Common octopus (Octopus vulgaris)
Morphology & Biology
The Common octopus (Octopus vulgaris) is a benthic cephalopod species which occurs on coastlines to the edge of the continental shelf at depths of up to 200m. This cephalopod can grow up to 1.3m in length and weigh up to 10kg. Octopods have 8 arms and above these arms is a head with two eyes. The organs are contained within a flexible portion called the mantle which sits above the head. Octopods feed using a beak which is on the underside of the head, at the base of the arms.
Adults of this species reach maturity between 170 and 470 days old. Males die shortly after mating and females often die after their eggs hatch. Females lay eggs in clusters inside confined areas such as abandoned mollusc shells, they then brood the eggs until they hatch. During the brooding period of around 1-2 months females mostly stop feeding.
There are typically two peaks in spawning per year across the range of this species although the timing of spawning periods varies geographically. Spawning may occur at the same time as migration inshore where conditions are more suitable for egg rearing. In the Mediterranean and Inland Sea of Japan the first peak occurs in April and May and the second in October. In the Atlantic Ocean, a stronger single peak is observed during May – June which is related to the presence of suitable environmental conditions, such as sea temperature. Males of this species use a modified arm known as a hectocotylus to pass sperm into the mantle of a female where fertilisation occurs.
The common octopus feeds on bivalves and crustaceans such as various species of crab. However, they are considered to be opportunistic feeders and may consume multiple types of food depending on availability. Diet is somewhat related to size and cannibalism has been documented with larger older individuals preying on smaller younger targets. Fish may also be preyed upon occasionally but this seems to be rare according to analysis of stomach contents and leftover prey found in shelters.
Distribution
The common octopus is found in coastlines throughout the world in temperate and tropical zones, except on the Pacific coast of North America and around Indonesia, Australia and New Zealand. The species may also be found along the Pacific coast of South America, although this is not certain.
Observations of the common octopus show that they spend most of the daylight hours hidden in holes or dens, making occasional short trips outside to hunt or look out for predators. During the night, they spend much longer away from holes to hunt or engage in other behaviours. Many octopuses return to the same hole after an excursion, but some seem to return to other holes, perhaps related to where they have been hunting.
Threats
The common octopus is under threat from unregulated fishing in some areas and organised commercial fisheries throughout its range. However, since they are widely distributed in non-fragmented areas, the IUCN considers the species to be of least concern. The current population trend is unknown and their main threat is from highly destructive bottom trawling, which may also damage their habitat by closing holes. Unidentified catches of octopuses could also contain a high amount of the common octopus, which would add significantly to the overall catches and may be a threat to isolated populations, e.g. in the Mediterranean Sea.
Fisheries and Aquaculture
Global catches of common octopus peaked in 1975 at around 110,000 tonnes after increasing rapidly from less than 10,000 tonnes in the 1950’s. Thereafter, catches were relatively stable until around 2000 where they declined once more and stabilised at the current level of less than 50,000 tonnes. There is however between 120,000 and 150,000 tonnes of global octopus catch which is not identified by species and contains an unknown proportion of the common octopus.
Important fisheries for the common octopus are in the Japan Inland Sea and by Spanish vessels off West Africa, where most of the global catch is taken. The common octopus is considered to be one of the most important cephalopod fisheries in the Mediterranean Sea due to its high economic value. They are mainly taken with lures, pots, otter trawls and hooks and lines, depending on the intensity of fishing. Some artisanal catches are made, but the majority of the catches are from industrial fishing vessels.
Interest in aquaculture production of the common octopus has been increasing over time and feasibility studies have shown that it may be a suitable species for aquaculture. Difficulties in the early life stages have limited aquaculture production largely to the growth of fisheries-caught sub-adults. Additionally, their ability to stick to any surface and escape from containment causes issues with aquaculture production.
Fun Fact
Although the common octopus has 8 arms which are all equally capable, they seem to prefer particular arms for different purposes. For example, when observed under experimental conditions, they seem to use a favourite arm to poke deeply into crevices.
Summary
The common octopus is a widely distributed cephalopod species which lives on the sea floor in areas of the continental shelf up to 200m in depth. They have a varied diet determined largely by availability of food items, although they often target crabs using their strong beaks to break the shells. They are considered to be of ‘least concern’ by the IUCN and commercial catches have declined from their peak in the 1970’s. Typically the common octopus is targeted using a mix of methods, including lures, otter trawls and traps among others. The most important fishery is by Spanish vessels in the Mediterranean Sea and although this species has a high economic value, difficulties in using this species in aquaculture production have so far prevented significant growth.
