Brodziak and Hendrlckson; Environmental effects on survey catches of Loligo pealei and ///ex illecebrosus 



13 



Parameters of the GLM model were estimated us- 

 ing ANOVA for both prerecruit and recruit catches 

 of each species. The significance of time, year, and 

 stratum effects were evaluated by using type-Ill 

 sums of squares that do not depend on the order in 

 which effects are added to the model (Searle, 1987). 

 Because daytime was the reference time period, the 

 diel coefficient for the daytime had the value 1. Point 

 estimates and confidence intervals of time zone KT, ) 

 and II (T|j) coefficients in relation to the daytime co- 

 efficient were computed whenever the diel effect was 

 significant. Given estimates of Tj and Tjj, catches iy^/^ ) 

 made during time zone I or II period can be corrected 

 to daytime catch units by dividing them by the diel 

 effects coefficient asy^/^ I Tj and y,,, / Tjj, respectively. 

 Diel-standardized, stratified mean catches ( .y ,/■ ) can 

 be expanded by the total number of sampling units 

 within the survey region (N) to provide minimum 

 swept-area estimates of juvenile or adult population 

 size (Ny^^'') and variance (A^- Var[ v,,'- |) within the 

 survey region using stratified random sampling es- 

 timators (Cochran, 1977). 



Results 



Within-year associations 



The neritic squid species exhibited different degrees 

 of within-year habitat associations than those exhib- 

 ited by the oceanic species. Results of the random- 

 ization tests of L. pealei catches with depth, time of 

 day, bottom temperature, and surface temperature 

 (Table 1) showed thatL. pealei catch was consistently 

 associated with each of these factors. Associations 

 were significant (P<0.05) in all years for depth, bot- 

 tom temperature, and surface temperature. For time 

 of day, associations were significant in all years ex- 

 cept 1980 (96%). In contrast, results of the random- 

 ization tests for/, illecebrosus (Table 2) indicated that 

 catches of this species were inconsistently associated 

 with only some of the factors. During the 28 years 

 analyzed, a total of 15, 13, 7, and 12 associations were 

 significant for depth, time of day, bottom tempera- 

 ture, and surface temperature, respectively. All four 

 factors were significantly associated with /. 

 illecebrosus catch during 1983; otherwise, there was 

 no apparent pattern of annual associations. Overall, 

 L. pealei exhibited consistent within-year associa- 

 tions, whereas /. illecebrosus exhibited variable 

 within-year associations with the four environmen- 

 tal factors. 



We compared the interquartile range of the catch- 

 weighted CDF of each factor to the interquartile 

 range of its unweighted CDF to see how associations 



varied across years. For brevity, the term "midrange" 

 denotes the "average interquartile range" in what 

 follows. For depth, this comparison of CDFs showed 

 whether L. pealei or /. illecebrosus preferred shal- 

 lower or deeper water in relation to observed depths. 

 The midranges of depth for L. pealei and /. 

 illecebrosus catches were 37-75 m and 79-149 m (Fig. 

 2A), respectively, whereas the midrange of all ob- 

 served depths was 51-166 m. ForL. pealei, the aver- 

 age of the median catch-weighted depth was 50 m, 

 about 35 m shallower than the average observed 

 depth and equal to the P2g of the observed depths. In 

 contrast, the average of the median catch-weighted 



