Temporal patterns in the acoustic presence of marine mammals off Elephant Island, Antarctica


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karolin.thomisch [ at ] awi.de

Abstract

To develop reliable and effective management and conservation strategies for marine mammals, a profound knowledge about their distribution, as well as on the location of key habitats are essential. The waters off Elephant Island (Antarctica) are thought to serve as a feeding ground for baleen whales; however, detailed long-term information on patterns in the distribution of marine mammals in this area is still lacking for many species. This study aimed to investigate i) the acoustic biodiversity, as well as ii) inter-annual patterns, and iii) intra-annual patterns in the acoustic presence of marine mammals off Elephant Island. For this purpose, passive acoustic data collected here from January 2013 to February 2016 were analyzed both visually (in the form of spectrograms) and aurally for the presence of marine mammal vocalizations. Daily acoustic presence of marine mammals was assessed based on species-specific vocal signatures. During the overall recording period, eight marine mammal species were identified: Antarctic blue whales (Balaenoptera musculus intermedia), fin whales (B. physalus), Antarctic minke (B. bonaerensis) whales, humpback whales (Megaptera novaeanglia), Killer whales (Orcinus orca), sperm whales (Physeter macrocephalus), Leopard seals (Hydrurga leptonyx) and crabeater seals (Lobodon carcinophaga). For some species, a temporal pattern in the acoustic presence was detected, whereas other species did not exhibit a temporal pattern in their acoustic presence, but were acoustically present either year-round or rather occasionally. Antarctic minke whales were acoustically present from June to September and absent during austral summer, indicating that their acoustic presence was linked to the formation of sea-ice. Furthermore, the annual number of days with Antarctic minke whale calls declined from 2013 to 2015, which might possibly be linked to an inter-annual decrease in the sea-ice extent off Elephant Island. The amount of days with killer whale vocalizations peaked during austral winter when the amount of days with Antarctic minke whale vocalizations reached its maximum, indicating a possible link between killer whale acoustic presence and the availability of their prey (Antarctic minke whales, amongst others). Vocalizations of both seal species occurred primarily during austral winter and spring, i.e. from September to December for leopard seals and during September and October for crabeater seals, which is in accordance with their breeding period and suggests that both species were breeding off Elephant Island. Besides, vocalizations of all four baleen whale species were detected during austral winter, possibly indicating that part of the populations remained in the Southern Ocean year-round. Hence, this study adds further evidence for the hypothesis of a complex migratory behavior of baleen whales. Overall, this study suggests that the Elephant Island region serves as an important feeding and breeding habitat for several marine mammal species either year-round or seasonally. The identification of such ecologically important areas with high (acoustic) biodiversity can considerably benefit future conservation applications, such as the designation of marine protected areas.



Item Type
Thesis (Bachelor)
Authors
Divisions
Primary Division
Programs
Primary Topic
Research Networks
Peer revision
Not peer-reviewed
Publication Status
Published
Eprint ID
49003
Cite as
Meister, M. (2017): Temporal patterns in the acoustic presence of marine mammals off Elephant Island, Antarctica , Bachelor thesis, University of Bremen.


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