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Marine Mammal Populations and Ocean Noise: Determining When Noise Causes Biologically Significant Effects Appendix D Draft Conceptual Plan for Workshop Discussion DEFINITION OF THE PROBLEM Throughout human history oceans have been important for transportation and commerce, biological and physical resource extraction, and defense. However, the vast expanse of the oceans precluded significant human impact until the coming of the industrial revolution. The transition from wind driven to mechanized shipping, was the first step in a continued increase in the initially unintentional and subsequently, with the development of sonar, intentional introduction of sound into the ocean. Because of the low loss characteristics of sound transmission, compared to light transmission, the use of sound had developed evolutionarily as the predominant long-range sensory modality for marine species. Thus as human use of the oceans increased with a concomitant increase in anthropogenic sound in the ocean, the conflict with evolutionarily adapted marine animals sound sensing systems was inevitable. Over 90 percent of the global trade is transported by sea. Shipping is the dominant sound in the world’s oceans at between 5 and 500 Hz. At other frequencies, anthropogenic noise does not predominate in the ocean sound energy budget, but can have important local impacts. For instance, seismic air guns associated with geophysical exploration for locating new oil and gas deposits run hundreds of thousands of miles of survey lines in just the Gulf of Mexico each year. In addition, commercial sonar systems are on all but the smallest pleasure craft. These sonars allow for safer boat-
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Marine Mammal Populations and Ocean Noise: Determining When Noise Causes Biologically Significant Effects ing and shipping, and more productive fishing. Military sonar systems are important for national defense. This intentional and unintentional introduction of sound in the ocean associated with activities beneficial to humans must be balanced against known deleterious effects on marine mammals. Strandings of beaked whales in certain environments are clearly associated with the use of mid-range tactical military sonar. There are documented behavioral responses of beluga whales to icebreakers 50 km away. Gray whales and killer whales have shown multi-year abandonment of critical habitats in response to anthropogenic noise. Although there are many documented, clearly discernable responses of marine mammals to anthropogenic sound, reactions are typically subtle, consisting of shorter surfacings, shorter dives, fewer blows per surfacing, longer intervals between blows, ceasing or increasing vocalizations, shortening or lengthening duration of vocalizations, and changing frequency or intensity of vocalizations. Although some of these changes become statistically significant in given exposures, it remains unknown when and how these changes translate into biologically significant effects at either the individual or the population level. The basic goal of marine mammal conservation is to prevent human activities from threatening marine mammal populations. The threat from commercial whaling was obvious, but it is harder to estimate the population consequences of activities that have less immediately dramatic outcomes, such as those with indirect or small but persistent effects. The life histories and habitat of marine mammals compounds these problems. Marine mammals are long lived and slow to mature. Many species have long periods of dependency. They are highly social and show behavioral plasticity, with complex development of behavior. Furthermore, many of these behaviors occur underwater where they are difficult to document. This makes it particularly difficult to estimate the effects that a short term exposure may have as it ripples through the lifetime of an individual, or as effects on different individuals ripple through the population. Even extreme effects, including death, are not necessarily observed. The status of any population is the consequence of the accumulation of many effects; resulting in marginal changes in survival and reproduction over time. In addition, the end result is often so far removed in time from the proximate causal events that they cannot simply be traced post hoc. The existence of several comparable populations with different status and different exposure can be used to reduce the number of candidate primary
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Marine Mammal Populations and Ocean Noise: Determining When Noise Causes Biologically Significant Effects causes of the decline. However, often such comparative populations are lacking. One way around this conundrum, well tested for issues of human health, is to study how individuals respond to exposure in the short term. Behavior and physiology are rapid response systems evolved to compensate for environmental variation within established limits. A standard method to evaluate risks of exposure to chemicals involves analyzing the short-term physiological responses to specific doses of a compound. Similar studies have been conducted to investigate how marine mammals respond to known exposures to sound. The goal of the NRC Committee on Characterizing Biologically Significant Marine Mammal Behavior is to develop a framework to relate short term acoustic dose:behavioral response relationships to potential population consequences. HISTORY OF NRC REPORTS The NRC has produced three reports on the effects of noise on marine mammals, in 1994, 2000 and 2003. The primary goal of the 1994 report was to recommend research on this topic, but the report noted that regulation of marine mammal research impeded critical research, and the report had an entire chapter on regulatory burdens. This chapter of the 1994 report focused especially on harassment of marine mammals. It pointed out that: Logically, the term harassment would refer to a human action that causes an adverse effect on the well-being of an individual animal or (potentially) a population of animals. However, “the term ‘harass’ has been interpreted through practice to include any action that results in an observable change in the behavior of a marine mammal….” (Swartz and Hofman, 1991, p. 27) As researchers develop more sophisticated methods for measuring the behavior and physiology of marine mammals in the field (i.e. via telemetry), it is likely that detectable reactions, however minor and brief, will be documented at lower and lower received levels of human-made sound…. In that case, subtle and brief reactions are likely to have no effect on the well being of marine mammal individuals or populations. (Swartz and Hofman, 1991, p. 28) The 2000 NRC report also has a chapter on regulatory issues focusing on acoustic harassment. This chapter continued to emphasize the importance of a criterion for significance of disruption of behavior: “It does not
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Marine Mammal Populations and Ocean Noise: Determining When Noise Causes Biologically Significant Effects make sense to regulate minor changes in behavior having no adverse impact; rather regulations must focus on significant disruption of behaviors critical to survival and reproduction …” (Swartz and Hofman, 1991, p 68). It went on to suggest a redefinition of Level B harassment as follows: Level B—has the potential to disturb a marine mammal or marine mammal stock in the wild by causing meaningful disruption of biologically significant activities, including, but not limited to, migration, breeding, care of young, predator avoidance or defense, and feeding. (Swartz and Hofman, 1991, p. 69) The third report of the NRC, Ocean Noise and Marine Mammals (2003), attempted to look at the world ocean noise budget between 1 and 200,000 Hz with particular attention to habitats that were important to marine mammals. The basic question the report tried to address was: What is the overall impact of human-made sound on the marine environment? The somewhat unsatisfactory answer was that the overall impact is unknown, but there is cause for concern. Other than shipping, the overall energy contribution of anthropogenic sound to the ocean noise budget is insignificant. However, total energy contribution is not the best currency to use in determining potential impact of human-made sound on marine organisms. The report made a number of recommendations with the overarching one being the need to better understand the characteristics of ocean noise, particularly from man-made sources and its potential impacts on marine life, especially those that may have population level consequences. STATEMENT OF TASK The statement of task for the present NRC Committee, the Committee on Characterizing Biologically Significant Marine Mammal Behavior, picks up on two issues noted above: the difference between statistically significant and biologically significant changes in behavior; and linking those short-term behavioral changes to possible population level consequences. The term “biologically significant” enjoys wide use in conservation and management literature, and increasingly in regulatory agency guidelines, but has not been well defined. The committee has been tasked to define “biologically significant” within the context of marine mammal behavioral responses to ocean acoustic sources with particular reference to those responses affecting marine mammal populations. The committee will produce a brief report that reviews and characterizes the current scientific
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Marine Mammal Populations and Ocean Noise: Determining When Noise Causes Biologically Significant Effects understanding of when animal behavior modifications induced by transient and non-transient ocean acoustic sources, individually or cumulatively, could threaten marine mammal stocks. Recommendations will be based on input from a scientific workshop, consideration of the relevant literature, and other sources. GOAL, PROPERTIES AND OUTPUT Develop a conceptual framework and produce a practical process to help regulators assess the risk that specific acoustic sources will have negative impacts on a marine mammal population by disrupting normal behavioral patterns. Desirable properties of such a process include one that is: accurate; precautionary and becomes more precautionary with greater uncertainty in the potential population level effects of the induced behavioral changes; is simple and transparent to the public, legal staff, and congress; leads to an iterative process which will improve risk estimates as data improve; is able to evaluate cumulative impacts of multiple low level disturbances; and ends up with a small number of parameters that are easy to estimate. COMMITTEE CONCEPTUAL APPROACH We propose a process to link acoustic stimuli to behavioral responses to functional outcomes of responses integrated over daily and seasonal cycles in a way that links to life history models. This sequence of stages is essential to link population models, which for seasonal breeders are typically structured on an annual basis, with studies that relate acoustic exposure to behavioral response, that typically work on time scales of hours. Table D-1 diagrams our approach. On the left we characterize the acoustic features of the sound stimulus of interest. The first stage of our framework involves a transfer function to predict behavioral responses to this sound. Ideally this function derives from controlled exposure experiments, supplemented by observational or correlational studies. This transfer function may vary depending upon the species, season, location, and age-sex of the subject. In the absence of data for the precise situation of interest, marine mammals should be grouped in this stage of the framework by their hearing capabilities, and only data from the same ear type should be used.
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Marine Mammal Populations and Ocean Noise: Determining When Noise Causes Biologically Significant Effects TABLE D-1 Transfer functions weighted by season, location, demographic characteristics. Topics highlighted in bold were emphasized at the workshop. Sound X-Fcn 1 Behavior Change X-Fcn 2 Function Impacted X-Fcn 3 Population Effect Transformation Function Modeling Orientation Life Freq Breathing Migration Survival Duration Vocalizing Feeding Children Level Diving Breeding Grandchildren Source Resting Nurturing Duty Cycle Mother-Infant Response to Predator Spatial relationships Homeostasis/Risk Factor (Allostasis) Avoidance Time and Energy
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Marine Mammal Populations and Ocean Noise: Determining When Noise Causes Biologically Significant Effects The output of the first transfer function predicts changes in observable behaviors or physiological measures as a function of sound exposure. The second stage of our framework must evaluate how much these changes in behavior compromise processes that are widely recognized as critical to life history. Where possible, we propose to break down these functional consequences into two time scales—diurnal and seasonal. Most marine mammals respond to diurnal changes with a cycle of activities that suggests the validity of integrating short term functional consequences over a minimum duration typical of the activity in undisturbed animals up to durations of 24 h when possible. These time scales can be studied with behavioral observations or tagging methods. Most marine mammals also show strong seasonal variations in behavior and physiology. As a first cut, our framework will then sum expected daily consequences over each season, depending upon expected exposure schedule to the sound of interest. The output of the second transfer function defines over a season, the extent to which exposure to a sound may have interfered with the subject’s ability to perform behavioral functions that may be critical to survival, growth, and reproduction. The third stage of our framework must estimate what impact this interference may have at the population level. We propose that this stage involves matrix population models structured to stratify each season by the amount of interference. Ideally this would involve models where there is some basis for estimating exposure and thus amount of interference for each individual or age-sex class, depending upon how the model is structured. The function relating interference to population effect ideally would derive from several years of observation of survival and reproduction in a population where effects of exposure can be predicted. For the purposes of this report, we will need to develop a preliminary method to estimate the likelihood of population effect. SOUND Ocean acoustic sounds can have a wide range of effects on marine mammals varying from minor annoyances to potentially deleterious effects on a population level. The sources of acoustic noise have been well described in the 2003 National Research Council’s (NRC) Ocean Studies Board report, which also described a variety of effects of noise on marine mammals. The discussion of the effects of noise on marine mammals in the 2003 NRC report concentrated on individual marine mammals with the implication that if enough individuals are affected in the same manner,
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Marine Mammal Populations and Ocean Noise: Determining When Noise Causes Biologically Significant Effects then the population will be affected. In this discussion, the focus will be on the effects of ocean acoustics that will have negative consequence on marine mammals on the population level. We will attempt to understand how different acoustic sources could modify behavior and hinder marine mammals from performing critical functions that could eventually have an impact on the population level. There are many questions concerning how acoustic signals can modify behavior on a time scale that would affect a population of marine mammals. Among various parameters of acoustic signals that should be considered include bandwidth, frequency range, intensity, modulation type, modulation rate, duration and duty cycles need to be considered. However, at our current level of understanding there is little understanding how any of these parameters, whether individually or corporately can affect or modify marine mammal behavior. Even in a simple case, we would expect that a narrow-band acoustic source will have little effectiveness in disturbing a dolphin’s ability to echolocate. Then the question is how broad in bandwidth does the acoustic interference need to be to disrupt or interfere with a dolphin’s ability to echolocate? There are many similar questions to which there are no obvious answers. BEHAVIOR Behavioral changes typically occur over time ranges of minutes to hours. The responses often increase monotonically with increasing signal intensity, but such changes are rarely linear. They are also strongly influenced by other signal characteristics such as frequency, rise time, duty cycle, novelty, and total energy content. The variability in behavioral responses is as likely due to changes in the state, condition, demographic status, or location of the animal as to characteristics of the sound source. Repeated presentations of the signal typically result in habituation in which the response is not as pronounced to subsequent signal presentations, but the converse can also occur in which the response becomes greater on subsequent presentations of the same signal, a condition known as sensitizitation. Individual variability of animals significantly reduces the capability of predicting behavioral change in response to acoustic stimuli. FUNCTION All organisms must perform a set of behavioral and physiological functions in order to survive, grow, and reproduce. Marine mammals must
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Marine Mammal Populations and Ocean Noise: Determining When Noise Causes Biologically Significant Effects have effective ways to avoid predation, feed, breed, and take care of their young. Many species migrate over long distances, and all must orient on smaller scales. Many pelagic species dive between the surface where they must breathe and great depths where they find and consume prey. Each of these behavioral activities may be affected by acoustic interference in different ways with different functional consequences. The main costs of interference are risks of injury, opportunity costs due to not detecting a signal, and costs of lost time and extra energy expenditure. If a diving animal responds to sound in a way that pushes the limits of diving physiology, the behavioral response itself could cause injury. If noise stimulates seals to stampede on a beach, or stimulates a cetacean to strand, this could cause death or injury. Similarly if an animal fails to detect an oncoming predator because of interfering noise, it could be killed or injured. Interpreting the indirect effects where behavioral responses to sound may injure or kill a marine mammal is straightforward. The other costs of lost opportunities, time, or energy require more interpretation to infer the consequences. If an animal incorrectly responds to a noise as if it were a predator, this response entails the costs of lost time and energy. A migrating animal could be affected in two different ways. If it uses acoustic cues to orient for migration, exposure to noise sufficient to mask these cues might interfere with orientation. Some migrating animals avoid exposure to noise; this deflection costs time and energy. If exposure to noise interferes with feeding, the primary costs are time lost if prey items are missed, and energy costs of lost prey intake and potentially increased costs of locomotion. The likely costs of noise to breeding and parental care both involve the costs of not detecting signals and the energy and time costs of any mechanisms they may have for compensating for noise to improve the probability of signal detection in noise. However, the consequences differ. In species that use acoustic communication in the mating system, a female might in the worst case fail to find a mate while she was receptive. This problem is likely to be worst for depleted populations that do not aggregate in mating centers. Noise may also interfere with the process by which males compete during the breeding season, by which females select a mate. All marine mammal young are dependent upon parental care. Many species use acoustic communication both to maintain contact between mother and young, and also for mother-offspring recognition. If increased noise prevented or delayed mother and young from reuniting after a separation, this could have negative consequences for the young. Many marine mammals learn their vocalizations. We are only just beginning to understand the intricacies of
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Marine Mammal Populations and Ocean Noise: Determining When Noise Causes Biologically Significant Effects vocal development in marine mammals, but increased noise might interfere with development of a fully functional system of vocal communication. OPERATIONAL PLANS The Committee held its first meeting 6−8 October 2003 at the National Academy of Sciences in Washington, D.C. and prepared this document conceptualizing and outlining a proposed approach to addressing the statement of task. The committee also identified those areas in which it needed assistance in completing the model leading from stimulus through a determination of biologically significant behavioral change to a population level effect. Four primary areas where additional expertise was needed were identified. For each of those areas, experts will be identified and invited to the next meeting of the committee on 5−8 March 2004, again at the National Academy of Sciences in Washington, D.C. That meeting will begin with a two day workshop. On the first day each of the invited experts will make a 15 minute presentation on how the gaps in the model can be bridged and how the deficiencies in the model can be rectified. On the morning of the second day, the experts within each area will meet together with one member of the committee to put together a synthesis and improvement of the individual presentations of the day before. In the afternoon, each of the four working groups will make a presentation to the full committee. The committee will spend the final two days in closed session writing the report. TRANSFER FUNCTION WORKING GROUP The overall purpose of the proposed model is three-fold. The first two purposes derive directly from the statement of task, identifying biologically significant behavioral changes and linking those changes to population level effects. The third purpose is to assist regulators in determining the likelihood that a given stimulus will lead to a specific behavioral change affecting a defined biological function which results in a given change in an identified population parameter. Between each of these operational units there are transfer functions which can be weighted by a variety of external factors such as season, location, and demographic characteristics of the exposed animals. Given the current state of knowledge, the committee recognizes that likelihood factors cannot be categorized on a finer scale than
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Marine Mammal Populations and Ocean Noise: Determining When Noise Causes Biologically Significant Effects high, moderate or low. The Transfer Function Modeling expert group will help the committee turn this heuristic model into an operational one. SOLICITATION OF PARTICIPATION We are all too aware of the questions and uncertainty surrounding our task. On the other hand, decisions affecting the fate of these populations must be made. We face the task given to us not with confidence that we can solve all the problems, but rather in the hope that the framework we develop can help to provide a scientific basis for ranking research and management priorities. We are soliciting your participation not only in helping to fill in significant areas in which the committee lacks sufficient experience or knowledge, but also your perspective, often from a very different background and experience, as to the overall approach of the committee to the statement of task. This model is being presented very much as a work in progress and we hope you will take this opportunity to help the committee to shape this model, or to convince the committee to abandon this model. Thank you.
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