Fig 1.
Azores archipelago with its nine islands and São Miguel area enlarged with bathymetry data.
Depth contours each 500 m. Notice the three different areas considered for the environmental variables processing: area Azores (bottom left corner); Area São Miguel (grey square marked in Azores area and enlarged map); and area south São Miguel (dashed square).
Fig 2.
Map of the study area with all the sightings registered between May 2008 and December 2014.
Black points are blue whale sightings (n = 89) and grey points correspond to the other species (n = 7711). Ponta Delgada is marked in the south coast as the base port.
Table 1.
Main environmental variables from which the others were derived.
Fig 3.
High resolution sea surface temperature daily map from MetOp data (only values with quality Index >2 were considered).
Colorbar for temperature (°C). Blank spaces are missing values or bad quality values masked. Sharp gradients can be seen in the area, some with more than 2°C of difference in less than 20 km. A) Image from the 20th of June 2010. It is clearly visible the cold water patch on the south coast of the island and a tongue of warm water retained by the platform on the south west. B) Image from the 9th of July 2010. Cold water in the west and north side of the island, retained as well in the SW due to the interaction with the bathymetry.
Fig 4.
GlobColour images for chlorophyll a concentration.
Warm colours represent higher concentrations of chlorophyll a. Blank spaces are missing values. Colorbar with log(chl a). A) Image from the 19th of December 2010. Chlorophyll concentrates on the north side of the island, especially N of João Bom (NW) and off Praia da Viola (NNE). Chlorophyll concentration seems to expand further NE. B) Image from the 10th of June of 2011. In this case, a local upwelling seems to occur in the W and SW of the island. It reaches quite high concentrations, but in a limited area.
Fig 5.
Time (hours) spent at sea per year and month.
Rough approximation of the effort carried out over the seven years of study.
Fig 6.
3D bathymetric map of the oriental group of the Azores.
We can appreciate a more confined area in the south of São Miguel, enclosed by the shallower platform on the west, and submarine mounts and Santa Maria to the south. Latitude and longitude (degrees) represented on the x and y axis, and depth (m) in the z. The colour bar represents depth, going from dark blue as maximum depth and increasing up to red-brownish which represents land (above 0m).
Fig 7.
Temporal distribution of blue whales between May 2008 and December 2014.
Dashed line shows the effort recorded, thus, hours spent at sea (left axis) each month along the 7 years of study. On the right of the graph, the year with the corresponding number of blue whale sightings in brackets is indicated. Sightings made in 2008 are grey, due to the late beginning of the data collection.
Fig 8.
Histograms of environmental values recorded in the study area against the ones associated with blue whale sightings.
A) Depth. B) Daily chlorophyll around São Miguel. It is noticeable how blue whales occur across a much smaller range of conditions than the available in the habitat.
Table 2.
Summary of the GAM results for the six obtained models.
Fig 9.
Smoothers showing the effect of distance from the coast on blue whale presence.
LD = low spatial daily, LW = low spatial weekly, LM = low spatial monthly, HD = high spatial daily, HW = high spatial weekly and HM = high spatial monthly. Black marks on the x-axis indicate the distribution of our observations.
Fig 10.
Distance to the coast of the recorded sightings.
Most of the sightings were done within 30 km from the coast (98.9%); 77.7% within 15 km from the coast.
Fig 11.
Smoothers showing the effect of seasonal EKE in the Azores archipelago for each of the six final models on blue whale presence.
LD = low spatial daily, LW = low spatial weekly, LM = low spatial monthly, HD = high spatial daily, HW = high spatial weekly and HM = high spatial monthly. Black marks on the x-axis indicate the distribution of our observations.
Fig 12.
Smoothers of the selected variables in the low spatial resolution final models.
All final models include distance to the coast and seasonal EKE for the Azores shown in Figs 9 and 11, apart from the variables here represented. A-B) Low spatial daily. C-E) Low spatial weekly. F-H) Low spatial monthly. Black marks on the x-axis indicate the distribution of our observations.
Fig 13.
Smoothers of the selected variables in the high spatial resolution final models.
All final models include distance to the coast and seasonal EKE for the Azores apart from the variables here represented. A-B) High spatial daily. C-D) High spatial weekly. E-I) High spatial monthly. Black marks on the x-axis indicate the distribution of our observations.