GXTLF OF MEXICO COMMERCIAL SHRIMP POPULATIONS 



387 



Other Gulf Populations 



Prochictioii of white slirinip in Gvilf arons other 

 than those ah'eady mentioned was neghgibh' (hir- 

 ing the 4-year study period. A trace was re- 

 corthHl from the Sanihel-Tortugas area (statistical 

 subarea 5j in 1959, and United States fleet land- 

 ings from the combined East Mexican Coast and 

 Obregon-Campeche areas ranged from less tlian 

 0.1 million pomuls in 1956 to 0.6 million pounds in 

 1958 (table 4). As noted earlier, wiiite shrimp 

 taken by United States fishermen comprisetl only 

 an estimated 1 percent of the totid j)ovmtlage of 

 tliis species harvested in Mexican w^aters. Data 

 are too sketchy to permit anal.yses of white shrimp 

 populations in these areas. 



SUMMARY 



Those phases of Gulf of Mexico fisheries con- 

 cerned with the catching, landing, ami initial 

 processing of commercial shrimps are briefiy 

 described. Knowledge of each species distribution 

 and habits, manner of capture, handling, etc., is 

 reviewed in an attempt to ensure proper inter- 

 pretation of production statistics as employed to 

 draw inferences about commercial shrimp popu- 

 lations. 



The Bureau of Commercial Fisheries continuous 

 survey- of Gulf shrimp fisheries is examined criti- 

 cally as to kind and ciuality of statistics collected. 

 Sources of inaccuracy in effort and landing statis- 

 tics are pointed out. Effort data, for example, are 

 incomplete due to an inability to determine the 

 extent of "searching" and nonproductive opera- 

 tions, and biased to varying degree in direction and 

 magnitude because of suspect sample projection 

 techniques. Data of overall commercial landings 

 are quite complete, but those for certain species 

 maj' be biased since distinction between species 

 is not always uiuform around the Gulf. Landings, 

 moreover, do not always represent actual catches, 

 or reflect the composition of available populations. 

 More often than not they result from (1) culling 

 catches dominated by small, nonpremium sin-imp, 

 or (2) extensive searching for concentrations of 

 premium-size shrimp. Commercial size-classifi- 

 cation statistics thereby suffer because their 

 capacity to depict actual size or age structure of 

 exploited populations is lessened. 



With real or potential biases being acknow ledged, 

 available statistics for each species are used (1) to 

 derive population densitj- indices and (2) to 



delineate and trace population spawning classes 

 (broods). Short- and long-term trends in popula- 

 tion strength are examined in light of trends in 

 corresponding yield. Untoward fluctuations in 

 yield are explained, where possible, in terms of 

 observed population characteristics and their 

 apparent relation to changes in environment and 

 intensity of exploitation. 



Commercial statistics reveal that over the period 

 1956-59, the Gulf of Mexico annually yielded 

 between 167 and 193 million pounds of slirimp to 

 United States fishermen. This represented an 

 average yearly expenditure of 169,000 daj's' 

 trawling time. About three-fourths of both total 

 effort and yield, respectivelj-, was expended in 

 and taken from waters along the United States 

 coast. Inshore landings and corresponding effort 

 averaged about 21 and 28 percent, respectively, 

 of United States totals. Although overall land- 

 ings varied mildly during the 4-j'ear study period, 

 those for certain species and in certain areas 

 fluctuated sharply, with fishing success in 1957 

 having been generally poor. 



Of the three major commercial species support- 

 ing Gulf of Mexico shrimp fisheries, brown shrimp 

 were the most important, contributing, on the 

 average, 56 percent of annual harvests. Greatest 

 production consistently came from offshore and 

 inshore waters along the northwestern Gulf coast, 

 with Texas waters recognized as this species center 

 of abundance. Over the period 1956-59, brown 

 shrimp population levels rose in the Apalachicola, 

 Pensacola-Mississippi River, and Louisiana Coast 

 areas, remained steady or fell only slightly in the 

 Texas Coast area, and fell perceptibly in the East 

 Mexican Coast area. Corresponding A-ield trends 

 either renuiined steady or rose in all areas. 

 Immediate consequences of increasing fisliing 

 intensity on declining populations in the Texas 

 and East Mexican Coast areas are prol)lematical. 



Serial alignment of monthly weight-frequency 

 curves derived from catch-iiy-size statistics gave 

 a crude picture of age structure in Gulf of Mexico 

 browm shrimp stocks. Progression of modes in- 

 ferred two periods of heiglitened si)awning activity 

 each year — one in late winter or early spring, the 

 other in late sunnner or early fall. Relative 

 strengtlis of these spawning classes (or broods) 

 obviously varied between as well as within yi-ars, 

 but, on the average, early-season classes appeared 

 to be the dominant ones. Superposition of 



