Marine Mammals and Low-Frequency Sound Progress Since 1994 (2000) / Chapter Skim
Currently Skimming:
2 Evaluation of the Marine Mammal Research Program
2 Evaluation of the Marine Mammal Research Program
Pages 21-40
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, in part due to concerns about potential effects on marine mammals and in part to the shorter distance between the ATOC sources and receivers. In fact, information obtained from HIFT indicated that a less intense sound source (HIFT used a level of 221 dB)
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was not able to demonstrate a lack of significant effects of ATOC transmissions on marine mammals. The MMRP did not provide unequivocal evidence about the effects of ATOC transmissions because (1)
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Although the MMRP observations did show some indications that the ATOC signal did not have a short-term effect on nearby populations of marine mammals and there were no obvious mass mortalities of marine mammals or abandonment of the ATOC source areas by marine mammal species under observation, there was little detailed observational evidence of the effect of the ATOC signal on individual whales. The MMRP results and the committee's evaluation of the significance of the results are given in Table 2.1.
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· A high diversity of species (including six endangered marine mammal species) and numbers of individuals was observed both when the ATOC source was on and off.
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· While humpback whales did not vacate the area during ATOC transmissions, some whales shifted from using areas near the sound source (<14 km from the source) to areas slightly farther away (14-28 km from the source)
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Two behavioral variables showed a significant increase with increasing exposure: the distance traveled and time taken between successive surfacings. No difference in the amount of energy in the band of humpback song was detected comparing 20 minutes before transmission, during, and after transmission, from one recorder placed offshore near the ATOC source and four recorders placed inshore near the main concentration of whales.
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Given evidence for changes in the diving behavior of whales exposed to low levels far from the source, there is a clear need to study changes in the behavior of whales near the ATOC source in order to evaluate the potential impact of behavioral disruption. It is uncertain whether a change in the time and distance between surfacings is a biologically meaningful measure of the effects of the ATOC source.
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aAn M-sequence signal is a phase-modulated tonal signal. compared with after at least 4 days without ATOC transmissions.
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The possible shift in distribution at great ranges from the source suggests the need for a behavioral study on responses to ATOC signals targeting animals near the source. · Kauai is an important habitat for the expanding population of humpback whales wintering in Hawaii.
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Elephant seals are important research subjects in relation to the effects of the ATOC source because they have sensitive low-frequency hearing (Kastak and Schusterman, 1998) , swim in the pelagic zone, and routinely dive near the depth of the deep sound channel.5 This species has breeding areas near the California ATOC source site, and these animals are excellent subjects for tag attachment (tags are subsequently removed or shed during molting; D
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Hawaii ATOC Source The Hawaiian observations focused on humpback whales and were planned to include aerial visual surveys, passive acoustic monitoring, and shore-based surveys of reactions to ATOC transmissions (off Kauai) and playbacks of humpback whale vocalizations (off Hawaii)
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of humpback whales to the ATOC source 14 km north of Kauai's coast. The Committee was told that aerial survey results suggested there may be resident populations of sperm whales and short-finned pilot whales (Globicephala macrorhynchus)
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7 concluded that "there were no acute or short-term effects of the ATOC transmissions on marine mammals."8 The Committee questions whether a conclusion this broad can be reached at this time using the data provided. The report does, in fact, present evidence for some short-term behavioral changes in response to the ATOC sound source by humpback whales.
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could provide more definitive information about the potential of ATOC sound to affect marine mammals and other organisms. Specifically, shore-based observations should be conducted for the entire 6 months of ATOC transmissions, and the effectiveness of observational methods should be validated using playbacks of relevant natural sounds conducted within visual range of the shore station.
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Other elements of the MMRP studied behavioral changes that are less relevant. For example, the Hawaii MMRP analyzed the distance traveled and time spent between surfacings for humpback whales and found a statistically significant trend for these measures to increase with increasing exposure to ATOC transmissions.
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Shorebased observations are important because they provide a means of observing marine mammals without introducing the confounding effects of nearby vessels. Although the shore site was probably outside the area within which an effect would be expected, such observations should have been able to determine whether inshore humpback whales, rather than offshore near the ATOC source, would be affected.
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However, the ATOC source cannot be operated at levels higher than 195 dB for technical reasons, and it is unknown whether higher levels would produce a measurable response without being unduly harmful to marine mammals. Therefore, the Committee suggested an alternative approach that of broadcasting noises other than ATOC signals that would affect marine mammal behavior in a way that is detectable by the same (or similar)
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Thus, it was difficult to assess the quality and significance of this work and to make suggestions for future ATOC-related marine mammal studies. In its 1996 report the NRC noted that such a situation, if it persisted, would compromise the Committee's future work, and it would not be able to conclude whether there are deleterious effects of the ATOC sound source on marine mammals (or other organisms)
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. ATOC investigators plan to conduct aerial surveys near the Kauai ATOC source to monitor the distribution and abundance of marine mammals to advance the understanding of possible long-term acoustic impacts (P.
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However, if it does proceed, monitoring of marine mammal behavior and responses to the ATOC transmissions should continue as an integral part of the experimental design in order to improve the ability to evaluate the impact of ATOC during the next 5 years of Hawaii ATOC transmissions. As part of this continued evaluation, there should be annual reports of all yearly data to an oversight body not associated with ATOC (e.g., the Marine Mammal Commission or National Oceanic and Atmospheric Administration)
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