DYNAMICS OF A PENAEID SHRIMP POPULATION AND MANAGEMENT 



IMPLICATIONS 



By Joseph H. Kutkuhn, Fishery Biologist (Research) 

 Bureau of Commercial Fisheries, Galveston, Tex. 



ABSTRACT 



In assessing present utilization of a stock of pink 

 shrimp (Penaeidae) that supports an important com- 

 mercial fishery in the eastern Gulf of Mexico, the inter- 

 action of population growth and mortality is critically 

 analyzed. Estimates of the parameters involved were 

 secured through a mark-recapture experiment wherein 

 a biological stain served as the marking agent. The 

 experiment was oriented in space and time so that ex- 

 ploitation of the marked population, which initially 

 consisted of individuals uniform in size, provided 

 measures of growth and mortality in the parent age 

 group during and immediately following its transition 

 from prerecruit to postrecruit status. Throughout the 

 experiment, the entire stock as well as the marked popu- 



lation were heavily fished. Upon examining the ques- 

 tion of whether or not the fishery's production could be 

 improved by postponing the start of fishing until the 

 shrimp reach a size greater than the 70 headless-count 

 designation now generally viewed as a practicable 

 minimum, it was noted that expected growth, although 

 relatively high, would be insufficient to offset sub- 

 stantial losses due to expected natural mortality. 

 Even with a moderate increase in growth rate, an 

 appreciably reduced natural mortality would have to be 

 indicated before such a move could be considered 

 feasible. Maximum potential yield in both weight 

 and value is obtained with the minimum acceptable 

 size that the fishery currently imposes. 



Broadly speaking, the basic goal of biological 

 research undertaken by the Bureau of Commercial 

 Fisheries is to gain the best possible understanding 

 of how fishing and the principal environmental 

 factors (once they are determined) govern the 

 size of commercial fishery resources, and hence 

 the yield of fish and fishery products. Its attain- 

 ment would, theoretically, enable us to establish 

 guidelines for maintaining any resource at about 

 that level where production or, perhaps, economic 

 advantage is highest. One should not gain the 

 impression, however, that such a level can be held 

 static over long periods of time, but recognize in- 

 stead that it is subject to fluctuation from year to 

 year in response to an everchanging environment 

 and thereby presupposes continual readjustment 

 of fishing intensity. 



Utilization is associated very closely with the 



Note.— Approved for publication December 21, 1962. 



FISHERY BULLETIN: VOLUME 65, NO. 2 

 774-711 O— 66 2 



concept of resource maintenance. In the con 

 notation of the phrase "conservation of natura 

 resources," maintenance and utilization are, in 

 fact, not mutually exclusive. But it is always 

 likely that long before research can produce a 

 scheme for effective resource maintenance, it will 

 provide ad interim some indication of how a re- 

 source should be best utilized. Fishery research, 

 which largely embraces the field of population 

 ecology (including dynamics), becomes most 

 efficient when it programs for short-term or inter- 

 mediate as well as long-term objectives. It is 

 noteworthy that the processes of achieving both 

 types of objectives very often require the same 

 basic data. 



For nearly as long as Gulf of Mexico shrimp 

 resources have been exploited, concern has pre- 

 vailed as to whether they have always been 

 utilized to best advantage. Many believe that 

 the minimum size of commercially acceptable 



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