Radio Telemetry

Radio Telemetry

The purpose of the study

The Seymour Salmonid Society carried out a radio tagging and tracking program of adult steelhead in the Seymour River over a period of three years.
The principle purpose of the research was to determine the movement patterns of fish once they were in the river and also to use the tagged fish to determine the counting efficiency of our snorkel surveys of adult steelhead in the Seymour River.
Secondary objectives included determining the movement patterns of both winter and summer steelhead; determining how many survived and returned to the ocean after spawning; and identification of spawning areas.

The technology behind this research

This research is made possible by the implantation of radio tags into the stomach of adult steelhead.
The tag itself consists of a power source, a transmitter that emits a unique code that enables us to identify each individual tagged fish and an antenna that comes out the mouth of the fish.
Once activated, these radio tags emit a signal every 5 seconds that is able to detected by a receiver with a directional aerial attached.
By looking at signal strength and direction, the approximate location of the fish can be determined.

What we did

This research was conducted on both summer and winter run adult steelhead.
Adult fish were caught in the river and had a radio tag inserted into them.
They also had a brightly coloured spaghetti tag attached just behind their dorsal fin on their back.
The purpose of this tag was to allow swimmers doing snorkel surveys to easily identify these fish as being radio tagged.

Once fish were tagged their movements in the river were tracked by going out with the receiver and looking for fish.
We tried to confirm the position of each tagged fish once a week.
Once we had around 20 fish tagged for each run of steelhead we got in the river in dry suits (usually late summer and fall for the summer run fish and late winter early spring for the winter run fish).
We swam the entire river counting steelhead, both tagged and not tagged.
The number of tagged fish we saw compared to the number of tagged fish that we knew were in the river gave us a swimmer efficiency for seeing steelhead in the river.
From this we were able to determine the approximate size of the entire run of fish in the river.

What we found out

We found that the summer run and winter run Steelhead populations were distinctive both in the time that they come into the river but also where they go in the river once they come in. See this animation.

It seems that the summer run Steelhead have been most impacted by the construction of the dam. Their movements going right up to the dam show that in the past they are likely to have migrated up into the upper part of the Seymour river and spawned there. This maybe why we do not see many wild summer run Steelhead in the river compared to hatchery fish.

We also were able to determine that our swim counting efficiency was around 30-35%. This means that if we counted around 30 or 35 summer run Steelhead in the river that it means that the total number of summer run Steelhead adults in the river at that time was likely to be around 100 Steelhead.