COMPARISON OF SAMPLING DEVICES FOR 



THE JUVENILE BLUE CRAB, 



CALLINECTES SAPIDUS^ 



The behavior of the blue crab, Callinectes sapidus 

 Rathbun, in the Chesapeake Bay varies consider- 

 ably with age, temperature, and molting cycle. 

 These behavioral differences make efforts difficult 

 to sample effectively the population densities in 

 the Chesapeake Bay and its tributaries. No single 

 gear type appears to sample effectively the blue 

 crab during winter and summer at all depths and 

 types of bottom. During winter blue crabs burrow 

 in the mud in the deeper channels of Chesapeake 

 Bay (Churchill 1917). This pattern is the basis for 

 an active winter dredge fishery in the lower 

 portion of the bay (Van Engel 1962). During a 3-yr 

 survey of blue crabs, Lippson^ found that juveniles 

 were also present in deeper waters in winter. 

 Comparative effectiveness of two dredges for 

 winter sampling of juvenile and adult blue crabs 

 was reported by Sulkin and Miller (1975). 



Blue crabs move about in relatively shallow 

 water in warm weather presumably because of the 

 abundance of food here and for protection among 

 submerged aquatics while in the soft shell 

 condition. During the summer 7.3 m otter trawls 

 have been found to be an effective gear to sample 

 the adult population of blue crabs (Lippson see 

 footnote 2). The otter trawl, with a small stretch 

 mesh (0.6 cm) liner in the cod end, is also effective 

 for catching juveniles in deeper water; however, 

 juveniles spend much of their time in shallow 

 waters during the warmer months. The push net 

 (Figure 1), beach seine, and small otter trawls 

 have all been used with some degree of success in 

 this shallow region. 



It is the purpose of this study to compare the 

 effectiveness of the push net, otter trawl, and crab 

 scrape (Figure 2) in catching juvenile blue crabs in 

 shallow water. 



Methods and Results 



Smith Island in the Chesapeake Bay has 

 extensive grassy (Zostera marina) beds which are 

 ideal habitats for juvenile crabs (Stevenson and 

 Confer 1978). This region was chosen to compare 



'Contribution No. 992HPEL from the Center for Environmen- 

 tal and Estuarine Studies, University of Maryland. 



^Lippson, R. L. 1969. Blue crab study in Chesapeake 

 Bay-Maryland. Nat. Resour. Inst. Q. Prog. Rep. 3, Ref No 

 69-33B:l-13. 



the catch effectiveness among a 3.7 m otter trawl, 

 81.3 cm push net, and a 96.5 cm modified crab 

 scrape during summer 1975. 



The otter trawl opened to a working width of 3.6 

 m. The gear was towed by the RV Chelae in depths 

 of 1-2 m for 0.7 km. The cod end was lined with 0.6 

 cm stretch mesh netting. The trawl door size was 

 30.5 cm X 61.0 cm and the length of the bridle was 

 45.7 m. 



The push net had a steel frame 81.3 cm wide and 

 60.9 cm high fitted with a 0.6 cm stretch mesh bag. 

 The leading edge had a 7 .6 cm diameter pipe which 



Figure l. — Push net used for blue crab fishing with the roller 

 bar on the leading edge. 



196 



FISHERY BULLETIN: VOL. 78, NO. 1, 1980. 



