An estimate of the tag -reporting 

 rate of commercial slirlmpers 

 in two Texas bays 



R. Page Campbell 

 Terry J. Cody 



Texas Parks and Wildlife Department 



100 Navigation Circle, Rockport, Texas 78382 



C.E. Bryan 

 Gary C. Matlock 

 Maury F. Osborn 

 Albert W. Green 



Texas Parks and Wildlife Department 



4200 Smith Scfiool Road, Austin, Texas 78744 



Tag return rates are used to esti- 

 mate exploitation rates for many 

 animal species including penaeid 

 shrimp. To avoid systematic under- 

 estimation of exploitation, the num- 

 ber of tagged animals recaptured 

 but not reported must be reliably 

 estimated (Paulik 1963, Youngs 1972, 

 Seber 1973). Some investigators 

 have offered rewards for tags to in- 

 crease the tag return rate, but have 

 incorrectly assumed that all or near- 

 ly all harvested tagged animals were 

 reported (Kutkuhn 1966) or the rate 

 of non-reporting remained the same 

 throughout the experiment (Klima 

 1974, Kutkuhn 1966). Studies to 

 measure the reporting rate of com- 

 mercially-caught shrimp were con- 

 ducted by Klima (1974) and Johnson 

 (1981). The numbers of shrimp placed 

 in both studies were small (n 71 and 

 20, respectively) and return rates 

 differed markedly (82% and 10%, 

 respectively). One drawback of these 

 studies is that tagged shrimp were 

 placed into the catch at shrimp 

 houses or in the final processing 

 stages, and not on the vessel dur- 

 ing shrimping operations. There- 

 fore, return rates during fishing 

 operations were not measured. 



Accurate reporting rates for re- 

 covered tags are essential for the 



determination of fishing mortality 

 rates. The objective of the present 

 study was to determine reporting 

 rates of tagged shrimp captured 

 during regular shrimping opera- 

 tions. To that end, tagged shrimp 

 were surreptitiously placed in un- 

 culled catches. The reporting rates 

 determined in this study are in- 

 tended for use in correcting fishing- 

 mortality estimates generated from 

 a tagging program conducted dur- 

 ing the same period. 



Materials and methods 



Texas Parks and Wildlife Depart- 

 ment (TPWD) personnel placed 

 tagged shrimp in the catch aboard 

 Galveston and Aransas Bays' com- 

 mercial bay and bait shrimp boats, 

 May-November 1984. TPWD per- 

 sonnel and game wardens boarded 

 shrimp vessels during bay shrimp- 

 ing operations. While a game war- 

 den distracted the crew by checking 

 licenses, other TPWD personnel 

 placed a single tagged shrimp in un- 

 culled catches (on deck) or in a live 

 bait box. To conceal surreptitious 

 placement of shrimp, 20 individuals 

 of the target species Penaeus aztec- 

 us or P. setiferus were measured to 

 the nearest mm total length (TL) on 



each vessel. A total of 219 shrimp 

 (115 brown and 104 white) were 

 surreptitiously placed aboard ves- 

 sels in Aransas (n 125) and Galves- 

 ton (n 94) Bay systems during the 

 study period. No more than 12 

 shrimp were surreptitiously placed 

 in each bay system in any one week. 



Each tag was a uniquely-num- 

 bered black vinyl streamer (95 mm 

 long X 4 mm wide) tapered at each 

 end (Klima et al. 1987). Each tag 

 was inserted between the second 

 and third abdominal segments of 

 the shrimp. Shrimp in Aransas Bay 

 were measured (TL) prior to place- 

 ment and after being returned by 

 the fisherman. Since lengths were 

 not required in the original study, 

 measurements were not recorded in 

 Galveston Bay. Lengths of shrimp 

 placed in the catches and lengths of 

 shrimp returned by fishermen were 

 compared using student's ^test. 

 Also, length frequencies of mea- 

 sured shrimp on commercial boats 

 (n 2402) and of shrimp surrep- 

 titiously placed (n 105) aboard 

 boats were compared visually using 

 length-frequency histograms. 



As part of a larger bay shrimp- 

 tagging program conducted jointly 

 by the TPWD and the National 

 Marine Fisheries Service (NMFS), 

 rewards were offered for tag re- 

 turns. The program was promoted 

 by distribution of posters to area 

 shrimp dealers and through news- 

 paper articles. No information was 

 provided to the public concerning 

 the surreptitious tagging activity. 



Reporting rates (n reported/n 

 placed, expressed as percent) were 

 estimated for each species and bay 

 system. Reporting rates and con- 

 fidence intervals were estimated for 

 the two bay systems combined. 

 Reporting rates between species 

 and between bay systems were 

 compared using a Chi-square test 

 (Sokal and Rohlf 1981). 



Manuscript accepted 11 June 1992. 

 Fishery Bulletin. U.S. 90:621-624 (1992). 



621 



