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Shaun P. Collin - One of the best experts on this subject based on the ideXlab platform.

  • retinal topography and spectral sensitivity of the Port Jackson Shark heterodontus PortusJacksoni
    The Journal of Comparative Neurology, 2020
    Co-Authors: Lauren R Peel, Shaun P. Collin, Nathan S Hart
    Abstract:

    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.

  • Electrosensory-driven feeding behaviours of the Port Jackson Shark (Heterodontus PortusJacksoni) and western shovelnose ray (Aptychotrema vincentiana)
    Marine and Freshwater Research, 2016
    Co-Authors: Ryan M Kempster, Nathan S Hart, Channing A. Egeberg, Shaun P. Collin
    Abstract:

    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.

  • comparative retinal anatomy in four species of elasmobranch
    Journal of Morphology, 2012
    Co-Authors: Nicole L Schieber, Shaun P. Collin, Nathan S Hart
    Abstract:

    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.

  • exogenous material in the inner ear of the adult Port Jackson Shark heterodontus PortusJacksoni elasmbranchii
    Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2011
    Co-Authors: Shaun P. Collin, Morena Mills, Ron Rasch, Ulrike E Siebeck
    Abstract:

    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.

Nathan S Hart - One of the best experts on this subject based on the ideXlab platform.

  • retinal topography and spectral sensitivity of the Port Jackson Shark heterodontus PortusJacksoni
    The Journal of Comparative Neurology, 2020
    Co-Authors: Lauren R Peel, Shaun P. Collin, Nathan S Hart
    Abstract:

    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.

  • Electrosensory-driven feeding behaviours of the Port Jackson Shark (Heterodontus PortusJacksoni) and western shovelnose ray (Aptychotrema vincentiana)
    Marine and Freshwater Research, 2016
    Co-Authors: Ryan M Kempster, Nathan S Hart, Channing A. Egeberg, Shaun P. Collin
    Abstract:

    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.

  • comparative retinal anatomy in four species of elasmobranch
    Journal of Morphology, 2012
    Co-Authors: Nicole L Schieber, Shaun P. Collin, Nathan S Hart
    Abstract:

    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.

Lorenz H. Frick - One of the best experts on this subject based on the ideXlab platform.

  • High Post-Capture Survival for Sharks, Rays and Chimaeras Discarded in the Main Shark Fishery of Australia?
    PloS one, 2012
    Co-Authors: Matias Braccini, Jason Adrian Van Rijn, Lorenz H. Frick
    Abstract:

    Most Sharks, rays and chimaeras (chondrichthyans) taken in commercial fisheries are discarded (i.e. returned to the ocean either dead or alive). Quantifying the post-capture survival (PCS) of discarded species is therefore essential for the improved management and conservation of this group. For all chondrichthyans taken in the main Shark fishery of Australia, we quantified the immediate PCS of individuals reaching the deck of commercial Shark gillnet fishing vessels and applied a risk-based method to semi-quantitatively determine delayed and total PCS. Estimates of immediate, delayed and total PCS were consistent, being very high for the most commonly discarded species (Port Jackson Shark, Australian swellShark, and spikey dogfish) and low for the most imPortant commercial species (gummy and school Sharks). Increasing gillnet soak time or water temperature significantly decreased PCS. Chondrichthyans with bottom-dwelling habits had the highest PCS whereas those with pelagic habits had the lowest PCS. The risk-based approach can be easily implemented as a standard practice of on-board observing programs, providing a convenient first-step assessment of the PCS of all species taken in commercial fisheries.

Matias Braccini - One of the best experts on this subject based on the ideXlab platform.

  • High Post-Capture Survival for Sharks, Rays and Chimaeras Discarded in the Main Shark Fishery of Australia?
    PloS one, 2012
    Co-Authors: Matias Braccini, Jason Adrian Van Rijn, Lorenz H. Frick
    Abstract:

    Most Sharks, rays and chimaeras (chondrichthyans) taken in commercial fisheries are discarded (i.e. returned to the ocean either dead or alive). Quantifying the post-capture survival (PCS) of discarded species is therefore essential for the improved management and conservation of this group. For all chondrichthyans taken in the main Shark fishery of Australia, we quantified the immediate PCS of individuals reaching the deck of commercial Shark gillnet fishing vessels and applied a risk-based method to semi-quantitatively determine delayed and total PCS. Estimates of immediate, delayed and total PCS were consistent, being very high for the most commonly discarded species (Port Jackson Shark, Australian swellShark, and spikey dogfish) and low for the most imPortant commercial species (gummy and school Sharks). Increasing gillnet soak time or water temperature significantly decreased PCS. Chondrichthyans with bottom-dwelling habits had the highest PCS whereas those with pelagic habits had the lowest PCS. The risk-based approach can be easily implemented as a standard practice of on-board observing programs, providing a convenient first-step assessment of the PCS of all species taken in commercial fisheries.

  • High Post-Capture Survival for Sharks, Rays and Chimaeras Discarded in the Main Shark Fishery of Australia?
    2011
    Co-Authors: Matias Braccini, Jay Van Rijn, Lorenz Frick
    Abstract:

    Most Sharks, rays and chimaeras (chondrichthyans) taken in commercial fisheries are discarded (i.e. returned to the ocean either dead or alive). Quantifying the post-capture survival (PCS) of discarded species is therefore essential for the improved management and conservation of this group. For all chondrichthyans taken in the main Shark fishery of Australia, we quantified the immediate PCS of individuals reaching the deck of commercial Shark gillnet fishing vessels and applied a riskbased method to semi-quantitatively determine delayed and total PCS. Estimates of immediate, delayed and total PCS were consistent, being very high for the most commonly discarded species (Port Jackson Shark, Australian swellShark, and spikey dogfish) and low for the most imPortant commercial species (gummy and school Sharks). Increasing gillnet soak time or water temperature significantly decreased PCS. Chondrichthyans with bottom-dwelling habits had the highest PCS whereas those with pelagic habits had the lowest PCS. The risk-based approach can be easily implemented as a standard practice of on-board observing programs, providing a convenient first-step assessment of the PCS of all species taken in commercia

Robert W Day - One of the best experts on this subject based on the ideXlab platform.

  • using rapid assessment and demographic methods to evaluate the effects of fishing on heterodontus PortusJacksoni off far eastern victoria australia
    Journal of Fish Biology, 2010
    Co-Authors: Javier Tovaravila, Robert W Day, Terence I Walker
    Abstract:

    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.

  • use of stochastic models to estimate the growth of the Port Jackson Shark heterodontus PortusJacksoni off eastern victoria australia
    Fisheries Research, 2009
    Co-Authors: Javier Tovaravila, Terence I Walker, V S Troynikov, Robert W Day
    Abstract:

    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.

  • 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, 2009
    Co-Authors: Javier Tovar-Ávila, Christopher Izzo, Terence I Walker, J. Matías Braccini, Robert W Day
    Abstract:

    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.