Distribution patterns and sexual segregation in chimaeras: implications for conservation and management

Abstract

Chimaeras such as Chimaera monstrosa and Hydrolagus mirabilis are commonly found in commercial bycatch of deep-sea fisheries in the Northeast Atlantic. Very little information exists on their life history, ecology or behaviour. Segregation of populations by sex and/or age classes has been demonstrated in several elasmobranchs, but whether segregation occurs in chimaeras, and if so what mechanisms are involved, remains unknown. This study investigates the distribution and sexual segregation of four species of chimaera (C. monstrosa, H. mirabilis, C. opalescens n. sp. and Harriotta raleighana) in relation to sex, size (maturity) class, bottom depth, and latitude. Data were obtained from annual trawl surveys undertaken by Marine Scotland, Aberdeen, from 1998–2009, at 400–2000 m in the Northeast Atlantic (55–59°N 5–11°W). A factorial General Linear Model (GLM) with planned contrasts indicated complex patterns of age- and sex-related segregation. All adult males and females were sexually segregated by depth: in all four species investigated females occurred at greater depths than males. Potential birthing grounds were identified for H. mirabilis. Latitudinal spatial segregation was not evident in relation to sex or maturity stage. The patterns of segregation reported here suggest a potential for differential exploitation of the sexes by spatially focused fisheries.