Original article Linkages between life history type and migration pathways in freshwater and marine environments for Chinook salmon, Oncorhynchus tshawytscha Rishi Sharma a, * , Thomas P. Quinn b a Quantitative Ecology and Resource Management, University of Washington, Seattle, WA 98195, USA b School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98195, USA article info Article history: Received 14 July 2011 Accepted 23 March 2012 Available online 28 April 2012 Keywords: Life history Migration Evolution Chinook salmon Conservation Fishing abstract Chinook salmon, Oncorhynchus tshawytscha, are commonly categorized as ocean-type (migrating to the ocean in their first year of life) or stream-type (migrating after a full year in freshwater). These two forms have been hypothesized to display different ocean migration pathways; the former are hypothesized to migrate primarily on the continental shelf whereas the latter are hypothesized to migrate off the shelf to the open ocean. These differences in migration patterns have important implications for management, as fishing mortality rates are strongly influenced by ocean migration. Ocean-type Chinook salmon predominate in coastal rivers in the southern part of the species’ range, whereas stream-type predominate in the interior and northerly rivers. This latitudinal gradient has confounded previous efforts to test the hypothesis regarding ocean migration pathways. To address this problem, we used a pair-wise design based on coded wire tagging data to compare the marine distributions of stream- and ocean-type Chinook salmon from a suite of rivers producing both forms. Both forms of Chinook salmon from the lower Columbia River, Oregon coast, lower Fraser River, and northern British Columbia rivers followed similar migration paths, contradicting the hypothesis. In contrast, recoveries of tagged Chinook salmon from the upper Columbia River, Snake River, and the upper Fraser River revealed migration patterns consistent with the hypothesis. These findings have important implications for our under- standing of these life history types, and also for the conservation and management of declining, threatened, or endangered stream-type Chinook salmon populations in the US and Canada. Ó 2012 Elsevier Masson SAS. All rights reserved. 1. Introduction The conservation of migratory animals depends on maintaining quality habitat and minimizing exploitation in each of the regions that they occupy, and passage between all necessary habitats. Migrations represent complex combinations of evolved and plastic responses to environmental conditions (Swingland and Greenwood, 1984; Dingle, 1996), complicating our understanding of the phenomenon. The world’s fisheries predominately exploit migratory species, so temporal and spatial distribution patterns are critical for conservation (Jennings et al., 2001). For anadromous fishes, the great majority of total growth is achieved at sea after having left less productive freshwater environments (Gross, 1987; McDowall, 1988). There are complex linkages between the life history patterns in these two environments, including the size, age, and timing of seaward migration, the duration of marine residence, and the size and timing of return migration (Quinn et al., 2009). Upon entering marine waters, juveniles can occupy a wide range of estuarine, nearshore, shelf, and open ocean habitats. Among the species of Pacific salmon and trout (Oncorhynchus, the best studied group), there is considerable variation in the spatial extent and duration of marine migrations (Quinn and Myers, 2004). Perhaps the most complex combination of life history and migration patterns is exhibited by Chinook salmon, Oncorhynchus tshawytscha. Towards the southern end of their range, and espe- cially in low elevations, juveniles typically migrate to sea in their first spring or summer of life. These were termed “sea-type” by Gilbert (1913) on the basis of scale pattern analysis. More recently, these Chinook salmon have been referred to as ocean-type, and this pattern is associated with relatively early emergence and rapid growth in freshwater (reviewed by Taylor, 1990a, 1990b; Healey, 1991). In higher elevations within the southern part of the range, and in all cases in the northern part of the range, Chinook salmon spend a full year in freshwater before migrating to sea at a larger size, as “stream-type” fish. Populations north of about 56  N latitude are virtually all dominated by or exclusively stream-type * Corresponding author. Present address: CRITFC, Suite 200, 729 NE Oregon St., Portland, OR 97232, USA. E-mail address: shar@critfc.org (R. Sharma). Contents lists available at SciVerse ScienceDirect Acta Oecologica journal homepage: www.elsevier.com/locate/actoec 1146-609X/$ e see front matter Ó 2012 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.actao.2012.03.002 Acta Oecologica 41 (2012) 1e13