scholarly journals Long-term patterns of abundance, residency and movements of bull sharks (Carcharhinus leucas) in Sydney Harbour, Australia

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Amy F. Smoothey ◽  
Kate A. Lee ◽  
Victor M. Peddemors
Keyword(s):  
Spatial Distribution ◽  
Austral Summer ◽  
Diel Pattern ◽  
Water Users ◽  
Carcharhinus Leucas ◽  
Nearshore Environments ◽  
Sydney Harbour ◽  
Bull Shark ◽  
Abundance And Distribution

AbstractBull sharks (Carcharhinus leucas) are known to frequent nearshore environments, particularly estuaries, resulting in interactions with humans. Knowledge of the behaviour of large individuals in temperate, estuarine environments is limited. This acoustic telemetry study reports on residency and movement patterns of 40 sub-adult and adult bull sharks in Sydney Harbour, a large temperate estuary, over seven years. Bull sharks exhibited clear seasonal patterns in their occurrence during the austral summer and autumn, with abundance peaking in January and February. This pattern was consistent between sexes and across all sizes. Bull sharks displayed weak diel differences in their spatial distribution, with individuals using areas further from the Harbour entrance more frequently during the day and at low tides. A diel pattern in depth use was apparent, with sharks utilising deeper water during daytime and moving shallower at night. Bull sharks had high individual inter-annual variability in their spatial distribution, however, when data were aggregated among all individuals and years, two locations of increased use were identified. Water temperature was the key predictor for seasonal movements and return behaviour to this estuary, suggesting that increasing water temperatures as a result of climate change may lead to higher shark abundance and possibly longer periods of residency in Sydney Harbour. Understanding the drivers for bull shark abundance and distribution will hopefully facilitate better education and shark smart behaviour by estuarine water-users, especially during summer and autumn months.

scholarly journals First evidence of multiple paternity in the bull shark (Carcharhinus leucas)

2017 ◽  
Vol 68 (1) ◽  
pp. 195 ◽  
Author(s):  
Agathe Pirog ◽  
Sébastien Jaquemet ◽  
Marc Soria ◽  
Hélène Magalon
Keyword(s):  
Multiple Paternity ◽  
Western Indian Ocean ◽  
Reproductive Behaviour ◽  
Selection Processes ◽  
Carcharhinus Leucas ◽  
Management Plans ◽  
Bull Shark ◽  
Zygotic Selection ◽  
First Time

The present study assessed the occurrence of multiple paternity in four litters of bull shark Carcharhinus leucas (n=5, 8, 9 and 11 embryos) sampled at Reunion Island in the Western Indian Ocean. Using 21 microsatellite loci, we revealed that two litters were generated from two sires each, demonstrating for the first time multiple paternity for this species. We also reported a high paternal skew (10:1 in Litter 1 and 7:1 in Litter 3), which may be because of post-copulatory or post-zygotic selection processes. These results contribute to a better understanding of the reproductive behaviour of the bull shark, which remains poorly documented. The present study must be expanded to assess the frequency of multiple paternity in this species, and to test for genetic or cryptic benefits (convenience polyandry), which is important for long-term conservation and management plans.

Long-term trends of bull shark (Carcharhinus leucas) in estuarine waters of Texas, USA

2013 ◽  
Vol 70 (1) ◽  
pp. 13-21 ◽  
Author(s):  
John T. Froeschke ◽  
Bridgette F. Froeschke ◽  
Charlotte M. Stinson
Keyword(s):  
Catch Per Unit Effort ◽  
Ecosystem Effects ◽  
Carcharhinus Leucas ◽  
Bull Shark ◽  
Mean Size ◽  
Long Term Trends ◽  
Monitoring Survey ◽  
Standardized Index ◽  
Federal Management

Increases in standardized catch per unit effort (CPUE) and mean length of bull shark (Carcharhinus leucas) were observed in coastal estuaries over a 35-year period (1976–2010). Trends in abundance and size were examined using fisheries-independent data from a long-term monitoring survey in Texas, USA. Catch, effort, and environmental covariates that affect bull shark distribution were used to create a standardized index of abundance. Increases in abundance and mean length were detected, potentially due to the initiation of federal management and restrictions on the use of gill nets in nearby Louisiana, USA, waters in 1995. This study provides a long-term perspective of two important demographic indicators (abundance and mean size) of bull shark and provides an encouraging signal in the Gulf of Mexico for a species whose stock status is unknown yet considered near threatened on the International Union for Conservation of Nature red list. Continuing research is needed to gauge effects of management and environmental impacts on shark resources as well as investigations into ecosystem effects of increasing predatory density in coastal waters.

Long-term monitoring provides insight into estuarine top predator (Carcharhinus leucas) resilience following an extreme weather event

2020 ◽  
Vol 639 ◽  
pp. 169-183
Author(s):  
P Matich ◽  
BA Strickland ◽  
MR Heithaus
Keyword(s):  
Habitat Use ◽  
Acoustic Telemetry ◽  
South Florida ◽  
Behavioral Variability ◽  
Catch Per Unit Effort ◽  
Ontogenetic Shifts ◽  
Carcharhinus Leucas ◽  
Acute Disturbance ◽  
Cold Snap

Chronic environmental change threatens biodiversity, but acute disturbance events present more rapid and immediate threats. In 2010, a cold snap across south Florida had wide-ranging impacts, including negative effects on recreational fisheries, agriculture, and ecological communities. Here, we use acoustic telemetry and historical longline monitoring to assess the long-term implications of this event on juvenile bull sharks Carcharhinus leucas in the Florida Everglades. Despite the loss of virtually all individuals (ca. 90%) within the Shark River Estuary during the cold snap, the catch per unit effort (CPUE) of age 0 sharks on longlines recovered through recruitment within 6-8 mo of the event. Acoustic telemetry revealed that habitat use patterns of age 0-2 sharks reached an equilibrium in 4-6 yr. In contrast, the CPUE and habitat use of age 3 sharks required 5-7 yr to resemble pre-cold snap patterns. Environmental conditions and predation risk returned to previous levels within 1 yr of the cold snap, but abundances of some prey species remained depressed for several years. Reduced prey availability may have altered the profitability of some microhabitats after the cold snap, leading to more rapid ontogenetic shifts to marine waters among sharks for several years. Accelerated ontogenetic shifts coupled with inter-individual behavioral variability of bull sharks likely led to a slower recovery rate than predicted based on overall shark CPUE. While intrinsic variation driven by stochasticity in dynamic ecosystems may increase the resistance of species to chronic and acute disturbance, it may also increase recovery time in filling the diversity of niches occupied prior to disturbance if resistive capacity is exceeded.

scholarly journals Feeding patterns of two sympatric shark predators in coastal ecosystems of an oceanic island

2017 ◽  
Vol 74 (2) ◽  
pp. 216-227 ◽  
Author(s):  
Clément Trystram ◽  
Karyne M. Rogers ◽  
Marc Soria ◽  
Sébastien Jaquemet
Keyword(s):  
Trophic Ecology ◽  
Dietary Habits ◽  
Stomach Contents ◽  
Nitrogen Isotope ◽  
Oceanic Island ◽  
Apex Predators ◽  
Coastal Habitat ◽  
Galeocerdo Cuvier ◽  
Carcharhinus Leucas ◽  
Bull Shark

Stomach contents and stable carbon and nitrogen isotope analyses (δ13C and δ15N) were used to investigate the trophic ecology of two apex predators, tiger sharks (Galeocerdo cuvier) and bull sharks (Carcharhinus leucas), from Reunion Island to describe their dietary habits at both the population and individual levels. In this oceanic island, the tiger and bull sharks were more piscivorous and teutophagous than noted in previous research from other localities. The δ13C values suggested that bull sharks depended on more neritic organic matter sources than tiger sharks, confirming a coastal habitat preference for bull sharks. Moreover, the total length of the bull shark influenced δ13C values, with smaller individuals being more coastal than larger individuals. All indicators suggest that there is a higher degree of similarity between individual tiger sharks compared with the more heterogeneous bull shark population, which is composed of individuals who specialize on different prey. These results suggest that the two species have different functions in these coastal habitats, and thus, they must be considered independently in terms of conservation and management.

Long-term changes in spatial distribution of birds responding to a group-selection timber harvest

2012 ◽  
Vol 36 (2) ◽  
pp. 313-327 ◽  
Author(s):  
Steven P. Campbell ◽  
Jack W. Witham ◽  
Malcolm L. Hunter
Keyword(s):  
Spatial Distribution ◽  
Group Selection ◽  
Timber Harvest ◽  
Long Term Changes

Cost determination and sustainable financing for rural water services in sub-Saharan Africa

Water Policy ◽  
2007 ◽  
Vol 9 (4) ◽  
pp. 373-391 ◽  
Author(s):  
Peter A. Harvey
Keyword(s):  
Sub Saharan Africa ◽  
Water Services ◽  
Innovative Strategies ◽  
Water Users ◽  
Sub Saharan ◽  
The Cost ◽  
National Governments ◽  
Cost Determination ◽  
Sustainable Financing

Access to safe, sufficient and affordable water in rural Africa will not increase unless sustainable financing strategies are developed which ensure the sustainability of existing water services. There is a strong need for international donors and national governments to confront the true costs associated with sustained service provision in order to develop practicable long-term financing mechanisms. This paper presents a systematic approach that can be applied to determine the overall cost of service delivery based on respective cost estimates for operation and maintenance, institutional support, and rehabilitation and expansion. This can then be used to develop a tariff hierarchy which clearly indicates the cost to water users of different levels of cost recovery, and which can be used as a planning tool for implementing agencies. Community financing mechanisms to ensure sustained payment of tariffs must be matched to specific communities and their economic characteristics; a blanket approach is unlikely to function effectively. Innovative strategies are also needed to ensure that the rural poor are adequately served, for which a realistic, targeted and transparent approach to subsidy is required.

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