Reduction of elasmobranch by-catch in the hake semipelagic near-bottom longline fishery in the Algarve (Southern Portugal)

Elasmobranch fish, particularly deep-sea sharks, are the most important component of the by-catch of the hake semipelagic near-bottom 'pedra-e-bola' longline fishery in the Algarve (South Portugal) and most of these fish are discarded. The effects of the removal of the lower hooks were evaluated, in terms of target and by-catch reductions, by quantifying the catches of each hook relative to the distance from the bottom. The analysis showed that most European hake (Merluccius merluccius), the target species of this fishery, were caught in the middle range of the hooks, with very few individuals caught near the bottom, whereas for sharks the situation was the opposite, with most hooked near the bottom. The removal of the lower three pairs of hooks would result in a small reduction in the catch of the target species, but a much more significant reduction in elasmobranch by-catch. In the specific case of the blackmouth catshark (Galeus melastomus), discard mortality would be further minimized due to the fact that the lower hooks capture significantly smaller animals that are always discarded compared with hooks that are more distant from the bottom

Vertebral Bomb Radiocarbon Suggests Extreme Longevity in White Sharks

Conservation and management efforts for white sharks (Carcharodon carcharias) remain hampered by a lack of basic demographic information including age and growth rates. Sharks are typically aged by counting growth bands sequentially deposited in their vertebrae, but the assumption of annual deposition of these band pairs requires testing. We compared radiocarbon (Δ14C) values in vertebrae from four female and four male white sharks from the northwestern Atlantic Ocean (NWA) with reference chronologies documenting the marine uptake of 14C produced by atmospheric testing of thermonuclear devices to generate the first radiocarbon age estimates for adult white sharks. Age estimates were up to 40 years old for the largest female (fork length [FL]: 526 cm) and 73 years old for the largest male (FL: 493 cm). Our results dramatically extend the maximum age and longevity of white sharks compared to earlier studies, hint at possible sexual dimorphism in growth rates, and raise concerns that white shark populations are considerably more sensitive to human-induced mortality than previously thought

Residency patterns and migration dynamics of adult bull sharks (Carcharhinus leucas) on the east coast of southern Africa:

Bull sharks (Carcharhinus leucas) are globally distributed top predators that play an important ecological role within coastal marine communities. However, little is known about the spatial and temporal scales of their habitat use and associated ecological role. In this study, we employed passive acoustic telemetry to investigate the residency patterns and migration dynamics of 18 adult bull sharks (195–283 cm total length) tagged in southern Mozambique for a period of between 10 and 22 months. The majority of sharks (n = 16) exhibited temporally and spatially variable residency patterns interspersed with migration events. Ten individuals undertook coastal migrations that ranged between 433 and 709 km (mean  = 533 km) with eight of these sharks returning to the study site

Age and growth of the spinner shark Carcharhinus brevipinna (Muller and Henle, 1839) off the KwaZulu-Natal coast, South Africa

Age and growth of the spinner shark Carcharhinus brevipinna off the KwaZulu-Natal coast of South Africa was investigated from vertebral growth ring counts of 67 specimens (54–213 cm precaudal length, PCL). Counts were made from sectioned vertebral centra by two readers. There was a statistically significant difference between the growth functions of both sexes and Von Bertalanffy growth functions were L&#8734 = 196.3 cm, k = 0.146 year-1 and t0 = -2.3 year for males; L&#8734 = 232.8 cm, k = 0.1 year-1 and t0 = -2.9 year for females. This difference was thought to be attributable to initially faster growth rate of males until maturity, after which their growth rate slowed below that of females. Number of growth rings at maturity was 8–10 for both males (150 cm PCL) and females (160 cm PCL). The oldest female and male in the sample had 17 (213 cm PCL) and 19 growth rings (192 cm PCL) respectively. Annual growth ring deposition could not be validated using marginal increment ratio analysis because of the small sample size. Geographic variation in growth rate and maximum attainable size was evident between the spinner shark populations of the Indian and Atlantic oceans. Although C. brevipinna grow slowly, the protective nets off the KwaZulu-Natal coast do not appear to have any detrimental effect on the population.Keywords: age, Carcharhinus brevipinna, growth, KwaZulu-Natal, shark, vertebraAfrican Journal of Marine Science 2002, 24: 1–

Do sawfish <i>Pristis</i> spp. represent South Africa's first local extirpation of marine elasmobranchs in the modern era?

<div><p>Largetooth sawfish <i>Pristis pristis</i> and green sawfish <i>P. zijsron</i> were not uncommon in catches made in KwaZulu‑ Natal (KZN) on the east coast of South Africa in the mid part of the last century but apparently have disappeared from this area. This paper traces the decline in sawfish catches from 1951 and assesses the current population status and local extinction risk, based on historical and current records up to 2012. Records were collected from research surveys, literature, media and museum specimens, and through contacting researchers and conservation managers who have worked in KZN coastal and estuarine areas. A total of 150 green sawfish, 7 largetooth sawfish and 89 unidentified sawfish records were located. Most sawfish (115) were caught during a four‑year (1967–1970) gillnetting survey conducted by the Oceanographic Research Institute in the St Lucia estuarine system while 91 were caught in the bather protection nets installed and maintained along the KZN coast by the KwaZulu‑Natal Sharks Board. Sawfish ranged from 63 to 533 cm total length (TL). Sawfish caught in the estuarine environments (mean TL 162 cm [SD 72], <i>n</i> = 95) were significantly smaller than those caught in the inshore marine environments (mean TL 310 cm [SD 109], <i>n</i> = 83), confirming the importance of estuaries as pupping and nursery areas. The St Lucia estuarine system, given the high abundance of sawfish, was determined to be the most important nursery area in KZN. The last sawfish encountered in KZN, which was not identified to species level, was caught in the bather protection nets in 1999 and released alive. Extinction probability analysis indicates that sawfish no longer occur in KZN waters. Anthropogenic changes to the St Lucia estuarine system, as well as to other KZN estuaries, gillnetting for bather protection, and illegal fish harvesting, coupled with a non‑adaptive life‑history style, may have precipitated the disappearance of sawfish from KZN waters.</p></div

DNA from historical and trophy samples provides insights into white shark population origins and genetic diversity

Characterizing genetic variation by retrospective genotyping of trophy or historical artifacts from endangered species is an important conservation tool. Loss of genetic diversity in top predators such as the white shark Carcharodon carcharias remains an issue, exacerbated in this species by declining, sometimes isolated philopatric populations. We successfully sequenced mitochondrial DNA (mtDNA) D-loop from osteodentine of contemporary South African white shark teeth (from 3 jaws), and from 34 to 129 yr old dried cartilage and skin samples from 1 Pacific Ocean and 5 Mediterranean sharks. Osteodentine-derived sequences from South African fish matched those derived from an individual’s finclips, but were generally of poorer quality than those from skin and cartilage of historical samples. Three haplotypes were identified from historical Mediterranean samples (n = 5); 2 individuals had unique sequences and 3 shared the contemporary Mediterranean haplotype. Placement of previously undescribed mtDNA haplotypes from historical material within both the Mediterranean and Pacific clades fits with the accepted intra-specific phylogeny derived from contemporary material, verifying our approaches. The utility of our methodology is in its provision of additional genetic resources from osteodentine (for species lacking tooth pulp) and cartilage of rare and endangered species held in often uncurated, contemporary and historical dry collections. Such material can usefully supplement estimates of connectivity, population history, and stock viability. We confirm the depauperate haplotype diversity of historical Mediterranean sharks, consistent with founding by a small number of Pacific colonizers. The consequent lack of diversity suggests serious challenges for the maintenance of this top predator and the Mediterranean ecosystem