Abstract
Age composition and growth rates of the squid Loligo vulgans (Lamark, 1797) were studied by examination of growth increments within statohths of 419 specimens (mantle length, ML, ranging from 32 to 400 mm). The squid were obtained by monthly sampling from the catches of commercial trawls off southern Portugal between March and September, 1993 The total number of growth increments in the mounted and ground statohths was counted using a semi-automatic image analysis system. ML was significantly correlated with both the statolith length, TSL and the number of increments, NI. The female statolith was slightly larger than the male statolith for the same mantle size. Growth rates of individuals showed high variability with an average estimated at 34.6 mm month1 for males and 33J5 mm month' for females. Growth in length between 70 and 280 days was best described by a power function for both sexes. The growth index of the statolith (TSL/NI) decreased with individual growth. This result may be related with the onset of sexual maturation. L. vulgans hatched throughout the year with two distinct peaks, in spring which is the mam breeding penod, and in autumn. The life cycle of the L. vulgans population on the south Portuguese shelf was completed in one year
Highlights
Interest in cephalopods has increased during the last three decades, because of increased exploitation (Caddy, 1995), and since it has been recognised that they play an important role in the marine ecosystem.To evaluate population biomass changes caused by natural or fishing mortality it is necessary to know the demographic structure, which implies a precise study of the age and growth of individuals
Traditional, indirect methods to determine age of cephalopods such as length frequency analysis cannot be used due to the rapid growth of individuals, their short life span, protracted spawning season, along with the migrations undertaken by many species (Caddy, 1991; Natsukan & Korrune, 1992; Natsukan, Mukai, Nakahama & Kubodera, 1993; Guerra & Rocha, 1994)
The aim of this paper is to evaluate the age and growth of L. vulgans based on statolith analysis in an area located among the other three previous studies
Summary
To evaluate population biomass changes caused by natural or fishing mortality it is necessary to know the demographic structure, which implies a precise study of the age and growth of individuals. Traditional, indirect methods to determine age of cephalopods such as length frequency analysis cannot be used due to the rapid growth of individuals, their short life span, protracted spawning season, along with the migrations undertaken by many species (Caddy, 1991; Natsukan & Korrune, 1992; Natsukan, Mukai, Nakahama & Kubodera, 1993; Guerra & Rocha, 1994).
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
