356 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



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EFFORT LANDINGS 



EAST MEXICAN COAST 



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OBREGON - CAMPEChE 



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Figure 9. — Effort expenditure and commercial shrimp 

 landings by United States trawlers operating off the 

 Mexican Gulf coast, 1956-59. 



The sinuous nature, of monthly yield curves 

 indicates to some extent the seasonal reproductive 

 patterns typical of the short-lived penaeid shrimps. 

 High correspondence between curves of effort and 

 yield generally reflects the techniques used to 

 estimate the former from the latter. 



EFFORT LANDINGS 



APALACHICOLA 



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TEXAS COAST 



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Figure 10. — Effort expended in and commercial shrimp 

 landings from inshore waters along the United States 

 Gulf coast, 1956-59. 



Exploitation of "table" shrimp by the United 

 States fleet in inshore (estuarine) waters bordering 

 the Gulf of Mexico is restricted to northern coastal 

 areas (table 3). Practicality all landings from such 

 waters consist of small shrimp, some of which are 

 dried, but most of which are now economically 

 machine-processed for canning. 



Of the four northern Gulf coast areas designated 

 in this report, the Louisiana Coast area claims 

 the greatest acreage of inshore waters. This is 

 reflected in its inshore shrimp production which, 

 dm-ing 1956-59, annually exceeded that of any 

 other area (fig. 10). Note, however, that while 

 inshore landings from adjacent areas exhibited 

 little tendency toward marked fluctuation, those 

 from the Louisiana marshes did, with adverse 

 lows occm-ring in 1957 and 1958. 



A breakdown of landings by years, coastal area 

 (offshore and inshore waters combined), and 

 species reveals major differences in amounts of the 

 various shrimps taken commercially from each 

 area (table 4). Relative to those of other species 

 belonging to the same taxon and occupying the 

 same range, fluctuations in a particular species 

 population as evidenced by its yield may be 

 masked wdien dealing with data of composite 

 landings. Obviously, the degree to which fluctua- 

 tions in each population comprising a multispecies 

 fishery govern overall jaeld patterns depends 

 largely upon how much the species overlap in 

 occurrence. Attempts to reconcile unusual drops 

 in total yield must therefore take into account 

 variations in the catches of each species contribut- 

 ing to it. Moreover, they must rely on available 

 commercial statistics to depict accurately in space 

 and time, the population size and structure. 



METHODS OF POPULATION APPRAISAL 



Before attempting to determine how commercial 

 fish and shellfish populations react to exploitation 

 and a varying environment, suitable indicators of 

 population size and composition must be obtained. 

 The capacity of commercial statistics to provide 

 these is wholly contingent upon the nature of the 

 species involved and the mechanics underlying its 

 exploitation. 



FISHABLE BIOMASS INDEX 

 Definition and Theory 



Shrimp, being demersal organisms capable of 

 instantaneous but limited vertical and lateral 



