GULF OF MEXICO COMMERCIAL SHRnrP POPULATIONS 



361 



mental factors on, exploited fish and shellfish 

 stocks incorporate devices known as mathematical 

 population models. In recent years there has 

 developed a specialized branch of fishery biology 

 devoted solely to the measurement of their pa- 

 rameters. These include, in the deterministic 

 sense, the basic constants of fecundity or recruit- 

 ment, growth, and mortality. Their estimation 

 presents no simple task, and it is significant to 

 note that valid measures of each are contingent 

 upon how well population age structure can be 

 delineated (Watt, 1959, p. 391). 



Means for separating commercial shrimp land- 

 ings into component age classes to secure a picture 

 of population age structure have not yet been 

 devised. Shrimp population research along classi- 

 cal lines is consequently precludeil. Differential 

 effects of fishing on shrimp broods at successive 

 ages, relationships between population size and 

 fishing intensity, parent-progeny relationships, 

 and estimation of natural mortality, for example, 

 remain undocumented in statistical terms. 



To extract the maximum amount of informa- 

 tion on shrimp population status from the kind 

 of data available, the alternative method of 

 generalizing on inferences drawn from graphic 

 integration and interpretation of yield, biomass, 

 and modal-weight curves is employed. Thus 

 comparative trends in yield and biomass should 

 establish, relatively speaking, whether specified 

 stocks adequately maintained themselves during 

 the period over which statistics were collected. 

 Simultaneous data on biomass (age) composition 

 and relative brood strengths aid in reconciling 

 significant deviations in stock mass and, with 

 constant fishing intensity, corresponding fluctu- 

 ations in yield. The latter information also pro- 

 vides a broader basis for speculating as to how 

 differential fishing on broods making up a given 

 biomass affects their collective potential from the 

 standpoints of jdeld and reproductive capacity. 



POPULATION TRENDS AND 

 CHARACTERISTICS 



BROWN SHRIMP 



General Occurrence and Features 



The brown shrimp is sought in offshore and 

 adjoining inshore waters of tlie Gulf of Mexico 

 from northwest Florida westward to Mexico. 

 Its commercial range covers approxinuitely 66,000 



square (nautical) miles of the Gulf's continental 

 shelf. 



Intensive exploitation of the brown shrimp did 

 not begin until the close of World War II. De- 

 clining abundance of the industry's mainstay, the 

 white shrimp, prompted a campaign to develop 

 markets for the ever-present brown slu-iiup, 

 which heretofore had never enjoyed comparable 

 market status. The first catches of any com- 

 mercial consequence were reportedly made off 

 Texas in about 1947, off Mississippi and Alabama 

 in 1950, and in the Gulf of Campeche in 1951 

 (U.S. Fish and Wildhfe Service, 1958). 



During the period 1956-59 this species ranked 

 number one, annually averaging 56 percent (by 

 weight) of shrimp landed at Gulf ports by United 

 States conunercial fishermen. In contrast the 

 second- and third-rank species, pink and white 

 shrimp respectively, contributed oidy 22 and 20 

 percent. Understandably, the brown shrimp cur- 

 rently attracts most of the attention being given 

 conservation of the Gulf of Mexico's collective 

 shrimp resources. 



Over its range of exploitation, the brown shrinip 

 exhibits a pronounced gradient of abundance. 

 Indices similarly derived for all species and areas, 

 and averaged over all months for (he years 1956 

 through 1959, revealed a steady increase from east 

 to west in the mean harvestable biomass of this 

 species (table 6). Maximum stock density now 

 occurs off Te.xas and eastern Mexico, this being 

 approached in terms of relative density only by 

 pink shrimp fished off southwest Florida and in the 

 Gulf of Campeche. Peak production from its 

 waters marks the Texas coast as the brown shrimp's 

 focal habitat and, coincidentally, the center of the 

 Gulf's extensive shrimp industry-. 



T.\BLE 6. — Mean annual index of fishahle biomass — 

 commercial shrimp populations in of shore Gulf of Mexico 

 waters, 11)56-59 



Area 



Sanibel-TortURas - 



.\palachicola ._ 



I'cnssicola-MisslsslppI River. 



I.ouisanu Coast 



Texas Coast - . 



F.itit Miilran Coast -. 



ObrcKon-Campeche 



Yucatan Coast ' 



Species 



Brown 



0. IS 

 .64 

 .S2 

 .88 



1.U 



Pink 



0.97 

 .29 

 .W 



White 



0.34 

 .22 

 4.'; 



.81 



I Not available. 



