PROJECT HIGHLIGHT:
This project will analyze scale morphometrics and otolith microchemistry to determine which juvenile Chinook life history strategies (lagoon or ocean rearing) are represented in the return adult spawning population on the Mattole River.
PROJECT SUMMARY:
Unencumbered by dams, the Mattole River is one of the last coastal watersheds in California that hosts a population of wild Chinook salmon without hatchery influence. As recently as the 1960s, the Mattole River supported spawning runs of Chinook salmon, but the populations have seen a steep decline in the last several decades, in part due to logging, roadbuilding, agricultural development and more. Thus, it is critical to understand how juvenile Chinook behavior and survival relates to adult population sizes.
This project evaluates the life history patterns and age of returning adult Chinook (between 2005-2024) to the Mattole River by examining the microchemistry and patterns in adult scales and otoliths (ear bones). The researchers assess whether certain juvenile life history strategies or environmental factors (e.g., temperature, flow) lead to a greater chance of surviving to adulthood by returning to reproduce in the Mattole River. The study aims to determine if juvenile Chinook that over-summer in the Mattole lagoon are represented in the return spawning population and explores variations in life history strategy across brood years and relationships to environmental factors.
Significant progress has been made on this research. Approximately 275 adult Chinook salmon otoliths have been mounted onto microscope slides and polished to prepare samples for laser ablation analysis. In January 2025, researchers used an Inductively Coupled Plasma Mass Spectrometer at Oregon State University's Keck Laboratory to analyze elemental concentrations in each otolith sample. Temperature loggers were also deployed in various locations in the Mattole Lagoon during summer 2024 to collect environmental data. Knowledge gained from this study will fill a gap in basic understanding of the Mattole lagoon and its rearing capacity, inform adaptive management decisions and provide insight to neighboring coastal watersheds that may begin to experience annual sandbars as environmental conditions shift.
Community Mentor: Nathan Queener (Mattole Salmon Group)