Global trends in teleost fisheries indicate significant population declines. Thus, alternative fisheries are being developed to meet the growing economic and nutritional demands of the expanding human population. Recently, it has been established that elasmobranch fisheries may fulfill these demands. As many elasmobranchs possess life-history characteristics that make them particularly vulnerable to overfishing, it is imperative to develop management strategies prior to the inception of these fisheries to ensure sustainable resource utilisation. In South Africa, elasmobranchs have been commercially exploited since the 1930s. Although generally considered an under-exploited resource, the potential for growth within these fisheries has been recognized. In 2005, the commercial shark fishery will undergo a transition from medium to long-term rights allocations. This represents an ideal opportunity for scientists and managers to develop precautionary species-specific management plans for commercially exploitable elasmobranch species. The soupfin shark (Galeorhinus galeus) is one of the principal target species in South Africa’s shark fisheries. Given its inherent susceptibility to overexploitation, G. galeus was selected as a management priority by South Africa’s regional fisheries organisation. The purpose of this study was to examine and describe the stock status of G. galeus in South Africa, and to develop a precautionary fishery management plan to ensure the sustainability of this resource. Age, growth, and mortality calculations for G. galeus were made from research survey data collected between 1996 and 1999. A small sample size precluded independent analyses of females. The maximum recorded age for G. galeus was 33 years. Estimated von Bertalanffy growth parameters from observed length-at-age for males and combined sexes were: L∞ 1542.8 mm TL, K 0.21 year⁻¹ , t₀ -2.79 year⁻¹ and L∞ 1560.3 mm TL, K 0.19 year¹, t₀ -3.03 year⁻¹, respectively. The age-at-50% maturity was determined to be 6 years, corresponding to 1011 mm TL for males and 1100 mm TL for combined sexes. Natural mortality was calculated as 0.126 yr⁻¹. The rate of instantaneous total mortality was calculated as 0.27 yr⁻¹. Catch trend analysis showed that catches and CPUE of G. galeus are increasing in the demersal longline fishery, and decreasing in the handline fishery. Decreasing catches and CPUE were observed in fishery-independent research survey data. The status of the soupfin shark stock was modelled using per-recruit analysis. The SB/R model indicated the soupfin shark is being optimally exploited and spawner biomass is at 43% of preexploitation levels. Current fishing levels ( F = 0.14 yr⁻¹) approximate the Fsb₄₀ level (F = 0.17 yr¹); thus, an increase in fishing pressure may lead to stock collapse. It was determined that the current age-at-capture (7.9 years) should be increased to 10 years, or 1420 mm TL, to maximize yield and minimize the possibility of recruitment failure. The results of this study indicate a need for immediate scientific and management intervention in South Africa’s soupfin shark fishery. An assessment report and fishery management plan for G. galeus was compiled, and several management options were proposed. These include the implementation of licence and size restrictions, as well as seasonal/area closures. The potential for an experimental gillnet fishery should be investigated.

The bull shark, Carcharhinus leucas, is an important euryhaline predator that is exploited throughout its range for meat and fins. This species is taxonomically paired with the pigeye shark, C. amboinensis. Validity of this group has not been directly tested using molecular markers. Genetic variation and phylogeny was examined with concatenated datasets of mitochondrial genes (cytb, cox1 and 12stRNA16s) for nineteen species, from three families within the order Carcharhiniformes. Whilst there were indications of species pairings within the genus, there was no evidence to suggest that the bull and pigeye sharks should be considered a species group. Phylogenetic analysis failed to resolve Carcharhinus, but confirmed Negaprion as a sister taxon and placed Prionace glauca within Carcharhinus. It remains unclear if the family Sphyrnidae, arose from a Rhizoprionodon or Scoliodon ancestor and future revision of this complex group of sharks is required. Like other large carcharhinid species, C. leucas exhibits a low reproductive rate and long generation times. It is susceptible to localised depletions and such declines have been documented. The global stock structure was assessed by analysing the mitochondrial control region in 245 individuals sampled from eight populations in three ocean basins. The bull shark exhibits relatively high haplotype diversity (0.896 ± 0.010) when compared to other globally-distributed sharks and the nucleotide diversity was similar to others from the genus (0.00465 ± 0.00014). There was significant stock structure found among populations (ΦST=0.736, p<0.00001) and among ocean basins (ΦCT=0.527, p=0.00653). Geneflow between the US Atlantic coastline and Gulf of Mexico was sufficient to consider the area to be a single panmictic population. Coalescent analyses suggest an Indian Ocean origin with population divergences associated with warm interglacials and increased habitat with drop in sea level during the recent Wisconsin glaciation. Seven discrete stock management units for bull sharks are proposed.

The blue shark (Prionace glauca) is a highly migratory pelagic elasmobranch that inhabits ocean basins globally. As a result, this shark is exposed to intensive ocean exploitation by commercial target fisheries, by-catch and for recreational pursuits globally. This top predator is therefore at high risk of becoming overfished. Advances to current knowledge of genetic population structure and diversity of this species would provide vital information required to initiate co-operative management approaches. In this study, the major histocompatibility complex (MHC) class IIa and IIβ genes were successfully isolated and characterised from blue sharks. Phylogenetic trees of the class II genes showed three major clades; one of teleost fish, one of tetrapods and one of sharks. The MHC class IIβ gene exon 2 primers successfully amplified partial sequences in blue sharks from several global locations. Analysis of sequences using denaturing gradient gel electrophoresis (DGGE) suggested the assay resolved different sequences up to one basepair, making the assay potentially very useful with further development. The class II genes presented in this study show conflicting evidence for the presence of more than one class II locus. To explore inheritance patterns of MHC exon 2 diversity, a single blue shark litter (mother + 19 pups) was cloned and sequenced, revealing evidence to suggest the possibility of more than one locus for class IIβ. Statistical analysis of parasite loads and diversities from blue shark spiral valves revealed no definitive population structure, supporting global and North Atlantic mtDNA and microsatellites genetic analyses presented here. The size (fork length) of sharks was found to be potentially influential when modelled with individual microsatellite heterozygosity and fork length. International co-operation will be required to prevent this species becoming extinct from global marine ecosystems. Reductions in numbers could lead to reduced genetic diversity, decreased immunity and ultimately an 'unhealthy' population.

Foraging presents a significant challenge for neonatal predators. Both physical maturation and predatory experience may improve predatory abilities. To tease apart which improvements in predatory abilities were due to increased maturation and which to increased experience, several experiments that isolated the effects of maturation and experience were conducted. Individual whitespotted bamboosharks, Chiloscyllium plagiosum, improved predatory efficiency with both maturation and experience. Physical maturation, when isolated from experience, improved predatory efficiency of naïve sharks foraging on shrimp, an elusive prey, but not of sharks foraging on worms, a non-elusive prey. Predatory experience, when isolated from maturation, improved predatory efficiency of sharks foraging on worms but not of sharks foraging on shrimp. Both maturation and experience are important in the development of whitespotted bamboosharks' predatory abilities and may influence the type of prey they can exploit. To determine whether whitespotted bamboosharksare able to retain the ability to capture and eat prey after a period of prey absence, sharks that had 20 days of foraging experience were denied access to live prey for 18 days, after which they were re-exposed to live prey. Predatory efficiency of sharks did not decrease during the 18 day prey-absence period. After sharks were re-exposed to live prey, their predatory efficiency was similar to that of sharks of the same age with equivalent experience but no prey-absence period, but was higher than that of naïve sharks. Whitespotted bamboosharks retain the ability to catch and consume prey after a short period of prey absence. This retention may improve their ability to forage on prey that is spatially or temporally patchy. To determine whether experience with one prey type affects the whitespotted bambooshark's ability to forage on novel prey, sharks that had 20 days of experience foraging on one type of prey (either worms or shrimp) were given foraging trials with the other prey. Experience with one prey improved sharks abilities to forage on novel; sharks foraging on novel prey were as efficient as sharks that had foraged on that prey for 20 days. Whitespotted bamboosharks can maintain or easily modify many predatory skills when foraging on novel prey.

In February of 2008, two 18-pounder carronades were discovered off the Oregon coast near Arch Cape in Clatsop County. In addition to the carronades, several associated artifacts were collected from the site, including lengths of chain, a heavy iron wedge and a mooring shackle. The carronades and associated artifacts were transported to Texas A&M University's Conservation Research Laboratory for long-term preservation and conservation. While the primary objective of this thesis is to detail the various methods used in conserving the Arch Cape artifact assemblage, the work also serves as an analysis of the carronades themselves. The design and caliber of the guns as well as historic accounts suggest the carronades are associated with Shark, a U.S. Navy schooner built at the Washington Navy Yard in 1821. During its 25-year career, Shark spent 18 years operating in the Atlantic Ocean suppressing piracy in the West Indies and the slave trade off the western coast of Africa. The schooner was also stationed in the Mediterranean Sea and the Pacific Ocean before a final survey in the Oregon Territory in 1846 resulted in its loss in the Columbia River. It was reported that part of Shark's wreckage with three attached carronades came ashore south of Hug Point. In January 1898, a winter storm revealed one of the carronades, which was recovered, along with the schooner's capstan, a cleat and a chock. The discovery of the pair of carronades in 2008 is strong evidence that these, along with the carronade recovered in 1898, are the three guns attributed to USS Shark's wreckage. This thesis will also analyze indentifying features on the carronades, such as maker's marks and serial numbers, and explore the origins of the guns, determining how they came to be on board the American schooner by referring to records such as the Woolwich proof books and armament lists. The harsh conditions of the coastal environment affect the assemblage in a number of ways. While much of the metal of the assemblage is stable and can be treated using electrolysis, the delicate organic materials must undergo specific treatments. Since these organic artifacts were treated primarily with silicone oil, the thesis will compare some of the final results of using this polymer passivation technology with different materials, such as wood, leather and cordage. Finally, in addition to detailing the conservation of the assemblage, this thesis describe the reverse engineering required to disassemble the carronades and gun carriages.

Despite being one of the most recognizable sea creatures in the world, sharks remain widely misunderstood by the public. Media coverage often sensationalizes them as dangerous creatures, when in reality, humans pose a much more significant threat to sharks than vice versa. Over the past few decades, overfishing has decimated populations worldwide as demand increases for byproducts such as meat, cartilage, and fins in particular, a crucial ingredient in the Chinese delicacy of shark fin soup. Finning, a particularly inefficient practice that promotes overfishing and waste, occurs when fishers cut off fins at sea and throw carcasses overboard. As sharks play an important role in marine ecosystems as apex predators and are slow to reproduce, increased attention to shark conservation is urgently needed. Although there have been attempts by international organizations such as the United Nations and by individual countries, current legislation has proven to be inadequate in combating shark exploitation. Though public awareness is on the rise thanks to increased media coverage and environmental advocacy, sharks still need greater protection in the face of overharvest and stock depletion. This thesis details the current state of shark exploitation, including shark biology, public perceptions of sharks, and current levels of shark finning, as well as the economics behind the trade. It also analyzes previous actions taken both at the international and national levels. Finally, it recommends further actions to be undertaken in order to preserve declining shark populations and keep them from extinction.

The silky shark Carcharhinus falciformis forms the primary elasmobranch bycatch in tuna purse seine fisheries using fish aggregating devices (FADs) in all of the world’s tropical oceans. Its life-history traits of slow growth, late maturation and low fecundity make it vulnerable to over exploitation, as is apparent from historical bycatch trends. Very little is known about the associative behaviour of this species with floating objects, information which is essential in formulating effective mitigation and management measures. This study aims to address this knowledge gap through the use of various electronic tagging techniques in conjunction with dietary analysis. Dietary data were collected from 323 silky sharks incidentally caught at FADs. Approximately 40 percent of the diet consisted of prey associated with FADs while the remaining 60 percent were non-associated species of crustaceans, cephalopods and fishes. These results suggest that the associative behaviour is not primarily driven by trophic enhancement, but is likely a combination of predator avoidance, social interactions and feeding. Fine-scale behavioural data from silky sharks associated with drifting FADs were collected through the use of acoustic telemetry techniques. Acoustic tags were implanted into 38 silky sharks (69- 116 cm TL) at eight FADs. FADs were equipped with satellite linked acoustic receivers and abandoned to drift freely. Presence/absence and swimming depth data were telemetered via the Iridium satellite system. A total of 300 d of behavioural data were collected from 20 tagged individuals. Individuals remain associated with the same FAD for extended periods (min = 2.84 d, max = 30.60 d, mean = 15.69 d). Strong diel patterns were observed in both association and swimming depth. Typically individuals moved away from FADs after sunset and return later during the night, then remain closely associated until the following evening. Vertical behaviour also changed around sunset with sharks using fairly constant depths, within the upper 25 m, during the day and switching to rapid vertical movements during the night, with dives in excess of 250 m recoded. Broader scale movement behaviour was investigated using pop-up archival satellite tags (PSATs). Tags were deployed on 46 silky sharks (86-224.5 cm TL) for a total of 1495 d. Light data were used to calculate geolocation estimates and reconstruct the sharks’ trajectories. Movement patterns differed between animals and according to deployment duration. Several extensive horizontal movements were observed, with an average track length of 3240 km during an average tag deployment of 44.02 d. Horizontal movement patterns were found to correlate very closely with drift patterns of FADs. Consequently, it appears that the movement behaviour of juvenile silky sharks is strongly influenced by the movement of drifting FADs in this region. Ghost fishing of silky sharks through entanglement in FADs was also investigated using data derived from PSATs as well as underwater visual censuses. Thirteen per cent of the tagged sharks became entangled in FADs and entangled sharks were observed in 35 percent of the 51 FADs surveyed. Using this information in conjunction with estimated time that sharks remained entangled in the FAD (from depth data from PSATs), and scaling up according to estimates of FAD numbers, it was found that between 480 000 and 960 000 silky sharks are killed annually in this manner in the Indian Ocean. Subsequent management measures in this region prevent the deployment of FADs with netting that could lead to entanglement. Overall, floating objects appear to play a significant role in the juvenile life stages of silky sharks in this region. While their association with floating objects is clearly advantageous in an evolutionary sense, under current tuna fishery trends, this behaviour is certainly detrimental for the population.

Passive acoustic monitoring has been successfully used on many elasmobranch species, but no such study has yet been published for the whale shark (Rhincodon typus). In some ways this is surprising as the known whale shark aggregation sites would seem to be ideal targets for this method. For this dissertation, two acoustic studies were carried out in Saudi Arabia and Tanzania. Each was performed in parallel with visual surveys and the Saudi population was also studied using satellite telemetry. Sighting and acoustic data were compared at both sites, and the results were mixed. The acoustic monitoring largely confirmed the results of visual surveys for the Saudi Arabian sharks, including seasonality, residency and a degree of parity and integration between the sexes that is unique to this site. Satellite tracks of tagged Saudi sharks were used to confirm that some animals migrated away from the aggregation site before returning in subsequent seasons, confirming philopatric behavior in this species. In contrast, the acoustic results in Tanzania demonstrated year-round residency of whale sharks in the area, despite seasonal declines in visually estimated abundance. Seasonal changes in habitat selection render the sharks at this site temporarily cryptic to visual sampling. The differing results are compelling because both the philopatric behavior demonstrated in Saudi Arabia and the cryptic residency of the Tanzanian sharks could explain the seasonal patterns in whale shark abundances reported at other aggregation sites. Despite their differences, both sites in this study can be classified as secondary whale shark nurseries and each may be a vital feeding ground for its respective population.

In this dissertation an innovative technology to study whale sharks, Rhincodon typus is presented. The Integrated Satellite and Acoustic Telemetry project (iSAT) combines underwater acoustic telemetry, autonomous navigation and radio frequency communications into a standalone system. The whale shark, a resident of the Saudi Arabian Red Sea, is the target of the study. The technology presented is designed to help close current gaps in the knowledge of whale shark biology; these are gaps that prohibit the design of optimal conservation strategies. Unfortunately, the various existing tracking technologies each have limitations and are unable to solve all the unanswered questions. Whale shark populations are increasingly threatened by anthropogenic activities such as targeted and indirect fishing pressure, creating an urgent need for better management practices. This dissertation addresses the current state-of-the-art of relevant technologies, including autonomous surface vehicles (ASVs), sensors for research in the ocean and remote monitoring of wild fauna (biotelemetry). iSAT contains components of all of these technologies, but the primary achievement of this dissertation is the development of iSAT’s Acoustic Tracking System (ATS). Underwater, the most efficient way of transmitting energy through long distances is sound. An electronic tag is attached to an animal and works as its acoustic identifier. iSAT’s hydrophone array detects the presence and direction of the acoustic signal generated by the tag. The expected performance, range, and capacity to tell the direction to the tag are explained and compared to the actual measured values. The first operational iSAT ATS is demonstrated. This work represents significant advancement towards a fully autonomous iSAT system. Developments on the power electronics, navigation, renewable energy harvesting, and other modules are included in this research. With the recent integration of digital acquisition systems, iSAT’s capabilities were increased to minimize its size and allow it to communicate with other acoustic systems. Future engineering works are still necessary to achieve a fully automated system, but the current developments with the ATS have immediate applications.

Thesis (Ph. D.)--Rhodes University, 2006. / Title from PDF t.p. (viewed on Apr. 12, 2007). Includes bibliographical references (p. 184-207).