Improving Hydroacoustic Data Collection and Processing Methods to Estimate Fish Abundance before and after Dam Removal

As part of a large scale river restoration project, two dams were removed from the lower reach of the Penobscot River, Maine, in an effort to restore this tidal river’s native fish populations. To estimate changes in fish abundance before and after dam removal, stationary hydroacoustic data were gathered prior to dam removal. Data were collected on both sides of the river using two side-looking transducers from 2010-2014, starting in May and ending in November each year. Data processing challenges arose from a variety of acoustic interferences, including: (1) a space-time varying interference line that required removal before automated analyses could be considered; (2) range-varying signal-to-noise ratios that complicated fish movement direction and target strength values; and (3) large side lobe beam patterns from elliptical transducers that exacerbated interference levels. We will present automated methods for solving these challenges that will enable us to extract more precise fish count numbers from larger quantities of data. We will also present challenges associated with gear deployment and new options for mounting side-looking transducers that will enhance the signal-to-noise ratio. These solutions are expected to improve the quality and quantity of data used to assess changes in pre- and post-dam removal fish abundances.