Behaviour

Niche partitioning of time, space or resources is considered the key to allowing the coexistence of competitor species, and particularly guilds of predators such as sharks.

However, the extent to which these processes occur in marine systems is poorly understood due to the difficulty in studying fine-scale movements and activity patterns in mobile underwater species.

Thanks for advancements in tracking technologies, scientists have discovered an intriguing behavioural trait amongst some marine species: They sometimes swim in circles.

When studying the navigational abilities of sea turtles, Tomoko Narazaki, a marine researcher at the University of Tokyo, observed that the turtles in her study would swim in circles so constantly “just like a machine.”

Using a modified version of the Stanford marshmallow test, researchers at the Marine Biological Laboratory (The University of Chicago) discovered that cuttlefish had the ability to delay gratification for a better reward—and those that were able to do it for a longer duration possessed better cognitive learning abilities.

The findings, which demonstrated the link between self-control and intelligence, was published recently in the Proceedings of the Royal Society B journal.

This finding was based on research by a team of biologists and mathematicians from Swansea University and the University of Essex. It involved 15 three-spined stickleback fish observed individually in a fish tank containing two, three or five plants in fixed positions.

Using high-resolution tracking data from video recording, the scientists made their observations on the following parameters: movement (time stationary, step length, turning angle and burst frequency) and behaviorial (distance travelled, space use, time in free water and time near objects).

Sleep is ubiquitous across the animal kingdom but despite anecdotal reports of sleep-like behaviour in nurse sharks and other seafloor-dwelling species, the question of whether sharks actually sleep has been intensely debated but remains unknown. A key criterion for separating sleep from other quiescent states is an increased arousal threshold. True sleep is characterised by a lack of movement that can be rapidly reversed and a decreased awareness of surroundings.

Zoologist Douglas Bastos from the National Institute of Amazonian Research in Manaus, Brazil, and his team have captured video footage of Volta’s electric eels hunting in groups of more than 100.

In the footage, the eels encircled shoals of tetra fish to form a “prey ball”, which they herded toward shallower waters. Then, two to ten of the eels swam closer to the ball to deliver jolts of electricity. The synchronised charge is so powerful that some of the fish are blasted out of the water. Stunned, they fall back into the water, and are consumed by the eels.

Lunge-feeding humpback whales plunge into dense schools of small fish to feed on them. However, these small fish tend to be pretty fast. So, just how do huge whales sneak up on such speedy prey if they are as huge and overbearing as a ... well, whale?

This question became the focus of a study at Stanford University. Its findings was subsequently published in the Proceedings of the National Academy of Sciences journal.

In a study involving 378 orcas (or killer whales), researchers observed the first non-human example of the "grandmother effect" in a menopausal species.

This is when post-reproductive grandmothers (in this case, orcas) assist other members of the species with their offspring, thereby improving the young ones’ chances of survival. It was found that these post-reproductive orcas had the largest beneficial impact on their grandoffspring’s survival chances.

Mirror self-recognition test

The standard method for testing whether an animal is self-aware is placing a mark on its body that cannot be viewed directly and then letting it have a look in a mirror. If the animal responds to its reflection and attempts to remove the mark it is considered evidence that the animal is self-aware.