Figure 1.
Estimated paths (with 50% and 95% confidence intervals) of 13 Atlantic bluefin tuna tagged in early June, 2009-2011 (≥45 d at liberty).
Five successive regions throughout the migratory pathways between the western Mediterranean and the North Atlantic Ocean are distinguished (A-E, black boxes): Balearic area (A), Strait of Gibraltar (B), western Iberian coast (C), Bay of Biscay (D), and North Atlantic area (E). Bold black lines represent five-day coverage of tag #39 track in each of these regions.
Figure 2.
Tracks (with 50% and 95% confidence intervals) from PSAT tags deployed in 2009 (red circles), 2010 (green circles) and 2011 (blue circles).
Paths are presented in four consecutive sequences covering the months of June and July. (A) Period between the tagging date (8, 9 or 14 June) and 17 June; this panel includes tracks from 11 tags (2 of 2009, 4 of 2010 and 5 of 2011). (B) 18 June-2 July; 11 tags (2 of 2009, 4 of 2010 and 5 of 2011). (C) 3-17 July; 11 tags (2 of 2009, 4 of 2010 and 5 of 2011). (D) 18-31 July; 10 tags (2 of 2009, 4 of 2010 and 4 of 2011).
Figure 3.
Median depths recorded by tag #39 through regions A-E (see Figure 1).
Depths are displayed with the vertical water temperature profile. The water column structure was estimated daily using a locally weighted scatterplot smoothing; then, a contourplot was made with the discrete temperature values (one value per meter and day). Solid line: daytime, dashed line: nighttime. Bars within the box of each region correspond to the respective track segments marked with bold lines in Figure 1.
Figure 4.
Depth time series of tag #39 through regions A-E in Figure 1.
Shaded areas denote nighttime. Solid lines represent the approximate bottom topography.
Figure 5.
Depth and water temperature time series from tag #25 in the Balearic area.
High-frequency shallow dives (HFSD profiles) were detected between midnight and sunrise (A, C, D); this pattern consisted of frequently repeated shallow dives (blue squares) below the bottom limit of the mixed layer (dashed line), which resulted in thermal oscillations (red squares) about the thermocline (dotted lines). Vertical profiles displaying deeper scattered dives and no clear oscillatory pattern (non-HFSD profiles) alternated with daily series of consecutive HFSD profiles (B); this pattern occurred several successive days following the last HFSD profile (E, F).
Figure 6.
Examples of high-frequency shallow diving behaviour (HFSD) from 12 fish on their spawning grounds.
Each panel shows one night of depth and water temperature time series from each tag used for the analysis of vertical movement patterns (see Table 3), except for Tag #25, which is shown in Figure 5. Tag ID is indicated at the top left of each panel.