I just read your report Don,and the most obvious thing that I took from it,if not overly simplistic answer,is possibly predation?It mentions an increase in brook trout over the same time period,which I think suggests two things?
One,that water quality isn't the issue,since as far as I know(?) browns can tolerate less favorable,warmer,siltier water conditions better than brookies can?A healthy brookie population is generally a good indicator of a healthy watershed.And two,that perhaps the increase in brookies is having a negative effect on the brown population thru predation on eggs and fry,if not directly responsible for the decrease?
Mink and otter are also mentioned but the effects of their predation seems to be dismissed as minimal,apparantly because they haven't been observed streamside very frequently,which is a mistake IMHO?
First of all,both mink and otter are generally elusive animals,mink especially so.Think back over the years how often you've actually seen mink in the wild?Not very often I'll bet?But they are there nonetheless.Hell,aside from walking 100s of miles of streams fishing over the years,I also trapped for the best part of 2 decades,and I can say without question I've trapped far more mink than I've ever seen running wild.Same goes for otters to a lesser extent,since they are substantially larger and more visible.Just because you don't see them doesn't mean they aren't there,and any trapper worth his skinning knife could walk a stream and observe the tell tale signs of mink and otter on streams where they are rarely if ever observed in the flesh.
On otters,they often have large territories or circuits that they run,covering miles and miles of interconnected lakes,streams and rivers.Sometimes that circuit takes them 2-3 weeks to run full circle.Otter trapping is often an exercise in patience,and setting on hot sign from yesterday might mean 2-3 weeks before that otter returns to that location.As predators,they can absolutely devastate sensitive,isolated trout populations during winter in small lakes,ponds,and beaver dammed streams where the trout can't escape.They will literally clean out a beaver pond of trout before moving on to the next.Lastly,it appears that the decline of trout began not long after the end of the fur boom in early 90's when fur prices crashed,lots of trappers hung up the steel and furbearer populations exploded in many areas.In NB,I witnessed the effect that an explosion of coyotes in the 90's contributed to the demise of our whitetails,which have never recovered to this day and I'm not optimistic ever will due to other contributing factors,most significantly the change in forestry practices over the last few decades.Eastern coyotes are a relatively new predator,first appearing in NB in the 50's,and filling the niche of wolves that were for all intents and purposes extirpated around the turn of the century,allowing whitetails to thrive almost predator free for close to a century.Coyote numbers for decades were kept in check by high fur prices,but when the fur market crashed,they overran the entire east coast,even finding their way across ice flows to PEI first and now NFLD also.That said,I don't think it's too big of a stretch to surmise that a lack of trapping pressure and the likely resultant increased mink and otter populations could have a serious effect on trout that were doing quite well when furbearers were kept in check thru trapping pressure?
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