Challenges for Diadromous Fishes in a Dynamic Global Environment

An Evaluation of Nature-Like Fishways for Passage of Anadromous Alewife

Abigail Franklin, Alex Haro, and Theodore Castro-Santos

doi: https://doi.org/10.47886/9781934874080.ch74

Nature-like fishways were designed in part as a response to poor or unknown passage efficiency of technical fishways, to address a desire to reconnect river corridors, and provide passage for all species occurring in a system (FAO 2002). The first naturelike fishways were developed in Austria, Germany, and France. A nature-like fishway typically consists of a wide, low-gradient channel with a 1:20 slope or less and a concave stream channel cross section. Natural cobble or boulder substrates are used to dissipate hydraulic kinetic energy and to reduce channel velocities to levels that allow fish to pass at sustainable (i.e., aerobic) swimming speeds. Naturelike fishways have been designed as bypass channels around dams, as roughened ramps constructed in association with a dam, and as stream restorations with complete dam removals. Fish are believed to find natural substrates more acceptable than concrete channels or channels with baffles in technical fishways (FAO 2002). The low velocities at the margins and hydraulic boundary layers of this fishway design allow for greater potential passage of small or weakly swimming species.

Evaluations of nature-like fishways in Europe have shown variable success. Nature-like fishways have been constructed in Canada and in the western and northeastern states in the United States, but have not been evaluated extensively for passage of North American species. The goal of this project was to evaluate a nature-like fishway design in the northeastern United States (Massachusetts) for passage of anadromous alewife Alosa pseudoharengus.

Alewife are a relatively small (maximum fork length = 40 cm) anadromous, iteroparous species that range from northeastern Newfoundland to South Carolina (ASMFC 1999). Alewife migrate from the ocean to their natal river when water temperatures increase in the spring months. They spawn in lentic waters, and adults leave freshwater quickly after laying their eggs. The juveniles feed on zooplankton and migrate downstream to the ocean when water temperatures drop in autumn (Loesch 1987). Alewife populations have been declining since the industrial age due to overharvest, poor water quality, and blockages to spawning habitat. Movements of alewife may be blocked by a structure creating a vertical hydraulic drop of only 20–30 cm (ASMFC 1999).

The National Oceanic and Atmospheric Administration Habitat Restoration Program funded the removal of the Billington St. Dam on Town Brook in Plymouth, Massachusetts, in 2002, with the goal of increasing spawning habitat. The dam was replaced with a 30-m-long perturbation boulder-style nature-like fishway. Passive integrated transponder telemetry was used to monitor the movements of alewife through the fishway, using methods described in Castro-Santos et al. (1996). Four antennas were placed across the fishway, and 400 fish were tagged internally with 20-mm tags in seven separate batches from April 19, 2006 to May 15, 2006. Water temperature and level were recorded using underwater data loggers. Water temperatures ranged from 9.968C to 23.588C over the field season.