Alaska’s largest free-flowing rivers

Quantifying salmon population dynamics, nutrient cycling, organic carbon processing versus transport, and contaminant flows (i.e., mercury in fish) across large, free-flowing boreal river systems.

Five inter-related projects funded through Arctic-Yukon-Kuskokwim Sustainable Salmon Initiative (AYKSSI) aim to develop and apply new analytical approaches to address these diverse and critical aspects of the boreal ecosystem. This work is a collaborative effort between the University of Washington, Alaska Department of Fish and Game, Orutsararmiut Native Council, US Fish and Wildlife Service, University of Utah, University of Montana Flathead Biological Station, and the US Geological Survey.


The Nushagak River salmon ecosystem

How do shifting habitat mosaics influence how reliable the production of Chinook and sockeye salmon are from the Nushagak River? We have been studying this question by exploiting the strontium isotopic variation across this watershed.

This project has been ongoing since 2009, starting with my PhD work at the University of Alaska Fairbanks. As a postdoc working with Daniel Schindler at the University of Washington, we have revamped and produced a new analytical framework that quantifies how salmon use river networks. The framework is based on using isotopic variation across rivers and how this variation is recorded in fish ear stones (otoliths).

Over the years this project has been funded by various agencies including: Bristol Bay Regional Seafood Development Association, Bristol Bay Science and Research Institute, Alaska Sea Grant, and the National Institute of Water Resources.

See our new paper in Science:Shifting habitat mosaics and fish production across river basins


space-time isotope models of provenance [Stimp]

Highly migratory species, especially those that experience high juvenile mortality, are hard to study. We developed a probabilistic analytical framework that determines habitat use of migratory animals through time by evaluating conditional probabilities of isotopic variation across landscapes, that which is recorded in sequentially growing tissues (e.g., otoliths and teeth), time-dependent geomorphic habitat preferences, directional movement patterns, and prior locations.

Below is a STIMP applied to the juvenile freshwater residence period of a Chinook salmon harvested in a coastal fishery on its way back to its natal origin somewhere in the Nushagak River. The STIMP shows how this fish used multiple habitats, including the lower river migration corridor, to achieve its total amount of growth in fresh water before migrating to the ocean.

Top panel is animation of habitat use; bottom is actual isotope trace through the otolith growth layers. Here is a link to the paper in Methods in Ecology and Evolution.

Freshwater seals

A cryptic population of harbor seals resides in Iliamna Lake, AK. Very little is known about their movements and foraging ecology. We used stable and radiogenic isotopes in the canine teeth of these seals to figure out if these seals ever move to the ocean (an 80km one-way swim), and, if not, how they integrate across the variety of trophic resources produced within the lake versus those produced in the ocean (i.e., the seasonally abundant adult sockeye salmon that return to the lake every summer). Here is a link to the paper in Conservation Biology.

Our results suggest these seals appear to be the only known freshwater obligate population of the Eastern Pacific harbor seal taxon. They also show evidence of a foraging ecology that is adapted to their unique ecological setting; most notable, one that is selective - emphasizing different foods at different times in their life.