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Assessing the salmon stocks is explained

By KARENLONGWEL
Tribune Staff Writer
The Williams Lake Tribune
Mar 02 2006

This past fall naturalists were thrilled to see salmon heading up several waterways in the area including the Horsefly River and the Williams Lake River. These salmon runs and all the runs of the Fraser River watershed are assessed regularly by the Department of Fisheries and Oceans Canada (DFO).

How and why the salmon assessments are done and the exciting, new technology used was the focus of a talk by DFO stock assessment/resource management biologist Keri Benner on Feb. 23 at the Nature Centre. Benner is the program head for the sockeye stock assessment/ resource management for the B.C. Interior area.

Horsefly is world renowned for its salmon runs, said Benner at the talk. This past year was dominant year in the cycle of salmon runs for Horsefly. Fisheries assessments since 1985 have identified large increases in the salmon numbers in the area, said Benner. Assessments have been done since the 1930's but the DFO took over in 1985. In 2005 DFO was expecting over a million salmon in the Horsefly system but they counted about 840,000. The reasons for the differences in the numbers are not yet known, said Benner.

The Chilcotin sockeye stocks, found in Chilko River, Chilko Lake and Taseko Lake are also assessed by DFO. This system has no cyclical dominance, said Benner.

In 2005, there were salmon in unexpected tributaries of the Fraser River. Salmon were seen in Hawks Creek and Williams Lake River in this area, said Benner.

Each year the DFO provides annual estimates of the number of Pacific salmon that return to spawn in the streams and rivers of the Fraser River watershed, said Benner. In addition to determining numbers, biological samples are collected from the returning fish for sex and age composition, spawning success, fecundity, parasites and general health of the stocks, she said.

The government of Canada has an international obligation to assess the Pacific salmon stocks because the fish cross USA/Canadian boarders. The Pacific Salmon Treaty was created to insure stocks originating in another country's waters are conserved, she added.

There are three traditional methods used in the salmon stock assessment in this area. Fish stocks are defined as a discrete population of a fish species that tends to inhabit the same waters and breed in the same stream, said Benner. In Horsefly over 80 stocks have been identified. The first method is a visual count, either from the land, a tower, boat or by helicopter, she said.

The second method is the use of enumeration fences. The fence is an enclosed area in which a Fisheries personal member can count fish. This method is one of the most accurate but not suitable for all water systems, said Benner.

The third method is called mark and recapture. It is used for a large population of fish and involves three steps - capture, tagging and recovery. Beach seining can be used in this method where crews of five or six people capture the fish in a large net. The crew will then tag the fish then recapture salmon at the end of the run and count both fish with tags and without tags to calculate total numbers.

The mark and recapture allows Fisheries a chance to gather biological samples including scales and otoliths (a boney structure in the brain). From the samples biologists can examine DNA and learn more about the health of the stock. Benner showed an enlarged slide of a salmon scale and explained how biologists can determine the type of salmon and it's age through the pattern on the scale. The pattern looks like a fingerprint or tree rings. Although they have the ability to rejuvenate scales after an injury, salmon keep most of their original scales for life.

Benner talked about three new enumeration techniques, which utilize modern technology. Last year a type of sonar technology was used in the Horsefly River. Fisheries used the Dual Frequency Identification Sonar or (DIDSON) for the first time for an entire period of sockeye arrival in the Horsefly River in 2005, said Benner. The sonar device produces video-like images using sound, said Benner. The technology was developed by the United States army to find mines. Currently there is no computer program to count the fish and people are still used to count the salmon on the video image, said Benner.

The sonar system was used in conjunction with the mark and recapture program.

The second new technology is the Remote Operated Vehicle, a type of self-propelled underwater camera, which transmits real time video to a computer on the surface. The ROV surveys conducted in Chilko and Quesnel Lakes in 2004 and 2005 confirmed deep water sockeye spawning to depths of 45 metres, said Benner.

The third technology is telemetric monitoring. Telemetry studies utilize radio tags inserted though the mouth of the salmon to be placed in the stomach. The salmon can then be tracked along the Fraser River. This technology may help explain the disparity often associated between in season estimates and terminal area counts, said Benner.