrephidae Dosidicus gigas (d Orbigny, 1835) 3,407 29.54 311 67 22,534 59.74 5,997 65 Mastigoteuthidae Mastigoteuthis spp. 44 0.38 22 5 1.86 0.005 1.8361 0.01979 Octopodidae Octopus spp. 1 0.01 1 0.2 0.01 0 0.0019 0.00002 Argonautidae Argonauta spp. 3,727 32.31 268 58 3,459.7 9.17 2,401.3 26 Unidentified cephalopods (mainly beaks) 1,116 9.68 35 8 106.41 0.28 75.3 1 Crustacea Malacostraca Isopoda 6 0.05 4 1 2.49 0.01 0.0506 0.00055 Penaeoidea 64 0.55 22 5 25.22 0.07 2.9543 0.03185 Solenoceridae Solenocera floera (Burkenroad, 1938) 59 0.51 4 1 17.75 0.05 0.4826 0.0052 Unidentified crustacea 16 0.14 16 3 13.64 0.04 0.6043 0.00651 Portunidae Euphylax dovii Stimpson, 1860 5 0.04 3 1 3.09 0.01 0.0334 0.00036 Portunus xantussi affinis (Faxon, 1893) 3 0.03 2 0.4 1.76 0.005 0.0133 0.00014

ARIZMENDI-RODRÍGUEZ ET AL.: FOOD HABITS OF SAILFISH OFF MAZATLÁN, MEXICO 781 Table 1. Continued. Item prey N % N FO % FO W % W IRI % IRI Unidentified brachyura 4 0.03 4 1 25.89 0.07 0.0893 0.00096 Chordata Osteichthyes Clupeiformes Clupeidae Ophistonema spp. 27 0.23 7 2 1,596.3 4.23 6.7523 0.07279 Opisthonema libertate (Günther, 1867) 2 0.02 1 0.2 204.7 0.54 0.121 0.0013 Sardinops caeruleus (Girard, 1854) 6 0.05 1 0.2 1.07 0.003 0.0118 0.00013 Engraulidae Engraulis mordax Girard, 1854 3 0.03 2 0.4 74.5 0.2 0.0966 0.00104 Stomiiformes Phosichthyidae Vinciguerria lucetia (Garman, 1899) 73 0.63 9 2 10.37 0.03 1.2837 0.01384 Aulopiformes Synodontidae Synodus spp. 125 1.08 24 5 51.76 0.14 6.329 0.06822 Synodus scituliceps Jordan and Gilbert, 1882 1 0.01 1 0.2 3.21 0.01 0.0037 0.00004 Lampriformes Trachipteridae Desmodema polystictum (Ogilby, 1898) 3 0.03 3 1 0.59 0.002 0.0179 0.00019 Ophidiiformes Ophidiidae 35 0.3 5 1 88.37 0.23 0.5807 0.00626 Batrachoidiformes Batrachoididae Porichthys analis Hubbs and Schultz, 1939 1 0.01 1 0.2 0.25 0.001 0.002 0.00002 Mugiliformes

782 BULLETIN OF MARINE SCIENCE, VOL. 79, NO. 3, 2006 Table 1. Continued. Item prey N % N FO % FO W % W IRI % IRI Mugilidae Mugil spp. 8 0.07 6 1 99.72 0.26 0.4325 0.00466 Mugil cephalus Linnaeus, 1758 18 0.16 18 4 1,198.7 3.18 12.96 0.13972 Beloniformes Belonidae Ablennes hians (Valenciennes, 1846) 2 0.02 2 0.4 19.71 0.05 0.0301 0.00032 Tylosurus acus pacificus (Steindachner, 1876) 6 0.05 4 1 415.56 1.1 0.9967 0.01074 Strongylura spp. 2 0.02 1 0.2 425.5 1.13 0.2474 0.00267 Exocoetidae Cheilopogon papilio (Clark, 1936) 10 0.09 9 2 21.26 0.06 0.2781 0.003 Hemiramphidae Hyporhamphus unifasciatus (Ranzani, 1842) 11 0.1 4 1 259.21 0.69 0.6761 0.00729 Oxyporhamphus micropterus (Valenciennes, 1847) 2 0.02 2 0.4 8.25 0.02 0.0169 0.00018 Beryciformes Holocentridae Sargocentron suborbitalis (Gill, 1863) 74 0.64 26 6 91.81 0.24 4.9697 0.05357 Gasterosteiformes Syngnathidae Hippocampus ingens Girard, 1858 4 0.03 3 1 9.32 0.02 0.0385 0.00041 Fistulariidae Fistularia corneta Gilbert and Starks, 1904 246 2.13 51 11 167.46 0.44 28.38 0.30596 Scorpaeniformes Scorpaenidae Sebastodes spp. 14 0.12 9 2 19.46 0.05 0.3362 0.00362

ARIZMENDI-RODRÍGUEZ ET AL.: FOOD HABITS OF SAILFISH OFF MAZATLÁN, MEXICO 783 Table 1. Continued. Item prey N % N FO % FO W % W IRI % IRI Perciformes Nemastistiidae Nematistius pectoralis Gill, 1862 1 0.01 1 0.2 5.86 0.02 0.0052 0.00006 Coryphaenidae Coryphaena equiselis Linnaeus, 1758 12 0.1 8 2 182.53 0.48 1.0159 0.01095 Carangidae 9 0.08 6 1 4.2 0.01 0.1155 0.00125 Caranx caballus Günter, 1868 18 0.16 12 3 490.08 1.3 3.7719 0.04066 Caranx orthogrammus (Jordan and Gilbert, 1882) 2 0.02 2 0.4 2.91 0.01 0.0108 0.00012 Caranx sexfasciatus Quoy and Gaimard, 1825 2 0.02 1 0.2 7.08 0.02 0.0078 0.00008 Caranx speciosus (Forsskal, 1775) 42 0.36 20 4 61.04 0.16 2.272 0.02449 Caranx vinctus (Jordan & Gilbert, 1882) 26 0.23 13 3 11.71 0.03 0.7201 0.00776 Chloroscombrus orqueta Jordan and Gilbert, 1883 17 0.15 12 3 10.56 0.03 0.4546 0.0049 Decapterus spp. 68 0.59 27 6 70.78 0.19 4.5323 0.04886 Decapterus macarellus (Cuvier, 1833) 1 0.01 1 0.2 0.22 0.001 0.002 0.00002 Decapterus macrosoma Bleeker, 1851 29 0.25 18 4 94.11 0.25 1.9475 0.02099 Elagatis bipinnulata (Quoy and Gaimard, 1825) 3 0.03 2 0.4 388.57 1.03 0.4562 0.00492 Naucrates ductor (Linnaeus, 1758) 58 0.5 14 3 19.35 0.05 1.6756 0.01806 Oligoplites altus (Günther, 1868) 2 0.02 2 0.4 2.05 0.01 0.0098 0.00011 Oligoplites saurus (Bloch and Schneider, 1801) 1 0.01 1 0.2 8.76 0.02 0.0069 0.00007 Selar crumenophthalmus (Bloch, 1793) 4 0.03 2 0.4 34.78 0.09 0.0548 0.00059 Selene peruviana (Guichenot, 1866) 106 0.92 18 4 87.58 0.23 4.4755 0.04824 Lutjanidae 2 0.02 1 0.2 0.08 0.0002 0.0038 0.00004 Sciaenidae Cynoscion parvipinnis Ayres, 1861 4 0.03 2 0.4 4.48 0.01 0.0201 0.00022 Umbrina roncador Jordan and Gilbert, 1882 50 0.43 29 6 96.24 0.26 4.3133 0.0465

784 BULLETIN OF MARINE SCIENCE, VOL. 79, NO. 3, 2006 Table 1. Continued. Item prey N % N FO % FO W % W IRI % IRI Chaetodontidae Johnrandallia nigrirostris (Gill, 1862) 46 0.4 20 4 54.86 0.15 2.351 0.02534 Ephididae Chaetodipterus zonatus (Girard, 1858) 90 0.78 26 6 140.9 0.37 6.4795 0.06985 Scombridae 21 0.18 5 1 37.57 0.1 0.3042 0.00328 Acanthocybium solandri (Cuvier, 1832) 2 0.02 2 0.4 0.51 0.001 0.0081 0.00009 Auxis spp. 312 3 63 14 1,021.1 2.71 73.64 1 Euthynnus lineatus Kishinouye, 1920 1 0.01 1 0.2 0.3 0.001 0.002 0.00002 Scomberomorus sierra Jordan and Starks, 1895 47 0.41 17 4 259.33 0.69 4.0206 0.04334 Scomber japonicus Houttuyn, 1782 87 0.75 27 6 113.83 0.3 6.1585 0.06639 Xiphiidae Istiophorus platypterus (Shaw in Shaw and Nodder, 1792) 3 0.03 2 0.4 0.96 0.003 0.0123 0.00013 Stromateidae Peprilus medius (Peters, 1869) 1 0.01 1 0.2 130.5 0.35 0.0766 0.00083 Tetraodontiformes Balistidae Balistes polylepis Steindachner, 1876 1,091 9.46 183 40 1,514.6 4.02 532.57 6 Tetradontidae Lagocephalus lagocephalus (Linnaeus, 1758) 24 0.21 19 4 325.99 0.86 4.4005 0.04744 Sphoeroides spp. 3 0.03 3 1 11.5 0.03 0.0366 0.00039 Sphoeroides annulatus (Jenyns, 1842) 59 0.51 23 5 52.02 0.14 3.2262 0.03478 Sphoeroides lobatus (Steindachner, 1870) 4 0.03 2 0.4 227.2 0.6 0.2752 0.00297

ARIZMENDI-RODRÍGUEZ ET AL.: FOOD HABITS OF SAILFISH OFF MAZATLÁN, MEXICO 785 Table 1. Continued. Item prey N % N FO % FO W % W IRI % IRI Diodontidae Diodon spp. 1 0.01 1 0.2 0.06 0.0002 0.0019 0.00002 Unidentified fish 89 0.77 89 19 906.42 2.4 61.03 0.65783 Vertebrae of fishes 5 0.04 2 0.4 9.24 0.02 0.0293 0.00032 Unidentified organic matter 52 0.45 52 11 210.2 0.56 11.32 0.12205 Reptilia Chelonidae Lepidochelys olivacea (Eschscholtz, 1829) 1 0.01 1 0.2 16.5 0.04 0.0113 0.00012 Total 11,534 100 463 37,720 100 9,276.7 100

786 BULLETIN OF MARINE SCIENCE, VOL. 79, NO. 3, 2006 Auxis spp. (8%) were the most important prey. We analyzed 39 stomachs with food during the cold season of 2003. The diet consisted of 25 prey items, of which the most important were D. gigas (55%), Argonauta spp. (32%), B. polylepis (7%), and Fistularia spp. (2%). In the warm season of 2003, 267 stomachs with 58 prey items were examined with the most important prey being: D. gigas (64%), followed by Argonauta spp. (31%), and B. polylepis (2%). Examination of the diet by sex involved 202 females (44%), 255 males (55%), and 6 of undetermined sex (1%). The trophic spectrum in both sexes was defined by cephalopods, fish, and crustaceans. The diet of females included 52 prey items, classified into 36 families, 44 genera, and 43 species. According to IRI, cephalopods were the most important food (90%), followed by fish (9.6%) and crustaceans (0.05%). The squid D. gigas was the most important prey (64% IRI), followed by Argonauta spp. (26%), and B. polylepis (7%). Similarly, The diet of males consisted of 55 prey items classified in 34 families, 45 genera, and 44 species. Cephalopods were the most important food (92.3% IRI), followed by fish (7.6%), and crustaceans (0.04%), with D. gigas the most important prey (65% IRI), followed by Argonauta spp. (26%), and B. polylepis (5%). Dietary overlap between the sexes was high (Cλ = 0.98), indicating that males and females fed largely on the same prey. Analysis by size class revealed that the largest number of stomachs analyzed (217) were obtained from the size 159.5 179.4 cm PL. Only three stomachs were obtained from fish 99.5 119.4 cm PL, with the most important being the cephalopod Argonauta spp. (87 %), B. polylepis (11%), and Decapterus spp. (2%). In the remaining four size classes (119.5 139.4 cm PL, 139.5 159.4 cm, 159.5 179.4 cm, and 179.5 199.4 cm), the most important prey were the cephalopods D. gigas and Argonauta spp. (90% IRI). Dietary overlap among size classes ranged from moderate to high, with higher overlap between size classes 99.5 119.4 and 179.5 199.4 cm (Cλ = 0.81). For both 119.5 139.4 vs 159.5 199.4 cm, and 119.5 139.4 vs 179.5 199.4 cm, Cλ = 0.65. Comparisons with previous studies of the feeding habits of sailfish in the Mazatlán area with ours suggested biomass changes in sailfish prey. In the Evans and Wares (1972) study, the main prey species were cephalopods (Argonauta spp. and unidentified squids) and fish (Polydactilus spp. and unidentified fishes). However, Rosas-Alayola et al. (2002) found three main prey species (D. gigas, Argonauta spp., and the fish Auxis spp.) in the same area. In our study, the two cephalopods (D. gigas, Argonauta spp.) were consumed most frequently, but D. gigas represented the greatest weight (Fig. 2). There was little overlap (Cλ = 0.079) between the results of our study and that of Evans and Wares (1972), but high overlap (Cλ = 0.68) with those of Rosas-Alayola et al. (2002). Discussion Sailfish off Mazatlán, Mexico, had a wide prey trophic spectrum (62 taxa), including cephalopods, fish, and crustaceans. The main prey form aggregations, such as cephalopods (D. gigas and Argonauta spp.). Sailfish fed on epipelagic prey (Auxis spp. and B. polylepis juveniles), but less on neritic and benthic prey. The high consumption of Argonauta spp. and jumbo squid D. gigas (91% of IRI), resulted in a low Levin s index, indicating that the sailfish is a specialist predator. However, sailfish are also opportunistic as reflected in the high prey diversity. These large predators fed on either available or abundant prey (Palko et al., 1981; Stillwell and Kohler, 1985), a tro-

ARIZMENDI-RODRÍGUEZ ET AL.: FOOD HABITS OF SAILFISH OFF MAZATLÁN, MEXICO 787 Figure 2. Comparison of weight percentage of main prey found in different studies of sailfish in the Mazatlán area. (A) Evans and Wares (1972); (B) Rosas-Aloyola et al. (2002); and (C) present study. phic behavior reported for sailfish and other billfish such as swordfish, blue marlin, and striped marlin (Brock, 1984; Nakamura, 1985; Stillwell and Kohler, 1985; Abitia- Cardenas et al., 1999; Abitia-Cardenas et al., 2002). Results of this study indicate that cephalopods and fish were the most important sailfish prey in the Mazatlán area, which is consistent with other studies conducted elsewhere. However, earlier reports frequently indicated a greater importance of fish over the cephalopods. In western Africa, Williams (1963) reported that sailfish fed on fish of the families Balistidae, Carangidae, Scombridae, and on cephalopods. In the Atlantic Ocean, Jolley (1977) found that they hunt fish from the Scombridae family, followed by squids and fish of the families Belonidae, Carangidae, Clupeidae, and Exocoetidae. In the Indo-Pacific, Nakamura (1985) reported that sailfish fed mainly on fish of the families Balistidae, Belonidae, Bramidae, Carangidae, Gempylidae, and Stromateidae, and on squids. Galván (1999) analyzed the trophic relationships of epipelagic predators in the eastern Pacific Ocean, and found that sailfish fed mostly on Vinciguerria lucetia, Decapterus macrosoma, Auxis spp., and D. gigas. Sailfish near Buenavista, Baja California Sur, Mexico preyed mainly on the fishes Etrumeus teres, Fistularia spp., Euthynnus lineatus, and Auxis thazard (Eldridge and Wares, 1974). Evans and Wares (1972) found that cephalopods, and the fishes Polydactylus spp., Fistularia spp., S. japonicus, and Mugil cephalus were the most important prey species in the Mazatlán area, but they did not identify the cephalopods. Rosas-Alayola et al. (2002) found that the cephalopods D. gigas and Argonauta spp., and the fish

788 BULLETIN OF MARINE SCIENCE, VOL. 79, NO. 3, 2006 Auxis spp. were the dominant preys in almost equal proportions in the sailfish diet around Mazatlán. Our results indicated that the two cephalopod species (D. gigas and Argonauta spp.) were the principal targets, with D. gigas the highest percentage consumed by weight. Nevarez-Martinez et al. (2006) found that more D. gigas was caught during 2001 and 2002 in the Gulf of California than in other years, and this high abundance of D. gigas likely led to its increased consumption by sailfish during those years. Oceanographic changes during El Niño La Niña period can also cause variation in D. gigas catches in the Gulf of California (Markaida, 2006). These studies indicate that the sailfish diet in different regions of the world consists primarily of two prey groups: fish and cephalopods, with cephalopods of primary importance in the Mexican Pacific waters. This importance of cephalopods likely reflects the abundance of this prey in northwestern Mexico. High predation on cephalopods is reported for other predators from the same area of the eastern Pacific Ocean (Brock, 1984; Robertson and Chivers, 1997; Markaida and Sosa-Nishizaki, 1998; Abitia-Cardenas et al., 2002; Olson and Galvan-Magaña, 2002). The only remnants we found of cephalopods (D. gigas and Argonauta spp.) in sailfish stomach contents were mandibles, indicating the rapid digestion of the soft squid muscle. Olson and Boggs (1986) found that the yellow fin tuna Thunnus albacares digests squids in 5 10 hrs. Furthermore, billfish gastric enzymes likely continue degrading organic matter after the fish have been caught during the early morning to afternoon sport fishing period (Abitia-Cardenas et al., 1998). We found the food of sailfish in an advanced state of digestion, probably a reflection of early morning feeding followed by protracted post-capture metabolic processes. The sailfish is a highly migratory predator found commonly in the 28 C isotherm (Miyabe and Bayliff, 1987). In Mexican Pacific studies, sailfish move over significant distances, spending more time during winter in Acapulco and the Gulf of Tehuantepec, and moving north (Baja California Sur) during summer and fall (Kume and Joseph, 1969). This type of migratory behavior also has been reported for sailfish from another surf area: sailfish migrate from the northwestern Gulf of Arabia, traveling distances from 2.5 to 697 km (Hoolihan, 2003). Kume and Joseph (1969) and Hoolihan (2003) concluded that water temperature influenced this migratory movement, but did not consider that migration maybe in response to prey availability. High prey abundance together with warmer water likely explain the high abundance of sailfish in the Mazatlán area (Badan, 1997). There was no difference in prey preference between the cold and warm seasons, suggesting that offshore of Mazatlán has a stable abundant prey, likely due to regional oceanographic characteristics (De La Lanza-Espino, 1991). High trophic overlap between sexes and sizes classes indicates that both sexes and different sizes may feed together. The feeding strategy of sailfish in Florida is to feed in groups: they swim in circles to prevent the prey schools from escaping, while one or two plunge into the school, striking the prey to immobilize them (Voss, 1953; Harvey, 1989). In summary, the results obtained here are consistent with the hypothesis that the southern Gulf of California is an important feeding area for sailfish. Comparisons of our results with three previous studies (Evans and Wares, 1972; Eldridge and Wares, 1974; Rosas-Alayola et al., 2002), indicates that the diet of sailfish has not changed significantly during the last three decades, due to the high abundance of preferred prey species in this feeding area.

ARIZMENDI-RODRÍGUEZ ET AL.: FOOD HABITS OF SAILFISH OFF MAZATLÁN, MEXICO 789 Acknowledgments We wish to thank the Instituto Politecnico Nacional for support received through COFAA and EDI. The first author thanks Consejo Nacional de Ciencia y Tecnología (CONACyT) and Programa Institucional de Formación de Investigadores (PIFI). Finally, thanks to T. Morey for editing the English language text. Literature Cited Abitia-Cárdenas, L. A. 2001. Dinámica trófico-energética del marlín rayado Tetrapturus audax (Philippi, 1887) en el área de Los Cabos, B. C. S., México. PhD Diss. UNAM. Mexico. D. F. 115 p., F. Galván-Magaña, and A. F. Muhlia-Melo. 1998 Trophic spectrum of striped marlin Tetrapturus audax (Philippi, 1887), off the coast of Cape San Lucas, Baja California Sur, Mexico. Rev. Biol. Mar. Ocean. 33: 277 290, A. F. Muhlia-Melo, V. H. Cruz-Escalona, and F. Galván-Magaña. 2002. Trophic dynamics and seasonal energetics of striped marlin Tetrapturus audax in the southern Gulf of California, Mexico. Fish. Res. 57: 287 295,, F. J. Gutiérrez-Sánchez., J. Rodríguez-Romero., B. Aguilar-Palomino, and A. Moehl, H. 1999. Diet of blue marlin Makaira mazara off the coast of Cabo San Lucas, Baja California Sur, Mexico. Fish. Res. 44: 95 100. Allen, G. R. and D. R. Robertson. 1994. Fishes of the tropical eastern Pacific. University of Hawai Press, Manoa. 332 p. Alvarez-Borrego, S. and R. A. Schwartzlose. 1979. Masas de agua del Golfo de California. Cienc. Mar. 6: 43 63. Anonymous. 2001. Programa de manejo. Complejo Insular Espíritu Santo, México. Componente del área de protección de flora y fauna Islas del Golfo de California. SEMARNAP- CONANP, Mexico. 194 p. Badan, A. 1997. La Corriente Costanera de Costa Rica en el Pacífico Mexicano. Pages 99 112 in M. F. Lavin, ed. Contribuciones a la Oceanografía Física en México, Monografía No. 3. Unión Geofisica Mexicana. 147 p. Brock, E. R. 1984. A contribution of the trophic biology of the blue marlin (Makaira nigricans Lacépède, 1802) in Hawaii. Pacif. Sci. 38: 141 149. Brusca, R. C. 1980. Common intertidal invertebrates of the Gulf of California. Univ. Arizona Press, Tucson. 513 p. Clarke, M. R. 1962. The identification of cephalopod beaks and the relationship between beak size and total body weight. Bull. Br. Mus. (Nat. Hist.). Zool. 8: 419 480.. 1986. A handbook for the identification of cephalopod beaks. Oxford Univ. Press, New York. 273 p. Clothier, C. R. 1950. A key to some southern California fishes based on vertebral characters. Calif. Dep. Fish Game. Fish. Bull. 79: 1 83. De La Lanza-Espino, G. E. 1991. Oceanografía de mares mexicanos. AGT. Editor. 569 p. Eldrige, M. B. and P. G. Wares. 1974. Some biological observations of billfishes taken in the eastern Pacific Ocean. Pages 89 101 in R. S. Shomura and F. Williams, eds. Species synopsis: Proc Int. Billfish Symp. Kailua-Kona, Hawaii, August 9 12, 1972. U.S. Dep. Commer., NOAA Tech. Rep. NMFS-SSRF-675. 675 p. Evans, D. H. and P. G. Wares. 1972. Food habits of the striped marlin and sailfish off Mexico and southern California. Fish Wildl. Serv. Res. Rep. 76: 1 10. Fischer, W., F. Krupp., W. Schneider., C. Sommer., K. E. Carpenter, and V. H. Niem. 1995a. Guia FAO para la identificación de peces para los fines de pesca. Pacífico centro-oriental. Vol. I. Plantas e invertebrados. FAO (U.N. Food and Agriculture Organization). I: 1 646.

790 BULLETIN OF MARINE SCIENCE, VOL. 79, NO. 3, 2006,,,, and. 1995b. Guia FAO para la identificación de peces para los fines de pesca. Pacífico centro-oriental. Vol. II y III. Vertebrados, Part 1 and 2 FAO (U.N. Food and Agriculture Organization). I and II: 647 1813. Galván, M. F. 1999. Relaciones tróficas interespecíficas de la comunidad de depredadores epipelágicos del Océano Pacífico Oriental. PhD Diss. Mar. Ecol., CICESE, B.C. Mexico. 212 p. Garth, J. S. and W. Stephenson. 1966. Brachyura of the Pacific coast of America, Brachyrhyncha: Portunidae. Allan Hancock Monogr. Mar. Biol. 1: 1 154. Harvey, G. C. McN. 1989. An historical review of recreational and artisanal fisheries for billfish in Jamaica, 1976 1988. ICCAT Col. Vol. Sci. Papers 30: 440 450. Hoolihan, J. 2003. Sailfish movement in the Arabian Gulf: A summary of tagging efforts. Mar. Freshw. Res. 54: 509 513. Iverson, L. K. and L. Pinkas. 1971. A pictorial guide to beaks of certain eastern Pacific cephalopods. Calif. Dep. Fish Game. Fish. Bull. 152: 83 105. Jolley, J. W. Jr. 1977. The biology and fishery of Atlantic Sailfish Istiophorus platypterus, from southeast Florida. Florida Mar. Res. Pub. 28: 1 31. Joseph, J., W. Klawe, and P. Murphy. 1974. A review of the longline fishery for billfishes in the Eastern Pacific Ocean. Pages 309 323 in R. S. Shomura and F. Williams, eds. Proc. Int. Billfish Symp. Kailua-Kona, Hawaii, August 9 12, 1972. Species synopsis. NOAA Tech. Rep. NMFS. part 2. 675 p. Krebs, C. J. 1989. Ecological methodology. Harper and Row, New York. 473 p. Kume, S. and J. Joseph. 1969. Size composition and sexual maturity of billfish caught by the Japanese longline fishery in the Pacific Ocean, east of 130 W. Bull. Far. Seas Fish. Res. Lab. (Shimizu) 2: 115 162. Labropoulou, M. and A. Eleftheriou. 1997. The foraging ecology of two pairs of congeneric demersal fish species: importance of morphological characteristics in prey selection. J. Fish Biol. 50: 324 340. Langton. R. W. 1982. Diet overlap between the Atlantic cod Gadus morhua, silver hake, Merluccius biliniaris and fifteen other northwest Atlantic finfish. U.S. National Marine. Fisheries Service Fish. Bull. 80: 745 759. Markaida, U. 2006. Population structure and reproductive biology of jumbo squid Dosidicus gigas from the Gulf of California after the 1997 1998 El Niño event. Fish. Res. 79: 28 37 and O. Sosa-Nishizaki. 1998. Food and feeding habits of swordfish, Xiphias gladius L., off western Baja California. Pages. 245 259 in I. Barrett, O. Sosa-Nishizaki, and N. Bartoo, eds. Biology and fisheries of swordfish, Xiphias gladius. Proc. Int. Symp. on Pacific swordfish, December 11 14, 1994, Ensenada, Mexico U.S. Dep. Commer., NOAA Tech. Rep. NMFS-142. 216 p. Miller, D. J. and S. C. Jorgensen. 1973. Meristic characters of some marine fishes of the western Atlantic Ocean. U.S. Fish Wildlf. Serv. Fish. Bull. 71: 301 312. Miyabe, N. and W. H. Bayliff. 1987. A review of the Japanese longline fishery for tunas and billfishes in the eastern Pacific Ocean, 1971 1980. Inter-Am. Trop. Tuna Comm. Bull. 19: 1 163. Monod, T. 1968. Le complexe urophore des poissons teleosteens. Memories de L Intitute Fundamental D Affrique Noire. 81: 705 p. Nakamura, I. 1985. FAO, Species catalogue Vol. 5 Billfishes of the world: An annotated and illustrated catalogue of marlins, sailfish, spearfish and swordfish know to date. FAO Fisheries Synopsis. (125) 5: 65 p. Nevárez-Martínez, M. O., F. J. Méndez-Tenorio, C. Cervantes-Valle, J. López-Martinez, and M. L. Anguiano-Carrasco. 2006. Growth, mortality, recruitment, and yield of the jumbo squid (Dosidicus gigas) off Guaymas, Mexico. Fish. Res. 79: 38 47 Olson, R. J. and C. H. Boggs. 1986. Apex predation by yellowfin tuna (Thunnus albacares): independent estimates from gastric evaluation and stomach contents, bioenergetics, and cesium concentrations. Can. J. Fish. Aquat. Sci. 43: 1760 1775.

ARIZMENDI-RODRÍGUEZ ET AL.: FOOD HABITS OF SAILFISH OFF MAZATLÁN, MEXICO 791 and F. Galvan-Magaña. 2002. Food habits and consumption rates of common dolphinfish (Coryphaena hippurus) in the eastern Pacific Ocean. Fish. Bull. 279 298. Ovchinnikov, V. V. 1970. Swordfishes and billfishes in the Atlantic Ocean: ecology and functional morphology. English translation by H. Mills, Israel Program for Scientific Translations, Jerusalem. 77 p. Palko, B. J., G. L. Beardsley, and W. L. Richards. 1981. Synopsis of the biology of the swordsfish Xiphias gladius Linnaeus. NOAA Tech. Rep. NMFS Circ. 441. FAO Fish. Synop. 127: 1 21. Pinkas, L., M. S. Oliphant, and L. K. Iverson. 1971. Food habits of albacore, bluefin tuna, and bonito in California waters. Calif. Dep. Fish Game. Fish Bull. 152: 105 p. Post, J. T., J. E. Serafy., J. S. Ault, T. R. Capo, and D. P. De Sylva. 1997. Field and laboratory observations on larval Atlantic sailfish (Istiophorus platypterus) and swordfish (Xiphias gladius). Bull. Mar. Sci. 60: 1026 1034. Robertson, K. M. and S. J. Chivers. 1997. Prey occurrence in pantropical spotted dolphins, Stenella attenuate, from the eastern tropical Pacific. Fish. Bull. 95: 334 348. Rosas-Alayola, J., A. Hernández-Herrera., F. Galván-Magaña., L. A. Abitia-Cárdenas, and A. F. Muhlia-Melo. 2002. Diet composition of Sailfish (Istiophorus platypterus) from the southern Gulf of California, Mexico. Fish. Res. 57: 185 195. Smith, P. E. and M. T. Zaret. 1982. Bias in estimating niche overlap. Ecology 63: 1248 1253. Stillwell, C. E. and N. E. Kohler. 1985. Food and feeding ecology of the swordfish Xiphias gladius in the western North Atlantic Ocean with estimates of daily ration Mar. Ecol. Prog. Ser. 22: 239 247 Thomson, D. A., L. T. Findley, and A. N. Kerstitch. 2000. Reef fishes of the Sea of Cortez. The Rocky-Shore Fishes of the Gulf of California. Univ. Texas Press. 353 p. Voss, G. L. 1953. A contribution to the life history and biology of the sailfish, Istiophorus americanus Cuv. and Val. In Florida waters. Bull. Mar. Sci. Gulf Carib. 3: 206 240. Williams, F. 1963. Longline fishing for tuna off the coast of east Africa 1958 1960. Indian J. Fish., (sect. A) 10: 233 390. Wolff, C. A. 1982. A beak key for eight eastern tropical Pacific cephalopods species, with relationship between their beak dimensions and size. Fish. Bull. 80: 357 370. Addresses: (D.I.A.-R., L.A.A.-C., F.G.-M.) Centro Interdisciplinario de Ciencias Marinas (CICIMAR-IPN), Apdo. Postal 592, La Paz, Baja California Sur, Mexico. C.P. 23000. (I.T.- E.) Facultad de Ciencias del Mar (FACIMAR-UAS). Mazatlán, Sinaloa, Mexico, C.P. 82000. Corresponding Author: (F.G.-M.) Email: <galvan.felipe@gmail.com>.