234 



Fishery Bulletin 93(2), 1995 



and 



Ah - 



r  xkxI 



where r - radius of net opening (0.3 m for bongo net); 

 d = depth of water column sampled. 



The maximum likelihood estimates of A and 6 for k 

 sample pairs are derived as follows: 



S„,+S h 



x=- 



and 



■'ni °fei 



k 



6 = min 



IX 



(=1 



X A "'^' 



V i=l 



where S  = number of larvae in the ith neuston 

 sample; 

 S bj = number of larvae in the j'th bongo 

 sample. 



This method assumes that the sample pairs are 

 drawn from a population that is distributed randomly 

 in the horizontal plane but stratified vertically 

 (Hobbs and Botsford, 1992). 



Plankton samples were preserved in the field with 

 a 5% formalin-seawater solution buffered with so- 

 dium tetraborate. Ichthyoplankton were sorted at the 

 Polish Plankton Sorting Center in Szczecin, Poland. 

 All fish eggs and larvae were removed and identi- 

 fied to the lowest possible taxa. Identifications were 

 later verified at the NMFS laboratory in Seattle. Up 

 to 50 larvae per taxon per station were measured to 

 the nearest 0.1 mm standard length (SL). 



Since sampling patterns and positions were dif- 

 ferent for each cruise, the study area was subse- 

 quently divided into 298 sectors of approximately 215 

 mi 2 (347 km 2 ). Data from stations within each sector 

 were pooled so that average distribution patterns 

 could be determined for the dominant neustonic taxa. 

 The number of tows in each sector over all seven 

 cruises are illustrated by various levels of stippling 

 (Fig. 2). The mean densities of individual taxa were 

 calculated for each sector by dividing the summed 



i i i i i i i i i i i i i i i i i i i i 



i i i i , 



11 i i i 



hP^FQ 



57 "00 



59°00N 



55°00 



1 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I " 53 "00 

 165°00W 163°00 161°00 159°00 157°00 155°00 153°00 151°00 149°00 147°00 145°00 



Figure 2 



Neuston sampling coverage and intensity per sector for all seven cruises combined (1981-86). 



