Fish in a Tidally Dynamic Region in Maine: Hydro Acoustic Assessments in Relation to Tidal Power Development

Fish ecology in regions of extreme tidal flows is poorly understood, but as these areas link on- and off-shore habitats, they are important to many marine and diadromous fish species. Strong tidal currents are also being targeted for energy extraction, but the effects of tidal energy devices on fish are unknown. The probability of fish encountering a tidal energy turbine is highly dependent on the vertical distribution of fish at the project site. In extremely tidal coastal areas, fish presence and distribution is heavily influenced by tidal, diel, and seasonal cycles. Understanding the vertical distribution of fish therefore requires sampling on a fine temporal and spatial scale. Stationary hydroacoustic surveys may be used to gather these data, as part of a BACI (Before, After, Control, Impact) type study design, to predict then monitor the effects of tidal energy devices on fishes. In May 2010, a down-looking, single-beam SIMRAD echosounder and a DIDSON (Dual-frequency IDentification SONar) unit were used to document the relative density of fish throughout the water column at a targeted pilot project site and a control site in Cobscook Bay, Maine. Stationary 24-hour surveys were carried out each season to examine variation in fish density and vertical distribution. Relative fish density was highest in spring and fall, and almost always increased near the bottom, regardless of tide or time of day. Tide and day/night had some effect on the vertical distribution of fish, but the effect was not the same each month. Results from these analyses will be used to predict the likelihood of fish encountering the turbine and to create a basis for comparison of data collected after device installation. Direct observation of fish reactions to a full-scale test device was carried out in September of 2010. A test turbine suspended below a floating research platform was monitored for 24 hours using two DIDSON units. A higher proportion of fish interacted with the device when it was still than when it was rotating. A greater portion interacted at night, and the type of interaction shifted from avoidance during the day to passing into the turbine at night. This behavioral shift was most obvious in small fish (\u3c10 cm), nearly all of which passed through the device at night; most large fish (\u3e20 cm) still avoided the turbine. Most fish were present at night during the slack tide. Combining the baseline knowledge of where fish are in the water column with knowledge of how they behave in close proximity to an operating tidal device will provide a more complete picture of the potential effects these devices could have once installed

Viehman and Zydlewski 2017 Fish Count Data

This .csv file contains the two-year time series of the hourly counts of fish that were used in the publication, with corresponding tidal and diel stages

Posílení úlohy lidových bytových družstev při rozvoji bydlení v obcích

Import 20/04/2006Prezenční výpůjčkaVŠB - Technická univerzita Ostrava. Ekonomická fakulta. Katedra (153) veřejné ekonomik

Data from: Multi-scale temporal patterns in fish presence in a high-velocity tidal channel

The natural variation of fish presence in high-velocity tidal channels is not well understood. A better understanding of fish use of these areas would aid in predicting fish interactions with marine hydrokinetic (MHK) devices, the effects of which are uncertain but of high concern. To characterize the patterns in fish presence at a tidal energy site in Cobscook Bay, Maine, we examined two years of hydroacoustic data continuously collected at the proposed depth of an MHK turbine with a bottom-mounted, side-looking echosounder. The maximum number of fish counted per hour ranged from hundreds in the early spring to over 1,000 in the fall. Counts varied greatly with tidal and diel cycles in a seasonally changing relationship, likely linked to the seasonally changing fish community of the bay. In the winter and spring, higher hourly counts were generally confined to ebb tides and low slack tides near sunrise and sunset. In summer and fall of each year, the highest fish counts shifted to night and occurred during ebb, low slack, and flood tides. Fish counts were not linked to current speed, and did not decrease as current speed increased, contrary to observations at other tidal power sites. As fish counts may be proportional to the encounter rate of fish with an MHK turbine at the same depth, highly variable counts indicate that the risk to fish is similarly variable. The links between fish presence and environmental cycles at this site will likely be present at other locations with similar environmental forcing, making these observations useful in predicting potential fish interactions at tidal energy sites worldwide

Echosounder setup in Cobscook Bay, Maine.

<p>The bottom support frame of the MHK tidal energy device was present during data collection. The gray area indicates the sampled volume used in this study. Device schematic provided by Ocean Renewable Power Company.</p

Wavelet transform of hourly fish counts.

<p>(a) Time series of hourly fish counts. Gaps in data that were filled using the method described in the text are shown in gray. Inset expands time series from July 2014. (b) Wavelet transform of log-transformed time series. Color indicates the magnitude of the wavelet power, with darker, redder colors indicating higher power. Black contours enclose areas of significance at the 5% significance level. The transparent white fill indicates the cone of influence, within which power values may be reduced by edge effects. Darkened rectangles indicate where gaps in the time series were filled. (c) Fish counts from each hour of each day of the time series, condensed here for easy comparison to a and b. An expanded version of c is shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0176405#pone.0176405.g008" target="_blank">Fig 8</a>. Darker, redder colors indicate higher fish counts. Horizontal curved lines indicate times of sunrise and sunset, and shaded rectangles indicate filled gaps in the time series.</p

Hourly fish counts.

<p>Rows are each hour of the day, and columns are every day of the time series, which spans July 2013 to July 2015. Darker, redder colors indicate higher hourly fish counts. Gaps in the time series (filled using method described in text) are indicated by darkened rectangles. Horizontal curved lines indicate time of sunrise and sunset. Points indicate times of low (open circles) and high (solid circles) slack tides. A condensed version of this figure is shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0176405#pone.0176405.g007" target="_blank">Fig 7c</a>.</p