Roberto Racca

Responsible Practices for Minimizing and Monitoring Environmental Impacts of Marine Seismic Surveys with an Emphasis on Marine Mammals

Marine seismic surveys, which use loud, primarily low-frequency sound to penetrate the sea floor, are known to disturb and could harm marine life. The use of these surveys for conventional and alternative offshore energy development as well as research is expanding. Given their proliferation and potential for negative environmental impact, there is a growing need for systematic planning and operational standards to eliminate or at least minimize impacts, especially when surveys occur in sensitive areas. Mitigating immediate impacts is obviously critical, but monitoring for short- as well as longterm effects and impacts is also needed. Regulatory requirements for both mitigation and monitoring vary widely from one country or jurisdiction to another. Historically, most have focused on acute effects but share a common objective of minimizing potential adverse impacts. Specific examples in different areas are given to illustrate general approaches for predicting, minimizing, and measuring impacts for operations in essentially any marine environment. The critical elements of a robust mitigation and monitoring plan for responsibly conducting marine seismic surveys include obtaining baseline ecological data; substantial advance planning, communication, and critical review; integrated acoustic and visual monitoring during operations; and systematic analysis of results to inform future planning and mitigation.

Marine mammal audibility of selected shallow-water survey sources

Most attention about the acoustic effects of marine survey sound sources on marine mammals has focused on airgun arrays, with other common sources receiving less scrutiny. Sound levels above hearing threshold (sensation levels) were modeled for six marine mammal species and seven different survey sources in shallow water. The model indicated that odontocetes were most likely to hear sounds from mid-frequency sources (fishery, communication, and hydrographic systems), mysticetes from low-frequency sources (sub-bottom profiler and airguns), and pinnipeds from both mid- and low-frequency sources. High-frequency sources (side-scan and multibeam) generated the lowest estimated sensation levels for all marine mammal species groups.

Development and Implementation of Criteria for Exposure of Western Gray Whales to Oil and Gas Industry Noise

Whether and how noise from human activities adversely affects marine life and what to do to mitigate negative impacts of industrial activities have been subjects of scientific research and regulatory interest for several decades, beginning with the observations of Payne and Webb (1971). In 1995, the US National Marine Fisheries Service (NMFS) began using underwater impulse noise criteria for estimating the physical injury to marine mammals [190 dB re 1 mPa root mean square (RMS) sound pressure levels for pinnipeds and most odontocete cetaceans and 180 dB re 1 mPa for mysticetes and sperm whales]. Subsequently, the High Energy Seismic Survey team (1999) concluded that exposure to air gun pulses with pulse-averaged received levels (RLs) above 180 dB re 1 mPa would likely result in significant behavioral, physiological, and/or hearing impacts. The NMFS has continued to use the 180-dB RL criterion for predicting injury from acoustic exposure for cetaceans and 190-dB RL for pinnipeds as well as a behavioral impact level of 160-dB RL; based primarily on observations of mysticete cetaceans reacting to air gun pulses (e.g., Malme et al. 1984), a 120-dB RL criterion has been applied by the NMFS in some conditions for some nonimpulsive “continuous” industrial noises.

Use of Preoperation Acoustic Modeling Combined with Real-Time Sound Level Monitoring to Mitigate Behavioral Effects of Seismic Surveys.

Underwater acoustic modeling is often used to estimate the injury radius around a seismic exploration source; only occasionally has it been applied to the mitigation of behavioral effects, where the safety boundary may extend to many kilometers. Such a mitigation strategy requires precise estimation of the sound field for many source locations and likely entails field validation over the course of the operation to ensure that mitigation regions are accurate. This article reviews the enactment of such an approach for a seismic survey off Sakhalin Island and examines how similar principles may be applied to other surveys under suitable conditions.

Current Status of Development of Methods to Assess Effects of Cumulative or Aggregated Underwater Sounds on Marine Mammals.

There are no standards for assessment of the cumulative effects of underwater sound. Quantitative assessments typically consider a single source, whereas qualitative assessments may include multiple sources but rarely identify response variables. As a step toward understanding the cumulative effects of underwater sound, we assessed the aggregated sounds of multiple sources received by migrating bowhead whales (Balaena mysticetus). The quantitative method models the sound field from multiple sources and simulates movement of a population through it. The qualitative method uses experts to assess the responses of individuals and populations to sound sources and identify the potential mechanisms. These methods increase the transparency of assessments.

Methods for Predicting Potential Impacts of Pile-Driving Noise on Endangered Sturgeon During Bridge Construction.

The potential impacts of pile-driving noise on Hudson River sturgeon during construction of the New NY Bridge were predicted. Abundance data for shortnose and Atlantic sturgeon derived from fisheries sampling were combined with data about the spatial extent of pile-driving noise. This approach was used to calculate the number of sturgeon that could occur within sound level isopleths exceeding peak and cumulative noise criteria used by the National Marine Fisheries Service to determine the incidental take of sturgeon. The number of sturgeon subject to the potential onset of physiological effects during pile driving was predicted to be 35-41 fish for each species.

Pile Driving at the New Bridge at Tappan Zee: Potential Environmental Impacts

A new bridge will be constructed to replace the aging Tappan Zee Bridge over the Hudson River in New York. Construction will potentially result in hydroacoustic impacts to the local fish fauna. As a consequence, a substantial environmental impact analysis had to be conducted to obtain construction permits. This paper describes the process of environmental analysis and some of the results of the studies that led up to the final permitting. The process included modeling of pile-driving acoustics, analysis of river ambient noise, analysis of test piling, and observations on fish behavior during these tests.

Coordinated management of anthropogenic noise from offshore construction off Sakhalin Island for protection of the western gray whale.

The main population of a critically endangered cetacean species, Eschrichtius robustus (western gray whale), spends the summer months foraging on benthos-rich feeding grounds in the near-shore waters of the Piltun-Astokh region off northeastern Sakhalin Island in the Russian Far East. Significant oil and gas interests also make this region a very active offshore development area, with activities ranging from subsea pipeline deployment to installation of hydrocarbon production platforms.

Assessment of cumulative effects of underwater sound: A collaborative approach.

A multidisciplinary team of scientists working under a research agreement between the University of California, Santa Barbara and BP America Production Company has undertaken a 2‐year project, currently ongoing, to develop one or more standardized and practical methods for assessing cumulative effects of anthropogenic underwater sound on marine mammals. The work of the team is based on access to existing scientific information without substantial involvement of additional primary research although topics for future research may be part of the eventual recommendations. While the final goal of the project is to conceptualize and specify widely applicable methodologies, case studies are being used to help formulate and test the feasibility of assessment frameworks. The primary case study involves the significant hydrocarbon related industrial activity that took place in the Beaufort Sea (Alaska and Canada) during late summer and autumn 2008 and its potential cumulative effect on the population of bowhead wha...

Acoustic monitoring of pile driving activities at the proposed NaiKun wind farm site.

Underwater sound level measurements were obtained during marine pile driving activities at the proposed NaiKun wind farm site in Hecate Strait, British Columbia, Canada. Three hollow steel piles 0.9 m in diameter were driven into the seafloor to secure in place a truss to support a meteorological instrumentation mast. The activities involved both vibro‐hammering and impact hammering. Measurements were collected at 10 m range to fulfill regulatory requirements for real‐time monitoring of the near‐source sound pressure levels and also at a selection of longer ranges to allow a characterization of the propagation conditions of the environment. A bubble curtain was utilized to mitigate the underwater noise generated by impact hammering after trial measurements over a few hammer strikes showed that unmitigated levels exceeded a regulatory threshold. Results from this study were used to derive source level estimates for a subsequent sound propagation modeling study conducted as part of the environmental assessm...