Offshore Wind Power Projects in the Great Lakes - Ministry of ...

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Offshore wind power projects in the Great Lakes: Background and science considerations for fish and fish habitat limiting comparability with post-construction monitoring data, while at Nysted trawling data suffered from low reproducibility (Hvidt et al. 2003), indicating that this gear type is not always reliable for monitoring purposes. Nearshore areas Recognizing their ecological importance and biological diversity, agencies are increasingly targeting smaller, nearshore fishes in their monitoring programmes, for example using multimesh gill nets such as the standardized NORDIC net, or broad-scale small mesh nets. Within several locations in the Great Lakes, the OMNR conducts variations on a small fish biodiversity survey, which includes multiple gear types such as small-mesh gill nets, seine nets, minnow traps, and fyke nets to capture species such as cyprinids, which aren’t typically captured in traditional assessment nets. Fyke nets and fry fyke nets have also been used in baseline fish community surveys at proposed offshore wind power project sites, including the Nysted wind farm (Hvidt et al. 2003), in order to complement gill net and trawl surveys and more fully characterize local species assemblages in the area. Fyke nets were also used by the Swedish Department of Fisheries during the monitoring program at the Lillgrund wind farm (Andersson 2011). To assess and monitor the status of nearshore sport and commercial fish species within the Great Lakes (and other locations), the OMNR conducts standard live release trap netting programs (Stirling 1999). Trap nets are size selective, tending to exclude very small fish. Standardized methods, gear descriptions and other technical information required to conduct Nearshore Community Index Netting (NSCIN) surveys are described in a manual available through the OMNR (see Appendix B). Surveys also exist that target certain species at critical periods, for example in OMNR’s Fall Walleye Index Netting Program which uses large, multi-mesh gill nets to target walleye just prior to spawning (Morgan 2002; Morgan & Snucins 2005). Fisheries acoustics The application of fisheries acoustics (or more generally, hydroacoustics) is an emerging, and now often preferred, technique for fisheries research and assessment both within the Great Lakes and elsewhere. Acoustic methods allow for rapid assessments of fish abundance and distribution patterns over relatively broad spatial scales with the added advantage of being non-destructive to Aquatic Research and Development Section 72
Offshore wind power projects in the Great Lakes: Background and science considerations for fish and fish habitat the fish being sampled (Simmonds & MacLennan 2005). In essence, this technique employs the principles of sonar to detect fish or other objects having densities different than water both within the water column and along the lake bottom. An acoustic echo sounder mounted to a moving or stationary vessel emits a pulse or beam of acoustic energy into the water. The acoustic beam is cone-shaped, expanding with increasing distance from the source. For this reason, vertical or down-looking hydroacoustics are most commonly employed in deeper waters and for non surface-oriented pelagic species, while horizontally aimed or side-scan transducers are more appropriate in shallower water or for species found closer to the water surface (Taylor & Maxwell 2007). When the pulse or beam of acoustic energy encounters an object, some of the energy gets reflected back to a transducer which detects and converts the returning echoes to electrical signals that can be processed and recorded by digital output devices. The ability of a given target or object to reflect acoustic signals is largely proportional to its size (or the volume of its air bladder in the case of fish) meaning that estimations of fish size using hydroacoustic surveys are possible. In general, acoustic surveys are conducted along pre-defined transects within the area of study, over set periods of time. Owing to the fact that many species exhibit more tightly aggregated schooling behaviour during the day, which can make individual counts more difficult, many hydroacoustic surveys are conducted between the hours of dusk and dawn to capture those periods where fish are more highly dispersed, yet still active. However, the timing of sampling and the duration of individual surveys will always depend on the specific objectives of the monitoring programme. Although hydroacoustic techniques can provide information on fish size, they cannot confirm fish identity directly (Appendix C). For this reason, sampling with more traditional fisheries assessment gear including gill or trawl nets is needed in conjunction with hydroacoustic surveys to verify the species composition in the area and calibrate the acoustic signals. In this way postprocessing and analysis of hydroacoustic data can also provide estimates of species composition, in addition to reliable estimates of abundance and spatial and temporal distribution patterns. Depending on the frequency of sound used, fisheries acoustics can also provide information on both large and small fish, as well as invertebrates such as plankton. Higher frequencies allow an assessment of smaller species like small prey fish and invertebrates while the lower frequencies provide an assessment of larger fish such as the species targeted by anglers. Aquatic Research and Development Section 73
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