Coded-Wire Tagging Coho Smolt

Anatomy of the Operation

Silver salmon spawn in the Moose River and off-shoot tributaries each year. Once the eggs have developed into salmon fry the young fish find their way into the many lakes connected to these streams where protection from predators and more abundant food supplies are found.

The young fry grow rapidly.....and after their first year a large portion of the previous year's spawning efforts begin the journey downstream to the sea. The remainder stay in the drainage for yet another year in freshwater....and a few will remain three years in freshwater before eventually heading to sea.

Each summer there are hundreds of thousands of 4 to 7 inch juvenile coho salmon starting their migration to saltwater.

The Buffalo Box
The Fish & Game weir is an impassable barrier errected temporarily on the Moose River and prevents the fish from continuing downstream. Personnel then channel batches of these smolt into a holding pen called the "Buffalo Box."

The Sandman
From here the fish are transferred by scoop net to a mixture of river water and anethesia chemical which quiets them for sorting into size groups.....those longer than 125mm and those shorter. The fish are then returned to holding tanks of flowing river water where they recover from their drowsiness within a minute or two.

Tatoo You
They are then transported by bucket to the tagging tent where they are again sedated for the next two steps. The first step involves clipping the adipose fin on the top side of the fish near its tail. This small appendage is similar to human tonsils....perhaps sometime in the past it served a function....but now its a very convenient way to mark a fish to indicate it has undergone some sort of handling and research.

Body Piercing
After the fin is clipped the next step is to inject an almost microscopic 1mm long piece of wire into the end of each smolt's snout. This is performed mechanically by an injection machine which cuts the wire to a precise length and then injects it in a split second.

The fish are then placed in a chute where a very sensitive magnetic sensor determines whether there is a tag in the fish as it passes by. If it doesn't detect the tiny piece of metal the sensor sends a signal to a "trap door" which diverts the fish to a temporary holding tank to be checked again. Once in a great while the tag may not stay in the fish and it will be given a new one on the next check. The sensor also records the total number of fish which have been tagged.

Making the Grade
If they pass the test they end up in a holding tank in the river where they begin their quick recover from the anethesia. Once an entire "batch" of fish are tagged and have recovered they are released back into the river to continue their journey to the ocean. Two hundred fish from each batch are delayed 24 hours before their release to insure that all are healthy and all tags have remained in the fish. This maintains the highest of quality control standards and insures good survival.

The department has plans to tag 95,000 smolt this season. Once this objective is achieved the tagging will be terminated. The weir will be left in place to count the remaining migrants and once they have all passed through the system the weir is removed. From this data the biologists will know what percentage of the total population has been tagged in this drainage.

Front End - Back End
This is only the front end of the study. Since silver salmon only remain in saltwater for one year before returning to spawn, they are an ideal subject to study since results come quickly. Later in the summer, technicians will be stationed at salmon canneries looking for any fish with their adipose fin clipped from the previous year's tagging program. Biologists stationed on the river will check the sport fishing catch for marked fish. The head is removed and by process of elimination smaller and smaller pieces of the head are checked with a sensor to recover the tag.

The tiny wire contains small notches along its length which represent a binary code number. All fish tagged with wire from a specific wire spool (10,000 tags per spool) will have the same code. This is read and cross-referenced in the tagging records to determine where this fish originated. Each spool's number is entirely unique and thus accuracy of the fish's origin in insured.

From the total coho salmon harvest (commercial, subsistence and sport) and the number of tagged fish recovered will come the data which Fish & Game management teams will review to determine effective management plans for this fishery.