FISHERY BULLETIN: VOL. 72. NO. 2 



10 20 30 40 50 60 70 80 90 100 



CUMULATIVE PERCENTAGE 



Figure 3. — Histogram illustrating the feeding habits of Etropus 

 crossotus by season of the year, locality, and standard length. 

 (N = number of stomachs analyzed for each bar, P = Poly- 

 chaetes, C = Crustacea other than those sjjecifically identified 

 in the bar, Ps = Pseudodiaptomus coronatus, M = moUusca, 

 and N = Neomysis americana.) 



series of figures was prepared which take these 

 parameters into consideration (Figures 3-8). 



year. This change in food habits does not appear 

 to reflect a reduction in the availability of Ps. 

 coronatus. Plankton samples taken in conjunction 

 with this and other studies have demonstrated 

 thatPs. coronatus is present during the winter in 

 numbers often exceeding those of other seasons of 

 the year. The change in food habits may reflect an 

 increased availability of Pa. pinnata rather than 

 a decrease in the availability of Ps. coronatus. 

 The increased availability of Pa. pinnata may 

 have been a function of an increase in absolute 

 numbers of the polychaetes or may have been due 

 to a change in the behavior patterns of the preda- 

 tor, prey or both. Studies of benthos associated 

 with stations in Ossabaw Sound, from which 

 many of the fishes were collected, indicate that 

 Pa. pinnata is the dominant benthic infaunal form 

 throughout the year on mud substrates and exhib- 

 its widely fluctuating standing crop levels (Stick- 

 ney and Perlmutter, unpubl. data). 



The possibility that the shift in food habits in 

 winter may have been a function of the size of 

 the fishes occurring in the estuaries during that 

 season was considered. Animals in the larger 

 size ranges did not dominate the winter samples 

 but were generally present during the spring 

 (Figure 4). Fish in the smallest groups were pre- 

 sent most often in the summer when Ps. coronatus 

 were highly dominant in the stomachs. Suitable 

 numbers of £■. crossotus were present throughout 



Etropus crossotus 



The food habits ofE. crossotus related to season 

 of the year, locality within the estuary (rivers as 

 opposed to sounds), and standard length are pre- 

 sented in Figure 3 indicating the percentage of 

 total numbers of food organisms contributed by 

 each taxa. E. crossotus was most abundant during 

 the spring and summer months (March through 

 August). Ps. coronatus was the dominant organ- 

 ism in the stomachs of E. crossotus during the 

 spring, summer, and fall. During the winter, 

 Ps. coronatus was displaced to a large extent by 

 the spionid polychaete Pa. pinnata and by N. 

 americana. Whereas Table 1 indicated that Pa. 

 pinnata was of general importance especially in 

 terms of frequency of occurrence in the stomachs. 

 Figure 3 indicates that this organism was more 

 important during the winter (December through 

 February) than during any other season of the 



10 20 30 40 50 60 70 80 90 100 



CUMULATIVE PERCENTAGE 



Figure 4. — Histogram of percentage of stomachs examined 

 during spring (March through May), summer (June through 

 August), fall (September through November), and winter 

 (December through February) for Etropus crossotus of various 

 standard length groups. 



520 



