SUMMARY What is the nature of evolutionary divergence of the jaw skeleton within the genus Oncorhynchus? How can two associated bones evolve new shapes and still maintain functional integration? Here, we introduce and test a ‘concordance’ hypothesis, in which an extraordinary matching of the evolutionary shape changes of the dentary and angular articular serves to preserve their fitting together. To test this hypothesis, we examined morphologies of the dentary and angular articular at parr (juvenile) stage, and at three levels of biological organization – between salmon and trout, between sister species within both salmon and trout, and among three types differing in life histories within one species, O. mykiss. The comparisons show bone shape divergences among the groups at each level; morphological divergence between salmon and trout is marked even at this relatively early life history stage. We observed substantial matching between the two mandibular bones in both pattern and amount of shape variation, and in shape covariation across species. These findings strongly support the concordance hypothesis, and reflect functional and/or developmental constraint on morphological evolution. We present evidence for developmental modularity within both bones. The locations of module boundaries were predicted from the patterns of evolutionary divergences, and for the dentary, at least, would appear to facilitate its functional association with the angular articular. The modularity results suggest that development has biased the course of evolution.
Chinook salmon (Oncorhynchus tshawytscha) are widely distributed across the globe, with native stocks in the North Pacific Ocean and self-sustained populations in both the Northern and Southern hemispheres. In their native range, Chinook salmon face many conservation and management challenges, including depleted stocks, loss of genetic diversity, and hatchery influences, whereas naturalized range expansion poses a threat to novel ecosystems. Therefore, ways to improve stock discrimination would be a useful tool for fishery managers. Here, we evaluated otolith shape variation in Chinook salmon as a potential tool for stock discrimination using wavelet coefficients and Fourier harmonics in three case studies at multiple spatial scales. We adopted a simple Classification Tree model that used otolith shape variation to separate Chinook salmon groups. We found best performance of the model occurring between hemispheres, followed by Oregon basins, within-watershed Elk River, Oregon, and lastly among South American basins. Otolith shape analysis is a promising tool for stock discrimination if used in conjunction with other methods to better understand plasticity of anadromous species that use pan-environmental systems.
Many adult hatchery‐origin Pacific salmon Oncorhynchus spp. return to their natal river but do not enter the hatchery, instead spawning in the river, where they can have detrimental genetic and ecological effects on naturally reproducing wild populations. This phenomenon is especially well documented in Elk River (Oregon) Chinook Salmon O. tshawytscha based on previous analyses of coded wire tag recoveries. Here, we used radio tags to compare the movements of natural‐ and hatchery‐origin Chinook Salmon (n = 11 and 15, respectively) to determine whether their behavior could explain the in‐river straying patterns of hatchery salmon. Most of the tagged hatchery‐origin (87%) and natural‐origin (73%) adults initially moved upriver to the vicinity of the Elk River Hatchery. Most natural‐origin adults then moved downstream of the hatchery entrance to spawn, but the movements of hatchery‐origin adults were different. Hatchery‐origin males and females had the highest and lowest variation in total distance moved, respectively. Our results are consistent with the hypothesis that while most hatchery‐origin salmon return to the vicinity of the hatchery, some fail to enter, perhaps because the hatchery’s odors were not perceived as distinct from those of the river or (in the case of hatchery‐origin males) because they stopped short of the hatchery after encountering spawning conspecifics. Thus, spawning distributions may not always reflect in‐river movements of Chinook Salmon, and we encourage fisheries managers to continue investigating methods that reduce potentially harmful interactions between hatchery‐ and natural‐origin fish.
BPA project number 1999-016-00 identifies the fish habitat limiting factors for Big Canyon Creek. According to these guiding documents, the greatest factors limiting fish production in Big Canyon Creek are summer low flows and high temperatures, sedimentation, riparian degradation, channel/bank instability, and passage of aquatic life. The fish distribution and abundance monitoring data was used as the basis for the prioritization and delineation of assessment units for this plan.
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