Academic literature on the topic 'Heterodontus portusjacksoni'

Heterodontus portusjacksoniwas obtained from the catches of commercial trawl, gillnet and longline fisheries operating in south-western Australian waters, in which this shark is an abundant bycatch species. Ninety per cent of theH. portusjacksonicaught by commercial trawling in a marine embayment were <400 mm in total length, whereas 99 and 100%, respectively, of the individuals taken by commercial gillnet and longline outside that embayment were >400 mm. Although the differences between the size compositions in the catches obtained by trawling vs both gillnetting and longlining, which were similar, are partly attributable to gear selectivity, they also reflect a use by juvenileH. portusjacksoniof protected nearshore waters as nursery areas and a tendency for larger juveniles and adults to occupy reef/rock habitats in a range of water depths. The fact that all but one of the numerousH. portusjacksoni>800 mm were females is reflected in the ratio of females to males differing significantly from parity in the gillnet and longline samples. Yolked oocytes usually take one year to develop to ovulatory size. Ovulation occurs in late winter to early summer and hatching takes place a year later when the embryo is 180–220 mm. The claspers of males commence rapid growth at a total length of ~450 mm, coincident with the onset of clasper calcification and gonadal maturation. The rate of clasper growth relative to total length reached a maximum at ~570 mm and then declined precipitously as the claspers approached full calcification. Based on gonadal criteria, theL50at maturity for females (805 mm) was nearly 40% greater than that for males (593 mm). Values of the deviance information criterion and marked overlap in their 95% confidence intervals demonstrate that theL50of 581 mm derived for males using full clasper calcification as the index of maturity was equally valid as the aboveL50derived for males at maturity using gonadal criteria. The capture of substantial numbers of juveniles by trawling and of females <L50at maturity by gillnetting and longlining may be having localized effects on the population structure ofH. portusjacksoniin south-western Australian waters.

Demographic analyses are used to assess the status and vulnerability of elasmobranchs but their accuracy is often affected by limited basic biological information. Although the Port Jackson shark Heterodontus portusjacksoni (Meyer) is currently not considered at threat, there is insufficient data for eastern Australia to assess this rigorously. The present study determined vital demographic rates of adult and juvenile H. portusjacksoni at four locations on the central and southern coast of New South Wales, Australia from January 2002 to December 2005 using underwater visual census, tag–recapture and samples obtained from a commercial fishery. Natural mortality was low in adults (0.063–0.074 year–1) and juveniles (0.225 year–1), but substantial at the embryonic stage (0.783–0.896 year–1). Adult growth rates (31.4–32.7 mm year–1) were slightly less than that of juveniles (36.8–37.5 mm year–1). Males at both stages grew slightly faster than females. However, H. portusjacksoni had slower growth rates than many other elasmobranch species. Having a low intrinsic rate of increase (r = 0.069 year–1), long generation times (μ1 = 22.5 year) and a low rebound potential, adults are the stage with the greatest impact on population growth. Hence, their life history strategy makes them susceptible to serious decline under exploitation, and management should strive to maintain the adult reproductive stock as a priority.

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.

ABSTRACTData presented in this study highlight the potential of allozyme electrophoresis in providing unequivocal genetic evidence for the identification of life cycle stages, particularly where species have complex life cycles. Adults of the nematode Echinocephalus overstreeti parasitize the elasmobranch Heterodontus portusjacksoni. The putative larval form which is morphologically dissimilar is found in two species of marine molluscs, Chlamys bifrons and Pecten albus. Electrophoretic analysis indicated that the adult and larval forms shared alleles at all of the 34 enzyme loci established. Furthermore, there were no fixed allelic differences between larval forms from different mollusc species.

The present study has tested statistically the hypothesis that the diets of four abundant and co-occurring elasmobranch species differ and change with body size and season and has determined the extent of any differences, to ascertain their potential for reducing competition for food resources. Non-metric multivariate analyses of volumetric contributions of dietary categories to stomach contents demonstrated that the dietary compositions of the rays Myliobatis australis and Aptychotrema vincentiana and the sharks Heterodontus portusjacksoni and Squatina australis in south-western Australian waters differed. M. australis fed predominantly on benthic invertebrates, whereas A. vincentiana consumed large volumes of teleosts. The durophagous H. portusjacksoni ingested a wide variety of prey, including gastropods, cephalopods, bivalves, echinoderms and teleosts, whereas S. australis ingested mainly teleosts and cephalopods. The extent and pattern of change in the diet with increasing body size varied among species. For example, the diet of H. portusjacksoni changed abruptly to larger, harder-bodied prey at ∼400-mm total length, whereas that of S. australis underwent small, gradual changes with increasing body size. The diets of each species changed seasonally. Inter- and intraspecific variations in dietary composition reduce the potential for competition between and within these abundant elasmobranch species in south-western Australian waters.

one of 353 port jackson sharks, heterodontus portusjacksoni, caught off the southern coast of western australia, was a hermaphrodite. the female reproductive tract consisted of a large (functional) right ovary with three large yolked ova, a small non-functional left ovary and two well-developed uteri and oviducal glands. the male tract comprised two conspicuous but undeveloped testes, two vas deferens and two calcified claspers with grooves. this individual represents the first published example of hermaphroditism in the order heterodontiformes and is a rare example of an elasmobranch with a complete suite of both male and female reproductive structures.

Research Doctorate - Doctor of Philosophy (PhD)
World shark populations are declining rapidly from the increased demand for shark meat and fins and from their capture as by-catch. Techniques to accurately and reliably estimate the age of elasmobranchs are required to understand life history and develop management strategies. Although some biological information exists for the harvested species, few of the many shark species caught as by-catch have been investigated. In the waters of New South Wales, Australia, the Port Jackson shark (Heterodontus portusjacksoni) is a non-targeted species, however it is a major contributor to the elasmobranch by-catch in the bottom trawl and prawn fisheries. Although some biological and ecological information exists on Port Jackson sharks from New South Wales, there is no understanding of suitable techniques to age this species and of the age structure of the New South Wales’ population. Hence, the main purpose for the present study was to determine a suitable technique to age Port Jackson sharks and thereby provide essential age and growth data for its future management, sustainable use and conservation. This study consisted of research into: (1) the macroscopic anatomy of the vertebral centra and dorsal spines from 652 H. portusjacksoni to explore their suitability as ageing structures; (2) a comparison of whole and sectioned vertebral centra and of whole and sectioned dorsal spines for ageing; (3) validation of the annual formation of growth bands; (4) a comparison of the effect of prior experience on readers’ ability to count annual growth bands in vertebral centra; and (5) the development of age-growth models for the New South Wales’ population of H. portusjacksoni. Two types of vertebral centra (trunk and caudal vertebrae) were found in the vertebral column. Both vertebrae consisted of a centrum, 2 ribs, 4 neural arches, basiopophyses and neural foramen and decreased in size from anterior to posterior. A strong linear relationship was identified between vertebral diameter (VD) and fork length (FL). Each dorsal spine was positioned anterior to the dorsal fin and consisted of a stem and the cap. A strong linear relationships were identified between spine base width (SBW) and FL. The existence of alternating opaque and translucent band pairs in both structures further suggested they may be suitable for ageing purposes. Validation (calcein and oxytetracycline injections, marginal increment analysis, and centrum edge analysis) confirmed that translucent band pairs were formed during the winter (September-November) and were annual in both vertebral centra and dorsal spines. Whole and sectioned vertebral centra and dorsal spines were individually examined to determine which method best estimated the age. Although both methods had individual low reading bias and high precision, there was a difference between the two methods. The average bias between the two methods using vertebral centra was -0.158 ±0.05 and the coefficient of variance (CV) was 92.32% for females and -0.157 ±0.03 and CV was 56.95% for males. This indicated that sectioned vertebral centra returned higher ages than whole vertebral centra. When comparing whole dorsal spine age estimates to sectioned dorsal spines, there was an average bias between methods of -0.22 ±0.026 and a low precision 73.09%. Again indicating that sectioned dorsal spines returned higher ages than whole dorsal spines. A comparison of ages estimated from sectioned vertebral centra and sectioned dorsal spines showed that vertebral centra aged older than dorsal spines. Although the two structures each had low reading bias and high reading precision, there were differences between the two structures. The average bias between the two structures was -0.4 ±0.03 and the CV was low (74.7%), indicating that there was a significant difference in age derived from the two structures. Therefore, great caution should be taken when choosing which structure to use for age estimation. Ages of sharks estimated from the recommended sectioned vertebral centra ranged from 0.2 to 32.5 years for females and 0.2 to 23.8 years for males. Four different growth models were compared using both sectioned vertebral centra and sectioned dorsal spines to estimate the best suitable growth curve. Out of the 4 growth models the Gompertz Growth Function (GGF) best described the growth of H. portusjacksoni. von Bertalanffy growth parameters estimated from ageing data using the GGF for females were t0 = 2.584 yr, k = 0.111, L∞ = 1134.1 mm FL, and for males t0 = 1.629 yr, k = 0.131, L∞ = 1012.9 mm FL. This indicates that H. portusjacksoni has a slow growth rate and a longer life span than most other elasmobranch species. The effect of reader’s experience on the bias and precision of age estimates of sectioned vertebral centra was determined in an experiment that compared the author (an experienced vertebral centra reader) with an experienced fish otolith reader, two readers recently trained in reading vertebral centra (but lacking experience), and two untrained and inexperienced readers. Bias and precision were determined for each reader from two ageing trials with the same structure three months apart. Between-trials bias for each reader (except the author)ranged from 0.033 to 0.13 and precision ranged from 8.2 to 19.5%, while the author had low bias 0.006 and high precision 1.1%. When comparing all the readers with the author, bias ranged from 0.033 to 0.13 with an 8.2 to 19.5% precision for trial one, and 0.017 to 0.5 with precision between 2.5 to 5.4% in trial two. The age-bias plots comparing the two trials all indicated that only the author was consistent. And the age-bias plots between the author and the other readers all indicated that neither experience in ageing teleost otoliths or limited training in ageing enhanced the bias or precision compared to inexperienced elasmobranch agers.

Research Doctorate - Doctor of Philosophy (PhD)
World shark populations are declining rapidly from the increased demand for shark meat and fins and from their capture as by-catch. Techniques to accurately and reliably estimate the age of elasmobranchs are required to understand life history and develop management strategies. Although some biological information exists for the harvested species, few of the many shark species caught as by-catch have been investigated. In the waters of New South Wales, Australia, the Port Jackson shark (Heterodontus portusjacksoni) is a non-targeted species, however it is a major contributor to the elasmobranch by-catch in the bottom trawl and prawn fisheries. Although some biological and ecological information exists on Port Jackson sharks from New South Wales, there is no understanding of suitable techniques to age this species and of the age structure of the New South Wales’ population. Hence, the main purpose for the present study was to determine a suitable technique to age Port Jackson sharks and thereby provide essential age and growth data for its future management, sustainable use and conservation. This study consisted of research into: (1) the macroscopic anatomy of the vertebral centra and dorsal spines from 652 H. portusjacksoni to explore their suitability as ageing structures; (2) a comparison of whole and sectioned vertebral centra and of whole and sectioned dorsal spines for ageing; (3) validation of the annual formation of growth bands; (4) a comparison of the effect of prior experience on readers’ ability to count annual growth bands in vertebral centra; and (5) the development of age-growth models for the New South Wales’ population of H. portusjacksoni. Two types of vertebral centra (trunk and caudal vertebrae) were found in the vertebral column. Both vertebrae consisted of a centrum, 2 ribs, 4 neural arches, basiopophyses and neural foramen and decreased in size from anterior to posterior. A strong linear relationship was identified between vertebral diameter (VD) and fork length (FL). Each dorsal spine was positioned anterior to the dorsal fin and consisted of a stem and the cap. A strong linear relationships were identified between spine base width (SBW) and FL. The existence of alternating opaque and translucent band pairs in both structures further suggested they may be suitable for ageing purposes. Validation (calcein and oxytetracycline injections, marginal increment analysis, and centrum edge analysis) confirmed that translucent band pairs were formed during the winter (September-November) and were annual in both vertebral centra and dorsal spines. Whole and sectioned vertebral centra and dorsal spines were individually examined to determine which method best estimated the age. Although both methods had individual low reading bias and high precision, there was a difference between the two methods. The average bias between the two methods using vertebral centra was -0.158 ±0.05 and the coefficient of variance (CV) was 92.32% for females and -0.157 ±0.03 and CV was 56.95% for males. This indicated that sectioned vertebral centra returned higher ages than whole vertebral centra. When comparing whole dorsal spine age estimates to sectioned dorsal spines, there was an average bias between methods of -0.22 ±0.026 and a low precision 73.09%. Again indicating that sectioned dorsal spines returned higher ages than whole dorsal spines. A comparison of ages estimated from sectioned vertebral centra and sectioned dorsal spines showed that vertebral centra aged older than dorsal spines. Although the two structures each had low reading bias and high reading precision, there were differences between the two structures. The average bias between the two structures was -0.4 ±0.03 and the CV was low (74.7%), indicating that there was a significant difference in age derived from the two structures. Therefore, great caution should be taken when choosing which structure to use for age estimation. Ages of sharks estimated from the recommended sectioned vertebral centra ranged from 0.2 to 32.5 years for females and 0.2 to 23.8 years for males. Four different growth models were compared using both sectioned vertebral centra and sectioned dorsal spines to estimate the best suitable growth curve. Out of the 4 growth models the Gompertz Growth Function (GGF) best described the growth of H. portusjacksoni. von Bertalanffy growth parameters estimated from ageing data using the GGF for females were t0 = 2.584 yr, k = 0.111, L∞ = 1134.1 mm FL, and for males t0 = 1.629 yr, k = 0.131, L∞ = 1012.9 mm FL. This indicates that H. portusjacksoni has a slow growth rate and a longer life span than most other elasmobranch species. The effect of reader’s experience on the bias and precision of age estimates of sectioned vertebral centra was determined in an experiment that compared the author (an experienced vertebral centra reader) with an experienced fish otolith reader, two readers recently trained in reading vertebral centra (but lacking experience), and two untrained and inexperienced readers. Bias and precision were determined for each reader from two ageing trials with the same structure three months apart. Between-trials bias for each reader (except the author)ranged from 0.033 to 0.13 and precision ranged from 8.2 to 19.5%, while the author had low bias 0.006 and high precision 1.1%. When comparing all the readers with the author, bias ranged from 0.033 to 0.13 with an 8.2 to 19.5% precision for trial one, and 0.017 to 0.5 with precision between 2.5 to 5.4% in trial two. The age-bias plots comparing the two trials all indicated that only the author was consistent. And the age-bias plots between the author and the other readers all indicated that neither experience in ageing teleost otoliths or limited training in ageing enhanced the bias or precision compared to inexperienced elasmobranch agers.