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Data available were gained from 20 individuals, with a mean body mass of 74.7 kg ± 2.2 kg, and a mean standard length of 151.0 cm ± 1.9 cm. Descent rate and ascent rate averaged 1.32 m/s ± 0.01 m/s and 1.41 m/s ± 0.01 m/s, correspondingly, on the other hand, bottom time and post-dive duration averaged 74.1 s ± 0.2 s and 66.5 s ± 0.1 s, respectively.
Number of dives per individual, including ND, APC, PD, and SD
Number of SD and PD per individual
Dive typologies
Dive typologies
A difference is present between the number of dives recorded for each Australian fur seal. Indeed, there are records close to 6000 dives for some individuals (W1715, W1749, W1759, W1811, W1923), though seals reaching just a couple of hundreds of dives are present as well (W1747, W1779, W1781, W1791, W1797, W1805, W1901, W1913). The same applies for the number of PD and SD, even if most individuals range from a total of 2 to 70 dives, there is the exception of W1759 which has 350 PDs and 50 SDs.
Distribution of dives during the diel cycle
Dives distribution
Dives distribution
All dive typologies are lower over the night period, but with a different distribution over the day, as time has an impact on them.
Dive typologies
Dive typologies
Ranges of descent rate, bottom time, ascent rate, post-dive duration for the different typologies of dives.
Differences in the ranges of dive characteristics are present for the different typologies of dive. In particular, APCs have a higher descent rate, which is due to the fact that APCs have been categorised on descent rate, but the same conclusion can be deduced even from the next descent rate. A large difference is not present for NDs, PDs, and SDs. The same pattern applies to ascent rate. On the other hand, PDs have a higher bottom time during the day, while APCs have a higher bottom time during the night, there is no large difference between all the other dive typologies. Post-dive duration is analogous for all the dive typologies.
Distribution of the different typologies of dives
Distribution of the different typologies of dives
Distribution of descent rate, bottom time, ascent rate, post-dive duration, and next descent rate for all the dive typologies.
From the LME fitted with an ANOVA, the typology of the dive, the time of the day, and the individual, as a random effect, have all a significant effect on the descent rate, ascent rate, bottom time, and post-dive duration. The inclusion of individuals as a random effect, plus the effects of the time of the day, the day phase (Day/Night), and the dive typology was supported in all models, even if with a variance between strength of repeatability.
From the GAMM models, differences in the dive behaviour between the dive typologies can be observed. The Descent Rate is particularly high for APC dives, especially during the day, while it peaks at dawn and dusk for PDs, and crests up in the late afternoon for SDs. Regarding bottom time, for APC dives it is higher during the night period (This can be the result of the bad visibility at night, therefore needing more time to search and spot prey). On the other hand, for PD dives, the bottom time is higher during the day and lower at night (As predators are subjected to scarce visibility as well, therefore, during the night period, AUFS are more covered by the darkness), the same applies for SD dives. Furthermore, Ascent Rate is the highest for APC dives, especially at dusk, which is the same period at which is highest even for PD (This can be linked to predator avoidance, the individuals want to stay as little as possible in the water column and go back to hide, as it is when sharks are most active). Moreover, for SD it gets higher with the passing of the hours. Concerning post-dive duration, APCs have their lowest time between 10 and 12, but it is mostly stable throughout the day, being foraging dives it makes sense to be stable. For PD dives, they are lower around dawn and dusk, suggesting that they want to spend as little time as possible at the surface when predators are around, and SD have their highest peak at 12, and it is lower during dawn and dusk. The trend of the next descent rate is similar to the descent rate.
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