GXJLF OF MEXICO COMMERCIAL SHRIMP POPULATION'S 



369 



(heads on) weigh 1 pound. Their fate after 

 leaving the bays has already been discussed. 



But what of the fall broods? E.xcept for repre- 

 sentation by small numbers of postlarvae and sub- 

 sequently an occasional juvenile, they do not 

 appear at entrances to or in inshore waters at the 

 times they might be expected. Commercial 

 trawling, even though greatly reduced at this time, 

 is still sufficient to confirm their presence or 

 absence in inshore waters during late fall and 

 winter months. Where, then, do members of fall 

 or early winter broods pass their prerecruitment 

 phase? The answer, logically, must be: in offshore 

 areas where spawning takes place and mass shore- 

 ward transport of eggs and larvae is held to a 

 minimum, or in nearshore areas when unsuitable 

 conditions preclude further movement of develop- 

 ing postlarvae into bays. From the standpoints 

 of browTi shrimp population d^-naraics and man- 

 agement, implications of this apparent phenome- 

 non warrant further attention. 



Summary of Jf-year status. — For the most part, 

 western portions of the northern Gulf of Mexico 

 brown shrimp stock showed no significant change 

 and all now appear to be in good condition. Over 

 the period 1956-59, the trend in amuial commercial 

 biomass was slightly upward \i\ Louisiana waters, 

 absent or oidy slightly downward in Texas waters, 

 and perceptibly downward in east Mexican waters. 



Though typically fluctuating, brown shrimp 

 yields from all waters, except Texas inshore waters 

 tended to rise during the period of study. Notable 

 departures from what might be considered normal 

 fluctuations were the relatively sharp declines in 

 amiual yields from Louisiana's offshore waters in 

 1957 and its inshore watei-s in 195S. The former 

 can be partly explained by the occurrence and 

 afterefifects of a damaging hurricane which im- 

 peded fishing operations duruig June and July. 

 The latter was due to the relatively poor success 

 of the spring brood of 1958. This, in turn, could 

 also be attributed to hurricane damage in the form 

 of reduced spawniing potential and nursery ground 

 capacity. 



The downward 4-year trend in fishable brown 

 shrimp biomass off eastern Mexico seemed to be 

 largely due to a low population level in 195S. 

 Figure 15C reveals that large individuals, members 

 of the 2 previous years' fall-winter broods, nor- 

 mally dominated annual yields. Exploitation of 

 broods produced in 1956 and 1957 was restricted 



to their medium-size and larger components, 

 except in 1957 when shrimp of rather small size 

 helped to make that year's catch the largest of the 

 4-year period. Assuming constant natural mor- 

 tality for all fall-winter broods, this had the effect 

 of preventing the 1956-57 winter brood from at- 

 taining its potential nnixinnim, thereby resulting 

 in a diminished available hionuiss during inid-195S. 



POPULATION TRENDS AND 

 CHARACTERISTICS 

 PINK SHRIMP 

 General Occurrence and Features 



During tlic period 1956 through 1959, catches 

 of pink shrimp averaged 22 percent of all shrimp 

 taken annually from the Gulf of Mexico by 

 United States fishennen. Conunercial landings 

 ranged from a high of 48. million pounds in 1956 

 to a low of 30.6 million pounds in 1959 (table 4). 

 Yielding only about one-fifth of the Gulf's overall 

 shrimp harvest, stocks of tins species nevertheless 

 constitute the sole support of important fisheries 

 in certain Gulf coast areas. 



Although pink sin-imp are sought over ap- 

 proximately 56,000 square (nautical) miles of 

 the continental shelf, only one-fourth of this area 

 contributes the preponderance of annual catches. 

 Harvestable concentrations are occasionall}- found 

 in the northern Gidf, but prinuiry stocks tend to 

 be restricted to its southeasterly perimeter. 

 Specifically, the latter occur off southwest Florida 

 (Sanibel-Tortugas) and northwest Yucatan 

 (Obregon-Campeche), their average densities 

 comparing favorably with or exceeding those 

 calculated for stocks of related species exploited 

 elsewhere in the Gulf (table 6). 



Biologically, the pink shrimp differs little from 

 other conunercial Penacidae. Anatomical features 

 are very similar to those of brown and white 

 shrimp. Its Ufe history, except for possible dif- 

 ferences in reproductive potential and in timing 

 of events, is also practicality identical to theirs, 

 with population development involving an oceanic 

 egg and larval phase, an estuarine postlarval and 

 juvenile phase, and an oceanic adult (progenitor) 

 phase. Growth is also comparable where the 

 pink shrimp occui-s with either or both the brown 

 and white species. And, as will be shown in a 

 later section, its population structure is similar. 



Ecological features distinguishing the pink 

 shrimp from its close relatives are not W(>11 rlcfined. 



