Disconcerting news; thanks for posting.
I've generally been an advocate of net pens simply from an economic view--the more fish on the market, the lower the demand for wild fish. Prior to this report, my impression was that most escapees of Atlantics involved adults. Some the escape numbers have been pretty spectacular over the last 10-20 years, but there is absolutely no evidence that these fish have reproduced to a point of producing a naturally reproduced adult Atlantic salmon (a few fry were observed in a one or two Vancouver Is. streams I believe, but no wild adults).
The escape of juveniles into any natural system can represent another story. While adults have been raised in a net pen there whole lives and are very ill equipped to life in the wild (not to mention being raised in the wrong ocean), it would make sense that juveniles would at least have the opportunity to adapt to conditions and, if they survived to maturity, could be more successful at reproducing. Another big concern is the effect of a large number of "foot long" juvenile Atlantics on wild juvenile salmon.
Lets hope WDFW took out stomachs to do stomach contents analysis on the fish to determine if they've been feeding on sub-yearling coho. If they escaped this spring, they could have made hay with outmigrating chinook and chums, as well. Since WDFW is considering an active removal program, all of the fish removed should be examined for what they're eating. Results can probably be published in the scientific literature since I do not believe anything like this has been studied. If it is found that substantial predation is occurring on juvenile salmon, the issue really needs addressing. If predation on chinook is occurring this would represent a direct take under ESA and depending on how happy the Feds get, may really shut things down.