Juvenile river residence and performance of Snake River fall Chinook salmon

Abstract

An animal's performance during its early life stage can greatly influence its survival to adulthood. Therefore, understanding aspects of early life history can be informative, particularly when designing management plans to rebuild a population. For a threatened population of fall Chinook salmon (Oncorhynchus tshawytscha) in the Snake River of Idaho, we reconstructed the early life history for 124 returning wild and hatchery adults using information recorded in their otoliths. Of our sampled wild adults (n = 61), 43% and 49% reared within the Snake River and Clearwater/Salmon rivers. We also found that only 21% of our sampled wild adults exhibited the historically common subyearling out‐migration strategy, in which juveniles exit freshwater shortly after hatching, while the remaining wild adults exhibited the yearling out‐migration strategy (i.e., individuals delay their freshwater exit). As expected, yearlings had, on average, a significantly larger body size than subyearlings at ocean entry. However, 35% of wild yearlings overlapped in size with wild subyearlings suggesting that spending more time in freshwater might not necessarily result in a larger body size. Lastly, we observed that variability in fork length at Snake River egress and ocean entry were best explained by migration strategy and where it reared, followed by hatch year and sex. Results from this study highlight the utility of adult otoliths in providing details about early life history, an understanding of which is critical to the conservation of Snake River fall Chinook salmon.

The incorporation of environmentally derived 87Sr/86Sr and Sr/Ca in early otolith formation of Chinook salmon

“…Data were recorded with a 0.262 s integration time. Measurement of the ratio of 87 Sr and 86 Sr was calculated and corrected through simultaneous measurement of 83 Kr, 84 Sr, 85 Rb and 88 Sr and followed procedures outlined in Chittaro et al (2019). Specifically, measurements were mass-bias corrected and corrected for interferences in 86 Kr, 87 Rb and Ca dimers using natural ratios, similar to Barnett- Johnson et al (2005).…”

Simultaneous determination of87Sr/86Sr and trace-element data in otoliths and other sclerochronological hard structures

“…Prior data for each otolith was collected using a 30 µm spot size. Each otolith was ablated using parallel laser scans from the edge to the core of the otolith (Figure 1), perpendicular to the sulcus, in the same manner as prior studies on this population (Hegg et al 2013, Chittaro et al 2019. The limited size of the otolith cores necessitated testing at only three laser spot sizes.…”

“…Fish otoliths grow in sequential layers of biogenic aragonite, preserving trace elements and isotopes unique to the environments the fish inhabits through its life (Campana 1999, Campana andThorrold 2001). These chemical tracers have been used to uncover the population structure of fish populations , Muhlfeld et al 2012, Brennan and Schindler 2017, as well as the details of their migratory paths (Hegg et al 2015, 2019, Sturrock et al 2015b, Chittaro et al 2019, sometimes with incredible precision on the landscape (Hamann and Kennedy 2012). Otoliths thus provide a high-resolution, broad scale, dataset of location, growth, and ontogeny across the life of the organism which is not possible in using tagging or tracking technologies (Hegg et al 2018).…”

“…Increasingly, researchers across the fields of animal hard-part and speleothem chronologies are using the improved analytical precision to understand chronologies with increasing resolution (Warter and Müller 2017). Scientists are also applying novel isotopic systems to reconstruct chronologies which in the past were confined largely to trace elements (Rüggeberg et al 2008, Füllenbach et al 2015, and combining isotopic compositions and trace element approaches to uncover multiple temporal records within the same structure (Zhou et al 2009, Griffiths et al 2010, Mallela et al 2011, Woodcock et al 2013, Chittaro et al 2019.…”

Hydropower peaking and stalled salmon migration are linked by altered reservoir hydraulics: A multidisciplinary synthesis and hypothesis

“…It appeared that a new ‘reservoir type’ life history had developed. These fish were the progeny of fall‐run adults that spawn primarily in the Clearwater River downstream of Dworshak Dam, emerge from redds relatively late in spring, develop slowly in cold hypolimnetic water (Perkins & Jager, 2011), migrate in late summer and autumn, overwinter in reservoirs as subyearlings and migrate seaward as yearlings the following spring (Connor et al, 2005; Chittaro et al, 2019). Despite this aberrant behavior, they appear to be genetically (Narum et al, 2007) and morphologically (Tiffan et al, 2000) similar to other fall Chinook salmon subyearlings from the Snake River that follow the usual summer outmigration pattern.…”