Meredith Thornton | University of Pretoria (original) (raw)

Papers by Meredith Thornton

J. Cetacean Res. Manage.

The southern right whale (Eubalaena australis; SRW) population in South Africa’s coastal waters h... more The southern right whale (Eubalaena australis; SRW) population in South Africa’s coastal waters has experienced marked changes since 2009, including altered feeding and migration behaviour, and decreased calving success. At the same time, anthropogenic activities in the area have increased. Based on this, an update on SRW mortalities and related anthropogenic factors is warranted. Building on the published information of Best et al. (2001a), data were collated on all SRW mortalities as well as non‐fatal ship‐strikes and entanglements along the South African coast between 1999 and 2019. A total of 97 SRW mortalities were recorded, including three that did not result in a stranding, of which the majority were classified as calves of the year. Most of these occurred on the Western Cape coast between the months of July to November, coinciding with the seasonal presence of the species in South African coastal waters. Eleven of these mortalities could be attributed to ship‐strikes whereas...

Humpback whale microsatellite data set (9 loci

Elucidating patterns of population structure for species with complex life histories, and disenta... more Elucidating patterns of population structure for species with complex life histories, and disentangling the processes driving such patterns, remains a significant analytical challenge. Humpback whale (Megaptera novaeangliae) populations display complex genetic structures that have not been fully resolved at all spatial scales. We generated a data set of nuclear markers for 3,575 samples spanning the seven breeding stocks and substocks found in the South Atlantic and western and northern Indian Oceans. For the total sample, and males and females separately, we assessed genetic diversity, tested for genetic differentiation between putative populations and isolation by distance, estimated the number of genetic clusters without a priori population information, and estimated rates of gene flow using maximum likelihood and Bayesian approaches. At the ocean basin scale, structure is governed by geographic distance (IBD p<0.05) and female fidelity to breeding areas, in line with current understanding of the drivers of broad-scale population structure. Consistent with previous studies, the Arabian Sea breeding stock was highly genetically differentiated (FST 0.034-0.161; p<0.01 for all comparisons). However, the breeding stock boundary between west South Africa and east Africa was more porous than expected based on genetic differentiation, cluster, and gene flow analyses. Instances of male-fidelity to breeding areas and relatively high rates of dispersal for females were also observed between the three substocks in the western Indian Ocean. This mismatch between demographic units and current management boundaries may have ramifications for assessments of the status and continued protections of populations still in recovery from commercial whaling

African Journal of Marine Science, 2021

The Antarctic blue whale Balaenoptera musculus intermedia was hunted to near extinction in the tw... more The Antarctic blue whale Balaenoptera musculus intermedia was hunted to near extinction in the twentieth century. Current data on the abundance and distribution of the species are lacking owing to the difficulty and expense of surveys under adverse weather conditions in open-ocean habitats, and to the small population size. The most recently accepted global abundance estimate, based on the middle survey (1997/1998) of three circumpolar Antarctic surveys conducted between 1991/1992 and 2003/2004, was less than 1% of the original pre-whaling population size. The present study used a visual line-transect survey off the Queen Maud Land coast of Antarctica, in an area between 0° and 18° E and south of 67° S, in January 2014, to estimate the abundance of Antarctic blue whales in this area. Effort-accounted densities of sightings averaged 13.3 individuals per 1 000 nautical miles of survey effort (CV = 0.26) and reinforce recent findings that the area has significantly higher densities than averaged in circumpolar surveys (0.17–1.48 per 1 000 nautical miles). Distance sampling resulted in a population density estimate of 0.019 whales nautical-mile−2 (CV = 0.24) and an estimated abundance of 1 026 Antarctic blue whales (CV = 0.20, 95% CI 632–1 450) in the surveyed area. Obtaining such current estimates of abundance is crucial for assessment of the conservation status of the Antarctic blue whale population and for monitoring its recovery.

Frontiers in Marine Science, 2021

The Indian Ocean humpback dolphin (Sousa plumbea) is “endangered” with likely less than 500 anima... more 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 ...

Aquatic Conservation: Marine and Freshwater Ecosystems, 2017

1. The Indian Ocean humpback dolphin was recently uplisted to 'Endangered' in the recent South Af... more 1. The Indian Ocean humpback dolphin was recently uplisted to 'Endangered' in the recent South African National Red List assessment. Abundance estimates are available from a number of localized study sites, but knowledge of movement patterns and population linkage between these sites is poor. A national research collaboration, the SouSA project, was established in 2016 to address this key knowledge gap. Twenty identification catalogues collected between 2000 and 2016 in 13 different locations were collated and compared. 2. Photographs of 526 humpback dolphins (all catalogues and photos) were reduced to 337 individuals from 12 locations after data selection. Of these, 90 matches were found for 61 individuals over multiple sites, resulting in 247 uniquely, well-marked humpback dolphins identified in South Africa. 3. Movements were observed along most of the studied coastline. Ranging distances had a median value of 120 km and varied between 30 km up to 500 km. Long-term site fidelity was also evident in the data. Dolphins ranging along the south coast of South Africa seem to form one single population at the western end of the species' global range. 4. Current available photo-identification data suggested national abundance may be well below previous estimates of 1,000 individuals, with numbers possibly closer to 500. Bearing in mind the poor conservation status of the species in the country, the development of a national Biodiversity Management Plan aimed at ensuring the long term survival of the species in South Africa is strongly recommended. At the same time, increased research efforts are essential, particularly to allow for an in-depth assessment of population numbers and drivers of changes therein. 5. The present study clearly indicates the importance of scientific collaboration when investigating highly mobile and endangered species.

Molecular ecology, Jan 3, 2016

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2015

Several studies revealed that anthropogenic activities often cause toxic concentrations of some e... more Several studies revealed that anthropogenic activities often cause toxic concentrations of some elements, such as mercury, which bio-accumulate through the marine food chain, impacting negatively on the health of animals in the top trophic levels, such as a variety of marine mammals. Moreover, analysis of cetacean skin has been reported to be a reliable, long-term and mostly non-invasive method to monitor bio-accumulation of chemicals in cetacean populations. Several elements, including trace elements, occur naturally in cetacean skin, although nothing is known about their distribution patterns and little about safe base line concentrations. In May 2009, 42 false killer whales (FKWs) beached and died at Kommetjie in the Western Cape of South Africa. Skin samples of these FKWs were collected and analysed to determine elemental distribution patterns. The concentrations and distribution patterns of the major, as well as detectable trace elements were determined in skin samples from ten randomly selected FKW individuals, using micro-PIXE (particle-induced X-ray emission) analysis. Results revealed differences between the distribution patterns of elements in the skin sections. Fe, for example, was found to be concentrated in the dermal papillae, whereas the highest Zn concentrations occurred in the epidermis and particularly in the epidermal papillae. Since these essential elements mediate factors such as host immunity, from skin integrity to humoral immunity, knowledge of their typical distribution patterns can be of great value in studies of bio-accumulation. This is the first report of micro-PIXE being employed to study elemental distribution in cetacean skin and the resulting elemental distribution maps can serve as reference in future environmental pollution studies.

dolphins to tagging attempts using remotely-deployed suction-cup tags

PLOS ONE, 2017

Southern Hemisphere humpback whales (Megaptera novaeangliae) generally undertake annual migration... more Southern Hemisphere humpback whales (Megaptera novaeangliae) generally undertake annual migrations from polar summer feeding grounds to winter calving and nursery grounds in subtropical and tropical coastal waters. Evidence for such migrations arises from seasonality of historic whaling catches by latitude, Discovery and natural mark returns, and results of satellite tagging studies. Feeding is generally believed to be limited to the southern polar region, where Antarctic krill (Euphausia superba) has been identified as the primary prey item. Non-migrations and / or suspended migrations to the polar feeding grounds have previously been reported from a summer presence of whales in the Benguela System, where feeding on euphausiids (E. lucens), hyperiid amphipods (Themisto gaudichaudii), mantis shrimp (Pterygosquilla armata capensis) and clupeid fish has been described. Three recent research cruises (in October/

1 Faculdade de Ciências do Mar e Ambiente Universidade do Algarve, Campus Gambelas, 8000-139 Fa... more 1 Faculdade de Ciências do Mar e Ambiente Universidade do Algarve, Campus Gambelas, 8000-139 Faro, Portugal. 2 Sackler Institute for Comparative Genomics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, USA. ...

African Journal of Marine Science, 2010

A mass stranding of false killer whales Pseudorca crassidens at Long Beach near the village of Ko... more A mass stranding of false killer whales Pseudorca crassidens at Long Beach near the village of Kommetjie (34°8.18′ S, 18°9.77′ E) on the Cape Peninsula, South Africa, in May 2009 is described. The estimated size of stranded group was 55 animals, which is close to the median size of P. crassidens groups that have stranded previously in South Africa (58). Five of the stranded individuals succumbed, 36 were euthanised and 14 were rescued. This was the eighth known mass stranding of this species to occur in South Africa, with all these events occurring on the irregular south-west coast of the Western Cape province.

Molecular Biology and Evolution, 2014

Ecosystem function and resilience is determined by the interactions and independent contributions... more 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.

Ibis, 2008

The bulk ore carrier Apollo Sea sank near Dassen Island, South Africa, on 20 June 1994 during a p... more The bulk ore carrier Apollo Sea sank near Dassen Island, South Africa, on 20 June 1994 during a period of winter storms. Approximately 10 000 African (Jackass) Penguins Spheniscus demersus were oiled, collected and transported to the SANCCOB rescue centre; 5213 were released after cleaning, 4076 with flipper bands. We believe that most of the penguins oiled during this incident reached an island or the mainland alive, and that there was no mass mortality in the wild at the time of the oil spill. Birds from all parts of the breeding range were oiled, but most were from Robben and Dassen Islands. The overwhelming majority of released birds made the transition from the rescue centre to the wild successfully; 2652 had been resighted a t breeding colonies within two years of their release; the cumulative number of birds was increasing steadily and an asymptote had not been reached by August 1996. There was a wide dispersal of released penguins, with recoveries and resightings over 1800 km of coastline between Algoa Bay and Walvis Bay.

Http Mc Manuscriptcentral Com Tmyc, Sep 1, 2010

Cutaneous fungi are known to affect parts of the outermost skin layers of mammals, including the ... more Cutaneous fungi are known to affect parts of the outermost skin layers of mammals, including the epidermis, stratum spinosum and stratum corneum, as well as mucocutaneous membranes, genitalia or external ears. Relatively little is known about fungal infections of Mysticete cetaceans and studies are needed to determine the fungal diversity associated with these marine mammals. This case report was aimed

In the eastern South Atlantic Ocean (Region B) humpback whales are distributed along the west coa... more In the eastern South Atlantic Ocean (Region B) humpback whales are distributed along the west coast of South Africa and winter in the Gulf of Guinea. The most recent data available suggest that Breeding stock B is possibly sub-structured, with B1 considered a breeding ground and B2 a summer feeding ground and a winter migration corridor. However questions remain over the population structure of B stock. Here, we present an assessment of temporal population structure in humpback whales on the west coast of Africa using maternally (mitochondrial DNA control region) and bi-parentally (10 microsatellites) inherited markers. We amplified, sexed, genotyped and sequenced a total of 2018 samples from B1 (Gabon, Angola, São Tomé) and B2 (West South Africa). The results showed significantly differentiation based on haplotype frequencies (F ST ) and molecular distances (Φ ST ) between B1 and B2; similar results were obtained with the microsatellite data, however very low gene flow was detected the two regions. For the temporal analysis, significant results were obtained only for haplotype frequency statistics (F ST ), where west South Africa seasons were significantly different from seasons in Gabon. When the samples were stratified by sex, significant differentiation at the haplotype level were found for both sexes and nucleotide level only for females. The direct detection of movements by genetically identified individuals, females and males, suggests that interchange occurs between regions. However, all movements to date are from a northbound to southbound direction. The results presented here indicate that there is some spatial and temporal population substructure in humpback whales in B stock.

African Journal of Ecology, Feb 29, 2000

This paper describes the pattern of daylight occurrence of humpback dolphins Sousa chinensis in A... more This paper describes the pattern of daylight occurrence of humpback dolphins Sousa chinensis in Algoa Bay, the Eastern Cape, South Africa, between May 1991 and May 1994. Two indices, the Sighting Index (SI) and the Total Recorded Dolphin Presence (TRDP), were used to quantify the dolphins' daylight occurrence. Humpback dolphins display a clear pattern of daylight occurrence in Algoa Bay and can be seen mostly in the morning, and, to a lesser extent, in the evening. This pattern varies little between seasons (with possible exception for the evening hours), follows the time of the solar day, is not related to the tidal cycle and is probably governed by the diurnal cycles of dolphins' prey.