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      Whale Shark ( Rhincodon typus) Seasonal Presence, Residence Time and Habitat Use at Darwin Island, Galapagos Marine Reserve

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          Abstract

          The life history of the whale shark ( Rhincodon typus), including its reproductive ecology, still remains largely unknown. Here, we present results from the first whale shark population study around Darwin Island, Galapagos Marine Reserve. Following a diversified approach we characterized seasonal occurrence, population structure and size, and described habitat use of whale sharks based on fine scale movements around the island. Whale shark presence at Darwin Island was negatively correlated with Sea Surface Temperature (SST), with highest abundance corresponding to a cool season between July and December over six years of monitoring. From 2011 to 2013 we photo-identified 82 whale sharks ranging from 4 to 13.1 m Total Length (TL). Size distribution was bimodal, with a great majority (91.5%) of adult female individuals averaging 11.35 m±0.12 m (TL±SE), all but one showing signs of a potential pregnancy. Population dynamics models for apparently pregnant sharks estimated the presence of 3.76±0.90 (mean ± SE) sharks in the study area per day with an individual residence time of 2.09±0.51 (mean ± SE) days. Movement patterns analysis of four apparently pregnant individuals tracked with acoustic tags at Darwin Island revealed an intense use of Darwin's Arch, where no feeding or specific behavior has been recorded, together with periodic excursions around the island's vicinity. Sharks showed a preference for intermediate depths (20–30 m) with occasional dives mostly to mid-water, remaining the majority of their time at water temperatures between 24–25°C. All of our results point to Darwin Island as an important stopover in a migration, possibly with reproductive purposes, rather than an aggregation site. Current studies carried out in this area to investigate regional scale movement patterns may provide essential information about possible pupping grounds for this enigmatic species.

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          Using open robust design models to estimate temporary emigration from capture-recapture data.

          Capture-recapture studies are crucial in many circumstances for estimating demographic parameters for wildlife and fish populations. Pollock's robust design, involving multiple sampling occasions per period of interest, provides several advantages over classical approaches. This includes the ability to estimate the probability of being present and available for detection, which in some situations is equivalent to breeding probability. We present a model for estimating availability for detection that relaxes two assumptions required in previous approaches. The first is that the sampled population is closed to additions and deletions across samples within a period of interest. The second is that each member of the population has the same probability of being available for detection in a given period. We apply our model to estimate survival and breeding probability in a study of hawksbill sea turtles (Eretmochelys imbricata), where previous approaches are not appropriate.
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            Horizontal Movements, Migration Patterns, and Population Structure of Whale Sharks in the Gulf of Mexico and Northwestern Caribbean Sea

            Whale sharks, Rhincodon typus, aggregate by the hundreds in a summer feeding area off the northeastern Yucatan Peninsula, Mexico, where the Gulf of Mexico meets the Caribbean Sea. The aggregation remains in the nutrient-rich waters off Isla Holbox, Isla Contoy and Isla Mujeres, Quintana Roo for several months in the summer and then dissipates between August and October. Little has been known about where these sharks come from or migrate to after they disperse. From 2003–2012, we used conventional visual tags, photo-identification, and satellite tags to characterize the basic population structure and large-scale horizontal movements of whale sharks that come to this feeding area off Mexico. The aggregation comprised sharks ranging 2.5–10.0 m in total length and included juveniles, subadults, and adults of both sexes, with a male-biased sex ratio (72%). Individual sharks remained in the area for an estimated mean duration of 24–33 days with maximum residency up to about 6 months as determined by photo-identification. After leaving the feeding area the sharks showed horizontal movements in multiple directions throughout the Gulf of Mexico basin, the northwestern Caribbean Sea, and the Straits of Florida. Returns of individual sharks to the Quintana Roo feeding area in subsequent years were common, with some animals returning for six consecutive years. One female shark with an estimated total length of 7.5 m moved at least 7,213 km in 150 days, traveling through the northern Caribbean Sea and across the equator to the South Atlantic Ocean where her satellite tag popped up near the Mid-Atlantic Ridge. We hypothesize this journey to the open waters of the Mid-Atlantic was for reproductive purposes but alternative explanations are considered. The broad movements of whale sharks across multiple political boundaries corroborates genetics data supporting gene flow between geographically distinct areas and underscores the need for management and conservation strategies for this species on a global scale.
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              How large is the world's largest fish? Measuring whale sharks Rhincodon typus with laser photogrammetry.

              Laser photogrammetry was found to be a promising new cost-effective technique for measuring free-swimming whale sharks Rhincodon typus. Photogrammetric measurements were more precise than visual size estimates by experienced researchers, with results from the two methods differing by 9· 8 ± 1· 1% (mean ±s.e.). A new metric of total length and the length between the fifth gill and first dorsal fin (r² = 0· 93) is proposed to facilitate easy, accurate length measurements of whale sharks in the field. © 2011 The Authors. Journal of Fish Biology © 2011 The Fisheries Society of the British Isles.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2014
                31 December 2014
                : 9
                : 12
                : e115946
                Affiliations
                [1 ]Charles Darwin Research Station, Puerto Ayora, Galapagos Islands, Ecuador
                [2 ]Department of Fish, Wildlife, and Conservation Biology, Colorado State University, Fort Collins, Colorado, United States of America
                [3 ]Turtle Island Restoration Network, Olema, California, United States of America
                [4 ]Galapagos National Park Directorate, Puerto Ayora, Galapagos Islands, Ecuador
                University of California Davis, United States of America
                Author notes

                Competing Interests: The authors have received funding from a commercial source, Lindblad Expeditions/National Geographic Funds, IWC Schaffhausen, but this does not alter adherence to PLOS One policies on sharing data and materials.

                Conceived and designed the experiments: DAM PSDL AH JRG. Performed the experiments: DAM PSDL FS JPJ AH JRG. Analyzed the data: DAM PSDL FS PFDJ JJ. Contributed reagents/materials/analysis tools: DAM PSDL FS JJ PFDJ. Wrote the paper: DAM PSDL PFDJ FS JJ JRG AH.

                Article
                PONE-D-14-27124
                10.1371/journal.pone.0115946
                4281130
                25551553
                98af8523-9a34-4f74-8cba-f3fbfad266f5
                Copyright @ 2014

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 19 June 2014
                : 27 November 2014
                Page count
                Pages: 22
                Funding
                This study has been funded by: Rapier Family Trust ( www.rapiertrust.com), Galapagos Conservancy ( www.galapagos.org), Lindblad Expeditions/National Geographic Funds ( www.expeditions.com), IWC Schaffhausen ( www.iwc.com). The funders provided funds to cover field trips to collect data.
                Categories
                Research Article
                Biology and Life Sciences
                Computational Biology
                Population Modeling
                Ecology
                Ecological Metrics
                Population Size
                Marine Ecology
                Marine Biology
                Marine Conservation
                Population Biology
                Population Metrics
                Custom metadata
                The authors confirm that, for approved reasons, some access restrictions apply to the data underlying the findings. Data cannot be made publicly available due to legal restrictions. Data are available from the Charles Darwin Foundation and Galapagos National Park Institutional Data Access by contacting: Mr. Galo Quezada, Environmental Management Direction, Applied Research Process, Galapagos National Park Directorate ( gquezada@ 123456galapagos.gob.ec ).

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