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Evidence for resource partitioning and competition 

 in nursery estuaries by juvenile flatfish 

 in Oregon and Washington 



Christopher N. Rooper (contact author) 



Donald R. Gunderson 



David A. Armstrong 



School of Aquatic and Fisheries Sciences 



University ot Washington Box 355020 



Seattle, Washington 98195 



Present address (for C. N Rooper) National Marine Fisheries Service 



Alaska Fisheries Science Center 



7600 Sand Point Way NE 



Seattle, Washington 98115-6349 

 Email address for C N. Rooper: Chris. Rooperfffinoaa gov 



Resource partitioning among co-oc- 

 curring species can provide evidence 

 that density-dependent survival can 

 be a function of interspecific competi- 

 tion. Of the early life history stages of 

 flatfish, the juvenile phase is thought 

 to be the most susceptible to density- 

 dependent mortality, and intraspe- 

 cific competition among individuals 

 is thought to lead to decreased sur- 

 vival of extremely strong year classes 

 (lies and Beverton, 2000). Juveniles 

 of multiple flatfish species are often 

 observed to coexist in a single nurs- 

 ery area (e.g., Burke et al., 1991; Hen- 

 derson and Holmes, 1991; Reichert 

 and van der Veer, 1991; Norcross et 

 al., 1997), but evidence for interspe- 

 cific competition is rarely examined. 

 We examined evidence for resource 

 partitioning and interspecific compe- 

 tition among juvenile flatfish species 

 co-occurring in nursery areas. 



Flatfish species often have juve- 

 nile nursery areas that are segre- 

 gated from the adult population. In 

 many cases, juveniles use shallow 

 nearshore habitats as nursery ar- 

 eas, and adults are found in deeper 

 offshore habitats (Gibson, 1994; van 

 der Veer et al., 2000). On the Pacific 

 coast of North America, estuaries are 

 typically smaller and occur less fre- 

 quently than in other areas such as 

 the Atlantic coast of North America. 

 Possibly because of the limited es- 

 tuarine habitat on the West Coast, 

 fewer species of marine fish and 



invertebrates use coastal estuaries 

 for nursery areas. In our study, we 

 examined the spatial distribution of 

 co-occurring juvenile flatfish popula- 

 tions within Pacific coast estuaries. 

 The four species examined were Eng- 

 lish sole iPleuronectes vetulus). Pacif- 

 ic sanddab (Citharichthys sordidus), 

 sand sole (Psettichthys melanostic- 

 tiis), and starry flounder iPlatichthys 

 stellatus). Juveniles of these species 

 are found in Oregon and Washington 

 estuaries during the summer, and 

 adults of each of these species con- 

 tribute to a lucrative trawl fishery on 

 the coastal shelf. 



To date, estuarine residency of 

 juvenile English sole has been well 

 documented (Krygier and Pearcy, 

 1986; Gunderson et al., 1990; Roop- 

 er et al., 2003); however, this is the 

 first comparison of the spatial dis- 

 tribution of the three other species 

 within estuaries, and is the first 

 study to encompass such a wide 

 region of coastal estuaries (rang- 

 ing over 400 km of coastline). The 

 goal of this study was to compare 

 the summer distribution of juvenile 

 English sole, starry flounder, sand 

 sole, and Pacific sanddab within 

 nursery estuaries over three years, 

 to determine whether the four flat- 

 fish species were spatially partition- 

 ing the nurseries. We also examined 

 the summer distribution in relation 

 to the abundance of species across 

 years and habitats in order to deter- 



mine the potential for interspecific 

 competition. 



Materials and methods 



Study area 



This study was carried out at four 

 estuaries on the Oregon and Wash- 

 ington coasts: Grays Harbor, Wil- 

 lapa Bay, Coos Bay, and Yaquina 

 Bay (Fig. 1). Seventeen to 20 trawl 

 sites were chosen within each estu- 

 ary, and each trawl site was classi- 

 fied into three habitat types: lower 

 main channel, lower side channel and 

 upper estuary. Habitat delineations 

 were previously identified by principle 

 component and discriminant function 

 analysis (Rooper et al., 2003). The 

 lower estuarine sites were on average 

 deeper (depth=5.1 m), colder (13. 6°C), 

 and more saline (28.5 ppt) than upper 

 estuarine sites because of their prox- 

 imity to the mouth of the estuary. On 

 average, lower side channel sites were 

 slightly warmer (15.6°C), shallower 

 (depth = 3.7 m) than the lower estu- 

 arine sites, and had extensive tide 

 flats that surrounded the sites and 

 were exposed during low tides. Upper 

 estuarine sites were typically shallow 

 (depth = 4.0 m), very warm (17.0-C), 

 less saline (25.1 ppt), and had a large 

 sediment size and a smaller area of 

 surrounding tidal flats (Rooper et al., 

 2003). 



Sampling procedures 



Trawl surveys of all four estuaries 

 were conducted in both June and 

 August from 1998 through 2000. In 

 each month all four estuaries were 

 sampled over two and a half weeks 

 and a total of 431 trawl hauls were 

 completed over the three summers. 

 The same sites were resurveyed 

 throughout all years of sampling; 

 however the exact trawl location 

 varied somewhat between sampling 



Manuscript submitted 8 September 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



3 November 2005 by the Scientific Editor. 



Fish. Bull. 104:616-622(2006). 



