Footage from remote-controlled submersibles reveals that male deep-sea squid struggle to differentiate between females and fellow males when mating in the faintly lit waters.

The male of the species has adopted a sexual strategy to mate with any deep sea squid it comes across.

Scientists report that factors such as bad light, similar male and female body size and the rarity of encounters are to be blamed for this indiscriminate behavior, resulting in marks slapped on the bodies of unsuspecting males in the form of spent sperm sacs.

A team led by Henk-Jan Hoving, a marine biologist at the Monterey Bay Aquarium Research Institute in California, found evidence of the squid's approach to sex when they examined screen grabs from video recorded at depths of 400 to 800 metres in the Monterey canyon off the coast of California. Remotely operated vehicles were used to explore the deep waters.

The report, published in the journal Biology Letters, focused on a squid species called Octopoteuthis deletron.

During mating among squids, the male releases a sperm-filled bag that discharges into the female's tissues. Males use a long tentacle-like appendage - a penis of sorts - to deposit small sperm-laden sacs, called spermatangia, on to females. Though the act is fast, it leaves empty sperm sacs on the female body as an outward sign of recent mating.

In the study, of the 108 squid filmed, it was possible to determine the sex of 19 females and 20 males. Among them, 10 females and nine males had visible sperm sacs on their bodies. Those left on the males were such that they must have been left by other males, the researchers have reported.