Hatfield and Cadrin: Geographic and temporal patterns in size and maturity of Loligo pealeii 



209 



north (SNE only, no GOM samples were taken in the win- 

 ter survey). The exception in winter were the few stage-3 

 and stage-4 females sampled. 



In the spring survey, the same pattern as in the winter 

 survey was observed; squid in the south were smaller than 

 in the north. In the spring survey, samples available from 

 south of Cape Hatteras (the limit of the MAB samples) 

 followed the same trend because the observed mean sizes 

 were smaller than the IVLAB samples. The exception to this 

 were maturity-stage- 1 squid. 



Discussion 



Survey analysis 



The high proportion of small squid (<50 mm ML) in the 

 winter and spring surveys corroborated the occurrence 

 of an early winter hatching event, documented from age 

 data determined by squid statolith analysis (Brodziak and 

 Macy, 1996; Macy^). 



Mean numbers-per-tow of juvenile squid in the MAB 

 were considerably higher than in the NE in all seasons 

 surveyed. Recruitment of squid into the population was 

 highest in autumn, but juvenile squid were distributed 

 more widely over the continental shelf in the spring. Per- 

 haps the MAB component of the L. pealeii stock was larger 

 because it is more stable — a result of the higher propor- 

 tion of squid recruited into the area each winter, spring, 

 and autumn. 



Murawski (1993) inferred a centering of the population 

 in the MAB subject to the issue that portions of the stock 

 are outside the area of the NEFSC surveys. Our data sug- 

 gested that the area south of Cape Hatteras may play an 

 important role in reproductive dynamics and recruitment 

 to the population, suggesting that a considerable portion 



of the stock is south of the surveyed area, particularly dur- 

 ing winter and spring. South of Cape Hatteras a second 

 loliginid species, L. plei. is abundant (Roper et al., 1984). 

 In our study, all Loligo specimens were examined carefully 

 to ensure that only L. pealeii were measured and included 

 in the biological analyses. 



Diel differences in catches of L. pealeii have been ob- 

 sei-ved in a number of studies (Summers, 1969; Serchuk 

 and Rathjen, 1974; Roper and Young, 1975; Sissenwine 

 and Bowman, 1978; Lange and Sissenwine, 1983; Lange 

 and Waring, 1992), where catches were consistently high- 

 er in daytime than at night. To account for diel effects 

 on minimum swept-area estimates of L. pealeii biomass 

 and stock size, nighttime catches were adjusted to daytime 

 equivalents by using the diel correction factors of Lange 

 and Sissenwine (1983). However, these correction factors 

 were not size specific. Brodziak and Hendrickson (1999) 

 applied size-specific diel correction factors to squid from 

 the autumn sui-vey (1967-94), splitting the data into pre- 

 recruits (<80 mm ML) and recruits (>80 mm ML). In the 

 autumn surveys the nighttime catch of prerecruits was 

 only 8.79c of the daytime catch. The nighttime catch of 

 recruits was 34'7( of the daytime catch. These differences 

 were attributed to the different feeding behavior of juve- 

 nile and adult squid, in that juvenile squid might need to 

 undertake more vertical migrations at night to meet their 

 higher metabolic requirements. In our present study, pre- 

 recruit nighttime catch differed to a lesser degree from the 

 daytime catch in the winter and spring (65% in the win- 

 ter surveys, and 51% in the spring surveys) than in the 

 autumn. In the winter surveys, nighttime catches of re- 

 cruits exceeded daytime catches by 31%. In spring, night- 

 time tows showed a lower catch of recruits, 72% of day- 

 time values, than in winter. Patterns of diel differences 

 reported in another study by Lange and Waring (1992) for 

 spring catches were similar to those in our study. Their 



