750 



Fishery Bulletin 94(4). 1996 



1969; Ruello, 1973; Edward, 1978; Glaister, 1978; 

 annual model of Browder, 1985; Vance et al., 1985; 

 Gracia, 1989), negative (Barrett and Gillespie, 1973, 

 1975; Barrett and Ralph, 1977), or absent (Glaister, 

 1978; Hettler and Chester, 1982). 



In this analysis, freshwater indices exhibited both 

 positive and negative influences on pink shrimp fore- 

 casts. Coefficients for L-67 surface water discharge 

 into ENP were always positive, although the nature 

 of the relationship is not as clear for September as it 

 is for June (Fig. 4). The two years with highest land- 

 ings (1980 and 1977) both occurred when there was 

 moderate L-67 water discharge. Lowest pink shrimp 

 production was associated with extremely low L-67 

 discharges during the drought of 1989-90. Coeffi- 

 cients for groundwater at well P37 (flowing toward 

 Florida Bay) were always positive whereas those for 

 well P38 (flowing toward Whitewater Bay) were al- 

 ways negative, but again the relationships to land- 

 ings are not clear (Fig. 5). In most cases, including 



the present one, the mechanisms behind any rela- 

 tionship between freshwater and penaeid shrimp 

 landings have not been determined experimentally. 

 It has been postulated that excessive freshwater may 

 prevent habitat utilization by postlarval penaeids 

 (Barrett and Gillespie, 1973, 1975) or may initiate 

 early movement of juvenile penaeids out of estuar- 

 ies (Vance et al., 1985). Hypersalinity is a more fre- 

 quent condition in Florida Bay (Mclvor et al., 1994). 

 Although the direct effects of hypersalinity on pink 

 shrimp are unknown, low surface water discharges 

 are associated with low landings. Examples of the 

 linkage of freshwater inputs to other marine organ- 

 isms include positive correlation with sea nettle, 

 Cluysaora quinquecirrha, abundance in Chesapeake 

 Bay (Cargo and King, 1990) and positive or negative 

 correlation with production by several commercial 

 fisheries in Maryland (Ulanowicz et al., 1982). 



Another class of variables typically included in 

 penaeid shrimp forecast models are indices of fish- 

 ing activity or standing crop prior to the forecast 

 period. The Texas brown shrimp forecast covers the 

 July-June period and is based on average weekly 

 CPUE by the Galveston Bay live bait shrimp fishery 

 during April-June, just prior to emigration of the 

 shrimp into the offshore fishery (Baxter and Sullivan, 

 1986). The Louisiana brown shrimp forecast also cov- 

 ers July-June, but it is based on inshore and off- 

 shore landings from the western half of the state 

 during May. 2 Descriptive models for Tortugas pink 

 shrimp (Browder, 1985) included indices for fishing 

 effort and CPUE that were usually positive in na- 

 ture and appeared to influence landings up to four 



