| Abstrakt: |
Diadromous fish use both freshwater and marine habitats to complete their life cycles, but dams restrict those connections, and as a result, many populations are historically low across their range. The Penobscot River, Maine, USA, once had large populations of diadromous fish and has recently been the focus of large restoration projects. Our objective was to assess the river restoration impacts in the estuary using mobile, multi-frequency echosounders (SIMRAD EK60 split-beam 38 and 120 kHz) to construct a time series of fish distribution using metrics of fish length and fish density, both seasonally and pre-restoration (2012–2014) versus post-restoration (2015–2019). Seasonally, fish size was the smallest in summer, while density and biomass were greater as compared to spring and fall. Between pre- and post-restoration years, fish length did not differ, and with a median of 4.7 cm, median density increased from less than 0.5 fish m−2 to greater than 1 fish m−2. Fish biomass was approximately three times greater in post-restoration years where it ranged 23 to 316 mt per survey than pre-restoration years where it ranged from 9 to 114 mt per survey. These patterns are consistent with a system undergoing restoration of migratory fish where larger adult fish migrate in the spring and their juveniles in the summer and fall. This study demonstrates the ecological impacts of river restoration on its estuary by quantifying multiple metrics (fish biomass, density, and size). [ABSTRACT FROM AUTHOR] |
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