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Fishery Bulletin 104(4) 



Bight, diamond turbot {Hypsopsetta guttulata) settle in 

 the upper portions of bays during January and March, 

 whereas California halibut (Paralichthys californicus) 

 are found closer to bay entrances and the open coast, 

 settling from March to September (Kramer, 1991). Set- 

 tlement timing has also been found to be an important 

 partitioning factor for common dab (Limanda limanda) 

 and plaice (Pleuronectes platessa) in a small Scottish 

 bay, where plaice settle earlier in the year than dab 

 (Steele and Edwards, 1970). Depth has been identified 

 as an important factor in partitioning nursery areas 

 for the common dab and age-0 plaice (Edwards and 

 Steele, 1968; Gibson, 1973). Juvenile flatfish in Alaskan 

 inlets have also been found to segregate with depth and 

 a number of other factors, such as temperature and 

 sediment type (Norcross et al., 1997). Habitat type has 

 also been found important in determining the spatial 

 segregation of northeast Atlantic flatfish assemblages; 

 ontogenetic shifts in habitat use occur in some species 

 (Walsh et al., 1999; Phelan et al., 2001). 



These studies indicate that flatfish species that ex- 

 ist together in nursery areas can partition resources 

 in a number of ways according to biological (i.e., diet) 

 or physical (i.e., depth or salinity) requirements, or ac- 

 cording to a combination of both biological and physical 

 requirements. Studies of shallow water habitats have 

 generally indicated that flatfish in nursery areas are not 

 limited by food resources (Evans, 1983). In west coast 



estuaries food resources can be quite high, especially 

 in intertidal areas (Gunderson et al., 1990; Dumbauld 

 et al., 2000). After review of diet studies documenting 

 feeding differences among Pacific sanddab and English 

 sole (Hogue and Carey, 1982; Thornburgh, 1980), as 

 well as the abundance of food within the nursery area, 

 we do believe it is unlikely that direct competition for 

 food is solely responsible for the apparent pattern in 

 estuarine distributions between the two species. We 

 suggest that the segregation observed in northwest es- 

 tuaries is most likely caused by differences in physical 

 conditions of the habitat. 



The four species of flatfish observed in the present 

 study probably partition the nursery estuaries along 

 gradients of salinity and temperature. Starry flounder 

 were found in upper reaches of the estuary to a greater 

 degree than the other species — a finding that is consis- 

 tent with their ability to tolerate low salinity (Orcutt, 

 1950). Starry flounder were most abundant in Yaquina 

 Bay, where the coverage of trawl survey sites extended 

 farther up the estuarine salinity gradient than in other 

 estuaries. The average salinity in June was 16-18 ppt 

 at the uppermost Yaquina Bay sites, whereas the aver- 

 age June salinity at sites in other estuaries was always 

 greater than 19 ppt. Salinity has been found to be an 

 important determinant of the distribution of other flat- 

 fish species (Coggan and Dando, 1988; Marchand, 1988; 

 Kerstan. 1991; Gibson, 1994; Marshall and ElHot, 1998). 



