934 



Fishery Bulletin 101(4) 



3830' 



Figure 1 



Study area and sampling locations. Symbols indicate type 

 and location of strata. Day and night tows were made at each 

 location. 



A grid was considered nontrough if no trough long axis 

 passed through it. Each grid was therefore assigned to one 

 of the four strata. Twelve grids were randomly selected in 

 each stratum, for a total of 48 unique sampling locations. 

 The fishermen also stated that time of day influenced 

 horseshoe crab catchability (Burke^; Eutsler"*; Munson^). 

 Therefore, grids were sampled both in daylight and at 

 night. The second tow in a grid (day or night) was made 

 near the location of the first to reduce location variability, 

 but slightly offset to avoid possible influence of the first 

 tow on the catch of the second. The second tow was also 

 made more than 24 hours after the first to avoid interac- 

 tions, but no more than four days later, to avoid introducing 

 other unknown variability Abundance estimates from the 

 daytime and nighttime samples were calculated separately 

 for comparison. 



Our study was conducted in the fall, between 10 Sep- 

 tember and 16 October 2001. The stock assessment model 

 adopted by the ASMFC requires abundance information on 

 newly mature crabs, and identification requires that crabs 

 have undergone a terminal molt. Crabs reportedly molt in 

 the late summer and fall in the Delaware Bay area (Burke^; 

 Eutsler"*; Munson-''). 



Sampling was conducted from a chartered 16.8-meter 

 commercial fishing vessel. For capturing horseshoe crabs, 

 commercial fishermen typically use a flounder trawl 

 equipped with a Texas sweep (Burke'^; Eutsler'*; Munson^; 

 Michels''). This modified sweep consists of a chain line in- 



^ Michels, S. 2001. Personal commun. Delaware Department 

 of Natural Resources and Environmental Control, Division of 

 Fish and Wildlife, 89 Kings Hwy, P.O. Box 1401, Dover, DE 19901. 



