the USFWS Lacey office collects biological information from a portion of each returning salmon run at Makah, Quilcene, and Quinault National Fish Hatcheries on the Olympic Peninsula. We record sex, length and species for each fish. We also collect scales from the side of the fish behind the dorsal fin to determine the age of the fish. These scales are placed on an adhesive strip on a card and returned to the office for analysis. Back at the office, each scale card is imprinted onto an acetate sheet using heat and pressure. The acetate sheets are then magnified with a microfiche reader so that the scales can be easily seen.
Rings (called circuli) form on each scale just like rings on tree trunks. The circuli are visible in the lighter area of the scale. The darker banded areas are called annuli--they are formed during the winter months when the fish grow more slowly. We can estimate the age of each fish by examining these rings.
The age data we gather is then used to estimate the age and survival rate of the returning salmon.
Here are some videos demonstrating the scale collection/analysis process:
