Publication abstract

Large-scale variation in seasonal swimming patterns by plaice in the North Sea.

E. Hunter*, R.J. Cotton, J.D. Metcalfe* & J.D. Reynolds

We examined the swimming activity of 139 mature female plaice, Pleuronectes platessa L. tagged with electronic data storage tags (DST1s and DST3s) to test whether swimming activity at different times of the year differed among areas of the North Sea with different average tidal current velocities ranging from fast (West), to intermediate (East), or slow (North). High swimming and tidal swimming activity were predicted for the western group, where fast-flowing tidal currents allow efficient selective tidal stream transport. Individual depth data were converted into binary records representing swim versus rest time, and repeated patterns of swimming activity were analysed according to cycle-length frequencies. Most swimming occurred during expected times of migration and spawning (October – March). Plaice infrequently spent more than 5 h in mid-water, and rarely left the sea-bed during summer. As predicted, DST1 tagged plaice (West release only), spent the longest times swimming (P > 0.001), but there was no significant effect of Area for DST3s (released in all areas), suggesting that swimming plays an important behavioural role in migration in addition to transport between feeding and spawning areas. Tidal patterns of activity occurred in all three sub-stocks, predominantly during the migratory period, albeit at a significantly lower frequency in the northern sub-stock. These data provide one of few examples where a fish stock’s behaviour has been recorded across a large part of its geographical range, and through all seasons of the year. The results have important implications for understanding the energetics of fish migration, and the availability of demersal stocks to capture by commercial and survey vessels.

Reference

E. Hunter*, R.J. Cotton, J.D. Metcalfe* & J.D. Reynolds (not yet published) Large-scale variation in seasonal swimming patterns by plaice in the North Sea. Marine Ecology Progress Series 392; 167–178