scholarly journals Oceanographic influences on a global whale shark hotspot in southern Mozambique

2014 ◽  
Author(s):  
Christoph A Rohner ◽  
Scarla J Weeks ◽  
Anthony J Richardson ◽  
Simon J Pierce ◽  
Marites M Magno-Canto ◽  
...  
Keyword(s):  
Time Series ◽  
Coastal Waters ◽  
Prey Availability ◽  
Sea Surface ◽  
Height Anomaly ◽  
Coastal Current ◽  
Whale Shark ◽  
Shelf Edge ◽  
Upwelled Water ◽  
Whale Sharks

Coastal aggregations of whale sharks Rhincodon typus around the world are generally seasonal and driven by prey availability. At a major aggregation site in southern Mozambique, whale sharks are, somewhat unusually, present and seen feeding throughout the year. We investigated potential oceanographic mechanisms that may regulate prey availability on the narrow regional shelf and hence account for this year-round whale shark hotspot. We used regional aerial surveys to show that the highest density of whale sharks (29 sharks 100 km-1) was near Praia do Tofo (23.85˚S, 35.55˚E). To investigate how the regional oceanography influences the enrichment of shelf waters, we used 5- and 9-year time series of hourly underwater temperature, and 10-year time series of remotely-sensed sea surface temperature, chlorophyll-a concentration and sea surface height anomaly data. We found that upwelling of cool, nutrient-rich water was common in the region throughout the year and describe three mechanisms, all of which are likely to stimulate productivity: (1) Shelf-edge upwelling and subsequent elevated plankton biomass in coastal waters north of Praia do Tofo, driven by the interaction of southward-propagating mesoscale eddies with the narrow shelf. In situ temperature data show that this interaction frequently leads to intense upwelling, up to 7.5˚C daily amplitude, throughout the year, but is most pronounced in spring/summer. (2) Divergent upwelling south of Praia do Tofo driven by the current flow along the shelf edge as it diverges from the coastline. This upwelling can occur throughout the year and is similar in intensity, but less frequent, than the shelf-edge upwelling. (3) Vortex-driven upwelling by the Delagoa Bight lee-eddy, which may increase phytoplankton biomass in the Bight and also force a northward coastal current that transports recently-upwelled water towards Praia do Tofo. We hypothesise that whale sharks aggregate in coastal waters around Praia do Tofo throughout the year because these upwelling mechanisms contribute to year-round productivity in the region.

scholarly journals Oceanographic influences on a global whale shark hotspot in southern Mozambique

2014 ◽  
Author(s):  
Christoph A Rohner ◽  
Scarla J Weeks ◽  
Anthony J Richardson ◽  
Simon J Pierce ◽  
Marites M Magno-Canto ◽  
...  
Keyword(s):  
Time Series ◽  
Coastal Waters ◽  
Prey Availability ◽  
Sea Surface ◽  
Height Anomaly ◽  
Coastal Current ◽  
Whale Shark ◽  
Shelf Edge ◽  
Upwelled Water ◽  
Whale Sharks

Coastal aggregations of whale sharks Rhincodon typus around the world are generally seasonal and driven by prey availability. At a major aggregation site in southern Mozambique, whale sharks are, somewhat unusually, present and seen feeding throughout the year. We investigated potential oceanographic mechanisms that may regulate prey availability on the narrow regional shelf and hence account for this year-round whale shark hotspot. We used regional aerial surveys to show that the highest density of whale sharks (29 sharks 100 km-1) was near Praia do Tofo (23.85˚S, 35.55˚E). To investigate how the regional oceanography influences the enrichment of shelf waters, we used 5- and 9-year time series of hourly underwater temperature, and 10-year time series of remotely-sensed sea surface temperature, chlorophyll-a concentration and sea surface height anomaly data. We found that upwelling of cool, nutrient-rich water was common in the region throughout the year and describe three mechanisms, all of which are likely to stimulate productivity: (1) Shelf-edge upwelling and subsequent elevated plankton biomass in coastal waters north of Praia do Tofo, driven by the interaction of southward-propagating mesoscale eddies with the narrow shelf. In situ temperature data show that this interaction frequently leads to intense upwelling, up to 7.5˚C daily amplitude, throughout the year, but is most pronounced in spring/summer. (2) Divergent upwelling south of Praia do Tofo driven by the current flow along the shelf edge as it diverges from the coastline. This upwelling can occur throughout the year and is similar in intensity, but less frequent, than the shelf-edge upwelling. (3) Vortex-driven upwelling by the Delagoa Bight lee-eddy, which may increase phytoplankton biomass in the Bight and also force a northward coastal current that transports recently-upwelled water towards Praia do Tofo. We hypothesise that whale sharks aggregate in coastal waters around Praia do Tofo throughout the year because these upwelling mechanisms contribute to year-round productivity in the region.

scholarly journals presence of whale sharks based on oceanographic variations in Cenderawasih Bay National Park, Papua, Indonesia

2021 ◽  
Vol 22 (11) ◽  
Author(s):  
JAFRY FERDINAN Manuhutu ◽  
DEWA GEDE RAKA WIADNYA ◽  
ABU BAKAR SAMBAH ◽  
ENDANG YULI HERAWATI
Keyword(s):  
National Park ◽  
Additive Model ◽  
Environmental Parameters ◽  
Analysis Data ◽  
Current Speed ◽  
Habitat Modeling ◽  
Sea Surface ◽  
Observation Data ◽  
Whale Shark ◽  
Whale Sharks

Abstract. Manuhutu JF, Wiadnya DGR, Sambah AB, Herawati EY. 2021. The presence of whale sharks based on oceanographic variations in Cenderawasih Bay National Park, Papua, Indonesia. Biodiversitas 22: 4948-4955. Oceanographic factors have an important role in the study of estimating the distribution of fish resource habitats. Sea Surface Temperature (SST), Sea Surface Chlorophyll (SSC), Current Speed, Sea Surface Height (SSH), and bathymetry are important parameters that have been used in estimating the habitat of certain species. Through analyzing these environmental factors, research on the appearance and distribution of whale shark habitats in the Cenderawasih Bay National Park in Papua, Indonesia, utilized field observation data and satellite imagery. This study applied data on the presence of whale sharks and oceanographic parameter data from satellite recordings during 2019 – 2020. Analysis of the relationship and habitat modeling between the monthly presence of whale sharks and environmental parameters was carried out through the Generalized Additive Model (GAM) statistical approach and spatial analysis through the Geographic Information System approach. In the GAM analysis, data on the presence of whale sharks was used as a response variable. In contrast, the predictor variables consisted of SST, SSC, current speed, SSH, and bathymetric data. The results showed that the highest frequency of whale shark presence occurred in the transitional monsoon, with an average presence of 31.77 ± 4.00 %. The study also showed that all predictors showed a highly significant relationship (P < 0.001) to the number of whale sharks present. SST values range from 30.3 – 31.3 °C, SSC of 0.39 – 0.86 mg/L, the current speed of 0.46 – 0.65 m/s, SSH showed 0.63 to 1.00 cm, and bathymetry between 40 – 50 m . In the GAM model, the SST and SSC parameters were the two most important parameters that affect the presence of whale sharks, followed by SSHD, depth (bathymetry), and current parameters.

scholarly journals Seasonal habitat use of whale sharks in the northern Gulf of Mexico, USA 2003 - 2013

2013 ◽  
Author(s):  
Jennifer A McKinney ◽  
Eric R Hoffmayer ◽  
Jim S Franks ◽  
Jill M Hendon ◽  
William B Driggers
Keyword(s):  
Home Range ◽  
Gulf Of Mexico ◽  
Habitat Use ◽  
Whale Shark ◽  
Shelf Edge ◽  
Northern Gulf Of Mexico ◽  
Use Patterns ◽  
Core Habitat ◽  
Whale Sharks ◽  
Satellite Tagging

Background: Reports of whale sharks (Rhincodon typus) in the northern Gulf of Mexico (GOM) date back to the 1930s. In 2003, the Northern Gulf of Mexico Whale Shark Research Program was established and began making directed efforts to document the regional occurrence, seasonal distribution and habitat preferences of whale sharks. Methods: Whale shark sightings data (WSS: 1989 – present; n=644) and tagging geoposition data (TD: 2009-2012; n=450) were used in seasonal kernel density (KD) analyses to delineate home range (95%) and core habitat (50%) use areas in the northern GOM. Kernel density estimation of distribution is a statistically robust manner of handling data sources with differing sampling designs (anecdotal vs. directed). Habitat use patterns from the two datasets were used to identify critical use areas. Results: In the study area, whale shark home range was 276,000 km2 (WSS) to 369,000 km2 (TD) in size, with 52,000 km2 (WSS) to 62,000 km2 (TD) being core habitat. Whale shark habitat use varied seasonally, with the largest home range occurring during summer (WSS: 213,000 km2) and fall (TD: 221,000 km2). Tag data revealed more winter habitat (75,000 km2) than the sightings dataset (41,000 km2), which was shifted further offshore to slope waters. Significant use patterns occurred along the continental shelf-edge, encompassing shelf-edge banks south of Louisiana, and near the mouth of the Mississippi River. Conclusions: The combination of sightings data and satellite tagging data represents an effective methodology for assessing seasonality of occurrence, distribution, and habitat use of whale sharks. Shelf-edge bank habitats were most commonly used by whale sharks in the region. Satellite tagging data provided additional evidence of connectivity between multiple jurisdictions, which lends support for international management of the species.

scholarly journals Does bathymetry drive coastal whale shark (Rhincodon typus)aggregations?

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e4904 ◽  
Author(s):  
Joshua P. Copping ◽  
Bryce D. Stewart ◽  
Colin J. McClean ◽  
James Hancock ◽  
Richard Rees
Keyword(s):  
Primary Productivity ◽  
Linear Models ◽  
Prey Availability ◽  
Extensive Literature ◽  
Whale Shark ◽  
Generalised Linear Models ◽  
Rhincodon Typus ◽  
Bathymetric Data ◽  
Mesopelagic Zone ◽  
Whale Sharks

BackgroundThe whale shark (Rhincodon typus) is known to aggregate in a number of coastal locations globally, however what causes these aggregations to form where they do is largely unknown. This study examines whether bathymetry is an important driver of coastal aggregation locations forR. typusthrough bathymetry’s effect on primary productivity and prey availability. This is a global study taking into account all coastal areas withinR. typus’range.MethodsR. typusaggregation locations were identified through an extensive literature review. Global bathymetric data were compared atR. typusaggregation locations and a large random selection of non-aggregation areas. Generalised linear models were used to assess which bathymetric characteristic had the biggest influence on aggregation presence.ResultsAggregation sites were significantly shallower than non-aggregation sites and in closer proximity to deep water (the mesopelagic zone) by two orders of magnitude. Slope at aggregation sites was significantly steeper than non-aggregation sites. These three bathymetric variables were shown to have the biggest association with aggregation sites, with up to 88% of deviation explained by the GLMs.DiscussionThe three key bathymetric characteristics similar at the aggregation sites are known to induce upwelling events, increase primary productivity and consequently attract numerous other filter feeding species. The location of aggregation sites in these key areas can be attributed to this increased prey availability, thought to be the main reasonR. typusaggregations occur, extensively outlined in the literature. The proximity of aggregations to shallow areas such as reefs could also be an important factor why whale sharks thermoregulate after deep dives to feed. These findings increase our understanding of whale shark behaviour and may help guide the identification and conservation of further aggregation sites.

scholarly journals Statistical Prediction of the South China Sea Surface Height Anomaly

2015 ◽  
Vol 2015 ◽  
pp. 1-9
Author(s):  
Caixia Shao ◽  
Weimin Zhang ◽  
Chunjian Sun ◽  
Xinmin Chai ◽  
Zhimin Wang
Keyword(s):  
Time Series ◽  
South China Sea ◽  
South China ◽  
Decadal Variability ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Statistical Prediction ◽  
Height Anomaly ◽  
China Sea ◽  
Sea Surface Height Anomaly

Based on the simple ocean data assimilation (SODA) data, this study analyzes and forecasts the monthly sea surface height anomaly (SSHA) averaged over South China Sea (SCS). The approach to perform the analysis is a time series decomposition method, which decomposes monthly SSHAs in SCS to the following three parts: interannual, seasonal, and residual terms. Analysis results demonstrate that the SODA SSHA time series are significantly correlated to the AVISO SSHA time series in SCS. To investigate the predictability of SCS SSHA, an exponential smoothing approach and an autoregressive integrated moving average approach are first used to fit the interannual and residual terms of SCS SSHA while keeping the seasonal part invariant. Then, an array of forecast experiments with the start time spanning from June 1977 to June 2007 is performed based on the prediction model which integrates the above two models and the time-independent seasonal term. Results indicate that the valid forecast time of SCS SSHA of the statistical model is about 7 months, and the predictability of SCS SSHA in Spring and Autumn is stronger than that in Summer and Winter. In addition, the prediction skill of SCS SSHA has remarkable decadal variability, with better phase forecast in 1997–2007.

scholarly journals Seasonal Occurrence, Horizontal Movements, and Habitat Use Patterns of Whale Sharks (Rhincodon typus) in the Gulf of Mexico

2021 ◽  
Vol 7 ◽  
Author(s):  
Eric R. Hoffmayer ◽  
Jennifer A. McKinney ◽  
James S. Franks ◽  
Jill M. Hendon ◽  
William B. Driggers ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Habitat Use ◽  
Continental Shelf ◽  
Site Fidelity ◽  
Seasonal Occurrence ◽  
Whale Shark ◽  
Shelf Edge ◽  
Rhincodon Typus ◽  
Aggregation Site ◽  
Whale Sharks

In the northern Gulf of Mexico (GOM), whale sharks (Rhincodon typus) form large aggregations at continental shelf-edge banks during summer; however, knowledge of movements once they leave aggregation sites is limited. Here we report on the seasonal occurrence of whale sharks in the northern GOM based on over 800 whale shark sightings from 1989 to 2016, as well as the movements of 42 whale sharks tagged with satellite-linked and popup satellite archival transmitting tags from 2008 to 2015. Sightings data were most numerous during summer and fall often with aggregations of individuals reported along the continental shelf break. Most sharks (66%) were tagged during this time at Ewing Bank, a known aggregation site off the coast of Louisiana. Whale shark track duration ranged from three to 366 days and all tagged individuals, which ranged from 4.5 to 12.0 m in total length, remained within the GOM. Sightings data revealed that whale sharks occurred primarily in continental shelf and shelf-edge waters (81%) whereas tag data revealed the sharks primarily inhabited continental slope and open ocean waters (91%) of the GOM. Much of their time spent in open ocean waters was associated with the edge of the Loop Current and associated mesoscale eddies. During cooler months, there was a net movement southward, corresponding with the time of reduced sighting reports. Several sharks migrated to the southwest GOM during fall and winter, suggesting this region could be important overwintering habitat and possibly represents another seasonal aggregation site. The three long-term tracked whale sharks exhibited interannual site fidelity, returning one year later to the vicinity where they were originally tagged. The increased habitat use of north central GOM waters by whale sharks as summer foraging grounds and potential interannual site fidelity to Ewing Bank demonstrate the importance of this region for this species.

scholarly journals Satellite tagging highlights the importance of productive Mozambican coastal waters to the ecology and conservation of whale sharks

2017 ◽  
Author(s):  
Christoph A Rohner ◽  
Anthony J Richardson ◽  
Fabrice R A Jaine ◽  
Michael B Bennett ◽  
Scarla J Weeks ◽  
...  
Keyword(s):  
Coastal Waters ◽  
Habitat Preferences ◽  
Movement Ecology ◽  
Whale Shark ◽  
Long Distance ◽  
Tropical Oceans ◽  
Whale Sharks ◽  
International Boundaries ◽  
Satellite Tagging ◽  
Analytical Approaches

Recent advances in tracking technologies and analytical approaches allow for deeper insights into the movement ecology of wide-ranging fishes. The whale shark Rhincodon typus is an endangered, highly migratory species with a wide, albeit patchy, distribution through tropical oceans. Aerial surveys along the southern Mozambican coast, conducted over a 5-year period, documented the highest densities of whale sharks to occur within a ~200 km long stretch of the Inhambane Province, with a pronounced hotspot adjacent to Praia do Tofo. We tagged 15 juvenile whale sharks with SPOT5 satellite tags off Praia do Tofo and tracked them for 1–87 days (mean = 26 days) as they dispersed from this area. Sharks travelled between 10 and 2,737 km (mean = 738 km) at a mean horizontal speed of 29 ± 30.7 SD km day-1. While several individuals left shelf waters and travelled across international boundaries, most sharks stayed in Mozambican coastal waters over the tracking period. We tested for whale shark habitat preferences, using sea surface temperature, chlorophyll-a concentration and water depth as variables, by computing 100 random model tracks for each real shark based on their empirical movement characteristics. Whale sharks spent significantly more time in cooler, shallower water with higher chlorophyll-a concentrations than model sharks, suggesting that feeding in productive coastal waters is an important driver of their movements. Our results show that, while whale sharks are capable of long-distance oceanic movements, they can spend a disproportionate amount of time in specific areas. The increasing use of large-mesh gill nets in this coastal hotspot for whale sharks is a clear threat to regional populations of this iconic species.

scholarly journals Seasonal habitat use of whale sharks in the northern Gulf of Mexico, USA 2003 - 2013

2013 ◽  
Author(s):  
Jennifer A McKinney ◽  
Eric R Hoffmayer ◽  
Jim S Franks ◽  
Jill M Hendon ◽  
William B Driggers
Keyword(s):  
Home Range ◽  
Gulf Of Mexico ◽  
Habitat Use ◽  
Whale Shark ◽  
Shelf Edge ◽  
Northern Gulf Of Mexico ◽  
Use Patterns ◽  
Core Habitat ◽  
Whale Sharks ◽  
Satellite Tagging

Background: Reports of whale sharks (Rhincodon typus) in the northern Gulf of Mexico (GOM) date back to the 1930s. In 2003, the Northern Gulf of Mexico Whale Shark Research Program was established and began making directed efforts to document the regional occurrence, seasonal distribution and habitat preferences of whale sharks. Methods: Whale shark sightings data (WSS: 1989 – present; n=644) and tagging geoposition data (TD: 2009-2012; n=450) were used in seasonal kernel density (KD) analyses to delineate home range (95%) and core habitat (50%) use areas in the northern GOM. Kernel density estimation of distribution is a statistically robust manner of handling data sources with differing sampling designs (anecdotal vs. directed). Habitat use patterns from the two datasets were used to identify critical use areas. Results: In the study area, whale shark home range was 276,000 km2 (WSS) to 369,000 km2 (TD) in size, with 52,000 km2 (WSS) to 62,000 km2 (TD) being core habitat. Whale shark habitat use varied seasonally, with the largest home range occurring during summer (WSS: 213,000 km2) and fall (TD: 221,000 km2). Tag data revealed more winter habitat (75,000 km2) than the sightings dataset (41,000 km2), which was shifted further offshore to slope waters. Significant use patterns occurred along the continental shelf-edge, encompassing shelf-edge banks south of Louisiana, and near the mouth of the Mississippi River. Conclusions: The combination of sightings data and satellite tagging data represents an effective methodology for assessing seasonality of occurrence, distribution, and habitat use of whale sharks. Shelf-edge bank habitats were most commonly used by whale sharks in the region. Satellite tagging data provided additional evidence of connectivity between multiple jurisdictions, which lends support for international management of the species.

scholarly journals Satellite tagging highlights the importance of productive Mozambican coastal waters to the ecology and conservation of whale sharks

2017 ◽  
Author(s):  
Christoph A Rohner ◽  
Anthony J Richardson ◽  
Fabrice R A Jaine ◽  
Michael B Bennett ◽  
Scarla J Weeks ◽  
...  
Keyword(s):  
Coastal Waters ◽  
Habitat Preferences ◽  
Habitat Choice ◽  
Aerial Survey ◽  
Whale Shark ◽  
Coastal Habitat ◽  
Long Distance ◽  
Gill Nets ◽  
Gill Net ◽  
Whale Sharks

The whale shark Rhincodon typus is an endangered, highly migratory species with a wide, albeit patchy, distribution through tropical oceans. Ten aerial survey flights along the southern Mozambican coast, conducted between 2004–2008, documented a relatively high density of whale sharks along a ~200 km stretch of the Inhambane Province, with a pronounced hotspot adjacent to Praia do Tofo. To examine the residency and movement of whale sharks in coastal areas around Praia do Tofo, where they may be more susceptible to gill net entanglement, we tagged 15 juveniles with SPOT5 satellite tags and tracked them for 2–88 days (mean = 27 days) as they dispersed from this area. Sharks travelled between 10 and 2,737 km (mean = 738 km) at a mean horizontal speed of 28 ± 17.1 SD km day-1. While several individuals left shelf waters and travelled across international boundaries, most sharks stayed in Mozambican coastal waters over the tracking period. We tested for whale shark habitat preferences, using sea surface temperature, chlorophyll-a concentration and water depth as variables, by computing 100 random model tracks for each real shark based on their empirical movement characteristics. Whale sharks spent significantly more time in cooler, shallower water with higher chlorophyll-a concentrations than model sharks, suggesting that feeding in productive coastal waters is an important driver of their movements. To investigate what this coastal habitat choice means for their conservation in Mozambique, we mapped gill nets during two dedicated aerial surveys along the Inhambane coast and counted gill nets in 1,323 boat-based surveys near Praia do Tofo. Our results show that, while whale sharks are capable of long-distance oceanic movements, they can spend a disproportionate amount of time in specific areas, such as along the southern Mozambique coast. The increasing use of large-mesh gill nets in this coastal hotspot for whale sharks is likely to be a threat to regional populations of this iconic species.

scholarly journals Storm-driven across-shelf oceanic flows into coastal waters

Ocean Science ◽  
2020 ◽  
Vol 16 (2) ◽  
pp. 389-403 ◽  
Author(s):  
Sam Jones ◽  
Mark Inall ◽  
Marie Porter ◽  
Jennifer A. Graham ◽  
Finlo Cottier
Keyword(s):  
Time Series ◽  
North Atlantic ◽  
Coastal Waters ◽  
Late Summer ◽  
Current Speed ◽  
Outer Shelf ◽  
Coastal Current ◽  
Winter Storm ◽  
Intense Storm ◽  
Shelf Flow

Abstract. The North Atlantic Ocean and northwest European shelf experience intense low-pressure systems during the winter months. The effect of strong winds on shelf circulation and water properties is poorly understood as observations during these episodes are rare, and key flow pathways have been poorly resolved by models up to now. We compare the behaviour of a cross-shelf current in a quiescent period in late summer, with the same current sampled during a stormy period in midwinter, using drogued drifters. Concurrently, high-resolution time series of current speed and salinity from a coastal mooring are analysed. A Lagrangian analysis of modelled particle tracks is used to supplement the observations. Current speeds at 70 m during the summer transit are 10–20 cm s−1, whereas on-shelf flow reaches 60 cm s−1 during the winter storm. The onset of high across-shelf flow is identified in the coastal mooring time series, both as an increase in coastal current speed and as an abrupt increase in salinity from 34.50 to 34.85, which lags the current by 8 d. We interpret this as the wind-driven advection of outer-shelf (near-oceanic) water towards the coastline, which represents a significant change from the coastal water pathways which typically feed the inner shelf. The modelled particle analysis supports this interpretation: particles which terminate in coastal waters are recruited locally during the late summer, but recruitment switches to the outer shelf during the winter storm. We estimate that during intense storm periods, on-shelf transport may be up to 0.48 Sv, but this is near the upper limit of transport based on the multi-year time series of coastal current and salinity. The likelihood of storms capable of producing these effects is much higher during positive North Atlantic Oscillation (NAO) winters.

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