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The 4th International Whale Shark Conference
- Conference date: 16-18 May 2016
- Location: Doha, Qatar
- Volume number: 2016
- Published: 15 May 2016
61 - 67 of 67 results
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Horizontal and vertical movements of the whale shark, Rhincodon typus, in the southern waters of Japan
Background Conservation of whale sharks is making remarkable advances through many studies ongoing in tropical and sub-tropical oceans. However, there have been few studies in the North Pacific Ocean. Some whale shark appearances, as well as by-catch by set-net and purse seining in the southern waters of Japan are reported every year. These waters are important for the conservation ecology of whale sharks because they are the northern limit of the whale shark's distribution and have high productivity influenced by the Kuroshio and Oyashio Currents. However, the habitat and movement of whale sharks around Japan in the North Pacific Ocean are poorly understood. Approach To investigate the habitat and movement of the whale shark, two whale sharks were tagged with PAT-tags (MK-10, Wildlife) and released off the coast of Kouchi, Japan in October 2013 (WS13: 4.2 m in total length) and June 2014 (WS14: 7.2 m). For biological studies and rearing trials, WS13 had been reared for 6 years and 4 months in the Osaka Aquarium of KAIYUKAN, Osaka, and WS14 had been reared for 4 months in the Osaka Aquarium Biological Research Institute of Iburi Center (OBIC) of KAIYUKAN, Kochi, Japan before tagging. The PAT-tags recorded ambient temperature, swimming depth and light level data for 30 and 90 days, respectively, until the detached from the whale shark. After the PAT-tag detachment, the tag floats to the surface and transmits the sampled data via the Argos satellite system. Geolocations of tagged sharks were estimated using light measurement data from the tag and sea surface temperature from the satellite. The horizontal and vertical movements were examined in relation to oceanographic conditions. Results The two sharks moved in the same direction to the east along the Kuroshio Current after being released, despite being released in different seasons. However, WS13 remained in the eddy in the south of the Kuroshio Current, while WS14 crossed the Kuroshio Current to north and remained in the eddy near the Kuroshio-Oyashio transitional area. The total distance WS13 traveled was 1,407 km over 30 days (48.5 km/day), and WS14 traveled 3,022 km over 90 days (29.0 km/day). The mean daily speed while moving along the Kuroshio Current was higher than while remaining in the eddy for both sharks. The primary swimming depth was surface mixed water where the temperature was above 20 °C. The two sharks spent most of their time near the surface above 10 m depth. Diving over the mesopelagic zone (>200 m depth) was rarely observed while the two sharks were traveling along the Kuroshio Current, and wasn't observed while the sharks remained in the eddy. The maximum swimming depth for WS13 was 632 m, and for WS14 was 1560 m, and lowest temperature recorded was 7.1 °C for WS13 and 2.4 °C for WS14 when the sharks were at their maximum depth. Conclusions In southern waters of Japan, horizontal movements of whale sharks are influenced by the Kuroshio Current and the eddy. Their vertical movements are regulated by the thermocline and the threshold temperature was around 20 °C
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Applications for genetic inference to characterise a cryptic life-stage in the whale shark
Background Research efforts on whale sharks have so far been limited to sub-adult males which make-up the vast majority of aggregations around the world. The movements of mature sharks, their reproductive techniques and key habitats remain poorly understood, whilst details of this demographic group are the most important to mitigate current threats. This quandary qualifies the use of indirect analyses such as genetic inference to characterise cryptic life-stages of the species. Approach Tissue samples will be collected from free-swimming whale sharks from locations around the WIO with past biopsy efforts providing additional tissue from every tropical ocean. Photographic identification, approximate visual size and gender information will be recorded for each individual. Microsatellite markers will be extracted from the samples using species-specific primers from previous studies. Additional open access sequences will be obtained via GenBank for appropriate locations. Software packages simulating modes of inheritance such as GERUD will be used to reconstruct parental genotypes. Results This is an outline of potential results of the study. Parental genotype reconstruction can provide information on: 1) Number of parents per litter – maternal genotypes will be reconstructed first as the likelihood of sampling littermates is higher than sampling offspring from different females who happened to mate with the same male. Paternal genotypes can be determined once the maternal genotypes are removed from the progeny sequences. 2) Juvenile recruitment – survival rate of individuals per litter, considering however that juvenile female whale sharks are underrepresented in the majority of sampling areas. Incomplete reconstruction of a parental genotype suggests incomplete offspring sampling. 3) Reproductive mode – i.e. monoor polyandry, demonstrated by single or multiple male genotypes per litter (respectively), which may confirm or refute the single only other demonstration of reproductive mechanism, monandry, in the species. 4) Breeding site fidelity – common and complete parental genotypes of either or both parents within an aggregation or in associated areas (assuming monandry) suggests that whale sharks return to or remain in a common area to pup whereas multiple incomplete genotypes may suggest random dispersal from any given pupping site. Conclusions The reproductive patterns of mature sharks, as inferred by these analyses, will define whale shark movements within their circumglobal range and may highlight important habitats such as breeding or pupping grounds. Resources for protecting the species will be limited and so must target these groups and areas to be most effective at mitigating threats and conserving the species.
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Improving laser-photogrammetry precision for estimates of whale shark total length and applying them to a previously unstudied aggregation of whale sharks at St. Helena Island
Authors: D. Harry Webb, Elizabeth Clingham, Alex Collier, Taylor Stoll and Dr. Alistair DM DoveBackground Laser-photogrammetry is a non-invasive technique used for size estimation in applications where traditional methods to determine length are either impractical or unreliable. Laser photogrammetry provides greater precision for measuring free-swimming whale sharks when compared to previous methods that compare whale sharks to objects of known size such as boat length, diver height, and rope length. These estimates are subject to the effects of water movement and visual distortion from refraction. Laser-photogrammetry uses a known reference distance projected onto a surface using pre-calibrated lasers to standardize measurements and utilizes ratios of pixel-counts to calculate a length estimate. Approach Laser-photogrammetry has been demonstrated as a useful technique for determining body length estimates in free-swimming whale sharks, Rhincodon typus (Rohner et al. 2011), but measures of variance have been lacking because repeat measurements on the same individual animals are rarely obtained. Georgia Aquarium houses 4 juvenile whale sharks that can be unequivocally identified and photographed repeatedly, and therefore provided an opportunity to refine the techniques described by Rohner. We then applied them to an aggregation of whale sharks at St. Helena Island. Results Using a similar laser-photogrammetry apparatus and body proportion equations for determining total length prescribed by Rohner, we observed relatively high variance on repeated measurements made on the same animal, such that confidence intervals for any given individual measurement estimate were unacceptably high. Using measures of central tendency from multiple measurements, rather than relying on single images, provided measurement estimates with acceptable confidence intervals for determining total length. We applied the central tendency technique to characterize lengths in a previously unstudied whale shark aggregation in the southern Atlantic Ocean off of St. Helena Island in 2015 and 2016. We used the mean of 4–27 repeated measurements to determine total length estimates of the individuals photographed in St. Helena during these time periods, instead of relying on single-point photos to determine length estimates for the study. Conclusions At 8.4–10.6 m total length, St. Helena animals are larger than those found in juvenile-dominated coastal aggregation sites like Yucatan, Mexico, but smaller than the large solitary females found in Galapagos. The central tendency approach represents a significant improvement to the photogrammetry method, but it increases workload significantly, so there is still a need to develop non-invasive measurement methods that are accurate, precise, and quick.
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Scarring instance and healing capabilities of whale sharks and possible implications
Authors: Freya C. Womersley, Savinien T. Leblond and David R.L. RowatBackground With increasing levels of tourism and other anthropogenic activities around whale shark aggregations globally there is an increased risk of physical damage to sharks from boat collisions. As such, documenting the occurrence of injuries to sharks can be a useful method of recording the impacts of tourism and other marine based activities as well as the effectiveness of management efforts. The seasonal whale shark aggregation off Djibouti has seen an increase in both physical scarring and tourism and is used here as a case study. Approach Scarring records and photos in the Djibouti whale shark database from 2009 to 2015 were reviewed to establish instance and effects of injury on the viability of whale sharks. To calculate the level of injury, in-water sighting data, which recorded scarring, were sorted into major or minor scar categories after the methods of Speed et al. (2008). Major scars were classified as being potentially life threatening and include fin amputation and lacerations penetrating the sub-dermal layer. The probable origin of the scars was also attributed where possible. To avoid overestimation of population scarring and to make results comparable across aggregations, minor scars (such as abrasions, small bites and nicks) were omitted. To quantify medium-term effects of injury, photographic evidence from returning whale sharks was reviewed to estimate healing rates. Healing rates were obtained using the maximum number of years between observing a fresh injury and a fully healed scar. A fully healed scar was defined as an injury with no non-skin/sub-dermal tissue visible. Results The incidence of major scarring recorded in the Djibouti aggregation varied during the study period from a minimum of 15.6% in 2011 to 27.3% in 2015. Of these, 57.9% were attributable to boat strikes in 2011 compared to 40% in 2015. Lacerations to fins showed the quickest healing rates. Sharks observed with fresh lacerations to the first dorsal fin indicative of propeller strikes showed scar-tissue growth on subsequent re-sighting and fully healed scars within a year. Lacerations to the main body of the sharks showed healing rates of a maximum of two years. Amputations showed a maximum healing time of one year but little capacity for tissue regeneration. However, one case of a partially amputated first dorsal fin showed full re-growth of the fin after five years, an instance that is exceptional and has not been recorded before. Conclusions When reviewing scar photos it is clear that whale sharks have the ability to tolerate major injuries through their extraordinary regenerative capabilities. This suggests that whale sharks can recover from boat strikes; however, sharks that did not survive strikes will not be re-recorded and would show as a loss from the dataset. Similarly, the long-term hindrances to normal behavior that are caused by major injuries remain largely unknown. The study reinforces the need for a series of regulations including speed limits to be implemented and enforced within the study site, Arta Marine Protected Area, Djibouti. This approach of recording scars can be applied to other shark populations to improve understanding of shark healing capabilities and the species as a whole.
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Stable isotope analysis for the whale shark in the waters off Taiwan
Authors: Chi-Ju Yu, Shoou-Jeng Joung, Kwang-Ming Liu, Hua-Hsun Hsu and Chia-Yen LinBackground The whale shark, Rhincodon typus, was utilized extensively in Taiwan before 1996. A quota management measure was put in place in 2002, and the whale shark fishery was completely banned in 2008. Biological studies including age and growth, and migration/ movement have been conducted. However, the feeding ecology of whale sharks in different life history stages and sexes in Taiwan waters (Northwest Pacific Ocean) is still unknown. Approach The stable isotope technique was used to analyze the tissue of whale sharks to understanding their feeding ecology. The ´13C value can be used to indicate the foraging habitat of fish, and the ´15N value can be used to estimate the relative position of the consumer in the ecosystem. The specimens (tissue) were taken from individuals entangled in set nets during the period 2008 – 2013 in Taiwan. Results In total, 66 tissue samples from 42 males and 24 females, ranging from 2.84 to 11.90 m TL (total length) were used in stable isotope analysis. Among these specimens 50 and 16 were from the eastern and western waters off Taiwan, respectively. The value of ´13C was from –13.68 to –18.42%, and the value of ´15N was from 5.17 to 13.01%. There was a positive relationship between ´13C and ´15N, and both ´13C and ´15N increased with body size. No gender or geographic difference was found in this study, but the range of stable isotope values of whale shark tissue was wider in eastern Taiwan waters. Conclusions In this study, ontogenetic changes in the diet of whale sharks were found. More specimens are needed to examine the differences in stable isotope values among different genders, seasons, and regions. The results derived from this study can provide useful information on the husbandry of whale sharks, which can help ecotourism operators become more knowledgeable about the ecology of whale sharks. In addition, the results can also be used as an important reference for ecosystem-based management in the future. Future work should focus on discussion on the habitat partition, utilization, and adaption in various marine environments for whale sharks.
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Intraspecific variability in diet and implied foraging ranges of whale sharks at Ningaloo Reef, Western Australia
Background The whale shark (Rhincodon typus Smith 1828) is the largest of the filter-feeding sharks and inhabits tropical and sub-tropical oceans worldwide. Evidence from anecdotal observations of feeding events and stomach content analysis have identified a wide range of planktonic and nektonic organisms including copepods, krill and small fish as whale shark prey. However, recent studies based on biochemical analysis (e.g. signature fatty acids (FA)) indicated that whale sharks in the western Indian Ocean had a wider foraging range than previous studies suggested, with important contributions from meso- and bathypelagic sources. However, it remains unknown if these results characterize the diet of whale sharks over the wider Indian Ocean. Here, we investigate the feeding ecology of whale sharks in the eastern Indian Ocean at Ningaloo Reef, Western Australia, by identifying differences in whale shark diet according to time of collection, sex and size-class and by examining likely food web linkages. Approach To examine whale shark feeding ecology we used signature FA analysis of both whale shark subdermal tissue and an extensive set of potential prey collected at Ningaloo Reef (Western Australia) in 2013 and 2014. Compared to other methods such as stomach content analysis, signature FA analysis provides both longer-term (up to months) dietary information and an assessment of spatial and temporal changes in the diet of predators. This is possible because some FA in animal tissues (e.g. long-chain (≥C20) polyunsaturated FA, LC-PUFA) can be used as biomarkers as they pass relatively unchanged from the low trophic levels where they are biosynthesized up the food chain. Results Whale shark sub-dermal tissue was low in lipid content (4 mg g–1 dry mass) which was dominated by phospholipids (72% of total lipid) with an energy density of 18.66 kJ g–1 dry mass. A significant intraspecific variability in whale shark FA profiles was observed resulting in four distinct groups of sharks in 2013 and five in 2014. As this variability was not related to sex or size-class, we suggest that it may be attributed to differences in the feeding habitats and thus different prey consumed by these groups of whale sharks. Variation in dietary patterns was also observed between years likely due to changes in the primary and secondary producers. Overall, examination of food web interactions showed that fatty acid profiles of whale sharks and their presumed collected prey were significantly different, suggesting that sharks fed over a wider range of habitats, including deeper waters, than we were able to access. Conclusions A significant component of whale shark diet may originate from benthic and deeper water habitats. High intraspecific variation in diet indicates that whale sharks are likely to forage over a range of distances and depths due to the challenge of inhabiting the patchy prey habitats of tropical and open ocean waters. Future studies should seek to combine signature FA analysis with other techniques such as stable isotopes, genetic and longterm tagging data to help better elucidate the feeding ecology of this iconic species.
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Human dimensions of whale shark provisioning in Oslob, Philippines
Authors: Jackie A. Ziegler, Joshua N. Silberg, Alessandro Ponzo and Philip DeardenBackground Whale shark tourism can provide an incentive to protect whale sharks and their habitats by making them worth more alive than dead. However, the sustainability of these tourism activities is critical to the long-term success of this approach. Whale shark tourism in Oslob is one of only two places in the world where tour operators feed whale sharks to facilitate tourist interactions. To date, no comprehensive studies have assessed tourists' attitudes towards whale shark provisioning. This study assesses tourists' support for whale shark provisioning, as well as their satisfaction with the tour experience in Oslob. Approach TripAdvisor comments of the Oslob whale shark watching experience (n=216) were thematically coded and analysed in NViVO 10. Tourist surveys were collected during the 2014 whale shark watching season in Oslob (n=761) in order to measure attitudes towards interactions with whale sharks. Survey results were coded and analysed in SPSS Version 21. Results TripAdvisor analysis identified four main issues with the experience in Oslob: crowding, provisioning, impacts on sharks, and pricing. Survey results suggest that foreign tourists were significantly more likely to feel crowded compared to national tourists, both in terms of number of other snorkelers (37% vs. 19%; χ2(1, N=629)=23.475, p=0.000, Cramer's V = 0.193) and number of boats (50% vs. 28%; χ2(1, N=623)=30.919, p=0.000, Cramer's V = 0.223), despite the fact that both groups reported encountering the same number of people. Both the survey and TripAdvisor analyses found no significant difference in overall satisfaction with the tour between foreign and national tourists. However, the TripAdvisor analysis did identify a foreign tourist segment termed ‘guilty pleasure’, which exhibited negative feelings towards the ethics of whale shark feeding and an unwillingness to return to Oslob, but still recommended the tour to others. These findings were reflected in the survey results. Foreign tourists were significantly less likely to be willing to participate in whale shark tourism in Oslob again (62%) compared to national tourists (90%; χ2(1, N=632)=67.686, p=0.000, Cramer's V = 0.327), but the vast majority of both foreign (93%) and national (99%) tourists would still recommend the tour (χ2(1, N=632)=18.153, p=0.000, Cramer's V = 0.169). Foreign tourists were also significantly less likely to support the feeding of whale sharks than national tourists (35% vs. 65%; χ2(2, N=635)=55.209, p=0.000, Cramer's V = 0.295), with a further 35% and 22% neutral on the topic, respectively. Although the majority of both groups felt the price of the tour was appropriate, foreign tourists were willing to pay significantly more for the whale shark experience than national tourists (US$63 vs. US$33; t=–6.020, p=0.000, rpb=0.245). Foreign tourists were willing to pay the most for an experience where sharks were not fed, but there was 100% chance of seeing a shark (US$64), followed by sharks fed with 100% chance of seeing sharks (US$43). National tourists on the other hand were willing to pay US$17 for an experience where there was 100% chance of seeing a shark regardless of whether the sharks were fed. Conclusions Few participants perceived the feeding of whale sharks as a negative activity, although foreign tourists were less supportive than national tourists. Most foreign tourists would recommend the tour to others despite their stated intention to not return and misgivings regarding the ethics of provisioning or potential impacts on whale shark health. More in-depth interpretation is necessary to inform tourists of the conservation status and threats facing whale sharks, as well as the potential impacts of tourism activities, both positive and negative. Furthermore, the number of boats and swimmers should be controlled in the whale shark viewing area to address crowding issues.
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