The Ups and Downs of Using Active Acoustic Technologies to Study Fish at Tidal Energy Sites

Acoustics, Biological/Ecological Effects: H. Viehman, D. Hasselman, J. Douglas; T. Boucher (2022/03/22)

Front. Mar. Sci. 9:851400.

doi: 10.3389/fmars.2022.851400

Active acoustic instruments (echosounders) are well-suited for collecting high-resolution

information on fish abundance and distribution in the areas targeted for tidal energy

development, which is necessary for understanding the potential risks tidal energy devices

pose to fish. However, a large proportion of echosounder data must often be omitted due

to high levels of backscatter from air entrained into the water column. To effectively use

these instruments at tidal energy sites, we need a better understanding of this data loss

and how it may affect estimates of fish abundance and vertical distribution. We examined

entrained air contamination in echosounder data from the Fundy Ocean Research Center

for Energy (FORCE) tidal energy test site in Minas Passage, Nova Scotia, where current

speeds can exceed 5 m·s-1. Entrained air depth was highly variable and increased with

current speed, and contamination was lowest during neap tides. The lower 70% of the

water columnandcurrent speeds<3m·s-1weregenerallywell-represented in the dataset.

However, under-sampling of the upper water column and faster speeds strongly affected

simulated fish abundance estimates, with error highly dependent on the underlying vertical

distribution of fish. Complementary sensing technologies, such as acoustic telemetry and

optical instruments, could be used concurrently with echosounders to fill gaps in active

acoustic datasets and to maximize what can be learned about fish abundance and

distribution at tidal energy sites.

Keywords: active acoustics, hydroacoustics, fish, entrained air, data quality, marine renewable energy, tidal energy, MHK