BIOLOGY OF OFFSHORE HAKE, MERLUCCIUS ALBIDUS, IN THE GULF OF MEXICO 1 Bennie A. Rohr and Elmer J. Gutherz 2 ABSTRACT Biological data of the offshore hake, Merluccius albidus, in the Gulf of Mexico are presented and compared with those of other species of Merluccius . The species has been found from Georges Bank to Rio de Janeiro, Brazil, in 192 to 1 , 1 70 m. In the Gulf of Mexico it occurs in greatest abundance in the De Soto Canyon area in depths of 350 to 1,000 m. Merluccius albidus are segregated by size and sex on the continental slope with juveniles, males, and young females found in depths less than 550 m and large, mature females found in depths exceeding 550 m. Mature males were smaller than females and grew at a reduced rate following the onset of sexual maturity. Males and young females were found on the upper slope and older mature females found on the lower slope. Spawning appeared to take place on or near the bottom in 330 to 550 m. Spawning in the southern latitudes appears to occur from late spring to early fall and may be more protracted at the southern limits of its range. Eggs and the earliest larval stages have been described only for M. albidus from New England. Merluccius albidus are opportunistic feeders preying primarily on fishes, squid, and crustaceans. Fishes make up about 75% of their diet, with species of Merlucciidae and Myctophidae consumed most frequently. Prey species exhibited diel movement, but the similarity between day and night catch rates of M. albidus suggests that offshore hake do not move far off the bottom in pursuit of prey. Density estimates suggested a small population of M. albidus in the northern Gulf of Mexico. Merluccius albidus stocks in 370 to 730 m on the De Soto Canyon slope north of Tampa, Fla., are estimated to be a minimum of 3.3 x 10 6 kg. Species of the genus Merluccius are distributed worldwide in temperate and tropical waters but are exploited primarily in temperate seas. Aspects of their biology, distribution, and utilization have been reported by numerous authors (Hickling 1927, 1933; Bigelow and Schroeder 1953, 1955; Graham 1956; Fritz 1960; Lozano Cabo 1965; Marak 1967; Botha 1969, 1971; Grinols and Tillman 1970; and Nelson and Larkins 1970). Northern Gulf of Mexico Merluccius are consid-ered to be divergent forms of M. albidus (Karnella 1973). Several of the above authors have com-mented on the similarity in life history patterns of various species of Merluccius. Offshore hake, M. albidus, display some of these same patterns, indicating that aspects of their life histories are similar to those documented for other species. Biological data concerning M. albidus are sparse. Those reported in this paper are limited primarily to the Gulf of Mexico. This study is a 'Contribution No. 453, Southeast Fisheries Center, Pas-cagoula Laboratory. 2 Southeast Fisheries Center Pascagoula Laboratory, National Marine Fisheries Service, NOAA, P.O. Drawer 1207, Pascagou-la, MS 39567. Manuscript accepted June 1976. FISHERY BULLETIN: VOL. 75, NO. 1, 1977. composite of published accounts, data acquired during resource assessment, gear evaluation and general exploratory cruises, and results of biological studies conducted by personnel of the Southeast Fisheries Center Pascagoula Labora-tory, National Marine Fisheries Service (NMFS), NOAA. MATERIAL AND METHODS Specimens were collected with a variety of bot-tom trawls (Table 1) equipped with mud rollers, loop chain, floats, and usually a tickler chain. The larger trawls (38 to 60 m headrope) were fished with wooden bracket doors and ground cables whereas the smaller trawls (12 and 22 m head-rope) utilized wooden chain doors. Mesh size on the larger trawls was 7.6 cm in the wings and body, 5.1 cm in the throat, and 4.5 cm in the cod end; smaller trawls had 5.1-cm mesh throughout with 3.8 cm in the cod end. In October 1971, a 22-m trawl with a 1.3-cm inner liner was used to collect juvenile M. albidus. Rough bottom areas were fished with a 12-m flat or semiballoon trawl and smooth areas with larger trawls (22 to 68 m). 147
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