743 



Abstract.— In this report I review 

 the biology of and fishery for pink 

 shrimp, Penaeus duorarum, harvested 

 from the Tortugas Grounds off south- 

 west Florida, and present models used 

 to forecast annual pink shrimp land- 

 ings in this area. Pink shrimp spawn 

 all year, and larvae recruit to nurser- 

 ies in the seagrass-mangrove ecosystem 

 surrounding Everglades National Park 

 and Florida Bay. Juveniles move out of 

 the nurseries all year, but catch per 

 unit of effort for smallest size classes 

 generally exhibits March and Septem- 

 ber peaks. Total landings usually rise 

 sharply in November and taper off af- 

 ter April. The fishery was relatively 

 stable during 1960-85, averaging 4,350 

 metric tons annually, but it has shown 

 a singular decline and potential recov- 

 ery since 1985. In 1987, I began fore- 

 casting annual landings by using mul- 

 tiple regression analyses of fishery 

 catch statistics and environmental fac- 

 tors that could affect survival, growth, 

 and recruitment. Potential predictor 

 variables from May through October 

 were investigated in order to release a 

 timely annual forecast by November. 

 Each year, the updated data set from 

 1966 onwards was examined to derive 

 the "best" forecast models. Important 

 predictor variables included indices of 

 fishing activity during the waning 

 months of the fishery (May-July) and 

 surface and ground water levels within 

 Everglades National Park during June- 

 September. Forecasts were within 

 ±20% of actual landings for five of eight 

 years, whereas forecast direction (in- 

 crease or decrease over the prior year) 

 was usually correct. Cause-effect rela- 

 tionships between predictor variables 

 and pink shrimp recruitment to the 

 fishery remain to be determined. 



Forecasting the fishery for pink shrimp, 

 Penaeus duorarum, on the 

 Tortugas Grounds, Florida 



Pete Sheridan 



Southeast Fisheries Science Center 

 National Marine Fisheries Service. NOAA 

 4700 Avenue U. Galveston. Texas 77551-5997 



Manuscript accepted 7 June 1996. 

 Fishery Bulletin 94:743-755 (1996). 



The pink shrimp, Penaeus duorarum, 

 fishery over the Tortugas Grounds, 

 southwest of Florida, averaged 

 4,525 metric tons (t) of shrimp tails 

 per year during 1960-80 (Nance 

 and Patella, 1989). Landings began 

 to decline in the mid-1980s, col- 

 lapsed to 2,000 t during 1988-91 for 

 no apparent reason, and rebounded 

 to over 4,000 1 in 1994. u Coincident 

 with this unprecedented decline, 

 the Gulf of Mexico Fishery Manage- 

 ment Council (GMFMC) requested 

 that the National Marine Fisheries 

 Service (NMFS) evaluate the possi- 

 bility of forecasting annual landings 

 for the Tortugas pink shrimp fish- 

 ery. The Gulf of Mexico Fishery 

 Management Council and NMFS 

 expected that such a model could 

 aid in the planning and evaluation 

 of management actions and could 

 assist shrimp fishermen in prepar- 

 ing for the upcoming fishing season. 

 NMFS has been forecasting annual 

 brown shrimp, P. aztecus, landings 

 for Texas since 1962 (Berry and 

 Baxter, 1969; Baxter and Sullivan, 

 1986) and for Louisiana since 1985. 2 

 Annual forecasts are released to the 

 fishing industry in newsletters and 

 direct mailings. Forecasting models 

 for the Tortugas pink shrimp fish- 

 ery have been proposed previously 

 (Yokel et al., 1969; Browder, 1985). 

 However, Yokel et al. never imple- 

 mented their model, and Browder 's 

 annual models provided relatively 

 poor forecasts for the three years 

 beyond her base data set (estimated 

 from Fig. 9 in Browder [1985] to be 



-24%, +53%, and +56% of actual 

 1981, 1982, and 1983 landings, re- 

 spectively). 



In this report I review both the 

 biology of and the fishery for pink 

 shrimp in southern Florida. I then 

 present empirical models used by 

 NMFS since 1987 to forecast annual 

 Tortugas pink shrimp landings. 

 These models are based on environ- 

 mental conditions in the primary 

 pink shrimp nurseries of Florida 

 Bay, Everglades National Park, and 

 adjoining coastal waters. Pink 

 shrimp production is likely linked 

 to survival and growth of juveniles 

 in these habitats. For example, high 

 water levels in Everglades National 

 Park during October-December 

 and January-March were associ- 

 ated with subsequent high pink 

 shrimp catches in January-March 

 and April-June, respectively (Brow- 

 der, 1985). A disruption in nursery 

 habitat functions, such as those re- 

 sulting from seagrass mortality 

 (Robblee et al., 1991) or freshwater 

 diversion (Light and Dineen, 1994), 

 may have been causes of previously 

 noted fluctuations in pink shrimp 

 harvest. 



1 Nance, J. M. 1994. A biological review 

 of the Tortugas pink shrimp fishery 

 through December 1993. Unpublished re- 

 port to the Gulf of Mexico Fishery Man- 

 agement Council, National Marine Fish- 

 eries Service, 4700 Avenue U, Galveston, 

 TX 77551, 11 p. 



- National Marine Fisheries Service. 

 1994. 4700 Avenue U, Galveston, TX 

 77551. Unpubl. data. 



