648 



Abstract — Data from ichthyoplankton 

 surveys conducted in 1972 and from 

 1977 to 1999 (no data were collected 

 in 1980) by the Alaska Fisheries Sci- 

 ence Center (NOAA, NMFS) in the 

 western Gulf of Alaska were used 

 to examine the timing of spawning, 

 geographic distribution and abun- 

 dance, and the vertical distribution 

 of eggs and larvae of flathead sole 

 iHippoglossoides elassodon). In the 

 western Gulf of Alaska, flathead sole 

 spawning began in early April and 

 peaked from early to mid-May on 

 the continental shelf. It progressed 

 in a southwesterly direction along the 

 Alaska Peninsula where three main 

 areas of flathead sole spawning were 

 indentified: near the Kenai Penin- 

 sula, in Shelikof Strait, and between 

 the Shumagin Islands and Unimak 

 Island. Flathead sole eggs are pelagic, 

 and their depth distribution may be a 

 function of their developmental stage. 

 Data from MOCNESS tows indicated 

 that eggs sink near time of hatching 

 and the larvae rise to the surface to 

 feed. The geographic distribution of 

 larvae followed a pattern similar to 

 the distribution of eggs, only it shifted 

 about one month later. Larval abun- 

 dance peaked from early to mid-June 

 in the southern portion of Shelikof 

 Strait. Biological and environmental 

 factors may help to retain flathead 

 sole larvae on the continental shelf 

 near their juvenile nursery areas. 



Temporal and spatial distribution and abundance 

 of flathead sole iHippoglossoides elassodon) 

 eggs and larvae in the western Gulf of Alaska 



Steven M. Porter 



Alaska Fisheries Science Center 

 7600 Sand Point Way NE 

 Seattle, Washington 98115 

 Email address: steve.porter@noaa gov 



Manuscript submitted 13 September 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 6 April 2005 by the Scientific Editor. 



Fish. Bull. 103:648-658 (2005). 



Flathead sole iHippoglossoides elas- 

 sodon) inhabit the continental shelf 

 waters of the North Pacific Ocean from 

 the northwest coast of North America 

 to the Sea of Okhotsk in Asia (Alder- 

 dice and Forrester. 1974). The west- 

 ern Gulf of Alaska is an important 

 area for adult, juvenile, and larval 

 flathead sole. The continental shelf 

 from the entrance to Prince William 

 Sound to Unimak Island contains the 

 highest relative abundance of adult 

 flathead sole (as expressed as kg/ha) 

 off the west coast of North America 

 (Fig. 1; Wolotira et al. 1 ). Adult flat- 

 head sole are most abundant between 

 depths of 100 and 200 m in this area 

 (Wolotira et al. 1 ). During the spring 

 adult flathead sole move from winter- 

 ing grounds on the upper continental 

 slope onto the continental shelf (Rose, 

 1982). Spawning flathead sole are 

 found from February to August, and 

 the greatest proportion of spawning 

 fish occurs in April and May at depths 

 between 100 and 200 m (Hirschberger 

 and Smith 2 ). Flathead sole eggs 

 range in size from 2.75 to 3.75 mm 

 (Matarese et al., 1989), and under 

 environmental conditions similar to 

 those they could experience in the 

 Gulf of Alaska (temperature = 5.5°C 

 and salinity=31 PSU) it takes them 

 about 15 days to hatch (Alderdice and 

 Forrester, 1974). During the spring, 

 flathead sole are the most abundant 

 pleuronectid larvae in western Gulf 

 of Alaska (Rugen 3 ). Standard length 

 at hatching is 6.89 ±0.40 mm (95% 

 ethanol-preserved size; S. Porter 

 unpubl. data). Under conditions that 

 flathead sole larvae could experience 

 in the Gulf of Alaska, first feeding 

 occurs about 1 week after hatching, 



and in about 2 weeks the yolk is 

 exhausted (Alderdice and Forrester, 

 1974). Copepod nauplii 150-350 fim 

 in size are their predominant prey 

 (Watts, 1988). In Auke Bay, Alaska, 

 flathead sole larvae undertake reverse 

 diel vertical migrations; they are con- 

 centrated near 5 m depth during the 

 day and then disperse over a wider 

 range of depths at night (Haldorson 

 et al., 1993). The bays of the Alaska 

 Peninsula and Kodiak Island provide 

 nursery areas for juvenile flathead 

 sole (Norcross et al., 1999). 



Studies of the drift of walleye pol- 

 lock (Theragra ehalcogramma) larvae 

 in Shelikof Strait have shown that 

 there are physical processes that can 

 slow the drift of these larvae out of 

 Shelikof Strait and keep them near 

 shore (Bailey et al., 1997). The pro- 



1 Wolotira, R. J., T. M. Sample, S. F. Noel, 

 and C. R. Iten. 1993. Geographic and 

 bathymetric distributions for many com- 

 mercially important fishes and shellfishes 

 off the west coast of North America, 

 based on research survey and commer- 

 cial catch data, 1912-84. NOAA Tech. 

 Memo. NMFS-AFSC-6, 184 p. Alaska 

 Fisheries Science Center, 7600 Sand 

 Point Way NE, Seattle, WA 98115. 



2 Hirschberger, W. A., and G. B. Smith. 

 1983. Spawning of twelve groundfish 

 species in the Alaska and Pacific coast 

 regions, 1975-81. NOAA Tech. Memo. 

 NMFS F/NWC-44, 50 p. Northwest and 

 Alaska Fisheries Center, 2725 Montlake 

 Boulevard East, Seattle, WA 98112. 



1 Rugen, W. C. 1990. Spatial and tem- 

 poral distribution of larval fish in the 

 western Gulf of Alaska, with emphasis 

 on the period of peak abundance of wall- 

 eye pollock (Theragra ehalcogramma) 

 larvae. U.S. Dep. Commer., NWAFC 

 Processed Rep. 90-01, 162 p. Alaska 

 Fisheries Science Center, 7600 Sand 

 Point Way NE, Seattle, WA 98115. 



