Wilber: Influence of Apalachicola River flows on Callmectes sapidus 



187 



esis of mass blue crab spawning near Apalachicola 

 Bay and larval transport down the gulf coast of Flor- 

 ida via the loop current (Oesterling and Evink, 1977). 



Several studies have addressed factors that influ- 

 ence interannual variation in blue crab abundance, 

 primarily concentrating on larval and post-larval 

 recruitment (reviewed in Lipcius and Van Engel, 

 1990). Lipcius and Van Engel (1990) found high 

 interannual, seasonal, and spatial variation in blue 

 crab abundances in a 17-year fishery-independent 

 dataset collected in the Chesapeake Bay. They ob- 

 served that years with high blue crab abundances 

 appeared to be dominated by the previous year class 

 because peak catches occurred in the summer. Years 

 with low abundances had peak abundances in the 

 fall, suggesting the dominance of the new year class. 

 This observation supports the contention that varia- 

 tion in recruitment plays a major role in determin- 

 ing interannual fluctuations. No interaction between 

 annual abundance and seasonal peak catch was 

 apparent for the Franklin or Wakulla County blue 

 crab landings, which may indicate either the true 

 absence of such a relation, the inadequacies of us- 

 ing fishery statistics, or a difference in growth rates 

 between the two regions that invalidates the use of 

 the same analysis. Interestingly, the fishery-inde- 

 pendent trawl data from the Chesapeake were sig- 

 nificantly (r 2 =0.33) correlated with the commercial 

 landings data. 



The influence of physical factors on blue crab 

 abundances has been documented in other areas, 

 such as a positive relationship between blue crab 

 landings and freshwater inflows in Georgia (Rogers 

 et al., 1990 5 ), an inverse relation between salinity 

 and juvenile blue crab abundances on the Texas 

 coast (More, 1969), and a positive relation between 

 blue crab productivity and vegetated area in the 

 Gulf of Mexico (Orth and van Montfrans, 1990). The 

 positive correlation between blue crab landings and 

 Apalachicola River flows of the previous year pro- 

 vides additional evidence of the importance of fresh- 

 water inflows to juvenile blue crabs. 



Apalachicola River flows have a significant impact 

 on estuarine productivity, as indicated by commer- 

 cial harvests of oysters (Wilber, 1992) and blue 

 crabs. Although statistical correlations do not indi- 

 cate the causal mechanisms underlying these asso- 

 ciations, the river's influence on estuarine salinities 

 as a mediating factor is deserving of further exami- 

 nation. Undoubtedly, the Apalachicola River affects 

 estuarine biota via mechanisms other than salinity 

 (Livingston, 1991). Factors such as the transport of 

 nutrients and organic matter, however, are unlikely 

 to result in a significant correlation between low 

 flows and oyster harvests two years later, unless 



food limitation is only measurably important for 

 newly settled oyster spat. In addition, the majority 

 of nutrient and detrital transport from the river 

 occurs during high flow periods in the spring 

 (Mattraw and Elder, 1982). There was no evidence 

 that above-average flows were associated with either 

 oyster or blue crab productivity. In both fisheries, 

 flows on the low end of the spectrum were most sig- 

 nificantly associated with landings. These signifi- 

 cant correlations were positive and incorporated 

 time lags, suggesting estuarine conditions during 

 low minimum flow periods were not favorable for 

 juveniles of either species. 



Acknowledgments 



The careful reviews of R. Hardy, G. Lewis, D. 

 Meeter, R. Lipcius, P. Steele, and R Wilber are grate- 

 fully acknowledged, as well as the technical support 

 of J. Bennett, J. McKenna, G. Miller, and D. 

 Tonsmeire. This work was supported by the North- 

 west Florida Water Management District and the 

 State of Florida's Surface Water Improvement and 

 Management (SWIM) Program. 



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