Distribution of red king crabs and Tanner crabs in the summer by habitat and depth in an Alaskan fjord

Abstract

A manned submersible was used in a fjord in southeastern Alaska to study the distributional patterns of the red king crab (Paralithodes camtschaticus) and the Tanner crab (Chionoecetes bairdi) in summer. The cove was divided into three zones: inner, middle, and outer. Six types of habitats, including sand-mud, rock, shell, debris, rock wall, and algae, were identified from video tapes. A relatively flat sand-mud habitat located at the center of the cove occupied 60% of the sea bottom. This large habitat was bordered by steep rocky walls on both sides in most parts of the fjord except in the inner zone. The density of red king crab decreased from the inner zone to the outer zone, while the density of the Tanner crab was more uniform throughout the cove. Highest crab density was found in the sand-mud habitat with an overall density of 51 crabs ha -1 for the red king crab and 41 crabs ha -1 for the Tanner crab. No crabs were found in rock wall and algae habitats. Both crab species displayed a dome-shaped distribution with depth with maximum density at intermediate depths. Red king crabs had a maximum density (86 crabs ha -1 ) at 70-80 m while the maximum density of Tanner crabs (105 crabs ha -1 ) was at 140-150 m of depth. Dense aggregations of juvenile red king crabs were observed in the inner cover, but no aggregations of mature red king and Tanner crabs were observed.