Jeff, I think it is a sure bet to state that native species population declines like that experienced by lake whitefish in Maine lakes are not simply a function of the introduction of one 'culprit" species- rainbow smelt. I also do understand that this is the drum TU often opts to beat to raise funds, but in nearly every instance there is a constellation of co-occurring environmental changes that contribute to the broader outcome.
https://www1.maine.gov/ifw/docs/fisheries-reports/2016/lakewhitefish_currentstatus.pdf
The author either opts to leave out, or fails to consider two co-occurring events that wracked poorly buffered lakes in the northeast in the 70's and 80's: 1.) Acid precipitation events from increased sulfur dioxide atmospheric concentrations. 2.) EPA mandated nitrogen and phosphorus emissions reductions resulting in marked dry fallout declines, with eventual concomitant declines in point source and surface runoff decreases in these two important nutrient classes as well.
Lake whitefish are benthic feeders, with a sub-terminal mouth that enables them to be efficient consumers of aquatic oligochaetes, fingernail clams, small gastropods, benthic invertebrates, and seasonally, non-pelagic fish eggs in oligotrophic systems. These systems are, by definition, not very productive. They also generally have low carbonate-bicarbonate buffering capacity making them highly susceptible to marked pH declines from sulfur dioxide inputs during spring/summer precipitation events, as well as that bound in snow pack and released, bolus fashion, during melt events during the course of a winter, as well as when snowpack loss occurs. Marked reductions in total productivity occurred during the interval the author fails to address as an adjunct driver to declines in lake whitefish stocks in many, but not all Maine lakes where Atlantic salmon and smelt were introduced. The loss of complete year-classes, as well as the resulting truncated age-class array through time of lake whitefish is prototypic of fish populations whose calcium metabolism is adversely impacted by acid precipitation driven shifts in pH. Yet, the author makes no mention of this...how odd.
The author does note that this interval was also noteworthy due to increased angler exploitation as sport fishers "discovered" lake whitefish as a sport fish. He makes one other very telling observation, by singling out one lake system which has sustained its lake whitefish population due to its "very rocky shoreline". As you are likely aware, acid precipitation impacted lakes are noteworthy for their enhanced light penetration,a secondary indicator of "lost" biogenic turbidity. I suspect that this particular lake system's rocky shoreline contributed significantly to preservation of adequate benthos populations to sustain lake white stocks due to the expanded surface area this type of substrate, combined with the expanded photic zone from the enhanced maximum depth of those wave-bands responsible for driving primary production via photosynthesis providing forage for macro invertebrates the lake whitefish exploit.
One of the marked but unforeseen secondary impacts of passage and enactment of the Clean Water and Clean Air acts in the late 1960s that has been recently documented extensively in the Great Lakes has been a decline in productivity of aquatic systems as dry fallout and point source inflow of N and P has markedly declined, along with the noteworthy declines of input rates of these two key nutrient classes via surface runoff as well. I suspect this trend is common in oligotrophic lakes in the northeast as well. In a fishery where sport fishing exploitation increased as productivity decreased in lake systems with already inherently low production at baseline does not bode well for the future of that fishery.
Noteworthy, too, in this overview is the complete lack of any consideration of adverse impacts that might be attributed to introduction of land-locked Atlantic salmon foraging on endemic lake whitefish stocks in these systems. Apparently, in Maine, hatchery origin Atlantic salmon feed solely on co-introduced smelt...with no need for secondary documentation that this actually occurred, nor consideration that these introduced salmon have contributed to lake whitefish stock declines. You folks are aware that a lake has the endemic capacity to produce a finite amount of fish biomass, annually and seasonally...when two non-native species are added, apparently only one of these can be construed as a causative agent in endemic fish stock declines? Does everyone who works in fishery biology in Maine have to have chronic "adipose fin disease" to get hired?
Yes, I also appreciate the ironic dichotomy of your reverence for shooting and consuming goldeneyes, while maintaining a high level of disdain for northern pike as table fare-fascinating.
. This time of year every year I get interested, but don?t follow through.