GULF OF MEXICO COMMERCIAL SHRIMP POPULATIONS 



377 



(luring the 4-year study period, experienced a 

 significant decline. 



Population characteristics. — Little information 

 on population age structure could be obtained 

 by plotting weight composition modes of monthly 

 Canipeche landings. As intimated above, weight 

 composition curves were almost exclusively 

 unimodal with large slu-imp predominating at 

 all times (fig. 25C). Conclusive evidence of 

 more than one period of heightened spawTiing 

 per year is lacking, but bimodal weiglit-frequenc}^ 

 curves lor spring landings in 1959 suggest that 

 two peaks in annual spawning activity may also 

 be characteristic of the Campeche pink shrimp 

 population. 



Summary oj 4-year status. — Accurate but re- 

 strictive statistics gave only a vague picture of 

 conditions in the Campeche pink shrimp popu- 

 lation. Composed primarily of large-size shrimp, 

 yields to United States fishermen declined sharply 

 over the period 1956-58, but increased measurably 

 during the next 2 years. Of significance was 

 the drop in apparent abundance of large shrimp 

 commencing in 1958 and sustained through 1959. 

 Whether this was caused by excessive fishing 

 alone, or by a combination of fishing and adverse 

 environmental conditions, will always remain 

 problematical. The Campeche fishery serves as 

 a good example of one in which a lack of all- 

 inclusive yield data (i.e., landings plus discards) 

 inhibits proper population analysis. If landing 

 statistics truly represented what was actually 

 caught, further investigation of the Canipeche 

 population's dynamics would be justified. 



POPULATION TRENDS AND 

 CHARACTERISTICS 



WHITE SHRIMP 

 General Occurrence and Features 



Once the primary objective of commercial 

 shrimping interests, the white shrimp now occupies 

 a relatively minor position in the Gulf of Mexico's 

 overall shrimp picture. For many years it 

 constituted tiie sole support of a thriving fishery' 

 in bays and bayous along the Louisiana-Texas 

 coast. There was no need to venture into the 

 open Gulf until about the mid-1930's when 

 prospects of an expanding market prompted the 

 fishery's extension. The offshore fisliery then 

 developed rapidly, reaching its zenith in the 



mid- 1 940 's. Gradually, however, and for reasons 

 not yet clear, domestic white shrimp supplies 

 diminished to the point where related species 

 began to attain competitive status. Accelerating 

 production of brown and pink slirinip from newly 

 discovered domestic and foreign grounds finally 

 overtook that of white shrimp in the mid-1950's. 

 The former two species have since maintained a 

 superior position. 



During the period 1956-59, white shrimp ranked 

 third behind brown and pink shrimp, annuallj- 

 averaging but 20 percent of all shrimp taken from 

 Gulf waters by United States fishermen. 

 Although subordinate on a Gulfwide basis, this 

 species, like the pink slirimp, still sustains local 

 fisheries in certain coastal areas. 



Because of its longer history as a commercial 

 species, the white slu-imp lias been studied more 

 extensively than all other species combined. 

 Nevertheless, there is still much to be learned 

 about its life history and habits. Taxonomicall}', 

 the white shrimp is very similar to the brown and 

 pink shrimp although distinction between it and 

 either of the latter two species is more clear-cut 

 than that between the brown and pink shrimp 

 themselves. Aside from their timing, events in 

 the white shrimp's life liistory follow the same 

 sequence and otherwise simulate those character- 

 istic of littoral penaeids. Growth appeai-s com- 

 parable to that of closely related varieties where 

 they and the white shrimp are subject to similar 

 ecological stresses. Reproductive jjotential is 

 also believed to be approximately equivalent 

 though much uncertainty prevails concerning 

 shrimp fecundity. Actual egg counts have never 

 been made for any species, but ova production in 

 the white shrimp has been estimated without 

 any indication of statistical reliability. King 

 (1948) mentions "* * * the half million or so 

 eggs which the average female will produce * * *" ; 

 Anderson, King, and Lindner (1949) state that 

 "A count made by the authors on the ripe ovaries 

 of a female, 172 mm. total length with sperma- 

 tophorc attached, revealed a total of approxim- 

 ately 860,000 eggs"; Lindner and Anderson (1954) 

 specify that "A female will lay about 500,000 eggs 

 at each spawning . * * *" 



As already noted, when two or more species 

 occur in the same general area, littoral Penaeidae 

 may also be discriminated on the basis of apparent 

 ecological requirements. Substrate quality li.i-; 



