First quantitative evidence of territorial behavior in squid near spawning substrates

In loliginid squids, solitary large males have been observed near the spawning grounds in several species, but little is known about their reproductive behavior. Here we describe the behavior of spear squid Heterololigo bleekeri in a 300 m³ tank near spawning substrates. Observations were recorded on their proximity to the spawning substrates, agonistic behavior, and mating behavior. In both of two rearing experiments, individual males were observed to remain near the spawning substrates and display more frequent agonistic behavior than the other males, suggesting they formed territories near the substrates. The territorial males did not monopolize the females themselves or mating opportunities, suggesting that the benefits of territorial tactics are related to the complex fertilization patterns of this species. To our knowledge, this is the first report of territorial behavior in a squid using quantitative data.