380 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



landings were down 61 and 53 percent. The low 

 1957 jneld must therefore be attributed more to a 

 reduction in population size and availability than 

 to poor fishing conditions and hence widespread 

 reduction of fishing operations during the season 

 of peak white shrimp density. Population re- 

 duction, in turn, may well have been attributable 

 to poor survival in the early-season spawning 

 class of 1957, excessive mortality having occurred 

 during larval and inshore phases when adverse 

 environmental conditions (high tides and exten- 

 sive flooding, excessive turbulence, etc.) due to 

 severe storms could be expected to exact the 

 greatest toll. 



On the average, growth rates in white shrimp 

 populations fished off the northeastern Gulf coast 

 were lower than those in populations off the north- 

 western Gulf coast. A more comprehensive 

 discussion of growth in upper Gulf white shrimp 

 stocks is deferred to a later section. 



Inshore population phases. — During the period 

 1956-59, conditions in the northeastern Gxilf's 

 inshore fisheries for white shrimp very nearly 

 paralleled those in adjacent offshore fisheries. 

 Differing chiefly in amplitude, seasonal and an- 

 nual yields in the Apalachicola and Pensacola- 

 Mississippi River areas experienced the same order 

 of fluctuation (figs. 26A and 27 A). Seasonally, 

 peak production of small shrimp in inshore waters 

 occurred 1 to 2 months earlier than that of some- 

 what larger shrimp in offshore waters. 



White shrimp comprised, on the average, about 

 45 percent by weight of all shrimp taken from in- 

 shore waters in both areas. Annual inshore 

 landings in the Apalachicola area averaged 1.5 

 times corresponding offshore landings, and ranged 

 from a high of 0.9 million pounds in 1958 to a low 

 of 0.3 million pounds the following year. In the 

 Pensacola-Mississippi River area the differential 

 between inshore and offshore landings increased 

 to a factor of 3.2, with inshore landings ranging 

 from a high of 5.8 miUion pounds in 1959 to a low 

 of 2.5 milhon pounds in 1957. 



Crude indices of seasonal white shrimp density 

 on inshore grounds reemphasize the dominant role 

 played by early-season spawning classes (fig. 27B). 

 Peak biomass is attained during the period Sep- 

 tember-November and occurs slightly in advance 

 of maximum seasonal biomass in contiguous 

 offshore waters (cf. fig. 26B). This reflects con- 

 tinuous migration of juveniles from inshore to 



offshore waters during that period. Late-season 

 spawning classes are barely evident in figure 27B 

 as very small modes recurring annually during 

 April-May in both areas and in most years. 



Summary of 4-year status. — Wliite shrimp pro- 

 duction exhibited similar patterns in offshore and 

 inshore fisheries during the period 1956-59. No 

 4-year trend was evident in the Apalachicola area, 

 but a very steep upward trend following sub- 

 stantial declines in 1957 was noted for fisheries in 

 the Pensacola-Mississippi River area. Inshore 

 production of small shrimp consistently exceeded 

 offshore production of larger shrimp in both areas. 

 Four-year trends in overall relative density 

 were comparable for offshore and inshore popula- 

 tion phases, being slightly up in both areas. No 

 relationship between intensity of fishing on either 

 inshore or offshore population phases and total 

 yields in the same and subsequent years was 

 apparent. The greatly reduced catch of white 

 shrimp from the Pensacola-Mississippi River area 

 in 1957 is at least partly attributed to the side 

 effects of uitense storm S3^stems which hit the 

 coast just west of the Mississippi River Delta in 

 June and August of that year. Extensive flooding 

 due to abnormally high tides and excessive runoff 

 is hypothesized as having caused higher-than- 

 normal inshore mortality in 1957's early -season 

 spawning class. 



Fluctuations in white shrimp population 

 strength and yield appeared to be largely governed 

 by environmental factors. Provided these do not 

 attain extreme proportions, and effort remains 

 constant or does not greatly exceed recent expendi- 

 tures, white shrimp landings in the Apalachicola 

 and Pensacola-Mississippi River areas should 

 stabihze at the same or just below levels recorded 

 for the period 1956-59. There is some indication 

 that white shrimp in the Apalachicola area could, 

 on the average, withstand shghtly heavier ex- 

 ploitation. 



Northwestern Gulf Populations 



Commercial yield. — The northwestern Gulf of 

 Mexico annually surpasses all other areas in the 

 production of white shrimp. Highest yields have 

 been consistently obtained from that portion of 

 the coastal stock inhabiting Louisiana's offshore 

 and inshore waters. 



In each of the years 1956 through 1959, the 

 Louisiana Coast area contributed, on the average, 



