Chapter 13: Vulnerability of chondrichthyan fishes of the Great Barrier Reef to climate change

This chapter addresses the potential impact of climate change on the chondrichthyan fauna of the Great Barrier Reef, that is, the sharks, rays, skates and holocephalans that occur within the Great Barrier Reef region. The terms ‘sharks and rays’ or ‘sharks’ are used throughout this chapter to describe this diverse group of fishes.This is Chapter 13 of Climate change and the Great Barrier Reef: a vulnerability assessment. The entire book can be found at http://hdl.handle.net/11017/13

Life history of the Critically Endangered largetooth sawfish: a compilation of data for population assessment and demographic modelling

© The authors 2021. Open Access under Creative Commons by Attribution Licence. Use, distribution and reproduction are un - restricted. Authors and original publication must be credited. The largetooth sawfish Pristis pristis is a Critically Endangered, once widespread shark-like ray. The species is now extinct or severely depleted in many former parts of its range and is protected in some other range states where populations persist. The likelihood of collecting substantial new biological information is now low. Here, we review all available life history information on size, age and growth, reproductive biology, and demography as a resource for population assessment and demographic modelling. We also revisit a subset of historical data from the 1970s to examine the maternal size−litter size relationship. All available information on life history is derived from the Indo-West Pacific (i.e. northern Australia) and the Western Atlantic (i.e. Lake Nicaragua-Río San Juan system in Central America) subpopulations. P. pristis reaches a maximum size of at least 705 cm total length (TL), size-at-birth is 72−90 cm TL, female size-at-maturity is reached by 300 cm TL, male size-at-maturity is 280−300 cm TL, age-at-maturity is 8−10 yr, longevity is 30−36 yr, litter size range is 1−20 (mean of 7.3 in Lake Nicaragua), and reproductive periodicity is suspected to be biennial in Lake Nicaragua (Western Atlantic) but annual in Australia (Indo-West Pacific). There was a weak relationship between litter size and maternal size in Lake Nicaragua, and lifetime reproductive output for an individual female from Lake Nicaragua was estimated as 73 pups. Future demographic models should aim to capture the variability and uncertainty in life history parameters for P. pristis and we encourage a conservative approach to any application for conservation and management

Overfishing and habitat loss drive range contraction of iconic marine fishes to near extinction

Extinctions on land are often inferred from sparse sightings over time, but this technique is ill-suited for wide-ranging species. We develop a space-for-time approach to track the spatial contraction and drivers of decline of sawfishes. These iconic and endangered shark-like rays were once found in warm, coastal waters of 90 nations and are now presumed extinct in more than half (n = 46). Using dynamic geography theory, we predict that sawfishes are gone from at least nine additional nations. Overfishing and habitat loss have reduced spatial occupancy, leading to local extinctions in 55 of the 90 nations, which equates to 58.7% of their historical distribution. Retention bans and habitat protections are urgently necessary to secure a future for sawfishes and similar species

Whole mitogenome sequencing refines population structure of the Critically Endangered sawfish Pristis pristis

The largetooth sawfish Pristis pristis (Linnaeus, 1758) is a highly threatened euryhaline elasmobranch that in recent times has undergone a significant range contraction. It now only remains in a few areas, with northern Australia being the main stronghold. Previous work using a single mitochondrial gene approach suggested the existence of regional barriers to gene flow in northern Australia. In this study, whole mitochondrial sequences of 92 P. pristis from 7 river drainages across northern Australia were used to refine the population structure. This approach revealed barriers to gene flow at a scale as fine as between adjacent river drainages. Except for those flowing into the Gulf of Carpentaria, all river drainages appeared to host a genetically distinct population. The apparent genetic homogeneity in the Gulf is probably due to freshwater connectivity between river drainages, either during the last glaciation event when the Gulf was a freshwater lake or through contemporary wet season flooding. These results suggest that each river drainage across the species' range should be considered a discrete management unit unless there is evidence of freshwater connectivity. More broadly, the improved resolution of population structure obtained with whole mitogenome analysis compared to single mitochondrial gene approaches suggests that female reproductive philopatry may have been overlooked in previous studies of some elasmobranch species

First records of the false catshark, Pseudotriakis microdon Capello, 1868, from the waters of eastern Australia and Indonesia

A new specimen of a rare deepwater chondrichthyan, the false catshark Pseudotriakis microdon Capello, 1868 is documented from the Coral Sea. This represents the first record of the species from off the east coast of Australia and only the second from Australian waters. The specimen, a 277cm total length (TL) mature male, was captured by exploratory deepwater dropline at a depth of 350m on 03/02/2004. Morphometrics are presented and compared to other published accounts. A further individual, a 287cm TL mature female captured by bottom longline operating at depths of 100-150m around Sawu, Dana and Raijua Islands, southeastern Indonesia, is documented from fish landing sites in Lombok, Indonesia. This individual was not retained and only its sex, maturity and TL were recorded. It represents the first record of P. microdon for Indonesia and for the northeast Indian Ocean. These specimens increase the known range of this rare, sporadically recorded, but widely distributed chondrichthyan

A rare contemporary record of the Critically Endangered Ganges shark Glyphis gangeticus

The first record of the Ganges shark Glyphis gangeticus from anywhere in its range in over a decade is reported from the Arabian Sea. One female specimen was recorded at Sassoon Docks in Mumbai, India in February 2016, measuring 266cm total length. In light of the Critically Endangered status of this species and its rarity, urgent management actions are needed to determine population size and trends in abundance in combination with fisher education and awareness campaigns. (c) 2018 The Fisheries Society of the British Isle

One panel to rule them all: DArTcap genotyping for population structure, historical demography, and kinship analyses, and its application to a threatened shark

With recent advances in sequencing technology, genomic data are changing how important conservation management decisions are made. Applications such as Close‐Kin Mark‐Recapture demand large amounts of data to estimate population size and structure, and their full potential can only be realised through ongoing improvements in genotyping strategies. Here we introduce DArTcap, a cost‐efficient method that combines DArTseq and sequence capture, and illustrate its use in a high resolution population analysis of Glyphis garricki , a rare, poorly known and threatened euryhaline shark. Clustering analyses and spatial distribution of kin pairs from four different regions across northern Australia and one in Papua New Guinea, representing its entire known range, revealed that each region hosts at least one distinct population. Further structuring is likely within Van Diemen Gulf, the region that included the most rivers sampled, suggesting additional population structuring would be found if other rivers were sampled. Coalescent analyses and spatially explicit modelling suggest that G. garricki experienced a recent range expansion during the opening of the Gulf of Carpentaria following the conclusion of the Last Glacial Maximum. The low migration rates between neighbouring populations of a species that is found only in restricted coastal and riverine habitats show the importance of managing each population separately, including careful monitoring of local and remote anthropogenic activities that may affect their environments. Overall we demonstrated how a carefully chosen SNP panel combined with DArTcap can provide highly accurate kinship inference and also support population structure and historical demography analyses, therefore maximising cost‐effectiveness