GULF OF MEXICO COMMERCIAL SHRIMP POPULATIONS 



381 



•- LOUISIANA COAST 

 •- TC«AS COAST 



LOUISIANA COAST 



Figure 28. — Yield and structure of white shrimp popula- 

 tions off the northwestern Gulf coast, 1956-59. 



72 percent of all white shrimp taken off the United 

 States Gulf coast. Of all species harvested offshore 

 within the area itself, white slirimp averaged 51 

 percent. Landings ranged from a low of 7.7 

 milhon pounds in 1957 to a high 17.9 million 

 pounds in 1959 (fig. 28A). The 1957 catch 

 represented a 55-percent drop from the level of 

 the previous year and restimulated widespread 

 concern for the white shrimp's future welfare 

 (Viosca, 1958). Annual landings have since 

 recovered, however, and in 1959 exceeded those 

 of 1956. But, present status of the white shrimp 

 notwithstanding, the question: "What caused the 

 long-term decline from a 1945 production peak 

 of well over 110 million pounds?"* remains 

 unanswered. 



Ranking second in offshore production, the 

 Texas Coast area contributed 20 percent of the 



> Data taken from "Fishery Statistics of the United States— 1956", Statis- 

 tical Digest Xo. 43, U.S. Fish and Wildlife Service, 1958. Since large-scale 

 exploitation of the brown shrimp was not yet underway, practically all of 

 this production is assumed to have consisted of white shrimp. 



white slirimp taken conunercially each year off 

 tlie United LStates Gulf coast. This constituted 

 but 9 percent of the weight of all species harvested 

 annually from olfsliorc waters within the area 

 itself. Landings ranged from 1.0 milUon pounds 

 in 1957 to 7.8 million pounds in 1958 (fig. 28A). 

 Seasonal distribution of wliite shrimp landings 

 in the Louisiana and Texas Coast areas differed 

 shghtly from that noted in areas east of the Delta. 

 Peak oflshore harvest took place annually about 

 a month earlier (in October as contrasted to 

 November), and at the same time as or immedi- 

 ately following peak brown shrimp production. In 

 addition, a secondary production mode usually 

 occurred in May. 



Fishahle biomass. — Because size selectivity 

 biases appeared minimal and all vulnerable sizes 

 therefore reasonably well represented, biomass 

 indices derived from offshore fishery statistics are 

 believed to give a reliable picture of white shrimp 

 population strength in the Louisiana Coast area. 

 This was not the case in the Texas Coast area 

 where purposive fishing for only the larger shrimp 

 sizes was again evident. Seasonal distributions 

 of biomass indices for both areas compared as to 

 position of modes on the time axes but differed as 

 to amplitude and relative displacement on the 

 quantity axes (fig. 28B). The fishable stock off 

 Louisiana maintained a higher average level over 

 the 4-year period, 1956-59, but fluctuated more 

 widely within and between seasons than did that 

 off Texas. Despite increasing yields, the former 

 apparently suffered a comparatively severe set- 

 back in 1957 from which it has not yet recovered. 

 The Texas stock, on the other hand, has remained 

 nearly stable, its fluctuating yields being largeh- 

 attributable to vicissitudes of the industry, 

 abundance of other varieties, etc. Midyear 

 modes which were barely evident on biomass 

 curves derived for the Apalachicola and Pensacola- 

 Mississippi River areas show quite prominently on 

 the Louisiana and Texas curves. 



Since seasonal modes on biomass curves for 

 adjacent statistical areas were usually positioned 

 at corresponding points in time, coastwise ihift 

 of white shrimp juveniles migrating seaward is 

 considered to liave been negligible. 



Population characteristics. — Evidence for two 

 annual periods of increased spawming activity in 

 upper Gulf coast wiiite shrimp stocks is amplified 

 in figure 28C. Good representation of vulnerable 



