Species distribution modelling of Bryde's whales, humpback whales, southern right whales, and sperm whales in the southern African region to inform their conservation in expanding economies

Jean Purdon; Fannie W Shabangu; Dawit Yemane; Marc Pienaar; Michael J Somers; Ken Findlay

doi:10.7717/peerj.9997

Species distribution modelling of Bryde's whales, humpback whales, southern right whales, and sperm whales in the southern African region to inform their conservation in expanding economies

PeerJ. 2020 Sep 22:8:e9997. doi: 10.7717/peerj.9997. eCollection 2020.

Authors

Jean Purdon¹, Fannie W Shabangu², Dawit Yemane^{2

3}, Marc Pienaar⁴, Michael J Somers⁵, Ken Findlay⁶

Affiliations

¹ Whale Unit, Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa.
² Fisheries Management Branch, Department of Environment, Forestry and Fisheries, Cape Town, South Africa.
³ University of Cape Town, Marine Research Institute, Cape Town, Western Cape, South Africa.
⁴ uLwazi Node, South African Environmental Observation Network, Pretoria, South Africa.
⁵ Mammal Research Institute, Centre for Invasion Biology, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa.
⁶ Centre for Sustainable Oceans, Cape Peninsula University of Technology, Cape Town, South Africa.

Abstract

In southern African waters, information about species distribution and habitat preferences of many cetacean species is limited, despite the recent economic growth that may affect them. We determined the relative importance of eight environmental variables (bathymetry, distance to shore, slope, chlorophyll-a, salinity, eastwards sea water velocity, northwards sea water velocity and sea surface temperature) as drivers of seasonal habitat preferences of Bryde's whales (Balaenoptera brydei), humpback whales (Megaptera novaeangliae), southern right whales (Eubalaena australis) and sperm whales (Physeter macrocephalus). Using presence only data from multiple sources, we constructed predictive species distribution models (SDMs) consisting of ensembles of seven algorithms for these species during both summer and winter. Predicted distribution for all cetaceans was high in southern Africa and, in particular, within the South African Exclusive Economic Zone (EEZ). Predictive models indicated a more pronounced seasonal variation for humpback, sperm and southern right whales than for Bryde's whales. Southern right whales occurred closer to shore during winter, humpback whales were more likely to occur along the east coast in winter and the west coast in summer, and sperm whales were more concentrated off the shelf in winter. Our study shows that ensemble models using historical, incidental and scientific data, in conjunction with modern environmental variables, can provide baseline knowledge on important environmental drivers of cetacean distribution for conservation purposes. Results of this study can further be used to help develop marine spatial plans and identify important marine mammal areas.

Keywords: Cetaceans; Ensemble models; Important marine mammal areas; South Africa; Species distribution models.

Grants and funding

Michael John Somers was funded by the DSI-NRF Centre of Excellence for Invasion Biology. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.