Species' conservation relies on understanding their seasonal habitats and migration routes. North Atlantic right whales (Eubalaena glacialis), listed as endangered under the U.S. Endangered Species Act, migrate from the southeastern U.S. coast to Cape Cod Bay, Massachusetts, a federally designated critical habitat, from February through May to feed. The whales then continue north across the Gulf of Maine to northern waters (e.g., Bay of Fundy). To enter Cape Cod Bay, right whales must traverse an area of dense shipping and fishing activity in Massachusetts Bay, where there are no mandatory regulations for the protection of right whales or management of their habitat. We used passive acoustic recordings of right whales collected in Massachusetts Bay from May 2007 through October 2010 to determine the annual spatial and temporal distribution of the whales and their calling activity. We detected right whales in the bay throughout the year, in contrast to results from visual surveys. Right whales were detected on at least 24% of days in each month, with the exception of June 2007, in which there were no detections. Averaged over all years, right whale calls were most abundant from February through May. During this period, calls were most frequent between 17:00 and 20:00 local time; no diel pattern was apparent in other months. The spatial distribution of the approximate locations of calling whales suggests they may use Massachusetts Bay as a conduit to Cape Cod Bay in the spring and as they move between the Gulf of Maine and waters to the south in September through December. Although it is unclear how dependent right whales are on the bay, the discovery of their widespread presence in Massachusetts Bay throughout the year suggests this region may need to be managed to reduce the probability of collisions with ships and entanglement in fishing gear.

Several marine autonomous recording units (MARUs) were deployed in northeastern Gulf of Mexico from 2010–2012 to study the acoustic ecology of Bryde's whales (Balaenoptera edeni) following the Deepwater Horizon oil spill. However, the acoustic repertoire of this sub-population is poorly documented, presently limiting the efficacy of acoustic monitoring applications. Numerous stereotyped, low-frequency signals from a putative biological sound source were found throughout the recordings. Sounds fell into three categories distinguished by spectral and temporal properties. Multiple calls overlapped temporally on individual MARUs, suggesting that multiple sources produced these sounds. The basic features are similar to those from other mysticetes, but they differ from any previously published sounds. Since Bryde's whales are the most common mysticete in the Gulf and have previously been observed within the recording area on multiple occasions, it is likely that Bryde's whales are the most probable source of these sounds. These results potentially identify a suite of previously undocumented calls from Bryde's whales, which could facilitate future passive acoustic monitoring efforts to better understand the population dynamics and status of this sub-population.

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