Stephanie Plön

Killer Whale Nuclear Genome and mtDNA Reveal Widespread Population Bottleneck during the Last Glacial Maximum

Ecosystem function and resilience is determined by the interactions and independent contributions of individual species. Apex predators play a disproportionately determinant role through their influence and dependence on the dynamics of prey species. Their demographic fluctuations are thus likely to reflect changes in their respective ecological communities and habitat. Here, we investigate the historical population dynamics of the killer whale based on draft nuclear genome data for the Northern Hemisphere and mtDNA data worldwide. We infer a relatively stable population size throughout most of the Pleistocene, followed by an order of magnitude decline and bottleneck during the Weichselian glacial period. Global mtDNA data indicate that while most populations declined, at least one population retained diversity in a stable, productive ecosystem off southern Africa. We conclude that environmental changes during the last glacial period promoted the decline of a top ocean predator, that these events contributed to the pattern of diversity among extant populations, and that the relatively high diversity of a population currently in productive, stable habitat off South Africa suggests a role for ocean productivity in the widespread decline.

A Systematic Health Assessment of Indian Ocean Bottlenose (Tursiops aduncus) and Indo-Pacific Humpback (Sousa plumbea) Dolphins Incidentally Caught in Shark Nets off the KwaZulu-Natal Coast, South Africa

Coastal dolphins are regarded as indicators of changes in coastal marine ecosystem health that could impact humans utilizing the marine environment for food or recreation. Necropsy and histology examinations were performed on 35 Indian Ocean bottlenose dolphins (Tursiops aduncus) and five Indo-Pacific humpback dolphins (Sousa plumbea) incidentally caught in shark nets off the KwaZulu-Natal coast, South Africa, between 2010 and 2012. Parasitic lesions included pneumonia (85%), abdominal and thoracic serositis (75%), gastroenteritis (70%), hepatitis (62%), and endometritis (42%). Parasitic species identified were Halocercus sp. (lung), Crassicauda sp. (skeletal muscle) and Xenobalanus globicipitis (skin). Additional findings included bronchiolar epithelial mineralisation (83%), splenic filamentous tags (45%), non-suppurative meningoencephalitis (39%), and myocardial fibrosis (26%). No immunohistochemically positive reaction was present in lesions suggestive of dolphin morbillivirus, Toxoplasma gondii and Brucella spp. The first confirmed cases of lobomycosis and sarcocystosis in South African dolphins were documented. Most lesions were mild, and all animals were considered to be in good nutritional condition, based on blubber thickness and muscle mass. Apparent temporal changes in parasitic disease prevalence may indicate a change in the host/parasite interface. This study provided valuable baseline information on conditions affecting coastal dolphin populations in South Africa and, to our knowledge, constitutes the first reported systematic health assessment in incidentally caught dolphins in the Southern Hemisphere. Further research on temporal disease trends as well as disease pathophysiology and anthropogenic factors affecting these populations is needed.

Sexual dimorphism in long-beaked common dolphins (Delphinus capensis) from KwaZulu-Natal, South Africa

We examined external morphometric parameters in incidentally caught long-beaked common dolphins (Delphinus capensis) from the east coast of South Africa for evidence of sexual dimorphism. We evaluated sexual dimorphism and allometric growth in 26 external body measurements from 211 individuals and assessed size and shape dimorphism. Most characteristics analyzed showed a negative allometric relationship to total body length for both males and females. Twenty-one measurements showed significant differences between the sexes. Among these were the 3 girth measurements, the length of the dorsal fin base, the distance between the tip of the upper jaw to the midpoint of the umbilicus, and the distance between the tip of the upper jaw to the center of the anus. Fourteen of the 26 characteristics analyzed showed significant differences in body shape between the sexes. Our results indicated that moderate sexual dimorphism is present in long-beaked common dolphins from this region, with males being both significantly longer and more robust than females. Sexual dimorphism in this species may be related to their mating or foraging strategies.

Revisiting acoustic deterrence devices: Long-term bycatch data from South Africa’s bather protection nets

The KwaZulu-Natal (KZN) Sharks Board in Durban, South Africa, has been managing bather protection nets off KZN’s most popular beaches since 1952 to mitigate shark-human interaction. The nets catch potentially dangerous sharks, but also take a bycatch of other marine megafauna, including the Indo-Pacific bottlenose dolphin Tursiops aduncus. A total of 1169 T. aduncus were caught between 1980 and 2015 (annual mean 32.5 ± 13.4). Most were young and immature. To mitigate cetacean bycatch, acoustic devices (pingers, whale alarms, and biosonar reflectors) were installed at selected beaches for some years between 1993 and 2015. On nets with pingers, most dolphins were caught close to active pingers, with 44 out of 72 animals (61%) caught within 50 m and 25 (35%) within 10 m. Bycatch varied inter-annually and between neighboring beaches both with and without pingers and there was no clear indication that pingers reduced bycatch. As this is an operational bather protection program, no controlled experiments on pin...

Comparison of soundscape contributors between two neighboring southern right whale nursing areas along the South African coast

Southern right whales (Eubalaena australis) were absent along the Eastern Cape coast, South Africa, for more than a century after overexploitation by land-based whalers in the early 1800s. Currently, mother-calf pairs in particular are again frequently sighted in this area, raising concerns about the effect of recent port developments on their occurrence in nursing areas. Soundscape contributors and sound levels of two neighboring nursing bays, St. Francis Bay (one recreational port) and Algoa Bay (two commercial ports), were compared to address this concern. Wind, southern right whales, fish, snapping shrimp, and close vessels were contributing to noise levels in both bays. Additional sound sources in Algoa Bay were surf-zone noise, dolphins, and distant vessels. The overall sound levels in Algoa Bay were 5-25 dB re 1 μPa2/Hz higher. However, mother-calf pair sightings per unit effort was 0.99 (St. Francis Bay) against 1.11 (Algoa Bay), resulting in a lack of evidence that mothers prefer quieter bays or ...

A standardized necropsy protocol for health investigations of small cetaceansin southern Africa

Globally, the increasing need to conduct both research and surveillance of the health of wild animal populations has been recognized as an important tool in conservation and management. While such studies on terrestrial wildlife are frequent in the southern African sub-region, their counterparts in the marine environment seem to be largely lacking. Here we report on our experience in establishing and testing a standardized necropsy protocol for small cetaceans adapted for the local context, with the specific aim of sampling for health investigations and monitoring. The necessity, challenge and value of regional standardization in data collection specifically aimed at health investigations, inter-disciplinary collaboration, long-term data banking, and sample storage are discussed in addition to practical and safety considerations. The developed protocol, focusing on the necropsy technique and tissue sample collection, as well as a list of required equipment are available as online supplementary material.