Gillnet size selectivity of shark and ray species from Queensland, Australia

Gillnets are size-selective fishing gears commonly used by industrial and small-scale fishers, so understanding selectivity can aid fisheries management by identifying suitable mesh sizes to optimize catches of target species while reducing bycatch. Few size selectivity parameters have been estimated for sharks, with even fewer for rays. Size selection parameters were estimated for seven species of sharks and two species of rays from the Queensland East Coast Inshore Finfish Fishery (ECIFF). Size frequency data from a fishery observer program on ECIFF vessels was used to fit a standard size selection model. Mesh size independent parameters, θ1 and θ2, were estimated for each species to define selectivity curves for different mesh sizes for each species. Parameter values were compared with previous studies that used the same method. Estimates of θ1 were similar among species within the same genus, such as Carcharhinus, Rhizoprionodon, and Sphyrna. Anoxypristis cuspidata had the largest θ1 and θ2 values, likely because of its toothed rostrum that affected catchability in gillnets. Our findings can be used for the ECIFF and other gillnet fisheries to aid in mesh size recommendations and risk mitigation

Crossing lines: a multidisciplinary framework for assessing connectivity of hammerhead sharks across jurisdictional boundaries

Conservation and management of migratory species can be complex and challenging. International agreements such as the Convention on Migratory Species (CMS) provide policy frameworks, but assessments and management can be hampered by lack of data and tractable mechanisms to integrate disparate datasets. An assessment of scalloped (Sphyrna lewini) and great (Sphyrna mokarran) hammerhead population structure and connectivity across northern Australia, Indonesia and Papua New Guinea (PNG) was conducted to inform management responses to CMS and Convention on International Trade in Endangered Species listings of these species. An Integrated Assessment Framework (IAF) was devised to systematically incorporate data across jurisdictions and create a regional synopsis, and amalgamated a suite of data from the Australasian region. Scalloped hammerhead populations are segregated by sex and size, with Australian populations dominated by juveniles and small adult males, while Indonesian and PNG populations included large adult females. The IAF process introduced genetic and tagging data to produce conceptual models of stock structure and movement. Several hypotheses were produced to explain stock structure and movement patterns, but more data are needed to identify the most likely hypothesis. This study demonstrates a process for assessing migratory species connectivity and highlights priority areas for hammerhead management and research

Negligible evidence for regional genetic population structure for two shark species Rhizoprionodon acutus (Rüppell, 1837) and Sphyrna lewini (Griffith & Smith, 1834) with contrasting biology

Biodiversity of sharks in the tropical Indo-Pacific is high, but species-specific information to assist sustainable resource exploitation is scarce. The null hypothesis of population genetic homogeneity was tested for scalloped hammerhead shark (Sphyrna lewini, n = 237) and the milk shark (Rhizoprionodon acutus, n = 207) from northern and eastern Australia, using nuclear (S. lewini, eight microsatellite loci; R. acutus, six loci) and mitochondrial gene markers (873 base pairs of NADH dehydrogenase subunit 4). We were unable to reject genetic homogeneity for S. lewini, which was as expected based on previous studies of this species. Less expected were similar results for R. acutus, which is more benthic and less vagile than S. lewini. These features are probably driving the genetic break found between Australian and central Indonesian R. acutus (F-statistics; mtDNA, 0.751–0.903, respectively; microsatellite loci, 0.038–0.047 respectively). Our results support the spatially homogeneous monitoring and management plan for shark species in Queensland, Australia

Elasmobranch bycatch in the demersal prawn trawl fishery in the Gulf of Papua, Papua New Guinea

The elasmobranch bycatch of the Gulf of Papua Prawn Fishery is investigated in detail for the first time. Fisheries observers collected data on the elasmobranch bycatch from a total of 403 trawl sets (1,273 hrs) in the Gulf of Papua. A total of 40 species of elasmobranchs were recorded ranging in size from a 12 cm disc width stingray to a 350 cm total length sawfish. High mortality rates were recorded (>80%), attributed to the long trawl durations (up to 4 hours). The future inclusion of bycatch reduction devices would likely reduce the number of larger elasmobranchs being caught, based on evidence from the prawn trawl fisheries of northern Australia, and is being investigated by the PNG National Fisheries Authority. Differences in catch compositions were detected across the management zones as well as between the two monsoonal seasons (SE Monsoon and NW Monsoon). Increased monitoring and additional research is required and management plans should address the elasmobranch bycatch and in particular their high mortality rate

Elasmobranch bycatch in the demersal prawn trawl fishery in the Gulf of Papua, Papua New Guinea

The elasmobranch bycatch of the Gulf of Papua Prawn Fishery is investigated in detail for the first time. Fisheries observers collected data on the elasmobranch bycatch from a total of 403 trawl sets (1,273 hrs) in the Gulf of Papua. A total of 40 species of elasmobranchs were recorded ranging in size from a 12 cm disc width stingray to a 350 cm total length sawfish. High mortality rates were recorded (>80%), attributed to the long trawl durations (up to 4 hours). The future inclusion of bycatch reduction devices would likely reduce the number of larger elasmobranchs being caught, based on evidence from the prawn trawl fisheries of northern Australia, and is being investigated by the PNG National Fisheries Authority. Differences in catch compositions were detected across the management zones as well as between the two monsoonal seasons (SE Monsoon and NW Monsoon). Increased monitoring and additional research is required and management plans should address the elasmobranch bycatch and in particular their high mortality rate

Emergent research and priorities for shark and ray conservation

Over the past 4 decades there has been a growing concern for the conservation status of elasmobranchs (sharks and rays). In 2002, the first elasmobranch species were added to Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Less than 20 yr later, there were 39 species on Appendix II and 5 on Appendix I. Despite growing concern, effective conservation and management remain challenged by a lack of data on population status for many species, human−wildlife interactions, threats to population viability, and the efficacy of conservation approaches. We surveyed 100 of the most frequently published and cited experts on elasmobranchs and, based on ranked responses, prioritized 20 research questions on elasmobranch conservation. To address these questions, we then convened a group of 47 experts from 35 institutions and 12 countries. The 20 questions were organized into the following broad categories: (1) status and threats, (2) population and ecology, and (3) conservation and management. For each section, we sought to synthesize existing knowledge, describe consensus or diverging views, identify gaps, and suggest promising future directions and research priorities. The resulting synthesis aggregates an array of perspectives on emergent research and priority directions for elasmobranch conservation

Long-term movement patterns of a coral reef predator

Long-term monitoring is required to fully define periodicity and patterns in animal movement. This is particularly relevant for defining what factors are driving the presence, location, and movements of individuals. The long-term movement and space use patterns of grey reef sharks, Carcharhinus amblyrhynchos, were examined on a whole of reef scale in the southern Great Barrier Reef to define whether movement and activity space varied through time. Twenty-nine C. amblyrhynchos were tracked for over 2 years to define movement patterns. All individuals showed high residency within the study site, but also had high roaming indices. This indicated that individuals remained in the region and used all of the monitored habitat (i.e., the entire reef perimeter). Use of space was consistent through time with high reuse of areas most of the year. Therefore, individuals maintained discrete home ranges, but undertook broader movements around the reef at times. Mature males showed greatest variation in movement with larger activity spaces and movement into new regions during the mating season (August-September). Depth use patterns also differed, suggesting behaviour or resource requirements varied between sexes. Examination of the long-term, reef-scale movements of C. amblyrhynchos has revealed that reproductive activity may play a key role in space use and activity patterns. It was unclear whether mating behaviour or an increased need for food to sustain reproductive activity and development played a greater role in these patterns. Reef shark movement patterns are becoming more clearly defined, but research is still required to fully understand the biological drivers for the observed patterns

Importance of environmental and biological drivers in the presence and space use of a reef-associated shark

As coral reef ecosystems come under increasing pressure from fisheries and climate change, understanding how species that rely on these habitats respond to changes within their environment is increasingly important. The presence and movement of 28 grey reef sharks Carcharhinus amblyrhynchos were monitored for 15 mo in the southern Great Barrier Reef in relation to environmental conditions and biological factors. Twenty-eight models including water temperature, atmospheric pressure, wind speed, rainfall and time (week or month), size and sex were tested against presence and activity space data and compared using Akaike information criterion (AIC). Model results for presence of individuals in relation to environmental conditions indicated that temperature and wind speed had weak effects, likely related to detectability. Models using 3 different measures of activity space indicated no relationship between shark activity space and environmental parameters. Week was a significant factor in the top performing activity space models, with males showing increased activity space during weeks in September, when mating is believed to occur. These results suggest changes in movement were biologically rather than environmentally driven. It appears that C. amblyrhynchos are adapted to a wide range of environmental conditions in coral reef habitats and that movement between or away from reef platforms is likely related to biological factors such as prey density, competition, reproduction or dispersal rather than environmental or seasonal changes

Using acoustic monitoring to evaluate MPAs for shark nursery areas: the importance of long-term data

The presence and movements of a population of young blacktip sharks (Carcharhinus limbatus) was monitored via a series of acoustic hydrophones over a period of three years to examine their use of a coastal nursery area. Data from this project were used to investigate the efficacy of hypothetical marine protected areas for this population. Small and large reserve designs were used to determine which would provide better protection for this population. The small reserve provided consistent levels of protection across years with sharks receiving good protection early in the summer season, but with declining protection thereafter. The large reserve provided less consistent levels of protection across years, but provided protection for a greater portion of time than the small reserve. Excursions from the small reserve were high early in the season and declined as sharks used this region less through the later portion of the summer. Excursions from the large reserve did not show any consistent pattern, but were also high early in the season and decreased through time as sharks used less of the reserve area. These results, coupled with previously calculated mortality estimates, revealed that the large reserve provided better protection for young sharks during their most vulnerable period within the nursery. We suggest that time-area closures for nursery populations of highly mobile shark species may be of value. Results of this study also show that long-term data may be critical to effective reserve design and placement, and assessment of reserve efficacy