Vignon M.,CNRS Host-Pathogen-Environment Interactions Laboratory |
Vignon M.,CNRS Insular Research Center and Environment Observatory |
Sasal P.,CNRS Host-Pathogen-Environment Interactions Laboratory |
Sasal P.,CNRS Insular Research Center and Environment Observatory |
And 4 more authors.
Marine and Freshwater Research | Year: 2010
Shark feeding is widespread throughout tropical, subtropical and temperate marine ecosystems and gives rise to controversy because there is little consensus regarding its management. There are few comprehensive reports that consider how shark feeding with bait might impact local fishes, despite the development of this practice during the last few decades. Although shark feeding might theoretically have parasitological effects on local non-target fish species in the vicinity of feeding areas, this aspect has never been investigated. During an extensive parasitological survey conducted between 2005 and 2007, a total of 1117 fish belonging to six common grouper and snapper species were sampled throughout the entire north coast of Moorea Island (French Polynesia), encompassing three localities where feeding has occurred frequently since the 1990s. Parasites exhibited no spatial patterns except for the infections on the blacktip grouper (Epinephelus fasciatus). On this species, the prevalence of larval cestodes that parasitise sharks as adults and the intensity of their infestation were significantly higher around shark-feeding localities compared with non-shark-feeding localities. Our results suggest for the first time that although long-term shark feeding has parasitological implications, the impacts appear limited, only involve cestode larvae from one host species and do not seem to affect the health of the fish we studied. © 2010 CSIRO.
Mertz E.M.,University of Pretoria |
Mertz E.M.,Oceans Research |
Bester M.N.,University of Pretoria
South African Journal of Wildlife Research | Year: 2011
An opportunistic observational study on human disturbance of a vagrant southern elephant seal that was hauled out on a tourist beach in Mossel Bay, South Africa, is presented. Incidences of pedestrians ignoring signage and the demarcation barrier around the seal raise questions about the management of such haulout events, pubic safety and the effects of disturbance.
Findlay K.,University of Cape Town |
Findlay K.,Eduardo Mondlane University |
Meer M.,Oceans and Coasts |
Elwen S.,University of Pretoria |
And 11 more authors.
Journal of Cetacean Research and Management | Year: 2011
Humpback whales within the southwestern Indian Ocean undertake annual migrations from summer Antarctic/Southern Ocean feeding grounds to winter breeding grounds in the tropical and sub-tropical coastal waters of Mozambique, Madagascar and the central Mozambique Channel Islands. Little is known of the inter-relationship of humpback whales on each of these wintering grounds, or the inter-relationship of these wintering grounds with the summer Antarctic feeding grounds. A line-transect survey of cetacean species was carried out in Mozambique coastal waters between Cabo Inhaca (26°00'S, 33°05'E) and just north of Mozambique Island (14°26'S, 40°53'E) and between the 20 and 200m isobaths, over the period 26 August to 7 September 2003. The majority (98.1%) of 951.8 n.miles of search effort carried out on this survey was in passing mode due to the high densities of whales encountered. Humpback whales were the only large whales to be identified and the distribution of 691 sightings of an estimated 1,130 individual humpback whales and 132 sightings of an estimated 154 large unidentified whales show distribution throughout the survey region. Two sightings of individual small whales were made in the region of Inhambane. In general, higher than expected sighting densities (based on survey effort) were recorded in the region between Cabo Inhaca and Xai-Xai, and in the region of the Pantaloon and David Shoals to the north east of Quelimane. Lower than expected sighting densities were recorded over the Sofala Banks. No distribution trends could be ascribed to environmental parameters, apart from whales being distributed in waters of higher salinities than expected, possibly due to turbidity associated with low salinity water arising from river input. Groups containing a cow and calf pair were distributed across the entire region surveyed. Analyses of unstratified data result in a total abundance estimate of 6,808 (CV = 0.14) humpback and unidentified whales in the 14,029.5 n.mile 2 area surveyed. As a result of the differences in width of the coastal shelf area along the coast of Mozambique, the line transect survey data were further analysed in four strata. Pooling of estimates over these four strata results in a total abundance of 6,664 whales (CV = 0.16), with highest densities in the southernmost stratum and the lowest densities in the narrow shelf region across the Sofala Banks. Similar analyses of humpback whales only resulted in abundance estimates of 5,930 (CV = 0.15) (unstratified data) and 5,965 whales (CV = 0.17) (data analysed by four strata). Although not directly comparable due to differing survey platforms, these estimates indicate the population to have increased since previous surveys in the early 1990s.
Delaney D.G.,Citizen Science Institute |
Delaney D.G.,Oceans Research |
Edwards P.K.,McGill University |
Leung B.,McGill University
Marine Biology | Year: 2012
Predicting spread is a central goal of invasion ecology. Within marine systems, researchers have increasingly made use of oceanographic circulation models to estimate currents and track species dispersal. However, the accuracy of these models for predicting biological patterns, particularly for non-native species, has generally not been validated. Particularly, we wished to examine the ability of models to predict physical and biological processes, which jointly determine the spread of marine larval organisms. We conducted two empirical studies-a recruitment study and a drift card study-along the coast of New England, USA, focusing on two invaders of concern-the European green crab (Carcinus maenas) and the Asian shore crab (Hemigrapsus sanguineus), to explicitly evaluate the ability of oceanographic models to predict patterns of spread. We used data from the large-scale drift card study to validate our ability to capture dispersal patterns driven purely by physical processes. Next, we conducted a recruitment study to evaluate our ability to reproduce patterns of biological dispersal. We were generally capable of reproducing drift cards patterns-suggesting that the physical mechanics in the model were predictive. However, predicted biological patterns were inconsistent-we were able to predict dispersal patterns for H. sanguineus but not for C. maenas. Our results highlight the importance of validating models and suggest that more work is necessary before we can reliably use oceanographic models to predict biological spread of intertidal organisms. © 2011 Springer-Verlag.
Findlay R.,Dalhousie University |
Gennari E.,Oceans Research |
Gennari E.,South African Institute For Aquatic Biodiversity |
Cantor M.,Dalhousie University |
And 2 more authors.
Behavioral Ecology and Sociobiology | Year: 2016
Abstract: White sharks (Carcharodon carcharias) are circumglobally distributed large apex predators. While ecologically important, there is very limited study of their social behaviour. Although evident in other large, apex marine predators (e.g. toothed whales) and smaller elasmobranchs (e.g. blacktip reef sharks), the ability of any large pelagic elasmobranch to demonstrate social preferences, tolerance or grouping behaviour is largely unknown. Here, we test whether white sharks in a near-coastal environment form non-random associations with other conspecifics or simply share the same space at the same time. We photo-identified 323 individuals—74 % juvenile females (175–300 cm)—during chumming events at six different sites in Mossel Bay, South Africa, over a 6-year period (2008–2013), and tested for grouping behaviour. We found evidence for random associations among individuals, though spatio-temporal co-occurrence of white sharks in close proximity was weakly structured according to sex and, potentially, body size. Such biological traits may play a minor part in structuring co-occurrence of individuals at fine spatio-temporal scales, which could reflect ontogenetic preferences in diet and site fidelity, or differing tolerance levels for conspecifics of different sexes and sizes. Our study strengthens the evidence that large pelagic shark species are generally solitary and display limited social behaviour. Significance statement: Large pelagic shark species are important top predators, but we know little about their social behaviour. We tested the ability of white sharks (C. carcharias) to form groups and display social preferences for other individuals when they congregate at scavenging events in a coastal environment, where social interactions may be more likely. We found that white sharks co-occur at random, displaying no preferred or avoided associations for other individuals. Nevertheless, there was a minor influence of biological traits, with individuals aggregating according to gender and, possibly, body size. While we hypothesise these effects could represent preferences in diet and site fidelity, or more tolerance for similar-sized individuals of the same sex, our study strengthens the evidence that white sharks are mostly solitary foragers. © 2016 Springer-Verlag Berlin Heidelberg