Brodziak and Hendrickson: Environmental effects on survey catches of Loligo pealei and ///ex lllecebrosus 



15 



with depth, whereas mean catches of recruits 

 peaked in zone III. The lowest mean catch of L. 

 pealei prerecruits and recruits occurred in the 

 deepest strata, zone IV. There was no signifi- 

 cant difference between mean catches of 

 prerecruits in depth zones II and III or recruits 

 in zones I and II or zones II and III (Fig. 3Al. 

 The mean ratio of prerecruit to recruit catches 

 was highest in depth zone I (Fig. 3B) and ex- 

 hibited a decHning trend with depth. However, 

 the mean ratio was not significantly different 

 in depth zones II, III, and IV. Overall, catches 

 of L. pealei prerecruits decreased with depth, 

 whereas recruit catches peaked at intermedi- 

 ate depths (111-185 m). 



For /. illecebrosus, mean catches exhibited 

 heterogeneity across depth zones (Fig, 3C), 

 where sample sizes for depth zones I, II, III, 

 and IV were 85, 283, 161, and 81 tows, respec- 

 tively. Mean catches of recruits increased with 

 depth and were highest in depth zone IV, 

 whereas mean catches of prerecruits were rela- 

 tively homogeneous across depths but were low- 

 est in zone II. For prerecruits, mean catches 

 were significantly different only between zones 



I and II (Fig. 3C). In contrast, mean catches of 

 recruits were significantly different between all 

 depth zones except zones III and IV and zones 



II and III. The mean ratio of prerecruit to re- 

 cruit catches peaked in zone I, whereas the 

 mean ratios in zones II, III, and IV were not 

 significantly different (Fig. 3B). Overall, catches 

 of/, illecebrosus prerecruits peaked in the shal- 

 lowest depth zone (27-55 m) but were similar 

 at greater depths. Similar to those of L. pealei. 

 catches of/, illecebrosus recruits increased with 

 depth as the ratio of prerecruit to recruit catch 

 decreased with depth. 



As expected, mean catch of L. pealei prerecruits 

 and recruits peaked during day and were low- 

 est at night (Fig. 4A). Sample sizes for time 

 zones I, II, and III were 518, 968, and 1 129 tows, 

 respectively. For prerecruits, mean catch by 

 time of day differed significantly for all three 

 time zones (Fig. 4A), whereas mean catches of 

 recruits were not significantly different between 

 those for time zone II and zone III. The mean 

 ratio of prerecruit to recruit catches peaked 

 during day and was lowest at night (Fig. 4B), 

 whereas the mean ratios for all time zones were 

 significantly different (Fig. 4B). Overall, catches 

 of both L. pealei prerecruits and recruits in- 

 creased during day, although the difference be- 

 tween day and night catches was more pro- 

 nounced for prerecruits. 



1967 1971 1975 1979 1983 1987 1991 1995 



Midnight 



6 PM- 



Noon 



6AM 



18 

 16 

 14 

 12 

 10 

 8 

 6 

 4 

 2 



25 



20 



15 



7. 10 



1967 1971 1975 1979 1983 1987 1991 1995 



1967 1971 1975 1979 1983 1987 1991 1995 



Year 



1967 1971 1975 



1979 

 Year 



1983 1987 1991 1995 



Figure 2 



Catch-weighted averages of (A) depth (m), (B) time of day (h), 

 (C) bottom temperature (^Cl. and (D) surface temperature (°C) 

 by year for L. pealei (solid circle) and/, illecebrosus (open square). 

 The 25"', 50'^ and 75'^ percentiles (Pjj, P^o. and P,^ , thin solid 

 lines) of the annual autumn distribution of each environmental 

 factor are provided for comparison. 



