Last modified on Oct 30, 2019

Due to the importance of age data for the management of Chinook salmon stocks, age estimates for Chinook salmon used by the Alaska Department of Fish and Game (ADF&G) need to be consistent. To help achieve this, we developed Salmon Scale Wiki. This Wiki acts as a living reference library when training and reading scales. In addition, Salmon Scale Wiki can be updated with procedures and scale patterns from across Alaska. The objectives of the Wiki include:

  • Train and provide resources for new and experienced age readers of Chinook salmon scales;
  • Facilitate discussion among age readers about methods used in Alaska, including scale collection, preparation, age estimation, storage, reporting, software, and equipment;
  • Define terms associated with Chinook salmon age estimation;
  • Share information of stock-specific Chinook salmon characteristics, including scale images from Chinook salmon sampled throughout Alaska;
  • Inform those estimating Chinook salmon ages about the consistency of age estimates for specific stocks;
  • Recommend methods to improve age estimation and propose research to help validate ages of Chinook salmon.

Follow the links above, go to the directory of the Wiki to find the sections that interests you, or read on to learn more about this project!

Project Background

Chinook salmon are highly-valued in subsistence, sport, and commercial fisheries across their range. Salmon harvests are important to Alaskans; thus, ADF&G manages salmon based on the sustained yield principle codified in the Alaska Administrative Code. To achieve sustained yield, the primary management target for major salmon stocks are spawning escapement goals. The sustained yield principle and escapement goal approaches were developed based on the Policy for the Management of Sustainable Salmon Fisheries (SSFP; 5 AAC 39.222) and the Policy for Statewide Salmon Escapement Goals (5 AAC 39.223).

Escapement goals are developed by modeling salmon populations using abundance estimates and data from brood tables. Abundance estimates come from commercial fish tickets, creel surveys, counts in rivers, and other sources. Brood tables are derived by relating the number of salmon that return from individual spawning (brood) years. Chinook salmon mature and return at multiple ages, so the number of fish from a single brood year is a sum of fish that returned at different years and ages. Salmon ages are often estimated from their scales and, like tree rings, salmon scales show seasonal changes in fish growth. Salmon growth slows in winter and is faster in summer, so years of growth on a scale are counted to estimate fish age.

Chinook salmon are anadromous, meaning they migrate from fresh to salt water. Most return to natal freshwater rearing locations to spawn and are semelparous, meaning they die shortly after spawning (Groot and Margolis 1991). They have a freshwater residence of 0–3 years followed by ocean residence of 1–7 years. Interpreting the scale growth patterns is at the core of age estimation.

With funding from the Pacific Salmon Commission (PSC), a meeting of Chinook scale readers from the Pacific Northwest and Alaska was held during April 2014 in Juneau, Alaska to present their current methods and criteria for age estimation. At the meeting, readers discussed similarities and differences among methods and jointly developed standards and quality control protocols applied to Chinook salmon scale age reading. Overall, the results from the meeting suggested that the general approaches to reading Chinook salmon scales were similar and that participants were willing to coordinate efforts to improve the age estimation process among agencies.

A study funded by the Saltonstall-Kennedy Grant Program, which provided support for the Wiki, was an outgrowth of the 2014 meeting. This study also examined the consistency of age estimation for Chinook salmon from scales by experienced personnel by time, age, and population. One component of this project was to develop scale age estimation protocols to improve the accuracy and consistency of these data. We hope to provide fisheries managers and other users with the best possible age data for Chinook salmon management. Then, population models can be refined, and stock assessments improved.


Groot, C., and L. Margolis, editors. 1991. Pacific salmon life histories. University of British Columbia Press, Vancouver, Canada.

This project received funding under award NA16NMF4270252 from NOAA Fisheries Service, in cooperation with the Saltonstall-Kennedy Grant Program. The statements, findings, conclusions, and recommendations are those of the author(s) and do not necessarily reflect the views of NOAA Fisheries.

Product names used in this publication are included for completeness and do not constitute product recommendation or endorsement.