GULF OF MEXICX) COMMERCIAL SHRIMP POPULATIONS 



385 



contributing factor. Comparatively speaking, in- 

 dices of mean biomass for offshore and insiioro 

 population phases suggested that white shrimp 

 spawning potential in 1956 and early 1957 was 

 more than adequate. 



Although effort expenditure fell off during the 

 latter iuilf of 1957, the decline was not sufficient 

 to account for the disproportionate drop in land- 

 ings. Effort expended on inshore and offshore 

 grounds in the I^ouisiana Coast area during 

 July-December, 1957, was 72 and 51 percent, 

 respectively, of that expended during the same 

 period in 1956. Corresponding landings, on the 

 other hand, were only 25 and 36 percent of those 

 recorded in 1956. About ttie same amount of 

 effort expended in Texas offshore waters during 

 the latter half of 1956 was recorded for 1957, but 

 the corresponding white shrimp catcli declined 

 43 percent. In contrast, the Texas inshore 

 fisherj' doubled its production of white siirimp 

 during the same period with only a 55-percent 

 increase in effort expenditure. Most of this, 

 however, came from bays along the southern half 

 of the Texas coast, outside the main area of storm 

 damage. 



Significantly', bro\\Ti shrimp landings from I^ou- 

 isiana's offshore waters were off 43 percent in the 

 last half of 1957 despite expectations of as success- 

 ful a spring brood for that year as was produced 

 the previous year. Note however, that this drop 

 was not out of line with the 49-percent drop in 

 corresponding effort expenditure. Recall also 

 that overall mean population biomass during 

 1957 was up in all northwestern Gulf areas. In 

 fact, brown shrimp landings from offshore waters 

 in the Texas Coast area increased 15 percent over 

 those for 1956. All evidence thus suggests that 

 coexistent brown shrimp populations did not 

 suffer the effects of those factors to whicli tiie 

 demise of the white shrimp population was attrib- 

 uted. Reduction of brown slirimp catches off 

 Louisiana (July-December, 1957) must therefore 

 be considered a result of a proportionate decrease 

 in shrimping effort brought about by extended 

 periods of unfavorable operating conditions. 



A similar conclusion cannot be drawn for the 

 western Gulf of Mexico white shrimp stock and the 

 fishery it sustains. Record low landings from 

 Louisiana waters in 1957 must be ascribed more to 

 a real decline in population strength than to 

 relaxed exploitation during a period when the 



white shrimp nonnally attains peak density and 

 availability. The import of factors contributing 

 to this decline is also manifested in the magnitude 

 of the following year's landings. Thus, notwith- 

 standing an immediate return of effort expenditure 

 to its 1956 level (figs. 8 and 10), restoration of 

 landings to their former level has lagged for 2 

 years. 



The effectiveness of newly enacted closed- 

 season laws (inshore waters: Louis'ana, 1958) in 

 bringing about this recovery appears questionable. 

 Most noteworthj', perhaps, is the fact that these 

 closures generally coincide with or occur shortly 

 after seasoiuil ebbs in the white shrimp's nursery 

 ground phases. Records show that in years prior 

 to enactment of the latest and most effective 

 closed-season law (1956-58), white shrimp landings 

 (inshore) over the period January-April, and 

 December, averaged but 6 percent of each year's 

 total. The closed season, mid-December through 

 April, in effect, protects (1) residuals of early- 

 season spawTiing classes, most of whose representa- 

 tives will have already passed to offshore waters b}* 

 the time the fishing season closes, and (2) late- 

 season broods, the postlarv^ae of which begin to 

 move into inshore areas at about the same time. 

 Most members of the less important late-season 

 classes will have attained commercial size when 

 the fishing season reopens in May. Though now 

 protected on inshore areas, these classes have 

 never contributed significantly to inshore or 

 offshore fisheries. 



On the other hand, early-season broods which 

 are fished heavily in inshore waters during late 

 August through November are the same broods 

 dominating the offshore fishery which reaches 

 peak production almost simultaneously. They 

 support the white shrimp fisliery but are not now 

 afforded anywhere near the extensive protection 

 given late-season broods." Nor is additional 

 protection called for !/«/e.s'.s- a significant relation- 

 ship between fishing rate and brood size (or 

 recruitment) manifests itself. 



Available statistics do not permit establishing 

 whether or not such a relationship prevailed. 

 But, despite im[)roveil yields, llie white shrimp 

 stock in the northwestern C-ulf has shown little 

 sign of recuperating from liie 1957 ebb. This 



" The closed season mid-July to mld-.\uKUSt offers early-season whii. 

 shrimp broods protection from excessive fishing on precommerciol si,-o< 

 Inshore production of brown shrimp has not been affected by cither cl).<ure 



