An analysis of environmental effects on survey catches of squids Loligo pealei and Illex illecebrosus in the northwest Atlantic

• Main Authors: Brodziak, Jon, Hendrickson, Lisa
• Format: Article in Journal/Newspaper
• Language: English
• Published: U.S. Dept. of Commerce 1999
• Subjects: Northwest Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/52865/; https://oceanrep.geomar.de/id/eprint/52865/1/3473.pdf

An analysis of environmental effects on autumn survey catches of two commercially exploited squid species, Loligo pealei and Illex illecebrosus, 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 temperature, and surface temperature on bottom trawl catches of L. pealei, a neritic species, and I. illecebrosus, an oceanic species. We examined habitat associations of both species by using randomization methods and found that L. pealei was consistently associated with all of the environmental factors examined. In comparison with L. pealei, catches of I. illecebrosus were much lower and associations with environmental factors were inconsistent. We also examined whether environmental conditions affected catches of juvenile and adult squid differentially. Depth had an important effect on the magnitude of juvenile and adult L. pealei catches, with the ratio of juvenile to adult catches decreasing with depth. Depth had a similar, but less pronounced, effect on I. illecebrosus catches. Time of day also affected L. pealei and I. illecebrosus catches. Catches of both species were lowest at night and diel effects were more pronounced for juveniles than for adults. Bottom and surface temperatures had a substantial effect on catches of juvenile and adult L. pealei but had a variable influence on I. illecebrosus catches. The joint effects of depth stratification, time of day, and annual squid abundance on survey catches were also analyzed to determine correction factors for diel differences in catchability of juvenile and adult squid. Significant diel differences in catchability were detected for juvenile and adult L. pealei and for juvenile I. illecebrosus and diel correction factors were determined for survey catches of these size categories. In contrast, significant diel differences in catchability of adult I. illecebrosus were not detected.