ORCID Profile
0000-0002-6127-8968
Current Organisation
James Cook University
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Publisher: CSIRO Publishing
Date: 2018
DOI: 10.1071/MF17163
Abstract: In the central west Pacific region, silky sharks (Carcharhinus falciformis) are commonly taken in fisheries, forming up to 95% of incidental elasmobranch bycatch. The present study examined the life history of silky sharks (n=553) from Papua New Guinean waters. Age was analysed using sectioned vertebrae, and a multimodel approach was applied to the length-at-age data to fit growth models. Females ranged in length from 65.0- to 253.0-cm total length (TL), with the oldest estimated at 28 years. Males ranged in length from 68.4 to 271.3cm TL and were aged to a maximum of 23 years. The logistic model provided the best fitting growth parameter estimates of length at birth L0=82.7cm TL, growth coefficient g=0.14year–1 and asymptotic length L∞=261.3cm TL for the sexes combined. Females reached sexual maturity at 204cm TL and 14.0 years, whereas males reached maturity at 183cm TL and 11.6 years. The average litter size from 28 pregnant females was 8 (range of 3–13). The growth parameters and late ages of sexual maturation for silky sharks in the central west Pacific suggest a significant risk from fisheries exploitation without careful population management.
Publisher: CSIRO Publishing
Date: 2023
DOI: 10.1071/PC22048
Publisher: Wiley
Date: 06-05-2022
DOI: 10.1111/JFB.15073
Abstract: The giant freshwater whipray Urogymnus polylepis is a threatened species that is vulnerable to riverine and coastal marine pressures. Despite its threatened status, the range of U . polylepis is still being determined. In this study, photographic evidence of U . polylepis in Myanmar was provided through market surveys (2017–2018) and social media (Sharks and Rays of Rakhine Facebook page, 2021). Urogymnus polylepis is exposed to fisheries and habitat degradation pressures in Myanmar therefore, conservation management is likely needed to ensure populations persist into the future.
Publisher: Wiley
Date: 08-09-2023
DOI: 10.1111/JFB.15537
Abstract: River sharks ( Glyphis spp.) and some sawfishes (Pristidae) inhabit riverine environments, although their long‐term habitat use patterns are poorly known. We investigated the diadromous movements of the northern river shark ( Glyphis garricki ), speartooth shark ( Glyphis glyphis ), narrow sawfish ( Anoxypristis cuspidata ), and largetooth sawfish ( Pristis pristis ) using in situ laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) on vertebrae to recover elemental ratios over each in idual's lifetime. We also measured elemental ratios for the bull shark ( Carcharhinus leucas ) and a range of inshore and offshore stenohaline marine species to assist in interpretation of results. Barium (Ba) was found to be an effective indicator of freshwater use, while lithium (Li) and strontium (Sr) were effective indicators of marine water use. The relationships between Ba and Li, and Ba and Sr were negatively correlated, while the relationship between Li and Sr was positively correlated. Both river shark species had elemental signatures indicative of prolonged use of upper estuarine environments, while adults appear to mainly use lower estuarine environments rather than marine. Decreases in Li:Ba and Sr:Ba at the end of the pre‐natal growth zone of P. pristis s les indicated that parturition likely occurs in freshwater. There was limited evidence of prolonged riverine habitat use for A. cuspidata . The results of this study support elemental‐environment relationships observed in teleost otoliths, and indicate that in situ LA‐ICP‐MS elemental characterization is applicable to a wide range of elasmobranch species as a discriminator for use and movement across salinity gradients. A greater understanding of processes that lead to element incorporation in vertebrae, and relative concentrations in vertebrae with respect to the ambient environment, will improve the applicability of elemental analysis to understand movements across the life history of elasmobranchs into the future. This article is protected by copyright. All rights reserved.
Publisher: Springer Science and Business Media LLC
Date: 02-08-2019
Publisher: Wiley
Date: 02-2023
DOI: 10.1002/ECE3.9837
Abstract: The Bull Shark ( Carcharhinus leucas ) faces varying levels of exploitation around the world due to its coastal distribution. Information regarding population connectivity is crucial to evaluate its conservation status and local fishing impacts. In this study, we s led 922 putative Bull Sharks from 19 locations in the first global assessment of population structure of this cosmopolitan species. Using a recently developed DNA‐capture approach (DArTcap), s les were genotyped for 3400 nuclear markers. Additionally, full mitochondrial genomes of 384 Indo‐Pacific s les were sequenced. Reproductive isolation was found between and across ocean basins (eastern Pacific, western Atlantic, eastern Atlantic, Indo‐West Pacific) with distinct island populations in Japan and Fiji. Bull Sharks appear to maintain gene flow using shallow coastal waters as dispersal corridors, whereas large oceanic distances and historical land‐bridges act as barriers. Females tend to return to the same area for reproduction, making them more susceptible to local threats and an important focus for management actions. Given these behaviors, the exploitation of Bull Sharks from insular populations, such as Japan and Fiji, may instigate local decline that cannot readily be replenished by immigration, which can in turn affect ecosystem dynamics and functions. These data also supported the development of a genetic panel to ascertain the population of origin, which will be useful in monitoring the trade of fisheries products and assessing population‐level impacts of this harvest.
Publisher: CSIRO Publishing
Date: 2019
DOI: 10.1071/PC18069
Abstract: Small-bodied coastal sharks are often caught as by-catch in fishing operations. Life-history information for these sharks is needed to ascertain the level at which these populations are potentially affected by fishing. This study determined the age, growth and maturity of Carcharhinus coatesi captured by prawn trawlers in the Gulf of Papua. Using vertebral aging and an information-theoretic multimodel approach, the von Bertalanffy growth model fit the data best parameters were L0=40.6cm±0.8, L∞=74.8cm±2.1, k=0.33year−1±0.06. Length-at-maturity analysis indicated that males reach maturity at L50=66.3cm (CI: 63.8, 71.4) and L95=71.6 (CI: 64.6, 74.2) cm while females matured at L50=71.4cm (CI: 61.5, 72.01) and L95=72.5cm (CI: 62.7, 74.0). Age-at-maturity estimates showed that both males (A50=5.1 years (CI: 4.6, 7.1), A95=6.4 years (CI: 5.1, 7.2)) and females (A50=5.3 years (CI: 3.5, 8.7), A95=7.4 years (CI: 3.6, 8.8)) reach maturity at about the same age. This study addresses the need for specific life-history information for a data-deficient species in a region that has remained relatively under-researched but in need of ongoing improvements to fisheries management.
Publisher: Oxford University Press (OUP)
Date: 07-11-2019
Abstract: The silky shark (Carcharhinus falciformis) is one of the most heavily fished tropical shark species globally, and currently there is increasing concern for its conservation status. However, large differences and ambiguity in life history parameter estimates among regions complicates its conservation and fisheries management. Using a Leslie matrix model that incorporated stochastic effects, we analysed the intraspecific demography of C. falciformis using available life history data from seven regions. Among regions, large differences were observed in generation time and age-specific reproductive contributions. Carcharhinus falciformis generally had low resilience to fishing mortality (F) throughout its distribution. Age-at-first-capture and age-at-last-capture management approaches resulted in substantial differences among regions. This was largely influenced by age-at-maturity. However, in scrutinizing some regional life history studies, it is likely that s ling design and methodological differences among regions have resulted in inaccuracies in life history parameter estimates and subsequent demographic attributes. This implies that age and life-stage-dependent management approaches using these possibly inaccurate life history parameters may be inappropriate. We suggest that a greater emphasis needs to be placed on eliminating human sources of error in elasmobranch life history studies to ensure management for wide-ranging species, such as C. falciformis, is most effective.
Publisher: Wiley
Date: 05-08-2021
DOI: 10.1002/AQC.3678
Abstract: Sawfish (Pristidae) are considered to be among the most threatened families of elasmobranch (sharks and rays). There is a need to gather information on the status of poorly known sawfish populations to assist in global recovery initiatives. This study used interviews with local fishers to investigate the presence of sawfish in southern Papua New Guinea (PNG) and their interactions with and uses and values for small‐scale fishers. A range of sawfish size classes are still encountered throughout southern PNG, while juvenile largetooth sawfish Pristis pristis were additionally reported in the freshwater reaches of all rivers surveyed. Reports of large size classes in estuarine and marine environments provide an optimistic outlook that sawfish populations persist throughout southern PNG. Most fishers that catch sawfish retain them for various uses including consumption and for the sale of meat, fins and occasionally rostra. Negative population trends including decreases in catch frequency and/or size classes were reported by 66% of interviewees, with the largest declines being reported in the Kikori River. The increasing technical capacity of small‐scale fishers, their preference for gillnetting and the emerging market for teleost swim bladder (a high‐value fishery product) present a major ongoing threat to sawfish in southern PNG. Furthermore, the tendency of fishers to kill or remove rostra from entangled sawfish results in high fishing mortality regardless of any use by the fisher. This study indicates that considerable community engagement will be necessary to manifest any legislative actions or increased enforcement on international trade regulations for sawfish in PNG. This is due to traditional land and waterway ownership values throughout PNG and the local perception of sawfish as a traditional food resource rather than an animal of intrinsic bio ersity value as perceived by global conservationists. Future research should consider exploring culturally appropriate conservation initiatives that are likely to achieve engagement and participation from local fishers.
Location: Switzerland
No related grants have been discovered for Michael Grant.