Variable prey consumption leads to distinct regional differences in Chinook salmon growth during the early marine critical period

Growth during the early marine critical period is positively associated with survival and recruitment for Pacific salmon Oncorhynchus spp., so it is important to understand how certain foraging strategies may bolster growth in estuarine and marine environments. To elucidate how spatiotemporal and demographic differences in diet contribute to growth rate variability, we analyzed stomach contents in tandem with morphometric and hormonal indices of growth for subyearling Chinook salmon O. tshawytscha captured in Puget Sound, Washington, USA. Regional dietary patterns indicated that fish caught in northern Puget Sound ate insects in the estuarine and nearshore habitats, followed by decapod larvae, euphausiids, or forage fish in the offshore zone. In southern Puget Sound, fish ate insects in the estuary but were more likely to eat mysids and other crustaceans in the nearshore zone. In the marine habitats adjacent to the San Juan Islands, subyearlings ate forage fish, and their stomachs were as much as 1.4 to 3 times fuller than salmon captured in other regions. Scale-derived growth rates and insulin-like growth factor-1 levels showed distinct growth advantages for San Juan Islands fish which were strongly associated with the early adoption of piscivory. However, consumption of larger crustaceans such as mysids and euphausiids was also associated with greater relative growth regardless of where individuals were captured. These findings highlight how spatiotemporal differences in prey quantity, prey profitability, and individual foraging strategies result in variable growth rates among salmon populations. Specifically, they emphasize the role of piscivory in promoting early marine growth for out-migrating Chinook salmon.

Thermal and structural history of underplated rocks from subduction initiation to thermal steady state: Easton Metamorphic Suite and related units, WA, USA

<p>Rocks of the Easton Metamorphic Suite and San Juan Islands preserve an inverted metamorphic sequence with ultramafic rocks underlain by amphibolite and high-temperature blueschist juxtaposed above low-temperature blueschists. The sequence is interpreted as a metamorphic sole and younger accreted rocks that formed during and after the initiation of Farallon plate subduction beneath North America in Jurassic time. Thermobarometry, Ar/Ar dating, and structural observations constrain a relatively continuous deformation history and the rheology of rocks during subduction.  The data suggest HT metamorphism and accretion of oceanic crust at the initiation of subduction was followed by rapid cooling, underplating, exhumation, and later underplating and HP/LT metamorphism that persisted for >30 m.y. at a thermal steady state.</p><p>The earliest deformation event in the metamorphic sole at ~10 kbar, 760 °C formed S<sub>1</sub><sup>A</sup> in amphibolite followed by cooling through hornblende closure temperature by 167 Ma. Strain was variable, with high strain in amphibolite interlayered with quartzite and quartz-mica schist and weaker S<sub>1</sub><sup>A</sup> fabric in homogeneous blocks of amphibolite. Metasomatism due to contact with hot hangingwall rocks may have occurred before, during, and after S<sub>1</sub><sup>A</sup>, as locally preserved blackwall assemblages occur at the contact of relatively undeformed amphibolite and ultramafic rocks, but metasomatic assemblages also overprint hornblende-dominated fabrics. Recrystallization during isoclinal folding of amphibolite formed a second fabric (S<sub>2</sub><sup>A</sup>) at 590°C, >165 Ma.  S<sub>2</sub><sup>A</sup> is mylonitic where amphibolite blocks are in contact with quartzite, quartz-mica schist, and tremolite schist; foliation in the schists is discordant to and wraps blocks.  The S<sub>2</sub><sup>A</sup> event overlaps with the earliest metamorphism and strong deformation (S<sub>1</sub><sup>N</sup>) of high-grade Na-amphibole schist at ~530°C, 10 kbar, which cooled below 400°C by 165 Ma. We interpret the Na-amphibole schist to have been underplated as a lower metamorphic sole during this event. Retrograde metamorphism, cooling, and partial uplift to ~350°C, 7 kbar by 157 Ma is evidenced by a crenulation cleavage in the Na-amphibole schist (S<sub>2</sub><sup>N</sup>) during brittle deformation in the amphibolite and metasomatic schist evidenced by glaucophane-filled fractures in hornblende. </p><p>Younger accretion and exhumation events occurred as HP/LT conditions persisted, including underplating of regional phyllite at ~7 kbar, ~320°C from ~154-142 Ma and metavolcanic greenschist-blueschist at ~7 kbar, 360°C at ~140 Ma.  Exhumation to ~5 kbar, ≤300˚C occurred between ~140-125 Ma during later deformation of greenschist-blueschist and underplating of structurally lower metagraywacke and greenstone.  Low-T fabrics are characterized by early pressure solution cleavage followed by tight to isoclinal folding and local shearing with weak to strong recrystallization in the second cleavage.  Strain partitioning at this stage was high, with non-coaxial strain focused in phyllite and flattening fabric dominant in metagraywacke.  No deformation is evident in the high grade rocks at this time, showing the locus of strain had stepped to lower structural levels.  Meso-scale and microstructures throughout the deformation history are consistent with initial high-T deformation and limited rheological differences between lithologies, rapidly followed by weakening of metasomatized rocks and lower-T ductile and ductile-brittle deformation where strong strength contrasts favored strain partitioning into weaker units.</p>

Genetic composition and conservation status of coastal cutthroat trout (Oncorhynchus clarki clarki) in the San Juan Islands, Washington

Understanding the conservation status of native fish populations is increasingly important because they are put at risk by mounting anthropogenic pressures, including climate change. Conventional approaches to assess fish populations can be logistically challenging and cost-prohibitive. As a result, resource managers often make assumptions about the status of fish populations based on limited information. The watersheds of Washington’s San Juan Islands were considered too small to support wild salmonid populations. Many streams flow only seasonally, and all have been subjected to varying degrees of anthropogenic impacts affecting their ecological integrity. Nonetheless, we found that at least five watersheds in the archipelago support populations of coastal cutthroat trout (Oncorhynchus clarki clarki). To better understand the conservation status of coastal cutthroat trout populations there, we genotyped approximately fifty trout in each of three watersheds: Cascade and Doe Bay creeks on Orcas Island and Garrison Creek on San Juan Island. Results suggest that two watersheds support native populations and one supports naturalized hatchery fish. The likely native coastal cutthroat trout diversity documented in the two watersheds contributes to the overall diversity of the species, demonstrates that species’ resiliency, and provides justification for conservation measures. Effective management and conservation planning in data-limited situations requires the use of a precautionary approach. Population genetics provide a useful tool for identifying vulnerable fish populations and understanding their relationships with other conspecific populations. This information can inform restoration goals and help identify and prioritize restoration and protection measures.