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With no substantive studies and relatively few anecdotal observations, any understanding of the presence and activities of bats over the oceans has traditionally been limited to occasional tales from lighthouse keepers and sailors. The possibility that various bats may purposely migrate or forage over large expanses of open water - rather than simply be the victims of errant storms - has largely gone unstudied. This lack of data is obviously not only tied to their nocturnal patterns, but also, quite simply, to the lack of safe and suitable observation platforms and the hazardous conditions that develop in areas far from land.

A recently released report for the Bureau of Ocean Energy Management (BOEM), however, is helping the environmental research community get over that hump. The report shares the methodology and results from three years of detecting bats in offshore environments off the New England coast, revealing a somewhat surprising finding: bats are active offshore.

Curiosity as to whether bats were regularly present over large expanses of open water - and, if so, when and under what conditions - coupled with increased interests in offshore energy development, caused Stantec to conduct a series of coastline and offshore investigations in summer 2009 along the coast of Maine. That effort, involving the deployment of passive acoustic detectors at 10 island and two peninsula locations, confirmed bats were present at least seasonally at every site and further affirmed the techniques and methods used in terrestrial settings were, with minor modifications, applicable to remote marine locations. Those positive findings bolstered our interest and led to two more years of study and 17 detector locations. Once again, each site recorded patterns of seasonal bat activity.

These collective findings, combined with increasing interest in offshore energy and concerns over commercial wind facility mortality, helped prompt follow-up studies in fall 2011 by both BOEM and the U.S. Department of Energy (DOE). The BOEM study intended to synthesize information on bats and their potential interactions with offshore wind facilities versus activities tracked on land and included a comprehensive literature review, a compilation of offshore and terrestrial acoustic studies along northeastern and Mid-Atlantic coastal regions of the U.S., and a statistical comparison of acoustic bat activity data gathered from inland, coastal, and offshore sites within that region.

The assembled database consisted of over 980,000 acoustic call files collected from 61 sites over 37,614 detector-nights between 2005 and 2012. Data from 33 sites were ultimately used to study whether acoustic activity patterns differed among location types. The final results were compiled in the recently released report entitled Information Synthesis on the Potential for Bat Interactions with Offshore Wind Facilities: Final Report.

As this BOEM-led effort continued, in spring 2012, Stantec also began a three-year DOE field investigation of bat activity in the Gulf of Maine, Mid-Atlantic coastal states and Great Lakes regions to collect regional quantitative data to better understand when, where, and why bats would be offshore.

The study has, to date, involved deployment of acoustic sensors at 36 locations, including a variety of coastline, island, buoy, offshore tower, and ship-based locations. Both migratory and non-migratory bat species have been detected at every site so far, involving both resident and migratory activity, meaning some of the bats are just quickly passing through, while others remain to use local habitats for longer seasonal periods.

The impact

The findings so far are significant for the research community for a few reasons. First, the data show that bats do frequent the offshore environment. Second, the fact that the equipment successfully gathered this data means that this type of passive surveying can work in challenging offshore conditions. Finally, the results not only broaden our general understanding of bat ecology, but also provide great insight as to when and how bats use open water environments and, in turn, help enable offshore energy development efforts to move forward with minimal risk to wildlife resources.

With these encouraging results, Stantec will continue to expand the study through 2014 in each of the three regions. The final analysis, due in spring 2015, will include a quantitative analysis of the influence of weather variables on offshore bat activity patterns. Ultimately, this comprehensive assessment will contribute to the knowledge base used by public officials and offshore energy developers to make more balanced decisions in developing and managing offshore resources - be they nocturnal, biological creatures or the physical sources of wind energy beyond U.S. shores.

Steve Pelletier, CWB, is the principal scientist for Stantec’s offshore acoustic bat research. He can be reached at steve.pelletier©stantec.com.

The BOEM report was prepared under contract between BOEM and Stantec Consulting Services Inc. The report has been technically reviewed by BOEM, and it has been approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of BOEM, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.


Caption: A silver-haired bat. Photo courtesy of Stantec.

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