Radio tags give rainbows an 'address'

Getting in tune with trout

Posted: Friday, June 01, 2001

The basic curriculum for catching fish goes like this: 1) find fish; 2) catch fish. What seems so simple can sometimes be impossible. The fish don't cooperate because they move around so much -- sometimes seemingly at whim -- and they don't leave a forwarding address. To further complicate matters, fish usually don't give an implicit reason for any sudden moves.

The Alaska Department of Fish and Game and the U.S. Fish and Wildlife Service are continuing to track these elusive creatures by giving the fish addresses. And all anglers can lend them a hand -- or a hook -- to help sustain future fish populations for coming generations.

"There are an estimated 50,000 rainbow trout annually caught in the Kenai River between Kenai and Skilak Lake," said Bruce King. "This area receives a heavy amount of fishing pressure."

King and Jeff Breakfield are Fish and Game fishery biologists, and they are two of the project leaders on the Kenai River Residence Species Investigation, which is a joint effort with Fish and Wildlife.

This study employs several methods. Over the past several years, 200 internal radio transmitters have been surgically implanted in rainbow trout in the Kenai River above Skilak Lake and the Russian River. The radios give off a signal that can be tracked from the air, from a boat or from a vehicle.

It is estimated that at present most of these "tagged" trout are in the river, with an estimated 15 radio-implanted rainbows in Skilak Lake and a few less in Kenai Lake, King said. The batteries on these radios are estimated to last three years. However, some of the two-year batteries installed on Dolly Vardens more than two years ago are still functioning.

"The 200 radio transmitters were paid for by the Kenai River Sportfishing Association at a cost of $40,000," King said.

Another method uses Floy dart tags. This is where anglers can get involved in the project and become a pen pal of a rainbow with an address.


Jeff Breakfield demonstrates proper handling of a captured rainbow trout by keeping it in the water and out of his hands.

Photo by Jerry McDonnell

If you catch a rainbow with a small green tag with black, six-digit numbers placed into the boney part of the fish just to the right-rear of the dorsal fin, write down the number, and the date and location (river mile) you caught it. In addition, "getting the length of the fish from snout to fork, its condition and its color from the angular would be great," King said.

Once Fish and Game has the information, the department will send a letter to the angler with the fish's travel history. The tags will remain in the fish for life. The recaptured fish -- the ones previously tagged -- are the key to the study.

"What may be interesting is that the tags placed to the right of the dorsal fin are old tags placed in the Russian River several years ago. The tags placed in the left side all indicate placement in the Kenai River," Breakfield said. "You may have to look carefully and wipe off the tag to read the number."

Breakfield and King are two of the people who have the chore of catching the rainbows and tagging and inspecting them. The fish must be handled very carefully to avoid injury or death, but the information recorded from the fish is invaluable.

Each fish caught is first handled properly by being netted, but not removed from the water. The net is continually submerged in the water as the fish is walked to the vicinity of the "drift boat data research collection center."

The length of the fish is measured from snout to fork, and it is examined for sex, fin wear, mouth damage, spawning condition and parasites in the gills.

A fish 20 to 22 inches long is estimated to be about 8 to 10 years old.

"We have caught a 28-inch fish and some 26-inch fish, but those were the biggest," Breakfield said.

Fin wear indicates spawning information.

"The lower lobe of the caudal fin gets rough and ragged during spawning," Breakfield said.

The condition of the caudal fin can show recent wear, old wear or no wear, which indicates the fish's history of digging its redd, or nest.

The fish's mouth also is examined.

"This is not a problem now, but there is a certain amount of hook-and-release mortality," King said. "This fish population has a high percentage of mouth damage, a condition found in the majority of large spawners."

Spawning conditions are categorized. A mature spawner is full of eggs or milt. A post spawner doesn't have eggs. A non-spawner is bright and called immature. A spawning rainbow takes on the dark green and deeper colors of a rainbow. Bright silver fish are those that are coming out of the lakes and are not spawning.

One result of the study has revealed that these rainbows are "skip spawners." It is estimated these upper Kenai River rainbows spawn every two to three years.

"The spawning takes such a toll on the fish that it may be that they need several years to recover. These are things we don't know exactly," King said.

Gill parasites have been found in the spawning fish in the river, which indicates the fish are picking them up in the river and not in the lakes.

Some theories from the study indicate 80 percent of the rainbows spend the winter in the lakes. About now, late May and early June, bright fish are coming into the river. Do they come in all at once or a few at a time? This also is an issue that needs further investigation.

"We think there are fewer fish in the river in July than in September," King said. "July and early August are the most stable months, when an estimated 5,000 fish are in the river between Kenai and Skilak Lake. They don't move in and out so much. In early August they start moving."

All these conditions can be monitored, so populations and growth rates can be calculated from this data. The data also determine annual closure dates while the fish are spawning. This is the information taken to the state Board of Fisheries to determine the fishing closures each year, King said.

Now, as the river is beginning to rise, what were exposed gravel bars last week are covered with water. The fish using these shallow spawning areas are very vulnerable. Breakfield said some fish have even been caught (unharmed) with eagle claw marks by the dorsal fins.

The study has to consider a fish with a lifespan of eight to 10 years, a fish that only spawns every two or three years, and a fish that doesn't spawn until it is 3 or 4 years old. Throw in mortality factors and knowledge of the simple quest to "find fish, catch fish" becomes more complex.

Biologists say the ongoing study does more than set seasons, it guides us to a productive legacy for anglers of the future.

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