Advection And Retention Of Larval Dungeness Crab Cancer Magister In Glacier Bay And Adjacent Areas

Abstract

Spatial and temporal variations of larval abundance of Dungeness crabs were investigated as indications of larval advection and retention in southeastern Alaska. Larvae were collected in five transects: upper Chatham, Icy Strait, Cross Sound, and Icy Point, May to September 1997-2004 and Cape Edward in June 1998-1999. Larval densities were higher in inland water transect and lowest in offshore transects. In all transects, larval densities were highest in June. Zoeae I (ZI) were predominant with a small portion of later larval stages (ZII to ZV) in May. In May and June, late stages (ZIV and ZV) co-occurred with ZI. Later larval hatching in 1997 and 2002 and earlier larval hatching in 1998 may have been related to water temperature during the egg incubation period. Late larval stages that co-occurred with early larval stages can be transported from southern parts of their range where hatching occurs earlier. Mixing, loss, and distribution of larval Dungeness crabs were investigated inside and outside of Glacier Bay, southeastern Alaska, biweekly from late May to mid-September and monthly in Icy Strait from late May to late August in 2004. Larvae were collected from two different portions of the water column: above and below the thermocline and at four stations in Icy Strait. Larval loss was markedly high for ZI, ZIV, and ZV, and relatively low for ZII and ZIII. ZI occurred from late May to late July. Larval stages progressed seasonally from ZI to ZV and density decreased from ZI through ZV. The larval densities at the inner and outer bay stations and at the shallow and deep depths were similar. Co-occurrence of late and early larval stages and larvae with different rostrum lengths may be evidence of mixing of larvae incubated in different thermal regimes. The pattern of larval stages in Alaskan sites was markedly different from other parts of the species range: many of the early and intermediate stages occurred within inland waters, as opposed to increasing abundance of later stages with distance offshore.