ROHR and GUTHERZ: BIOLOGY OF MERLVCCIUS ALBIDUS 



penaeid shrimp and suggests selective feeding by 

 M. albidus. Stomachs of M. albidus contained a 

 higher frequency of P. megalops than Hymen- 

 openaeus robustus even at those stations where//. 

 robustus was more abundant. Abundance of these 

 two species was based on the catch rates when they 

 were taken together. This preference may indicate 

 a feeding migration to depths of greater abun- 

 dance of P. megalops. 



Merluccius albidus are active predators with 

 type and size of prey varying as follows: juveniles 

 (90 to 149 mm SL) contained primarily shrimp 29 

 to 45 mm TL with a few fragments of fishes and 

 squid; maturing adults (150 to 299 mm SL) 

 contained a variety of fishes 100 to 240 mm TL, 

 with one 320-mm TL trichiurid, crustaceans 40 to 

 130 mm TL, and squid 38 to 160 mm ML (mantle 

 length); adults (larger than 300 mm SL) contained 

 primarily Stomiatoidei fishes 100 to 240 mm TL, 

 macrourids 150 to 255 mm TL, trichiurids up to 

 500 mm TL, caridean shrimp 49 to 80 mm TL, and 

 squid 70 to 170 mm ML. 



AGE AND GROWTH 



Otoliths have been used successfully to estimate 

 ages of several species of Merluccius. Annual 

 growth patterns for M '. productus were defined and 

 used to establish age composition (Nelson and 

 Larkins 1970). Botha (1969) used otoliths to es- 

 tablish the growth rates of both M. capensis andM. 

 paradoxus and concluded that zonation and 

 composition of the otoliths from various species of 

 Merluccius were similar. 



Otoliths of M. albidus have well-defined opaque 

 and hyaline zones which increase in number with 

 size and age of the fish. However, an analysis of the 

 complex banding pattern in 206 pairs of otoliths 

 from juveniles (7 to 14 cm TL) was impossible, 

 because all bands were not defined and slow 

 growth rings (hyaline bands) did not agree with 

 age estimates based on length frequencies. Simi- 

 lar difficulties were encountered in the analysis of 

 otoliths from 56 males (15 to 34 cm TL) and 171 

 females (15 to 54 cm TL). 



The tentative age structure presented for Gulf of 

 Mexico M . albidus was based on length frequency 

 data (Figure 8, Table 10). Harding-Cassie age- 

 class lines were computed (Harding 1949; Cassie 

 1954) based on the lengths of 1,839 males and 

 2,852 females taken in October 1971 and Sep- 

 tember 1973. Calculated mean lengths were very 

 similar to those shown on Table 10 for both male 



12 -i 



MALES 



N = l,839 



FEMALES 



N=2,852 



20 30 40 50 



STANDARD LENGTH (cm) 



FIGURE 8. — Length frequency and modal size for ages to 5 for 

 Merluccius albidus from the east Mississippi Delta and west De 

 Soto Canyon slope October 1971 and September 1973. 



TABLE 10. — Tentative ages with midpoint of modal size groups of 

 northern Gulf of Mexico Merluccius albidus. 



and female M. albidus. Longevity of M. albidus is 

 unknown, but Botha (1971) reported that Cape 

 hake live at least 11 yr. Juvenile male and female 

 M. albidus are about the same size, but males are 

 slightly larger than females at age 1. However, 

 females are significantly larger by age 2 with 

 difference becoming more evident as the fish 

 becomes older (Figures 8, 9; Table 10). The largest 

 male caught during this study was 404 mm SL and 

 0.6 kg while the largest female was 680 mm SL 

 and 4 . 1 kg. The growth rate until age 1 was similar 

 in both sexes. Thereafter, males which mature 

 earlier use a proportion of their available energy 

 to produce sexual products which may result in 

 their reduced growth and smaller size. Because 

 females mature later, they direct more of their 

 energy toward growth for a longer period of time 

 resulting in their larger size. 



Female M . albidus between ages 4 and 5 grow at 

 a rate about equal to that reported for female M. 

 productus (Nelson and Larkins 1970; Table 11). 



155 



