Hueter et al.; Horizontal and vertical movements of Isurus paucus in the northwestern Atlantic Ocean 
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Figure 4 
Depth profile for the 150-d track of a longfin mako {Isurus paucus-, LFM2) tagged with 
a pop-up satellite archival tag off the northwestern coast of Cuba in 2015. The time- 
series depth data points are color-coded by diel period. The daily maximum depth is 
based on all received summary data sources for this shark. The line for weekly mean 
depth at nighttime corresponds with values on the right axis. Note that the left axis 
is split in 2 places. 
perature distributions were not significantly different 
for these sharks (K-S test: F=0.989), and both sharks 
spent the largest proportion of their time in waters 
with a temperature range of 24-27°C (Fig. 6B). Large 
proportions of time in cold temperatures were observed; 
LFMl and LFM2 spent 19.6% and 14.5% of their time 
in temperatures <12°C, respectively. We separated the 
binned histogram data for LFM2 into 12-h blocks of 
time that roughly corresponded to day (0800-2000) 
and night (2000-0800). The differences between day 
and night for time at depth (K-S test: P=0.536; Fig. 60 
and time at temperature (K-S test: P=0.9895; Fig. 6D) 
were not significant but further highlighted the DVM 
pattern. 
Plotting time-series depth and temperature data for 
LFM2 was useful for visualizing dynamic patterns in 
vertical movement, although the relatively low resolu- 
tion of these data (10-min intervals) precluded accurate 
calculations of ascent and descent rates. This shark 
spent daytime periods largely at depth (mean daily 
depth: 321.7 m); however, we noted upward vertical for- 
ays during these periods that appeared to be regularly 
timed and came closer to the surface when the tem- 
perature at depth was coldest (Fig. 7). The depth profile 
in Figure 7D shows that LFM2 experienced a change 
in temperature as high as 18.8°C during its upward 
movements but spent a relatively brief period of time in 
the warmer, near-surface waters (approximately 10-15 
min) before initiating descent. When we examined this 
daytime pattern over LFM2’s entire track, we found an 
inverse linear relationship between temperature and 
vertical speed (coefficient of multiple determination 
[i?2]=0.63; Fig. 8A). 
In contrast, vertical speed during the night for this 
shark did not appear to be correlated with tempera- 
ture (i?^=0.001). For LFM2, mean vertical speed in the 
daytime (2.3 m/min) was higher than in the nighttime 
(1.91 m/min; P=0.0133). Mean vertical speed at dawn 
(3.46 m/min) did not differ from that at dusk (3.48 
m/min; P=0.921}, although both crepuscular periods 
showed that this shark traveled at significantly higher 
speeds than during day and night (F<0.0001). Further, 
we examined the durations between the upward day- 
time forays from depths of 250-531 m for the entire 
track of LFM2 («=36) and found that they ranged from 
1.2 to 3.8 h. The results of a linear regression indicate 
that the duration between these forays was correlated 
with the mean temperature experienced by this shark 
at depth {R^=0.60; Fig. 8B). Time-series data further 
revealed that LFM2 did not always remain in near-sur- 
face waters during the night because forays to depths 
>250 m were not uncommon, particularly during the pe- 
riod February-May (Fig. 9). Unlike the regularly timed 
daytime movements from depth (>250 m) toward the 
surface, the nighttime dive profiles for this shark were 
more variable and indicated a period of bottom time 
