368 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



SEB SURFACE TEWPEOftTUOE 

 PEMSACOLA. CI.A 

 IMOHThl' AVERAOESI 



SEA SUeSUOFACE lEMPEBi 

 QALVESTON . TEIAS 



12 FATHOMS) 



Figure 16. — Sea temperatures at selected locations along 

 the northern Gulf of Mexico coast. 



Sources: A. and M. College of Texas (1952); A. and !\I. 

 College of Texas (1955), data collected by U.S. Coast and 

 Geodetic Survey; U.S. Fish and Wildlife Service (Unpub- 

 lished data); A. and M. College of Texas (1955), data 

 collected by U.S. Fish and Wildlife Service. 



20-40 fathoms, is therefore a matter for conjecture. 



Assuming reasonable correspondence in the 

 shape and displacement of annual shore-surface 

 and offshore-bottom temperature curves, it may 

 be concluded with the aid of figure 16 that peak 

 spawning activity in the upper Gulf's brown 

 shrimp stock is associated with initiation of: (1) 

 a rapidly increasing rate of temperature change 

 in the spring, and (2) a rapidly decreasing rate of 

 change in the fall. 



A knowledge of underlying mechanisms not- 

 withstanding, the fact that semiannual broods 

 sustain the upper Gulf's commercial fishery 

 further complicates brown shrimp population 

 studies. Since successive broods are not sub- 

 jected to the same environmental stresses, 

 parameters of reproductivity, growth, and mor- 

 tality may be expected to vary widely from brood 

 to brood and from area to area. This would offer 

 potential difficulty in attempts to project yields 

 -on a calendar year basis. 



Inshore population phases. — Closed seasons and 

 minimum size limits restrict the annual harvest of 

 brown shrimp from inshore waters of the north- 

 western Gulf. Most stringently regulated are 

 Texas estuaries from which only negligible 

 amounts (commercial: human consumption) were 

 taken during the 4-year period under study (fig. 

 17A). Louisiana's inshore catches, on the other 



A COMMERCIAL YIELD (mlllloni of pound! , h*aO*-« 

 •-LOUISIANA COAST 

 o-TEXAS COAST 



CLOSES Se.50.. - . -J,;.:. CO.., 



Figure 17. — Total and average yield of brown shrimp 

 populations in inshore waters along the northwestern 

 Gulf coast, 1956-59. 



hand, were considerably greater but also fluctuated 

 markedly. Actually, average annual brown 

 shrimp production from Louisiana bays ap- 

 proached that of the adjacent offshore fishery and 

 exceeded that of all other inshore waters on the 

 upper Gulf coast. As also noted in the eastern 

 Gulf, annual production ma-xima for the western 

 Gulf's inshore waters usually occurred slightly 

 before those for offshore waters (cf. figs. 13 A and 

 17A). Comparison of inshore average yield and 

 offshore biomass curves revealed a similar corre- 

 spondence. 



The dynamics of population phases supporting 

 inshore commercial fisheries provoke some in- 

 teresting specidation about the western Gulf of 

 Mexico brown shrimp stock as a whole. There is 

 no debating the fact that spring broods, first 

 appearing en masse as 3- to 4-week-old larvae at 

 the entrances to insliore waters during late March 

 to mid-April, sustain inshore fisheries for the en- 

 suing 2 or 3 months. Juvenile brown shrimp, for 

 instance, comprised 87 to 99 percent, respectively, 

 of commercial bait shrimp landings from Gal- 

 veston Bay in June and July, I960.* These 

 shrimp grow rapidly during the inshore phase 

 and, by the time they begin migrating to offshore 

 waters, usually in June and July, they may attain 

 a size equivalent to that at which 42 specimens 



< Galveston Bay bait slirimp landing.s for June and July, 1960, totaled 0.20 

 and 0.16 million pounds, respectively. 



