Geology topics

Research about Pilgrim River

Source-linked reports with geographic coverage including Pilgrim River.

2 recordsLinked to original sources

USGS2021

Egg retention of high-latitude sockeye salmon (Oncorhynchus nerka) in the Pilgrim River, Alaska, during the Pacific marine heatwave of 2014–2016

Ocean and freshwater conditions can influence spawning success of Pacific salmon ( Oncorhynchus spp.) by governing the energy content of fish at the start of and during the spawning migration. Ocean conditions determine the energy stores of fish at the freshwater entry, while freshwater conditions determine how quickly stored energy is depleted as individuals migrate to spawning grounds in natal rivers and lakes. We assessed the occurrence of sockeye salmon ( Oncorhynchus nerka ) egg retention (failure to deposit eggs) in a high-latitude (~ 65°N) watershed that has a large, inter-annual variation in the number of returning adults. We also explored relationships between ocean and freshwater conditions with egg retention of female sockeye salmon. The proportion of females with egg retention (> 50 eggs) varied by threefold (12 to 36%) across years (2013 to 2020) and was related to ocean conditions represented by the North Pacific Index (NPI). Egg retention was more common in years with low NPI values (a stronger Aleutian Low) in association with the Pacific marine heatwave of 2014–2016 that disrupted food webs. This initial study contains the first empirical data observing the influence of ocean conditions on egg retention for any Pacific salmon population. The lack of any relationship between egg retention and freshwater temperatures was consistent with water temperatures primarily occurring below thresholds associated with heat stress related mortality (< 18 °C). Understanding the amount of egg retention and how environmental drivers influence egg retention within Pacific salmon populations provides insights for managers assessing the number of successful spawners and helps refine escapement-based management efforts.

Alaska↗

USGS2019

Energy depletion and stress levels of Sockeye Salmon migrating at the northern edge of their distribution

The physiological challenge for anadromous fish to migrate upriver is influenced by river temperature, but the impacts of river temperature can be difficult to predict due to an incomplete understanding of how temperature influences migration costs, especially in high‐latitude (>60°N) ecosystems. To assess temperature influences on migrating Pacific salmon Oncorhynchus spp., we measured heat shock protein 70 (HSP70), as an indicator of cellular stress, and energy content of Sockeye Salmon Oncorhynchus nerka throughout their upriver migration in the Pilgrim River, Alaska. Although HSP70 was elevated as fish moved to the spawning grounds and was higher in fish with low energy content, HSP70 did not increase with warmer river temperatures. We verified in an experiment that HSP70 abundance in Sockeye Salmon does respond to temperatures above 20.5°C. Over the 4 years of sampling, energy content decreased at similar rates as Sockeye Salmon moved upstream. We expected Sockeye Salmon energy levels would be lower when migrating in warmer river temperatures; however, we found higher energy levels occurred with higher temperatures in the Pilgrim River. We hypothesize that the relationship between temperature and energy content is due to river temperatures often occurring below optimal temperatures for migration. Lower temperatures could be energetically costly or reduce migration rates, both of which would result in lower energy content with cooler temperature. Understanding interactions between environmental drivers and physiological responses will help managers anticipate future changes for Sockeye Salmon at the northern edge of their distribution.

Alaska↗