Strontium mineralization of shark vertebrae

Determining the age of sharks using vertebral banding is a vital component of management, but the causes of banding are not fully understood. Traditional shark ageing is based on fish otolith ageing methods where growth bands are assumed to result from varied seasonal calcification rates. Here we investigate these assumptions by mapping elemental distribution within the growth bands of vertebrae from six species of sharks representing four different taxonomic orders using scanning x-ray fluorescence microscopy. Traditional visual growth bands, determined with light microscopy, were more closely correlated to strontium than calcium in all species tested. Elemental distributions suggest that vertebral strontium bands may be related to environmental variations in salinity. These results highlight the requirement for a better understanding of shark movements, and their influence on vertebral development, if confidence in age estimates is to be improved. Analysis of shark vertebrae using similar strontium-focused elemental techniques, once validated for a given species, may allow more successful estimations of age on individuals with few or no visible vertebral bands. © 2016 Macmillan Publishers Limite

Oceanographic conditions associated with white shark (Carcharodon carcharias) habitat use along eastern Australia

Management of species with wide-ranging migrations is a complex issue, made more challenging when the species is both protected and poses a risk to humans. Understanding the oceanic conditions associated with shark habitat use can help develop mitigation strategies or warning systems that meet both conservation and human safety objectives. Using satellite tracks from 77 juvenile and sub-adult white sharks tagged over 10 yr, we modelled individual movement patterns using hidden Markov models and applied generalised additive (mixed) models to explore correlations between movement patterns (presence−absence, habitat selection and behavioural state) and oceanographic and bathymetric variables. White sharks used the whole of the continental shelf, down to depths of 350 m on the continental slope. Sharks were present over a wide range of sea surface temperatures (SSTs; 10−27°C), with the highest probability of occurring at ~20°C. However, the number of average daily tag positions was greatest when SST was between 14 and 18°C, and sharks were more likely to exhibit area-restricted movement when SST was between ~19 and 23°C. Sharks were more likely to be present and selected habitats in productive areas with moderate to high surface chl a concentrations as well as thermal and productivity fronts. Although mesoscale eddies did not influence the likelihood of individuals being present in an area, there was a higher density of sharks in cold-core eddies compared to warm-core eddies. This study indicates that white shark presence and dispersal may be linked, perhaps via prey distribution, to oceanic conditions, potentially assisting development of suitable shark bite mitigation strategies

Socio-economic implications of the KwaZulu-Natal sardine run for local indigenous communities

The economic and social effects of the annual sardine run on the indigenous community on the south coast of KwaZulu-Natal, South Africa, were assessed using data gathered from questionnaires and personal interviews with 329 members of the community. Their knowledge, perceptions and attitudes about the sardine run, as well as their level of involvement in, and the financial benefits accrued from it, were also assessed. Although around two-thirds of those interviewed were aware of the sardine run and just over half participated in it, only some 17% benefited financially from it. However, despite this low level of participation, the financial benefit to the community could amount to R17–18 million, and as much as R34–54 million if a multiplier effect of 2–3 is applied. There was a high level (over 70%) of willingness to learn  more about the event, and to become more involved in training exercises that would allow local people to take advantage of opportunities arising from the sardine run. It is recommended that management strategies and development plans should be implemented towards assisting the indigenous communities to become more involved in the sardine run.Keywords: ecotourism, indigenous community, KwaZulu-Natal, marketing, sardine run, socio-economic, South Coast, sustainable tourismAfrican Journal of Marine Science 2010, 32(2): 399–40

The KwaZulu-Natal sardine run: shoal distribution in relation to nearshore environmental conditions, 1997–2007

The nearshore presence of sardine Sardinops sagax on the KwaZulu-Natal (KZN) coast was investigated using sightings data collected by the KZN Sharks Board from 1997 to 2007. The spatio-temporal distribution of sardine was described in relation to that of their predators and to environmental conditions, and subjected to generalised linear model (GLM) and generalised additive model (GAM) analyses. Variables describing spatio-temporal conditions performed best in the models (r2 = 0.52) with seasonal effects, specifically June  and July, making the greatest contribution towards sardine presence.  The contribution of the years 2003, 2006 and 2007, and the KZN North Coast, was significantly lower. The predator variables were highly significant (r2 = 0.48) with Cape gannets Morus capensis, followed by the sharks/gamefish and common dolphins Delphinus capensis, being most closely associated with sardine presence. Environmental variables were not as influential in the GLM models (r2 = 0.23), but some variables were useful in describing conditions favouring sardine presence, namely calm current conditions, light north-westerly land breezes and stable atmospheric conditions. Increasing sea surface temperature (SST), moderate north to south currents, large swells and turbid water had a negative impact upon sardine presence. North-easterly and north-westerly winds and north to south currents had a cooling effect upon nearshore SSTs, whereas south-easterly winds and increasing air temperatures caused nearshore warming. Results are discussed in the context of developing an understanding of the mechanisms that govern fine-scale movements of sardine shoals during the KZN sardine run, with a view to predicting such movements.Keywords: bottlenose dolphin, Cape gannet, common dolphin, Delphinus capensis, Morus capensis, sardine run, Sardinops sagax, SST, Tursiops aduncusAfrican Journal of Marine Science 2010, 32(2): 293–30

Abundance and distribution of avian and marine mammal predators of sardine observed during the 2005 KwaZulu-Natal sardine run survey

Opportunistic observations to determine the relative abundance and distribution of marine mammal and seabird predators of sardine   Sardinops sagax were carried out during a dedicated multidisciplinary research survey off the South African east coast in June and July of 2005 that was timed to coincide with the annual sardine run. Associations between different predator species, between predators and clupeoids, and between predators and oceanographic variables, were examined. Species’ distributions were primarily separated by  latitude and distance from shore. Bryde’s whale Balaenoptera edeni, African penguin Spheniscus demersus, Cape cormorant Phalacrocorax capensis and West Coast round herring Etrumeus whiteheadi were  predominantly found in the cool southern part of the survey region. Peak sardine run activity occurred within 4 km of shore at the northward limit of a strip of cool water