Table 3, —Coefficients of association between the six most abundant species, by 

 Cole's Index. Value scale extends from +1 (perfect association) 

 to -1 (perfect disassociat ion) 



from late spring until the following early spring 

 gradually displaced the tidewater silverside 

 (figure 5). Atlantic menhaden generally re- 

 mained the principal spring-fall migrant, but 

 downstream was replaced by the bay anchovy 

 during late fall and early spring. 



The catch-per-unit-effort, by species, during 

 3-month intervals, is summarized in appendix 

 table 2. In addition, the monthly catch of all 

 species, with corresponding range in fork 

 lengths, is listed by station in appendix table 3, 



The occurrences of the principal species 

 appear to be related. Interspecific association 



Cv Drlnodon 

 vone gatus >. 



Figure 6. — Interspecific association between the six most 

 abundant species occurring in White Creek, Del. Solid 

 lines indicate positive association; broken lines, nega- 

 tive association. 



of the six most abundant species was deter- 

 mined from 820 samples in 2 x 2 contingency 

 tables and Cole's Index (Cole, 1949, 1957). This 

 coefficient indicates what proportion of the 

 association possible was actually found within 

 the series of collections. Range of coefficients 

 may vary from +1 when species occur together 

 as many times as possible, to - 1 when species 

 occur together the minimum number of times. 

 Coefficients (table 3) ranged from 0.592 to 

 -0.1 27. The relative occurrence is diagrammed 

 in figure 6. Chi-square values resulted in 

 probabilities =0.15 for M. menidia paired with 

 M . beryllina and F. heteroclitus . All other P 

 values were less than 0.5, indicating association 

 coefficients were statistically significant. 



SEASONAL OCCURRENCES OF 

 SMALLEST SPECIMENS 



The sequence in availability of the smallest 

 specimens taken (table 4) provides a clue to 

 spawning time of the various species in local 

 waters. Of the clupeid fishes collected, only 

 the Atlantic menhaden occurred in larval 

 stages. Although the smallest Atlantic men- 

 haden (22 mm.) occurred in May, their first 

 appearance was made in collections during 

 Novennber. The greatest number of species in 

 the list of small specimens were available in 

 late spring; however, the smallest cyprinodont 

 larvae (10 mm.) were collected from June to 

 August. This group included important resi- 

 dents: the mummichog, striped killifish, 

 sheepshead minnow, and rainwater killifish. 



