A dorsal-fin photo-identification technique paired with a non-invasive parallel laser photogrammetry technique was used to non-invasively identify individual Sphyrna mokarran over time. Based on the data collected over a duration of 59 days, 16 different S. mokarran (mean±s.d. pre-caudal length: 220⋅82±13⋅66 cm; mean±s.d. cephalofoil width: 71⋅38±7⋅94 cm) were identified using dorsal-fin photo-identification, with a mean±s.d. shark re-sighting frequency of 4⋅05±3⋅06 at-sea days. The results illustrate a high S. mokarran sighting rate and therefore, the utilization of parallel laser photogrammetry and dorsal-fin photo-identification may be a plausible multi-year approach to aid in non-invasively determining the growth rate and inter-annual site fidelity of these animals.
ABSTRACT In many fisheries, some component of the catch is usually released. Quantifying the
effects of capture and release on fish survival is critical for determining which practices are sustainable,
particularly for threatened species. Using a standardized fishing technique, we studied
sublethal (blood physiology and reflex impairment assessment) and lethal (post-release mortality
with satellite tags) outcomes of fishing stress on 5 species of coastal sharks (great hammerhead,
bull, blacktip, lemon, and tiger). Species-specific differences were detected in whole blood
lactate, partial pressure of carbon dioxide, and pH values, with lactate emerging as the sole
parameter to be significantly affected by increasing hooking duration and shark size. Species-specific
differences in reflex impairment were also found; however, we did not detect any significant
relationships between reflex impairment and hooking duration. Taken together, we ranked each
species according to degree of stress response, from most to least disturbed, as follows: hammerhead
shark > blacktip shark > bull shark > lemon shark > tiger shark. Satellite tagging data
revealed that nearly 100% of all tracked tiger sharks reported for at least 4 wk after release, which
was significantly higher than bull (74.1%) and great hammerhead (53.6%) sharks. We discuss
which mechanisms may lead to species-specific differences in sensitivity to fishing and suggest
that observed variation in responses may be influenced by ecological and evolutionary phenomena.
Moreover, our results show that certain species (i.e. hammerhead sharks in this study) are
inherently vulnerable to capture stress and mortality resulting from fisheries interactions and
should receive additional attention in future conservation strategies.
Many sharks have life history characteristics (e.g., slow growth, late age at maturity, low fecundity, and long gestation periods) that make their populations vulnerable to collapse due to overfishing. The porbeagle (Lamna nasus), bull shark (Carcharhinus leucas), great hammerhead (Sphyrna mokarran), and smooth hammerhead (S. zygaena), are all commercially exploited. The population genetic structure of these species was assessed based on globally distributed sample sets using mitochondrial control region (mtCR) sequences and/or nuclear markers. Complex patterns of evolutionary and demographic history were inferred using coalescent and statistical moment-based methods. All four species showed statistically significant genetic partitioning on large scales, i.e., between hemispheres (L. nasus mtCR φST = 0.8273) or oceanic basins (C. leucas nuclear FST = 0.1564; S. mokarran mtCR φST = 0.8745, nuclear FST = 0.1113; S. zygaena mtCR φST = 0.8159, nuclear FST = 0.0495). Furthermore, S. zygaena mtCR sequences indicated statistically significant matrilineal genetic structuring within oceanic basins, but no intrabasin structure was detected with nuclear microsatellites. S. mokarran showed statistically significant genetic structure between oceanic basins with both nuclear and mitochondrial data, albeit with some differences between the two marker types in fine scale patterns involving northern Indian Ocean samples. A microsatellite assessment of C. leucas demonstrated no population structuring within the Atlantic or Indo-Pacific, with the exception that samples from Fiji were differentiated from the remaining Indo- Pacific Ocean locations. In contrast, the L. nasus mitochondrial and nuclear ITS2 sequences revealed strong northern vs. southern hemispheric population differentiation, but no differentiation within these hemispheres. These geographic patterns of genetic structure were used to determine the source of fins obtained from the international fin trade and to develop forensic tools for conservation.
ABSTRACT The Government of Costa Rica and the Government of Ecuador
have submitted a proposal for the inclusion of the Great
Hammerhead Shark (Sphyrna mokarran) on CMS Appendix II for
the consideration of the 11th Meeting of the Conference of the
Parties (COP11), 4-9 November 2014, Quito, Ecuador.
The proposal is reproduced under this cover for a decision on its
approval or rejection by the Conference of the Parties.
ABSTRACT We provide pilot data from a satellite-tracked great hammerhead shark Sphyrna mokarran in the Atlantic, representing the first such data on this species in the literature. The 250 cm shark was tagged off the coast of the middle-Florida Keys (USA) and transmitted for 62 d. During this time it migrated a minimum distance of ~1200 km northeast from the coast of Florida, into pelagic international waters of the Northwest Atlantic. When compared to the primary literature, this migration represented a northeasterly range extension for this species off the continental slope in the Atlantic. The significance of this range extension is discussed in terms of the vulnerability of S. mokarran to target and non-target fisheries.
The life histories of two globally endangered hammerhead sharks, Sphyrna lewini and Sphyrna mokarran, were examined using samples collected from a range of commercial fisheries operating along the east coast of Australia. The catch of S. lewini was heavily biased towards males, and there were significant differences in von Bertalanffy growth parameters (L(∞) and k) and maturity [stretched total length (L(ST)) and age (A) at which 50% are mature, L(ST50) and A(50)] between those caught in the tropics (L(∞) = 2119 mm, k = 0·163, L(ST50) = 1471 mm, A(50) = 5·7 years) and those caught in temperate waters (L(∞) = 3199 mm, k = 0·093, L(ST50) = 2043 mm, A(50) = 8·9 years). The best-fit estimates for a three-parameter von Bertalanffy growth curve fit to both sexes were L(∞) = 3312 mm, L(0) = 584 mm and k = 0·076. Males attained a maximum age of 21 years and grew to at least 2898 mm L(ST). The longevity, maximum length and maturity of females could not be estimated as mature animals could not be sourced from any fishery. Length at birth inferred from neonates with open umbilical scars was 465-563 mm L(ST). There was no significant difference in length and age at maturity of male and female S. mokarran, which reached 50% maturity at 2279 mm L(ST) and 8·3 years. Sphyrna mokarran grew at a similar rate to S. lewini and the best-fit estimates for a two-parameter von Bertalanffy equation fit to length-at-age data for sexes combined with an assumed mean length-at-birth of 700 mm were L(∞) = 4027 mm and k = 0·079. Females attained a maximum age of 39·1 years and grew to at least 4391 mm L(ST). The oldest male S. mokarran was 31·7 years old and 3691 mm L(ST). Validation of annual growth-band deposition in S. mokarran was achieved through a mark, tag and recapture study.
The relationship between form and function is often used to elucidate the biological
role of a structure. Hammerhead sharks offer a unique opportunity to study form and
function through phylogeny. Because sphyrnid sharks display a range of cranial
morphologies this group can be used to address questions about the evolution of cranial
design and investigate the effects of changes in head morphology on feeding structures
and bite force. Geometric morphometrics, volumetric analyses, morphological
dissections, and phylogenetic analyses of the cephalofoil were used to gain insight into
changes in cranial design through evolutionary history. External morphometrics and
internal volumetric analyses indicated that while the external shape of the cephalofoil and
placement of the sensory structures is variable through evolutionary history, the volumes
of the internal cranial elements do not change. Constructional constraints within the
cephalofoil were confined to sensory structures while feeding morphology remained
relatively unchanged. Analysis of the morphology and biomechanics of the feeding
apparatus revealed that through phylogeny the feeding system does not change among
sphyrnid species. However, size-removed bite force was lower than predicted for all
sphyrnid species except Sphyrna mokarran. Despite differences in head morphology between sphyrnid and carcharhinid sharks, the feeding bauplan is conserved in sphyrnid
sharks with few changes to the feeding structures. Instead the chondrocranial and
sensory structures are modified around the relatively static feeding core. Finally, the
durophagous S. tiburo was found to consume hard prey in a manner that is
biomechanically and morphologically different from other durophagous fishes.
Furthermore, the diet of S. tiburo is constrained by the properties of its preferred prey.