Fish And Chips

By Scott Putnam, Idaho Department of Fish and Game While last year's chinook salmon season is only a memory to most anglers, Idaho Fish and Game is already working towards future salmon seasons by counting young salmon smolts as they make the trip west. As part of the smolt monitoring program lead by senior fisheries research biologist Ed Buettner, Fish and Game operates three large fish traps on the Snake, Clearwater and Salmon Rivers to study the spring out-migration of juvenile chinook salmon and steelhead trout to the Pacific Ocean. Migration secrets of salmon and steelhead are slowly being uncovered with the help of tiny microchips called Passive Integrated Transponders, or PIT tags, which are the size of a rice grain and weigh a mere .06 grams. Each tag consists of a microchip, a chip-capacitor and an antenna encapsulated in glass, making it impervious to almost everything. Each tag has a unique code that gives each fish its own identification number for life. "The information provided by PIT tags is invaluable," Buettner said. "With PIT tag technology, we are now able to build a life history of a particular fish or group of fish." After being netted from the trap's live well and then anesthetized, a PIT tag is injected into the juvenile fish's abdominal cavity. Chinook and steelhead as small as 2.5 inches can be tagged. After tagging, each juvenile fish, or smolt, is measured and inspected for injuries or previous research identification marks. All of this information is recorded in a computer database. The smolts are then quickly returned to the river once they have fully recovered from the anesthetic. PIT tags provide unique identification, not long-range tracking. However, strategically located PIT tag readers can help to study migration habits and movements to and from specified areas. For example, readers are located on the three Fish and Game fish traps and at the main stem Snake River and Columbia River dams. The Snake River smolt trap is located downstream of the interstate bridge between Lewiston and Clarkston. The Clearwater River trap is located upstream of the Potlatch mill at a site commonly known by anglers as the Cat Hole. The Salmon River trap is located in the Twin Bridges area near Whitebird. These interrogation sites record passage dates and times for migrating fish. As a smolt passes a reader antenna, the reader turns on the tag circuitry by radio because PIT tags have no internal battery, thus the term "passive." Most tags are read within three to nine inches of the antenna. The reader then translates the code sent back from the tag and records tag number, location, date and time. With the data recorded at each monitoring site that the migrating smolts pass, biologists can determine precise and accurate migration timing and survival for tagged fish. This knowledge can then be used to answer specific questions. For example, biologists can determine how long it takes a fish to get from point A to point B and then correlate that with environmental factors such as water flow, water temperature or turbidity. Data has shown that juvenile spring and summer runs of chinook salmon that migrate in years with higher flows survive at higher rates than juveniles migrating years with lower flows. Fish and Game can also determine survival from point A to point B and uncover smolt to adult survival. PIT tags are an important tool for managing these magnificent fish. By applying the knowledge gained, biologists are better able to ensure the survival of the species and hopefully provide future angling opportunity. Scott Putnam is a senior fisheries technician working out of the Clearwater Region. He has worked for IDFG since 1998.