Science Alone Won’t Do It! South Africa’s Endangered Humpback Dolphins Sousa plumbea Face Complex Conservation Challenges

Abstract

The Indian Ocean humpback dolphin (Sousa plumbea) is “endangered” with likely less than 500 animals remaining in South African waters. Established in 2016, the SouSA Consortium is a formalised network of scientists and conservationists to combine knowledge and research efforts, and make coordinated decisions with the aim of conserving the species. The first collaborative project collated available photo-identification data in an attempt to refine a national population estimate and investigate movements between research sites. This work was able to identify 250 uniquely marked individuals, with the population divided into the south-coast (Agulhas bioregion) and east-coast (Natal bioregion) populations. Environmental factors almost certainly play a role in the declining numbers of the species in South African waters. However, individual threats and solutions are challenging to identify as the South African marine environment is undergoing significant natural and anthropogenic changes with major shifts in the distribution and numbers of some prey, competitor and predator species. Therefore, we believe that a continued investigation of potential contributing factors and their interaction will take too long, inevitably resulting in another case of documenting extinction. With this in mind, we present the results of a SWOT (Strengths, Weaknesses, Opportunities, and Threats) analysis in an effort to help us identify the next steps to take toward the conservation of humpback dolphins in South African waters. We unanimously conclude that no single cause for the rapid decline of humpback dolphins in South African waters can be identified, and that the cumulative effects of multiple stressors, which are difficult to pinpoint and mitigate, are impacting population numbers. While highlighting the need for continued research, we suggest a shift toward more action-focused conservation efforts, the first concrete steps being the development of a Conservation Management Plan with input from other stakeholders.

Histomorphological stratification of blubber of three dolphin species from subtropical waters

“…These changes can lead to lower prey availability for marine mammal populations, resulting in poorer health and condition (Simmonds & Isaac, 2007). Marine mammals are top predators of the marine food web and are increasingly being recognized as important indicators for ocean health (Fossi et al, 2020; Plön et al, 2021). Using body condition as a sentinel parameter to monitor ecosystem health, recent studies have used the adipocyte index (AI) obtained from biopsy samples of live humpback whales ( Megaptera novaeangliae ; Castrillon et al, 2017) as a rapid, nonlethal and low‐cost method to monitor body condition.…”

Population distribution, connectivity and differentiation of Indo‐Pacific humpback dolphins in Chinese waters: Key baselines for improving conservation management

“…• We urge that the current known distribution areas of humpback dolphins along the coast of southern China should be protected under a more ambitious country-led conservation scheme that can integrate interregional collaborative efforts (cf. Plön et al, 2021;Minton et al, 2022). Considering that humpback dolphins display high site fidelity and occupy small home ranges, place-based conservation (e.g.…”

“…Inter‐population gene flow is limited and population isolation may be geographically widespread. Third, the population differentiation of humpback dolphins is supported, not only by genetic inter‐population divergence among different regions, but also by geographical variability in humpback dolphin morphology (osteology, body coloration and pigmentation) and behaviour (whistles and group size). Based on these up‐to‐date advances in critical baselines, the following conservation recommendations are made: We urge that the current known distribution areas of humpback dolphins along the coast of southern China should be protected under a more ambitious country‐led conservation scheme that can integrate interregional collaborative efforts (cf. Plön et al, 2021; Minton et al, 2022). Considering that humpback dolphins display high site fidelity and occupy small home ranges, place‐based conservation (e.g.…”

“…The Sousa genus (i.e. humpback dolphins) is considered to contain some of the most endangered delphinid species worldwide (Jefferson & Smith, 2016; Li, 2020; Plön et al, 2021; Minton et al, 2022). According to most recent taxonomic information, at least four species have been identified in this genus: the Indo‐Pacific humpback dolphin ( Sousa chinensis ), the Indian Ocean humpback dolphin ( Sousa plumbea ), the Australian humpback dolphin ( Sousa sahulensis ) and the Atlantic humpback dolphin ( Sousa teuszii ) (Frère et al, 2008; Mendez et al, 2013; Jefferson & Rosenbaum, 2014).…”

Low mitochondrial genetic diversity in the Indian Ocean humpback dolphin Sousa plumbea in South African waters

“…Over the last 2 decades, there have been fewer sightings of humpback dolphins, group sizes have decreased, predominant behaviours have changed (Koper et al 2016, Bouveroux et al 2018 and maximum ranging distances have increased (Vermeulen et al 2017). These observations are likely due to changes in food availability, anthropogenic disturbances, a possible decline in population numbers (Koper et al 2016, Bouveroux et al 2018 or a result of these cumulative impacts (Plön et al 2021). A decline in population numbers can result in a concurrent decrease in genetic diversity (Frank ham 1996, Willi et al 2007, Banks et al 2013), but when diversity levels are already low, the capacity to detect further reductions is reduced.…”