A re-examination of the growth of the gummy shark (Mustelus antarcticus) from Queensland, Australia

The gummy shark (Mustelus antarcticus) is endemic to Australia and is the target of commercial fisheries in southern Australia. However, the Queensland population is subjected to low levels of fishing mortality. The present study re-analysed a limited length-at-age dataset collected from central Queensland to estimate growth parameters in a Bayesian framework, with informative priors for size-at-birth and maximum size. Growth parameters were estimated using a multi-model approach. This study showed that M. antarcticus caught in Queensland exhibits slow growth compared with conspecifics in southern Australia, and females grow slower and larger than do males. The combined length-at-age data for males and females was best described by the von Bertalanffy growth function and the growth parameters were L∞ = 1852 mm (total length, TL), L0 = 261 mm TL and k = 0.044 year−1 for males and females combined. The ‘BayesGrowth’ R package offers a simple method to minimise bias in the estimation of growth parameters from a limited length-at-age dataset in a Bayesian framework

A re-examination of the growth of the gummy shark (Mustelus antarcticus) from Queensland, Australia

The gummy shark (Mustelus antarcticus) is endemic to Australia and is the target of commercial fisheries in southern Australia. However, the Queensland population is subjected to low levels of fishing mortality. The present study re-analysed a limited length-at-age dataset collected from central Queensland to estimate growth parameters in a Bayesian framework, with informative priors for size-at-birth and maximum size. Growth parameters were estimated using a multi-model approach. This study showed that M. antarcticus caught in Queensland exhibits slow growth compared with conspecifics in southern Australia, and females grow slower and larger than do males. The combined length-at-age data for males and females was best described by the von Bertalanffy growth function and the growth parameters were L∞ = 1852 mm (total length, TL), L0 = 261 mm TL and k = 0.044 year−1 for males and females combined. The ‘BayesGrowth’ R package offers a simple method to minimise bias in the estimation of growth parameters from a limited length-at-age dataset in a Bayesian framework

Conservation successes and challenges for wide-ranging sharks and rays

Overfishing is the most significant threat facing sharks and rays. Given the growth in consumption of seafood, combined with the compounding effects of habitat loss, climate change, and pollution, there is a need to identify recovery paths, particularly in poorly managed and poorly monitored fisheries. Here, we document conservation through fisheries management success for 11 coastal sharks in US waters by comparing population trends through a Bayesian state-space model before and after the implementation of the 1993 Fisheries Management Plan for Sharks. We took advantage of the spatial and temporal gradients in fishing exposure and fisheries management in the Western Atlantic to analyze the effect on the Red List status of all 26 wide-ranging coastal sharks and rays. We show that extinction risk was greater where fishing pressure was higher, but this was offset by the strength of management engagement (indicated by strength of National and Regional Plan of Action for sharks and rays). The regional Red List Index (which tracks changes in extinction risk through time) declined in all regions until the 1980s but then improved in the North and Central Atlantic such that the average extinction risk is currently half that in the Southwest. Many sharks and rays are wide ranging, and successful fisheries management in one country can be undone by poorly regulated or unregulated fishing elsewhere. Our study underscores that well-enforced, science-based management of carefully monitored fisheries can achieve conservation success, even for slow-growing species

Estimating IUCN Red List Population Reduction: JARA—A Decision-Support Tool Applied to Pelagic Sharks

The International Union for Conservation of Nature\u27s (IUCN) Red List is the global standard for quantifying extinction risk but assessing population reduction (criterion A) of wide‐ranging, long‐lived marine taxa remains difficult and controversial. We show how Bayesian state–space models (BSSM), coupled with expert knowledge at IUCN Red List workshops, can combine regional abundance data into indices of global population change. To illustrate our approach, we provide examples of the process to assess four circumglobal sharks with differing temporal and spatial data‐deficiency: Blue Shark (Prionace glauca), Shortfin Mako (Isurus oxyrinchus), Dusky Shark (Carcharhinus obscurus), and Great Hammerhead (Sphyrna mokarran). For each species, the BSSM provided global population change estimates over three generation lengths bounded by uncertainty levels in intuitive outputs, enabling informed decisions on the status of each species. Integrating similar analyses into future workshops would help conservation practitioners ensure robust, consistent, and transparent Red List assessments for other long‐lived, wide‐ranging species

Overfishing Drives Over One-Third of All Sharks and Rays Toward a Global Extinction Crisis

The scale and drivers of marine biodiversity loss are being revealed by the International Union for Conservation of Nature (IUCN) Red List assessment process. We present the first global reassessment of 1,199 species in Class Chondrichthyes-sharks, rays, and chimeras. The first global assessment (in 2014) concluded that one-quarter (24%) of species were threatened. Now, 391 (32.6%) species are threatened with extinction. When this percentage of threat is applied to Data Deficient species, more than one-third (37.5%) of chondrichthyans are estimated to be threatened, with much of this change resulting from new information. Three species are Critically Endangered (Possibly Extinct), representing possibly the first global marine fish extinctions due to overfishing. Consequently, the chondrichthyan extinction rate is potentially 25 extinctions per million species years, comparable to that of terrestrial vertebrates. Overfishing is the universal threat affecting all 391 threatened species and is the sole threat for 67.3% of species and interacts with three other threats for the remaining third: loss and degradation of habitat (31.2% of threatened species), climate change (10.2%), and pollution (6.9%). Species are disproportionately threatened in tropical and subtropical coastal waters. Science-based limits on fishing, effective marine protected areas, and approaches that reduce or eliminate fishing mortality are urgently needed to minimize mortality of threatened species and ensure sustainable catch and trade of others. Immediate action is essential to prevent further extinctions and protect the potential for food security and ecosystem functions provided by this iconic lineage of predators

A re-examination of the growth of the gummy shark (Mustelus antarcticus) from Queensland, Australia

The gummy shark (Mustelus antarcticus) is endemic to Australia and is the target of commercial fisheries in southern Australia. However, the Queensland population is subjected to low levels of fishing mortality. The present study re-analysed a limited length-at-age dataset collected from central Queensland to estimate growth parameters in a Bayesian framework, with informative priors for size-at-birth and maximum size. Growth parameters were estimated using a multi-model approach. This study showed that M. antarcticus caught in Queensland exhibits slow growth compared with conspecifics in southern Australia, and females grow slower and larger than do males. The combined length-at-age data for males and females was best described by the von Bertalanffy growth function and the growth parameters were L∞ = 1852 mm (total length, TL), L0 = 261 mm TL and k = 0.044 year−1 for males and females combined. The ‘BayesGrowth’ R package offers a simple method to minimise bias in the estimation of growth parameters from a limited length-at-age dataset in a Bayesian framework

Comparison of life histories of two deep-water sharks from eastern Australia: the piked spurdog and the Philippine spurdog

Deep-water sharks have low biological productivity and are vulnerable to exploitation with species-specific regional life history required to enable effective management. The present study describes the life history of two squalids collected from Australia: (1) the piked spurdog (Squalus megalops) from the tropical Great Barrier Reef; and (2) the Philippine spurdog (S. montalbani) from New South Wales. Maximum observed ages for males and females were 18 and 25 years for S. megalops and 28 and 27 years for S. montalbani. Multiple growth models were all well supported and indicated very slow growth rates for both species. The tropical S. megalops population was smaller and older at maturity than previously reported temperate populations. Males were mature at 352-mm stretched total length (LST) and 12.6 years, whereas females were mature at 422 mm LST and 19.1 years. Squalus montalbani males were mature at 700 mm LST and 21.8 years, whereas females were mature at 800 mm LST and 26 years. Fecundity was lower for S. megalops than S. montalbani with two to three compared with nine to 16 embryos. Both species have a conservative life history, although in the event of overfishing the longer-lived, later-maturing and deeper-dwelling S. montalbani is likely to take longer to recover than S. megalops

Evidence for inter- and intraspecific trophic niche separation among deepwater elasmobranchs on the southern Great Barrier Reef, Australia

Quantifying the trophic structure and interactions of deepwater (>200 m depth) elasmobranch assemblages is required to improve our understanding of deepwater ecosystems and the impacts of increased deepwater exploitation. To this end, we investigated the trophic ecology of deepwater elasmobranchs on the Great Barrier Reef (GBR) using a stable isotope (delta C-13 and delta N-15) approach. Our study included 4 species captured in the southern GBR deepwater eastern king prawn trawl fishery: the eastern spotted gummy shark Mustelus walkeri, the piked spurdog Squalus megalops, the pale spotted catshark Asymbolus pallidus, and the Argus skate Dentiraja polyommata. The delta C-13 and delta N-15 values of all 4 species ranged from -18.6 to -16.2 parts per thousand and 8.3 to 13.8 parts per thousand, respectively. The small C-13 range was likely due to the limited number of unique carbon baseline sources typically found in deepwater environments. Despite this, 3 of the 4 species exhibited relatively low core (40% SEA b ) isotopic niche overlap (<1 to 44%). Isotopic niche separation may be driven by multiple interacting factors including morphology, feeding strategies, or resource partitioning to reduce competition. Isotope analysis also provided evidence for intraspecific variation; S. megalops, D. polyommata and M. walked exhibited significant increases in delta N-15 (similar to 3 parts per thousand) and delta C-13 (similar to 2 parts per thousand) with size. Latitude, longitude, and depth had statistically significant but comparatively minor effects on isotope values (<= 1 parts per thousand) of the 4 species. Cumulatively, our results indicate that isotopic variation among deepwater elasmobranchs on the GBR is principally driven by size and species-level differences in resource use

Near-infrared spectroscopy for shark ageing and biology

Accurate and reliable age estimates of sharks are important for informing management that will achieve sustainable outcomes for populations. Age is the foundation of many of the essential parameters, such as growth rate and productivity, that are used in demographic analyses and fisheries assessments (Cailliet et al., 2006; Campana, 2001). Here, "sharks" is used as a general term to refer to sharks, rays, and chimaeras, therwise known as chondrichthyans. Traditionally, to estimate age in sharks, growth bands are counted in their hard parts. Vertebrae or dorsal fin spines are primarily used, although caudal thorns have also been found suitable for ageing in a few species of skates (Cailliet, 2015; Goldman et al., 2012; Serra-Pereira et al., 2008). As sharks age, calcified material accumulates in these structures and can produce visible band pairs that, when formation periodicity has been validated, enable age determination (Goldman et al., 2012; see also Chapter 10 in this volume). Counting these band pairs requires experience and time to achieve consistent results, and repeated reads are necessary to ensure precision of the counts (Cailliet et al., 2006). It also can require time-consuming preparation, such as sectioning of the structures and enhancement with stains to improve clarity and readability of the band pairs (Irvine et al., 2006b; Matta et al., 2017). In addition, this approach normally requires the lethal removal of the structures used for ageing from an individual. Given the vulnerability of many shark species to exploitation (Dulvy et al., 2014), nonlethal methods for ageing would be beneficial. These issues prompted investigation of near-infrared spectroscopy (NIRS) as a complementary approach to shark ageing. Although NIRS requires traditional band counts of some age structures, it can greatly reduce the time taken to estimate age from a structure and has the potential to be nonlethal (Rigby et al., 2014, 2016b). This chapter reviews how NIRS works and the application and considerations for use of NIRS in shark ageing