1 These were glued to the animal’s fur on the neck behind the head Ixazomib chemical structure with quick-setting epoxy. The tags were configured to attempt Fastloc GPS locations every 10 min provided the seal was at the sea surface. Both seals were captured and tagged in the Molène archipelago, western Brittany, France. During their whole track duration (172 and 204 d, respectively), both seals crossed the English Channel, back and forth, moving directly from one colony
to another. We consider here two such transits of the English Channel from the United Kingdom to known seal haul-out sites. These movements occurred outside the breeding or molting season of gray seals in the French colonies, but there could be breeding in the Isles of Scilly at that time of the year (September). Seal B24 departed from the Isles of Scilly (UK) and arrived at the Isle of Molène (France) after 43.5 h (Fig. 1). B23 crossed
the English Channel (Fig. 2) in 48 h between Porthleven (UK) to the Nature Reserve of Les Sept Iles (France). At total, 158 Fastloc GPS locations were obtained for seal B23 over its crossing the English Channel (mean = 3.3 locations per hour) and 148 for seal B24 (mean = 3.4 locations per hour). Hourly ground track locations were then determined using linear interpolation of the raw track data. In the English Channel, tidal currents dominate current patterns due to wind, wave, and thermohaline effects Serine Protease inhibitor (Sentchev et al. 2009). For this reason, we estimated the currents along the seals’ pathways using a tidal model. We used a 2-D model that estimates currents averaged over the whole water column (TELEMAC software, Hervouet 2007), which has been shown to be very effective for modeling tidal propagation in coastal waters (Nicolle et al. 2009, Davies et al. 2011). The model was initially developed for numerical simulations of tides and storms surges (Chevaillier 2011) and it was validated through extensive Y-27632 solubility dmso comparisons with the sea level and sea current measurements in
the Bay of Biscay and in the English Channel. In this study we define: “Ground Track” (GT) as a series of movement vectors built from the GPS time-stamped location fixes; “bearing” as the direction of a Ground Track vector; and “heading” as the direction a seal is pointing. A seal’s ground track, D, can be represented as a sum of drifting and swimming vectors: D = Dd + Ds. We calculated the drift, Dd, as a Lagrangian transport displacement experienced by a passive particle in tidal flows (TELEMAC, Hervouet 2007). The measured surface velocities of the tracked seals were not used for the numerical simulations. These are the result of both the swimming speed of the seal and the current’s speed, and we aimed at modeling the animals’ movements from a data set completely distinct from the “real” seal data before comparison of the model vs. the track of the seals. We compared two navigation rules.