<strong>Draft</strong> <strong>TRT</strong> <strong>Document</strong> – <strong>for</strong> <strong>Discussion</strong> <strong>Purposes</strong> – OK to circulateThe Puget Sound Steelhead Technical Recovery Team (<strong>TRT</strong>) was established onFebruary 3, 2008.The <strong>TRT</strong> includes:Ed Conner, Seattle City LightBob Hayman, Skagit CooperativeJeff Hard, Northwest Fisheries Science Center, NMFSRobert Kope, Northwest Fisheries Science Center, NMFSGino Luchetti, King CountyAnne R. Marshall, Washington Department of Fish and WildlifeJim Myers, Northwest Fisheries Science Center, NMFSGeorge Pess, Northwest Fisheries Science Center, NMFSBrad Thompson, US Fish and Wildlife ServiceGenetics Contributors:Kenneth I. Warheit, Washington Department of Fish and WildlifeGary Winans, NMFS!Graphics!and!GIS!Mapping!Support:!Damon Holzer, Northwest Fisheries Science Center, NMFSMindi Sheerer, Northwest Fisheries Science Center, NMFS4
<strong>Draft</strong> <strong>TRT</strong> <strong>Document</strong> – <strong>for</strong> <strong>Discussion</strong> <strong>Purposes</strong> – OK to circulateIntroductionOne of the goals of the Puget Sound Steelhead Technical Recovery Team (PSS-<strong>TRT</strong>) is to identify historical demographically independent populations (DIPs) ofsteelhead (Oncorhynchus mykiss) in the Puget Sound Distinct Population Segment (DPS).Firstly, we consider historical population structure because the historical template is theonly known sustainable configuration <strong>for</strong> the DPS. Secondly, we consider demographicpopulations as fundamental biological units and the smallest units <strong>for</strong> viability modeling.For each putative DIP, where possible, we describe the historical abundance andproductivity, life history, phenotypic diversity, and spatial distribution of spawning andrearing groups. Understanding these population characteristics is critical to viabilityanalyses, recovery planning, and conservation assessments. In many cases, thepopulations we identify will be the same as, or similar to, those identified by stateagencies and tribal governments. Washington Department of Fisheries (WDF) et al.(1993) identified steelhead populations in their Salmon and Steelhead Stock Inventory(SASSI) and further refined them in the WDFW (2005) Salmonid Stock Inventory (SaSI)document. Alternatively, differences in population structure may occur as a result ofinherent differences in the criteria used to define populations and the underlyingmanagement purpose of some classification schemes. In the end, there is likely to besome uncertainty in historical populations presented in this document; however, wepresent a reasonable scenario that can then be used as a template <strong>for</strong> establishing asustainable DPS. The populations identified in this document are those considered whenanswering the recovery goal question: “How many and which populations are necessary<strong>for</strong> persistence of the DPS?”Definition of a PopulationThe definition of a population that we apply is defined in the viable salmonidpopulation (VSP) document prepared by the National Marine Fisheries Service (NMFS)<strong>for</strong> use in conservation assessments <strong>for</strong> Pacific salmonids (McElhany et al. 2000). In theVSP context, NMFS defines an independent population much along the lines of Ricker’s(1972) definition of a stock. That is, an independent population is a group of fish of thesame species that spawns in a particular lake or stream (or portion thereof) at a particularseason and which, to a substantial degree, does not interbreed with fish from any othergroup spawning in a different place or in the same place at a different season. For ourpurposes, not interbreeding to a “substantial degree” means that two groups are isolatedto such an extent that exchanges of individuals among the populations do notsubstantially affect the population dynamics or extinction risk of the independentpopulations over a 100-year period (McElhany et al. 2000). The exact level ofreproductive isolation that is required <strong>for</strong> a population to have substantially independentdynamics is not well understood, but some theoretical work suggests that substantialindependence will occur when the proportion of a population that consists of migrants isless than about 10% (Hastings 1993). Thus independent populations are units <strong>for</strong> whichit is biologically meaningful to examine extinction risks that are intrinsic factors, such asdemographic, genetic, or local environmental stochasticity. In general, the conditionsnecessary to maintain demographic independence (isolation) are not as strict as theconditions to maintain reproductive or genetic independence at the population level.5
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