Zeppelin et al.: Sizes of walleye pollock and Atka mackerel consumed by Eumetopias jubatus 515 



Table 2 



Estimated mean fork length of walleye pollock and Atka mackerel consumed by Steller sea lions based on selected structures 

 with or without application of condition-specific digestion correction factors (DCFsl. Data sets exclude all structures graded as 

 heavily digested. Remaining total sample sizes of elements in 1 ) are given along with proportion of grade "good" structures (n«). 

 For data sets where DCFs were applied, 95'r confidence intervals (95% CI) were estimated by using bootstrap resampling pro- 

 cedures (Tollit et al., 2004b, this issue). 



Species 



Structure code 



DCF 



/!' 



Mean FLlcml 



SDlcm) Range (cm) 



95% CI 



Walleye pollock 



Atka mackerel 



INTE 



HYPO 



PHAR 



ANGU 



QUAD 



DENT 



OTOL 



All 



INTE 



HYPO 



ANGU 



QUAD 



DENT 



OTOL 



All 



No 



Yes 



No 



Yes 



No 



Yes 



No 



Yes 



No 



Yes 



No 



Yes 



No 



Yes 



No 



Yes 



No 



Yes 



No 



Yes 



No 



Yes 



No 



Yes 



No 



Yes 



No 



Yes 



No 



Yes 



60 



60 



38 



38 



23 



23 



136 



136 



134 



134 



187 



187 



88 



88 



666 



666 



601 



601 



238 



238 



488 



488 



161 



161 



80 



80 



117 



117 



1685 



1685 



0.45 

 0.45 

 0.55 

 0.55 

 0.61 

 0.61 

 0.40 

 0.40 

 0.34 

 0.34 

 0.37 

 0.37 

 0.03 

 0.03 

 0.35 

 0.35 



0.58 

 0.58 

 0.42 

 0.42 

 0.45 

 0.45 

 0.37 

 0.37 

 0.28 

 0.28 

 0.06 

 0.06 

 0.45 

 0.45 



43.7 

 47.0 

 44.2 

 47.2 

 32.2 

 34.5 

 36.1 

 40.2 

 35.1 

 44.5 

 28.6 

 36.7 

 23.7 

 28.4 

 33.1 

 39.3 



33.5 

 34.2 

 31.1 

 32.9 

 30.2 

 31.8 

 25.3 

 26.6 

 22.5 

 27.9 

 30.3 

 34.7 

 30.7 

 32.3 



8.0 



8.5 



7.2 



7.8 



14.3 



14.8 



8.4 



9.0 



12.0 



15.3 



11.8 



15.1 



12.0 



14.8 



12.4 



14.3 



5.0 

 5.1 

 4.8 

 5.5 

 4.7 

 5.1 

 5.4 

 5.6 

 7.7 

 8.0 

 4.0 

 4.8 

 5.9 

 5.9 



16.7- 



16.7- 



30.5- 



34.9- 



9.7- 



10.9- 



10.6- 



10.6- 



9.4- 



11.9- 



3.1- 



3.7- 



4.6- 



4.6- 



3.1- 



3.7- 



19.5- 

 19.5- 

 18.8- 

 19.3- 

 17.3- 

 17.3- 

 14.8- 

 15.3- 

 13.0- 

 17.7- 

 21.2- 

 21.2 

 13.0- 

 15.3- 



59.4 

 65.9 

 60.4 

 62.7 

 53.1 

 5.3.1 

 55.3 

 60.6 

 ■57.8 

 ■70.8 

 -57.2 

 ■70.2 

 46.8 

 -57.1 

 60.4 

 -70.8 



46.8 



49.6 

 46.2 

 48.3 

 43.0 

 ■46.1 

 40.6 

 -41.4 

 -38.7 

 ■44.1 

 -40.6 

 -47.0 

 ■46.9 

 -49.6 



44.9-49.8 

 44.5-50.6 

 25.2-44.5 

 38.5-42.4 

 38.8-49.6 

 30.3-42.4 

 17.0-32.4 

 35.9-42.4 

 33.4-35.0 

 32.4-34.6 

 31.7-33.3 

 25.1-28.4 

 24.0-33.0 

 33.5-35.8 

 31.7-33.4 



Significant differences were found in the proportion 

 of Atka mackerel stage classes between 1998 and 1999 

 on summer rookery sites (P=0.05, x 2 =6.0, df=2 ) and 

 winter haul-out sites (P=0.01, ^ = 9.9, df=2) and be- 

 tween 1998 and 2000 winter haul-out sites (P=<0.01, 

 Fisher's exact test). Significant seasonal differences 

 were found only in 1998 (P=0.03, r = 7.1, df=2) which 

 may be the result of the small sample size in winter 

 2000. In summer and winter, annual differences in 

 size of Atka mackerel consumed by Steller sea lions 

 corresponded to changes in the length distribution of 

 Atka mackerel resulting from exceptionally strong year 

 classes in 1995 and 1998 (Lowe et al., 2001). The 1995 

 year class is represented as a mode around 30 cm in 

 1998 (3-year-old fish), 35 cm in 1999 and >40 cm in 



2000 (Fig. 4). The 1998 year class is represented most 

 clearly as 2 year olds (mode 20-25 cm) in summer 2000 

 (Fig. 4). Strong annual modes found in our data match 

 those recorded in surveys of Atka mackerel in the Ber- 

 ing Sea and Gulf of Alaska (Lowe et al., 2001). 



For walleye pollock and Atka mackerel there was no 

 difference in the mean size of fish caught by the com- 

 mercial fishery among years (P>0.4, one-way ANOVA). 

 There was a significant difference (P<0.05, one-way 

 ANOVA) in the size of fish caught between seasons. 

 This difference is likely due to aggregations of spawning 

 adult fish caught during the roe fishery. In the winter 

 there is a 56% overlap between the size of fish caught in 

 the commercial pollock fishery and those taken by sea 

 lions and a 54% overlap in the size taken by the Atka 



