Update on NOAA-NMFS Acoustical Guidelines


On Monday we submitted our critique and suggestions for the NOAA-NMFS Acoustical Exposure Guidelines for “Level A takes.” These guidelines establish regulatory thresholds for just how much noise we humans can make before the damage to marine mammals requires a higher level of scrutiny, permission, or mitigation.

It is easy to be skeptical about such guidelines. On the one hand they help protect marine life from excessive over-exposure to human generated noise – but the entire premise presupposes that humans will be exceeding noise levels to the extent that we need guidelines to keep us within some regulatory constraint (one eyebrow raised here…). But it is our mission to roll up our sleeves and participate, with the hopeful outcome of contributing to a set of guidelines that are meaningful, and useful.

Our over-arching critique is that the proposed guidelines are a significant improvement over the legacy guidelines, mostly due to segregating marine mammals into their particular hearing ranges and creating “weighting curves” that reflect what they can hear. For example blue whales vocalize with – and we presume hear very low frequencies that are well below human pitch discrimination, and definitely below what dolphins and porpoises can hear – so they are categorized as “Low Frequency (LF) Cetaceans.” Porpoises can hear extremely high frequencies well above what the blue whales can hear – so they are categorized as “High Frequency (HF) Cetaceans.”

LF, MF, and HF Cetacean weighting curves.

LF, MF, and HF Cetacean weighting curves.

Under this rubric there are five categories of exposure curves (LF, MF, and HF Cetaceans, Seals, and Sea Lions) which are tailored to the hearing sensitivities of the subject animals with the intent of knowing what sorts of noises might, or might not damage particular animals in their respective hearing groups. The legacy guidelines grouped all exposures based exclusively on how loud a noise was regardless of whether an animal could perceive that sound. This has resulted in inconsistencies in application with incongruous results (dolphins riding bow waves of seismic survey vessels comes up in these discussions). These inconsistencies has led to regulators not taking regulatory thresholds seriouslyor worse.

In practice these segregated weighting curves will yield lower take estimates – for now, but the Guidelines provide for easier revision as the science comes in that more accurately reflect impacts. There remain many problems with the Guidelines: A paucity of data from too few captive animals; only speculative data on LF Cetaceans (baleen whales), and assumptions about hearing acuity and mechanics based on terrestrial animals. Much of this we pointed out in our first round of comments; much of which was addressed – although not necessarily resolved in the revised guidelines.

In the end I fall back on my original premise that needing to have exposure guidelines like these says a lot about human hubris and how we justify the damage we wreck on the ocean and those creatures that call it home. I hope our comments provide some measure of relief.