The Ecology of Pacific herring (Clupea pallasii) and Spiny dogfish (Squalus acanthias) in Puget Sound, Washington

Puget Sound is an ecologically diverse and economically important estuary on the U.S. west coast that has been extensively urbanized over the last 150 years. To slow and reverse signs of ecological degradation, policy makers and resource managers have implemented a growing number of restoration measures and have called for an ecosystem-based approach to management. This dissertation aids these efforts by addressing knowledge gaps in the ecology of two abundant species in the Puget Sound food web: Pacific herring ( Clupea pallasii) and Spiny dogfish (Squalus acanthias). In Chapter One and Two, I evaluated the effects of variation in environmental conditions on the abundance and growth rates of young-of-the-year Pacific herring, respectively, from the Skagit River estuary. Interannual variation in abundance was positively correlated with an index of upwelling-favorable winds and uncorrelated with river flow or regional sea surface temperatures. Herring body size during the first half of the growing season was positively related to temperature during the egg / larval stages, but by late summer growth was density-dependent and may have been mediated by a density-dependent distribution shift into prey-poor waters during periods of high abundance. In Chapter Three, I examined interannual variation in the age and size composition of Pacific herring spawners from three stocks located in northern, central, and southern Puget Sound. The mean age and size of herring in all three stocks have declined over the past two decades. Finally, in Chapter Four I examined intrapopulation variation in the trophic ecology of Spiny dogfish using delta 15N and delta13C sampled in both muscle and liver tissues. I found that similarities in delta15N and delta 13C of individuals sampled in the same tow exceeded between-tow differences among individuals and that body size, sex and sampling period had little influence on the isotopic ratios. This pattern suggests that dogfish either aggregate in large schools for several months or that dogfish forage over a limited spatial range. The results of these studies offer new insights into the ecology of Pacific herring and Spiny dogfish and highlight the need for additional basic research on the biota of Puget Sound.