by Smalma » Wed Feb 02, 2011 9:14 am
Robbo -
Yes what we are talking about are those blackmouth areas, which of course is really anywhere there are immature Chinook that actively feeding. The worst of the areas might be those that are producing those exceptional 30 or even 40 # blackmouth.
As you know Chinook migrate long distances with Washington fish going to SE Alaska and beyound and while doing so are feeding which of course means that they end experiencing some fishing mortality. That fishing on mixed age classes of fish have significant selection from older larger fish.
Frist those marine areas typically have minimum size limits; say 24 inches. Because individual grow at different rates the very fastest growing individual reach the legal threshold for harvest sooner than its slower growing cousins. That means it is exposed to potential of harvest/fishing mortality longer. That of course means the fast growing fish are less likely to survive and pass on its genes to the next generation.
Second as you mentioned when fish is good we anglers almost always will opt to keep the larger fish while releasing the smaller fish. That is another selection against the best fish - either the fastest growing or oldest fish.
And finally even a low level fishery and significantly alter the potential age structure of the spawning populatiuon post fishing. Just as an example lets assume that we have hypothical Chinook population that in lack of any fishing would have 1,000 3 year spawners, 1,000 4 year spawners, 1,000 5 year old spawners and 1,000 at 6 year of age. Further let's assume that 10% of the population is caught every year. The result wouild be instead of 4,000 spawners there would be only 3,095 spawners and more importantly instead of equal numbers of 3 year olds and 6 years old there would now be 900 three year olds and only 656 six years old. It would not take very many generations to see significant changes in the population age structure. The rate of that change increases with increased fishing rates.
The good news as illustrated by those Chilean Chinook is that Chinook populations generally what to have diverse age structure including significant numbers of old/large fish as shown in those photos. If we want to see those fish again we know where to look.
In a related matter the Elwha clearly historically had the type of habitat that selected for extremely large Chinook - fish more than 100 pounds. However even once those fish are allowed access to the habitat following the removal of the dams we will not see those fish. Why because even though the habitat is selecting for those big fish the ocean fisheries at the same time is selecting for younger/smaller fish. The likely result is that the result wild population say 25 years from now may well have larger individuals than say some of the interior sound rivers they likely will not be anything close to once was.
Tight lines
Curt