Inter-annual variability in growth and maturation of the swordtip squid Uroteuthis edulis in Yilan Bay off northeastern Taiwan

Abstract

The swordtip squid Uroteuthis edulis, distributed in the temperate and tropical neritic waters in the Indo-Pacific region, is a crucial component of marine ecosystems and is a target species of fisheries in the Northwest Pacific. Although studies have elucidated the growth and maturation of the squid in the southern East China Sea (ECS) shelf, few have assessed the population biology of the squid in waters in the vicinity of the southern ECS. We collected samples of swordtip squid from a trawler in Yilan Bay (YLB) between January 2011 and December 2012 to examine the growth and maturation of the squid based on statolith microstructures and the inter-annual variability in certain parameters as well as the potential underlying mechanisms. The average dorsal mantle length (ML) of the squid was significantly higher in 2011 than in 2012 in both sexes. The ML-body weight relationship differed significantly between 2011 and 2012 in both sexes. Squid hatching peaked in summer (June and August)in 2011 and spring (March and April) in 2012. The average ML-at-age data were described using the exponential function and power function for female and male squid, respectively. Female squid matured to 139 mm at 133 days in 2011 and to 133 mm at 137 days in 2012. Male squid matured to 160 mm at 151 days in 2011 and to 148 mm at 133 days in 2012. However, the ML- and age-at-maturity of the squid in YLB were lower than those of the squid in the southern ECS shelf. These results indicate that YLB is one of the feeding grounds for squid that have hatched in the southern ECS shelf and have been transported southward intermittently to YLB. Further study of the population structure and potential population connectivity of the squid in the entire ECS shelf is warranted to obtain data for the development of effective conservation and management measures for the squid and its fisheries in the Northwest Pacific.