TRENDS TOWARD DECREASING SIZE OF BROWN SHRIMP, 



PENAEUS AZTECUS, AND WHITE SHRIMP, PENAEUS SETIFERUS, IN 



REPORTED ANNUAL CATCHES FROM TEXAS AND LOUISIANA* 



Charles W. Caillouet. Frank J. Patella, and Wiluam B. Jackson^ 



ABSTRACT 



An exponential model adequately characterized the size composition (expressed as a regression of 

 transformed cumulative percentage of weight on size category) of reported annual catches of brown and 

 white shrimp in Texas and Louisiana from 1959 to 1976. Louisiana catches contained considerably 

 greater proportions of small shrimp than did Texas catches. For both species and States, there was a 

 significant trend toward increase m proportion of small shrimp in the catches over the period. 



The size composition of a stock has long been used 

 as a simple criterion for assessing the status of a 

 fishery (Henderson 1972; Ricker 1975). Decreas- 

 ing average size of individuals can be an indica- 

 tion of increasing mortality (usually equated 

 with increased fishing mortality) or decreasing 

 growth (usually attributed to overcrowding). This 

 paper develops a new and simple approach to as- 

 sessing size composition of catches, and uses it to 

 detect differences and trends in size composition 

 of brown shrimp, Penaeus aztecus, and white 

 shrimp, P. setiferus, catches in Texas and 

 Louisiana. 



We chose to compare Texas and Louisiana 

 shrimp fisheries because 1) they are regulated by 

 substantially different laws (Christmas and Et- 

 zold 1977), resulting in different size distribu- 

 tions of shrimp harvested within the two States, 

 and 2) they are adjacent States which together 

 produced the bulk (75%) of the reported shrimp 

 catch from inshore and offshore waters of the U.S. 

 coast of the Gulf of Mexico in 1975. Inshore refers 

 to estuarine or bay waters landward of barrier 

 islands, and offshore refers to waters Seaward of 

 barrier islands. 



Texas shrimp laws provide for licenses, limits 

 on number and size of trawls used per boat in- 

 shore, limits on trawl mesh size, daily limits on 

 inshore catch, and size limits on food shrimp (not 



'Contribution No. 79-21G from the Southeast Fisheries 

 Center Galveston Laboratory, National Marine Fisheries Ser- 

 vice, NOAA. 



^Southeast Fisheries Center Galveston Laboratory. National 

 Marine Fisheries Service, NOAA, 4700 Avenue U, Galveston, 

 TX 77550. 



on bait shrimp) during the fall ( 15 August-15 De- 

 cember) open season inshore and during all open 

 seasons offshore. No size limits are imposed on 

 food shrimp during the spring 1 15 May-15 July) 

 open season inshore. All offshore areas are closed 

 to shrimping from 1 June to 15 July, and offshore 

 areas within 7 fathoms are closed from 16 De- 

 cember to 1 February. No nighttime shrimping is 

 allowed inshore. These laws lead to a fishing 

 strategy emphasizing the harvest of larger 

 shrimp offshore, with considerable restriction of 

 harvest of smaller shrimp inshore. 



Louisiana shrimp laws provide for licenses, 

 limits on number and size of trawls used per boat 

 inshore, limits on trawl mesh size, and size limits 

 during the fall open season (third Monday in Au- 

 gust to 21 December), with the exception that size 

 limits are removed for brown shrimp after 15 

 November. No size limits are imposed during the 

 spring open season (opened not later than 25 May 

 and extending 50 days thereafter unless closure 

 is warranted to protect young white shrimp). 

 Nighttime shrimping with "butterfly nets" (wing 

 nets) is allowed inshore. These laws encourage a 

 fishing strategy emphasizing harvest of consider- 

 able quantities of small shrimp inshore as well as 

 harvest of larger shrimp offshore. 



Brown and white shrimp spend the juvenile 

 and subadult phases of their life cycles inshore, 

 and the adult and larval phases offshore (Cail- 

 louet and Patella 1978), thus recruitment to the 

 fishery begins in the juvenile or subadult phases. 

 The entire life cycle is completed within a year, 

 therefore the shrimp crop in a given year depends 

 upon recruitment in that year. Environmental 



Manuscript accepted April 1979. 



FISHERY BULLETIN: VOL, 77. NO 4. 1980, 



985 



