Size and body weight estimation of "gould octopus" Octopus mimus A. Gould, 1852 (Cephalopoda: Octopoda) from beak measurements in northern Peru

Octopus mimus is an octopod of interest to benthic fisheries in Peru and an important species in food webs. Its beaks or jaws can be found in the stomach contents of various species, making them a useful tool for species identification, as well as for estimating age and biomass. This study aimed to establish regression formulas between beak measurements and mantle length (ML) and body weight (W) of O. mimus specimens caught in the adjacent waters of the Lobos de Afuera Islands, Peru. Two hundred fifty beaks were analyzed. Our results showed that the most useful beak measurements for estimating the ML were upper hood length (UHL) and the length of the baseline of the lower beak (LBL). These measures fit logarithmic and exponential equations, respectively. For W, the best measurements were upper crest length (UCL) and LBL, both of which fit exponential equations. This study could be useful in analyzing the diet and trophic ecology of its predator species. It is the first study to develop a regression formula from O. mimus beak measurements to estimate ML and W.