Dataset Information

Molecular tools for identification of shark species involved in depredation incidents in Western Australian fisheries.

ABSTRACT: Shark depredation is an issue of concern in some Western Australian recreational and commercial fisheries where it can have economic, social and ecological consequences. Knowledge of the shark species involved is fundamental to developing effective management strategies to mitigate the impacts of depredation. Identification of the species responsible is difficult as direct observation of depredation events is uncommon and evaluating bite marks on fish has a high degree of uncertainty. The use of trace DNA techniques has provided an alternative method for species identification. We demonstrate proof of concept for a targeted DNA barcoding approach to identify shark species using trace DNA found at bite marks on recovered remains of hooked fish. Following laboratory validation, forensic analysis of swabs collected from samples of bitten demersal fish, led to the definitive identification of shark species involved in 100% of the incidences of depredation (n = 16).

SUBMITTER: Fotedar S

PROVIDER: S-EPMC6329513 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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Publications

Molecular tools for identification of shark species involved in depredation incidents in Western Australian fisheries.

Fotedar Seema S Lukehurst Sherralee S Jackson Gary G Snow Michael M

PloS one 20190111 1

Shark depredation is an issue of concern in some Western Australian recreational and commercial fisheries where it can have economic, social and ecological consequences. Knowledge of the shark species involved is fundamental to developing effective management strategies to mitigate the impacts of depredation. Identification of the species responsible is difficult as direct observation of depredation events is uncommon and evaluating bite marks on fish has a high degree of uncertainty. The use of ...[more]

PMID: 30633772

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Project description:Depredation in marine ecosystems is defined as the damage or removal of fish or bait from fishing gear by predators. Depredation raises concerns about the conservation of species involved, fisheries yield and profitability, and reference points based on stock assessment of depredated species. Therefore, the development of accurate indicators to assess the impact of depredation is needed. Both the Reunion Island and the Seychelles archipelago pelagic longline fisheries targeting swordfish (Xiphias gladius) and tuna (Thunnus spp.) are affected by depredation from toothed whales and pelagic sharks. In this study, we used fishery data collected between 2004 and 2015 to propose depredation indicators and to assess depredation levels in both fisheries. For both fisheries, the interaction rate (depredation occurrence) was significantly higher for shark compared to toothed whale depredation. However, when depredation occurred, toothed whale depredation impact was significantly higher than shark depredation impact, with higher depredation per unit effort (number of fish depredated per 1000 hooks) and damage rate (proportion of fish depredated per depredated set). The gross depredation rate in the Seychelles was 18.3%. A slight increase of the gross depredation rate was observed for the Reunion Island longline fleet from 2011 (4.1% in 2007-2010 and 4.4% in 2011-2015). Economic losses due to depredation were estimated by using these indicators and published official statistics. A loss of 0.09 EUR/hook due to depredation was estimated for the Reunion Island longline fleet, and 0.86 EUR/hook for the Seychelles. These results suggest a southward decreasing toothed whale and shark depredation gradient in the southwest Indian Ocean. Seychelles depredation levels are among the highest observed in the world revealing this area as a "hotspot" of interaction between pelagic longline fisheries and toothed whales. This study also highlights the need for a set of depredation indicators to allow for a global comparison of depredation rates among various fishing grounds worldwide.

Project description:The conservation status of several pelagic shark species is considered vulnerable with declining populations, yet data on shark fishing mortality remain limited for large ocean regions. Pelagic sharks are increasingly retained by mixed-species fisheries, or are discarded and not reported by selective fisheries for tunas (Thunnus spp.) or swordfish (Xiphias gladius). We estimated the fishing mortality of sharks (landings plus discard mortalities) in a South African-flagged pelagic longline fishery with diverse targeting and discard behaviour. A hierarchical cluster analysis was used to stratify the fleet according to the relative proportions of tunas, swordfish, blue sharks (Prionace glauca) and shortfin mako sharks (Isurus oxyrinchus) landed by individual vessels between 2013 and 2015. A spatial analysis of logbook data indicated that subfleets operated in distinct fishing areas, with overlap. Approximately 5% of all commercial longlines set during 2015 were sampled by a fisheries-independent observer, and the species, discard ratios and physical condition at discard of 6 019 captured sharks were recorded. Blue sharks and shortfin makos dominated observed shark catches, which were comprised of nine species and two species groups. Some 47% of observed sharks were retained and 20% were discarded in good physical condition. Only 4% of shortfin makos were discarded, compared to 68% of blue sharks. Blue shark discard mortality rates were twice as high as published at-vessel mortality rates, suggesting that onboard handling, among other factors, contributed to discard mortalities. Extrapolation to total fishing effort indicated a near 10-fold increase in blue shark and shortfin mako fishing mortality compared to an earlier study (1998-2005). Escalating shortfin mako fishing mortality was attributed to increased targeting to supply higher market demand. Discarding of blue sharks by selective fishing for tunas and swordfish had a greater impact on their fishing mortality than retention by shark-directed fleets. Higher levels of observer sampling are required to increase confidence in discard ratio estimates.

Project description:Overfishing is a major threat to the survival of shark species, primarily driven by international trade in high-value fins, as well as meat, liver oil, skin and cartilage. The Convention on the International Trade in Endangered Species of Wild Fauna and Flora (CITES) aims to ensure that commercial trade does not threaten wild species, and several shark species have recently been listed on CITES as part of international efforts to ensure that trade does not threaten their survival. However, as international trade regulations alone will be insufficient to reduce overexploitation of sharks, they must be accompanied by practical fisheries management measures to reduce fishing mortality. To examine which management measures might be practical in the context of a targeted shark fishery, we collected data from 52 vessels across 595 fishing trips from January 2014 to December 2015 at Tanjung Luar fishing port in East Lombok, Indonesia. We recorded 11,920 landed individuals across 42 species, a high proportion of which were threatened and regulated species. Catch per unit effort depended primarily on the number of hooks and type of fishing gear used, and to a lesser degree on month, boat engine power, number of sets and fishing ground. The most significant factors influencing the likelihood of catching threatened and regulated species were month, fishing ground, engine power and hook number. We observed significant negative relationships between standardised catch per unit effort and several indicators of fishing effort, suggesting diminishing returns above relatively low levels of fishing effort. Our results suggest that management measures focusing on fishing effort controls, gear restrictions and modifications and spatiotemporal closures could have significant benefits for the conservation of shark species, and may help to improve the overall sustainability of the Tanjung Luar shark fishery. These management measures may also be applicable to shark fisheries in other parts of Indonesia and beyond, as sharks increasingly become the focus of global conservation efforts.

Dataset Information

Molecular tools for identification of shark species involved in depredation incidents in Western Australian fisheries.

Publications

Molecular tools for identification of shark species involved in depredation incidents in Western Australian fisheries.

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