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

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.

Two’s company, three’s a crowd: fine-scale habitat partitioning by depth among sympatric species of marine mesopredator

“…Indeed globally, the number of skates and rays landed has been higher than landings of sharks since about 1975, suggesting skate populations may be at greater risk of overexploitation than in prior decades (Field et al 2009, Dulvy et al 2014. Previous research into species distributions and habitat preferences in the Rajidae is sparse and has relied principally on trawl data, either from fisheries (Serra-Pereira et al 2014), or from fishery independent surveys (Compagno et al 1991, Dulvy et al 2000, Hunter et al 2005b, Hunter et al 2006, Compagno & Ebert 2007, Maravelias et al 2012, Martin et al 2012. Studies such as these are typically very large scale and lack information about fine scale movements and behaviours which can significantly affect species interactions and distributions (Hussey et al 2015a).…”

Population structure and historical demography of the thorny skate (Amblyraja radiata, Rajidae) in the North Atlantic

“…Tagging studies (mark/recapture) conducted for Rajidae species have indicated traveling distances on the order of hundreds of kilometers, (Templeman 1984;Walker et al 1997;Hunter et al 2005) as compared to traveling distances on the order of thousands of kilometers for many bony and cartilaginous fishes Queiroz et al 2005) supporting the hypothesis of regional population structure in A. radiata. A closer look within the Rajidae, however, reveals that A. radiata travels the farthest-between 1.4 and 3 times as far as R. clavata (Templeman 1984;Walker et al 1997).…”

The use of external electronic tags on fish: an evaluation of tag retention and tagging effects

“…), to attach acoustic tags and DSTs. A common method has been to attach a loose-hanging tether from the electronic tag to a wire saddle through the dorso-lateral musculature, secured by a Peterson disc on the other side, for species such as Atlantic cod (Gadus morhua) and plaice (Pleuronectes platessa) [49,50] or through fin musculature for thornback ray (Raja clavata) [51]. The purpose of the Peterson tag is to spread the tension and reduce cutting of the wire through the skin and muscle.…”