384 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Enactment of such laws obviously implies 

 that excessive fishing on certain population seg- 

 ments was or could have been primarily respon- 

 sible for the fishery's downfall. Indeed, Viosca 

 (1959), without any supporting evidence or 

 explanation of probable mechanics, blames over- 

 fishing along with the 1952-57 drought. Aided 

 by fairly complete and up-to-date statistics, one 

 can now better speculate as to what did cause 

 the demise of the Louisiana white shrimp fishery 

 in 1957, and whether or not the aforementioned 

 laws have been or will be effective in bringing 

 about its recovery. 



Closed seasons during the 4-year study period 

 precluded complete pictures of white shrimp 

 density patterns on inshore trawling grounds in 

 the Louisiana and Texas Coast areas. As already 

 mentioned, Louisiana exercised spring and winter 

 closures beginning in 1958. From 1956 through 

 1958, Texas restricted large-scale commercial 

 operations on its inshore waters to the periods 

 March-mid-July and September-mid-December. 

 In 1959 it eliminated the "spring" season and 

 restricted commercial bay operations to the 

 period mid-August-mid-December. 



Despite resulting discontinuity, abundance 

 curves derived for inshore population phases in 

 both areas nevertheless suggest the occurrence of 

 two annual modes (fig. 29B). A continuous 

 curve for the Louisiana Coast area in 1956 and 

 a practically complete curve for the Texas Coast 

 area in 1958 verify a spring surge in abundance 

 (April-May), and a dominant fall wave with 

 peak varying annually between the months 

 September to December. Close correspondence 

 between catch and abundance patterns for inshore 

 and adjacent offshore fisheries emphasizes, as 

 Lindner and Anderson (1956) also point out, the 

 proximity of inshore and offshore environments 

 constituting white shrimp habitat. In contrast, 

 the time lapse in migration from inshore to 

 offshore grounds is considerably greater for 

 brown shrimp due to the greater distances in- 

 volved. Seasonal density and yield for the latter 

 species, as shown earlier, reach a maximum in 

 offshore waters a month or more following peak 

 abundance and catch in contiguous inshore 

 waters. 



Annual and 4-year trends in white shrimp 

 abundance on the northwestern Gulf's inshore 

 grounds generally corresponded to those describing 



population phases on offshore grounds (cf. figs. 

 28-29 A and B). The significant feature in every 

 case but one was the sharp drop in overall popu- 

 lation levels in 1957, inshore phases in the Texas 

 Coast area apparently escaping the effects of 

 whatever caused the widespread decline. These 

 effects manifested themselves through markedly 

 reduced white shrimp production in inshore and 

 oft'shore fisheries as far east as the Pensacola- 

 Mississippi River area. 



Failure of the 1957 fisheries in the Pensacola- 

 Mississippi River area has been partially attrib- 

 uted to the poor success of that year's early 

 season spawning class. Side effects of intense 

 storms striking the coast west of the Delta were, 

 in turn, conjectured as having been the cause. 

 Since these storms centered in the Louisiana 

 Coast area, it is hypothesized further that they 

 contributed in even greater degree to population 

 damage and production decline there. Thought 

 to have wrought the most damage was hurricane 

 "Audrey" which hit the coast just east of the 

 Louisiana-Texas border on June 27. Storm 

 surges brought tides of almost 14 feet above mean 

 sea level (m.s.l.) in the Cameron, La., area; 4 

 feet above m.s.l. in Garden Island Bay, La., 250 

 miles to the east; and 3 feet above m.s.l. at Port 

 Aransas, Tex., 220 miles to the west. Low-lying 

 areas in Louisiana were inundated up to 25 miles 

 inland (Moore and staff, 1957). Tropical storm 

 "Bertha", not quite attaining hurricane intensity, 

 shortly followed "Audrey", striking the coast in 

 the same general area on August 9. The highest 

 accompanying tide, 4.7 feet above m.s.l., was 

 recorded in Vermilion Bay, La. 



The occurrence of these storms coincided with 

 periods of peak inshore and nearshore concentra- 

 tions of (1) migrating juveniles representing the 

 1956 late-season brood, and (2) late postlarvae 

 and juveniles representing the 1957 early-season 

 brood. Although the mechanics involved are 

 obscure, it is conceivable that factors such as: 

 extended periods of high salinity, destruction of 

 cover and food supplies, and excessive turbulence, 

 all induced by extraordinarily high tides, acted 

 corporately to disperse and otherwise exert 

 greater-tiian-normal mortality in white shrimp 

 populations during vulnerable inshore phases. 



Excessive fishing on spawning populations 

 giving rise to late-season and early-season broods 

 in 1956 and 1957, respectively, is discounted as a 



