Historically the Chinook and pink salmon had parsed the various spawning habitats (pinks using shallower and smaller gravels while the Chinook deeper and larger gravels/stones) for their spawning. This worked well for both species maximizing the collective success of both. While these strategies may work to some extent on the Skagit basin in other basins it has broken down completely will huge negative impacts on the success of natural spawning Chinook.
In basins like the Stillaguamish where the gravel size has been reduced to the point that both species are competing for many of the spawning site. The result is that are very limited unmolested spawning opportunity for Chinook. Even 3 decades it was common on the NF Stilli to see female Chinook that begins the process of spawning to be mobbed by dozens of pinks to the site with a negative impact on the success of that Chinook redd and its eggs. It has been a successful strategy for pinks to use mass spawning with waves of spawning fish. Each wave while digging up many of the eggs from previous spawners find gravels that have cleared of much of the finer sediments creating a better environment for the survival of those later eggs.
Historically it was common to see a female Chinook spend 10 days or so on her redd site. Much of that time was not in the redd construction process but rather in protecting that site from other spawning fish. This helped protect the redd and the buried eggs from the jostling from fish spawning on that site until the eggs had a chance to develop pass their most fragile stage where even minimal jostling would result in elevated egg mortality.
As the pinks mob a Chinook redd site (within the numbers potentially numbering a 100 or more fish) the female Chinook attempts to defend that redd site by chasing the pinks away. As the numbers of pinks increase this activity becomes a doomed exercise. Within 2 or 3 days the Chinook reaches a state of exhaustion and death leaving the redd site unprotected and its eggs vulnerable to increased mortalities.
Declining Chinook productivity in the Puget Sound region is likely influenced by the confluence of competition between species, decreased substrate stability and size, increased flooding, lower summer flows and decreased Chinook size and fecundity.
A further thought on pinks and Chinook, I find it interesting that on the NF Stillaguamish Chinook have not meet its escapement goal in at least 4 decades. Meanwhile the pinks which should be more vulnerable to flood impacts have consistently met or exceeded its escapement goals several times a decade. Meanwhile to the south on the Green, Puyallup, and Nisqually the Chinook remain in trouble while pink escapements are often an order of magnitude larger than historical goal. How can that be? Certainly, part of the answer is that ocean conditions favor the pinks. But an aspect rarely discussed is that once pinks hatch, they quickly migrate downstream and through the estuaries within days of hatching. While the Chinook require several months of rearing in the river and/or the estuary before successfully transition to a more marine environment. I think the fact the Chinook are not making that transition is a statement on the poor condition (at least for Chinook) of that freshwater and estuary habitat.
Curt
