FISHERY BULLETIN: VOL. 76, NO. 2 



vironmental conditions in the field can be ob- 

 served for this species. 



METHODS 



Several alternatives for the measurement of 

 growth for Emerita analoga were possible, includ- 

 ing all those mentioned above. Field caging did not 

 seem practical, and laboratory impoundment does 

 not provide information on the growth rate in the 

 field situation. Mark and recapture techniques are 

 adaptable to the species ( Dillery and Knapp 1970), 

 but considerable time and effort can be expended 

 for very little data return. The usual recapture 

 rate is low, 10% or so at best, unless unusual 

 circumstances, e.g., a fishery, exist. Modal size 

 class analysis can give an index of average growth, 

 but can be misleading without corroborative evi- 

 dence from the laboratory or some other method of 

 growth measurement. Unfortunately, no such cor- 

 roborative data exist for E. analoga. As a result of 

 these considerations, an instantaneous growth 

 rate method was chosen to estimate growth for 

 this species. This method as applied toE'. analoga 

 is described in the following sections. 



Localities 



Two locations were chosen on the basis of their 

 proximity and on preliminary observed differ- 

 ences in their environmental conditions. One site, 

 the beach of Goleta Bay adjacent to the University 

 of California Santa Barbara campus, is bathed in 

 relatively warm water (mean surface temperature 

 for 1974 and 1975: 13.7°C) that is relatively turbid 

 (average lateral visibility: <1 m). 



The second site, a bay on the northwest corner of 

 Santa Cruz Island, is about 42 km (25 mi) south of 

 the coast of Santa Barbara, and experiences much 

 different water conditions. At this location, water 

 clarity is almost always excellent (10-20 m of lat- 

 eral visibility), indicating a relative lack of sus- 

 pended materials. In addition, Neushul et al. 

 (1967) described current patterns in the vicinity 

 which indicate that this site is bathed in a colder 

 water mass originating in the north. The mean 

 surface temperature measured at the Santa Cruz 

 Island site during 1974 and 1975 was 12.1°C. 



Sampling 



Sand crabs were gathered and separated into 

 size classes by methods described fully in Wenner 



370 



et al. ( 1974). The use of an automatic size sorting 

 sieve permitted measurement of a large number of 

 live crabs rapidly. Samples were taken approxi- 

 mately biweekly at Santa Cruz Island and Goleta 

 in 1974 and monthly at Goleta in 1975. The crabs, 

 separated into size classes, were then placed in 

 screen compartments in sand in a continuous flow 

 seawater table for a period of 5 days. Every day 

 each compartment was checked for molts, and the 

 number of molts and molt increments were re- 

 corded. Where multiple molts occurred in any size 

 class on 1 day, premolt and postmolt carapace 

 length were paired by rank from least to greatest 

 measure. This procedure might tend to reduce the 

 variance in molt increment slightly, but no sig- 

 nificant differences were found between single 

 molt and multiple molt records for 20 molt incre- 

 ment observations during May-July at Goleta in 

 1974 (0.5<P<0.6, t = 0.667, df = 36). 



Water temperature data were taken at the time 

 of sampling, and water temperature was moni- 

 tored throughout the 5-day holding period. Water 

 samples were also taken monthly from July to 

 October 1975. The water was filtered through 

 preashed, preweighed Whatman^ GF-C glass fiber 

 filter paper under 4-5 lb vacuum, after coarse filt- 

 ration through a 2-mm screen. Efford (1966) 

 suggested that E. analoga can handle particles 

 between 5 fxm and 2 mm. The filter paper filtered 

 particles down to approximately 5 fim in size. 

 Thus an approximation of the range of particle 

 sizes utilized by E. analoga was filtered from the 

 water. Filterable solids (grams/liter) were mea- 

 sured in this way from both sites. 



Instantaneous Growth Rate Rationale 



Given that two parameters of crustacean 

 growth, i.e., molt increment and molt frequency, 

 are the factors which need be estimated, a method 

 is required which minimizes handling effects but 

 which still allows observation of size-specific 

 changes in these measures. 



Prolonged impoundment in a laboratory situa- 

 tion tends to affect both the molt increment and 

 molt frequency; however, aspects of the crusta- 

 cean molt cycle provide an advantage if crabs are 

 held in the laboratory for a short period of time. 

 Drach (1939) described the molt cycle of Cancer 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



