Cuvier's Beaked Whale

Deep Diving

Most of the data collected on the dive patterns of Cuvier’s beaked whale were short term until a study by Schorr et al. in March 2014, which amassed a total of 3732 hours of dive data via satellite tagging. The data they collected includes an astonishing dive of 2992m depth, lasting 137.5 minutes, 1888m deeper than their previously recorded maximum dive depth and 45% longer than the previously maximum dive length. The time spent at the surface averaged at less than 2 minutes per stretch, which is a very short window for gas exchange to occur, especially in relation to the often long length of dive times. As well as this, a longer time was spent at the surface before individuals embarked on their deepest dives. This suggests that there is some level of planning involved in the length and depth of the dives.  In between the long, deep dives, the whales embarked on many smaller dives and some long stretches near to the surface were recorded. All but one of the 22 long surface stretches were recorded during the night time, which correlated with the data from previous studies. The deepest dives were also recorded at night, which could suggest that the deeper dives require a longer recovery period (Schorr et al., 2014). Despite this difference, similar dive patterns were found across day and night, indicating that the deep diving is not in response to vertical migration of prey species, and is fairly randomly spread (Schorr et al., 2014).

 

The pattern of deep and shallow dives of a particular whale over 48 hours, extracted from Schorr, 2014.

The pattern of deep and shallow dives of a particular whale over 48 hours, extracted from Schorr, 2014.

The rate of deep dive foraging trips seems to vary from 7 to 12 times a day (Tyack et al., 2006; Schorr et al., 2014). This variation could be a function of the quality and quantity of the food availability at each of different dive area, as a higher food availability would mean a lower number of dives would be required in order to satisfy the whale’s needs, or it could simply be down to the differences in foraging ability of individual whales.

The descent portion of the deep dives has been found to be faster than the ascent (Schorr et al., 2014). During the descent, the whales tend to travel at a constant speed and at a steeper, more uniform angle, whereas during the ascent the slopes were much shallower, and the speed slower and much more variable (Tyack et al., 2006). It was also found that during the ascent Ziphius only actively swam for around 41% of the time, alternating between gliding and short bursts of swimming (Tyack et al., 2006). This is possibly in order to conserve energy and reduce the level of oxygen that is required by the muscles, or could simply be due to exhaustion.

Tagging device on visible on a Ziphius. Extracted from http://whaleopedia.org/

Tagging device on visible on a Ziphius. Extracted from http://whaleopedia.org/

Mid-frequency active sonar use was seen to affect the diving behaviour of Cuvier’s beaked whale. Simulated exposure of the whales to this sonar resulted in quick movement of the whales away from the source of the sonar, an increase in the length of the dive periods, and foraging activity coming to a halt. There is a possibility that the deepest dives were affected by sonar, however the particular whale that underwent the deepest dive was sufficiently far from any source of sonar to influence it.

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