FISHERY BULLETIN: VOL. 76, NO. 2 



Table 2. — Summarized growth data for sand crabs from Goleta Bay and Santa Cruz Island in 

 1974 and 1975. Mean -jz SD is given for each measure. 



sampling period. Also, the island site crabs gained 

 about a third less in carapace length at each molt 

 than the mainland animals (Table 2). Thus, sand 

 crabs at the island beach would take about three 

 times as long as the Goleta Bay crabs to reach a 

 given size, growing at the observed rates. Calcula- 

 tion of the instantaneous rate of growth (molt in- 

 crement -;- intermolt period) for the two beaches in 

 1974 gives values of 0.035 mm/day for Goleta Bay 

 and 0.012 mm/day for Santa Cruz Island 



Separation of the Santa Cruz Island samples 

 into two equal time periods (May-early July, late 

 July-September) yielded an interesting observa- 

 tion. The later group of samples showed a much 

 lower growth rate than did the earlier, which can 

 be explained by the steady decline in molt incre- 

 ment (Figure 2). The relatively high value (0.9 

 mm) in late May could represent a peak, but the 

 island site was not sampled prior to May. The 

 pattern of molt increment vs. time for Goleta Bay 

 (Figure 2) was different, showing peaks in July 

 and September. The decrease in August may 



I 2 



10- 



X GOLETA 



SANTA CRUZ ISLAND 



08- 



06- 



o 



5 04- 



= 0.2 



MAR APR MAY JUNE JULY AUG. SEPT OCT 



1974 



Figure 2. — Molt increment vs. time for sand crabs from Goleta 

 Bay and Santa Cruz Island. Each point is a mean for that sample 

 date. 



reflect changes in the number of maximum size 

 males, which decrease in molt increment as they 

 approach maximum size, and also may reflect an 

 influx of juvenile crabs into the population in Au- 

 gust. The first peak corresponds in time with the 

 peak water temperature for the sample period 

 (Figure 1). This may be a result of a physiological 

 response to temperature hy E. analoga. Crabs ob- 

 served in the laboratory at different temperatures 

 fed at different rates. Those in warmer water fed 

 most often (Fusaro 1977). 



At both locations, molt increment was positively 

 correlated with size (Figure 3). The difference be- 

 tween means of molt increment from the two loca- 

 tions was 0.3 mm, amounting to about one-half of 

 an average molt increment for the Santa Cruz 

 Island beach population. 



Molt frequency data could not be correlated with 

 carapace length at either location, although a 

 generally similar trend existed in most samples. A 



4 6 8 10 12 14 16 IJ 



PREMOLT CARAPACE LENGTH (MM) 



Figure 3. — Regression of mean molt increment on premolt 

 carapace length for grouped size class data of sand crabs from 

 Goleta Bay (+'s) and from Santa Cruz Island (O's). Regression 

 line equations are y =0.0932X + 0,1829 for Goleta Bay and 7 = 

 0.0776X - 0.0041 for Santa Cruz Island. Correlation coefficients 

 are 0.98 for Goleta Bay and 0.92 for Santa Cruz Island. Vertical 

 bars at each point represent ± 1 SD. 



372 



