ROHR and GUTHERZ: BIOLOGY OF MERLUCCIUS ALBIDUS 



slope ( 280 to 550 m) during both June and October. 

 Only 1.3% of all males taken were caught in 

 depths exceeding 550 m, with 613 m being the 

 maximum depth at which males were taken. 

 Females were found throughout the depth ranges 

 surveyed (Figures 5, 6, 7). 



Location of M. albidus on the slope appeared to 

 be dependent on gonad maturation stage and size 

 of individuals. In 1971, stage 4 males dominated at 

 all depths where males were collected except in 

 280 to 370 m; neither ripe (stage 5) nor spent 

 (stage 6) males were taken (Figures 6, 7). In 1973, 

 the data showed a predominance of stage 4 males 

 though a few ripe and spent males were found 

 (Table 5). Males, regardless of maturation stage, 

 were always taken in depths less than 550 m. The 

 predominance of stage 4 male M. albidus in the 

 autumn of 1971 and 1973 (Figure 7, Table 5) 

 suggests that stage 4 is an advanced resting stage, 

 with these fish not spawning until the following 

 spring. The stage 4 males were probably in the 

 spawning cycle in the spring of 1971 and 1973 

 (Figure 6, Table 5) and would have spawned some 

 time during the summer based on a spring- 

 summer spawning period for M. albidus. 



Female M. albidus of all sizes and maturation 

 stages were found throughout the depth range 

 surveyed. Young females mixed with males and 

 juveniles on the upper slope, but larger females 

 predominated on the lower slope. Lower slope 

 females, larger than 250 mm SL, caught in the 

 autumn were in the gonad resting stage and would 

 not spawn until spring or summer. Females in 

 stages 2-4 were most frequently caught as they 

 were in the prespawning and/or resting stages. 

 The paucity of ripe or spent females caught in 

 trawls is evident from Figures 6 and 7 and Table 5. 

 The few ripe and spent females (stages 5, 6) caught 

 in 1973 (Table 5) were partially a result of the 

 depths at which fishing operations were con- 

 ducted, as few stations exceeded 600 m. Ripe and 

 spent female M. albidus were found lower on the 

 slope than were stages 2-4. 



Eggs and early larval stages (first 84 h) of M. 

 albidus off Martha's Vineyard (New England) 

 were described by Marak (1967), but larvae larger 

 than 4 mm SL are unreported. Egg and early lar- 

 val development of M. albidus in the Gulf of 

 Mexico and the tropical Atlantic may be similar to 

 that off New England, although hatching may be 

 more rapid in warmer latitudes than the 6 to 8 

 days reported by Marak (1967). Larvae reared by 

 Marak (1967) ranged in length at hatching from 

 3.05 to 3.75 mm, averaging 3.5 mm and were rel- 

 atively undeveloped. The yolk was small and was 

 rapidly assimilated after hatching, thereby neces- 

 sitating early initiation of feeding. 



FOOD HABITS 



All hake species are opportunistic feeders 

 (Grinols and Tillman 1970). In the Gulf of Mexico, 

 M . albidus feed on a large variety of items found on 

 and off the bottom (Table 6). 



A feeding pattern based on adaptive zones of 

 prey species (i.e., epipelagic, mesopelagic, and 

 benthic) suggests that hake feed primarily on ben- 

 thic and mesopelagic organisms (Table 7). The 

 lack of a day-night differential in bottom trawl 

 catch rates (Table 8) suggests that M. albidus feed 

 on or near the bottom since a differential would be 

 expected if M. albidus moved well off the bottom to 

 feed. 



Merluccius albidus apparently feed at about the 

 same rate throughout the day except near dawn 

 (0500-0700, Table 9). The higher incidence of food 

 in the stomach during daylight hours corresponds 

 to the time when the mesopelagic fauna are closer 

 to the bottom. This hypothesis is reinforced as 81% 

 of the myctophids were found in stomachs from 

 fish caught during daylight hours (0700-1800), 

 and in only 1% of the stomachs from fish caught at 

 dusk (1800-2000). The mesopelagic fauna leaves 

 the bottom at dusk and moves higher in the water 

 column, thus becoming unavailable as prey to the 

 hake. Stomachs from specimens caught at night 



TABLE 5. — Maturation stages in Gulf of Mexico Merluccius albidus for May and September 

 1973 listed as percentage of occurrence. 



May 



September 



Mississippi Delta-west 



De Soto Canyon slope 



344-730 m 



Dry Tortugas slope 

 353-595 m 



Mississippi Delta-west 

 De Soto Ci 



anyon slope 

 330-503 m 



Gonad 

 state 



Females 

 N = 1 ,069 



Males 

 N =59 



Females 

 N =323 



Males 

 N =525 



Females 

 N = 2,083 



Males 

 N = 1 ,430 



153 



