FISHERY BULLETIN: VOL. 84, NO. 1 



geographic range is listed as from the Faroe bank 

 to northern Angola in the eastern Atlantic, the 

 Mediterranean, and from Davis Straits to northern 

 Brazil in the western Atlantic (Marshall and Iwamoto 

 1973). 



In the Norfolk Canyon area the depth of capture 

 of N. aequalis was from 330 to 1,109 m. The greatest 

 number in a trawl was 40 in November of 1974, and 

 the highest biomass per trawl was 300 g in Septem- 

 ber 1975. Nezumia aequalis comprised up to 8.9% 

 of a trawl catch by number and 3.1% by weight. The 

 analysis of variance of the mean depths of the head 

 length groups gave a F value of 3.32 (F(table; a = 

 0.01) = 2.11). The Student-Newman-Keuls analysis 

 showed only one subset, probably because of the low 

 sample size Examination of Figure 7 suggests head 

 length increased with depth, and the slope of the line 

 was significantly different from zero. 



Although its bathymetric range was extensively 

 sampled, densities were low and few mature speci- 

 mens were captured (Fig. 8). These findings are in 

 contrast to the distribution and abundance of its 

 cogener, N. bairdii, suggesting competitive exclu- 

 sion. Alternately, Norfolk Canyon populations ofN. 

 aequalis may represent expatriation from denser 

 populations in the Gulf of Mexico or on the Blake 

 Plateau. 



The temperature range for N. aequalis captured 

 in the Norfolk Canyon area was from 4.3° to 8.0 °C 

 (Fig. 6). The average temperature of collection was 

 5.3°C. 



Nezumia bairdii (Goode and Bean 1877) 



Nezumia bairdii is a relatively small macrourid 

 with a reported head length of up to 60 mm (Mar- 

 shall and Iwamoto 1973). During our study the head 

 lengths varied from 12 to 66 mm with the weight 

 of the largest specimen being 295 g. The geographic 

 range of N. bairdii extends from the Straits of 

 Florida north to the Grand Banks (Marshall and 

 Iwamoto 1973). Nezumia bairdii is captured com- 

 monly between 90 and 183 m in the northern part 

 of its range and appears to undergo tropical sub- 

 mergence because it is found primarily between 548 

 and 731 m in the southern parts of its range The 

 inclusive depth range is 90-2,285 m (Goode and Bean 

 1885; Marshall and Iwamoto 1973). One anomalous 

 catch at a depth of 16.5 m was recorded in Vineyard 

 Sound (Bigelow and Schroeder 1953), but this was 

 most likely a discard from a commercial fishing 

 vessel. 



Within the study area the depth of capture ranged 

 from 270 to 1,644 m (Fig. 3). The largest catch in 



a half hour tow was 76 fish and the greatest biomass 

 per half hour tow was 5.7 kg. Nezumia bairdii com- 

 prised up to 30% of the demersal fish catch in 

 number and up to 15% of the biomass. 



In the January plot (Fig. 9), the head length in- 

 creased slightly with depth. The regression line of 

 the mean depth of each head length class showed 

 a positive slope significantly different than zero. By 

 June (Fig. 9) the regression line showed a highly 

 significant positive slope and three distinct size 

 groups separated by depth were evident. The first 

 group included those fish <30 mm HL, the second 

 group was from 30 to 42 mm HL, and the third group 

 was >43 mm HL. The head lengths at the start of 

 maturity for females (27 mm) and males (32 mm) cor- 

 respond well with the dividing line between size 

 groups one and two, as defined by depth distribu- 

 tion. Also, N. bairdii females and males can be fully 

 mature at 44 and 45 mm HL, respectively (Fig. 10). 

 These values are close to the division between the 

 second and third size groups noted above The three 

 size groups appear to reflect maturity stages as well 

 as size differences, and this may contribute to the 

 bathymetric differences. The first group consisted 

 of all immature fish that were not found in deep 

 water in June The second group could be termed 

 the transitional group because it included fish that 

 were just starting to mature and those more highly 

 developed. Since this group included such a diverse 

 spectrum of maturity, it encompassed portions of the 

 depth ranges of both immature and mature fish. The 

 third group consisted of all mature fish and was not 

 found in water shallower than approximately 600 m 

 in June In September, the larger fish had reached 

 their deepest limit, and immature N. bairdii were 

 virtually absent deeper than 1,000 m. By November 

 (Fig. 9), the largest fish were returning to shallower 

 water to complete what appears to be a seasonal 

 migration cycle 



Examination of histological sections of gonads 

 showed that the only spent N. bairdii were captured 

 on the September cruise Although no ripe fish were 

 caught on any cruise, these spent fish suggest that 

 N. bairdii spawns in July or August, coincident with 

 the time when the mature fish are inhabiting their 

 deepest level. 



Marshall's (1965) hypothesis concerning reproduc- 

 tion of certain macrourids states that fertilization 

 takes place at the bottom. Subsequently the eggs, 

 which are buoyant, develop and hatch on their way 

 upward to the seasonal thermocline The larvae then 

 maintain themselves just below the thermocline, in 

 order to take advantage of the plankton that tends 

 to accumulate there in the density gradient. In con- 



42 



