EXPERIMENTAL DESIGN 



While one of our objectives was to learn whether king 

 crab could escape from various styles of pots, we also 

 wanted to estimate the effect of confinement or possible 

 injury during escape on crab viability. Tagged undersize 

 king crab (120-139 mm eye socket to posterior margin of 

 the carapace) and legal-size king crab (150-169 mm long) 

 were placed in pots and returned to the sea floor. Follow- 

 ing a predetermined "soak" (period on the bottom) of up 

 to 16 days, pwts were recovered to identify those crab 

 remaining, including those alive or dead, and new untag- 

 ged king crab that entered the pots during the soak. Tag- 

 ged king crab were also released from the vessel into 

 Chiniak Bay (free-release) to permit observation of any 

 difference in returns between 1) those confined to pots 

 until their escape and 2) crab subjected only to the tag- 

 ging process. Four factors — escape, mortality, new 

 entries, and tag returns — were then compared with 

 length of soak. Since each factor might be influenced by 

 pot design, we selected styles in use by Kodiak area 

 fishermen. 



Results of preliminary experiments conducted in 1974 

 prompted us to expand the study during 1975 to include 

 escape £md recovery data from other styles of pots. We 

 also wanted to learn whether presence of bait (chopped 

 herring in bait containers) or dead king crab influenced 

 the entry or escape rate. 



As a further estimate of effects upon viability caused 

 by confinement, some tagged crab, remaining in study 

 pots that had been soaked for 10-16 days, were released 

 at the surface from recovered pots to observe their recov- 

 ery rate — compared with crab that had escaped during 

 the soak. 



MATERIALS AND METHODS 



Many styles of king crab pots are used in the Alaska 

 fishery regularly as well as experimentally by fishermen 

 and researchers. 



Description of Pots 



The principal types of commercial crab pots were 

 tested to determine whether size, shape, or tunnel con- 

 figuration might affect crab escapement. Whenever pos- 

 sible, gear and handling techniques were those used in 

 the commercial fishery so that derelict pot conditions 

 would be simulated. 



Most pots were box-shaped (Fig. 2A). Pot dimensions 

 were 183-213 cm (6-7 ft) square and 76-99 cm (30-39 in) 

 high. Weight varied between about 182 and 318 kg (400 

 and 700 lb) each, depending upon the size and amount of 

 steel used. Tunnel entrance frames varied from 89 by 19 

 cm (35 by Vh in) to 102 by 20 cm (40 by 8 in). Several 

 mesh sizes between 10 and 20 cm (4 and 8 in) were used 

 on various pots. 



The nesting pyramid-shaped pot had a steel-framed 

 base 203 cm (80 in) square with a top frame 122 cm (48 



in) square, 61 cm (24 in) above the base (Fig. 2B). The 

 frame was enclosed with 15-cm (6-in) mesh except for the 

 fiberglass top and circular tunnel which provided a 43- 

 cm (17-in) diameter entrance. This style pot is mostly 

 used by small vessels having limited deck storage. Seven 

 of these pots occupy a space 203 cm (80 in) square by 157 

 cm (62 in) high. 



Ray Spagnola, master of the MV Tammy hired to fish 

 the study pots, had some custom-made nesting pyramid 

 pots which we designated as "radical pyramid pots" 

 (Fig. 2C). This pot's dimensions were 213 cm (84 in) 

 square at the base with a 122 cm (48 in) upper square 

 frame. Vertical height was 86 cm (34 in) . The tunnel con- 

 sisted of a web-covered steel frame angled 29 cm (11 'A 

 in) down into the pot. Extra framing for a dumping door 

 on one side caused the pots to be unbalanced. Part way 

 through the experiment, counterweights were placed op- 

 posite the door. 



Small, light-weight nesting conical pots, of the type 

 used by Japanese fishermen for snow crab in the Bering 

 Sea, were recently entered into use in the Kodiak area 

 king crab fishery aboard small boats (Fig. 2D). These 

 conical pots were 152 cm (60 in) in diameter at the base, 

 tapering to 81 cm (32 in) at a height of 69 cm (27 in). A 

 23-cm (9-in) long tapered plastic collar diminishing from 

 53 cm (21 in) at the top to 41 cm (16'/4 in) at the orifice 

 served as a tunnel. They were designed to be fished at in- 

 tervals along a groundline, in contrast to heavy king crab 

 pots which are fished individually from a buoyline. 



Selecting, Handling, and Tagging Crab 



Two sizes of king crab were selected, smaller than and 

 larger than minimum commercial size of about 145 mm 

 carapace length. Five female crab were included in the 

 1974 experiments, but the shells of most were too fragile 

 to withstand the handling associated with tagging and 

 return to pots. Consequently, females were excluded dur- 

 ing 1975. 



Crab for the experiments were captured in pots usually 

 soaked 1-2 days in Chiniak Bay. Fishing depth ranged 

 about 70-164 m (38-90 fathoms). The vessel moved the 

 fishing gear within the central Chiniak Bay area to in- 

 crease catch of crab in the desired size rcmges and to re- 

 main near test pots ab-eady concentrated in one area. 



Crab were inspected and metisured after removal from 

 fishing pots; rejected crab were immediately returned to 

 the sea. A carapace dart tag was placed through the dor- 

 sal shell on the posterior left side (Powell 1964). Ini- 

 tially, a hole was punched through the shell to accom- 

 modate the nylon tag barb. The barb was then pushed 

 through the shell hole to hold in place a colored plastic 

 disk bearing a serial number and legend. Tagging was 

 rapid, and tagged crab usually remained on deck less 

 than 30 min before the filled test pot was set. 



Test pots were balanced on the vessel rail, when filled 

 with tagged crab, so they could be pushed over even 

 though heavily weighted. Occasionally a crab was in- 

 jured when one or more of its legs protruded through the 

 meshes and were crushed between the pot frame and 



