Using ecosystem-services assessments to determine trade-offs in ecosystem-based management of marine mammals

Recovery of carbon benefits by overharvested baleen whale populations is threatened by climate change

Despite the importance of marine megafauna on ecosystem functioning, their contribution to the oceanic carbon cycle is still poorly known. Here, we explored the role of baleen whales in the biological carbon pump across the southern hemisphere based on the historical and forecasted abundance of five baleen whale species. We modelled whale-mediated carbon sequestration through the sinking of their carcasses after natural death. We provide the first temporal dynamics of this carbon pump from 1890 to 2100, considering both the effects of exploitation and climate change on whale populations. We reveal that at their pre-exploitation abundance, the five species of southern whales could sequester 4.0 × 105 tonnes of carbon per year (tC yr-1). This estimate dropped to 0.6 × 105 tC yr-1 by 1972 following commercial whaling. However, with the projected restoration of whale populations under a RCP8.5 climate scenario, the sequestration would reach 1.7 × 105 tC yr-1 by 2100, while without climate change, recovered whale populations could sequester nearly twice as much (3.2 × 105 tC yr-1) by 2100. This highlights the persistence of whaling damages on whale populations and associated services as well as the predicted harmful impacts of climate change on whale ecosystem services.

Auditory evoked potential in stranded melon-headed whales (Peponocephala electra): With severe hearing loss and possibly caused by anthropogenic noise pollution

Highly concentrated live mass stranding events of dolphins and whales happened in the eastern coast of China between June and October 2021. The current study adopted the non-invasive auditory evoked-potential technique to investigate the hearing threshold of a stranded melon headed whale (Peponocephala electra) at a frequency range of between 9.5 and 181 kHz. It was found that, at the frequency range of from 10 to 100 kHz, hearing thresholds for the animal were between 20 and 65 dB higher than those of its phylogenetically closest species (Pygmy killer whale). The severe hearing loss in the melon headed whale was probably caused by transient intense anthropogenic sonar or chronic shipping noise exposures. The hearing loss could have been the cause for the observed temporal and spatial clustered stranding events. Therefore, there is need for noise mitigation strategies to reduce noise exposure levels for marine mammals in the coastal areas of China.