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No Documented Scientific Evidence of Adverse Effects on Population Sustainability With these three terms in mind, it is critically important to understand that BOEM's conclusion in our August 2014 Science Note, and its Programmatic Environmental Impact Statement (PEIS), refers to effects on population sustainability, rather than effects on individual animals. We know from studies by BOEM and others that marine mammals can react to sound, sometimes moving away and sometimes changing their vocalizations. One prominent concern is whether anthropogenic sounds may "mask" communications between some marine mammals. However, as BOEM concluded in the PEIS, and reiterated in the 2014 Science Note, potential finks between these effects and the sustainability of species or stocks have not been demonstrated. For example, because of its abundance, the bottlenose dolphin heads the class in number of potential exposures to air gun sound levels with potential effects on behavior Yet Federal stock assessments for the dolphin do not identify air gun seismic surveys as adversely impacting stock sustainability in the Gulf of Mexico, where air gun surveys are routine. It is also important to understand that BOEM does not expect that 138,000 individual marine mammals, or anything close to that number, will have their hearing injured by air guns if seismic surveys are permitted on the Atlantic Outer Continental Shelf BOEM published numbers for potential air gun survey "takings" of marine mammals in its PEIS. The highest numbers estimated for a particular species are for the bottlenose dolphin, as noted above, and in its case the PEIS estimated potential for Level A takings of up to 11,748 individual bottlenose dolphins a year from air gun surveys and potential for up to 1,151,442 Level B takings. But the number of modeled "takes" in the PEIS is by design highly over-estimated to err on the side of protection, and it does not consider key mitigation measures that will be required to prevent "taking." One such requirement, for example, is that seismic survey vessels maintain "exclusion zones" around vessels whose boundaries are set to avoid any injury to marine mammal hearing. If a marine mammal enters the zone, or appears on a course to enter, trained observers call for immediate shut down of the air guns until the animals are clear of the area. Therefore, even those numbers included in the PEIS are far in excess of those takes we anticipate, given the mitigation measures that will be employed. Need for More Research A final point warrants mention. BOEM does not and should not assume that lack of evidence for adverse population -level effects of air gun surveys means that those effects may not occur What we know is a function of the effort and intelligence put into evaluating effects as well as what is actually happening in nature. Since 1998, BOEM has invested over $50 million on protected species and noise - related research, including marine mammals. We have also convened workshops for acoustic experts to help us identify questions for future research. But BOEM needs to keep looking -- hard and well -- for adverse effects.of offshore oil and gas activities on the environment, including sound. And we have asked our environmental studies program to make this a priority I'll conclude by noting that BOEM's 2014 Science Note has been cited publicly by both industry and environmental NGOs alike in presenting their respective positions on seismic surveys. BOEM is responsible for providing environmental safeguards in development of offshore resources, and our Science Note was intended to help the public understand our thinking on that task. I hope this follow-on Science Note is a helpful explanation. As always, your feedback is important to us, so please feel free to contact us. Sincerely, William Y. 13rowm. Chief Environmental Officer, Bureau of Ocean Energy Management The Bureau of Ocean Energy Management (BOEM) promotes energy independence, environmental protection and economic development through responsible, science -based management of offshore conventional and renewable energy resources. 215