Abstract. — Regression and 

 time series analyses were used to 

 investigate the relation between 

 Apalachicola River flows and blue 

 crab, Callinectes sapidus, harvests 

 in and around Apalachicola Bay, 

 Florida. Apalachicola River flows 

 in one year were positively corre- 

 lated with Franklin County blue 

 crab landings during the next year 

 (r 2 =0.32, P<0.001, 1952-90), and 

 the strength of the correlation in- 

 creased when only more recent 

 years were examined (r 2 =0.49, 

 P=0.001, 1973-90). In this area, 

 blue crabs mature to a harvestable 

 size by one year of age. Apala- 

 chicola River flows were also cor- 

 related with neighboring Wakulla 

 County blue crab landings with a 

 one-year time lag (r 2 =0.52, 

 P=0.001, n=l7), but were not asso- 

 ciated with blue crab landings for 

 the remaining west coast of 

 Florida. The mean monthly flow 

 from September to May, termed 

 the growout period, was the pa- 

 rameter most highly correlated 

 with the following year's blue crab 

 landings. Of five north Florida riv- 

 ers examined, the Apalachicola 

 River was most highly correlated 

 with Franklin and Wakulla 

 County blue crab landings. 



Results of this study further 

 document the influence of Apal- 

 achicola River flows on estuarine 

 productivity. The positive relation 

 between flows and blue crab har- 

 vests a year later suggests that 

 low flow conditions in the estuary 

 during the growout period nega- 

 tively affect juveniles. Although 

 the underlying causes of the corre- 

 lations are not known, the effect of 

 inflows on estuarine salinity is one 

 of several possible mechanisms 

 that warrants further investigation. 



The influence of Apalachicola River 

 flows on blue crab, Callinectes 

 sapidus, in north Florida 



Dara H. Wilber 



1 640 Oak Ridge Road. Vicksburg. MS 39 1 80 



Manuscript accepted 20 July 1993 

 Fishery Bulletin 92:180-188 1 1994) 



River flow affects many character- 

 istics of estuaries, including salin- 

 ity, turbidity, and nutrient and de- 

 trital concentrations. Changes in 

 flow, therefore, may significantly 

 affect estuarine biota, the extent to 

 which may be inferred by examin- 

 ing historical relations between 

 flow and productivity. Apalachicola 

 Bay, Florida, like many estuaries, 

 is subject to changes in freshwater 

 inflow related to factors such as 

 rainfall and upstream demands for 

 agricultural, municipal, and indus- 

 trial uses. Plans to reallocate fresh- 

 water resources (U.S. Army Corps 

 of Engineers, 1989 1 ) have renewed 

 interest in the question of how 

 freshwater inflows are related to 

 productivity in the Apalachicola 

 River and Bay system. This study 

 examined the historical relation- 

 ship between Apalachicola River 

 flows and estuarine productivity. 



One method of characterizing the 

 importance of freshwater inflow to 

 estuarine productivity is to corre- 

 late historical flow data with the 

 commercial catch (landings) of es- 

 tuarine-dependent species (Fun- 

 icelli, 1984). Commercial landings 

 are used to estimate estuarine pro- 

 ductivity because they are often 

 the only available long-term 

 records from which species abun- 

 dance can be inferred. Long-term 

 records are available for several 

 commercially important species in 

 Apalachicola Bay, including oysters 

 and blue crabs, which have differ- 

 ent trophic requirements and es- 

 tuarine residency patterns. By ex- 

 amining associations between 



these species and Apalachicola 

 River flows, effects of freshwater 

 delivery upon estuarine productiv- 

 ity can be evaluated. Associations 

 between freshwater inflows and 

 Apalachicola oyster harvests have 

 been previously addressed (Wilber, 

 1992). The present study examines 

 the influence of Apalachicola River 

 flows on local and regional commer- 

 cial blue crab, Callinectes sapidus, 

 landings. Other north Florida riv- 

 ers were also examined to estimate 

 the relative importance of the 

 Apalachicola River to blue crab 

 landings with respect to these 

 drainages. 



Blue crabs in the Gulf of Mexico 

 reach a harvestable size within a 

 year of age (Perry, 1984) and com- 

 prise a significant portion of the 

 commercial landings by 18-months 

 of age (Steele, 1992 2 ). Blue crabs 

 enter the Apalachicola estuary as 

 megalopae and young juveniles, 

 reaching peak juvenile abundances 

 in the winter (Livingston, 1983). 

 Young crabs concentrate in the less 

 saline portions of the bay, whereas 

 egg-bearing females remain in the 

 higher-salinity gulf waters where 

 they spawn. It has been proposed 

 that adult female blue crabs along 

 the Florida gulf coast migrate to 



1 U.S. Army Corps of Engineers, Mobile 

 District. 1989. Draft Post Authorization 

 Change Notification Report for the Real- 

 location of Storage from Hydropower to 

 Water Supply at Lake Lanier, Georgia, 

 320 p. 



2 P. Steele, Florida Marine Research Inst., 

 108th Ave. SE, St. Petersburg, FL 33701, 

 pers. commun. 1992. 



180 



