321 research outputs found
Population size estimate of Indo-Pacific bottlenose dolphins in the Algoa Bay region, South Africa
No full textThis study estimates the population size of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in the Algoa Bay region on the Eastern Cape coast of South Africa. Mark-recapture analyses were performed on photo-identification data collected on 54 occasions during a 3-yr-study period. Using a photographic data set of over 10,000 ID-images, 1,569 individuals were identified, 131 of which were photographed on more than one occasion. Using the POPAN formulation in the software program MARK, a total population of approximately 28,482 individuals (95% CI = 16,220-40,744; CV = 0.220), was estimated (estimate corrected for the proportion of distinctive individuals in the population). This is the largest population estimate to date for this species along the South African coast, suggesting that the bottlenose dolphins inhabiting the Algoa Bay region represent part of a substantially larger population that ranges along a considerable length of the South African coast. © 2009 by the Society for Marine Mammalogy.link_to_subscribed_fulltex
Goose barnacles on seals and a penguin at Gough Island
No full textDuring a survey of seals in September and October
2009 at Gough Island, South Atlantic Ocean, we
recorded goose barnacles (Lepas australis) attached to the pelage of two of the 12 elephant seals (Mirounga leonina) inspected and one of the seven vagrant Antarctic fur seals (Arctocephalus gazella) which were found amongst the resident Subantarctic fur seals (A. tropicalis). We also recorded a goose barnacle attached to a Northern rockhopper penguin (Eudyptes chrysocome moseleyi)
Long distance breeding dispersal of a southern elephant seal
No full textSouthern elephant seals range extensively during regular foraging excursions. Despite this they are highly
philopatric and long range dispersal is rare. At Gough Island, southern Atlantic Ocean, we observed a breeding
adult male elephant seal during September 2009 which had been tagged on its natal beach at Marion Island,
southern Indian Ocean, in November 1998. The individual was resighted only once on Marion Island – six
months after tagging. This 3,860 km movement represents dispersal (and likely gene flow) between distinct
populations from different elephant seal geographical provinces. Given the polygynous breeding system of this
species, the presence of this single male may have a disproportionate genetic effect on the small number of
southern elephant seals breeding at Gough Island
Goose barnacles hitchhike on satellite-tracked southern elephant seals
No full textGoose barnacles (Lepas australis) attached to
satellite-relay data loggers were carried by three southern elephant seals (Mirounga leonina) from Marion Island. Their movements across the Polar Frontal Zone are presented, providing further evidence that megafauna are potential vectors for the transport of species into the Southern Ocean
Editorial: tracking marine megafauna for conservation and marine spatial planning
No full textDespite their important role in ecosystems, the widespread and increasing threats faced by many marine megafauna taxa has led to a poor conservation status of many species (e.g., Rees et al., 2016; Dias et al., 2019; Nelms et al., 2021; Jorgensen et al., 2022). Understanding and mitigating the threats faced by marine megafauna is challenging (Lascelles et al., 2014; Reisinger et al., 2022) because both the threats and the marine environment are highly dynamic in space and time, and animals’ occurrences vary with shifts in environmental and oceanographic conditions at different scales. Additionally, these animals are often highly mobile, making it difficult to pinpoint the occurrences of different individuals in specific locations.There are several definitions for the term ‘marine megafauna’. For example, Estes et al. (2016) define marine megafauna as species with maximum reported mass >45 kg, including 338 extant species of cetaceans, pinnipeds, sirenians, the sea otter (Enhyrda lutris), the polar bear (Ursus maritimus), the emperor penguin (Aptenodytes forsteri), marine reptiles, bony and cartilaginous fishes, cephalopods, and the giant clam (Tridacna gigas). Here, we take the view of Authier et al. (2017), who do not impose a strict body mass threshold, but consider marine megafauna to be a coherent group based on their ecological similarities (at or near the top of food webs, with no or few predators) and that share conservation issues.This Research Topic covers a broad taxonomic representation, spanning seabirds, cetaceans, sea turtles, pinnipeds, elasmobranchs, teleosts, a sirenian, the polar bear, and a large crustacean, the red king crab (Paralithodes camtschaticus). Articles submitted address how biologging is being used to understand the movement behaviour and distribution of marine megafauna, and how this information can play a key role to prioritise conservation goals. The resulting 34 articles illustrate how biologging is informing conservation of marine megafauna, and in light of these studies, we discuss challenges, methodological implications and future directions for biologging in conservation
Abundance estimates of killer whales at subantarctic Marion Island
No full textKiller whales Orcinus orca are apex predators known to have important effects on
marine ecosystems. A fundamental step towards understanding their role in ecosystems, and vital for
their informed management and conservation, is the rigorous estimation of their abundance. Studies
concerning this species have used mark-recapture analytical techniques to estimate abundance, but
enumeration of identifiable individuals is more common. This study estimated the abundance of killer
whales occurring inshore at subantarctic Marion Island. Mark-recapture analyses were performed
using nearly 10 000 photographs taken from 2006 to 2009. Using careful quality control criteria, we
identified 37 ind. The evident capture heterogeneity violates the underlying assumptions of the open
population POPAN parameterization in the software program MARK we initially used. We thus used
the simpler Chapman modified Lincoln-Petersen estimator, calculating a population size of 37 ind.
(95% CI = 29 to 44) for the period 2006 to 2007 and 32 ind. (95% CI = 30 to 33) for 2007 to 2008. Both
estimates are close to the catalogue size, suggesting that enumeration is an accurate measure of
abundance in this study. Our results are comparable to recent abundance estimates for the neighbouring
Crozet Archipelago (~1000 km due east). No rigorous approach has been used previously to
estimate the abundance of killer whales at Marion Island. This estimate provides a foundation for
further research related to the sociality and potential ecological impact of this population of killer
whales in the Southern Ocean.The
Department of Science and Technology (administered through
the National Research Foundation).http://www.int-res.comam2017Mammal Research InstituteZoology and Entomolog
Pseudostalked barnacles Xenobalanus globicipitis attached to killer whales Orcinus orca in South African waters
No full textSeveral records describe pseudostalked barnacles Xenobalanus globicipitis attached to killer whales Orcinus
orca, yet little is known of this association in Southern African waters. Here we describe Xenobalanus
prevalence on killer whales in South African waters and assemble previous records. Killer whales were
photographed opportunistically between July and September 2013. Sex and age class were determined, and if
Xenobalanus were present, attachment site and colony size noted. A prevalence of 50% was recorded, with
barnacles most commonly observed on the dorsal fin and tail flukes. The high prevalence of Xenobalanus on
killer whales in South African waters and lack thereof on killer whales at Marion Island implies that these are
separate populations, and thus we suggest Xenobalanus prevalence is an additional means to distinguish
between these populations.National Research Foundation (NRF) Thuthuka programme, the South African Department of Science and Technology through the NRF, the Mohamed bin Zayed Species Conservation Fund (project number: 10251290) and the International Whaling Commission’s Southern Ocean Research Partnership.http://link.springer.com/journal/125262016-12-31hb201
The effect of prey abundance and fisheries on the survival, reproduction, and social structure of killer whales (Orcinus orca) at subantarctic Marion Island
No full textMost marine apex predators are keystone species that fundamentally influence their ecosystems through cascading top-down processes. Reductions in worldwide predator abundances, attributed to environmental and anthropogenic-induced changes to prey availability and negative interactions with fisheries, can have far-reaching ecosystem impacts. We tested whether the survival of killer whales (Orcinus orca) observed at Marion Island in the Southern Indian Ocean correlated with social structure and prey variables (direct measures of prey abundance, Patagonian toothfish fishery effort, and environmental proxies) using multistate models of capture-recapture data spanning 12 years (2006 to 2018). We also tested the effect of these same variables on killer whale social structure and reproduction measured over the same period. Indices of social structure had the strongest correlation with survival, with higher sociality associated with increased survival probability. Survival was also positively correlated to Patagonian toothfish fishing effort during the previous year, suggesting that fishery-linked resource availability is an important determinant of survival. No correlation between survival and environmental proxies of prey abundance was found. At-island prey availability influenced the social structure of Marion Island killer whales, but none of the variables explained variability in reproduction. Future increases in legal fishing activity may benefit this population of killer whales through the artificial provisioning of resources they provide.</span
The fishery for Antarctic krill – conflicts between industrial production, protection of biodiversity, and legal governance
No full textThe Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) is responsible for conserving the Antarctic marine ecosystem, where conservation also includes the management of commercial fisheries. The largest fishery (by weight) in Antarctic waters is that for Antarctic krill, a species vital to biogeochemical cycles and carbon sequestration, and a critical dietary item for a broad guild of marine predators. Fishing interests grew from the 1960s onwards, but catches then declined following the breakup of the Soviet Union. Now catches are again increasing, CCAMLR has been developing a revised krill fishery management framework intended to reduce ecosystem risks to predators at critical times of year. At the CCAMLR meeting in 2024, ongoing development of the revised framework was considered, however no progress was made. Progress is urgent, since part of the existing management approach was not renewed. Consequently, by default, catches in the southwest Atlantic may now aggregate in space and time; the interim catch limit for krill (620,000 t) can now be taken from anywhere and at any time, including at times and in places critical to krill predators, possibly with unintended consequences. Allowing catches to aggregate in space and time is something CCAMLR has long sought to avoid. Existing voluntary measures implemented by the fishery will help distribute catches, but are no substitute for de jure management. In addition to risks to the ecosystem, the current situation also presents risks for fishing nations and for CCAMLR itself. Rapid progress with the revised management framework now depends upon rebuilding consensus.</p
Seal bites at sub-Antarctic Marion Island: Incidence, outcomes and treatment recommendations
No full textSeal biologists at Marion Island (Southern Ocean) are in frequent contact with seals. During research activities, biologists may be bitten by seals, yet no standardised protocol for treating such bites is in place. Information on 22 seal bite cases at Marion Island was collected. Treatment of these bites varied, reflecting a need for standardised protocols for the treatment of bites. Recommendations for the in-field treatment of bites are presented. Five of the 22 cases had some symptoms which resembled ‘seal finger’ – a zoonotic infection, usually of the hands, that is contracted after a person comes into contact with tissues of seals or is bitten by one. However, in four of these cases, symptoms subsided within 4 days without antibiotic treatment; in the fifth case antibiotics were administered and symptoms subsided in 4 days. There is little evidence of the occurrence of seal finger at Marion Island, but this deserves further investigation.</p
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