An 18-year study of the Octopoteuthis deletron, a little-known squid which dwells a depth of 400 to 800m, found that males attempt to mate with any deep sea squid it comes across, whether male or females.

With deep sea conditions favouring darkness, little difference between the sexes and rare encounters with fellow squids, a study led by U.S.-based researchers found that males are either unaware or unconcerned whether the object of their attention is female or male.

Publishing the findings in the Royal Society Biology Letters journal, the scientists explained that due to having a single and short reproductive period during their already limited lifespan squids will mate with a partner regardless of its gender during their 'reproductive window'.

Henk-Jan Hoving, a marine biologist at the Monterey Bay Aquarium Research Institute in California, and his team found evidence of the squid's approach to sex when they examined screen grabs from video recorded at depths of 400-800 metres in the Monterey submarine canyon off the coast of California and realised as many males as females carried spent sperm sacs on their bodies, a sure sign that males had attempted to mate with them.

"Deep-sea squid are extremely important in the oceanic food webs as tuna and many other fish feed primarily on them. However, our knowledge of these animals is very limited," Hoving told the Guardian.

"Squid, including deep-sea species, only reproduce once and they have to find mates in time in an environment where encounters between individuals of the same species are few and far between."

The scientists also explain that with encounters often being short, mating "indiscriminately and swiftly" could help males boost their reproductive chances as wasting sperm appeared less costly for the males than perfect their ability to spot females.

The sexual strategy used is typical of the "live fast and die young" life strategy adopted by many types of squid, octopus and similar species the scientists added.

The Octopoteuthis deletron, which lives in the eastern Pacific, measures up to 15cm in height and has eight long, hooked arms.

For the study, scientists based at the Monterey Bay Aquarium Research Institute in California, USA, studied 39 male and female individuals between 1992 and 2010 to try and learn more about their behaviour.

They found that while ten out of 19 females had recently been mated with, so had nine out of 20 males.

"Apparently, the costs involved in losing sperm to another male are smaller than the costs of developing sex discrimination and courtship, or of not mating at all," the researchers said.

Same sex coupling has already been observed in more than 1,000 different animal species including penguins, dolphins and primates.

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