Comparative morphology of rostral cartilages in extant mackerel sharks (Chondrichthyes, Lamniformes, Lamnidae) using CT scanning

A comparative study of rostral morphology of extant mackerel sharks (Lamniformes, Lamnidae) is presented. Based on computed tomography (CT) scans of fresh specimens, 3D reconstructions, dried museum chondrocrania and the available literature, detailed morphological descriptions of the rostral cartilages are provided for the type species of all three extant lamnid genera, namely Carcharodon carcharias (Linnaeus, 1758), Isurus oxyrinchus Rafinesque, 1810 and Lamna nasus (Bonnaterre, 1788), and compared with those of I. paucus Guitart Manday, 1966 and L. ditropis Hubbs & Follett, 1947. Despite intraspecific variation, the rostral cartilages of all extant lamnids present significant differences that allow genusand species-level identification, which is especially of use to identify fossil rostral nodes of these particular taxa. The main differences were found to be in overall calcification of the rostrum (Lamna > Isurus > Carcharodon), general configuration of the rostral open space, position of the base of the lateral rostral cartilages, (non-)abutting lateral cartilages, (absent) rostral keels and shape of the rostral node. In cross section, the base of the rostral node is rounded in Lamna, Y-shaped in Isurus and uncalcified in juvenile and subadult Carcharodo (tesserae absent)

Spatio-temporal genetic tagging of a cosmopolitan planktivorous shark provides insight to gene flow, temporal variation and site-specific re-encounters

Migratory movements in response to seasonal resources often influence population structure and dynamics. Yet in mobile marine predators, population genetic consequences of such repetitious behaviour remain inaccessible without comprehensive sampling strategies. Temporal genetic sampling of seasonally recurring aggregations of planktivorous basking sharks, Cetorhinus maximus, in the Northeast Atlantic (NEA) affords an opportunity to resolve individual re-encounters at key sites with population connectivity and patterns of relatedness. Genetic tagging (19 microsatellites) revealed 18% of re-sampled individuals in the NEA demonstrated inter/multi-annual site-specific re-encounters. High genetic connectivity and migration between aggregation sites indicate the Irish Sea as an important movement corridor, with a contemporary effective population estimate (Ne) of 382 (CI = 241–830). We contrast the prevailing view of high gene flow across oceanic regions with evidence of population structure within the NEA, with early-season sharks off southwest Ireland possibly representing genetically distinct migrants. Finally, we found basking sharks surfacing together in the NEA are on average more related than expected by chance, suggesting a genetic consequence of, or a potential mechanism maintaining, site-specific re-encounters. Long-term temporal genetic monitoring is paramount in determining future viability of cosmopolitan marine species, identifying genetic units for conservation management, and for understanding aggregation structure and dynamics

Population connectivity of the highly migratory shortfin mako (Isurus oxyrinchus Rafinesque 1810) and implications for management in the Southern Hemisphere

Published: 20 November 2018In this paper we combine analyses of satellite telemetry and molecular data to investigate spatial connectivity and genetic structure among populations of shortfin mako (Isurus oxyrinchus) in and around Australian waters, where this species is taken in recreational and commercial fisheries. Mitochondrial DNA data suggest matrilineal substructure across hemispheres, while nuclear DNA data indicate shortfin mako may constitute a globally panmictic population. There was generally high genetic connectivity within Australian waters. Assessing genetic connectivity across the Indian Ocean basin, as well as the extent that shortfin mako exhibit sex biases in dispersal patterns would benefit from future improved sampling of adult size classes, particularly of individuals from the eastern Indian Ocean. Telemetry data indicated that Australasian mako are indeed highly migratory and frequently make long-distance movements. However, individuals also exhibit fidelity to relatively small geographic areas for extended periods. Together these patterns suggest that shortfin mako populations may be genetically homogenous across large geographical areas as a consequence of few reproductively active migrants, although spatial partitioning exists. Given that connectivity appears to occur at different scales, management at both the national and regional levels seems most appropriate.Shannon Corrigan, Andrew D. Lowther, Luciano B. Beheregaray, Barry D. Bruce, Geremy Cliff, Clinton A. Duffy, Alan Foulis, Malcolm P. Francis, Simon D. Goldsworthy, John R. Hyde, Rima W. Jabado, Dovi Kacev, Lindsay Marshall, Gonzalo R. Mucientes, Gavin J. P. Naylor, Julian G. Pepperell, Nuno Queiroz, William T. White, Sabine P. Wintner and Paul J. Roger

Population structure and biology of shortfin mako, Isurus oxyrinchus, in the south-west Indian Ocean

Abstract. The population structure, reproductive biology, age and growth, and diet of shortfin makos caught by pelagic longliners (2005–10) and bather protection nets (1978–2010) in the south-west Indian Ocean were investigated. Themean fork length (FL) of makos measured by observers on longliners targeting tuna, swordfish and sharks was similar, and decreased from east to west, with the smallest individuals occurring near the Agulhas Bank edge, June to November. Nearly all makos caught by longliners were immature, with equal sex ratio. Makos caught by bather protection nets were significantly larger, males weremore frequent, and 93%ofmales and 55%of females weremature. Agewas assessed from band counts of sectioned vertebrae, and a von Bertalanffy growthmodel fitted to sex-pooled length-at-age data predicted a birth size (L0) of 90 cm, maximum FL (LN) of 285 cm and growth coefficient (k) of 0.113 y 1. Males matured at 190 cm FL, aged 7 years, and females at 250 cm, aged 15 years. Litter sizes ranged from nine to 14 pups, and the presence of gravid females in bather protection nets suggested that some pupping occurred in shelf waters. Teleosts (mainly Trachurus capensis) occurred in 84 % of stomachs collected on longliners, whereas elasmobranchs (63.5%) were most common in samples collected from bather protection nets, followed by teleosts (43.1%) and cephalopods (36.5%). Larger prey siz

Evidence for multiple paternity and confirmation of an Indo-Pacific origin of blacktip shark Carcharhinus limbatus occurring in South Africa

The blacktip shark Carcharhinus limbatus is a cosmopolitan species found in warm-temperate, subtropical and tropical waters around the world. The research here aimed to assess whether multiple paternity exists in South African C. limbatus and to confirm phylogeographic patterns previously observed within the species. A minimum and maximum frequency of 50% and 71% multiple paternity, respectively, were observed in 14 litters genotyped with five microsatellite markers. Based on the mitochondrial control region, relatively high nucleotide and haplotype diversity characterised the South African sampling population, and pairwise φST values indicated that it significantly differed from the populations of the Pacific and the western Atlantic oceans. The haplotype network showed thatthe South African samples were grouped closely with the Australian, Indo-Pacific and West African C. limbatus samples, which is suggestive of an Indo-Pacific origin for this population. This study is the first to report multiple paternity in this species. Furthermore, the results reveal that C. limbatus from South Africa is genetically diverse and phylogeographically distinct from most other C. limbatus populations.Keywords: elasmobranchs, genetic divergence, haplotypes, microsatellites, mitochondrial DNA, polyandry, phylogeographic analysi

Ontogenetic vertebral growth patterns in the basking shark <i>Cetorhinus maximus</i>

Age and growth of the basking shark Cetorhinus maximus (Gunnerus) was examined using vertebral samples from 13 females (261 to 856 cm total length [TL]), 16 males (311 to 840 cm TL) and 11 specimens of unknown sex (376 to 853 cm TL). Vertebral samples were obtained worldwide from museums and institutional and private collections. Examination of multiple vertebrae from along the vertebral column of 10 specimens indicated that vertebral morphology and band pair (alternating opaque and translucent bands) counts changed dramatically along an individual column. Smaller sharks had similar band pair counts along the length of the vertebral column while large sharks had a difference of up to 24 band pairs between the highest and lowest count along the column. Our evidence indicates that band pair deposition may be related to growth and not time in this species and thus the basking shark cannot be directly aged using vertebral band pair counts

South Africa preliminary investigation of vertebral growth rings in the basking shark Cetorhinus maximus(Gunnerus)

Conference Abstracts AES/ASIH , Norman , Oklahoma , May 26-31 200

Spatial and ontogenetic variation in growth of nursery-bound juvenile lemon sharks, Negaprion brevirostris: a comparison of two age-assigning techniques

We compared growth rates of the lemon shark, Negaprion brevirostris, from Bimini, Bahamas and the Marquesas Keys (MK), Florida using data obtained in a multi-year annual census. We marked new neonate and juvenile sharks with unique electronic identity tags in Bimini and in the MK we tagged neonate and juvenile sharks. Sharks were tagged with tiny, subcutaneous transponders, a type of tagging thought to cause little, if any disruption to normal growth patterns when compared to conventional external tagging. Within the first 2 years of this project, no age data were recorded for sharks caught for the first time in Bimini. Therefore, we applied and tested two methods of age analysis: ( 1) a modified 'minimum convex polygon' method and ( 2) a new age-assigning method, the 'cut-off technique'. The cut-off technique proved to be the more suitable one, enabling us to identify the age of 134 of the 642 previously unknown aged sharks. This maximised the usable growth data included in our analysis. Annual absolute growth rates of juvenile, nursery-bound lemon sharks were almost constant for the two Bimini nurseries and can be best described by a simple linear model ( growth data was only available for age-0 sharks in the MK). Annual absolute growth for age-0 sharks was much greater in the MK than in either the North Sound (NS) and Shark Land (SL) at Bimini. Growth of SL sharks was significantly faster during the first 2 years of life than of the sharks in the NS population. However, in MK, only growth in the first year was considered to be reliably estimated due to low recapture rates. Analyses indicated no significant differences in growth rates between males and females for any area