Salmonid Population Monitoring Programs

Adult Escapement Monitoring

Each year adult salmon and steelhead return to the Mattole River in the fall and winter to spawn, or reproduce.  The MSG conducts surveys throughout the watershed during this time to observe and record the amount of fish and redds, or nests, in which they lay their eggs.  Information collected about the salmon during a survey includes the species, sex, size, and location.  When possible, scale samples from salmon carcasses are taken for genetic information.  A salmon’s scale provides information similar to growth rings on trees.  Biologists can discover the age of the fish, how long it lived in the river or the ocean, and what the water conditions were like during that time.  This information is used to create a population estimate, and to guide habitat restoration planning.

Downstream Migrant Trapping

Spring and early summer is the season for young salmon and steelhead to migrate to the ocean.  The MSG monitors these fish as they swim downstream by trapping them in a rotary screw trap (pictured above) or a fyke net trap (pictured below).  A percentage of migrating fish are funneled into a tank, and each day they are “processed” and then released.  Processing involves documenting the number of each species, and their size.  This information is used to create a population estimate, and to guide habitat restoration planning.

Summer Stealhead Abundance Survey

The Mattole Watershed is home to a distinct population of steelhead that return to the Mattole every spring, and live in the river until fall and winter to spawn with the rest of the salmon when they return.  Each year the MSG hosts a group of volunteers to survey the entire watershed to record the number of summer steelhead.  The surveyors snorkel through the river and record the number and size of adult fish seen.  Temperature readings, invasive species, and habitat data are also recorded during these surveys.  The Summer Steelhead Survey weekend provides a snapshot of the status of the entire watershed at a single time.

Juvenile Distribution and Abundance Survey

Underwater dives, conducted in conjunction with water quality and temperature surveys, provide data on juvenile abundance throughout the watershed.  Dive surveys record where fish are located, their numbers (abundance), and how long they remain in their respective locations.  Surveys are conducted from spring through fall, when fish survival is most difficult, and most crucial.  Information from dive surveys is combined with water quality measurements and habitat data to show how fish react to their environment as it changes.  This helps guide habitat restoration planning.

MSG staff setting up a downstream migrant trap

To view the complete list of MSG monitoring reports, see the page Reports and Documents