Researchers from Flinders University have been studying Dana octopus squid to determine why they are a common staple in sperm whales’ diets.
Scientists have discovered that the large size and nutrients found in the Dana octopus squid (Taningia danae) make it an important food source for large marine animals and a valuable part of the food chain.
Deep-sea discoveries
Dana octopus squid can grow up to 2.3 metres long, weighing around 160 kg. They are difficult to research due to their deep sea home, however scientists were able to recover several deceased Taningia danae bodies from the Great Australian Bight for the project.
The marine animal is known as an ‘octopus squid’ because it does not have long tentacles that separate the two species. Instead, the species has tentacles which shrink as it ages. Some believe that Taningia danae may exhibit bioluminescent qualities as well, due to the yellow photophores found on the end of its two longest tentacles, the largest light-producing organs in any animal.
Illustration of the Dana octopus squid compared to the Southern calamari squid and famous Giant squid (Architeuthis dux), which can grow up to 13m.
Fishing for answers
The recent study was conducted by Flinders University using octopus samples found in remote waters off the coast of South Australia.
Bethany Jackel, marine biologist from the College of Science and Engineering at Flinders University, says that these creatures are rich with nutrients and calories
“While the tissues have very low amounts of calories per gram, their sheer size means they actually have more calories than all other fish in the Southern Ocean, aside from toothfishes.
“This makes them a great source of food for large predators like the sperm whale because, instead of having to hunt lots of smaller fishes or squids to gain calories, they could hunt a single Taningia danae and get the same amount or even more.”
Hard beaks of Dana octopus are often identified in the stomachs of sperm whales, large sharks and seals. The size of these beaks can be compared to the iconic Giant Squid, which can grow up to 13 metres long.
According to co-author of the study Dr Ryan Baring, the levels of nitrogen and fatty acids found in the octopus tissue suggests they sit high on the food web, most likely feeding on deep-sea fish and smaller squid
“This relatively unknown species is an important part of the food webs of the Southern Ocean and the Great Australian Bight,” says Dr Baring.
“They eat deep-sea fishes and squids and in turn become calorie-rich food items for large predators including sperm whales, elephant seals and deep-sea sharks.
“Their movements between the Southern Ocean and the Great Australian Bight might also be an important way for nutrients to move between these two areas, especially from the nutrient-rich Great Australian Bight to the nutrient-poor deep Southern Ocean.
“The Southern Ocean is relatively poor in nutrients compared to the continental shelf in the Great Australian Bight, so maybe they visit to feed on this more nutrient-rich food web.”
The study has been published in the journal Frontiers in Marine Science, and suggests that the deep-sea squid is vital to sustaining marine ecosystems.
To read about research into another important species, click here.