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Culum Brown - One of the best experts on this subject based on the ideXlab platform.
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preliminary observations on the movement ecology of a crested horn shark Heterodontus galeatus
Journal of Fish Biology, 2021Co-Authors: Nathan Charles Bass, Joanna Day, Tristan L Guttridge, Nathan A Knott, Culum BrownAbstract:The residency and movements of a single acoustically tagged female crested horn shark (Heterodontus galeatus) were monitored in Jervis Bay, Australia. The individual was intermittently detected by receivers throughout the 8-year study period and showed preference for particular rocky reefs in terms of its residency indices and duration of residency events. This individual exhibited lower residency and dissimilar movement patterns to that of the well studied and sympatric Port Jackson shark (Heterodontus portusjacksoni), highlighting the need for research into the basic life history and movement ecology of H. galeatus. This article is protected by copyright. All rights reserved.
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residency and movement patterns of adult port jackson sharks Heterodontus portusjacksoni at a breeding aggregation site
Journal of Fish Biology, 2021Co-Authors: Nathan Charles Bass, Johann Mourier, Joanna Day, Tristan L Guttridge, Nathan A Knott, Catarina Vila Pouca, Culum BrownAbstract:Examining the movement ecology of mesopredators is fundamental to developing an understanding of their biology, ecology and behaviour, as well as the communities and ecosystems they influence. The limited research on the residency and movements of benthic marine mesopredators has primarily used visual tags, which do not allow for the efficient and accurate monitoring of individual space use. In this study, the authors investigated the residency and movement patterns of Port Jackson sharks Heterodontus portusjacksoni (Meyer 1793) at a breeding aggregation site in Jervis Bay, south-eastern Australia, using passive acoustic telemetry to further our understanding of the movement ecology of these important mesopredators. Between 2012 and 2014, individuals were tagged with acoustic transmitters, and their residency and movements within the bay were monitored for up to 4 years. H. portusjacksoni showed strong preferences for particular reefs within and between breeding seasons. Males had significantly higher residency indices at their favoured sites relative to females, suggesting that males may be engaging in territorial behaviour. Conversely, female H. portusjacksoni exhibited higher roaming indices relative to males indicating that females may move between sites to assess males. Finally, H. portusjacksoni showed temporal variation in movements between reefs with individuals typically visiting more reefs at night relative to the day, dusk and dawn corresponding with their nocturnal habits.
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Effects of reward magnitude and training frequency on the learning rates and memory retention of the Port Jackson shark Heterodontus portusjacksoni
Animal Cognition, 2020Co-Authors: Dennis D. U. Heinrich, Culum Brown, Catarina Vila Pouca, Charlie HuveneersAbstract:The development of adaptive responses to novel situations via learning has been demonstrated in a wide variety of animal taxa. However, knowledge on the learning abilities of one of the oldest extant vertebrate groups, Chondrichthyes, remains limited. With the increasing interest in global wildlife tourism and shark feeding operations, it is important to understand the capacities of these animals to form associations between human activities and food. We used an operant conditioning regime with a simple spatial cognitive task to investigate the effects of reinforcement frequency and reward magnitude on the learning performance and memory retention of Port Jackson sharks ( Heterodontus portusjacksoni ). Twenty-four Port Jackson sharks were assigned one of four treatments differing in reward magnitude and reinforcement frequency (large magnitude–high frequency; large magnitude–low frequency; small magnitude–high frequency; small magnitude–low frequency). The sharks were trained over a 21-day period to compare the number of days that it took to learn to pass an assigned door to feed. Sharks trained at a high reinforcement frequency demonstrated faster learning rates and a higher number of passes through the correct door at the end of the trials, while reward magnitude had limited effects on learning rate. This suggests that a reduction in reinforcement frequency during tourism-related feeding operations is likely to be more effective in reducing the risk of sharks making associations with food than limiting the amount of food provided.
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acoustic accelerometry reveals diel activity patterns in premigratory port jackson sharks
Ecology and Evolution, 2019Co-Authors: Julianna Kadar, Monique Ladds, Johann Mourier, Culum BrownAbstract:: Distinguishing the factors that influence activity within a species advances understanding of their behavior and ecology. Continuous observation in the marine environment is not feasible but biotelemetry devices provide an opportunity for detailed analysis of movements and activity patterns. This study investigated the detail that calibration of accelerometers measuring root mean square (RMS) acceleration with video footage can add to understanding the activity patterns of male and female Port Jackson sharks (Heterodontus portusjacksoni) in a captive environment. Linear regression was used to relate RMS acceleration output to time-matched behavior captured on video to quantify diel activity patterns. To validate captive data, diel patterns from captive sharks were compared with diel movement data from free-ranging sharks using passive acoustic tracking. The RMS acceleration data showed captive sharks exhibited nocturnal diel patterns peaking during the late evening before midnight and decreasing before sunrise. Correlation analysis revealed that captive animals displayed similar activity patterns to free-ranging sharks. The timing of wild shark departures for migration in the late breeding season corresponded with elevated diel activity at night within the captive individuals, suggesting a form of migratory restlessness in captivity. By directly relating RMS acceleration output to activity level, we show that sex, time of day, and sex-specific seasonal behavior all influenced activity levels. This study contributes to a growing body of evidence that RMS acceleration data are a promising method to determine activity patterns of cryptic marine animals and can provide more detailed information when validated in captivity.
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lack of social preference between unfamiliar and familiar juvenile port jackson sharks Heterodontus portusjacksoni
Journal of Fish Biology, 2019Co-Authors: Catarina Vila Pouca, Culum BrownAbstract:This study investigated whether captive-reared juvenile Port Jackson sharks Heterodontus portusjacksoni choose to aggregate and if familiarity is one of the mechanisms driving social preference. In a controlled binary-choice experiment, juvenile sharks were given the option to associate or not with unfamiliar conspecifics, or to associate or not with familiar conspecifics. In neither group did juvenile H. portusjacksoni actively choose to associate with conspecifics, but familiarity decreased the proportion of time spent near a conspecific only during the initial phase of the experiment. Treatment (1 or 3 shoal mates), sex and size had no effect on aggregation behaviour. These findings suggest that familiarity is not a driver of social preferences in juvenile H. portusjacksoni, contrary to results in another shark species. Additionally, adult H. portusjacksoni form large aggregations during the breeding season and actively associate with familiar sex and size-matched individuals, thus our results suggest the species undergoes an ontogenetic shift in social behaviour.
Charlie Huveneers - One of the best experts on this subject based on the ideXlab platform.
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Effects of reward magnitude and training frequency on the learning rates and memory retention of the Port Jackson shark Heterodontus portusjacksoni
Animal Cognition, 2020Co-Authors: Dennis D. U. Heinrich, Culum Brown, Catarina Vila Pouca, Charlie HuveneersAbstract:The development of adaptive responses to novel situations via learning has been demonstrated in a wide variety of animal taxa. However, knowledge on the learning abilities of one of the oldest extant vertebrate groups, Chondrichthyes, remains limited. With the increasing interest in global wildlife tourism and shark feeding operations, it is important to understand the capacities of these animals to form associations between human activities and food. We used an operant conditioning regime with a simple spatial cognitive task to investigate the effects of reinforcement frequency and reward magnitude on the learning performance and memory retention of Port Jackson sharks ( Heterodontus portusjacksoni ). Twenty-four Port Jackson sharks were assigned one of four treatments differing in reward magnitude and reinforcement frequency (large magnitude–high frequency; large magnitude–low frequency; small magnitude–high frequency; small magnitude–low frequency). The sharks were trained over a 21-day period to compare the number of days that it took to learn to pass an assigned door to feed. Sharks trained at a high reinforcement frequency demonstrated faster learning rates and a higher number of passes through the correct door at the end of the trials, while reward magnitude had limited effects on learning rate. This suggests that a reduction in reinforcement frequency during tourism-related feeding operations is likely to be more effective in reducing the risk of sharks making associations with food than limiting the amount of food provided.
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Effects of auditory and visual stimuli on shark feeding behaviour: the disco effect
Marine Biology, 2017Co-Authors: Laura A. Ryan, R.d. Mccauley, S. P. Collin, Jan M. Hemmi, Enrico Gennari, Ryan M Kempster, Lucille Chapuis, Charlie Huveneers, Kara E. Yopak, Caroline C. KerrAbstract:Sensory systems play a central role in guiding animal behaviour. They can be manipulated to alter behavioural outcomes to limit negative interactions between humans and animals. Sharks are often seen as a threat to humans and there has been increasing interest in developing shark mitigation devices. Previous research has concentrated on stimulating the electrosensory and olfactory systems of sharks, whereas the influence of light and sound on their behaviour has received little attention. In this study, the effects of an intense strobe light and a loud, artificial sound composed of mixed frequencies and intensities on shark behaviour were assessed. We tested these stimuli individually and in combination on wild-caught captive Port Jackson (Heterodontus portusjacksoni) and epaulette (Hemiscyllium ocellatum) sharks in aquaria and on wild great white sharks (Carcharodon carcharias) in the field. When presented alone and in combination with sound, the lights reduced the number of times that the bait was taken by both H. portusjacksoni and H. ocellatum in captivity. The strobe light alone, however, did not affect the behaviour of white sharks, but when presented in combination with sound, white sharks spent significantly less time in proximity to the bait. As the lights and sound presented in this study did not show a pronounced deterrent effect on C. carcharias, we do not advise their use as a strategy for mitigating shark–human interactions. However, due to the potential effectiveness of strobe lights in deterring other species of sharks, there may be applications for this approach in the reduction of fisheries bycatch.
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from egg to hatchling preferential retention of fatty acid biomarkers in young of the year port jackson sharks Heterodontus portusjacksoni
Journal of Fish Biology, 2014Co-Authors: Crystal Beckmann, Charlie Huveneers, James G Mitchell, Laurent Seuront, David A J StoneAbstract:The muscle and liver fatty acid composition of young-of-the-year (YOY) Port Jackson sharks Heterodontus portusjacksoni were investigated to determine the effects of a known dietary lipid source v. maternal input as demonstrated by egg yolk fatty acid profiles. Ten Heterodontus portusjacksoni egg yolks were collected in situ and compared with four hatched H. portusjacksoni fed a known diet in a controlled feeding experiment of 185 days. This study demonstrated that fatty acids are probably conservatively transferred from egg yolks to YOY H. portusjacksoni, while diet did not have a large effect on the fatty acid composition of the liver or muscle.
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inter tissue differences in fatty acid incorporation as a result of dietary oil manipulation in port jackson sharks Heterodontus portusjacksoni
Lipids, 2014Co-Authors: Charlie Huveneers, Crystal Beckmann, James G Mitchell, David A J StoneAbstract:Fatty acid profile analysis is a tool for dietary investigation that may complement traditional stomach contents analysis. While recent studies have shown that the liver of sharks fed different diets have differing fatty acid profiles, the degree to which diet is reflected in shark blood serum and muscle tissue is still poorly understood. An 18-week controlled feeding experiment was undertaken using captive Port Jackson sharks (Heterodontus portusjacksoni). Sharks were fed exclusive diets of artificial pellets treated with fish or poultry oil and sampled every 6 weeks. The fatty acid profiles from liver, blood serum, and muscle were affected differently, with the period from which significant differences were observed varying by tissue and diet type. The total fatty acid profiles of fish oil and poultry oil fed sharks were significantly different from week 12 onwards in the liver and blood serum, but significant differences were only observed by week 18 in the muscle tissue of sharks fed different diets. The drivers of dissimilarity which aligned with dietary input were 14:0, 18:2n-6, 20:5n-3, 18:1n-9 and 22:6n-3 in the liver and blood serum. Dietary fatty acids accumulated more consistently in the liver than in the blood plasma or muscle, likely due to its role as the central organ for fat processing and storage. Blood serum and muscle fatty acid profiles were influenced by diet, but fluctuated over-time. The low level of correlation between diet and muscle FA profiles is likely a result of low levels of fat (<1 %) in the muscle and the domination of structural, cell-membrane phospholipids in shark muscle tissues. Our findings describe inter-tissue differences in the incorporation of fatty acids from the diet to consumer, which should be taken into account when interpreting dietary patterns from fatty acid profiles.
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brief communication from egg to hatchling preferential retention of fatty acid biomarkers in young of the year port jackson sharks Heterodontus portusjacksoni
2014Co-Authors: Crystal Beckmann, James G Mitchell, Laurent Seuront, Charlie HuveneersAbstract:The muscle and liver fatty acid composition of young-of-the-year (YOY) Port Jackson sharks Heterodontus portusjacksoni were investigated to determine the effects of a known dietary lipid source v. maternal input as demonstrated by egg yolk fatty acid profiles. Ten Heterodontus portusjacksoni egg yolks were collected in situ and compared with four hatched H. portusjacksoni fed a known diet in a controlled feeding experiment of 185 days. This study demonstrated that fatty acids are probably conservatively transferred from egg yolks to YOY H. portusjacksoni, while diet did not have a large effect on the fatty acid composition of the liver or muscle.
Shaun P. Collin - One of the best experts on this subject based on the ideXlab platform.
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Behavioural sleep in two species of buccal pumping sharks (Heterodontus portusjacksoni and Cephaloscyllium isabellum)
Journal of sleep research, 2020Co-Authors: Michael L. Kelly, Caroline C. Kerr, Jan M. Hemmi, Stefan Spreitzenbarth, John A. Lesku, Craig A. Radford, Shaun P. CollinAbstract:Sleep is known to occur in most, if not all, animals studied thus far. Recent studies demonstrate the presence of sleep in flatworms and jellyfish, suggesting that this behaviour evolved early in the evolution of animals. Sharks are the earliest known extant, jawed vertebrates and may play an important role in understanding the evolutionary history of sleep in vertebrates, and yet, it is unknown whether they sleep. The Port Jackson (Heterodontus portusjacksoni) and draughtsboard (Cephaloscyllium isabellum) sharks are both benthic, buccal pumping species and remain motionless for extended periods of time. Whether these periods of prolonged inactivity represent sleep or quiet wakefulness is unknown. A key criterion for separating sleep from other quiescent states is an increased arousal threshold. We show here that inactive sharks of both species require significantly higher levels of electric stimulation before they show a visible response. Sharks deprived of rest, however, show no significant compensatory increase in restfulness during their normal active period following enforced swimming. Nonetheless, increased arousal thresholds in inactive animals suggest that these two species of shark sleep - the first such demonstration for members of this group of vertebrates. Further research, including electrophysiological studies, on these and other sharks, is required for a comprehensive understanding of sleep in cartilaginous fishes.
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retinal topography and spectral sensitivity of the port jackson shark Heterodontus portusjacksoni
The Journal of Comparative Neurology, 2020Co-Authors: Lauren R Peel, Shaun P. Collin, Nathan S HartAbstract:In this study, we investigated the visual system of the Port Jackson shark Heterodontus portusjacksoni, a shallow-dwelling benthic species and generalist predator endemic to the temperate coastal waters around southern Australia. Measurements of retinal spectral sensitivity in juvenile sharks, made using single flash and heterochromatic flicker photometry under conditions of dark- or light-adaptation, indicated a peak sensitivity at around 500 nm, with no evidence of a spectral shift with increasing levels of light adaptation. Histological sections of the retina revealed a heavily rod dominated retina containing only a few small cell profiles in the photoreceptor layer that might represent a sparse cone population or may be immature rods. Assessment of retinal topography in juvenile sharks indicated the presence of a distinct specialisation for increased visual spatial acuity in the form of a horizontal streak of higher rod photoreceptor (~80,000 rods mm-2 ) and ganglion cell (~1,800 cells mm-2 ) densities across the horizontal meridian of the eye. This specialization would be adaptive for panoramic sampling of the part of the visual field corresponding to the substrate-water interface and remove the need for H. portusjacksoni to move its eyes extensively when resting on the sea floor. The estimated upper limit of spatial resolving power in juvenile H. portusjacksoni was 3.14 cycles deg-1 , which is at the lower end of values measured in elasmobranchs. Taken together, these results suggest that the retina of H. portusjacksoni is well adapted for nocturnal vision.
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Electrosensory-driven feeding behaviours of the Port Jackson shark (Heterodontus portusjacksoni) and western shovelnose ray (Aptychotrema vincentiana)
Marine and Freshwater Research, 2016Co-Authors: Ryan M Kempster, Nathan S Hart, Channing A. Egeberg, Shaun P. CollinAbstract:Elasmobranch fishes (sharks, skates and rays) possess a highly sensitive electrosensory system that enables them to detect weak electric fields, such as those produced by potential prey organisms. Despite several comparative anatomical studies, the functional significance of interspecific variation in electrosensory system morphology remains poorly understood. In the present study, we directly tested the electrosensitivity of two benthic elasmobranchs that share a similar habitat and feed on similarly sized prey items (Port Jackson sharks, Heterodontus portusjacksoni, and western shovelnose rays, Aptychotrema vincentiana), but differ significantly in their electrosensory system morphology. Aptychotrema vincentiana possesses almost five times the number of electrosensory pores of H. portusjacksoni (~1190 and ~239 respectively), yet both species are able to initiate feeding responses to electric-field gradients below 1 nV cm–1, similar to other elasmobranch species tested. However, A. vincentiana showed a greater ability to resolve the specific location of electrosensory stimuli, because H. portusjacksoni would more often overshoot the target and have to turn around to locate it. These results suggested that differences in abundance and distribution of electrosensory pores have little to no effect on the absolute electrical sensitivity in elasmobranchs, and instead, may reflect species-specific differences in the spatial resolution and directionality of electroreception.
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comparative retinal anatomy in four species of elasmobranch
Journal of Morphology, 2012Co-Authors: Nicole L Schieber, Shaun P. Collin, Nathan S HartAbstract:Using both light and transmission electron microscopy, we examined the retinal anatomy of four elasmobranch species with differing ecologies: the bull shark Carcharhinus leucas, Port Jackson shark Heterodontus portusjacksoni, epaulette shark Hemiscyllium ocellatum and pink whipray Himantura fai. Their retinas are typical of other vertebrates, having three nuclear and two synaptic layers, but are characterised by very large horizontal cells, low densities of ganglion cells (many of which are displaced to the inner nuclear and inner plexiform layers) and the presence of numerous myelinated axons within the nerve fibre layer. Carcharhinus leucas, H. fai and H. ocellatum have duplex retinas containing both rods and single cones. The peak ratio of rods to cones is much lower in C. leucas (4:1) and H. fai (3:1) compared to H. ocellatum (19:1), reflecting differences in diel activity patterns. No cones were observed in the retina of H. portusjacksoni, which is strongly nocturnal. The cones of H. fai lack a distinct myoid and their nuclei are located in a discrete layer sclerad to the external limiting membrane (ELM), whereas those of C. leucas and H. ocellatum have an obvious myoid, and their nuclei are located vitread to the ELM. No double/twin cones were observed in any species. Incorporating data from other studies, there is a clear correlation between rod outer segment volume and visual ecology in elasmobranchs, with smaller volumes found in partly diurnal pelagic species and larger volumes in benthic nocturnal species. This trend may reflect fundamental differences in visual temporal resolution between active and more sedentary species.
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exogenous material in the inner ear of the adult port jackson shark Heterodontus portusjacksoni elasmbranchii
Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2011Co-Authors: Shaun P. Collin, Morena Mills, Ron Rasch, Ulrike E SiebeckAbstract:Previous studies have suggested that the inner ear of some benthic species of elasmobranchs contain only exogenous material within their otoconial organs, a unique feature within vertebrates. However, these examinations have not accounted for the possibility of otoconial degeneration or used modern experimental methods to identify the materials present. Both of these issues are addressed in this study using inner ear samples from the adult Port Jackson shark, Heterodontus portusjacksoni. A comparison of the otoconial mass in fixed specimens over short and medium time scales reveals that over those timescales the degeneration of calcium carbonate-based otoconia does not occur and confirms that calcium carbonate-based otoconia are not found within the otoconial organs of H. portusjacksoni. Additionally, microanalysis of the chemical composition and ultrastructure of the otoconial mass using energy dispersive X-ray microanalysis and scanning electron microscopy confirms that the entire otoconial mass is comprised of exogenous silicon dioxide particles, bound within a carbon matrix. This exogenous material is suggested to play an equivalent role to the otoconia found in other species of elasmobranchs, and allows both hearing and vestibular control to occur in benthic sharks that spend their lives foraging within a sandy substrate.
Robert W Day - One of the best experts on this subject based on the ideXlab platform.
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using rapid assessment and demographic methods to evaluate the effects of fishing on Heterodontus portusjacksoni off far eastern victoria australia
Journal of Fish Biology, 2010Co-Authors: Javier Tovaravila, Robert W Day, Terence I WalkerAbstract:A rapid semi-quantitative ecological risk assessment method (productivity and susceptibility analysis) indicated that, despite its low biological productivity, the Port Jackson shark Heterodontus portusjacksoni is at low risk to all fishing methods in far-eastern Victoria, Australia, under the present fishing practices, because of its low catch susceptibility. The risk to this population, however, would increase if the shark gillnet fishery operating in the region were to retain the species as a by-product. Demographic analysis indicated that the species has medium intrinsic population growth rate and potential rebound in comparison with other chondrichthyan species, juveniles have higher elasticity than mature females and both juvenile and mature females have higher elasticities than hatchlings. Because of its low biological productivity and moderate resilience to the effects of fishing, cautious management measures will be necessary to ensure the sustainable use of H. portusjacksoni if its marketing increases in the future. Information on the dynamics of a population that is valuable to provide management advice can be obtained through demographic methods, but rapid assessment methods can also provide complementary information on the effects of fishing by considering the catch susceptibility of the population to each fishing method.
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use of stochastic models to estimate the growth of the port jackson shark Heterodontus portusjacksoni off eastern victoria australia
Fisheries Research, 2009Co-Authors: Javier Tovaravila, Terence I Walker, V S Troynikov, Robert W DayAbstract:Abstract Three stochastic models were used to describe the growth of Heterodontus portusjacksoni off eastern Victoria, Australia. The models are based on a reparametrization of the von Bertalanffy growth model to take account of length-at-age heterogeneity, and incorporate random variation of the von Bertalanffy growth coefficient (k), using three different probability distribution functions (pdfs): Weibull, gamma and log-normal. They were fitted to the lengths of 179 specimens (79 females and 100 males), and associated age estimates obtained by counting growth bands in the inner trunk dentine layer of the dorsal-fin spines. The species is relatively long-lived (maximum estimated age of 35 years for females and 28 years for males) and slow growing, but has rapid growth during the early stages of life. All the models provided similar growth parameters and length-at-age quantiles. However, Kullbacḱs information mean indicated that the stochastic model assuming a log-normal distribution fitted the length-at-age data better for both females (L∞ = 1337, E(k) = 0.059, t0 = 5.294) and males (L∞ = 1125, E(k) = 0.075, t0 = 4.944) than the models assuming other distributions. The χ2 likelihood ratio test indicated that females and males grow differently.
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Assessing growth band counts from vertebrae and dorsal-fin spines for ageing sharks: comparison of four methods applied to Heterodontus portusjacksoni
Marine and Freshwater Research, 2009Co-Authors: Javier Tovar-Ávila, Christopher Izzo, Terence I Walker, J. Matías Braccini, Robert W DayAbstract:Four methods for counting growth bands using vertebrae and dorsal-fin spines of the Port Jackson shark, Heterodontus portusjacksoni, are compared. Both calcified structures presented observable growth bands, allowing cross comparison among structures for the first time in a shark species. Whole and sectioned vertebrae and dorsal fin-spines possess highly visible growth bands and intra-reader band counts resulted in similar precision indices with little systematic bias. However, inter-reader growth band count plots showed possible biases in counts from sectioned vertebrae and sectioned dorsal-fin spines. Sectioned vertebrae and whole and sectioned dorsal-fin spines produced similar growth band counts, whereas whole vertebrae produced significantly lower counts. The similar readability, precision indices, growth band counts and apparent absence of biases between counts for a single reader would indicate that sectioned vertebrae and whole and sectioned dorsal-fin spines are both potentially useful and acceptable methods for band counting. However, inter-reader comparisons are necessary to avoid acceptance of biased estimations, resulting in over- or under-estimations of age. Validation for all age classes is essential to determining accurate age estimations for this and other species.
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dorsal fin spine growth of Heterodontus portusjacksoni a general model that applies to dorsal fin spines of chondrichthyans
Canadian Journal of Fisheries and Aquatic Sciences, 2008Co-Authors: Javier Tovaravila, Christopher Izzo, Terence I Walker, Matias J Braccini, Robert W DayAbstract:A prospective model of dorsal-fin spine growth in chondrichthyans is devised by studying the growth of spines from captive and wild Heterodontus portusjacksoni injected with several fluorochromes. ...
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reproduction of Heterodontus portusjacksoni in victoria australia evidence of two populations and reproductive parameters for the eastern population
Marine and Freshwater Research, 2007Co-Authors: Javier Tovaravila, Terence I Walker, Robert W DayAbstract:Significant differences in the length–frequency composition of catch samples, mass–length relationships and length-at-maturity found between Heterodontus portusjacksoni from western and far-eastern Victoria, suggest the presence of at least two separate breeding populations off south-eastern Australia, with some mixing between these regions. In each region females attain a larger size than males, and collectively those sharks in western Victoria are smaller, present higher mass-at-length, and lower length-at-maturity than those in far-eastern Victoria. These regional differences might be a result of sampling bias, length-selective fishing mortality, environmental conditions, or genetic differences. However, tagging evidence from previous studies and the presence of two bio-geographic provinces in the region support the hypothesis of two separate breeding populations. The essential reproductive parameters for H. portusjacksoni population analysis in far-eastern Victoria were determined, using a novel method to estimate fecundity and the ovarian cycle of an egg-laying species. In this region, females have between 6 and 20 pre-ovulatory oocytes (average = 14, n = 29, standard deviation = 3.71) before the reproductive season. The species has an annual reproductive cycle correlated with water temperature, with ovulation starting during late winter to early spring and a ~6 month egg-laying period. The period from the onset of vitellogenesis to ovulation of oocytes is ~18 months.
Terence I Walker - One of the best experts on this subject based on the ideXlab platform.
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trawl capture of port jackson sharks Heterodontus portusjacksoni and gummy sharks mustelus antarcticus in a controlled setting effects of tow duration air exposure and crowding
Fisheries Research, 2010Co-Authors: Lorenz H Frick, Terence I Walker, Richard D ReinaAbstract:Abstract Delayed effects of fisheries capture on the physiology and condition of sharks are poorly understood, but information on the post-release fate of sharks that have been incidentally captured, handled, and released is important to elaborate effective fisheries management measures for by-catch shark species. By-catch is often substantial during commercial trawling operations, and fish are exposed to a multitude of different stressful stimuli during trawl capture. We subjected Port Jackson sharks, Heterodontus portusjacksoni, and gummy sharks, Mustelus antarcticus, to trawl capture in a controlled setting to investigate effects of tow duration, exposure to air, and crowding in the codend, and monitored their condition via repeated blood sampling during a 72-h recovery period subsequent to the capture event. Port Jackson sharks experienced a low degree of physiological disturbance in response to our capture treatments and no mortality was observed during or after any experiments. Conversely, homeostatic balance of gummy sharks was severely disrupted by trawl capture, and immediate and delayed mortality was substantial (up to 87%) during some experiments. Moribund gummy sharks showed significantly increased blood lactate (>15 mmol/L) and potassium levels (>8 mmol/L) compared with surviving sharks, but these differences did not become evident until 6–12 h after the capture event. There was no strong evidence for an increase in physiological disturbance with increasing tow duration in either species. Extended periods of air exposure (>10 min) following a capture event may lead to additional physiological stress, but simulated crowding as performed in the present study did not result in increased physiological stress compared with trawl capture of individual animals. The results of this study suggest that trawl capture may lead to significant immediate and delayed mortality in gummy sharks, and that extended air exposure on deck may further exacerbate the deleterious effects of capture stress.
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using rapid assessment and demographic methods to evaluate the effects of fishing on Heterodontus portusjacksoni off far eastern victoria australia
Journal of Fish Biology, 2010Co-Authors: Javier Tovaravila, Robert W Day, Terence I WalkerAbstract:A rapid semi-quantitative ecological risk assessment method (productivity and susceptibility analysis) indicated that, despite its low biological productivity, the Port Jackson shark Heterodontus portusjacksoni is at low risk to all fishing methods in far-eastern Victoria, Australia, under the present fishing practices, because of its low catch susceptibility. The risk to this population, however, would increase if the shark gillnet fishery operating in the region were to retain the species as a by-product. Demographic analysis indicated that the species has medium intrinsic population growth rate and potential rebound in comparison with other chondrichthyan species, juveniles have higher elasticity than mature females and both juvenile and mature females have higher elasticities than hatchlings. Because of its low biological productivity and moderate resilience to the effects of fishing, cautious management measures will be necessary to ensure the sustainable use of H. portusjacksoni if its marketing increases in the future. Information on the dynamics of a population that is valuable to provide management advice can be obtained through demographic methods, but rapid assessment methods can also provide complementary information on the effects of fishing by considering the catch susceptibility of the population to each fishing method.
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stress related physiological changes and post release survival of port jackson sharks Heterodontus portusjacksoni and gummy sharks mustelus antarcticus following gill net and longline capture in captivity
Journal of Experimental Marine Biology and Ecology, 2010Co-Authors: Lorenz H Frick, Richard D Reina, Terence I WalkerAbstract:Abstract Information on effects of fisheries capture on the physiology and post-release condition of sharks is urgently needed to design and implement effective fisheries management plans for shark stocks around the world, but obtaining data on post-release condition in the wild is very difficult. We used a controlled setting to subject Port Jackson sharks ( Heterodontus portusjacksoni ) and gummy sharks ( Mustelus antarcticus ) to varying durations of gill-net and longline capture stress for up to 360 min and monitored their condition via repeated blood sampling during a subsequent 72-h recovery period. Changes in plasma metabolites and electrolytes of Port Jackson sharks in response to our experimental treatment were small and no mortality was observed, suggesting that Port Jackson sharks are resilient to capture stress. In contrast, gummy sharks reacted very sensitively to capture stress, with severely disrupted acid–base and electrolyte balances, and immediate and delayed mortality was substantial (up to 70%) following gill-net capture. Moribund gummy sharks had very high plasma concentrations of lactate and potassium. Management measures for shark species that are susceptible to capture stress should aim to reduce the probability of interactions of that species with fishing gear.
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the physiological response of port jackson sharks and australian swellsharks to sedation gill net capture and repeated sampling in captivity
North American Journal of Fisheries Management, 2009Co-Authors: Lorenz H Frick, Richard D Reina, Terence I WalkerAbstract:Abstract Studying postrelease effects of fisheries capture on chondrichthyans in the wild poses considerable logistical challenges. We report a laboratory-based technique to (1) simulate gill-net capture of sharks, which allows monitoring the condition of animals during recovery from a controlled capture event, and (2) assess effects of sedation, serial blood sampling, and repeated exposure to experimental treatment on stress-related blood variables. Exposing Port Jackson sharks Heterodontus portusjacksoni and Australian swellsharks Cephaloscyllium laticeps to 30 min of simulated gill-net capture elicited behavioral stress (struggling and elevated ventilation rate) and minor physiological stress (elevated plasma lactate) responses but did not cause any mortality. Sedation of Australian swellsharks affected some stress-related blood variables. Repeated handling of Port Jackson sharks and Australian swellsharks at short intervals may result in elevated stress levels, but repeated exposure to simulated captu...
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use of stochastic models to estimate the growth of the port jackson shark Heterodontus portusjacksoni off eastern victoria australia
Fisheries Research, 2009Co-Authors: Javier Tovaravila, Terence I Walker, V S Troynikov, Robert W DayAbstract:Abstract Three stochastic models were used to describe the growth of Heterodontus portusjacksoni off eastern Victoria, Australia. The models are based on a reparametrization of the von Bertalanffy growth model to take account of length-at-age heterogeneity, and incorporate random variation of the von Bertalanffy growth coefficient (k), using three different probability distribution functions (pdfs): Weibull, gamma and log-normal. They were fitted to the lengths of 179 specimens (79 females and 100 males), and associated age estimates obtained by counting growth bands in the inner trunk dentine layer of the dorsal-fin spines. The species is relatively long-lived (maximum estimated age of 35 years for females and 28 years for males) and slow growing, but has rapid growth during the early stages of life. All the models provided similar growth parameters and length-at-age quantiles. However, Kullbacḱs information mean indicated that the stochastic model assuming a log-normal distribution fitted the length-at-age data better for both females (L∞ = 1337, E(k) = 0.059, t0 = 5.294) and males (L∞ = 1125, E(k) = 0.075, t0 = 4.944) than the models assuming other distributions. The χ2 likelihood ratio test indicated that females and males grow differently.