FACTORS CONTROLLING GROWTH AND SURVIVAL OF 



CULTURED SPOT PRAWN, PANDALUS PLATYCEROS, 



IN PUGET SOUND, WASHINGTON 



John E. Rensel* and Earl F. Prentice^ 



ABSTRACT 



Environmental factors affecting growth and survival of juvenile and yearling spot prawns, Pandalus 

 platyceros. were studied at two sites in Puget Sound, Washington. It was thought that higher water 

 temperatures at the southern site would promote increased growth rates, but intense plankton blooms 

 and rapid fluctuations of water temperature induced high mortalities. Moribund prawns recovered 

 quickly when placed in epibenthic cages that received cooler, relatively plankton-free water. 



Although the cooler central Puget Sound site was judged suitable for prawn culture, fluctuations in 

 temperature and plankton abundance caused moderate mortalities here as well. 



Since 1970, several commercial marine aquacul- 

 ture projects utilizing floating net pens for the 

 culture of Pacific salmon, Oncorhynchus spp., 

 (Mahnken 1975) have been developed in the 

 Pacific Northwest. Development of companion 

 crops to be grown in net pens with the salmon 

 would enable growers to diversify and increase the 

 return on their investments. The spot prawn, 

 Pandalus platyceros Brandt, (herein referred to as 

 prawn) may be a potential companion crop for 

 several reasons: 1) it is adaptable to the sides as 

 well as the bottom of net pens; 2) it can reproduce 

 in captivity (Rensel and Prentice 1977); 3) it grows 

 more rapidly and reaches a larger size than other 

 pandalids (Butler 1964); 4) it consumes a variety 

 of foods including dead fish; 5) it is gregarious and 

 is normally not cannibalistic; and 6) it can be cul- 

 tured in the laboratory (Wickins 1972; Kelly et al. 

 1976; Prentice^). 



The objective of the present study was to deter- 

 mine the effects of environmental factors on 

 growth and survival of juvenile and adult prawTis 

 held separately but near to salmon rearing pens at 

 two differing salmon aquaculture sites. It was 

 hypothesized that higher water temperatures at 



'Squaxm Island Tribe. Route 1, Box 257, Shelton, WA 98584. 



^Northwest and Alaska Fisheries Center, National Marine 

 Fisheries Service, NOAA, 2725 Montlake Boulevard East, 

 Seattle, WA 98112. 



^Prentice, E.F 1975. Spot prawn culture: status and poten- 

 tial. In C. W Nygaard (editor). Proceedings of a seminar on 

 shellfish farming in Puget Sound, Oct. 7, 1975, Poulsbo, Wash. 

 Processed Rep., lip. Wash. State Univ. Coll. Agric, Coop. Ext. 

 Serv, Pullman, WA 99163. 



the more southern site would produce increased 

 growth rates. 



METHODS 



Two sites were utilized for the experiments, 

 Clam Bay and Henderson Inlet, both in Puget 

 Sound, Wash. (Figure 1). At the National Marine 

 Fisheries Service (NMFS) laboratory at Clam Bay, 

 floating net pens for salmon research were 

 situated at the end of a pier. Depth under the pens 

 ranged from 9 to 14 m, depending on the stage of 

 the tide. Data collected over several years indi- 

 cated that the site had good water exchange with 

 tidal currents reaching 0.4 kn at maximum flood 

 and 1.0 kn at maximum ebb. The growth rate of 

 prawns cultured previously at the site (Rensel and 

 Prentice 1978) approximated that found in a wild 

 population (Butler 1964). 



The Henderson Inlet site (Figure 1) was at the 

 location of a commercial log rafting operation. In 

 1973, a pilot-scale salmon aquaculture project was 

 initiated by the Weyerhaeuser Company and the 

 Washington Sea Grant Office at the site, and hy- 

 drographic data were collected (Snyder et al.'*). 

 Because of the inlet's shallow depth (10 m mid- 

 channel), configuration, and location, seawater 

 exchange is more restricted and tidal currents less 



Manuscnpt accepted December 1979. 

 FISHERY BULLETIN: VOL. 78, NO. 3, 1980. 



••Snyder, B. R, A. J. Didier, Jr., and E. O. Salo. 1974. The 

 culture of salmon at Willapa Bay Grays Harbor, and Henderson 

 Inlet in southern Puget Sound. Final Report Jan. 1973 to Feb. 

 1974. Univ Wash., Coll. Fish., Fish. Res. Inst., Seattle, WA 

 98195,211 p. 



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