Sharks were tracked with (A) ARGOS satellite transmitters (deployed in the Azores and above the ETA OMZ) and (B) pop-off satellite-linked archival transmitters (PSAT) (deployed in west and central …
Correlated random walk models (black circles) for three representative sharks (A – S1, B – S34, and C – S36; coloured track) are overlaid on dissolved oxygen concentrations at 100 m (left panels). …
Daily minimum-maximum depth plots (shaded area) for sharks 47 and 52–54, overlaid on DO concentration data (left panels) and water temperature (right panels) from the surface to 1700 m. Red and blue …
Daily minimum–maximum depth plots (shaded area) for sharks 47 and 52–54, overlaid on oxygen partial pressure data, dissolved oxygen (DO), water temperature, and salinity from the surface to 1700 m. …
The percentage of tag-recorded time spent by blue sharks per day in the upper 500 m of the water (A and C) and maximum daily dive (MDD) depths (B and D) in relation to the dissolved oxygen (DO) …
Vertical depth use ratio (left panel) between waters above the OMZ (red) and adjacent waters outside the area of OMZ (blue) for sharks 47 and 52 (A and B); depth use ratio comparing depth …
Left panels show percentage times of shark 47 and the right panels show shark 54.
Left panels show percentage times of shark 52 and right panels shark 53.
Predicted response of modelled shark MDD depth (m) to (A) dissolved oxygen (DO) at depth, (B) sea surface temperature (SST), and (C) net primary productivity at depth (NPP). Modelled shark MDD depth …
Spanish and Portuguese longline fishing vessels (n = 322) were GPS satellite-tracked between 2003 and 2011 with the vessel monitoring system (VMS). Black dotted line: oxycline (3.5 ml O2 l−1 at 100 …
(A) The mean catch per unit effort (CPUE) of blue sharks by Spanish pelagic longline vessels in the area of the OMZ (2013–2018). Horizontal lines denote the six data transects shown in B–G. The …
(A) The mean CPUE of blue sharks by Spanish longliners in the area of the oxygen minimum zone (OMZ). Horizontal lines (B–G) denote the six data transects. Right-hand panels (B–G) indicate that …
Catch per unit effort of blue shark (mean CPUE: kilograms of blue shark/grid cell/fishing set) along (A) the 20.5°N transect of the northern boundary of the eastern tropical Atlantic (ETA) oxygen …
DNR denotes a tag that did not report.
Shark ID | % Time upper 250 m | Number dives below 600 m | Maximum dive depth | |||
---|---|---|---|---|---|---|
OMZ | Outside | OMZ | Outside | OMZ | Outside | |
S1 | 59.7 | 69.9 | 2 | 6 | 680 | 696 |
S39 | 98.5 | 83.8 | 0 | 19 | 288 | 1464 |
S47 | 90.7 | 74.0 | 0 | 29 | 520 | 1400 |
S48 | 88.8 | 92.9 | 2 | 7 | 1174 | 1390 |
S49 | 98.6 | - | 1 | - | 930 | - |
S50 | DNR | 85.7 | 1 | 2 | 804 | 1463 |
S51 | 88.4 | 87.2 | 0 | 2 | 336 | 712 |
S52 | 97.6 | 89.2 | 2 | 24 | 984 | 1480 |
S53 | 98.0 | 84.7 | 3 | 1 | 1552 | 1264 |
S54 | 97.9 | 92.1 | 0 | 7 | 272 | 1384 |
Mean | 90.9 | 84.4 | 1.1 | 10.8 | 754.0 | 1250.3 |
S.D. | 12.5 | 7.8 | 1.1 | 10.5 | 419.5 | 316.4 |
Std. error, standard error; R2 (adj), adjusted r-squared for the model; s, smooth; edf, estimated degrees of freedom; Ref df, estimated residual degrees of freedom. SST, sea surface temperature; DO, …
Estimate | Std. error | T value | p-value | ||
---|---|---|---|---|---|
MDD depth (m) (n = 1085) | (intercept) | 347.58 | 14.39 | 24.16 | <0.001 |
edf | Ref. df | F | p-value | ||
R2(adj) = 0.081 | s(DO) | 2.24 | 2.24 | 8.668 | <0.001 |
s(PP) | 2.183 | 2.183 | 10.16 | <0.001 | |
s(SST) | 3.895 | 3.895 | 4.144 | 0.002 |
FAO fishing area | Hypoxic (OMZ) or normoxic (more oxygenated) | Mean number of fishing days (per grid cell) | Fishing intensity (%) |
---|---|---|---|
FAO 34 (N Atlantic) | OMZ area | 72.7 | 65.0 |
Normoxic area | 62.5 | 57.9 | |
FAO 47 (S Atlantic) | OMZ area | 20.2 | 61.6 |
Normoxic area | 31.3 | 56.7 |
Longline catch of blue sharks were taken from Spanish pelagic longline vessel logbooks and aggregated into 1 × 1° grid cells. Each data transect analysed extended from 15.5°W to 46.5°W.
Transect latitude (°N) | Number of longline sets | Total blue shark catch in all transect grid cells (tonnes) | Peak catch per unit effort (CPUE) (kg/grid cell/day) | Dissolved oxygen (ml O2 l−1 at 100 m) at peak CPUE |
---|---|---|---|---|
20.5 | 665 | 3148 | 7025.02 | 3.49 |
15.5 | 1045 | 4021 | 6195.48 | 2.16 |
12.5 | 399 | 1436 | 6294.53 | 1.65 |
11.5 | 506 | 2006 | 4778.71 | 2.39 |
10.5 | 477 | 1815 | 5736.87 | 2.36 |
9.5 | 377 | 1386 | 5769.6 | 2.70 |
Summary data for satellite-tagged blue sharks.
Testing habitat selection of blue sharks above the eastern tropical Atlantic (ETA) oxygen minimum zone (OMZ).
Real blue shark movements were compared to correlated random walk models for those sharks tagged in the Azores that encountered the ETA OMZ off western Africa. Proportion test described in Jaine et al., 2014; ns, non-significance.
Fishing activity information for the different major fishing areas in the Atlantic.
Shaded rows denote FAO area encompassing a permanent oxygen minimum zone.