Science Advisory Report  2015/005

Review of Mitigation and Monitoring Measures for Seismic Survey Activities in and near the Habitat of Cetacean Species at Risk

Summary

• Oil and gas exploration and mapping activities in areas frequented by cetacean species listed under the Species at Risk Act (SARA) has led to a need to review the Statement of Canadian Practice with respect to the Mitigation of Seismic Sound in the Marine Environment (SOCP) and evaluate its effectiveness for avoiding SARA-prohibited impacts (killing, “harm” and “harassment” of individuals and “destruction” of critical habitat) on SARA-listed cetaceans.
• Building on previous advice, the potential effects on SARA-listed cetaceans of seismic airgun sounds produced during seismic surveys were examined to identify potential consequences and pathways of effects linked to killing, “harm” and “harassment” of individuals and “destruction” of critical habitat (using the most recent definitions of these terms available) (Table 1).
• Possible sound exposure metrics that could be used to determine quantitative thresholds for avoiding SARA-prohibited impacts were discussed (Table 2). Potential sound exposure metrics do exist for a number of potential effects such as auditory physiological effects, changes in vocalization patterns, hampered passive acoustic detection of prey, predators and conspecifics, and hampered avoidance of anthropogenic threats. In most cases; however, standardized descriptors of these metrics used by the wider scientific community do not exist.
• Single independent thresholds to avoid SARA-prohibited impacts could not be determined at this time as little information is available on quantitative linkages between sound exposure and response metrics for cetaceans. Permanent (PTS) and temporary hearing threshold shifts (TTS) could potentially be used to establish thresholds for avoiding physiological effects resulting in the killing, “harm” and “harassment” of individuals, but these would only in-part address SARA-prohibited impacts and additional thresholds would be needed for potential effects on behavior and ecology. Further research and analyses are required to relate sound exposure metrics to quantitative thresholds for the various physiological, behavioral and ecosystem effects caused by exposure to seismic surveys that could result in SARA-prohibited impacts.
• Given the uncertainties that remain around thresholds for avoiding SARA-prohibited impacts, implementation of precautionary and reliable risk-reducing mitigation measures is likely to be the most effective approach for minimizing potential negative impacts on SARA-listed cetaceans. Thus, despite the inability to recommend quantitative thresholds, the mitigation measures of the SOCP were reviewed in a precautionary manner in reference to reducing/avoiding SARA-prohibited impacts on SARA-listed cetaceans using the Scotian Shelf population of northern bottlenose whales, North Atlantic right whales and Atlantic blue whales as case studies.
• It was concluded that most of the mitigation measures of the SOCP likely reduce the potential negative impacts of seismic airgun sounds on individuals, but to varying degrees and with some caveats (Table 3). For example, effectiveness may be limited by the availability of information on distribution, abundance and behavior of a species, or by the specific manner in which the mitigation measure is conducted. Implementation of the multiple measures of the SOCP as a whole is likely to be more effective than any one measure on its own, and the SOCP provides flexibility for enhancing mitigation measures to meet SARA requirements as it states that operators may be required to put in place additional or modified mitigation measures for species of concern.
• The SOCP focuses on reducing significant adverse effects on individuals and populations mainly through efforts to reduce potential physical injury to animals in close proximity of airgun arrays, but does not provide specific mitigation measures for reducing impacts that may occur at greater ranges from the sound source (i.e., beyond the safety zone) or for reducing impacts on habitat. Planning seismic surveys to avoid significant adverse effects or to avoid displacing/diverting listed marine mammals are considered the only measures within the SOCP that address preventing the potential “harm” or “harassment” of individuals beyond the established safety zone or “destruction” of critical habitat.
• Planning seismic surveys to avoid spatial and temporal overlap with areas where SARA-listed cetaceans are anticipated to be present is considered the most effective mitigation measure to reduce impacts on individuals and their critical habitat, but is dependent upon adequate information on distribution and abundance. In many cases, research effort is needed prior to seismic survey activities to sufficiently determine species occurrence so that spatial and temporal avoidance measures can be effectively applied. Furthermore, avoidance of spatial and temporal overlap may not always be possible as seismic surveys are usually limited to a specific area of interest and year-round resident species cannot be avoided.
• The safety zone radius should be the most conservative of either 500 meters or a radius determined using propagation models based on the best available data and science for a pre-determined acoustic threshold (which has yet to be established), taking into account to the extent possible the species, environment and sound source context, and which should be validated with field measurements.
• To effectively monitor a safety zone for cetaceans, seismic survey activities and cetacean detection methods should be designed to maximize the likelihood of detecting SARA-listed cetaceans to achieve a target probability of detection within the safety zone consistent with SARA requirements (which has yet to be established). Enhanced real-time monitoring methods/technologies such as extended pre ramp-up observation periods, limiting seismic survey operations to good visibility conditions, having an adequate number of experienced and qualified Marine Mammal Observers (MMOs) searching, use of additional monitoring platforms, enhancing visual observations with passive acoustic monitoring (PAM) efforts and/or other monitoring technologies should be considered. A combination of detection methods/technologies may be required to achieve the target probability of detection.
• The effectiveness of ramp-up procedures or reduction of the airgun array to a single source element as a mitigation measure during seismic surveys is not fully understood, though some modeling and behavioral response studies are currently being conducted to investigate effectiveness.
• To comply with SARA by avoiding SARA-prohibited impacts, research efforts to increase our understanding of distribution and abundance over time, the behavioral and physiological responses of cetaceans to seismic airgun sounds, and the consequences of such responses on the habitat use, health, reproduction, survival and recovery of impacted species are required. This will be especially important in areas where seismic surveys overlap the distribution of SARA-listed cetaceans. Such studies have been and continue to be conducted by the international science community and are important for increasing our knowledge of the extent of the impacts of seismic surveys on cetaceans. To be most relevant for effective management, this research should be focused on risk or harm reduction rather than full knowledge of the basic biology behind impacts, which could take many years build a complete understanding of and thus delay useful mitigation measures.
• Explicitly designed research studies will be necessary to evaluate the efficacy of mitigation measures that have been implemented during seismic surveys for reducing the impacts of seismic airgun sounds on SARA-listed cetaceans. Such studies will need to be designed with rigorous data collection protocols and sufficient statistical power and sensitivity to allow for detection and quantitative analysis of potential negative effects at ranges from the sound source where SARA-prohibited impacts may occur, including beyond the defined safety zone.

This Science Advisory Report summarizes the results of the March 25-27, 2014 “Review of Mitigation and Monitoring Measures for Seismic Survey Activities in and near the Habitat of Cetacean Species at Risk".  Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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