Fish Scale Image Analysis of the Atlantic Salmon Ecosystems Research Team
Using Atlantic salmon scales to assess smolt and adult populations.
Since 1992, we have conducted research on Atlantic salmon scales collected during annual field activities for assessing smolt and adult populations. Results from scale studies contribute to and inform stock assessments and support population dynamics research.
The Atlantic Salmon Ecosystems Research Team’s image analysis labs process numerous Atlantic salmon scales—imaging, aging, measuring, and analyzing—to support research into Atlantic salmon population dynamics and ecology.
The salmon image analysis labs at the Northeast Fisheries Science Center are located in our Orono and Woods Hole Laboratories. These labs process over 1,000 salmon scales annually to assist population dynamics research. With the Maine Department of Natural Resources we monitor salmon smolts as they make their way from their natal river to the ocean each year.
Analyzing scales helps us determine age, rearing origin, and growth rates and patterns throughout Atlantic salmon life history. Ages from the different life stages help scientists understand many aspects of the fish’s life history, such as:
- Survival and mortality
- Age at maturity and spawning
- Freshwater and marine residence
1. Collecting Scale Samples
Whether we’re collecting scales from juvenile salmon or adults, we usually use the same method. The sampler uses a small knife to wipe the slime coat from a small area of the fish, then carefully lifts scales off the fish, and places them in a small envelope for storage.
2. Collecting Data from the Fish
We store the scales in an envelope with all the associated information written on it:
- Date of sample
- Fish species and life stage
- Fork length
- Presence or application of tags or clips
- Disposition (i.e., “rel” means released, but sometimes fish are retained for other research)
- Any other pertinent notes
We later enter the data into a computer database.
3. Preparing Scales for Examination
We place the scales between two glass slides for viewing under a microscope.
4. Taking Images for Viewing and Computer Analysis
Our image analysis system consists of a microscope with a digital microscope camera, which is attached to a computer. We save scale images to the computer and then use image analysis software to measure scale features.
5. Reading Scales
From scales and scale images, we can read the age of the fish and whether it was born wild or in a hatchery. We can see how many years it spent in a river before migrating to the ocean as a smolt and how many years it spent as an adult salmon in the ocean.
Results and Preliminary Results
Scales provide age and growth data. By looking at these data collected over a number of years, we can see trends that help us understand what is happening in the endangered Atlantic salmon populations we are studying.
Collaborators and Partners
● Tim Sheehan
● Brandon Ellingson
● Graham Goulette
Publications and Reports
- Atlantic Salmon Assessments
- Retrospective analysis of marine growth and relationships to return rates of Penobscot River Atlantic salmon
- Non-stationary effects of growth on the survival of North American Atlantic salmon (Salmo salar)
- 2011 Report of the Workshop on Age Determination of Salmon (WKADS)
- 2012 Report of the Second Workshop on Age Determination of Salmon (WKADS 2)
- ICES Workshop on scale, otolith, biochronology archives (WKBIOARC)
- Scale pattern analysis discriminates Atlantic Salmon by river reach rearing origin