Vignaud T.M.,CNRS Insular Research Center and Environment Observatory |
Maynard J.A.,CNRS Insular Research Center and Environment Observatory |
Maynard J.A.,Cornell University |
Leblois R.,French National Institute for Agricultural Research |
And 7 more authors.
Molecular Ecology | Year: 2014
This study presents genetic evidence that whale sharks, Rhincodon typus, are comprised of at least two populations that rarely mix and is the first to document a population expansion. Relatively high genetic structure is found when comparing sharks from the Gulf of Mexico with sharks from the Indo-Pacific. If mixing occurs between the Indian and Atlantic Oceans, it is not sufficient to counter genetic drift. This suggests whale sharks are not all part of a single global metapopulation. The significant population expansion we found was indicated by both microsatellite and mitochondrial DNA. The expansion may have happened during the Holocene, when tropical species could expand their range due to sea-level rise, eliminating dispersal barriers and increasing plankton productivity. However, the historic trend of population increase may have reversed recently. Declines in genetic diversity are found for 6 consecutive years at Ningaloo Reef in Australia. The declines in genetic diversity being seen now in Australia may be due to commercial-scale harvesting of whale sharks and collision with boats in past decades in other countries in the Indo-Pacific. The study findings have implications for models of population connectivity for whale sharks and advocate for continued focus on effective protection of the world's largest fish at multiple spatial scales. © 2014 John Wiley & Sons Ltd.
Rohner C.A.,Marine Megafauna Foundation |
Rohner C.A.,University of Queensland |
Rohner C.A.,CSIRO |
Richardson A.J.,CSIRO |
And 4 more authors.
Journal of Fish Biology | Year: 2011
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 (r 2 = 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.
PubMed | Georgia Aquarium, University of Washington, Brown University, University of North Carolina at Wilmington and 7 more.
Type: | Journal: PeerJ | Year: 2015
What are the greatest sizes that the largest marine megafauna obtain? This is a simple question with a difficult and complex answer. Many of the largest-sized species occur in the worlds oceans. For many of these, rarity, remoteness, and quite simply the logistics of measuring these giants has made obtaining accurate size measurements difficult. Inaccurate reports of maximum sizes run rampant through the scientific literature and popular media. Moreover, how intraspecific variation in the body sizes of these animals relates to sex, population structure, the environment, and interactions with humans remains underappreciated. Here, we review and analyze body size for 25 ocean giants ranging across the animal kingdom. For each taxon we document body size for the largest known marine species of several clades. We also analyze intraspecific variation and identify the largest known individuals for each species. Where data allows, we analyze spatial and temporal intraspecific size variation. We also provide allometric scaling equations between different size measurements as resources to other researchers. In some cases, the lack of data prevents us from fully examining these topics and instead we specifically highlight these deficiencies and the barriers that exist for data collection. Overall, we found considerable variability in intraspecific size distributions from strongly left- to strongly right-skewed. We provide several allometric equations that allow for estimation of total lengths and weights from more easily obtained measurements. In several cases, we also quantify considerable geographic variation and decreases in size likely attributed to humans.
News Article | November 30, 2016
Giant manta rays had been known to feed on zooplankton near the ocean surface, but a new joint study by The University of Queensland and the Marine Megafauna Foundation has discovered they are also deep-ocean predators. UQ School of Biomedical Sciences PhD student Katherine Burgess said the giant manta ray was one of the marine world's iconic animals, but little was known about its feeding habits. "The previous knowledge of giant manta ray diet was based on observations of feeding activity on surface water zooplankton at well-known aggregation sites," Ms Burgess said. "Giant mantas are found in tropical and temperate waters worldwide. They can grow up to seven metres across, weighing up to 1350kg, although their average size is four to five metres. Ms Burgess said the study began in 2010 and focused on Isla de la Plata, off the Ecuador mainland, that seasonally hosted the world's largest aggregation of giant manta rays. The giant manta ray is listed as vulnerable on the International Union for Conservation of Nature's Red List of Endangered Species because its population has decreased drastically over the past 20 years due to overfishing. Ms Burgess said researchers normally looked at stomach contents to determine an animal's diet, but such a potentially distressing or lethal procedure was not appropriate with a vulnerable species. "We studied the giant manta rays' diet using biochemical tests, such as stable isotope analysis, which works on the 'you are what you eat' paradigm," she said. "These tests can determine what animals have been eating by examining a piece of tissue from a muscle biopsy from a free-swimming animal." Ms Burgess said the study suggested the majority of the giant manta rays' diet was from deep sources rather than surface zooplankton. Professor Anthony Richardson, a scientist with UQ's School of Mathematics and Physics and CSIRO's Oceans and Atmosphere division, said the research found an average 27 per cent of the giant manta rays' diets came from surface zooplankton and 73 per cent was from "mesopelagic" sources including fish from 200m to 1000m below the ocean surface. "The deep ocean is the next frontier for open ocean fisheries, and we are only just realising the potential reliance on this zone by threatened marine megafauna," Professor Richardson said. The research, published in the Royal Society Open Science journal, was a collaboration between The University of Queensland, the Marine Megafauna Foundation and Proyecto Mantas Ecuador. More information: Katherine B. Burgess et al. , predator of the deep? Insight into the diet of the giant manta ray through stable isotope analysis, Royal Society Open Science (2016). DOI: 10.1098/rsos.160717
News Article | December 8, 2015
Elitza Germanov has embarked on a PhD project comparing whether these filter feeding animals are being harmed by the presence of microplastics in Indonesia, the Philippines and off the coast of Western Australia. "The increasing levels of marine plastic debris are a large-scale, global environmental problem and the waters of South-East Asia are some of the worst areas on the planet," said Ms Germanov. "After China, Indonesia is the second highest producer of plastic waste in the world, with the Philippines ranked third. "Currently, an approximately 3.22 million tons of mismanaged plastic waste is being disposed of in Indonesia annually, with up to 40 per cent entering the marine environment." Ms Germanov said that, although there was considerable knowledge about plastic pollution, very little was understood about microplastics, which are pieces smaller than 5 millimetres in length. "I am interested in the health effects of microplastics on filter feeders like manta rays and whale sharks," Ms Germanov said. As part of her PhD, Ms Germanov will measure the levels of microplastics in the feeding grounds of manta rays and whale sharks in the three countries and measure the levels of microplastics in the guts of the animals. Working with the Murdoch University's Separation Science and Metabolomics Laboratory, Ms Germanov will establish how levels of plastic associated toxins such as pesticides and industrial chemicals are building up in the animals. "Hopefully this work will encourage communities to find better solutions for waste management," she said. Ms Germanov's research is being conducted with the support of the Marine Megafauna Foundation.
PubMed | University of KwaZulu - Natal, Marine Megafauna Foundation, University of Queensland and CSIRO
Type: | Journal: PeerJ | Year: 2015
Whale sharks Rhincodon typus are globally threatened, but a lack of biological and demographic information hampers an accurate assessment of their vulnerability to further decline or capacity to recover. We used laser photogrammetry at two aggregation sites to obtain more accurate size estimates of free-swimming whale sharks compared to visual estimates, allowing improved estimates of biological parameters. Individual whale sharks ranged from 432-917 cm total length (TL) (mean SD = 673 118.8 cm, N = 122) in southern Mozambique and from 420-990 cm TL (mean SD = 641 133 cm, N = 46) in Tanzania. By combining measurements of stranded individuals with photogrammetry measurements of free-swimming sharks, we calculated length at 50% maturity for males in Mozambique at 916 cm TL. Repeat measurements of individual whale sharks measured over periods from 347-1,068 days yielded implausible growth rates, suggesting that the growth increment over this period was not large enough to be detected using laser photogrammetry, and that the method is best applied to estimating growth rates over longer (decadal) time periods. The sex ratio of both populations was biased towards males (74% in Mozambique, 89% in Tanzania), the majority of which were immature (98% in Mozambique, 94% in Tanzania). The population structure for these two aggregations was similar to most other documented whale shark aggregations around the world. Information on small (<400 cm) whale sharks, mature individuals, and females in this region is lacking, but necessary to inform conservation initiatives for this globally threatened species.
PubMed | Marine Megafauna Foundation, Australian Institute of Marine Science, University of Western Australia, Marine Conservation Society Seychelles and MRAG Ltd
Type: Journal Article | Journal: Royal Society open science | Year: 2016
Germanov E.S.,Marine Megafauna Foundation |
Marshall A.D.,Marine Megafauna Foundation
PLoS ONE | Year: 2014
Manta rays (Genus Manta) are economically important for fisheries and tourism in Indonesia. These species have been listed by the International Union for the Conservation of Nature Red List as Vulnerable to extinction; therefore, human exploitation of manta rays must be regulated. A better understanding of the habitat use and movement patterns of manta rays in Indonesia is needed in order to employ effective conservation measures. To gain better insight into the movements of Manta alfredi we used 'Manta Matcher', an online database with an integrated automated matching algorithm, to compare photographs from 2,604 encounters of M. alfredi collected by recreational divers and dive operators throughout Indonesia over a nine-year period. This photographic comparison revealed that manta rays migrated between regional sanctuaries such as Nusa Penida, the Gili Islands, and the Komodo National Park (up to 450 km straight-line distance). The areas between these sanctuaries are heavily fished and trafficked by ships, and when manta rays travel through these regions they risk being fished and injured by ship strikes. These long-range manta ray movements suggest connectivity between M. alfredi populations in neighboring islands and raise concerns about the future management of regional populations. It is recommended that a national conservation strategy be developed to protect the remaining populations in the country. © 2014 Germanov, Marshall.
PubMed | Lamar University, Marine Megafauna Foundation and Southern Illinois University Carbondale
Type: | Journal: PeerJ | Year: 2015
Sharks and rays are increasingly being identified as high-risk species for extinction, prompting urgent assessments of their local or regional populations. Advanced genetic analyses can contribute relevant information on effective population size and connectivity among populations although acquiring sufficient regional sample sizes can be challenging. DNA is typically amplified from tissue samples which are collected by hand spears with modified biopsy punch tips. This technique is not always popular due mainly to a perception that invasive sampling might harm the rays, change their behaviour, or have a negative impact on tourism. To explore alternative methods, we evaluated the yields and PCR success of DNA template prepared from the manta ray mucus collected underwater and captured and stored on a Whatman FTA Elute card. The pilot study demonstrated that mucus can be effectively collected underwater using toothbrush. DNA stored on cards was found to be reliable for PCR-based population genetics studies. We successfully amplified mtDNA ND5, nuclear DNA RAG1, and microsatellite loci for all samples and confirmed sequences and genotypes being those of target species. As the yields of DNA with the tested method were low, further improvements are desirable for assays that may require larger amounts of DNA, such as population genomic studies using emerging next-gen sequencing.
PubMed | Marine Megafauna Foundation, University of Queensland, King Abdullah University of Science and Technology and CSIRO
Type: Journal Article | Journal: Journal of plankton research | Year: 2015
Large planktivores require high-density prey patches to make feeding energetically viable. This is a major challenge for species living in tropical and subtropical seas, such as whale sharks