Mondragon, J., S. J. Taggart, A. G. Andrews, J. K. Nielsen, and J. de ...

Jennifer Mondragon and others 85MethodsIn July and August 2002, the relative abundance ofTanner and red king crabs was estimated by systematicallysampling 415 stations throughout Glacier Bay. Crabs werecollected using conical, top-loading, commercial Tanner crabpots. To target juvenile and female crabs, a commercial shrimppot was attached to each of the conical Tanner crab pots witha 20 m tether. A U.S. Geological Survey research vessel, theUSGS R/V Alaskan Gyre, was used to deploy and retrieve crabpots. Sixteen pots were set each afternoon and pulled the nextmorning after a soak time of 15 to 20 hours. As the pots wereretrieved, we counted and identified all organisms to species.Carapace sizes, width for Tanner crabs, and length for kingcrabs, were measured to the nearest millimeter with verniercalipers.Results and DiscussionTanner crabs were widely distributed throughout GlacierBay, and 69 percent of the pots captured at least one crab. Theonly area where crabs were consistently not captured was themain channel of the lower Bay, between Willoughby Islandand the mouth of the Bay (fig. 1). The absence of Tannercrabs in this area suggests poor habitat for this species. Theexistence of a habitat barrier could restrict movement ofTanner crabs between Glacier Bay and Icy Strait. If this is thecase, the Tanner crab population in the Bay may be dependenton larval flux for connectivity between the larger crabmetapopulations in southeastern Alaska.Densities of Tanner crabs were not significantly differentbetween the reserve network and the area open to commercialfishing in the central Bay (fig. 2). However, densities ofadults and juvenile Tanner crabs varied among reserves; theaverage catch of adults was higher in the East Arm, GeikieInlet, Scidmore-Charpentier Inlet, and the central Bay thanthe other two reserves (fig. 2). The higher density of juvenilecrabs in the reserves was due to their high concentrations inWachusett Inlet and the distal ends of Scidmore-CharpentierInlet, both narrow glacial fjords (fig. 1). These areas possiblyrepresent nursery areas for Tanner crabs. If so, their inclusionin the marine reserves is particularly important for long-termeffectiveness.In contrast to the widespread distribution of Tanner crabs,red king crabs were highly aggregated; 73 percent of the kingcrabs were captured in seven adjacent stations near the mouthof the East Arm reserve (fig. 1). These data indicate thatdesign of an effective marine reserve for red king crab willrequire detailed sampling to delineate patches of high density.Conclusions and Management ImplicationsOur data show that reserves in close proximity havevery different abundances of king and Tanner crabs; not allreserves are created equal. This study demonstrates the valueof systematic sampling for marine reserve design and location.The ongoing marine reserve research in Glacier Bay willprovide valuable information to managers, scientists, and thepublic to evaluate the utility of reserves as a management toolfor solving local, national, and global marine conservationissues.Average CPUEAdult Tanner CrabAverage CPUEJuv. Tanner Crab2015105086420p=0.065p