Google recently released a worldwide timelapse of aerial photos over the last 30 years. Zooming in to western Washington, the Earth Engine shows how our landscape has changed since the mid 1980s.
Over the same time period, tribal harvest of coho and chinook has declined. In some places tribes don’t even fish for certain species anymore.
This chart shows combined coho and chinook catch during that time:
The dramatic change illustrated by Google Earth Explorer represents a slew of impacts on salmon productivity, including polluted and warming water and a decline in spawning and rearing habitat..
This is pretty well understood, when you protect and restore salmon habitat, more salmon survive. A study on the Columbia River spelled this out pretty clearly:
The analysis showed significantly higher survival of juvenile fish from areas with large numbers of habitat actions compared to those from areas with fewer actions. The results were consistent across various models used to assess fish survival: Nearly all models that considered habitat important showed a positive correlation between habitat improvements and juvenile survival.
The treaty tribes are continually tracking these indicators by updating the State of Our Watersheds Report. The report tracks indicators such as forest health, impervious surface and shoreline armoring.