Underwater sounds are very important in social communication of harp seals (Pagophilus groenlandicus) because they are the main means of long- and short-distance communication. Individual harp seals must try to avoid being masked and emit only those calls that will benefit them. Underwater vocalizations of harp seals were recorded during the breeding season. The physical characteristics associated with antimasking attributes of 16 call types were examined. Rising frequency or increasing amplitude within calls were not common. Most of the calls ended abruptly (range 145–966 dB/s), but call onset was more gradual. At high calling rates (95.1–135 calls/min) there were significantly more calls overlapping temporally than at medium (75.1–95 calls/min) or low (35–75 calls/min) calling rates, but even at the highest calling rates, 79.1% of the calls were not overlapped. When 2, 3, or 4 calls overlapped, there were significantly fewer frequency separations of less than 1/3 octave than would be expected by chance. This is important because sounds that are separated by less than 1/3 octave likely mask each other. When 2–4 calls are occurring simultaneously, only 4.5% to 14.2% are masked by virtue of being within 1/3 octave from their nearest neighbor. None of the overlappping calls was of the same type. This suggests that the seals are actively listening to each other’s calls and are not randomly using the different call types. Harp seals use frequency and temporal separation in conjunction with a wide vocal repertoire to avoid masking each other.

Shortly after the Deepwater Horizon oil spill began in April 2010, a widely spaced passive acoustic monitoring array was deployed in the northeastern Gulf of Mexico to document the impacts of this unprecedentedly large and deep offshore oil spill on oceanic marine mammals. The array was subsequently maintained for over a decade. Here we document decadal density declines for seven of eight monitored species groups, including sperm whales (up to 31%), beaked whales (up to 83%), and small delphinids (up to 43%). Declines were observed both within and outside of the surface oil footprint. Though not conclusively linked to the oil spill, the broad spatial and temporal scale of these declines observed for disparate marine mammal species is consistent with Deepwater Horizon impacts. These declines have exceeded and outlasted post-spill damage assessment predictions, suggesting that the offshore ecosystem impacts of Deepwater Horizon may have been larger than previously thought.

En México no se conoce el tamaño de las poblaciones de la tonina (Tursiops truncatus) debido a su granmovilidad y al ocasional intercambio de individuos entre poblaciones. El objetivo de este estudio fue determinarla abundancia de toninas en la zona norte de Veracruz. De marzo de 2005 a diciembre de 2007 se realizaron 50navegaciones con un esfuerzo total de 236.7 horas. Los resultados obtenidos de la foto-identificación de toninas, seemplearon en el modelo Jolly-Seber y se estimó con este modelo un total de N=302 ±113 organismos para toda el áreade estudio. Para Tamiahua, se estimó una población de N=177 ± 10 delfines y para Tuxpan N=161 ± 68 delfines. Estosresultados sugieren que existe un mínimo intercambio de delfines entre zonas y por tanto, las poblaciones no estánaisladas; sin embargo, los organismos tienen preferencia por ciertas áreas. La foto-recaptura de algunos individuos enla zona de Tamiahua confirma que la fidelidad al sitio se ha mantenido por 13 años. Es probable que esto se deba aque cada una de las zonas presenta estuarios con alta productividad que son ideales para refugio y crianza de las toninas.