388 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



seasonal spawning and temperature patterns 

 suggested that increased spawning activity was 

 more closely related to temperature reversals than 

 to some fixed or optimum spawning temperature. 

 Contributing an average of but 22 percent 

 yearly to Gulf of Mexico shrimp landings, pink 

 shrimp ranked second to brown shrimp. Al- 

 though of relatively minor status on a Gulfwide 

 basis, the species does contribute significantly to 

 the local economy in certain areas. Indeed, since 

 it is the only species of commercial importance 

 occurring off south Florida, the pink shrimp con- 

 stitutes the sole support of the valuable Sanibel- 

 Tortugas fishery. Practically all Gulf of Mexico 

 pink shrimp production originates in the Sanibel- 

 Tortugas and Gulf of Campeche areas. 



Semiannual periods of increased spawning ac- 

 tivity also characterize the Sanibel-Tortugas pink 

 shrimp stock. During the period covered by 

 available statistics, relative strengths of early- 

 season and late-season broods appeared roughly 

 equivalent. 



From 1956 through 1959, commercial yields 

 of pink shrimp from the Sanibel-Tortugas area 

 suffered a gradual decline. This reflected a down- 

 ward trend in stock biomass which developed 

 despite a nearly constant (annual) fishing inten- 

 sity. Whether the effects of too high a sustained, 

 overall fishing intensity were just beginning to 

 manifest themselves dm-ing the study period could 

 not be verified due to the lack of prior effort data. 

 The likelihood of excessive fishing being the pri- 

 mary causative factor is considered remote, how- 

 ever, and diminishing population levels are thought 

 to be more a result of greater utilization of small 

 shrimp. Increasingly heavy exploitation of new 

 recruits as they enter the fishery and before their 

 average growth rate reaches a maximum appears 

 to have systematically reduced annual available 

 biomass. 



Annual pink shrimp landings from the Gulf of 

 Campeche also experienced a significant downward 

 trend over the period 1956-59. But due to the 

 Campeche fishery's highly selective nature and, 

 consequently, the limited utility of resulting sta- 

 tistics, detailed appraisal of the underlying popu- 

 lation was not attempted. 



Closely approaching pink shrimp from a pro- 

 duction standpoint, white shrimp ranked third in 

 importance to the Gulf of Mexico shrimp industry. 



comprising about 20 percent of annual shrimp 

 landings. Practically all of this species came from 

 northern Gulf waters with the Louisiana Coast 

 area each year contributing roughly 72 percent 

 of United States Gulf coast totals. 



Analyses of monthly size composition data in- 

 dicated protracted spawning in white shrimp 

 stocks with heightened activity occurring at the 

 beginning and close of each spawning season, 

 April-December. Relative strengths of corre- 

 sponding spawning classes differed from year to 

 year while early-season classes appeared consist- 

 ently superior to late-season classes. Average 

 growth compared with that of brown and pink 

 shrimp but varied between early- and late-season 

 classes, and among corresponding classes in dif- 

 ferent years. Attainment of commercial size is 

 prolonged in late-season classes due to slowed 

 growth during winter months. 



Over the period 1956-59, annual white shrimp 

 jaelds remained relatively stable in the Apalachi- 

 cola area and rose in the Texas Coast area. Popu- 

 lation trends were slightly up in both areas. In 

 contrast, white shrimp fisheries in the Pensacola- 

 Mississippi River and Louisiana Coast areas ex- 

 perienced a severe setback in 1957. Recovery 

 lias been fairly rapid in both areas with 1959 

 landings approaching 1956 levels. But, while 

 white shrimp bionuvss displayed an upward trend 

 during 1958-59 in the Pensacola-Mississippi River 

 area, population recovery in the Louisiana Coast 

 area lagged perceptiblj'. 



The sharp decline of important white shrimp 

 fisheries in 1957 is largely attributed to factors 

 associated with intense storm systems which are 

 believed to have compounded expected natural 

 mortality during inshore phases of that year's 

 early-season spawning class. Too heavy fishing 

 on the dominant early-season spawning class in 

 1958 is postulated as having postponed a popu- 

 lation recovery trend in the Louisiana Coast area. 

 Relaxed pressure seemingly initiated one in 1959. 

 Closed inshore seasons first enforced in 1958 can- 

 not be credited with having expedited recovery 

 since they mainly include periods during which 

 fishable white shrimp normally exhibit minimal 

 density. White shrimp population strength ap- 

 pears primarily governed by the environment, but 

 excessive fisliing intensity too soon after a cata- 

 strophic ebb may stifle quick recovery. 



