English sole transport during pelagic stages on the Pacific Northwest coast and habitat use by juvenile flatfish in Oregon and Washington estuaries

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English sole transport during pelagic stages on the Pacific Northwest coast and habitat use by juvenile flatfish in Oregon and Washington estuaries

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Title: English sole transport during pelagic stages on the Pacific Northwest coast and habitat use by juvenile flatfish in Oregon and Washington estuaries
Author: Rooper, Christopher Nethercote
Abstract: Trawl surveys of four West Coast estuaries were conducted to determine the spatial and temporal patterns of juvenile English sole residence during 1998--2000. Additional data from 1983--1988 was also analyzed. Juvenile English sole were present in both June and August with densities in the range of 1000--2000 fish*ha-1 across all estuaries.The occurrence of interannual variability in juvenile English sole abundance and the appearance of multiple cohorts in nursery estuaries were addressed by examining transport in the California Current. The larval trajectories for English sole demonstrated that passive larval drift does not account for the patterns in sole distribution in estuaries. In most cases cohorts of English sole larvae were transported north or south off the Oregon-Washington shelf prior to the conclusion of development. However, based on model trajectories, egg stage was carried offshore before hatching in only 6 of 19 cases, and it is suspected that spawn timing occurs during periods of onshore transport to insure that eggs move inshore where they may be retained in local hydrographic features.The relationship of large (TL > 50-mm) and small (TL <50-mm) English sole cohorts to estuarine habitat were also examined. Both small and large cohort English sole utilized lower side channel locations at significantly higher densities than other estuarine areas. Small English sole also showed significant relationships with both bottom temperature and depth. These patterns in habitat use were consistent across all estuaries and indicate that English sole utilized shallow depth areas where temperatures were optimal for growth, and more extensive tidal flats were available. The analysis also indicated a carrying capacity may exist for large English sole in nursery estuaries.The distribution of additional flatfish species was analyzed to examine spatial partitioning of nursery estuaries. The analysis of density anomalies indicated that the four flatfish species were exploiting different sections of each estuary. Densities of sanddab and sand sole were higher in lower main channel sites close to the estuary mouth, that were more oceanic than other parts of the estuary, while starry flounder were more common in the upper sections of the estuary where salinity was typically lower and temperature warmer.
Description: Thesis (Ph. D.)--University of Washington, 2002
URI: http://hdl.handle.net/1773/5378

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