FISHERY BULLETIN: VOL. 73, NO. 4 



15 - 



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 o 



Q. 



£ 



10 



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f. N. Pacific 

 Cenfral 



Subarctic 

   I  



_L 



X 



330 33.5 34.0 34.5 



Salinity (%o) 



35.0 



Figure 5.— Zoogeographical temperature-salinity (T-S) capture 

 diagram for Bentheogennema hurkenroadi n. sp. Relevant water 

 masses in darkest bands; medium band in T-S envelope for the 

 station 65 nautical miles off Newport, Oreg. (NH 65); single lines 

 indicate T-S diagram for sampling stations other than NH 65 

 where this shrimp was captured. 



males and <12-mm females) were not observed to 

 migrate as high in the water column as adults. 

 Vinogradov (1968) earlier stated that the intensity 

 of diurnal migration of zooplankters increases 

 with age, and migration may be absent in early 

 stages of development, and our observations con- 

 cur with this. 



More shrimp were caught in nighttime than 

 daytime tows. This may be explained by enhanced 

 visual avoidance of the net during the day (Pearcy 

 and Laurs 1966). However, the lack of obvious 

 differences in size structure between day and 

 night caught shrimp (Figure 6) argues against 

 increased daytime avoidance, as larger more 

 mobile animals should be preferentially sampled 

 at night. Another explanation for the increased 

 nighttime catch, as suggested for Acanthephyra 

 purpurea Milne-Edwards and Gennadas valens 

 (Smith) by Foxton (1970a, b), is migration up from 

 below our maximum sampling depth of 1,000 m. 

 Such a migration is indicated by the high concen- 

 trations between 600 and 1,000 m both day and 



Table 1. -Seasonal diel vertical distribution to a depth of 1,000 m of mature males (>11 mm c.l.), mature females (>12 mm c.l.), and 

 sexually immature male and female Bentheogennema hurkenroadi at a sampling location 65 nautical miles (120 km) off Newport, Oreg. 

 Oat. 44°35'N-long. 125°30'W). 



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