A Contribution to the Trophic Biology of the Blue Marlin ( Makaira nigricans Lacepede , 1802 ) in Hawaii

A study of the trophic biology of 87 blue marlin caught in Hawaiian waters indicates that these opportunistic predators consume a diverse array of prey. The data suggest that the diet of blue marlin is influenced by the locality of capture. Thus, surface (troll)-caught blue marlin from near the Hawaiian Islands consume numerous larvae, postlarvae, and juveniles ofinshore species, prey relatively rare in marlin taken on the high seas. Volumetrically, these inshore forms are oflittle consequence and probably contribute little to the energy requirements of blue marlin. As shown in other studies, small tunas are the single most important component of Hawaiian blue marlin diets. MATERIALS AND METHODS ecological information (size, location, and time of catch) to obtain a better understanding of their trophic biology. Stomachs for analysis were obtained from blue marlin caught in the 27-29 July 1981 and 16-20 August 1982 Hawaiian International Billfish Tournaments (HIBT). In these tournaments fish are taken off the Kona, Hawaii, coast in an area from Upolu Point (20 'N lat.) to South Point (19°00' N lat.) and from the shore westward to 156°20' W long . The HIBT rules require records of catch location, time of hookup, fight time, and gear used. Effort in both years was similar with 75 boats each fishing an 8-hour day. Small variations in effort expended could be due to differences in the number of lines fished per boat, the method offishing (live bait or plastic lures), or due to the time spent fighting an individual fish. These differences are probably small , however, thus allowing direct comparison of catches. Once landed all fish were weighed , length measurements taken, sex determined, stomach removed and cut open and the contents labeled and placed in 0.5 mm mesh bags which were immersed in 10 percent formalin . All stomachs were sampled on the day of capture. At the time of sampling care was taken not to confuse any bait with other stomach 141 THERE HAS BEEN CONSIDERABLE interest in the feeding habits of the blue marlin (Makaira nigricans). This is probably due to its large size (to 800 kg), game qualities, reputed pugnacity, and its position as a terminal predator in the ocean. Most trophic studies of this species have simply identified and determined the relative importance of food items consumed in a given geographic region. Usually there ha s been little other concurrent ecological information available to the investigator, and sample sizes are often small. These difficulties have resulted in a situation where some information is available on what is consumed by blue marlin from a number of geographical localities but little else is known of their trophic biology. This paper reports on the food and feeding habits of 87 blue marlin taken off Hawaii during one-week tournaments in each of two consecutive summers utilizing concomitant I This is Hawaii Institut e of Marine Biology Contri bution no. 689 and Ocean Resource s OfficeContribution no. 15. This research was supported by the Universit y of Hawaii Sea Grant College Program under Institutional Gr ant No. NA81-AA-D-0070 from NOAA, Officeof Sea Gran t, U.S. Department of Commerce, and the Office of the Marine Affairs Coordinator, subsequently the Ocean Resourc es Office (Hawaii Department of Planning and Economic Development). Manuscript accepted 22 December 1983. 2 University of Hawai i, Hawaii Institute of Marine Biology, P.O. Box 1346, Kaneohe, Hawaii 96744.