FISHERY BULLETIN: VOL. 71, NO. 1 



between vertical columns. Since the differences 

 in shrimp catches between port and starboard 

 vertical columns were not significant during tows 

 either with or without separator panels, later 

 comparisons of the effect of mesh size on shrimp 

 catches were made between the starboard and 

 port vertical columns. 



As might be expected, significant differences 

 were evident for both horizontal rows on the 

 sampler and repetitive tows. The differences in 

 shrimp vertical distribution (horizontal rows) 

 are discussed later in the paper. Differences 

 in catch during repetitive tows were anticipated 

 as shrimp samples were collected over several 

 months on several shrimp beds. 



DAYTIME VERTICAL DISTRIBUTION 

 OF SHRIMP 



In March 1969 a series of eight tows were made 

 with the shrimp sampler in 71 fm off Destruction 



6r 



5 - 



§4 



o 



CD 



6r 



3 - 



o 



z 

 < 



a 



I - 



10 20 30 40 50 60 70 80 90 100 

 PERCENT 



Figure 3. — Percentages of pinheads (shrimp less than 

 15-mm carapace length) and marketable shrimp in 

 catches off Destruction Island, Wash., taken by the 

 shrimp sampler without separator panels (four tows). 

 The percentages indicate the percent composition at each 

 1-ft interval. Total weights for both pinhead and mar- 

 ketable shrimp increased near the seabed. 



o 4 



I- 

 t- 

 o 



o 



z 

 < 



I- 



o 



MarKetable 

 shrimp 



_i_ 



_!_ 



_!_ 



-L. 



_!_ 



_!_ 



10 20 30 40 50 60 70 80 90 100 



PERCENT 



Figure 4. — Percentages of pinheads (shrimp less than 

 15-mm carapace length) and marketable shrimp in catch- 

 es off Destruction Island, Wash., taken in four tows of 

 the shrimp sampler with separator panels. The per- 

 centages indicate the percent composition at each 1-ft 

 interval. Total weights for both pinhead and marketable 

 shrimp increased near the seabed. 



Island, Wash. Principal objectives were to de- 

 termine if differences in number and size com- 

 position of shrimp would occur with increasing 

 height off bottom. Four hauls were made with- 

 out separator panels and four hauls with uni- 

 form 2-inch mesh across the front of the sam- 

 pler. The greatest number of unmarketable 

 (less than 15-mm carapace length) and mar- 

 ketable (15-mm carapace length or greater) 

 shrimp were taken in sampler openings near the 

 seabed. The ratio of marketable to unmarket- 

 able (pinhead) shrimp increased with distance 

 off bottom (Figures 3 and 4). The relationship 

 between distance off bottom and length-frequen- 

 cy of shrimp is s-hown in Figure 5 for the same 

 series of tows. This figure indicates that shrimp 

 were most abundant near the seabed and a high 

 percentage were small. 



Additional tows with the sampler under a va- 

 riety of conditions (weather, time of day, season) 



246 



