Seasonal index = 1 + log N 



M, 



where N = total number collected, 



Di = days collected in the i th season, 



C; = months collected in the i th season, 



Mi = number of months in the i th season. 



Although arbitrary in its design, this index does 

 contain the elements implicit in the meaning of 

 seasonality, and the lower the seasonal index for a 

 species the more seasonal is its occurrence. 



Species were ranked by number of specimens, frequen- 

 cy of appearance (number of days collected), weight, and 

 seasonality (seasonal index). For each of these categories 

 the values were ordered and the highest value was given a 

 rank of one, the second highest a rank of two, etc. In 

 determining rank of importance, the individual ranks for 

 each species were weighted equally and summed. The 

 ordered sums were then ranked as "importance" (Table 

 10). In the surf and tidal pool combined, M. menidia was 

 the most important species, followed by A. cribrarius, T. 

 carolinus, M. littoralis and M. curema, A. mitchilli, and 

 F. majalis. 



Relationships Between Environmental 

 Variables and Occurrence 



A major objective of this study was to determine the 

 relationships of the occurrence of the fauna to certain en- 

 vironmental variables using multiple regression techni- 

 ques. The collections made in the surf were chosen for 

 more detailed analyses. Effects of environmental 

 variables on collections made in the tidal pool were not 

 examined because conditions at the time of pool forma- 

 tion were not known. 



Five of the most important species in the surf were 

 selected to determine which environmental variables are 

 important to their occurrence. The species chosen were 



Arenaeus cribrarius, Anchoa mitchilli, Menidia menidia, 

 Trachinotus carolinus, and Menticirrhus littoralis. Mugil 

 curema was not chosen because it was present in only 9 of 

 the 51 surf collections. Five variables (duration of effort, 

 water temperature, salinity, height of sea, and visibility 

 of Secchi disc) were chosen for analysis. We used 

 stepwise regression techniques to choose the "best" 

 equation (Draper and Smith 1966) for each of the five 

 selected species in the following manner: 



1. Occurrence was plotted versus environmental 

 variables and the data were linearized, where 

 necessary; 



2. Simple correlation coefficients between occurrence 

 and the environmental variables were computed; 



3. Using the multiple regression model, Y = /3 +^ l Z , + 

 |3 2 Z 2 + . . . +(3 P Z p +e , where Y = occurrence, and 

 Z , is some function of one of the five selected en- 

 vironmental variables, X l ,X l X 5 , a stepwise 



regression was preformed to identify those 

 parameters which account for the attributable 

 variations in the model; and 



4. For each final regression equation residuals were 

 analyzed. 



Variation within months, which we did not consider 

 significant, was removed by using monthly averages for 

 all data. Only temperature showed a marked seasonal 

 effect. The mean number of specimens per collection was 

 plotted for each species versus mean water temperature 

 (by months). The pattern for A. cribrarius (Fig. 1) was 

 typical of all species except M. menidia (Fig. 2). Menidia 

 menidia was much more abundant at the lower water 

 temperatures, while the converse was true for the other 

 species. Figures 1 and 2 indicate the possible utility of 

 the square of water temperature as an additional in- 

 dependent variable because the relationships appear to 

 be curvilinear functions. 



Table 10.— Rank of the seven most important species collected during Folly Beach survey (Oct. 1969-Oct. 1971). Ranks are in 

 parentheses. Appearance equals number of days collected (because of this the number of days collected in surf and tidal pool 

 combined does not equal number of days collected in surf plus number of days collected in tidal pool). 









Appear- 



Weight 



Seasonal 



Sum of 



Impor- 





Species 



Number 



ance 



(g) 



index 



ranks 



tance 



Surf: 



Menidia menidia 



1.485(1) 



36(1) 



4,025(1) 



109.7(1) 



4 



1 





Arenaeus cribrarius 



417(2) 



32(3) 



3,209(2) 



76.6(2) 



9 



2 





Menticirrhus littoralis 



291(4) 



34(2) 



831(5) 



72.9(3) 



14 



3 





Anchoa mitchilli 



362(3) 



29(4.5) 



350(6) 



63.7(4) 



17.5 



4 





Trachinotus carolinus 



266(5) 



29(4.5) 



1,018(4) 



62.0(5) 



18.5 



5 





Mugil curema 



121(6) 



9(6) 



2,591(3) 



11.7(6) 



21 



6 



Tidal pool: 



Menidia menidia 



630(2) 



18(1) 



2,201(1) 



31.2(1) 



5 



1 





Trachinotus carolinus 



710(1) 



13(3) 



501(3) 



21.8(2) 



9 



2 





Fundulus majalis 



341(4) 



15(2) 



734(2) 



20.9(3) 



11 



3 





Mugil curema 



545(3) 



7(4) 



118(4) 



8.5(4) 



15 



4 



Surf and 



Menidia menidia 



2,115(1) 



40(1) 



6,226(1) 



126.9(1) 



4 



1 



tidal pool 



Arenaeus cribrarius 



422(4) 



35(2) 



3,218(2) 



76.7(2) 



10 



2 



combined: 



Trachinotus carolinus 



976(2) 



29(5) 



1,519(4) 



76.2(3) 



14 



3 





Menticirrhus littoralis 



294(7) 



34(3) 



843(5) 



73.0(4) 



19 



4.5 





Mugil curema 



666(3) 



14(7) 



2,709(3) 



29.2(6) 



19 



4.5 





Anchoa mitchilli 



372(5) 



30(4) 



365(7) 



66.5(5) 



21 



6 





Fundulus majalis 



344(6) 



16(6) 



744161 



23.0(7) 



25 



7 



12 



