412 



Fishery Bulletin 98(2) 



Scale in miles 

 10 la IS 



Chesapeake 

 Bay 



Figure 1 



Map of Chesapeake Bay with positions of the dredge efficiency experiments conducted 

 between November 1992 and March 1995. 



of area swept by a standard tow (see Pennington 

 and Volstad, 1994). As a result, sampling individu- 

 als randomly from the target population generally 

 is not feasible. The possible dependence of animal 

 capture probability on environmental conditions, or 

 on the characteristics of individual animals, such as 

 body size, is another important practical problem. 



In our study we assumed that each crab has an 

 equal probability of being caught by the dredge within 



each experimental area. The catching efficiency of 

 the dredge, however, may vary significantly between 

 experimental sites because of different bottom topo- 

 graphy and sediment types. The possible effect of 

 body size on catching efficiency was evaluated by 

 comparing mean carapace width and size-frequency 

 distributions between removals. Assume, for exam- 

 ple, that large crabs have a higher probability of 

 capture than small crabs. In this case the mean cara- 



