Rediscovering Penobscot River American Shad: Establishing Baselines Prior to Restoration

American shad were historically abundant in the Penobscot River, Maine; however the run has decreased drastically in the last 200 years due to a combination dam construction and habitat loss. American shad cannot pass the head-of-tide dam (Veazie Dam; 48 rkm), and access only a small portion their historic range. Though no formal population assessment has occurred, conservative management estimates range from 0 - 1000.  The planned removal of the two lowest main-stem dams, Veazie Dam and Great Works Dam (rkm 60), installation of a fish lift at the third dam (Milford Dam; rkm 62), and other passage improvements are expected to restore shad access to 93% of their historic range. A large-scale fry stocking program has been proposed to complement increased habitat access and accelerate population recovery. In light of both the restoration project and the proposed stocking program, we sought to collect baseline data on Penobscot shad presence and migratory behavior, and abundance.

In 2010, we radio tagged twenty adult American shad, and tracked their migrations throughout the lower Penobscot River system. Fixed Dual-Frequency Identification Sonar (DIDSON) imaging surveys of were also conducted at the base of Veazie Dam throughout the spring in 2009-2010. Both these efforts will be continued and expanded in 2011. Our 2010 results indicate that shad residence times ranged from 0.31 – 25.44 days (mean 8.47 days) post-tagging. While few radio-tagged shad migrated to the base of Veazie Dam, 35% of tagged fish moved to within three rkm of the dam. American shad recaptures were concentrated in an area five rkm below Veazie Dam near the previously breached Bangor Dam. This breached dam is a potential passage barrier at low tide; however spawning activity was observed immediately upstream of this site.  Analysis of the hydroacoustic data indicates that DIDSON technology is an effective tool for measuring lengths of imaged fish and for estimating numbers of fish encounters. DIDSON images were used to identify four Penobscot River fish species (alewives, American shad, Atlantic salmon, and sea lamprey) based on length and schooling behavior, and to develop length-frequency distributions of migratory American shad.