O'NEIL and WEINSTEIN: FEEDING HABITATS OF SPOT 



0_ 

 10_ 



20. 

 30. 

 40_ 

 50. 

 60- 

 70- 

 80_ 

 90_ 

 100 



CAL 



P I 



U I D 



PLA 

 ~f(ZW 



-OLI 

 J-MISC 



APR 

 75 



MAY 

 3/259 



-NER 

 •OST 

 -SPI 



JUN 



2/238 



JUL 

 2/111 



AUG 

 1/68 



SEP 

 68 



-DET 

 -U ID 

 ~Na 



OCT 

 16/53 



Figure 8. — Cluster analysis of monthly differences in prey utilization for young-of-year spot at Blevins Creek, 

 VA, 1982. Prey abbreviations listed in Table 1. Ratios at base of each column represent number of empty 

 stomachs/total sample. 



DISCUSSION 



As Livingston (1982) stated, "While food habits 

 of fishes have been studied extensively, specific 

 relationships of trophic interactions, habitat par- 

 titioning, and spatial/temporal variability of 

 coastal fishes remain largely undetermined." 

 While a more comprehensive understanding of 

 these processes awaits properly designed experi- 

 ments and hypothesis testing, several common 

 patterns have begun to emerge. Despite the ap- 

 parent abundant resources of the estuary as a 

 whole, there seems to be a consistent "tracking" 

 (among species) of these resources, reminiscent 

 of resource partitioning in other aquatic sys- 

 tems (e.g., coral reefs). Individual species distri- 

 butions are probably controlled by physiological 

 constraints, predation pressure, and the 

 availability of food (or a combination of these fac- 

 tors). That this tracking process, if real, may re- 

 sult from periodic scarcity of food in estuaries was 

 tentatively stated by Thayer et al. (1974) and 

 only recently reinforced by the studies of Weis- 

 burg and Lotrich (1986). The latter authors used 

 experimental techniques to demonstrate food lim- 

 itation occurring in the mummichog Fundulus 

 heteroclitus, among fishes perhaps the most 



"perfectly" adapted food general ist in the estuary. 



We did not observe differences in relative full- 

 ness of spot stomachs between the two creek local- 

 ities examined (O'Neil and Weinstein, unpubl. 

 data). Therefore, suitable food appears to be read- 

 ily available in both creeks. The types of prey 

 utilized in each area, however, were different and 

 generally followed the temporal and spatial dis- 

 tributions of the dominant macrobenthos in these 

 creeks (Robert Diaz'*). Spot apparently feed oppor- 

 tunistically on the available resources present in 

 the tidal creeks and shoals at any one time and do 

 well throughout the estuary. There were no dif- 

 ferences in growth rates or condition of spot ob- 

 served in the tidal creeks in our study (Weinstein 

 and O'Neil^). Thus, from an energetics stand- 

 point, spot seem able to achieve similar growth 

 rates in different creeks (and corresponding salin- 

 ity regimes). 



Hodson et al. ( 1981) noted that individual stom- 

 achs of small spot captured in the Cape Fear estu- 

 ary were typically dominated by a single food cat- 



''Robert Diaz, Virginia Institute of Marine Science, Glouces- 

 ter Point, VA 23062, pers. commun. July 1983. 



^Weinstein, Michael P., and Steven P. O'Neil. manuscr. in 

 prep. Virginia Institute of Marine Science, Gloucester Point, 

 VA 23062. 



793 



