Hostname: page-component-7c8c6479df-hgkh8 Total loading time: 0 Render date: 2024-03-27T02:34:42.458Z Has data issue: false hasContentIssue false

migratory behaviour of the thornback ray, raja clavata, in the southern north sea

Published online by Cambridge University Press:  06 October 2005

e. hunter
Affiliation:
centre for environment, fisheries and aquaculture science, lowestoft laboratory, lowestoft, suffolk, nr33 0ht, uk
a.a. buckley
Affiliation:
centre for environment, fisheries and aquaculture science, lowestoft laboratory, lowestoft, suffolk, nr33 0ht, uk
c. stewart
Affiliation:
centre for environment, fisheries and aquaculture science, lowestoft laboratory, lowestoft, suffolk, nr33 0ht, uk
j.d. metcalfe
Affiliation:
centre for environment, fisheries and aquaculture science, lowestoft laboratory, lowestoft, suffolk, nr33 0ht, uk

Abstract

although depleted throughout the european continental shelf, the relatively high density of thornback rays raja clavata, in the thames estuary (uk) makes it an important stock centre and potential focus for species management. to describe spatial and temporal distribution, 197 thornback rays were tagged with electronic data storage tags (dsts) and released in the thames estuary in october 1999 and 2000, and 100 rays tagged with conventional tags in 2000. fifty-one per cent of dsts and 48% of conventional tags were returned. fishery-independent estimates of position (‘geolocations’) between the time of release and recapture using the tidal location method were possible using 75 individual data records of between 31 and 423 days. ninety-six per cent of rays were recaptured within the thames estuary. the rays were located in water of 20–35 m depth during the autumn and winter, then migrated into shallower water (<20 m depth) during the spring. fishery-independent analysis of distribution demonstrated that the rays were more widely distributed in the southern north sea during the autumn and winter. the range contracted in spring, when the fish moved into the inner thames estuary. no gross behaviour differences were observed between males and females. displacement and dispersion coefficients calculated from geolocation data demonstrated clear annual cycles, indicative of migration. these movements were not apparent from the mark–recapture data, a fishery-related effect. the extent of migration as determined from experiments with dsts was approximately three times greater than that suggested by conventional tagging data alone.

Type
research article
Copyright
© 2005 marine biological association of the united kingdom

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)