Shima et al : Spatial distribLition of Themgra cha/cogramma in tine Gulf of Alaska 



311 



derstood to be the "distribution of numbers offish amongst 

 those species." Confidence inter\'als were calculated by 

 jack-knifing the diversity index (Magurran. 1988). 



Results 



All pollock 



Three-dimensional contingency tables indicated whether 

 occurrence of pollock was mutually independent of all 

 combinations of bottom depth, geographic region, dis- 

 tance from land, and year. The three-dimensional con- 

 tingency tables for all three null hypotheses of mutual 

 independence resulted in rejection of the null hypothesis 

 (P<0.001). The null hypotheses considered for the three- 



dimensional and partial contingency tables are listed in 

 Table 2. A summary of the distribution of stations within 

 categories of the three physical characteristics is given 

 in Table 3. All the hypotheses of partial independence on 

 combinations of two of the physical characteristics could 

 be rejected (P< 0.001). When each physical characteristic 

 was tested separately, the only hypothesis that could not 

 be rejected (a=0.05) was the independence of pollock occur- 

 rence against geographic region (P=0. 097, Table 2). Graphs 

 of pollock occurrence versus each of the physical charac- 

 teristics revealed distinctive patterns (Fig. 4). The graphs 

 indicated that pollock are most frequently observed in the 

 100-200 m bottom depth interval and the 0-20 nmi dis- 

 tance category (Fig. 4, A and B). However, this interpre- 

 tation may be an artifact of the percentage of stations 

 sampled within each category (Table 3). For all years, the 



