temperatures, but this corresponded with the low- 

 est tides in June, which occurred at midday; on 

 days with high winds there were few crabbers. 

 This was probably due to a lowered chance of suc- 

 cess because waves on the beach made crabs 

 difficult to see. 



The estimated use of the beach by crabbers cor- 

 responded with the daily availability of crabs on 

 the beach that I observed by sample crabbing. This 

 availability appeared to be affected by current and 

 tide height. Two hours before low tide, the water 

 level over the eelgrass portion of the beach, where 

 most crabs were found, was generally >1 m. As the 

 tide went out and the water became shallower, I 

 observed few crabs in water <0.15 m deep. The 

 current also appeared to have effects. When the 

 tide approached its lowest level, the current be- 

 came slack, at which time I observed few crabs. 

 Even on days when a large number of crabs were 

 active an hour before the low, few would be evident 

 at low slack. 



The monthly use curves enabled me to take a 

 single aerial survey count of crabbers using a sur- 

 veyed beach at any time during the low tide period 

 and predict the total crabber use at the beach 

 during the entire low tide period. 



I adjusted the total calculated Puget Sound 

 beach use by crabbers during the 1974 aerial sur- 

 veys by two factors: the number of crabbers 

 excluded because beaches were not surveyed and 

 the improper identification of people as crabbers 

 who were not actually crabbing. Between 1969 

 and 1973, at least one aerial survey at low tide was 

 conducted over every Puget Sound beach, and all 

 important crabbing beaches were identified. From 

 this data I estimated that the 1974 aerial surveys 

 included 959( of the crabbers and other recreation- 

 ists on the beaches at any given low tide. At the 

 same time 1974 aerial surveys were made over 

 Mission Beach, I made actual counts of crabbers on 

 the beach. The average overcount of crabbers by 

 the aerial survey was 15.5%. 



Total Puget Sound intertidal crabber use for all 

 low tides from April through August was roughly 

 estimated by dividing the total Mission Beach 

 counts on the days of the aerial surveys, April 

 through July, by the adjusted total Puget Sound 

 beach count. The quotient was designated as the 

 percentage of Mission Beach use relative to the 

 adjusted total beach count (Table 3). Due to poor 

 visibility on the day scheduled, no aerial survey 

 was conducted in August, so I used averaged data 

 from the preceding 4 mo. I estimated the total 

 crabber use on all beaches for each month by divid- 

 ing the percentage Mission Beach use of the total 

 adjusted beach count into the total crabber use of 

 Mission Beach for each month. 



In order to estimate the total crabs caught in 

 Puget Sound by intertidal sport crabbers, I needed 

 to know whether the average catch over a low tide 

 period at other Puget Sound beaches was the same 

 as that at Mission Beach. Six other beaches in 

 Puget Sound that had different levels of crabber 

 utilization were sampled on a random basis by 

 personnel from the Washington Department of 

 Fisheries. Their levels of crabber use ranged from 

 a few to 70 crabbers per tide. Four of the six 

 beaches had three or more surveys, and these were 

 compared with Mission Beach by Wilcoxon Rank 

 Sum Tests (Hollander and Wolfe 1973). The four 

 beaches had W values of 13.5, 9.5, 46.5. and 106, 

 which in all cases were greater than the computed 

 values of 6, 6, 39, and 66. Thus the null hypothesis 

 that there were equal catches per crabber at the 

 different beaches could not be rejected. This im- 

 plies that the number of crabbers at a beach is 

 self-regulating in that crabbers tend to adjust 

 their level of effort to the rate of return, and that 

 rates of return for all crabbers at different beaches 

 remains fairly constant. 



This same pattern of utilization was observed in 

 the recreational trout fisheries in California lakes, 

 where the angling effort adjusted proportionally 

 to the numbers of catchable-size trout (Butler and 



Table 3.— Estimate of the total monthly crabber use in the intertidal Dungeness crab sport fishery for Puget Sound beaches, 



April-August 1974. 



'Average of four previous rnonths 



290 



