You wouldn't want to get caught between these two sea monsters. This pair of massive deep-water foes are waging war in Antarctic waters, and it's eat or be eaten.
Given it weighs up to half a tonne and measures more than 2.5 metres in length without taking into account its long tentacles, we know surprisingly little about the colossal squid.
It was first identified in 1925 based on remains found in the stomach of a sperm whale. But other than it being whale food and living in the deep seas of Antarctica, "literally nothing is known about the colossal squid," says Vladimir Laptikhovsky of the Centre for Environment, Fisheries and Aquaculture Science in Suffolk, UK.
Now Laptikhovsky and his team have revealed one of the squid's secrets – they seem to have a taste for the Antarctic toothfish, another deep-water giant.
Like the colossal squid, the Antarctic toothfish is a predator that usually lives in eternal darkness, somewhere between 1 and 2 kilometres below the ocean surface. They can grow up to 2 metres in length and can live to be 40 years old. "It is a voracious predator that feeds on different fish, squid and shrimps," says Laptikhovsky.
Colossal squid have occasionally been observed attacking and feeding on Antarctic toothfish as they were being hauled in by fishers. Now Laptikhovsky and his colleagues have shown that, far from this being a rare occurrence, colossal squid regularly attack Antarctic toothfish.
They examined more than 8000 toothfish caught by fishing vessels between 2011 and 2014. The team found that 71 toothfish showed clear signs of colossal squid attack – scratches made by the squid's suckers and hooks, and deeper wounds gouged by its beak.
"Taking into account the size of adult squid, the toothfish probably is its most common prey species, because no other deep-sea fish of similar size are available around the Antarctic," says Laptikhovsky.
But the toothfish do seem to get their revenge. The team also found the remains of colossal squid arms, tentacles, beaks and bodies inside the stomachs of 57 toothfish.
Because Antarctic toothfish are about half the size of an adult colossal squid, Laptikhovsky says they probably only attack juvenile, old or wounded squid.
"Prior to these findings, there was little solid evidence of what colossal squid might eat," says Kat Bolstad of the Auckland University of Technology in New Zealand.
She is also searching for clues about the squid's mysterious life. Over the past 11 years Bolstad has examined four large squid and several smaller specimens. "We actually have a set of colossal gut contents from a 2014 specimen that we are planning to analyse over the next couple of months, so that may also help us fill in a few puzzle pieces," she says.
Colossal and chewy
It is thanks to the colossal squid's deep-sea feud that we now know what these creatures taste like – Laptikhovsky once had the chance to sample a tentacle that was stuck to a toothfish after a failed attack.
"The piece of tentacle was boiled and I tried it without using any spice or sauce to get an impression of the taste," says Laptikhovsky. "It was okay, better than the widely fished jumbo squid. I would say it tasted like a shortfin squid, a bit chewier because of the size."
Journal reference: Journal of Natural History, DOI: 10.1080/00222933.2015.1040477
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