Trout conservation strategies for the Rapid River

Habitat protection:

Key nursery areas, recently identified, should receive the highest level of protection from potentially adverse land use activities (timber harvesting, road construction/maintenance, seasonal residential developments on the shorefront or in the watershed, etc.). Also, it is essential that the connectivity of habitats critical to Rapid River trout be maintained. These habitats include Pond in the River and Umbagog Lake, which provide important mid-summer and over wintering habitat for Rapid River trout. For this reason the Department does not support proposals to construct a barrier to isolate the Rapid from Umbagog Lake. The impoundment formed by a barrier would also have the effect of eliminating important riverine habitat, as well as eliminating riverine fishing opportunities.

Reduce interspecific competition from landlocked salmon:

Landlocked salmon, which were introduced to this drainage late in the 19th century, are competitors with trout in the Rapid River. Competition for limited spawning substrate has been documented, and we have evidence that young salmon compete with trout for nursery space, particularly during the late summer period. In addition, there is likely strong competition for food among most age classes of each species. Therefore, our trout conservation plan should include efforts to reduce salmon numbers. The Department has moved forward to achieve this by relaxing salmon harvest regulations.

Trout genetics:

Studies to determine the genetic characteristics of the Rapid’s brook trout population were completed in 2004. These studies indicated that Rapid River trout were genetically distinct from other Maine populations, but were very closely related to trout from the upper Kennebago River drainage and the lower Magalloway River. In the event that natural reproduction fails due to predation and competition from bass, a stock enhancement program, using large spring yearling fish of the Rapid River strain or a similar strain from a nearby drainage, could potentially preserve fishing opportunities for these very special fish.

Minimize impacts from smallmouth bass:

Eradicating bass from this immense and biologically complex ecosystem is impossible because their reproductive potential is very high and habitat for all life stages is excellent. Based on our current knowledge, controlling bass numbers in Pond in the River through large-scale removal efforts (such as boat-electrofishing) is not likely to succeed due to their high reproductive potential and the presence of excellent habitat, including in downstream Umbagog Lake. Moreover, there is some evidence to suggest that massive removal may actually exacerbate bass production by reducing competition among themselves, and/or by increasing their reproductive success. Also, there is the likelihood that large adult brook trout, which are present in Pond in the River during times when electrofishing would occur, could be severely injured or killed by high power outputs required for effective bass removal. The Department concludes that large-scale efforts to remove bass from Pond in the River would be ineffective, costly, and potentially injurious to adult trout.

Studies conducted since 2003 indicate critical habitat for very young trout, the life stage most vulnerable to bass, is concentrated in the Rapid River rather than in Pond in the River, so any bass control program should focus on the river.

In northern climates, abiotic (climatic) forces have been shown to exert a powerful influence on smallmouth bass populations. Climatic forces, be they natural (such as spring and summer air temperatures) or anthropogenic (such as stream flows in regulated rivers), generally control bass reproduction, recruitment, and growth processes to a far greater extent than angler exploitation. Therefore, identifying abiotic factors that act as stressors to smallmouth bass recruitment and growth should take precedence over intensive, technical approaches. Techniques should have practical management application, be sensitive to water level/flow considerations in both upstream and downstream waters, and be sustainable over time.

A number of fishery researchers have determined that water levels and flow velocities can influence habitat use, energetics, and growth of smallmouth bass. For example:

  • In lakes or streams, nest abandonment and/or reduced egg and fry survival can occur with a rapid rise or fall in water level. A rise of just a few inches may displace advanced fry newly raised from the nest.
  • In streams, bass nests located in areas where flow velocities exceed 0.10 ft/sec may fail to produce a brood. Swim-up fry may be displaced from nest sites at even slower velocities.
  • Bass fry less than 1 inch long have difficulty maintaining position if current velocities exceed 0.7-1.0 ft/sec. The probability of displacement of advanced fry (1-1.5 in) may be 100% where stream velocities exceed 0.8 ft/sec.
  • Optimal growth of fingerling bass appears to occur at velocities of 0.3 to 0.4 ft/sec; velocities above 0.5 ft/sec may result in reduced foraging and growth rates. (Note: first-year growth is a critical determinant of over-winter survival of bass fingerlings in northern climates).
  • High winter discharges may “flush” age 0 smallmouth bass from winter refuge habitat.

The feasibility and effectiveness of manipulating flow velocities to “stress” smallmouth bass was evaluated in the Rapid River from 2005 to 2007. These studies showed that manipulating river flows from Middle Dam during the bass spawning season has the potential to limit bass numbers, thereby improving survival of brook trout. Department biologists are currently working closely with staff from FPLE (the owner and operators of Middle Dam) to implement a systematic program of carefully timed flow pulses to control bass numbers in the Rapid, within the constraints imposed by the other water users in the Androscoggin River drainage.

Written by:

Dave Boucher
Fishery Biologist
Rangeley Lakes Region
April 2008

For more information, please contact:

Dave Boucher, Regional Fishery Biologist
689 Farmington Road
Strong, Maine 04983-9419
Telephone: (207) 778-3322 Ext. 22