386 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



o 

 o 

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CJ 



YIELD 



10 20 30 



FISHING INTENSITY 



Figure 30. — Relationship between fishable white shrimp 

 biomass and fishing intensity in successive early-season 

 spawning classes, Louisiana Coast, 1956-59. [Yield is 

 in thousand-pound units.] 



could be due to too heavy fishing pressure having 

 been exerted too soon after e.xtreme population 

 setbacks. If each year's dominant early-season 

 spawning classes are roughlj' separated by ana- 

 lyzing only those statistics for the months July- 

 December, plots of mean annual biomass against 

 corresponding fishing intensity mildly suggest such 

 a possibihty (fig. 30). In Louisiana's oflshore 

 waters, quadrupled fishing intensity in 1958 had 

 the apparent effect of delaying initiation of a 

 recovery;' trend until the following year. Unfor- 

 tunately for the white shrimp, 1958 was a year in 

 which record high shrimp prices induced extra- 

 heavy fishing to recover losses suffered the pre- 

 ceding year. Most of this was directed at brown 

 shrimp with the low-level white shrimp population 

 suffering coincidentally. Effects of exploitation 

 inshore are also well illustrated and, in fact, may 

 well have been the controlling factors. A doubling 



of the fishing intensity in 1958 seemingly con- 

 tributed to the decline in the offshore population 

 phase the same year, and in itself may have stifled 

 an earlier upsurge in the overall population. 

 Relaxation of fishing pressure on the inshore phase 

 in 1959 resulted in concomitant recoverj' in off- 

 shore (spawning) population phases. 



In summary, the question is not so much one of 

 whether, following periods of high natural mor- 

 tality, fishing intensity should be regulated at all, 

 but one of deciding at what season such regulation 

 would be most effective. Little benefit can be 

 expected from suspending fishing in inshore 

 waters when population phases there are at 

 minimal density. On the other hand, closed 

 seasons in offshore waters supporting multispecies 

 fisheries are out of the question altogether. 



Summary of Jf-year stoiws.— White shrimp pro- 

 duction in the Louisiana and Texas Coast areas 

 experienced a sharp drop in 1957. Since then, 

 trends in the more important offshore and inshore 

 fisheries have been up, but return to 1956 produc- 

 tion levels has been slow. Incomplete data for 

 1960 indicate that former high levels will be 

 attained or surpassed this year. 



Analysis of effort and catch statistics revealed 

 that the low production in 1957 reflected a severe 

 population decline. This in turn was attributed 

 to the dire effects of intense stornt systems which 

 are believed to have compounded expected natural 

 mortality during inshore phases in that year's 

 early-season spawning class. Further analysis 

 eliminated, insofar as available data permitted, the 

 possibility that excessive fishing on spawning 

 stocks or proportionatelv reduced fishing intensity, 

 rather than poor survival alone, had resulted in 

 the diminished landings. 



Trends in overall stock strength were up in the 

 Texas Coast area but gave httle hint, despite im- 

 proved yields, of population recovery in the Louisi- 

 ana Coast area. Too heavy fishing on dominant 

 early-season spawning classes in 1958 caused 

 postponement of a recovery trend. Rt?laxed 

 pressure initiated one in 1959. A direct "within- 

 season" relationship between (1) fishing intensity 

 on inshore phases and (2) strength of offshore 

 phases was suggested. Closed inshore seasons 

 first enforced in 1958 were largely ineffectual in 

 bringing about a recovery in that portion of the 

 coastal stock supporting Louisiana's white shrimp 

 fishery. 



