Effects of habitat complexity and relative larval supply on the establishment of early benthic phase red king crab (Paralithodes camtschaticus Tilesius, 1815) populations in Auke Bay, Alaska

Abstract

Between September 1996 and May 1998, the influence of habitat complexity and larval supply on the establishment of early post-settlement populations of red king crab (Paralithodes camtschaticus) was studied in situ in Auke Bay, southeast Alaska. Dive transects and suction dredge surveys conducted during fall 1996 and spring 1998 indicated that late age 0 to 1+ red king crabs were located only in the most complex habitat. This pattern was similar to patterns observed for early age 0 crabs, using settlement pails, during the summer of 1997. Early instars recruited into settlement pails containing ambient sediment at both the rocky cobble and shell-hash sites, but no settlement could be detected in muddy habitat. Population density of benthic age 0+ crab peaked in mid-July, then dropped throughout the summer, and greater densities were always observed in rocky cobble than in shell-hash. Simultaneous use of passive larval collectors ruled out the possibility that these patterns were simply a reflection of larval supply. Rather, the highest levels of larval supply were associated with the muddy site at which no settlement could be detected. The availability of complex habitat, defined simply as substrate rich in available crevice space that is scaled to the body size of the crab instars, appeared to be the primary determinant of the value of nursery habitat, and it is likely to be the critical factor determining early post-settlement survivorship within the population. Such considerations are vital to management of red king crab fisheries where complex nursery habitat is likely to be relatively rare and where conflicts with trawl fisheries and other anthropogenic disturbances to bottom habitat are a potential concern.