Alewife migration patterns within the Mill Pond drainage system

Stockwell, Jason; Lamon, David

"Executive Summary: · The populations of spawning alewife at the Mill Pond Drainage System (MPDS) in Somesville, has increased from less than 1,000 in 2005 to more than 13,000 in 2010. · The current population is less than half the size and comparatively younger than the population in the 1950s. These patterns can be attributed to the current re-building of the MPDS population. · MPDS population is expected to greatly increase starting in 2011 as the progeny from relatively larger 2007 and 2008 spawning runs start to mature and recruit to the spawning population. · Larger, older fish entered the 2010 spawning run earlier than younger, smaller sigh, consistent with patterns from the 1950s in MPDS and other alewife runs in New England. This patter suggests frequent sampling throughout spawning runs is necessary to characterize spawning populations in an unbiased manner. · Individual growth (size at-age) of alewife in 2010 was lower than in the 1950s. This was unexpected because compensatory growth with the current lower abundances (i.e., more available resources per individual) should produce increased individual growth. · Approximately 2.5% of the fish entering the MPDS system at the head-of-the-tide fish ladder (HOTFL) migrated through Somes Pond to Long Pond in 2010. Only 5% of fish entering the HOTFL in the 1950s migrated to Long Pond. These data, along with unsuccessful stocking attempts in Long Pond in the 1980s, suggest Long Pond has low alewife production potential, insufficient spawner abundance to promote positive population growth, and/or fish passage impediments. (Research recommendations:) · Future research including “pulse” stocking efforts in Long or Somes Pond, surveys of juvenile alewife abundance and condition in Long Pond, enumeration of juvenile out-migration from Long Pond, and/or application of passive integrated transponders (PIT tags) would test several proposed hypotheses about the apparent inability to establish a sustainable run of alewife into Long Pond. · Because of the extensive historic data from the 1950s and the existing monitoring infrastructure, MPDS provides a unique and timely opportunity to better understand the impacts of a changing environment on alewife population dynamics. To accomplish this, directed monitoring and research an MPDS are required over the next three to five years. · Mount Desert Island could serve as a “laboratory” fro large-scale, multi-disciplinary restoration initiative that addresses ecosystem structure and function, with anadromous alewife as a focal point, using a scientifically-rigorous approach." Table 1 lists the age distribution of adult alewives counted at the fish ladder in the Mill Pond from 1954-1959 and 2005-2010. /STUDY LOCATIONS:/ /MOUNT DESERT ISLAND/Mill Pond/ Somes Pond/ Long Pond/