The Ecology and Ontogeny of Juvenile Cephalopods in Scottish Waters

Aspects of the ecology and ontogeny of cephalopod juveniles found in Scottish and adjacent waters were investigated, including their species composition, distribution, abundance, and seasonality of occurrence. Cephalopod specimens were collected from a variety of sources including inshore and offshore plankton surveys, beam trawling surveys, demersal trawling surveys, pelagic surveys of the Rockall Trough (SMBA 1973-1978), Continuous Plankton Recorder Survey, and historical collections of Cephalopoda in the Royal Scottish Museum Edinburgh. The area of coverage extended from 53°30°N-64°N, and from 8°E-15°W. The neritic cephalopods obtained consisted of Sepia elegans, Rossia macrosoma, Sepietta oweniana, Sepiola atlantica, Sepiola aurantiaca, Loligo forbesi, Alloteuthis subulata, Todaropsis eblanae, and Eledone cirrhosa. Oceanic species obtained from the Rockall Trough included Brachioteuthis riisei, Teuthowenia megalops, Gonatus steenstrupi, Galiteuthis armata, Chiroteuthis veranyi, Histioteuthis bonnellii, Histioteuthis reversa, and "Cirroteuthis" massyae. Peak abundances of these oceanic paralarvae occurred in May-June. Juveniles of neritic species (i.e. Sepiolinae and Eledone cirrhosa) were also found over the Rockall Trough and were believed to have been advected by offshore currents. Rossia macrosoma and Sepietta oweniana were more common along the west coast, S. oweniana in particular, was found in large numbers in the Minch and egg masses of this species were recorded in Raasay Sound during January-March. Sepiola atlantica was a widespread and common neritic species, though it was more abundant along the east coast and in the North Sea. Beam trawling surveys were carried out to determine the population biology and ecology of this species from Loch Ewe (west coast). Sepiola aurantiaca was less common although also widespread in distribution. Sepiolinae juveniles were often obtained in plankton hauls during most months of sampling. Eledone cirrhosa juveniles occurred in the plankton between January-September, with settlement probably occurring at 8.6mm DML.