Weight change of pink shrimp, 

 Pandalus jordani after commercial 

 harvest and handling 



Robert W. Hannah 



Oregon Department of Fish and Wildlife 

 Marine Region, 2040 SE Marine Science Drive 

 Newport, OR 97365 



Neil T. Richmond 



Oregon Department of Fish and Wildlife 

 Charleston Marine Laboratory 

 4475 Boat Basin Boulevard 

 Charleston, OR 97420 



The northeast Pacific trawl fishery 

 for pink shrimp, Pandalus jordani, 

 is unusual in that it is primarily 

 managed by an aggregate size limit. 

 Vessels are required to land catches 

 with a minimum average size of 353 

 shrimp per kg (160 shrimp per lb). 

 The regulation is intended to limit 

 fishing mortality on age-one shrimp, 

 and also to maintain the economic 

 value of the catch (PFMC, 1981). The 

 decision to retain shrimp from a par- 

 ticular tow is made by fishermen at 

 sea; however, the regulation is en- 

 forced when the shrimp are landed 

 in port, up to five days later. In gen- 

 eral, a knowledge of how commer- 

 cial fishing practices can influence 

 the average weight of target species 

 is important for effective manage- 

 ment by an aggregate size limit 

 (Kirkley and DuPaul, 1989). Accord- 

 ingly, the objective of this study was 

 to quantify changes in the average 

 weight of pink shrimp from initial 

 retention to shoreside delivery, us- 

 ing normal commercial handling and 

 icing procedures. 



Methods 



To assess the weight change of 

 shrimp from commercial handling 

 practices, we compared the weight 

 of shrimp samples taken directly 

 from the trawl nets of commercial 

 804 



vessels at sea to the weight of the 

 same samples during the subse- 

 quent shoreside delivery. Four to 

 eight replicate samples of approxi- 

 mately 500 g were collected from 

 each tow and weighed to the near- 

 est 0.1 g with a magnetically damp- 

 ened triple beam balance. The ac- 

 curacy of the scale was checked by 

 using a known weight prior to each 

 trip and again prior to weighing 

 the samples at the dock. The scale 

 used had also been previously 

 tested for accuracy at sea with 

 blind weighings and had been 

 shown to produce measurements 

 with a coefficient of variation of 

 less than 0.5% under a variety of 

 sea conditions'. Each sample was 

 placed in a 5-mm mesh bag, labeled 

 and passed to a crew member. 

 Shrimp were taken directly from 

 the vessel's hopper and were not 

 washed prior to weighing and bag- 

 ging. The crew was instructed to 

 distribute the sample bags 

 throughout the other shrimp from 

 the same tow. After placement of 

 the samples, the crew shoveled and 

 raked flake ice into the layers of 

 shrimp, according to that vessel's 

 normal procedures. 



1 M. Saelens and R. W. Hannah. 1988. Or- 

 egon. Dep. of Fish and Wildlife, Newport, 

 OR 97365. Unpub. data. 



At the completion of the fishing 

 trip, the bags were retrieved dur- 

 ing unloading and inspected for 

 punctures. Punctured bags were dis- 

 carded. Each intact sample was 

 opened, placed in a tub with a 

 7-mm mesh bottom to drain for one 

 minute, and weighed again with the 

 same scale. An estimate of the per- 

 centage of ice in the gross load was 

 obtained from processing plant 

 records. 



Weight change was expressed as 

 a percentage of the original sample 

 weight. The average percent weight 

 change for all samples combined, for 

 each trip and for each day of fishing, 

 was compared to a hypothetical 

 weight loss of zero percent by using 

 a one sample /-test. To facilitate 

 comparisons of weight change be- 

 tween trips or between individual 

 days of fishing, 95% confidence in- 

 tervals were constructed for each 

 estimate of average weight loss. 

 Scatter plots of percent weight 

 change for individual samples ver- 

 sus elapsed time were constructed 

 for each trip and for all trips com- 

 bined. Each graph was tested for a 

 significant slope with simple linear 

 regression. 



Results and discussion 



Seven sampling trips were com- 

 pleted aboard commercial shrimp 

 vessels between April and August 

 1988, lasting from 1 to 5 days. We 

 recovered 70% of the mesh bags in- 

 tact, resulting in weight change es- 

 timates for 713 samples from 132 

 tows. Elapsed time from catch to 

 unloading ranged from 4 to 121 

 hours. 



Percent weight change for the 

 combined samples showed an ap- 

 proximately normal distribution 

 centered on a mean weight loss of 

 2.2%, with a 99% confidence inter- 



Manuscript accepted 4 June 1993. 

 Fishery Bulletin, U.S. 91:804-807 ( 1993). 



