22 



Fishery Bulletin 97(1), 1999 



consistently seen on sonar returning to the seabed.'^ 

 In contrast, the ratios of juvenile to adult catches of 

 /. illecebrosus were considerably lower than those for 

 L. pealei. In part, this difference in ratios between 

 species may reflect the importance of cannibalism 

 for larger /. illecebrosus adults during autumn ( O'Dor 

 and Dawe, in press). Although diel effects on I. 

 illecebrosus juvenile catches were similar to L. pealei, 

 they were less consistent. 



We found that bottom temperature had a signifi- 

 cant effect on catches of L. pea/e; juveniles and adults. 

 This generally corroborated prior studies. In particu- 

 lar. Summers (1969) observed that large catches of 

 L. pealei during winter were restricted to bottom tem- 

 peratures of 8°C or higher. This lower temperature 

 limitation was supported by Serchuk and Rathjen 

 (1974) and Vovk( 1978) who reported that the major- 

 ity of L. pealei catches during autumn occurred at 

 bottom temperatures of roughly 9-14°C. Similarly, 

 in our study, much of the L. pealei catch occurred at 

 11-15°C. However, catches ofL.pea/ez juveniles were 

 highest when bottom temperatures exceeded 16°C, 

 whereas catches of adults were highest when bot- 

 tom temperatures were 11-16°C. Our results sug- 

 gest that L. pealei juveniles generally prefer warmer 

 bottom temperatures than do adults that appear to 

 prefer intermediate bottom temperatures. This dif- 

 ference in temperature preference might be expected 

 if minor differences in temperature have a substan- 

 tial impact upon growth rates of young squid 

 (Forsythe, 1993). 



In contrast to bottom temperature, catches of L. 

 peo/e; juveniles and adults had a similar pattern with 

 respect to surface temperature. The highest catches 

 of both L. pealei juveniles and adults occurred at tem- 

 peratures of 15-2 1°C, whereas catches were lowest 

 for temperatures below 15°C. Although L. pealei 

 catches might be expected to increase with warmer 

 water temperatures, adult catches peaked at inter- 

 mediate bottom and surface temperatures and then 

 declined at higher temperatures. This decline sug- 

 gested that the higher temperature ranges observed 

 in the survey were not optimal for L. pealei adults. 

 Overall, the strong association of L. pealei with wa- 

 ter temperature suggested that annual variation in 

 patterns of ocean temperature affects the distribu- 

 tion and influences growth and survival of this ner- 

 itic species. 



In comparison to L. pealei, the less frequent asso- 

 ciations of /. illecebrosus catches with bottom and 

 surface temperatures suggested that temperature 

 has a variable influence on the distribution of /. 



5 Goodwin, G. 1997. Captain ofF/V Relentless and F/ V Per- 

 sistence. Davisville, Rhode Island, 02882. Personal commun. 



illecebrosus from Cape Hatteras to the Gulf of Maine. 

 Other studies generally supported the notion that /. 

 illecebrosus are distributed over a broad range of tem- 

 peratures. In particular, Whitaker (1980) reported 

 that /. illecebrosus catches occurred over a wide range 

 of bottom temperatures of 7-27°C, but that roughly 

 807( of the catch was taken in 8-10°C waters. 

 Murawksi ( 1993) examined the mean latitudinal oc- 

 currence of/, illecebrosus in relation to bottom and 

 surface temperatures during autumn NEFSC bot- 

 tom trawl surveys but found no statistically signifi- 

 cant relationship. Rowell et al. ( 1985b) reported that 

 /. illecebrosus appear to prefer bottom temperatures 

 in excess of 6°C during summer on the Scotian Shelf, 

 but that temperature did not appear to be a limiting 

 factor In the present study, much of the/, illecebrosus 

 catch occurred at bottom temperatures of 9-13°C and 

 surface temperatures of 13-20°C. In comparison to 

 L. pealei, I. illecebrosus appeared to prefer cooler 

 bottom temperatures and surface temperatures. 

 However, in contrast with L. pealei, bottom tempera- 

 ture had a similar affect on catches of juvenile and 

 adult /. illecebrosus. Surface temperature affected 

 catches of juveniles and adults differently and, in 

 particular, adult /. illecebrosus catches increased with 

 surface temperature. Overall, /. illecebrosus catches 

 occurred over a broader range of water temperatures 

 in comparison with L. pealei, as might be expected 

 of an oceanic species with a range that extends from 

 temperate to boreal waters. 



Because the bottom trawl gear used on the NEFSC 

 autumn survey only fishes 3.2 m above the seabed, 

 diel differences in squid catches are expected when 

 squid migrate vertically to acquire prey or to avoid 

 predators. Significant differences were detected be- 

 tween catches by time of day for both juvenile and 

 adult L. pealei. As a consequence, it was inferred that 

 diel correction factors were appropriate for survey 

 catches of this neritic species. In contrast, diel ef- 

 fects on survey catches of adult /. illecebrosus were 

 not significant and diel correction factors were not 

 developed for this oceanic species. The diel catcha- 

 bility of L. pealei presents some challenges for the 

 analysis and interpretation of bottom trawl survey 

 data to estimate squid population totals. On one 

 hand, diel correction factors developed in this study 

 can be applied to time zone I and II catches to pro- 

 vide a stratified mean catch per tow adjusted to day- 

 light units. Resampling techniques, such as mirror- 

 match bootstrapping, could be applied to estimate 

 its variance (Smith, 1997) under appropriate distri- 

 butional assumptions. In this case, all sur\'ey data 

 could be used at the expense of additional computa- 

 tional cost and potential bias induced by applying 

 the diel correction factors to all survey strata. On 



