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Diet of blue marlin Makaira mazara off the coast of Cabo San Lucas, Baja California Sur, Mexico
Fisheries Research 44 (1999) 95±100
Short communication
Diet of blue marlin Makaira mazara off the coast of Cabo San Lucas, Baja California Sur, Mexico Leonardo Andres Abitia-Cardenasa,*, Felipe Galvan-MaganÄaa, Francisco Javier Gutierrez-Sancheza, Jesus Rodriguez-Romerob, Bernabe Aguilar-Palominoc, Almei Moehl-Hitza a
Centro Interdisciplinario de Ciencias Marinas, IPN, Apartado postal 592, Baja California Sur, CP 23000, La Paz, Mexico b Centro de Investigaciones Biologicas del Noroeste, AC, Mexico c Centro de EcologõÂa Costera, Universidad de Guadalajara, Mexico Received 9 October 1998; received in revised form 6 May 1999; accepted 25 May 1999
Abstract Analysis of the stomach contents of 204 blue marlin (Makaira mazara) caught by the sport-®shing ¯eet of Cabo San Lucas in the southern Gulf of California is presented. The specimens sampled were caught during the summer and fall of 1987, 1988, and 1989 when the sea is warm (28±308C). Blue marlin were found to feed on 35 prey species, 3 of which represented 90% of the total stomach contents by frequency of occurrence. The main prey were epipelagic organisms from the oceanic zone and demersal ®shes from the neritic zone. The most important prey were bullet mackerel Auxis spp., young ®nescale trigger®sh Balistes polylepis, and the giant squid Dosidicus gigas. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Blue marlin; Food habits; Coast of Mexico
1. Introduction The Indo-Paci®c blue marlin Makaira mazara (Jordan and Snyder) is a large predatory marine ®sh widely distributed through the Paci®c and Indian ocean and abundant in tropical regions (Nakamura, 1985; Joseph et al., 1988). Along the coast of Mexico and especially near Cabo San Lucas, three species of bill®sh, blue marlin, striped marlin Tetrapturus audax (Philippi), and sail®sh Istiophorus platypterus Shaw *Corresponding author. Tel.: +52-112-25344; fax: +52-11225322 E-mail address: [email protected] (L.A. Abitia-Cardenas)
and Nodder are commonly caught. Deep waters occur relatively close to Cabo San Lucas, which brings these bill®sh within range of an active sport-®shing ¯eet. Despite the popularity of blue marlin as a game ®sh because of its large size (up to 625 kg) and spectacular acrobatics when caught on rod and reel, little is known of their trophic biology in the eastern Paci®c ocean. Only one study has been done, Eldrige and Wares (1974) identi®ed the stomach contents of 15 blue marlin caught by sport ®shermen off Buena Vista, Baja California Sur, Mexico during 1970. The purpose of this study was to expand the understanding of the seasonal changes in the diet and feeding behavior of blue marlin, which because of
0165-7836/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 5 - 7 8 3 6 ( 9 9 ) 0 0 0 5 3 - 3
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L.A. Abitia-Cardenas et al. / Fisheries Research 44 (1999) 95±100
size and speed is considered one of the top predators in the trophic web in the ocean off the coast of Mexico. 2. Methods Blue marlin were caught by trolling with live bait, mainly chub mackerel Scomber japonicus and jacks Caranx spp., or with jigs by the sport-®shing ¯eet out of Cabo San Lucas, BCS (228530 N, 1098540 W) (Fig. 1). Stomachs were sampled in port during summer and fall of 1987, 1988, and 1989. Each marlin was weighed to the nearest kg and its postorbital length (eye-fork length) measured to the nearest cm. The stomach contents were removed and ®xed in 10% formalin. The stomach contents in each taxonomic category were enumerated (N) and the volume (V) measured to the nearest ml. These two measures and the frequency of occurrence (FO) were combined to calculate the index of relative importance (IRI) of Pinkas et al. (1971), to provide a more representative summary of the dietary composition. The Kruskal±Wallis test (Sokal and Rohlf, 1981), was used to compare the effect of the year/season on occurrence values of prey.
The analysis included six seasons from three years (summer and fall of 1987, 1988, and 1989). Diet breadth was calculated using Levin's standardized index (Krebs, 1989). This index ranges from 0 to 1; low values (<0.6) indicating diet dominated by few prey items (specialist predator) and higher values (>0.6) indicating generalist diets (Labropoulou and Eleftheriou, 1997). 3. Results The size of the blue marlin analyzed ranged from 188 to 290 cm postorbital length (PL) (mean221.5 19.8 cm standard deviation), with weights between 88 and 334 kg (mean17554.7 kg). Two hundred and four stomachs were examined; 176 (86.3%) contained food, 19 (9.3%) were empty, and 9 (4.4%) had regurgitated their contents. There were 35 prey species identi®ed; 7 cephalopods, 2 crustaceans, and 26 ®sh. Osteichthyes (®sh) was the major food group eaten by the blue marlin by volume (89.6%), number (76.5%), occurrence (95%) and index of relative importance (92.6%). The most important species were the bullet mackerel Auxis spp., young ®nescale trig-
Fig. 1. Map showing the location of the study area off the tip of Baja California, Mexico.
L.A. Abitia-Cardenas et al. / Fisheries Research 44 (1999) 95±100
97
Fig. 2. The major prey species found in the stomachs of blue marlin presented as percentages of number of individuals, volume, frequency of occurrence, and IRI.
ger®sh Balistes polylepis and California pilchard Sardinops caeruleus. Cephalopods were second most important by volume (10.3%), number (22%), occurrence (21.8%), and IRI (7.3%). The family Ommastrephidae, which includes four species, were found in 22.7% of the stomachs. The giant squid Dosidicus gigas was the most important species (Fig. 2). During the summer and fall of the three years, ®sh were the most important prey. Auxis spp. were the most common prey, having the highest frequency occurrence values (Table 1). The Kruskal±Wallis showed signi®cant differences among seasons values of food consumed (X86.44; df5, 204; P<0.001). In considering diet breadth, there were a large number of food components (35 in total). However, the clear dominance of the prey species Auxis spp. (bullet mackerel), D. gigas (giant squid), and B. polylepis (young ®nescale trigger®sh), determined that the results obtained by Levin's index were low for all seasons (Bi <0.43). 4. Discussion The diversity of prey species found in blue marlin stomachs in this study (35 prey species identi®ed) implies an opportunistic predator feeding on forage from various trophic levels and with a wide range of prey size and morphology. This last conclusion was also reported for Hawaiian blue marlin examined by
Brock (1984). However, in spite of consuming a large number of species, this predator selects a reduced number of prey of the epipelagic (more than 80% originate in this environments) and demersal zone. Evidence of the high degree of food specialization of this species is the large consumption of the prey species Auxis spp., D. gigas, and B. polylepis. The prey composition of blue marlin, showed seasonal differences during 1987, 1988, and 1989 in the coast off Cabo San Lucas, which probably is the effect of the number differences of food components registered among seasons, this number ¯uctuated between a maximum of 35 and a minimum of 5 prey species (Table 1). However only two prey, the bullet mackerel Auxis spp. and the giant squid D. gigas, occurred during all seasons with more than 78% of the frequency of occurrence. The bullet mackerel was the most important prey in the diet of blue marlin, probably by the presence of warm water masses from the Tropical Eastern Paci®c (Alvarez, 1993), and because bullet mackerel are very common in this oceanic area (95% of larval catch) according to Klawe et al. (1970) and Olson and Boggs (1986). In other areas of the eastern Paci®c ocean, Auxis spp. are common prey of yellow®n tuna (Olson and Boggs, 1986) and bill®sh (Eldrige and Wares, 1974; Abitia et al., 1997). Also the abundance of bullet mackerel is well known in the eastern Paci®c, and could be a potential world-wide ®shery resource.
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L.A. Abitia-Cardenas et al. / Fisheries Research 44 (1999) 95±100
Table 1 Seasonal absolute values and percentages of the frequency of occurrence values of the stomach contents of blue marlin from Cabo San Lucas, BCS, Mexico Prey
1987
1988
Summer
Fall
FO
FO (%)
FO
FO (%)
12 1 5 1 1 2 1
44.44 3.70 18.52 3.70 3.70 7.41 3.70
11 2 1 1 1 1 7
35.48 6.45 3.23 3.23 3.23 3.23 22.58
1 0 2 0 0 0 1
1 1
3.70 3.70
1 2
3.23 6.45
Osteichthyes Clupeidae Etrumeus teres Sardinops caeruleus Exocoetus spp Oxyporhamphus micropterus Hyporhamphus spp Merluccius productus Diplectrum spp Carangidae Caranx caballus Caranx caninus Caranx vinctus Chloroscombrus orqueta Decapterus muroadsi Selar crumenophthalmus Coryphaena hippurus Microlepidotus inornatus Chaetodon falcifer Auxis spp Katsuwonus pelamis Scomber japonicus Balistes polylepis Xanthichthys mento Lagocephalus lagocephalus Scorpaena spp Lophiomus setigerus
0 1 2 0 1 1 0 1 0 1 1 0 1 1 6 1 1 1 12 1 4 1 1 5 1 1
0.00 3.70 7.41 0.00 3.70 3.70 0.00 3.70 0.00 3.70 3.70 0.00 3.70 3.70 22.22 3.70 3.70 3.70 44.44 3.70 14.81 3.70 3.70 18.52 3.70 3.70
0 1 6 2 2 2 0 1 0 1 4 0 2 2 1 1 1 1 15 3 6 13 1 3 1 1
0.00 3.23 19.35 6.45 6.45 6.45 0.00 3.23 0.00 3.23 12.90 0.00 6.45 6.45 3.23 3.23 3.23 3.23 48.39 9.68 19.35 41.94 3.23 9.68 3.23 3.23
Total stomachs examined
27
Mollusca Dosidicus gigas Ommastrephes spp Stenoteuthis oualaniensis Thysanoteuthis rhombus Octopus spp Ocythoe tuberculata Argonauta spp Arthropoda Euphylax dovii Pleuroncodes planipes
31
The giant squid D. gigas was important in the diet of blue marlin. This squid is found in subtropical and tropical waters and is very common at the surface at night and in waters from 200 to 2,000 m depth
1989
Summer
Fall
FO
FO
6.67 0.00 13.33 0.00 0.00 0.00 6.67
0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 12 0 0 0 0 0 0 0 15
Summer
Fall
FO (%)
FO
FO
FO (%)
1 0 0 0 0 0 0
5.56 0.00 0.00 0.00 0.00 0.00 0.00
7 0 0 0 0 0 0
11.48 0.00 0.00 0.00 0.00 0.00 0.00
1 0 0 0 0 0 0
4.17 0.00 0.00 0.00 0.00 0.00 0.00
0.00 0.00
0 1
0.00 5.56
0 0
0.00 0.00
0 0
0.00 0.00
0.00 0.00 6.67 0.00 0.00 0.00 0.00 0.00 6.67 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 80.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
1 1 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 0 10 0 1 0 0 0 0 0
5.56 5.56 0.00 0.00 0.00 0.00 16.67 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 55.56 0.00 5.56 0.00 0.00 0.00 0.00 0.00
0 0 0 0 0 0 0 0 0 2 4 1 0 0 0 1 0 0 45 0 0 1 0 0 0 0
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.28 6.56 1.64 0.00 0.00 0.00 1.64 0.00 0.00 73.77 0.00 0.00 1.64 0.00 0.00 0.00 0.00
0 0 2 0 0 0 2 0 0 0 0 0 0 9 4 1 0 0 11 0 0 5 0 0 0 0
0.00 0.00 8.33 0.00 0.00 0.00 8.33 0.00 0.00 0.00 0.00 0.00 0.00 37.50 16.67 4.17 0.00 0.00 45.83 0.00 0.00 20.83 0.00 0.00 0.00 0.00
FO (%)
18
61
FO (%)
24
off Cabo San Lucas (Sato, 1976). The presence of this species can be associated with tropical water masses at the entrance of the Gulf of California and with the occurrence of schools of epipelagic prey
L.A. Abitia-Cardenas et al. / Fisheries Research 44 (1999) 95±100
species from the neritic and oceanic zones, which are commonly consumed by the giant squid (Erhardt et al., 1986). The occurrence of benthic prey species (e.g. Lophiomus setigerus, Scorpaena spp., Chaetodon falcifer) and demersal prey species (e.g. M. productus, Diplectrum spp.) may indicate that blue marlin also feed near the bottom. Telemetric studies have shown that bill®sh such as blue marlin have a daily vertical migration, swimming in deep waters during the day and remaining close to the surface at night (Holland et al., 1990). Unlike the trophic spectrum found by Eldrige and Wares (1974), we did not ®nd the ®sh Euthynnus lineatus, Remora brachyptera, or ¯ying ®sh (family Exocoetidae) as principal prey. However, in general, the prey we found were similar to those listed in studies on blue marlin from other geographic areas (e.g. Nakamura, 1942; Royce, 1957; Erdman, 1962; Strasburg, 1970; Nakamura and Rivas, 1972; Rivas, 1974). The tip of Baja California is a region with a large number of predator ®sh. The prey fauna is also diverse, as indicated by this study and Abitia et al. (1997). The richness of fauna is caused by the presence of local upwelling and oceanographic fronts (Grif®ths, 1968; Hanamoto, 1974), which produce and maintain the supplies of nutrients by complex horizontal and vertical components of water movement, maximizing physical condition for primary productivity. They provide an optimal environmental for the growth of large phytoplankton, which are used by large herbivores such as planktivorous ®sh (e.g. herring, anchovies) and ®nally in turn are used by the apex predators (e.g. tuna, bill®sh, shark) (Daly and Smith, 1993). Acknowledgements We wish to thank Robert J. Olson of the InterAmerican Tropical Tuna Commission, and Kim Holland of the University of Hawaii for comments and review of this manuscript. Thanks to Ellis Glazier, CIBNOR, for editing the English-language text. Thanks are also to extended to Consejo Nacional de Ciencia y TecnologõÂa and Instituto Politecnico Nacional (COFAA) for their support.
99
References Abitia, C.L.A., Galvan, M.F., Rodriguez, R.J., 1997. Food habits and energy values of prey of striped marlin, Tetrapturus audax off the coast of Mexico. Fish Bull. 95, 360±368. Alvarez, B.S., 1993. Gulf of California. In: Ketchum, B.H. (Ed.), Estuaries and Enclosed Seas. Elsevier, New York, pp. 247±449. Brock, E.R., 1984. A contribution of the trophic biology of the blue marlin (Makaira nigricans Lacepede, 1802) in Hawaii. Pacif. Sci. 38, 141±149. Daly, K.L., Smith Jr., W.O., 1993. Physical-biological interactions influencing marine plankton production. Annu. Rev. Ecol. Syst. 24, 555±585. Eldrige, M.B., Wares, P.G., 1974. Some biological observations of billfishes taken in the eastern Pacific Ocean, 1967±1970. In: Shomura, R.S., Williams, F. (Ed.), Species Synopsis, Proceedings of the International billfish symposium, Part 2. KailuaKona, Hawaii, 9±12 August 1972, pp. 302±308. US Department of Commerce, NOAA Technical Report. NMFS-SSRF-675, pp. 89±101. Erdman, D.S., 1962. The sport fishery for blue marlin off Puerto Rico. Trans. Am. Fish. Soc. 91, 225±227. Erhardt, N., Solis, A., Pierre, J., Ortiz, J., Ulloa, P., Gonzalez, G., Garcia, F., 1986. AnaÂlisis de la biologõÂa y condiciones del stock del calamar gigante Dosidicus gigas en el Golfo de California, durante 1980. Ciencia Pesquera. INP MeÂxico, vol. 5, pp. 63±76. Griffiths, R.C., 1968. Physical, chemical, and biological oceanography of the entrance to the Gulf of California, spring of 1960. US Fish Wildl. Serv. Spec. Sci. Rep. Fish., vol. 573, 47 pp. Hanamoto, E., 1974. Fishery-oceanographic studies of striped marlin Tetrapturus audax, in waters off Baja California. I. Fishing conditions in relation to the thermocline. In: Shomura, R.S., Williams, F. (Ed.), Species synopsis, Proceedings of the International Billfish symposium, Kailua-Kona, Hawaii, 9±12 August 1972 US Department of Commerce, NOAA Technical Report. NMFS-SSRF-675, pp. 302±308. Holland, K.N., Brill, R.W., Chang, R.K.C., 1990. Horizontal and vertical movements of Pacific blue marlin captured and released using sportfishing gear. Fish Bull. 88, 397±402. Joseph, J., Klawe, W., Murphy, P., 1988. Tuna and billfish. Fish without a country. Inter-American Tropical Tuna Commission. La Jolla California, 69 pp. Klawe, W.L., Pella, J.J., Leet, W.S., 1970. The distribution, abundance and ecology of larval tunas from the entrance to the Gulf of California. Inter-Am. Trop. Tuna Comm. Bull. 14, 507± 544. Krebs, C.J., 1989. Ecological methodology. Harper and Row, New York, 550 pp. Labropoulou, M., Eleftheriou, A., 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. Nakamura, H., 1942. On the ecology of the istiophorid fishes of Taiwan waters. (In Japanese) Sci. Fish. Assoc., Fac. Agr. Tokyo Imp. Univ. Suisan Gakkwai Ho. 9, pp. 45±51. Nakamura, I., 1985. FAO Species catalogue, vol. 5. Billfishes of the world. An annotated and illustrated catalogue of marlins,
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sailfishes, spearfishes and swordfishes known to date. FAO Fish. Synopsis 125(5), 1±65. Nakamura, E.L., Rivas, L.R., 1972. Big game fishing in the northeastern Gulf of Mexico during 1971. Natl. Mar. Fish Serv. Panama City, Fla., 20 pp. Olson, R.J., Boggs, C.H., 1986. Apex predation by yellowfin tuna (Thunnus albacares); independent estimates from gastric evaluation and stomach contents, bionergetics, and cesium concentrations. Can. J. Fish. Aquat. Sci. 43, 1760±1775. Pinkas, L., Oliphant, M.S., Iverson, L.K., 1971. Food habits of albacore, bluefin tuna, and bonito in California waters. Calif. Dep. Fish Game, Fish Bull. 152, 105 pp. Rivas, L.R., 1974. Synopsis of biological data of blue marlin Makaira nigricans Lacepede 1802. In: Shomura, R.S.,
Williams, F. (Ed.), Proceedings of the International billfish symposium, Kailua-Kona, Hawaii, 9±12 August 1972, Part 3. US Department of Commerce. NOAA Technical Report. NMFS-SSRF-675, pp. 302±308. Royce, W.F., 1957. Observations on the spearfishes of the Central Pacific. U.S. Fish Wildll. Serv. Fish. Bull. 57, 497±554. Sato, T., 1976. Resultados de la pesca exploratoria para Dosidicus gigas (D'Orbigny) frente a California y MeÂxico, FAO. Informes de Pesca 170 (Suppl. 1), 62±68. Sokal, R.R., Rohlf, F.J., 1981. Biometry: the principles and practice of statistics in biological research, 2nd ed. W.H. Freeman and Co., New York, NY, 859 p. Strasburg, D.W., 1970. A report on the billfishes of the Central Pacific ocean. Bull. Mar. Sci. 20, 575±604.
Short communication
Diet of blue marlin Makaira mazara off the coast of Cabo San Lucas, Baja California Sur, Mexico Leonardo Andres Abitia-Cardenasa,*, Felipe Galvan-MaganÄaa, Francisco Javier Gutierrez-Sancheza, Jesus Rodriguez-Romerob, Bernabe Aguilar-Palominoc, Almei Moehl-Hitza a
Centro Interdisciplinario de Ciencias Marinas, IPN, Apartado postal 592, Baja California Sur, CP 23000, La Paz, Mexico b Centro de Investigaciones Biologicas del Noroeste, AC, Mexico c Centro de EcologõÂa Costera, Universidad de Guadalajara, Mexico Received 9 October 1998; received in revised form 6 May 1999; accepted 25 May 1999
Abstract Analysis of the stomach contents of 204 blue marlin (Makaira mazara) caught by the sport-®shing ¯eet of Cabo San Lucas in the southern Gulf of California is presented. The specimens sampled were caught during the summer and fall of 1987, 1988, and 1989 when the sea is warm (28±308C). Blue marlin were found to feed on 35 prey species, 3 of which represented 90% of the total stomach contents by frequency of occurrence. The main prey were epipelagic organisms from the oceanic zone and demersal ®shes from the neritic zone. The most important prey were bullet mackerel Auxis spp., young ®nescale trigger®sh Balistes polylepis, and the giant squid Dosidicus gigas. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Blue marlin; Food habits; Coast of Mexico
1. Introduction The Indo-Paci®c blue marlin Makaira mazara (Jordan and Snyder) is a large predatory marine ®sh widely distributed through the Paci®c and Indian ocean and abundant in tropical regions (Nakamura, 1985; Joseph et al., 1988). Along the coast of Mexico and especially near Cabo San Lucas, three species of bill®sh, blue marlin, striped marlin Tetrapturus audax (Philippi), and sail®sh Istiophorus platypterus Shaw *Corresponding author. Tel.: +52-112-25344; fax: +52-11225322 E-mail address: [email protected] (L.A. Abitia-Cardenas)
and Nodder are commonly caught. Deep waters occur relatively close to Cabo San Lucas, which brings these bill®sh within range of an active sport-®shing ¯eet. Despite the popularity of blue marlin as a game ®sh because of its large size (up to 625 kg) and spectacular acrobatics when caught on rod and reel, little is known of their trophic biology in the eastern Paci®c ocean. Only one study has been done, Eldrige and Wares (1974) identi®ed the stomach contents of 15 blue marlin caught by sport ®shermen off Buena Vista, Baja California Sur, Mexico during 1970. The purpose of this study was to expand the understanding of the seasonal changes in the diet and feeding behavior of blue marlin, which because of
0165-7836/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 5 - 7 8 3 6 ( 9 9 ) 0 0 0 5 3 - 3
96
L.A. Abitia-Cardenas et al. / Fisheries Research 44 (1999) 95±100
size and speed is considered one of the top predators in the trophic web in the ocean off the coast of Mexico. 2. Methods Blue marlin were caught by trolling with live bait, mainly chub mackerel Scomber japonicus and jacks Caranx spp., or with jigs by the sport-®shing ¯eet out of Cabo San Lucas, BCS (228530 N, 1098540 W) (Fig. 1). Stomachs were sampled in port during summer and fall of 1987, 1988, and 1989. Each marlin was weighed to the nearest kg and its postorbital length (eye-fork length) measured to the nearest cm. The stomach contents were removed and ®xed in 10% formalin. The stomach contents in each taxonomic category were enumerated (N) and the volume (V) measured to the nearest ml. These two measures and the frequency of occurrence (FO) were combined to calculate the index of relative importance (IRI) of Pinkas et al. (1971), to provide a more representative summary of the dietary composition. The Kruskal±Wallis test (Sokal and Rohlf, 1981), was used to compare the effect of the year/season on occurrence values of prey.
The analysis included six seasons from three years (summer and fall of 1987, 1988, and 1989). Diet breadth was calculated using Levin's standardized index (Krebs, 1989). This index ranges from 0 to 1; low values (<0.6) indicating diet dominated by few prey items (specialist predator) and higher values (>0.6) indicating generalist diets (Labropoulou and Eleftheriou, 1997). 3. Results The size of the blue marlin analyzed ranged from 188 to 290 cm postorbital length (PL) (mean221.5 19.8 cm standard deviation), with weights between 88 and 334 kg (mean17554.7 kg). Two hundred and four stomachs were examined; 176 (86.3%) contained food, 19 (9.3%) were empty, and 9 (4.4%) had regurgitated their contents. There were 35 prey species identi®ed; 7 cephalopods, 2 crustaceans, and 26 ®sh. Osteichthyes (®sh) was the major food group eaten by the blue marlin by volume (89.6%), number (76.5%), occurrence (95%) and index of relative importance (92.6%). The most important species were the bullet mackerel Auxis spp., young ®nescale trig-
Fig. 1. Map showing the location of the study area off the tip of Baja California, Mexico.
L.A. Abitia-Cardenas et al. / Fisheries Research 44 (1999) 95±100
97
Fig. 2. The major prey species found in the stomachs of blue marlin presented as percentages of number of individuals, volume, frequency of occurrence, and IRI.
ger®sh Balistes polylepis and California pilchard Sardinops caeruleus. Cephalopods were second most important by volume (10.3%), number (22%), occurrence (21.8%), and IRI (7.3%). The family Ommastrephidae, which includes four species, were found in 22.7% of the stomachs. The giant squid Dosidicus gigas was the most important species (Fig. 2). During the summer and fall of the three years, ®sh were the most important prey. Auxis spp. were the most common prey, having the highest frequency occurrence values (Table 1). The Kruskal±Wallis showed signi®cant differences among seasons values of food consumed (X86.44; df5, 204; P<0.001). In considering diet breadth, there were a large number of food components (35 in total). However, the clear dominance of the prey species Auxis spp. (bullet mackerel), D. gigas (giant squid), and B. polylepis (young ®nescale trigger®sh), determined that the results obtained by Levin's index were low for all seasons (Bi <0.43). 4. Discussion The diversity of prey species found in blue marlin stomachs in this study (35 prey species identi®ed) implies an opportunistic predator feeding on forage from various trophic levels and with a wide range of prey size and morphology. This last conclusion was also reported for Hawaiian blue marlin examined by
Brock (1984). However, in spite of consuming a large number of species, this predator selects a reduced number of prey of the epipelagic (more than 80% originate in this environments) and demersal zone. Evidence of the high degree of food specialization of this species is the large consumption of the prey species Auxis spp., D. gigas, and B. polylepis. The prey composition of blue marlin, showed seasonal differences during 1987, 1988, and 1989 in the coast off Cabo San Lucas, which probably is the effect of the number differences of food components registered among seasons, this number ¯uctuated between a maximum of 35 and a minimum of 5 prey species (Table 1). However only two prey, the bullet mackerel Auxis spp. and the giant squid D. gigas, occurred during all seasons with more than 78% of the frequency of occurrence. The bullet mackerel was the most important prey in the diet of blue marlin, probably by the presence of warm water masses from the Tropical Eastern Paci®c (Alvarez, 1993), and because bullet mackerel are very common in this oceanic area (95% of larval catch) according to Klawe et al. (1970) and Olson and Boggs (1986). In other areas of the eastern Paci®c ocean, Auxis spp. are common prey of yellow®n tuna (Olson and Boggs, 1986) and bill®sh (Eldrige and Wares, 1974; Abitia et al., 1997). Also the abundance of bullet mackerel is well known in the eastern Paci®c, and could be a potential world-wide ®shery resource.
98
L.A. Abitia-Cardenas et al. / Fisheries Research 44 (1999) 95±100
Table 1 Seasonal absolute values and percentages of the frequency of occurrence values of the stomach contents of blue marlin from Cabo San Lucas, BCS, Mexico Prey
1987
1988
Summer
Fall
FO
FO (%)
FO
FO (%)
12 1 5 1 1 2 1
44.44 3.70 18.52 3.70 3.70 7.41 3.70
11 2 1 1 1 1 7
35.48 6.45 3.23 3.23 3.23 3.23 22.58
1 0 2 0 0 0 1
1 1
3.70 3.70
1 2
3.23 6.45
Osteichthyes Clupeidae Etrumeus teres Sardinops caeruleus Exocoetus spp Oxyporhamphus micropterus Hyporhamphus spp Merluccius productus Diplectrum spp Carangidae Caranx caballus Caranx caninus Caranx vinctus Chloroscombrus orqueta Decapterus muroadsi Selar crumenophthalmus Coryphaena hippurus Microlepidotus inornatus Chaetodon falcifer Auxis spp Katsuwonus pelamis Scomber japonicus Balistes polylepis Xanthichthys mento Lagocephalus lagocephalus Scorpaena spp Lophiomus setigerus
0 1 2 0 1 1 0 1 0 1 1 0 1 1 6 1 1 1 12 1 4 1 1 5 1 1
0.00 3.70 7.41 0.00 3.70 3.70 0.00 3.70 0.00 3.70 3.70 0.00 3.70 3.70 22.22 3.70 3.70 3.70 44.44 3.70 14.81 3.70 3.70 18.52 3.70 3.70
0 1 6 2 2 2 0 1 0 1 4 0 2 2 1 1 1 1 15 3 6 13 1 3 1 1
0.00 3.23 19.35 6.45 6.45 6.45 0.00 3.23 0.00 3.23 12.90 0.00 6.45 6.45 3.23 3.23 3.23 3.23 48.39 9.68 19.35 41.94 3.23 9.68 3.23 3.23
Total stomachs examined
27
Mollusca Dosidicus gigas Ommastrephes spp Stenoteuthis oualaniensis Thysanoteuthis rhombus Octopus spp Ocythoe tuberculata Argonauta spp Arthropoda Euphylax dovii Pleuroncodes planipes
31
The giant squid D. gigas was important in the diet of blue marlin. This squid is found in subtropical and tropical waters and is very common at the surface at night and in waters from 200 to 2,000 m depth
1989
Summer
Fall
FO
FO
6.67 0.00 13.33 0.00 0.00 0.00 6.67
0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 12 0 0 0 0 0 0 0 15
Summer
Fall
FO (%)
FO
FO
FO (%)
1 0 0 0 0 0 0
5.56 0.00 0.00 0.00 0.00 0.00 0.00
7 0 0 0 0 0 0
11.48 0.00 0.00 0.00 0.00 0.00 0.00
1 0 0 0 0 0 0
4.17 0.00 0.00 0.00 0.00 0.00 0.00
0.00 0.00
0 1
0.00 5.56
0 0
0.00 0.00
0 0
0.00 0.00
0.00 0.00 6.67 0.00 0.00 0.00 0.00 0.00 6.67 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 80.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
1 1 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 0 10 0 1 0 0 0 0 0
5.56 5.56 0.00 0.00 0.00 0.00 16.67 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 55.56 0.00 5.56 0.00 0.00 0.00 0.00 0.00
0 0 0 0 0 0 0 0 0 2 4 1 0 0 0 1 0 0 45 0 0 1 0 0 0 0
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.28 6.56 1.64 0.00 0.00 0.00 1.64 0.00 0.00 73.77 0.00 0.00 1.64 0.00 0.00 0.00 0.00
0 0 2 0 0 0 2 0 0 0 0 0 0 9 4 1 0 0 11 0 0 5 0 0 0 0
0.00 0.00 8.33 0.00 0.00 0.00 8.33 0.00 0.00 0.00 0.00 0.00 0.00 37.50 16.67 4.17 0.00 0.00 45.83 0.00 0.00 20.83 0.00 0.00 0.00 0.00
FO (%)
18
61
FO (%)
24
off Cabo San Lucas (Sato, 1976). The presence of this species can be associated with tropical water masses at the entrance of the Gulf of California and with the occurrence of schools of epipelagic prey
L.A. Abitia-Cardenas et al. / Fisheries Research 44 (1999) 95±100
species from the neritic and oceanic zones, which are commonly consumed by the giant squid (Erhardt et al., 1986). The occurrence of benthic prey species (e.g. Lophiomus setigerus, Scorpaena spp., Chaetodon falcifer) and demersal prey species (e.g. M. productus, Diplectrum spp.) may indicate that blue marlin also feed near the bottom. Telemetric studies have shown that bill®sh such as blue marlin have a daily vertical migration, swimming in deep waters during the day and remaining close to the surface at night (Holland et al., 1990). Unlike the trophic spectrum found by Eldrige and Wares (1974), we did not ®nd the ®sh Euthynnus lineatus, Remora brachyptera, or ¯ying ®sh (family Exocoetidae) as principal prey. However, in general, the prey we found were similar to those listed in studies on blue marlin from other geographic areas (e.g. Nakamura, 1942; Royce, 1957; Erdman, 1962; Strasburg, 1970; Nakamura and Rivas, 1972; Rivas, 1974). The tip of Baja California is a region with a large number of predator ®sh. The prey fauna is also diverse, as indicated by this study and Abitia et al. (1997). The richness of fauna is caused by the presence of local upwelling and oceanographic fronts (Grif®ths, 1968; Hanamoto, 1974), which produce and maintain the supplies of nutrients by complex horizontal and vertical components of water movement, maximizing physical condition for primary productivity. They provide an optimal environmental for the growth of large phytoplankton, which are used by large herbivores such as planktivorous ®sh (e.g. herring, anchovies) and ®nally in turn are used by the apex predators (e.g. tuna, bill®sh, shark) (Daly and Smith, 1993). Acknowledgements We wish to thank Robert J. Olson of the InterAmerican Tropical Tuna Commission, and Kim Holland of the University of Hawaii for comments and review of this manuscript. Thanks to Ellis Glazier, CIBNOR, for editing the English-language text. Thanks are also to extended to Consejo Nacional de Ciencia y TecnologõÂa and Instituto Politecnico Nacional (COFAA) for their support.
99
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