Feedingecologyofthelesserweever, Echiichthys vipera (Cuvier,1829),onthe westerncoastofPortugal By R. Vasconcelos, N. Prista, H. Cabral and M. J. Costa Instituto de Oceanografia, Faculdade de Cie ˆncias da Universidade de Lisboa, Campo Grande, Lisboa, Portugal Summary The feeding ecology of the lesser weever, Echiichthys vipera, from the adjacent coastal areas of the Douro and Tagus estuaries (Portugal) was studied between October 2000 and July 2002. The stomach contents of 246 individuals were analysed and diet was characterized by the numerical, gravi- metric, occurrence and vacuity indices. Variation of feeding habits with fish length (<95 and >95 mm) and geographical area was considered. Diet of the lesser weever comprised a large variety of prey (28 species), the most important of which were crustaceans (numerical index, NI ¼ 93.5%; occurrence index, OI ¼ 75.6%), namely Mysidacea (especially Schisto- mysis sp.), Amphipoda (mainly Gammarus subtypicus) and Isopoda (Idotea spp.), and also Teleostei (mostly larval stages that posted a gravimetric index, GI ¼ 53.0%). Diet varied with fish length, with large individuals showing a larger diversity of prey items. Furthermore, specimens from Douro also showed a higher diversity of prey items than those from Tagus. More than 50% of the stomachs were empty, being the highest vacuity values relative to smaller fishes as well as to individuals from the Tagus estuary adjacent coastal area. Introduction Lesser weever, Echiichthys vipera (Cuvier 1829), occurs in the eastern Atlantic from the Skagerrak and the Shetland Isles to Morocco and throughout the Mediterranean (Lewis, 1980; Tortonese, 1986). It is generally found on clean sandy bottoms from low-tide mark to 50 m depth (Wheeler, 1969, 1978). This species can reach 150 mm in standard length (Tortonese, 1986) and is considered the most dangerous of the European weevers for its poison and frequent occurrence very near to beaches (Tortonese, 1975). As are all members of the Trachinidae family, E. vipera is a bottom-dwelling fish which lies buried in the sandy sea-bed during the day and emerges to forage at night (Lewis, 1976; Wheeler, 1978). Little that is known of the feeding ecology of the lesser weever is from studies conducted in the southern North Sea (Creutzberg and Witte, 1989), on the Atlantic coast of France (Quiniou, 1978; Sorbe, 1981; Dauvin, 1988) and on the coast of Morocco (Collignon and Aloncle, 1960), being unknown in the Iberian Margin. These studies report that the E. vipera diet consists mainly of small benthic organisms, chiefly Crustacea (Mysidacea, Amphipoda, Isopoda and Decapoda), Teleostei, and also Mollusca and Polychaeta. Although E. vipera is among the five most abundant species of the fish assemblage from the coastal zones adjacent to the Tagus estuary (Prista et al., 2003) as well as the Douro estuary (Vasconcelos, 2001), there is a complete lack of knowledge on the ecology of this species for the Portuguese coast. This paper focuses on the feeding ecology of E. vipera in the western coast of Portugal (north-eastern Atlantic), including diet variation with predator size and geographic area. Materialsandmethods Sampling surveys took place every 2 months, from October 2000 to July 2002, at six sites in the adjoining coastal area of the Douro estuary and six sites in the adjoining coastal area of the Tagus estuary (Fig. 1). Fish captures were made during daylight, from 6.00 to 21.00 hours, at an average depth of 13 m (minimum 2.8 and maximum 19.6 m), using a bottom otter-trawl (with a tickler-chain along the head rope and a cod end with 18 mm mesh size) and frozen immediately after catch. All specimens of E. vipera were measured (total length with a precision of 1 mm) in the laboratory and weighed (wet weight with a precision of 0.01 g). A total of 246 lesser weever specimens were dissected, the digestive tract removed and preserved in 70% ethanol solution. Individuals of E. vipera ranged in length from 54 to 134 mm. Stomach contents were identified to the lowest taxonomic level possible. Numbers and weights (wet weight with a precision of 0.0001 g) of food items were registered. The contribution of each prey to the lesser weever diet was assessed through three indices. The numerical index (NI) represents the number of individuals in each food category expressed as a percentage of the total individuals in all food categories. The gravimetric index (GI) consists of the total wet weight of a food category expressed as a percentage of the overall weight of stomach contents. The occurrence index (OI) represents the percentage of stomachs containing one or more individuals of each food category (Hyslop, 1980). Feeding activity was evaluated by the vacuity index (VI), defined as the percentage of empty stomachs, and by the mean weight of food per stomach (Hyslop, 1980). Both estimates were calculated for each hour of the day, between 6 and 21 h, i.e. when the trawls were made. In order to evaluate differences in feeding intensity during these periods, a Kruskal–Wallis test was performed to weight of food per stomach data and considering three periods: from 6 to 10 h; from 10 to 14 h; and from 14 to 21 h. These periods were established in order to have a relatively equable number of samples in each period. In order to evaluate differences in diet with respect to fish length, individuals were divided into two length classes: below and above 95 mm, approximately the length limit between II-group and III-group age classes, at which growth rates become much lower (Creutzberg and Witte, 1989). Individuals J. Appl. Ichthyol. 20 (2004), 211–216 Ó 2004 Blackwell Verlag, Berlin ISSN 0175–8659 Received: July 10, 2003 Accepted: November 29, 2003 U.S. Copyright Clearance Centre Code Statement: 0175–8659/2004/2003–0211$15.00/0 www.blackwell-synergy.com