Search

The blue shark is a highly migratory species with a worldwide distribution, making it susceptible to multiple fishing fleets across the globe. In southern Brazil, it is an important target, comprising up to 40% of the total biomass landed by the commercial surface longline fleet. This study aims to contribute to a better understanding of how the species uses the region and to update its life‐history information available for future assessments. Over five consecutive years (2018–2022) of landings and onboard monitoring, we gathered size data and vertebral samples to describe the species size composition in the region, as well as its seasonal and interannual variability and to update estimated life‐history parameters. The results showed that southern Brazil is mainly inhabited by large juvenile males that arrive during winter (July–September) and stay until spring (October–December), when their frequency decreases. Small adult males are present throughout the year but in higher frequencies during summer. A small number of adult females are present with higher frequencies during spring and summer, which decreases during the austral autumn and winter. Some variability in the presence of each life stage was observed among years. The estimated life‐history parameters were as follows: L∞: 255.02 cm fork length (FL), k: 0.20, L0:35.68 cm FL for males; L∞: 246.47 cm FL, k: 0.23, L0:36.77 cm FL for females; and L∞: 269.58 cm FL, k: 0.18, L0:36.19 cm FL for pooled sexes. However, the estimated values must be cautiously interpreted, as the obtained samples cannot be construed as representative of the entire harvested stock due to the lack of consistent presence of some life stages in the study region. [ABSTRACT FROM AUTHOR]

Three species of Southern Ocean skates, Bathyrajaeatonii,Bathyrajairrasa and Bathyrajamurrayi, are commonly caught as incidental by-catch in fisheries around Heard Island and McDonald Islands of the Kerguelen Plateau. We used length-at-age data to present the species' life history information (age, growth and maturity for the first-time). Length- and age-at-maturity analyses revealed that B.irrasa matured at > 6 years old and > 1000 mm total length (TL), which was older and larger than B.murrayi (> 5 years old and > 400 mm TL) but similar to B.eatonii (> 5 years old and > 900 mm). We fitted growth models using a multi-model Bayesian framework. Our findings support the assumption that B.irrasa is slow growing and late maturing compared to B.eatonii and B.murrayi, consequently putting it at greater risk to fishery-induced increases in mortality compared to other species (e.g., B.murrayi). This is the first-time age and growth has been estimated for these species, however sample sizes for B.murrayi and B.eatonii were small and hence growth models should be interpreted with caution. Our results represent vital information for population projection models and can therefore assist in the development and/or revision of current by-catch limits to inform ongoing management strategies and conservation efforts. [ABSTRACT FROM AUTHOR]

In the central west Pacific region, silky sharks (Carcharhinus falciformis) are commonly taken in fisheries, forming up to 95% of incidental elasmobranch bycatch. The present study examined the life history of silky sharks (n = 553) from Papua New Guinean waters. Age was analysed using sectioned vertebrae, and a multimodel approach was applied to the length-at-age data to fit growth models. Females ranged in length from 65.0- to 253.0-cm total length (TL), with the oldest estimated at 28 years. Males ranged in length from 68.4 to 271.3 cm TL and were aged to a maximum of 23 years. The logistic model provided the best fitting growth parameter estimates of length at birth L0 = 82.7 cm TL, growth coefficient g = 0.14 year-1 and asymptotic length L∞ = 261.3 cm TL for the sexes combined. Females reached sexual maturity at 204 cm TL and 14.0 years, whereas males reached maturity at 183 cm TL and 11.6 years. The average litter size from 28 pregnant females was 8 (range of 3-13). The growth parameters and late ages of sexual maturation for silky sharks in the central west Pacific suggest a significant risk from fisheries exploitation without careful population management. [ABSTRACT FROM AUTHOR]

Total lengths ( LT) at age and growth rates for south-west Pacific Galeocerdo cuvier were estimated from vertebral growth-band counts of 202 sagitally sectioned centra from 112 females (71-430 cm LT), 79 males (72-351 cm LT) and 11 of unknown sex. Captive growth data were also examined to complement vertebral age estimations. The sexes combined modelled growth coefficient ( k = 0·08) was smaller than previously reported for G. cuvier populations elsewhere. Split-band and narrow banding patterns were identified as potential sources of age underestimation in this species. [ABSTRACT FROM AUTHOR]

The removal of large predatory sharks from the world's oceans poses profound threats to marine community structure and species conservation. Effective management of exploited shark stocks requires a sound understanding of the life histories of target species. Here we provide the first assessment of age and growth for Carcharhinus brevipinna in Australian waters, and for C. obscurus and C. plumbeus in eastern Australian waters, based on interpretations of vertebral growth bands. In doing so, we provide arguably among the most robust growth parameters to date for the abovementioned taxa on the bases of genetic validation and sample size and distribution, but acknowledge equally a range of limitations—most notably those associated with vertebral ageing and our lack of age validation. Comparatively, the three species displayed both contrasts and consistencies in their growth characteristics off Australia's southeast coast. For all three sharks, rates of growth were greatest in the years immediately after birth, males grew more rapidly than females in the juvenile phase, and females were observed to grow larger, live longer and were generally larger at any given age. Longevity and all modelled growth parameters (L∞, k and L0), however, differed among the three species, and appeared to challenge the findings for conspecific populations in other parts of the world. The validity of these latter comparisons is, however, compromised by a range of confounding factors. Nevertheless, we provide the least conservative k estimates for C. obscurus and C. plumbeus of those previously reported, and extend maximum age estimates for C. brevipinna. In this way, our results have important implications for the assessment of natural mortality, productivity, and hence resilience to stock depletion, in these species in southeastern Australian waters. [ABSTRACT FROM PUBLISHER]

Abstract: The determination of age for large, harvested species such as chondrichthyans is important to the estimation of growth and other key life history parameters such as natural mortality, age-at-maturity, longevity, and recruitment. Vertebrae from 760 wobbegongs (275 Orectolobus ornatus, 232 O. maculatus, and 253 O. halei) were collected between June 2003 and December 2007 at seven locations in eastern Australia (Queensland and New South Wales) to estimate growth parameters for these species. A multi-model inference (MMI) information theoretical approach including four candidate models, with back-calculated estimates of length in earlier life stages to account for limited numbers of pup and juvenile wobbegongs, was used to determine the most appropriate growth model for each species. The models that combined observed and back-calculated lengths-at-age did not provide a better fit than the model using observed lengths-at-age data only. Taking into account biologically meaningful estimations of L ∞ and k, the models with the best fit to the data were the logistic growth function for O. ornatus and O. halei, and the von Bertalanffy growth model for O. maculatus. Using these models, growth parameters obtained were: 999, 1630 and 2128mm total length for L ∞ and 0.19, 0.09 and 0.20 for k, while the maximum number of growth bands was 20, 22, and 27, for O. ornatus, O. maculatus, and O. halei, respectively. All three species were monomorphic, with similar growth rates for males and females. Verification and validation undertaken using edge and marginal increment analyses, as well as chemical marking of captive and wild wobbegongs, suggested that growth band deposition in orectolobids is more likely to be linked to somatic growth than seasonality. This study is the first to use chemically marked wild Orectolobiformes to investigate growth band deposition rate. Five orectolobid species have now been shown not to deposit growth bands following a synchronous annual pattern, in contrast to that inferred for most other chondrichthyan species. The growth parameters estimated in this study are crucial for stock assessments and for demographic analyses to assess the sustainability of commercial harvests. [Copyright &y& Elsevier]

Age and growth of the whiskery shark, Furgaleus macki, from southwestern Australia were examined using vertebral ageing and tag-recapture data. The readability of bands on the vertebral centra varied markedly between individuals. Four readers were used to make band counts, with the most experienced reader having the lowest ‘index of average percent error’ and the highest level of agreement with final counts. Marginal increment analysis indicated that opaque bands form in January. With parturition occurring from August to October, size data suggests that the first band is probably formed 15–17 months after birth. The age at maturity was estimated to be 4.5 years for males, and 6.5 years for females. The oldest male was 10.5 years, and oldest female was 11.5 years. Von Bertalanffy growth parameters for males were L∞=121.5 cm fork length, K=0.423 year-1, t0=-0.472 years, were L∞=120.7 cm fork length, K=0.369 year-1, t0=-0.544 years for females, and were L∞=118.1 cm fork length, K=0.420 year-1, t0=-0.491 years for combined sexes. Data from a tag recapture study were analysed using a maximum likelihood method to verify the estimates of growth parameters from vertebral ageing. Von Bertalanffy growth parameters from the tag recapture study were L∞=128.2 cm fork length, K=0.288 year-1, t0=-0.654 years. The two methods of estimating growth parameters produced similar results, with rapid growth until approximately 5 years of age, after which there was little increase in length. [ABSTRACT FROM AUTHOR]