FISHERY BULLETIN: VOL. 78. NO. 3 



Figure l.— Puget Sound, Washington, 

 with sites of spot prawn studies at Hen- 

 derson Inlet and Clam Bay. 



HENDERSON 

 INLET 



than at Clam Bay. Surface water at the inlet was 

 warmer and more turbid, but dissolved oxygen and 

 salinity were similar to Clam Bay. 



Five-month-old juvenile prawns, reared at the 

 NMFS Clam Bay laboratory, were used in the 

 study. The prawns were transferred to net pens 

 and cultured from July to November 1974 at Hen- 

 derson Inlet and from July 1974 until March 1975 

 at Clam Bay. Initial carapace lengths (distance 

 from the base of the eyestalk to the posterior mid- 

 dorsal edge of carapace) of the juvenile prawns 

 averaged 5.3 mm ( n = 135 at each site, SD = 1.70) 

 for all experimental lots. Weight of the prawns was 

 not initially determined. We obtained wild prawns 

 from commercial fishermen on Hood Canal (Puget 

 Sound) in May 1974 and held them in a common 

 pen for 3 wk at each site prior to distribution to 

 rearing pens. The culture period was from June 

 1974 to March 1975. At the start of the experi- 



ment, the average carapace length was 25.8 mm ( n 

 = 336, SD = 1.68), and the average weight was 

 11.1 g(SD = 2.25). These prawns are referred to as 

 yearlings as defined by the weight and length 

 range (6.4-15.4 g, 21.2-28.5 mm) reported by But- 

 ler (1964) for a wild population. 



Juvenile prawns were cultured in rectangular, 

 knotless nylon net pens (stretched measure 6.7 

 mm), 2.16 m square x 1.8 m deep. Weights were 

 attached externally to the corners of the pens to 

 maintain their shape. Covers made of black plastic 

 sheeting were placed over the pens to reduce light 

 and discourage bird predation. Each pen was di- 

 vided into three equal chambers by vertical net 

 panels. The total immersed net area was 6.3 m^/ 

 chamber. Each chamber was stocked with 45 

 prawns for an initial density of 7.1 prawns/m^. 



Pens used for the yearling prawns were also 

 covered with plastic sheeting. These pens were the 



782 



