Victor M. Peddemors

Isolation and genetic diversity of endangered grey nurse shark (Carcharias taurus) populations

Anthropogenic impacts are believed to be the primary threats to the eastern Australian population of grey nurse sharks (Carcharias taurus), which is listed as critically endangered, and the most threatened population globally. Analyses of 235 polymorphic amplified fragment length polymorphisms (AFLP) loci and 700 base pairs of mitochondrial DNA control region provide the first account of genetic variation and geographical partitioning (east and west coasts of Australia, South Africa) in C. taurus. Assignment tests, analysis of relatedness and Fst values all indicate that the Australian populations are isolated from South Africa, with negligible migration between the east and west Australian coasts. There are significant differences in levels of genetic variation among regions. Australian C. taurus, particularly the eastern population, has significantly less AFLP variation than the other sampling localities. Further, the eastern Australian sharks possess only a single mitochondrial haplotype, also suggesting a small number of founding individuals. Therefore, historical, rather than anthropogenic processes most likely account for their depauperate genetic variation. These findings have implications for the viability of the eastern Australian population of grey nurse sharks.

Decadal trends in shark catches and effort from the New South Wales, Australia, Shark Meshing Program 1950-2010

The New South Wales (NSW) government has operated a program of netting beaches for the protection of swimmers and surfers against shark attack since 1937 in Sydney, and since 1949 in Newcastle and Wollongong. The scope and directives of the Shark Meshing Program have remained constant since its inception, with operational modifications in net specifications in 1972, changes in spatial deployment in 1972, 1987 and 1992, and the elimination of winter netting since 1989. This markedly increased meshing effort in 1972, and again in 1987. In the present study, we examine the trends in catch and effort for the period from 1950–1951 to 2009–2010 over this 200-km section of the NSW coast. Significant temporal trends in species, size and sex composition are described herein. Catches were consistently dominated by three shark taxa, hammerhead sharks (Sphyrna spp.), whaler sharks (Carcharhinus spp.) and Australian angel sharks (Squatina australis), although their relative contributions to catches varied over time. Catch per unit effort has significantly declined for five of the most abundant shark taxa over the study period, increasing only for a single taxon, the sevengill shark (Notorynchus cepedianus). Catches of larger, potentially dangerous white sharks (Carcharodon carcharias) and tiger sharks (Galeocerdo cuvier) saw fewer large animals being caught over time. This pattern was not observed across other taxa. Four different monthly trends were observed in landings of the most abundant eight taxa, reflecting differences in the biology of the catch species. The current study also provides useful information on catches and sizes of grey nurse (Carcharias taurus) and white sharks before and after their protection in NSW waters in 1984 and 1998, respectively.

Conservation challenges of sharks with continental scale migrations

Understanding movement and connectivity of populations is increasingly important as human and climate change pressures become more pervasive, but can be problematic in difficult to observe species such as large marine predators. We examined the movements of bull sharks, Carcharhinus leucas, using acoustic telemetry arrays along the east coast of Australia. Approximately half of 75 individuals released in temperate waters moved into tropical reef regions, with both sexes undertaking long-range movements and multiple individuals making return trips. Only 3% of 39 individuals released in tropical reef habitats moved south to temperate waters, but approximately 25% moved to southern reef or subtropical coastal areas. These results reveal complex linkages along the east coast of Australia which suggest a tropical reef based population comprised of individuals that migrate to multiple regions. Connectivity between locations along the east coast of Australia creates important conservation challenges for resource managers in multiple jurisdictions.

A video and photographic study of aggregation, swimming and respiratory behaviour changes in the Grey Nurse Shark (Carcharias taurus) in response to the presence of SCUBA divers

The Grey Nurse Shark (Carcharias taurus) is a popular attraction for shark eco-tourism using SCUBA. The species is also ‘globally Vulnerable’ (IUCN 2008. List of Threatened Species. www.iucnredlist.org/). Magic Point (off Maroubra) in Sydney is favoured by recreational SCUBA divers wishing to observe these sharks. The objective of this study was to experimentally test the level of the activities of recreational SCUBA divers on shark behaviour. This study assessed the shark responses to diver group size (4, 8 and 12), time of day (am, noon and pm) and diver distance from the sharks (3 m and 6 m). The study found that diver activity does affect the aggregation, swimming and respiratory behaviour of sharks at this site, albeit at short-term levels. Diver group size had no significant effect on shark aggregation, but the proximity of divers to the sharks was crucial. Shark distribution in the cave changed significantly in the presence of divers at 3 m distance from the cave, but stayed unchanged at 6 m. This was particularly apparent in the presence of large groups of 12 divers at 3 m distance when sharks increased their swim speed and ventilation mechanism from ‘active’ to ‘RAM’ ventilation. Such change coincided with a sudden decrease in ventilation frequency. Our research suggests that these effects are short-term and that sharks resume their behaviour once the divers retreat. If divers abide by the current code of practice for diving at this site, it is unlikely that their activities will substantially impact Grey Nurse Sharks in the long term.

Optimising the design of large-scale acoustic telemetry curtains

Broad-scale acoustic telemetry networks are being established worldwide. The 10-year anniversary of the Integrated Marine Observing System’s Animal Tracking Facility provided the opportunity to assess the efficiency of one of the first national-scale acoustic telemetry networks. Acoustic networks are comprised of acoustic receiver arrays that detect high-frequency transmitters attached to animals that pass within detection range. Herein we assessed the efficiency of eight curtains to detect passing animals by calculating the standardised mean number of detections and transmitters detected at each station. The aim was to determine how many receivers could be decommissioned from each curtain while maintaining its integrity (i.e. detection of all species passing the array). Pivotal locations were defined as the furthest station at which all species would still be detected and where at least 75% of the detections and transmitters would still be detected. By applying these criteria, we were able to improve the cost-effectiveness of our network significantly, reducing the number of stations from 132 to 85 (64% of the original network), yet still retaining 84% of total detections, 86% of transmitters and 100% of detected species. The present study provides a useful framework for refining acoustic telemetry networks.

Strontium mineralization of shark vertebrae

Determining the age of sharks using vertebral banding is a vital component of management, but the causes of banding are not fully understood. Traditional shark ageing is based on fish otolith ageing methods where growth bands are assumed to result from varied seasonal calcification rates. Here we investigate these assumptions by mapping elemental distribution within the growth bands of vertebrae from six species of sharks representing four different taxonomic orders using scanning x-ray fluorescence microscopy. Traditional visual growth bands, determined with light microscopy, were more closely correlated to strontium than calcium in all species tested. Elemental distributions suggest that vertebral strontium bands may be related to environmental variations in salinity. These results highlight the requirement for a better understanding of shark movements, and their influence on vertebral development, if confidence in age estimates is to be improved. Analysis of shark vertebrae using similar strontium-focused elemental techniques, once validated for a given species, may allow more successful estimations of age on individuals with few or no visible vertebral bands.

Experimental Evaluation of Shark Detection Rates by Aerial Observers

Aerial surveys are a recognised technique to identify the presence and abundance of marine animals. However, the capability of aerial observers to reliably sight coastal sharks has not been previously assessed, nor have differences in sighting rates between aircraft types been examined. In this study we investigated the ability of observers in fixed-wing and helicopter aircraft to sight 2.5 m artificial shark analogues placed at known depths and positions. Initial tests revealed that the shark analogues could only be detected at shallow depths, averaging only 2.5 m and 2.7 m below the water surface for observers in fixed-wing and helicopter aircraft, respectively. We then deployed analogues at shallower depths along a 5 km-long grid, and assessed their sightability to aircraft observers through a series of transects flown within 500 m. Analogues were seen infrequently from all distances, with overall sighting rates of only 12.5% and 17.1% for fixed-wing and helicopter observers, respectively. Although helicopter observers had consistently higher success rates of sighting analogues within 250 m of their flight path, neither aircraft observers sighted more than 9% of analogues deployed over 300 m from their flight paths. Modelling of sighting rates against environmental and experimental variables indicated that observations were affected by distance, aircraft type, sun glare and sea conditions, while the range of water turbidities observed had no effect. We conclude that aerial observers have limited ability to detect the presence of submerged animals such as sharks, particularly when the sharks are deeper than ∼2.6 m, or over 300 m distant from the aircrafts flight path, especially during sunny or windy days. The low rates of detections found in this study cast serious doubts on the use of aerial beach patrols as an effective early-warning system to prevent shark attacks.

Patterns of Occurrence of Sharks in Sydney Harbour, a Large Urbanised Estuary

Information about spatial and temporal variability in the distribution and abundance of shark-populations are required for their conservation, management and to update measures designed to mitigate human-shark interactions. However, because some species of sharks are mobile, migratory and occur in relatively small numbers, estimating their patterns of distribution and abundance can be very difficult. In this study, we used a hierarchical sampling design to examine differences in the composition of species, size- and sex-structures of sharks sampled with bottom-set longlines in three different areas with increasing distance from the entrance of Sydney Harbour, a large urbanised estuary. During two years of sampling, we obtained data for four species of sharks (Port Jackson, Heterodontus portusjacksoni; wobbegong, Orectolobus maculatus; dusky whaler, Carcharhinus obscurus and bull shark, Carcharhinus leucas). Only a few O. maculatus and C. obscurus were caught, all in the area closest to the entrance of the Harbour. O. maculatus were caught in all seasons, except summer, while C. obscurus was only caught in summer. Heterodontus portusjacksoni were the most abundant species, caught in the entrance location mostly between July to November, when water temperature was below 21.5°C. This pattern was consistent across both years. C. leucas, the second most abundant species, were captured in all areas of Sydney Harbour but only in summer and autumn when water temperatures were above 23°C. This study quantified, for this first time, how different species utilise different areas of Sydney Harbour, at different times of the year. This information has implications for the management of human-shark interactions, by enabling creation of education programs to modify human behaviour in times of increased risk of potentially dangerous sharks.

Genetic relatedness reveals total population size of white sharks in eastern Australia and New Zealand

Conservation concerns exist for many sharks but robust estimates of abundance are often lacking. Improving population status is a performance measure for species under conservation or recovery plans, yet the lack of data permitting estimation of population size means the efficacy of management actions can be difficult to assess, and achieving the goal of removing species from conservation listing challenging. For potentially dangerous species, like the white shark, balancing conservation and public safety demands is politically and socially complex, often leading to vigorous debate about their population status. This increases the need for robust information to inform policy decisions. We developed a novel method for estimating the total abundance of white sharks in eastern Australia and New Zealand using the genetic-relatedness of juveniles and applying a close-kin mark-recapture framework and demographic model. Estimated numbers of adults are small (ca. 280–650), as is total population size (ca. 2,500–6,750). However, estimates of survival probability are high for adults (over 90%), and fairly high for juveniles (around 73%). This represents the first direct estimate of total white shark abundance and survival calculated from data across both the spatial and temporal life-history of the animal and provides a pathway to estimate population trend.

Biology of angel sharks (Squatina sp.) and sawsharks (Pristiophorus sp.) caught in south-eastern Australian trawl fisheries and the New South Wales shark-meshing (bather-protection) program

Two species of angel shark (Squatina australis, S. albipunctata) and two species of sawshark (Pristiophorus nudipinnis, P. cirratus) are frequently caught in south-eastern Australia. Little is known of the biology of these elasmobranchs, despite being caught as secondary target species in large numbers. The present study collected morphometric and reproductive data from sharks caught in shark-control nets, commercial fishing trawlers and research trawlers in south-eastern Australia. All four species had female-biased sexual size dimorphism, but growth curves between sexes did not differ. Male S. australis individuals were fully mature at ~800-mm total length, male P. nudipinnis at ~900mm, and male P. cirratus at ~800mm. Anterior pectoral margins could be used to determine total length in all species. No morphometric measurement could reliably separate Squatina spp. or Pristiophorus spp., although S. albipunctata over 1000-mm total length had larger eyes than did S. australis.