Abstract.— An analysis of environ- 

 mental ei'fects on autumn survey 

 catches of two commercially exploited 

 squid species, Loligo pealei and Illcx 

 illecchrosiis. was conducted. Research 

 survey data collected during 1967-94 

 were used to determine the significance 

 and relative importance of average 

 depth of tow, time of day, bottom tem- 

 perature, and surface temperature on 

 bottom trawl catches of L. pealei. a ner- 

 itic species, and /. illecebrosus. an oce- 

 anic species. We examined habitat as- 

 .■-(iciations of both species by using ran- 

 domization methods and found that L. 

 pealei was consistently associated with 

 all of the environmental factors exam- 

 ined. In comparison with L. pealei, 

 catches of /. illecebrosus were much 

 lower and associations with environ- 

 mental factors were inconsistent. We 

 also examined whether environmental 

 conditions affected catches of juvenile 

 and adult squid differentially. Depth 

 had an important effect on the magni- 

 tude of juvenile and adult L. pealei 

 I catches, with the ratio of juvenile to 

 ' adult catches decreasing with depth. 

 Depth had a similar, but less pro- 

 nounced, effect on /. illecebrosus 

 catches. Time of day also affected L. 

 pealei and /. illecebrosus catches. 

 Catches of both species were lowest at 

 night and diel effects were more pro- 

 nounced for juveniles than for adults. 

 Bottom and surface temperatures had 

 a substantial effect on catches of juve- 

 nile and adult L. pealei but had a vari- 

 able influence on /. illecebrosus catches. 

 The joint effects of depth stratification, 

 time of day, and annual squid abun- 

 dance on survey catches were also ana- 

 lyzed to determine correction factors for 

 diel differences in catchability of juve- 

 nile and adult squid. Significant diel 

 differences in catchability were de- 

 tected for juvenile and adult L. pealei 

 and for juvenile /. illecebrosus and diel 

 correction factors were determined for 

 survey catches of these size categories. 

 In contrast, significant diel differences 

 in catchability of adult /. illecebrosus 

 were not detected. 



An analysis of environmental effects on 

 survey catches of squids Loligo pealei and 

 ///ex illecebrosus in the northwest Atlantic 



Jon Brodziak 



Northwest Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 2030 S Marine Science Drive 

 Newport, Oregon 97365-5296 

 E-mail address: |on.brodziak(a'noaa gov 



Lisa Hendrickson 



Northeast Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 166 Water Street 

 Woods Hole, Massachusetts 02543-1026 



Manuscript accepted 19 March 1998. 

 Fish. Bull, 97:9-24 (1999). 



An analysis of environmental ef- 

 fects on survey catches of two com- 

 mercially exploited squid species, 

 Loligo pealei and Illex illecebrosus, 

 was conducted for the continental 

 shelf of the United States in the 

 northwest Atlantic. Research sur- 

 vey data, collected during autumn, 

 were used to determine the signifi- 

 cance and relative importance of 

 average depth of tow, time of day, 

 bottom temperature, and surface 

 temperature on bottom trawl catches 

 of L. pealei, a neritic species, and /. 

 illecebrosus, an oceanic species. 

 Both squids grow rapidly (Brodziak 

 and Macy, 1996; Dawe and BeckM, 

 appear to live less than one year 

 (Hurley et al., 1985; Macy, 1995; 

 Brodziak and Macy, 1996; Dawe and 

 BeckM. and undertake seasonal 

 migrations in response to fluctua- 

 tions in food availability, water tem- 

 perature, and spawning (Lange and 

 Sissenwine, 1983; Rowell et al., 

 1985a; O'Dor and Coelho, 1993). 

 The rapid growth and short lifespan 

 of these sympatric species suggest 

 that environmental conditions were 

 probably important determinants of 

 their distribution and abundance on 

 the continental shelf. 



We investigated whether there 

 was empirical evidence of habitat 



associations for both species by ap- 

 plying the habitat association 

 method of Perry and Smith (1994). 

 This randomization method ac- 

 counted for the stratified random 

 sampling design of the Northeast 

 Fisheries Science Center (NEFSC) 

 survey and tested whether catches 

 within a year were associated with 

 depth, time of day, surface tempera- 

 ture, and bottom temperature. 

 Within-year associations that were 

 consistent through time indicated 

 which environmental conditions af- 

 fected distribution and also pro- 

 vided a qualitative indication of 

 habitat preferences. 



We also examined whether envi- 

 ronmental conditions affected catches 

 of juvenile and adult squid differ- 

 entially. Juveniles and adults of 

 both species tend to differ in their 

 food habits ( Vovk, 1972; Vinogradov 

 and Noskov, 1979; Macy, 1982; 

 Maurer and Bowman, 1985 ) and, as 

 a result, may use different habitats 

 for feeding. We compared the effects 

 of average depth of tow, time of day. 



' Dawe, E. G., and P. C. Beck. 1992. Popu- 

 lation structure, growth, and sexual matu- 

 ration of short-finned squid at Newfound- 

 land, Canada, based on statolith analy- 

 sis. ICES Council Meeting. Shellfish 

 Committee/K, 3.3 p. 



