Movements of sub-adult Chinook salmon, Oncorhynchus tshawytscha, in Puget Sound, Washington, as indicated by ultrasonic tracking

Salmonids show a wide variety of migration patterns. Such variation is especially prevalent in Chinook salmon, Oncorhynchus tshawytscha. This species migrates to coastal and open ocean waters, and the tendency to use these different marine environments varies markedly among populations. For example, some Chinook salmon that enter Puget Sound do not migrate to the sea as juveniles in their first year but rather remain as “residents” through (at least) the following Spring. Known locally as blackmouth, these fish are the focus of extensive sport fisheries. In this study, we used acoustic telemetry to examine questions surrounding resident Chinook salmon in Puget Sound. The overall objective of this study was to determine the extent to resident and migratory behavior patterns are distinct or ends of a continuum of movement patterns, and then characterize the movements of resident fish. We first assessed the proportion of fish, caught and tagged as immature residents (inferred from the locations and dates of capture), that remained within Puget Sound and the proportion that moved to the coastal region, and tested the hypotheses that origin (wild or hatchery), location and season of tagging, fish size and condition factor would influence the tendency to remain resident. Second, we characterized the movements by resident fish with Puget Sound at a series of different spatial scales: movement among the major basins, travel rates, and areas of concentration within Puget Sound. Third, we tested the model of seasonal north-south movement patterns by examining the distribution of detections over the whole area and year. Because residents represent a significant portion of the Puget Sound Chinook salmon Evolutionarily Significant Unit, currently listed as Threatened under the U. S. Endangered Species Act, better understanding of their movements in Puget Sound will help identify critical habitat use patterns and evaluate fishery management objectives as the species crosses jurisdictional boundaries

Segmented Regression Analysis Results: Puget Sound Scale.

<p>Model coefficients (a_<i>1</i>, <i>b</i>_<i>1</i>, and <i>b</i>_<i>2</i>), standard errors (SE), breakpoints, and <i>R</i>² values resulting from fitting segmented regression models to time series of developed land cover in six habitat areas, at the Puget Sound scale.</p><p>^a<i>b</i>_<i>1</i> represents the slope for the first part of the time series (1986-breakpoint year) in ha/year.</p><p>^b<i>b</i>_<i>2</i> represents the slope for the second part of the time series (breakpoint year-2008) in ha/year.</p><p>Segmented Regression Analysis Results: Puget Sound Scale.</p

Akaike’s Information Criterion for Simple and Segmented Regression Analyses: Puget Sound Scale.

<p>Akaike’s Information Criterion corrected for small sample sizes (AICc), calculated for two regression models (simple and segmented) in six habitat areas, at the Puget Sound scale. The difference in AICc (where Δ AICc = simple AICc—segmented AICc) is also provided.</p><p>^a Δ AICc >4 indicates support for the segmented regression model.</p><p>Akaike’s Information Criterion for Simple and Segmented Regression Analyses: Puget Sound Scale.</p

Changing Trends in Developed Land Cover: Watershed Scale.

<p>Heat map illustrating trends in developed land cover (regression slopes), summarized at the watershed scale for six habitat areas. Warmer colors indicate increasingly positive slopes; cooler colors increasingly negative slopes. A change in cell color between the first and second cell within a habitat-by-watershed combination indicates a substantially better fit of the segmented regression, compared to the simple regression (i.e., Δ AICc >4), hence <i>b</i>_<i>1</i> and <i>b</i>_<i>2</i> are shown. If Δ AICc was <4, both cells depict <i>b</i>_<i>0</i> for the simple regression, unless the <i>b</i>_<i>0</i><i>p</i>-value exceeded 0.05, in which case both cells were assigned <i>b</i>_<i>0</i> = 0. Note that the North Central sub-region has no corresponding watershed and, therefore, was omitted (but see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124415#pone.0124415.s002" target="_blank">S2 File</a>).</p

Percentage of Developed Cover in 1986 vs. Annual Change in Developed Land Cover (<i>b</i>_<i>2</i><i>– b</i>_<i>1</i>): Watershed Scale.

<p>The relationship between the percentage of developed land cover in 1986 and the difference in the annual rate of change in the percentage of developed cover before and after the breakpoint (<i>b</i>_<i>2</i><i>– b</i>_<i>1</i> in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124415#pone.0124415.e002" target="_blank">Eq 2</a>), for each of six habitat areas. Positive values on the <i>y</i>-axis indicate that the slope of the right-hand segment (latter part of the time series) exceeds the slope of the left-hand segment (earlier part of the time series); negative values indicate the opposite.</p

Trends in Developed Land Cover Adjacent to Habitat for Threatened Salmon in Puget Sound, Washington, U.S.A.

<div><p>For widely distributed species at risk, such as Pacific salmon (<i>Oncorhynchus</i> spp.), habitat monitoring is both essential and challenging. Only recently have widespread monitoring programs been implemented for salmon habitat in the Pacific Northwest. Remote sensing data, such as Landsat images, are therefore a useful way to evaluate trends prior to the advent of species-specific habitat monitoring programs. We used annual (1986-2008) land cover maps created from Landsat images via automated algorithms (LandTrendr) to evaluate trends in developed (50-100% impervious) land cover in areas adjacent to five types of habitat utilized by Chinook salmon (<i>O</i>. <i>tshawytscha</i>) in the Puget Sound region of Washington State, U.S.A. For the region as a whole, we found significant increases in developed land cover adjacent to each of the habitat types evaluated (nearshore, estuary, mainstem channel, tributary channel, and floodplain), but the increases were small (<1% total increase from 1986 to 2008). For each habitat type, the increasing trend changed during the time series. In nearshore, mainstem, and floodplain areas, the rate of increase in developed land cover slowed in the latter portion of the time series, while the opposite occurred in estuary and tributary areas. Watersheds that were already highly developed in 1986 tended to have higher rates of development than initially less developed watersheds. Overall, our results suggest that developed land cover in areas adjacent to Puget Sound salmon habitat has increased only slightly since 1986 and that the rate of change has slowed near some key habitat types, although this has occurred within the context of a degraded baseline condition.</p></div

Percentage of Developed Land Cover in 1986: Watershed Scale.

<p>Percentage of developed land cover at the start of the time series in 1986, summarized at the watershed scale for six habitat areas. Format is identical to that in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124415#pone.0124415.g003" target="_blank">Fig 3</a>.</p