Octopus mimus

Octopus mimus is an octopus of the family Octopodidae, described by Gould in 1852 ^[1]. It is known in Peru as «pulpo» ^[2]. It is a benthic resource of great weight in Peru's small-scale fishery and is in high demand on the international market ^[3]. On the IUCN Red List it is assessed as Least Concern ^[4].

Males and females can be told apart at a glance: the species is sexually dimorphic, and males have one arm modified for mating, the hectocotylised arm ^[2].

Its status as a species is under debate. With mitochondrial genes, the genetic distance between Octopus mimus and Octopus hubbsorum from the Mexican Pacific turned out very low (from 0 % to 1.6 %), and the authors suggest they could be a single species ^[5]. A whole-genome analysis of 67 individuals from Mexico and Peru found, by contrast, two main lineages, a warm-water one in the north and a cold-water one in the south, and described the complex as a grey zone of speciation ^[6].

The authors of a genetic study place it in shallow eastern Pacific waters from Peru to Chile, and Octopus hubbsorum further north, between the Gulf of California and Oaxaca ^[5]. Between the two lineages lies a broad mixing belt spanning the transition between the South Equatorial Current and the Humboldt Current System; according to the authors, El Niño events intermittently weaken the oceanographic barriers and favour contact and genetic exchange between them ^[6].

At Matarani, Arequipa, monthly sampling of landings between May 1995 and April 1996 gave 2.1 males per female; mature females appeared mainly in spring and summer, and mating was concentrated in summer ^[2]. Males matured from 9.5 cm and females from 12.5 cm dorsal body length, and some females showed a new cycle of oocyte formation, a sign that not all of them die after tending their eggs ^[2].

From 1339 specimens from Ilo, Pucusana and Callao, females were estimated to reach spawning size at 14.3 cm mantle length, and from that size it was suggested that octopuses under 1 kg not be caught ^[7]. In a marine protected area in Ecuador, females matured at a larger size (1234 g; 165 mm mantle) than males (487 g; 114 mm), and the presence of mature females in every month sampled suggests a long spawning period ^[8].

Its diet is varied and includes crustaceans, molluscs, fishes and echinoderms ^[7]. At the Lobos de Afuera Islands, an examination of 304 specimens gathered from November 2020 to November 2021 found 18 prey types from three main groups, crustaceans, molluscs and bony fishes; the snapping shrimp Synalpheus spinifrons dominated in every season, and cannibalism and microplastics were recorded ^[9]. The study describes it as a generalist, opportunistic predator ^[9].

It is in turn prey for other animals: its beaks turn up in the stomach contents of several species, and 250 beaks from Lobos de Afuera were used to derive formulas that estimate the octopus's mantle length and weight from them ^[10].

Its global category is Least Concern ^[4]. The microplastics found in its stomachs at Lobos de Afuera led to a recommendation to keep watch on how plastic litter affects it ^[9].

Not medical advice. For a sting, a poisoning or an allergy, seek medical care.

In specimens collected in Sechura Bay and off the Illescas Reserved Zone during 2016, Octopus mimus had arsenic concentrations above the maximum levels set for human consumption, but not cadmium ^[11]. Most of the hazard quotients (THQ) and hazard indices (HI) computed were below 1, which the authors read as no health risk from non-cancer effects ^[11]. For inorganic arsenic, however, the estimated cancer risk across the shellfish studied always exceeded the reference threshold ^[11].

Among the octopuses of the eastern Pacific, it is the one small-scale fishers pursue most ^[8]. In Peru, catches during the 1997-1998 El Niño were 6 times higher than during the 1982-1983 El Niño ^[7].

Its farming has also been trialled at the La Arena Aquaculture Centre in Casma: octopuses grew 185 and 369 g per month in tanks and 120.6 g per month on longlines at sea, mating took place in animals over 1.5 kg, and paralarvae survived at most 17 days at 21 and 22 °C ^[3].

Studies of the species in Peru have worked with octopuses from the north of the country, at the Lobos de Afuera Islands ^[9], and with landings at Matarani ^[2] and at Ilo, Pucusana and Callao ^[7].