Biological and ecological traits of Bathynomus giganteus and Bathynomus miyarei (Crustacea: Isopoda): Contribution to the conservation of deep‐sea in southern Brazil

Abstract

Abstract This study aimed to determine biological and distributional aspects of deep‐sea giant isopods Bathynomus giganteus and Bathynomus miyarei to assess their extinction risk. Bathynomus giganteus (663 specimens) and B. miyarei (649 specimens) were collected during five research cruises involving 265 h of sampling effort during 32 fishing operations of circular pots, baited traps, ranging from 400 and 1,000 m deep, between 26 and 29°S adjacent to the Brazilian coast. A trend towards larger, sexually mature animals in shallower regions was observed for both species, and depth was the most important environmental variable influencing the animals’ distribution. Bathynomus giganteus were collected between 600 m and 1,000 m depth, while the highest densities of B. miyarei were at shallower depths, between 400 and 600 m. The sex ratio was equal for both B. giganteus and B. miyarei for different seasons, latitudes and bathymetries. The sexual maturity of B. giganteus was estimated at 340–345 mm total length for males and between 280–290 mm for females. Bathynomus miyarei males’ sexual maturity was estimated in the 225–230 mm size class. Bathynomus giganteus showed reproductive activity throughout the year. The longevity of B. giganteus was estimated at 6 years for males and 7.7 years for females. The longevity of B. miyarei was estimated at 9 years for males and 6 years for females. Extinction risk assessment for B. giganteus, which has a greater latitudinal and bathymetric distribution, was evaluated as Least Concern. However, B. miyarei was evaluated in the Data Deficient category.