The inner the Bay of Fundy, in particular Minas Passage, has been identified as one of the primary
locations in eastern Canada for the installation of tidal in-stream energy conversion (TISEC)
devices. The interaction of fish populations with TISEC devices and the long term impact of these
interactions is a major source of uncertainty in the development of tidal energy. In addition, the
prevalence and natural behaviour of fishes at many potential development sites, including Minas
Passage, is poorly understood. Unfortunately, the physical characteristics of the Passage, water
clarity, and tidal currents/flow precludes effective use of many conventional fish monitoring tools
such as video for close-in turbine interaction studies and the deployment of trawling gear.
Conventional Simrad EK60 split-beam echosounding (120 kHz) was employed in Minas Passage
during eight seasonally distributed 1 to 2 tidal cycle duration acoustic surveys to investigate fish
spatial-temporal distributions and behaviours both in the FORCE turbine test sites near Black Rock
and extending across the adjacent wider Passage. Split-beam surveys were complemented with a 2-
D Simrad-Mesotech MS 2000 multi-beam (200 kHz) sonar and custom software for the extraction
of relative volume backscatter, a still experimental but emerging fish detection technology (Melvin
et al. 2003). Two new acoustic monitoring technologies, namely the CodaOctopus 3-D multi-beam
sonar (375 kHz) for short range turbine interaction studies and the ASL bottom mounted
echosounder (125 kHz) for long-term point site monitoring were also evaluated.
The best quality and most reliable Minas Passage fish data were obtained from the split-beam
system. Extensive, calibrated split-beam results are presented in graphic and tabular form for both
the acoustic volume backscatter (Sv) and target strength (TS) regimes. Briefly, backscatter levels in
both the Channel and near the initial TISEC test site peaked strongly in June, the culmination of an
upward trend initiating in March. These observations are consistent with the late spring - early
summer influx of herring (mainly adult) and other seasonally transient species. August backscatter
levels were measurably lower but subsequently rose modestly until November, consistent with the
anticipated late summer and fall sea-going exodus of anadromous young-of-the-year springspawning species through the Channel. Backscatter levels declined during mid-winter prior to the influx of spring-spawning herring. This interpretation was also supported by the split-beam analysis of fish target strengths (TS’s) with strongest mean TS’s in May and August when migratory fish
species may be moving though the Passage. Column biomass estimates ranged from < 1 to 7.5
tons/km2 on employing a backscatter to biomass conversion appropriate to herring. Acoustic
backscatter levels delineated seasonally complex and sometimes contrasting patterns of vertical fish
distribution in the Channel and in the shallower test site area, patterns which appeared to be
additionally influenced by diel fluctuations in ambient light levels and by tidal phase. Mid-water
column fish concentrations observed at the test site could potentially interact with tidal turbines.
Backscatter vs. depth data from these surveys should assist evaluation of potential fish stock
interactions with future tidal turbine configurations. September 2010 observations of the in-place
OpenHydro turbine by both survey systems revealed strong, seemingly buoyant acoustic wakes
proceeding from the downstream side of the turbine although normal turbine operation was unlikely
at this time.
Quantification of both the split-beam and multi-beam systems was seriously hampered by tidal
turbulence generated backscatter (bubbles) affecting the top 10 - 20 m of the water column and
frequently deeper. This effect was most prominent in the test site area except near slack tide.
2 Bubble cloud effects proved especially intractable in the MS 2000 multi-beam analysis in spite of
custom tools employed to minimize their effect along with the effects of radiated vessel noise and
cross instrument acoustic interference. When reliable multi-beam fish data could be extracted,
results were generally consistent with those of the more noise immune split-beam system.
Sea tests of the CodaOctopus 3-D sonar and ASL Profiler were restricted to less turbulent waters
than Minas Passage. The Coda sonar displayed a maximum detection range in the order of 30 m for
acoustic test targets representative of individual adult herring – and, by inference, lesser ranges for
many smaller fishes of interest in Minas Passage. While the Coda unit was suitably packaged for
autonomous underwater deployment, such operation was characterized by high power consumption,
critical operational adjustments, firmware signal processing of uncertain quantitative characteristics,
and excessively high levels of real-time signal decimation. The system was also very costly for a
high risk environment. These characteristics in combination appeared to make the Coda unit
unsuited for the autonomous monitoring of fish stocks or for the monitoring of the full (OpenHydro)
turbine aperture from a spatially remote bottom deployment. The unit might have some potential
for short range turbine aperture observations if mounted on the turbine superstructure itself with
remotely supplied power and high speed (fiber-optic), real-time data and control links to shore.
The ASL profiler, trial deployed on bottom in a high speed tidal channel in Passamaquoddy Bay,
performed well, obtaining a continuous, low noise full water column (approx. 50 m) profile of fish
backscatter including an apparent marine mammal detection. The unit is low cost, self-contained,
and engineered for autonomous operation with sufficiently modest power requirements and ample
data storage to make multi-month deployments feasible. While probably unsuited to close-range
turbine aperture monitoring, such a unit, properly housed and protected, has potential for
continuous, fixed-location, high vertical resolution monitoring of water column backscatter levels
including transitory events in Minas Passage or elsewhere.