Freshwater and Estuarine sharks
Current projects
- Distribution and abundance of Glyphis spp. in Northern Australia and their potential interactions with commercial fisheries
- Life history and demography of bull (Carcharhinus leucas) and pig-eye (C. amboinensis) sharks in northern Australia
- Background
- Aims and Objectives
- Contacts
Distribution and abundance of Glyphis spp. in Northern Australia and their potential interactions with commercial fisheries
At present the distribution, abundance and habitat of endangered speartooth sharks (Glyphis spp.) in northern Australia are unknown. These species are known to have a large potential range and vary their distribution seasonally. Glyphis are caught as by-catch by recreational and commercial fisheries, but the extent of this threat is not known. Our project has two core elements.
- We propose develop a monitoring protocol that will also
- Determine the distribution and abundance of Glyphis spp., integrating commercial and recreational fishery catch data and fishery-independent surveys.
- By combining the data for distribution and abundance with commercial catch records we will estimate the interaction and impact of commercial and recreational fishers. Furthermore, although not the main focus of this study, we will also collect the same information for sawfish (including Pristis microdon) during surveys.
Background
Speartooth sharks (Glyphis spp.) are among the least-known of elasmobranches globally (Martin 2005) and they are currently listed as Critically Endangered by the IUCN (Pogonoski et al. 2003). Nationally, they are identified as key species within the Northern Planning Area (National Ocean Office 2004) for which there is little basic biological information available. They are also possibly at the greatest risk of extinction from fishing by-catch, habitat modification and global climate change (Compagno et al. 1995; Martin 2005). Although the ecological consequences of their possible extinction are unknown, these large predators likely occupy a key marine and estuarine niche in North Australian marine ecosystems.
A collection of more information on their distribution, habitat use and basic biology will lead to a higher likelihood of persistence if precautionary management and conservation measures based on these data are adopted in the near future (Myers 1997). Although at present Glyphis spp. do not have a formal recovery plan, data are required under Issue 12 of the National Plan of Action for the Conservation and Management of Sharks to implement ecological risk assessments.
The current distribution of Glyphis spp. in northern Australia is known for only a few river systems from north Western Australia to Queensland (Taniuchi et al. 1991; Last et al. 1994; Larson 2002; Thorburn et al. 2004; Martin 2005). In the Northern Territory, both Glyphis species 'A' and 'C' are known to inhabit the Adelaide River system, and species 'C' has also been found in the Mary and East, West and South Alligator Rivers. These studies indicate that species 'A' and 'C' exploit a range of salinities, from freshwater to seawater, thus suggesting a large area of potential distribution in the Northern Territory's river systems. Likewise, little data have been collected on the basic biology (e.g., survival, fertility, growth, behaviour) of Glyphis spp. Most caught specimens were immature, leading to the suggestion that rivers act as essential nursery habitats.
The proposed study therefore will contribute to the conservation and management of freshwater sharks (Glyphis spp.) through a better understanding of both fine- and broad-scale foraging patterns that describe the ecological patterns of habitat use and potential overlap with fisheries.
Aims and objectives
We propose to measure the current distribution and abundance of Glyphis spp. across the Northern Territory at the appropriate spatial scales to assess their potential interaction with fisheries. This will provide the urgent information required for the conservation of these species as required under the National Shark Plan of Action, and under the joint objectives for the priority issues for the conservation and management of freshwater sharks and sawfish species listed as threatened undert the Environmental Protection and Biodiversity Conservation Act (EPBC 1999).
Specific aims
The specific project objectives are to assess Glyphis spp. population distribution, abundance to environmental parameters (e.g., salinity, depth, current flow, turbidity) and assess the overlap and impact of commercial fishing at the appropriate spatial scales for conservation and management.
- Develop a broad-scale monitoring protocol for Glyphis spp. around northern Australia, integrating commercial, recreational and independent survey data. Initially, we will focus our efforts at a broad spatial scale (Northern Territory). This will allow us to determine the distribution of Glyphis spp. across the Northern Territory while raising public awareness, and to develop networks and survey protocols in conjunction with local commercial and recreational fishermen. Independent surveys in known and unsurveyed river systems such as the Daly, Roper and MacArthur Rivers will be used to update distribution maps. Using commercial fishing data along with recreational and independent survey will provide catch data across the spectrum of fishing activity and give fishers the responsibility for the conservation and management of these species.
Our surveys coupled with archived and current log book data will allow quantitative assessment of Glyphis spp. interactions with fisheries and an understanding of the extent of current harvest rates. - Population abundance and fisheries interactions: from commercial fisheries observer data and fisheries-independent surveys, we will determine the spatio-temporal patterns of local abundance and intra-specific patterns of habitat use. This aspect of the project will also provide information on the levels of by-catch, the potential impact of commercial fishing operations and indicate possible mitigation measures.
- Population demographics and ecology: Individual measurements collected during surveys and analysis of logged catch data will provide detailed information on age-size relationships within populations. Data collected will include length, age, state of maturity and fertility.
Value Adding: Biopsy samples for genetic analyses will also be collected during surveys and captures for a project lead by Drs Helen Larson (NT Museum) and Karen Gibb (Bioscience North Australia, Charles Darwin University) and subsequent biochemical analyses of diet and habitat use using stable isotope techniques.
Downloads
- Presentation: Glyphis shark project 2007
- View online questionnaire
- Letter to fishers re: questionnaire
- Freshwater and estuarine shark identification guide (PDF, 122KB)
- Freshwater shark and sawfish questionnaire (PDF, 848KB)
- Barra Classic 2007 Handout (PDF, 2.82MB)
Contact details
Dr Iain C. Field
School for Environmental Research,
Charles Darwin University
Ellengowan Drive, Darwin NT 0810
Ph: 08 8920 9230
Fax: 08 8920 9222
Assoc Prof Corey J.A. Bradshaw
Research Director - Marine Impacts
University of Adelaide and SARDI
Ph: 08 8303 5842
Fax: 08 8303 4347
corey.bradshaw@adelaide.edu.au
Dr Mark G. Meekan
Australian Institute of Marine Science
Ellengowan Drive, Darwin NT 0810
Ph: 08 8920 9240
Fax: 08 8920 9222
Dr Rik C. Buckworth
Northern Territory Fisheries, Department of Primary Industries, Mines and Fisheries, Northern Territory Government
GPO Box 3000, Darwin, NT 0801
Ph: 08 8999 2135
Fax: 08 8999 2002
rik.buckworth@nt.gov.au
Life history and demography of bull (Carcharhinus leucas) and pig-eye (C. amboinensis) sharks in northern Australia
Bull and pig eye sharks are both common across northern Australia, but are classified by the IUCN red list as globally Threatened and Data-Deficient, respectively. These classifications emphasise the need for a clear definition of their life history traits, movement and demography to facilitate an accurate assessment of population and species viability. The Northern Territory supports extensive fishing operations with a high recorded percentage shark by-catch that includes these two species (Salini et al., 2007), so careful management of this harvest is needed to avoid population declines and to ensure ecosystem stability and biodiversity is maintained. The goal of this project is to provide the necessary life history, population structure and ecological data to enable managers to implement effective biodiversity conservation strategies for shallow coastal marine ecosystems within northern Australia. The strength of this project is the provision of robust estimates of life history and demographic traits of the bull and pig eye shark. This will require collection of individuals from all size classes. Similarly, the robustness of age- and species-specific habitat use and population structure requires the collection of animals from separate river systems across northern Australia. Currently, the majority of specimens are being supplied by the northern shark and barramundi fisheries and as such, sampling bias is associated with gear selectivity and limited to productive fishing areas.
Background
Bull (C. leucas) and pig eye sharks (C. amboinensis) are common in shallow coastal tropical and subtropical waters (Last and Stevens, 1994). As apex predators their abundance is naturally low relative to lower trophic level predators, which when combined with their low fecundity and late maturation, make them particularly susceptible to over-exploitation by humans (Camhi et al., 1998;F.A.O., 1999;Stevens, 2002;D.E.H., 2004). The high susceptibility of both these species and a lack of knowledge of their basic life history traits and demography stresses the urgency of improving our understanding of both intra- and inter- species interactions to enable accurate estimates of extinction risks and to design appropriate management strategies. Additionally, the ecological similarity between these two species provides and excellent opportunity to improve out understanding of the relative importance of the niche differentiation and neutral theories in defining marine ecosystems and maintaining biodiversity.
Aims and objectives
We will quantify the population structure and vital rates (survival, fecundity) of C. leucas and C. amboinensis to determine the extinction risk of both species. Secondly, we will describe the ecological relationship between these two species show how inter-and intra-species interactions drive the ecological processes that maintain ecosystem stability.
Specific aims
- Determine the age structure and growth dynamics of C. leucas and C. amboinensis across northern Australia. This will allow us to convert size-based to age-based estimates of survival.
- Determine the reproductive potential of C. leucas and C. amboinensis across northern Australia. This will enable us to determine resilience to future stochastic events whether they are a result of anthropogenic or natural causes.
- Quantify niche partitioning between C. leucas and C. amboinensis. This aspect of the project will help us to understand the ecological processes driving ecosystem biodiversity and stability and show how these change through ontogeny.
- Outline age and species-specific habitat use. This will help define population structure and further highlight both inter- and intra- species interactions. Furthermore this will identify areas of habitat that are important for species persistence.
- Genetic assessment of population structure of C. leucas and C. amboinensis.. Genetic analyses enable management strategies to maximise genetic diversity and hence increase the likelihood of each species containing alleles that might enable successful adaptation in a changing environment.
Contacts
Bree Tillett
PhD Candidate
School for Environmental Research,
Charles Darwin University
Ellengowan Dr, Darwin NT 0810
Ph: 08 8920 9211
Fax: 08 8920 9222
bree.tillett@cdu.edu.au
Dr Corey J.A. Bradshaw
School for Environmental Research, Charles Darwin University
Ellengowan Drive, Darwin NT 0810
Ph: 08 8946 6713
Fax: 08 8946 7720
corey.bradshaw@cdu.edu.au
Dr Mark G. Meekan
Australian Institute of Marine Science
Ellengowan Drive, Darwin NT 0810
Ph: 08 8920 9240
Fax: 08 8920 9222
Dr Iain C. Field
School for Environmental Research,
Charles Darwin University
Ellengowan Drive, Darwin NT 0810
Ph: 08 8920 9230
Fax: 08 8920 9222
