Biological Projects

During spawning runs, biologists have the opportunity to count the number of fish traveling upstream and to try to ensure that adequate numbers of spawners and their nutrients are brought back to the freshwater system. Different tools are used depending on the river's characteristics, its remoteness and the level of funding available. These tools include aerial surveys, counting towers, sonar, and weirs.

Salmon are the main fish species biologists try to gather information on. This is because managers need to ensure that enough salmon of each species are entering drainages each year. Biologists and managers try to keep track of escapement numbers, the annual estimated number of adult salmon for each population that escapes past the fisheries to spawn. Fishermen are allowed to harvest salmon only when managers believe that there will be enough salmon spawning to generate healthy salmon runs in the future. The most useful and desirable tool for biologists would provide a daily tally of the number of each species that head to the spawning-grounds. These daily tallies would combine to provide an accurate escapement count. Fisheries managers would also like to know the age and sex composition of each run to help determine the reproductive potential of the fish entering the system and which parent year these returning fish were hatched from.

Aerial Surveys:
The least expensive way to count salmon is from the air when the salmon are at the peak of spawning. Groups of salmon, like the one shown at left, are counted. Aerial surveys provide an index estimate than can be compared from year to year. For some river systems, these aerial spawning ground surveys provide the only data about salmon runs. Biologists also fly in-season surveys prior to the peak of spawning just to get an idea of how many salmon are entering freshwater. Aerial surveys alone do not provide age or sex composition data for the salmon counted.

Counting Towers:
Counting towers are used in clear rivers to count the passage of salmon. Total hourly passage is estimated from shorter counting periods. The towers give the technicians a higher vantage point from which to make counts (see photo of Goodnews River counting tower at left). Fish are captured using nets to determine the age and sex composition.

Sonar:
Sonar is useful to count fish in water that is too turbid for visual counts. The sonar equipment is expensive and requires some technical expertise to operate. In the photo at right, a researcher is reading data collected using sonar on the Togiak River. Sonar provides a total count of fish passage of all species, and does not identify species individually. Fish are captured using nets to determine the species, age, and sex composition.

Weirs:
Weirs that funnel the fish into counting chutes and sampling boxes have been used by fisheries professionals for decades. The photo at left shows the modern floating weir design which allows rafts and motorboats to cross over the weir with little effort. These weirs consist of a picket fence made of PVC pipe that is anchored to the stream bottom on one end while the upper end is allowed to float downstream. All the fish are then funneled through one gate which allows biologists to get a good view of the fish to determine the number of each species passing upstream. The advantage of this tool is that every fish is potentially accounted for, and fish can be funneled into live boxes were they can be easily sampled for age and sex composition.