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

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.

Reproduction and feeding habits of the River Catfish Eutropiichthys vacha (Hamilton, 1822) (Siluriformes, Schilbidae) in an impacted habitat: Kotri hydrodam, River Indus, Pakistan

“…Furthermore, as the gonads increase in size filling most of the abdominal cavity, stomachs shrink to their lowest. Similar observations were noted in Oreochromis niloticus in Abu-Zabal Lake in Egypt (Kariman et al (2009), Hotoscopelus kroyeri in the Northwest Atlantic (Mazhirina and Filin 1987) and Trachurus trachurus off Portugal (Garido et al 2008) among others. Highest % of full stomachs was recorded during June, which also correlated with higher GaSI indicating that feeding intensities increased rapidly soon after spawning.…”

Interdecadal and spatial variations of diet composition in horse mackerel Trachurus trachurus

“…Fish from both the decades were classified according to L T , gutted mass, sex, maturity stage, level of fat content, area and season of the year. The fullness index was used to classify individual stomachs (Garrido et al , 2008). The masses of the whole stomach and of the stomach content were measured with a 0·1 mg precision.…”

“…Given that the diet composition of T. trachurus varies with size, and the threshold size separating fish by diet composition can be placed at c. 20 cm for the Portuguese coast (Cabral & Murta, 2002), only data collected from fish >20 cm L T for both data sets were used. Since feeding intensity is similar for individuals of both sexes (Garrido et al , 2008), data from males and females were included in the analysis. Only the stomachs of fish collected during autumn (September, October and November) and summer months (June, July and August) were used, given that those periods correspond to the peak of T. trachurus feeding intensity off Portugal, which is probably related to the seasonality of prey abundance (Garrido et al , 2008).…”

“…The horse mackerel Trachurus trachurus (L. 1758) is a member of the trachurid sub‐family, which is widely distributed in the world's seas, and is commonly found from the waters off West Africa and Cape Verde Islands to the Norwegian Sea, including Iceland, as well as in the Mediterranean and Black Seas. Trachurus trachurus feeding intensity off the Portuguese coast was studied using a semi‐quantitative method (Garrido et al , 2008), showing that the diet varied seasonally, being higher during spring and autumn and lower during winter months. The seasonal pattern of feeding intensity is probably related to the seasonality of prey abundance and species composition.…”

“…Significant interannual differences in the fullness of T. trachurus stomachs were observed in extensive data collected from research cruises off the Portuguese coast. In the last decade, a slight decreasing trend of stomach fullness was observed (Garrido et al , 2008). The comparison of the diet composition of T. trachurus during periods of high and low feeding intensity would allow the investigation of the degree of adaptability of the fish to different feeding environments.…”