Marine mammal baseline, Johan Castberg 2021

**Overview**

Acoustic data were recorded at the Johan Castberg field in the southern Barents Sea at three locations from October 2018 until June 2019 to assess the presence of marine mammals and characterise the underwater soundscape. The marine mammal analysis was focused on two stations (PAMEast and PAMNorth) as the third (PAMWest) stopped recording early and the data suffered from poor audio quality.

Five marine mammal species were detected during the study: fin whale, humpback whale, killer whale, sperm whale and a dolphin species whose signals were tentatively attributed to white-beaked dolphins on the basis of sighting records in the area and habitat preference of this species. These species were generally detected at similar levels at PAMEast and PAMNorth, except for dolphins, which were more common at PAMNorth. Dolphins showed a pronounced seasonal pattern of occurrence, with very few detections in winter.

Killer whale occurred sporadically, their occurrence peaking in November and March, possibly coinciding with that of prey species. Along with dolphins, sperm and fin whales were the most commonly detected species, occurring throughout the study, albeit slightly less frequently in late winter than during the rest of the year.

Humpback whale detections peaked in March, which may be associated with the transit of migrating animals through the area as they return to feed on spring spawning herring.
The data are provided in the form of two .csv files formatted according to the Darwin Core terminology used by the Global Biodiversity Information Facility (GBIF).

The “EQ_marine_mammals_JC_baseline_sampling_events” file lists the geographic attributes of the survey. The “EQ_marine_mammals_JC_baseline_associated_occurrences” file lists the marine mammal detections (reported as % days with acoustic detections per species and month), which can be linked to the “sampling_events” file through the “eventID” column present in both files. For further information on the Darwin Core terminology, use the following link: [Darwin Core quick reference guide - Darwin Core (tdwg.org)](https://dwc.tdwg.org/terms/)

The full Johan Castberg report can be accessed here: [https://cdn.equinor.com/files/h61q9gi9/global/09796aacc40a85b06fa41ecb70c91ed8b30c6e08.pdf?johan-castberg-acoustic-monitoring-2021.pdf](https://cdn.equinor.com/files/h61q9gi9/global/09796aacc40a85b06fa41ecb70c91ed8b30c6e08.pdf?johan-castberg-acoustic-monitoring-2021.pdf)