1. INTEGRATION OF REMOTE SENSING DATA WITH TURSIOPS TRUNCATUS SIGHTINGS
IN THE PELAGIE ISLANDS
Roberto Ligi1, Achille Ciappa1, Cristina Giacoma2, Marta Azzolin2, Paola Richard3, Irene Galante3
1)Telespazio, 2)Università degli Studi di Torino,
3)CTS – Settore Conservazione Natura
Introduction
In the framework of the LIFE Del.Ta project Nature 2003 NAT/IT/163 a methodology integrating satellite remote sensing with conventional ‘in situ’ data has been developed and experimented in order to obtain the ecological information relevant to the preparation of the Common Bottlenose Dolphin (Tursiops truncatus) Action Plan for the Pelagie Islands area. Sensors on board of the remote sensing satellite acquire environmental data and observations describing the behaviour of many oceanic and terrestrial phenomena. Satellite data have some advantages compared to other kind of data because large areas can be simultaneously observed, and the observations can be frequently repeated with the same characteristics of acquisition.
The habitat of a marine species in terms of geophysical parameters, biological characterization and oceanographic dynamic is directly or indirectly observable by satellite through the measurements of environmental parameters like Sea Surface Temperature (SST) and chlorophyll concentration. The LIFE Nature project 2003 NAT/IT/163 activities include the realization of maps based on the measurements of SST and surface chlorophyll concentration by satellite and in-situ observations of dolphin. Results for 2004 (period March-December) regarding the relationship between dolphins distribution and satellite data are presented.
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LIFE 2003 NAT/IT/000163
Satellite maps of Chlorophyll and Sea Surface Temperature (SST)
The presence of coastal gyres over the African continental shelf is evidenced in fig.3 and 4 where maps of chlorophyll are shown for two dates of September. These data are obtained by MODIS sensor, on board of TERRA satellite. In these images the variability of coastal gyres (identified by higher values of chlorophyll) is shown: these structures usually confined on the shelf (on the left) occasionally can reach the southern coast of Lampedusa Island (on the right). Sea Surface Temperature (SST) fields (fig. 5, 6), also obtained by MODIS satellite data, evidence the variability around the coasts of Lampedusa, probably due to the location on the edge of the shelf.
Tursiops truncatus sightings around Lampedusa Island
Locations of sightings of Tursiops truncatus collected during field surveys realized during 2004 are shown in figure 7. Satellite maps of sea surface temperature (SST) and chlorophyll have been produced for each day of sighting, and SST and chlorophyll values have been extracted for each location.
SST data are plotted in fig. 8 with circles, symbols at the bottom of the plot indicate unavailable data (due to cloud coverage).In the same figure averaged values around the island of Lampedusa (obtained on a square 20x20 Km around the island) are represented by black dots. The comparison of sighting temperature with average values can give some indications on the potential selection of preferential temperature by Tursiops.
Oceanographic features in the Sicily Channel
The central part of the Mediterranean Sea is an exchange area between water masses of the Eastern and Western Mediterranean basins. In particular, the Sicily Channel is interested at the surface by the penetration of light Atlantic waters moving from west to east (MAW, Modified Atlantic Water) and the opposite movement of deeper dense waters formed in the Levantine basin eventually flowing through the Gibraltar Strait (LIW, Levantine Intermediate Water). The westwards flow of deep dense water, investigated during recent oceanographic campaigns in the Sicily Channel, is almost constant during the year and characterized by different water masses (as EMWD, Eastern Mediterranean Deep Water) rich of nutrients as nitrates and silicates.
Fig.1 - Bathymetry of the Sicily Channel and location of Pelagie Islands.
Fig.7. Distribution of dolphins sightings around the Lampedusa Island collected in year 2004.
Fig.8. Distribution of SST values relative to sightings of dolphins for julian day.
Fig.3 and 4 - Chlorophyll Concentration measured by MODIS satellite data for September 3 and 15, 2004.
Most of data are available for two periods, approximately at beginning of July and at the end of August. In July sightings occurred in water colder than the average value (in fig.6) with most of the circles located over the black dots. Fig. 9 shows the frequency distribution of all recordings of temperature at location: most sightings were recorded at 26-27°C.
In fig.10 the chlorophyll distribution of sightings shows a wide distribution of values probably due to the occasional influence of coastal waters on the southern coast of Lampedusa, where most of the sightings occurred. In particular at the end of August sightings occurred more frequently in waters with higher values of chlorophyll compared to the averaged values.
Observed current regimes 
Pelagie Islands (Lampedusa, Linosa and Lampione) emerge between the African and the Italian coastal plateau and for this reason are interested by two different dynamical regimes: strong current jets on the northern side along bathymetric slopes and coastal anti-cyclonic gyres over the continental shelf, in the southern area of the archipelago.
The surface circulation pattern observed from June to September, when most of the sightings occurred, is in accordance with the seasonal climatological circulation pattern (fig.2).
Fig.10. Distribution of chlorophyll values relative to sightings of Tursiops for julian day.
Fig.9. Cumulative distribution of temperature of sightings.
The analysis of this study give the following indications:
Sightings of Tursiops truncatus mainly occur over the continental shelf along the southern coast of
Lampedusa. This area is interested by weaker currents regime if compared to the northern side;
Sightings in July occurred more frequently in colder water than surroundings, in September in waters
richer of chlorophyll compared to the surrounding;
The preferential temperature range found for total dolphin sightings is °C.
These preliminary results will be critically analysed in the next steps of this project. During next ‘in situ’ campaigns possibilities to integrate remote sensing data with a wider extended range of data will be further pursued.
Fig.2. Surface circulation pattern observed from satellite derived sequences of chlorophyll maps from June to September 2004.
Fig.5 and 6 - Sea Surface Temperature measured by MODIS satellite data of September 3rd, In fig.6, which is a zoom over Lampedusa area, the points represent the dolphins sighting for that day.
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