Porter: Temporal and spatial distribution and abundance of eggs and larvae of Hippoglossoides elassodon 



657 



Some species of flatfish spawn offshore (e.g., ar- 

 rowtooth flounder and Pacific halibut, Bailey and Pic- 

 quelle, 2002), but the present study has shown that 

 flathead sole spawn on the continental shelf. Flathead 

 sole nursery areas have been found to be in the bays 

 of the Alaska Peninsula and Kodiak Island (Norcross 

 et al., 1999), and it is crucial that the larvae remain 

 on the shelf near their nursery areas. Changes in egg 

 density may be a mechanism for retaining flathead sole 

 larvae on the shelf. For arrowtooth flounder and Pacif- 

 ic halibut larvae in the western Gulf of Alaska, it has 

 been suggested that deep water currents (100-400 m 

 depth in sea valleys and in troughs in the continental 

 shelf) transport these larvae from the offshore areas 

 where they hatch to their nearshore nurseries (Bai- 

 ley and Picquelle, 2002). By sinking when they are 

 nearing hatching, flathead sole eggs that have drifted 

 southwesterly (i.e. away from nursery areas) with the 

 surface currents can be brought back (along with newly 

 hatched larvae) toward inshore juvenile nursery areas. 

 Alternatively, the act of sinking as they near hatching 

 may be a way for newly hatched larvae to avoid preda- 

 tion by keeping them out of the surface waters where 

 they are likely to encounter predators. The physical 

 environmental conditions of Shelikof Strait may also 

 serve to retain flathead sole larvae on the shelf. In 

 May 1994 when the Alaska Coastal Current flow was 

 strong and to the southwest, larvae drifted southward 

 but remained on the continental shelf. In May 1996 

 when the flow was weak, disorganized, and moving 

 somewhat to the northeast, the larvae remained at vir- 

 tually the same location for the entire month because 

 surface current flow in Shelikof Strait was weakened 

 and reversed because of anomalous atmospheric con- 



ditions. Under both flow regimes larvae remained on 

 the continental shelf in southern Shelikof Strait. Ed- 

 dies may also be an important retention mechanism 

 for flathead sole larvae because entrainment in one 

 of these could slow drift. Under typical conditions in 

 Shelikof Strait (i.e., strong southwesterly current flow), 

 eddies frequently occur and they drift slower than 

 the water surrounding them (Kendall et al., 1996). 

 They can also remain nearly stationary for two weeks 

 (Schumacher et al., 1993). Both biological and environ- 

 mental factors may work together to retain flathead 

 sole larvae on the continental shelf and keep them 

 near their nursery areas. 



Acknowledgments 



I would like to thank Debbie Blood and Angie Lind 

 for determining developmental stages of flathead sole 

 eggs, and Susan Picquelle for assistance with egg 

 and larval distribution charts. Kevin Bailey and Jeff 

 Napp provided helpful comments on an early draft of 

 this manuscript. Two anonymous reviewers offered 

 improvements. This research is contribution FOCI- 

 0475 to NOAA's Fisheries-Oceanography Coordinated 

 Investigations. 



Literature cited 



Alderdice, D. R, and C. R. Forrester. 



1974. Early development and distribution of the flathead 

 sole (Hippoglossoides elassodon). J. Fish. Res. Board 

 Can. 31:1899-1918. 



