Two Anomalously Warm Years in the Northern California Current: Impacts on Early Marine Steelhead Diet Composition, Morphology, and Potential Survival

Abstract

Juvenile steelhead Oncorhynchus mykiss enter the northern California Current ecosystem from the Columbia River and other Pacific Northwest coastal rivers and include several populations that are listed under the U.S. Endangered Species Act. However, relatively little is known about the response of these populations to interannual variability in ocean conditions. In 2015 and 2016, anomalous ocean conditions, called the warm “Blob,” persisted in the northern California Current, increasing ocean temperatures by over 2.5°C. To determine how steelhead respond to such major shifts in temperature, we compared diet composition, stomach fullness, size, and body condition of juvenile steelhead collected in 2015 and 2016 to those of a subset of steelhead collected in previous surveys (2001, 2002, 2004, and 2006–2011) that included warm, cool, and neutral ocean years. In addition, we used bioenergetics models to assess the importance of the marine environment in contributing to changes in steelhead condition under different ocean temperature scenarios. Steelhead from 2015 and 2016 exhibited some of the poorest body condition values but were the largest sizes across all years evaluated. Steelhead diet composition varied between warm and cold years and between warm and average years, with steelhead consuming more insects, juvenile rockfishes, and rare and unidentified fish in warm years. Unusual taxa, including gelatinous salps (2015 and 2016) and juvenile smelts (2016), were consumed during Blob‐influenced years. Bioenergetics models indicated that interannual variability in growth was influenced by changes in temperature and feeding conditions in the marine environment, with significant differences in growth between warm and cold ocean years apparent as early as day 2 of the simulated marine residence. These findings highlight the potential for warm ocean years to influence the diet composition and morphology of Columbia River steelhead populations and may lead to a better understanding of factors influencing survival of juvenile steelhead during early marine residence.

State of the California Current 2019–2020: Back to the Future With Marine Heatwaves?

“…The combination of coastal taxa, offshore taxa, and greater than average biomass of total ichthyoplankton suggests that generally favorable conditions existed for out-migrating juvenile salmon at the NHL in 2020 (Supplementary Table 1). Salmon growth and trophic habits change significantly during warmer ocean conditions (Daly and Brodeur, 2015;Thalmann et al, 2020), and the survival of juvenile salmon that out-migrated since the MHW of 2014-2016 has been uniformly poor. However, uncertainty in prey conditions was greater than usual because of the large fluctuation in temperatures from 2019 to 2020.…”

Is Marine Survival for Puget Sound’s Wild Steelhead Really That Bad? A Nisqually River Case Study Evaluating Estimates of Productivity and Survival of Oncorhynchus mykiss

“…While increased marine mammal predation (Berejikian et al 2016) and anthropogenic impacts (Sobocinski et al 2018) have been identified as primary causes, the relationship between mortality incurred in the Salish Sea versus the Pacific Ocean for steelhead has not been well studied. Additionally, the early marine period has been identified as a critical period for all anadromous salmonids (Smith and Ward 2000; Beamish and Mahnken 2001; Quinn 2018) and basin‐scale ocean process in the northern Pacific Ocean have been shown to influence the condition of early ocean‐migrating steelhead (Thalmann et al 2020); therefore, it is important to understand how mortality incurred in Puget Sound compares with that in the Pacific Ocean. It is possible that ocean survival rates among fish that have survived Puget Sound are high relative to coastal stocks.…”

A Dynamic Stress-Scape Framework to Evaluate Potential Effects of Multiple Environmental Stressors on Gulf of Alaska Juvenile Pacific Cod

“…Output from the stress-scape visualization indicated that juvenile Pacific Cod experienced moderately higher potential growth during heatwave years compared to more normal environmental conditions. Accelerated growth is a common bioenergetic response of teleost fishes to warmer ocean conditions, with increased temperatures contributing to increased metabolism and faster growth as long as caloric and oxygen requirements are adequately met, until an upper limit above which growth will begin to decline (e.g., Beauchamp, 2009;Thalmann et al, 2020). These results suggest that warmer temperatures during the juvenile life stage led to faster growth than would be expected during normal ocean conditions.…”