Journal of applied physiology (Bethesda, Md. : 1985), Jan 30, 2017
Accelerometry is increasingly used to quantify physical activity (PA) and related energy expendit... more Accelerometry is increasingly used to quantify physical activity (PA) and related energy expenditure (EE). Linear regression models designed to derive PAEE from accelerometry-counts have shown their limits, mostly due to the lack of consideration of the nature of activities performed. Here we tested whether a model coupling an automatic activity/posture recognition (AAR) algorithm with an activity-specific count-based model, developed in 61 subjects in laboratory conditions, improved PAEE and total EE (TEE) predictions from hip-worn triaxial-accelerometer (ActigraphGT3X+TM) in free-living conditions. Data from two independent subject groups of varying body mass index and age were considered: 20 subjects engaged in a 3h urban-circuit, with activity-by-activity reference PAEE from combined heart-rate and accelerometry monitoring (ActiheartTM); and 56 subjects involved in a 14-day trial, with PAEE and TEE measured using the doubly-labeled-water method. PAEE was estimated from accelerom...
Journal of Experimental Marine Biology and Ecology, 2009
Understanding environmental cues determining behaviour and habitat use of species of conservation... more Understanding environmental cues determining behaviour and habitat use of species of conservation concern is crucial if one aims at implementing sustainable management of these natural resources. In this way, here, we investigate the thermal and trophic conditions encountered by the critically endangered leatherback sea turtle Dermochelys coriacea during its nesting season in French Guiana where high bycatch rates have been reported. Mean sea water temperatures obtained in situ by animal-borne recorders were 26.6 ± 0.7°C in the water column, with all but one turtle remaining in water N 25°C during the inter-nesting interval. In terms of prey availability, regular jellyfish stranding events were recorded during the nesting season, on a 1.25-km long section of the nesting beach. The occurrence of jellyfish was supported by benthic trawls performed on the continental shelf, with a total of 45.4 kg of jellyfish collected in 3.5 h exclusively in coastal waters 10 to 20 m deep where water transparency was between 0.8 and 3 m. This is consistent with the at sea distribution area of gravid leatherbacks during their inter-nesting intervals, as they spent almost 70% of their time diving in shallow (b 20 m deep) waters in front of the Maroni River estuary. In French Guiana, leatherback's gelatinous prey are thus present in very shallow water close to the nesting site and may be easily exploited by active gravid leatherbacks. This suggests that French Guiana female leatherbacks may be influenced by local trophic conditions and actively prospect productive areas overlapping with local fisheries ground.
POSTER PRESENTED AT PISCES 2012 ANNUAL MEETING. Jellyfish outbreaks can adversely impact human he... more POSTER PRESENTED AT PISCES 2012 ANNUAL MEETING. Jellyfish outbreaks can adversely impact human health and economic activities. In the North Atlantic and Pacific Oceans, the highly venomous lion’s mane jellyfish, Cyanea capillata, is a hazard for open-water swimmers and fishermen. Furthermore, in several coastal seas, C. capillata is suspected to impact on fish larvae survival and recruitment; and is thought to be involved in part of the chronic plankton-related mortality of fish farmed in northern Europe. Understanding the factors driving the distribution of this species is therefore critical in order to develop strategies to limit its detrimental impacts. Using acoustic tracking technique (Vemco V9 continuous transmitters) and drogue deployments, we investigated the horizontal and vertical movements of individual C. capillata (n = 5) in a coastal area off Dublin, Ireland. The distance travelled by individual jellyfish over the duration of the tracking (2.7-7.7 h) ranged from 1.6 to...
Long-term records on jellyfish distribution and abundance are essential to investigate how jellyf... more Long-term records on jellyfish distribution and abundance are essential to investigate how jellyfish populations and the frequency of bloom events may be affected by environmental changes (e.g. climate change). However, over the past few years, it has become clear that such data are lacking in many places. Meanwhile, the popularization of the Internet and mobile technologies have brought a new dawn for citizen science programs, and logically, programs aiming at collecting jellyfish sightings were launched in several countries. Inspired by these programs, in 2010, the French association Mer et Littoral launched the program called Opération Méduses with the aim to raise awareness about the marine environment by engaging with the public, and to collect data that could be useful to scientists. At the moment, the program is collecting information on 13 different species (scyphozoans and hydrozoans). The number of participants and of sightings is increasing each year. The main results fro...
The conservation of threatened sea turtle species requires a better understanding of their ecolog... more The conservation of threatened sea turtle species requires a better understanding of their ecology and basin-wide distribution, and thus requires the development of new innovative tools. In the present study, we investigate the possibility to adapt the Spatial and Ecosystem Population Dynamics Models (SEAPODYM) – initially developed for tuna – to leatherback turtles (Dermochelys coriacea) in the North-Atlantic Ocean. The first part of the study examined the obvious changes that are needed in the model to take into account the specific biological characteristics of the leatherback turtle. Then the oceanic features (temperature and primary production) experimented by turtles on their nesting grounds and their foraging grounds were described. The seasonality of animals’ movement between these two areas was also analysed. These first results were used to set the parameters of the models. Finally, we ran the first simulations of habitat index and spatial population dynamics. The model sh...
The broad-scale distribution and abundance of Scyphomedusae in Irish waters
... My gratitude extends to all on board the RV Celtic Explorer, the RV Corystès, and the N/O Tha... more ... My gratitude extends to all on board the RV Celtic Explorer, the RV Corystès, and the N/O Thalassa, scientific staffs and crew members alike. Special thanks go to Eugene Mullins, Mairead Sullivan, Sean O'Connor, Ross Fitzgerald, Robert Bunn, and Pascal Laffargue. ...
Proceedings of the Royal Society B: Biological Sciences, 2012
Over-fishing may lead to a decrease in fish abundance and a proliferation of jellyfish. Active mo... more Over-fishing may lead to a decrease in fish abundance and a proliferation of jellyfish. Active movements and prey search might be thought to provide a competitive advantage for fish, but here we use data-loggers to show that the frequently occurring coastal jellyfish (Rhizostoma octopus) does not simply passively drift to encounter prey. Jellyfish (327 days of data from 25 jellyfish with depth collected every 1 min) showed very dynamic vertical movements, with their integrated vertical movement averaging 619.2 m d 21 , more than 60 times the water depth where they were tagged. The majority of movement patterns were best approximated by exponential models describing normal random walks. However, jellyfish also showed switching behaviour from exponential patterns to patterns best fitted by a truncated Lévy distribution with exponents (mean m ¼ 1.96, range 1.2 -2.9) close to the theoretical optimum for searching for sparse prey (m opt % 2.0). Complex movements in these 'simple' animals may help jellyfish to compete effectively with fish for plankton prey, which may enhance their ability to increase in dominance in perturbed ocean systems.
Mobilités actives et santé : apports et limites d’un protocole de mesure de la marche et du vélo combinant des capteurs de mouvements (GPS et accéléromètres)
ABSTRACT Urban mobility represents a set of complex behaviors, which are difficult to measure. In... more ABSTRACT Urban mobility represents a set of complex behaviors, which are difficult to measure. Independently of individual choices and motivations, these behaviors may be influenced by urban environmental characteristics. The level of physical activity is well recognized as a major determinant in the development of several chronic diseases, such as cardiovascular diseases, diabetes, the obesity and some cancers. Increasing the PA level in the population through the promotion of active mobility is considered as a public health priority in France. However, there is a lack of data for analyzing active mobility (walking and cycling) as a health behavior. One of the main research challenges in this field is to better measure active mobility (in a real life context) and, at the same time, to better locate and identify places where the activity is performed. In this pilot study, we describe a method for collecting and processing data on active mobility combining motion sensors capacities (GPS and accelerometer) and implementing collected data in a Geographic Information System. Despite some limitations, the use of multi-sensor may hold potentials for collecting objective data on active mobility at a large scale.
Cross-flows (winds or currents) affect animal movements . Animals can temporarily be carried off ... more Cross-flows (winds or currents) affect animal movements . Animals can temporarily be carried off course or permanently carried away from their preferred habitat by drift depending on their own traveling speed in relation to that of the flow . Animals able to only weakly fly or swim will be the most impacted (e.g., ). To circumvent this problem, animals must be able to detect the effects of flow on their movements and respond to it . Here, we show that a weakly swimming organism, the jellyfish Rhizostoma octopus, can orientate its movements with respect to currents and that this behavior is key to the maintenance of blooms and essential to reduce the probability of stranding. We combined in situ observations with first-time deployment of accelerometers on free-ranging jellyfish and simulated the behavior observed in wild jellyfish within a high-resolution hydrodynamic model. Our results show that jellyfish can actively swim countercurrent in response to current drift, leading to significant life-history benefits, i.e., increased chance of survival and facilitated bloom formation. Current-oriented swimming may be achieved by jellyfish either directly detecting current shear across their body surface or indirectly assessing drift direction using other cues (e.g., magnetic, infrasound). Our coupled behavioral-hydrodynamic model provides new evidence that current-oriented swimming contributes to jellyfish being able to form aggregations of hundreds to millions of individuals for up to several months, which may have substantial ecosystem and socioeconomic consequences . It also contributes to improve predictions of jellyfish blooms' magnitude and movements in coastal waters.
Climate change and overfishing may lead to ecosystem instability and may benefit nonexploited org... more Climate change and overfishing may lead to ecosystem instability and may benefit nonexploited organisms such as jellyfish. In the Irish Sea, an increase in jellyfish abundance was evident (r 2 5 0.29, P 5 0.03) in a 16-year time-series (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009) collected during juvenile fish surveys. Jellyfish abundance correlated positively with sea surface temperature (SST) over the preceding 18 months (r 5 0.65, p ACF o0.001) and copepod biomass in the previous year (r 5 0.56, p ACF 5 0.03) and negatively with spring (February-May) precipitation (r 5 À0.57, p ACF 5 0.02). Principal components regression indicated that climatic indices explained 68% of the interannual variability in jellyfish abundance (P 5 0.003), where the components were based on the North Atlantic Oscillation Index, SST and precipitation. The frequency of cnidarian material present in Continuous Plankton Recorder (CPR) samples has also increased since 1970, with a period of frequent outbreaks between 1982 and 1991. Before this period, the herring stock in the northern Irish Sea declined rapidly to a low level, potentially stimulating structural change in the ecosystem. In 1985, there was a step decrease in CPR copepod biomass and in 1989, a step increase in the phytoplankton colour index, suggesting a cascading regime shift during the 1980s. Subsequent overexploitation of gadids, coupled with warm temperatures and the poor recruitment of cod, led to the rapid decline in cod biomass from 1990. While the biomass of sprat has decreased in the last decade, the herring stock has recovered partially. Reductions in demersal fishing pressure since 2000, intended to stimulate cod recovery, appear to have facilitated further rises in haddock biomass. Since the 1980s regime shift, sea temperatures have increased, the fish community has altered and jellyfish abundance has risen such that jellyfish and haddock may now play an increasingly important role in the ecosystem.
There is concern that jellyfish populations are proliferating in the Northeast Atlantic and that ... more There is concern that jellyfish populations are proliferating in the Northeast Atlantic and that their socio-economic impacts will increase. Using information from the Irish Groundfish Survey, data are presented on the distribution of the mauve stinger, Pelagia noctiluca, over an area .160 000 km 2 around Ireland and the UK in 2009. The species accounted for 93% of the overall catch of gelatinous organisms, with an average catch biomass of 0.26 + 2.3 kg ha 21 . The study area was divided into four subregions (North, West, Southwest, and South), and the distribution and abundance of P. noctiluca displayed both inter-and intraregional variations. Individual bell diameters ranged from 1 to 13.5 cm (median 4.5 cm, s.d. 1.2 cm), and the size distribution also varied spatially. It is the first time that such detailed information has been made available for P. noctiluca in a part of the Northeast Atlantic where its impact on the salmon aquaculture industry can be considerable. Finally, the possibility of using annual datasets from this type of fisheries survey to develop time-series that, in the future, will allow investigation of relationships between long-term variations of P. noctiluca populations and climatic factors in the area is addressed.
The presence of Mnemiopsis leidyi A. Agassiz, 1865 along the French coasts of the Eastern English... more The presence of Mnemiopsis leidyi A. Agassiz, 1865 along the French coasts of the Eastern English Channel and the North Sea (EEC-NS) was established via morphological observation and molecular evidence. The earliest records were from surveys carried out in autumn 2005 in Le Havre harbour (Bay of Seine, EEC) and coincided with the historical introduction of the species in other Northern European waters. Since 2009, the species has also been frequently observed along the French coast of the North Sea. Results indicate M. leidyi has established a selfsustaining population in the Bay of Seine, which may act as a source population for northern European harbours via commercial shipping.
Cnidaria scyphozoa spatial variations temporal variations quantitative distribution stratificatio... more Cnidaria scyphozoa spatial variations temporal variations quantitative distribution stratification western European shelf Irish Sea a b s t r a c t Monitoring the abundance and distribution of taxa is essential to assess their contribution to ecosystem processes. For marine taxa that are difficult to study or have long been perceived of little ecological importance, quantitative information is often lacking. This is the case for jellyfish (medusae and other gelatinous plankton). In the present work, 4 years of scyphomedusae by-catch data from the 2007e2010 Irish Sea juvenile gadoid fish survey were analysed with three main objectives: (1) to provide quantitative and spatially-explicit species-specific biomass data, for a region known to have an increasing trend in jellyfish abundance; (2) to investigate whether year-to-year changes in catch-biomass are due to changes in the numbers or in the size of medusa (assessed as the mean mass per individual), and (3) to determine whether inter-annual variation patterns are consistent between species and water masses. Scyphomedusae were present in 97% of samples (N ¼ 306). Their overall annual median catch-biomass ranged from 0.19 to 0.92 g m À3 (or 8.6 to 42.4 g m À2 ). Aurelia aurita and Cyanea spp. (Cyanea lamarckii and Cyanea capillata) made up 77.7% and 21.5% of the total catch-biomass respectively, but species contributions varied greatly between sub-regions and years. No consistent pattern was detected between the distribution and inter-annual variations of the two genera, and contrasting inter-annual patterns emerged when considering abundance either as biomass or as density. Significantly, A. aurita medusae were heavier in stratified than in mixed waters, which we hypothesize may be linked to differences in timing and yield of primary and secondary productions between water masses. These results show the vulnerability of time-series from bycatch datasets to phenological changes and highlight the importance of taking species-and population-specific distribution patterns into account when integrating jellyfish into ecosystem models.
At-sea distributions of large scyphozoan jellyfish across the Irish Sea were studied using visual... more At-sea distributions of large scyphozoan jellyfish across the Irish Sea were studied using visual surface counts from ships of opportunity. Thirty-seven surveys were conducted along two[100 km long transects between Ireland and the UK from April to September in 2009 and 2010. Five species were recorded but only Aurelia aurita and Cyanea capillata were frequently observed. The first formal description of the seasonal changes in the abundances and distributions of these two species in the study area is provided. The highest densities of these species were more likely to be found *30 km offshore, but large aggregations were present both in coastal and offshore waters. Evidence for aggregations of medusae along physical discontinuities was provided by coupling jellyfish observations with simultaneous records of environmental parameters. The value of surveys from ships of opportunity as cost-effective semi-quantitative tools, to develop local knowledge on jellyfish abundance, distribution, and phenology is discussed.
Journal of Experimental Marine Biology and Ecology, 2009
Understanding environmental cues determining behaviour and habitat use of species of conservation... more Understanding environmental cues determining behaviour and habitat use of species of conservation concern is crucial if one aims at implementing sustainable management of these natural resources. In this way, here, we investigate the thermal and trophic conditions encountered by the critically endangered leatherback sea turtle Dermochelys coriacea during its nesting season in French Guiana where high bycatch rates have been reported. Mean sea water temperatures obtained in situ by animal-borne recorders were 26.6 ± 0.7°C in the water column, with all but one turtle remaining in water N 25°C during the inter-nesting interval. In terms of prey availability, regular jellyfish stranding events were recorded during the nesting season, on a 1.25-km long section of the nesting beach. The occurrence of jellyfish was supported by benthic trawls performed on the continental shelf, with a total of 45.4 kg of jellyfish collected in 3.5 h exclusively in coastal waters 10 to 20 m deep where water transparency was between 0.8 and 3 m. This is consistent with the at sea distribution area of gravid leatherbacks during their inter-nesting intervals, as they spent almost 70% of their time diving in shallow (b 20 m deep) waters in front of the Maroni River estuary. In French Guiana, leatherback's gelatinous prey are thus present in very shallow water close to the nesting site and may be easily exploited by active gravid leatherbacks. This suggests that French Guiana female leatherbacks may be influenced by local trophic conditions and actively prospect productive areas overlapping with local fisheries ground.
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