Fig 1.
Global and regional context for satellite tracking studies of whale sharks.
(a) Synoptic global sea surface temperature (SST) data represent the dynamic nature and large scale of the equatorial Pacific upwelling system, where whale sharks were tagged for this study. This NOAA 5-day analysis, centered on 15 October 2016, is from the time of year during which tracked whale sharks occupied equatorial habitat. The tag deployment site is near Darwin’s Arch (1.673°N, 91.989°W, open circle). Other sites from published studies where satellite tags have been deployed on whale sharks are shown (filled circles). (b,c) Long-term mean SST and surface chlorophyll-a concentrations derived from satellite remote sensing data. Numbers 1–3 identify thermo-biological frontal zones examined in relation to tracking data from whale sharks.
Fig 2.
Photograph of a whale shark, Rhincodon typus, near Darwin’s Arch, Galápagos.
This 12.5 m TL apparently pregnant female was tagged on 7 September 2012 (WS-31 in [23]).
Fig 3.
Daily positions are colored according to time for each tracking period: (a) 8 July 2011 to 1 March 2012, and (b) 3 September 2012 to 25 January 2013. The number of sharks tracked is indicated in each panel. The location labeled ‘D’ is the tag deployment site, Darwin’s Arch (1.673°N, 91.989°W).
Fig 4.
Association of whale sharks with the northern equatorial upwelling front.
Synoptic examples are from the first (a-c) and second (d-f) tracking periods (Fig 3). Dates on images are the mid-point of 3-day mean SST, and corresponding shark positions during each 3-day period are overlaid (white circles). The number of sharks represented in each image is noted.
Fig 5.
Association of whale sharks with the northern equatorial upwelling front.
Meridional SST profiles (gray lines) are shown for each shark tag that provided > 10 positions (a-o) and separately for all shark tags that provided fewer positions (p). Means for each subset are overlaid (black lines). WS-G is “George” (c), the only male whale shark tracked.
Fig 6.
Statistical summary of northern equatorial frontal occupancy.
Results are from both tracking periods. (a) The map shows the subset of daily position data examined (n = 494). (b) 2D histogram of meridional SST sections across all shark positions. The distance axis represents meridional distance relative to the shark, with zero at the shark position and positive distance north. Mean SST at all shark locations is noted and marked by the vertical white line. (c) Histogram of shark positions in relation to the upwelling front. Positions < 100% are in the front; positions > 100% are north of the front (see Materials and Methods).
Fig 7.
Surface and subsurface observations of whale shark habitat.
Surface and water column observations across the northern equatorial upwelling front when occupied by a 4 m TL female whale shark (WS-3 in [23]). (a) Map shows track of WS-3 during westward movement. The final four positions (open circles) coincided with a ship survey along 110°W (red line). These four positions were acquired 26–29 July 2011 and are overlaid on SST for the 3-day period centered on 27 July 2011 in (b). The 5°N to equator portion of the full ship section (most relevant to the shark habitat) was occupied between 30 July and 2 August 2011. (c-f) Water column properties along the ship section; gray triangles mark the locations of the CTD profiles; sigma-t represents density; u is zonal velocity. The vertical lines mark the latitude range occupied by WS-3 between 26 and 29 July 2011. Gray contours mark the temperature range 22 to 26°C (Fig 8a).
Fig 8.
Temperature range occupation and zonal current influence in the equatorial region.
(a) Subsurface temperature analysis is based on TAT data from 13 tags. Represented separately are WS-3 tag data and the subset of WS-3 tag data during which the shark transited across a ship survey (Fig 7a). (b) Histograms of zonal speeds of (1) shark movements and (2) surface currents at shark locations.
Fig 9.
Association of whale sharks with the eastern boundary upwelling system front.
(a-f) Synoptic examples of SST and shark position data. Data are from the first tracking period (Fig 3a). Dates on images are the mid-point of 3-day means, and corresponding shark positions during each 3-day period are overlaid (white circles). The number of sharks represented in each image is noted. (g) The map shows a subset of position data for which zonal sections could effectively resolve SST gradients across eastern margin habitat. (h) Zonal SST sections across each shark position (gray lines) and the mean (black line). The distance axis represents zonal distance relative to the shark, with zero at the shark position and positive distance east. Mean SST at the shark locations is noted and marked by the horizontal line. (i) Location of shark positions relative to the front; percent distance is between the temperature minimum (caused by coastal upwelling) and the SST gradient slope break (e.g. near 200 km west of the shark positions in the mean profile in (h)).
Fig 10.
Occupancy of a wind-jet system oceanic front.
Tracking data are from the largest whale shark in this study (WS-37 in [23]; 12.8 m TL) during (a) 31 October to 9 December 2012, (b) 10 December 2012 to 3 January 2013, and (c) 4 to 18 January 2013. SST images represent the average for the corresponding tracking periods.