Using Otolith Microchemistry to Infer Life Histories of American Shad Habitat Use in the Penobscot River, Maine

Removals of Veazie and Great Works Dams were completed by 2013 in conjunction with upstream fish passage modification projects as part of the Penobscot River Restoration Project. Prior to these changes, upstream passage of American shad was negligible through Veazie Dam, such that available freshwater spawning and rearing habitat was limited to a 16 km tidal reach below the dam. Juveniles were sampled by trawl from the estuary in 2011 and 2012 and migrant adults were sampled during 2013, 2014, and 2015 via angling and opportunistically as mortalities in the Milford Dam fishway. Otoliths extracted from these fish were analyzed using a high resolution ICP-MS coupled to a laser ablation system. For each sample, ablated material along a transect extending from the core to the edge of the otolith provided data on ²⁵Mg, ⁵⁵Mn, ⁸⁵Rb, ⁸⁸Sr, ¹³⁸Ba and ⁴⁸Ca relative to otolith annuli. Using otolith micro-chemical analysis (i.e. Sr:Ca ratios) data will be used to infer patterns of salinity experience in this spatially restricted population prior to reconnection with upriver habitat following dam removal.