BEARDSLEY: DESIGN AND EVALUATION OF A SAMPLER 



be uprig-ht, stable, less than 3 inches off the sea- 

 bed, and perpendicular to the direction of tow. 

 Fishing trials were then conducted on popu- 

 lations of pink shrimp and spot shrimp, Pandalus 

 platyceros, in 40-60 fm of water in Dabob Bay, 

 Wash. Most shrimp were taken near the seabed 

 (Figure 2), but substantial numbers of pink 

 shrimp were taken as high as 5 to 6 ft off bottom. 



6r 



A 



2 

 O 



O 



m 



I 3 







Spot shrimp 



Pink shrimp 



J i_ 



_i_ 



J i_ 



_i_ 



_i_ 



_i_ 



_!_ 



200 400 600 800 1,000 1,200 

 NUMBER OF SHRIMP 



Figure 2. — Vertical distribution of pink and spot shrimp 

 taken in four tows in Dabob Bay, Wash. Numbers of 

 shrimp are totals for the 1-ft intervals. 



whereas no spot shrimp were found higher than. 

 3 to 4 ft. This phenomenon was interpreted as 

 a behavioral difference between the two species 

 rather than a difference due to physical size as 

 one might expect the larger spot shrimp to jump 

 higher off the seabed. 



Subsequent fishing trials with the shrimp sam- 

 pler were conducted on pink shrimp beds of com- 

 mercial importance off Grays Harbor, Wash. A 

 total of nine tows were made without separator 

 panels and nine with 2-inch mesh across the front 

 of the sampler. Total weights and carapace 

 lengths for shrimp in all sampler openings in 

 each of the vertical columns for each fishing mode 

 were pooled (54 samples) . The means for these 

 data are presented in Table 1. 



These data were further analyzed using a 

 three-way factorial analysis of variance with the 

 three main effects being vertical columns and 

 horizontal rows of the sampler and repetitive 

 tows (Table 1). In tows without separator 

 panels the weights of shrimp in vertical columns 

 were significantly different (F = 3.24), but a 

 comparison of starboard and port vertical col- 

 umns revealed their difference was not signifi- 

 cant (F = 0.430) at the 5% significance level. 

 The average of starboard and port colmns for 

 shrimp weight was significantly different from 

 weights for the center column (F = 6.06) . Anal- 

 ysis of the data for carapace length of shrimp 

 without separator panels and for both shrimp 

 weight and carapace length with 2-inch sepa- 

 rator panels indicated no significant difference 



Table 1. — Comparison of pink shrimp caught with and without 2-inch mesh separator 

 panels on the front of the shrimp vertical distribution sampler. Means and F values were 

 computed from 54 samples (i.e., six vertical openings over a nine-tow repetition). 



* Weight in grams,- length in millimeters. 



2 Not significantly different at 5% significance level. 



245 



