806 



Fishery Bulletin 91(4), 1993 



20 



-20 



20 



40 



60 



80 



100 120 



140 



Hours after capture 



Figure 1 



Percent weight change versus elapsed time from capture to 

 unloading for samples of trawl caught pink shrimp (N = 713) 



Billiard and Collins ( 1978), that iced Pandalus borea- 

 lis gained 11% in weight in the first 1.5 days and 

 maintained this gain for 8.5 days. However, the dif- 

 ferent methods used readily explain the different 

 findings of the two studies. Bullard and Collins ( 1978) 

 worked with shrimp which had been held at -1.7° C 

 for two hours and then rinsed and drained for 30 

 minutes to produce stable weights prior to icing. The 

 shrimp employed in this study were very fresh, some- 

 times jumping off the scales. If the average weight 

 loss observed in this study occurs very rapidly, per- 

 haps owing to loss of fluids just after the shrimp have 

 died, or from the initial crush of the catch in the 

 hold, such a loss could not have been detected in the 

 Bullard and Collins (1978) experiment. It is not clear 

 what percentage of ice was used by Bullard and 

 Collins (1978), but they refer to it as "an excess of 

 ice." Given the weight gain observed in some of the 

 samples in this study, and the modest percentages of 

 ice (Table 2), the results of the two studies are not 

 inconsistent. Perhaps, however, the differences do sug- 

 gest the importance of studying the weight change of 

 shrimp under both laboratory and actual commercial 

 fishing conditions. 



An average weight loss of 2.2% from capture to un- 

 loading is sufficiently small as to be insignificant from 

 a management standpoint. The minimum aggregate 

 size limit of 353 shrimp per kg (160 shrimp per lb), 

 which is intended to provide some protection from har- 

 vest for age-one shrimp, is based on average size-at- 

 age data. Interannual and geographic variability in 

 shrimp growth easily exceeds 2.2 c /r (Hannah and Jones, 

 1991). The findings of this study are significant how- 

 ever, principally in that they demonstrate that the 

 change in weight of pink shrimp that should be ex- 

 pected, when using normal icing procedures, is fairly 

 small. Accordingly, fishermen can readily comply with 

 the minimum size regulation. 



Interestingly, there were daily average weight change 

 values which exhibited a significant positive change 

 (Table 1), probably owing to absorption of meltwater 

 from the ice. Samples from two trips showed large 

 deviations from the average weight change which were 

 readily explainable. On trip 3, the vessel ran out of ice 

 on the final day of fishing, and, on trip 6, some spoil- 

 age was found throughout the load suggesting inad- 

 equate icing. In both cases the samples showed high 

 weight loss values, 5.9% and 4.6% respectively. 



These data suggest that there are small but fairly 

 consistent losses in average weight of pink shrimp 

 between commercial capture and unloading, at least 

 when the shrimp are adequately iced. The results of 

 this study appear to conflict with the findings of 



Acknowledgment 



This project was financed in part with Federal 

 Interjurisdictional Fisheries Act funds through the U. 

 S. National Marine Fisheries Service. The Oregon 

 shrimp industry was crucial to the success of this 

 project, particularly the owners and operators of the 

 following fishing vessels: Betty A, Florence May. 

 Maranatha, Olympic, Pacific Hooker and Pacific Hus- 

 tler. Steve Jones, Mark Saelens, and Jean McCrae all 

 participated in the at-sea sampling. Rick Starr con- 

 ceived of this project and designed the sampling strat- 

 egy. Terry Link assisted with sample workup and ves- 

 sel arrangements. 



