Horse mackerel (Trachurus trachurus) stomach fullness off Portugal: index calibration and spatio-temporal variations in feeding intensity

Abstract

Abstract Garrido, S., Murta, A. G., Moreira, A., Ferreira, M. J., and Angélico, M. M. 2008. Horse mackerel (Trachurus trachurus) stomach fullness off Portugal: index calibration and spatio-temporal variations in feeding intensity. – ICES Journal of Marine Science, 65: 1662–1669. An index for stomach fullness used in the routine biological sampling of horse mackerel from Portuguese waters was calibrated about the correspondent stomach mass. The fullness scale comprises four levels (1, empty; 2, <50% filled; 3, >50% filled; 4, bursting) that are easily attributed to whole stomachs during the sampling process. Significant differences were found among the four levels of the fullness scale in their relative stomach masses, indicating that the index can be used for the semi-quantitative analysis of feeding intensity in this species. The fullness index was applied to study spatio-temporal variations in horse mackerel feeding off the Portuguese coast, using data collected from 1985 to 2006 on commercial vessels and research cruises. There was no significant difference in feeding intensity between sexes. Smaller horse mackerel and those in the resting stage of reproduction fed more intensively than larger and spawning fish. Feeding intensities of fish from the southern and northwest coasts of Portugal were greater than for those captured along the southwest coast. Horse mackerel feeding intensity was greater at dawn and varied seasonally, being higher during spring and autumn and lower during winter. Interannual variation in feeding intensity of horse mackerel captured along the west coast of Portugal revealed a significant but slight decrease in recent years.