Browsing by Author "Sousa, Luis"
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- Agonistic and predatory behaviour of the lizardfish Synodus saurus (Linnaeus, 1758) (Actinopterygii: Synodontidae) from the AzoresPublication . Soares, Marta S. C.; Barreiros, João P.; Sousa, Luis; Santos, Ricardo S.The behaviour of the lizardfish Synodus saurus, a common demersal predator in Azorean waters, is described. A total of 25 hours’ qualitative diurnal underwater observations were carried out between July 2000 and January 2001. Behavioural aspects are presented, illustrated with diagrams based on in situ observations. S. saurus is a cryptic predator that feeds mainly of small pelagic, gregarious fish; it is primarily associated with soft bottom substrate. Besides remaining camouflaged buried beneath the sand, S. saurus is a highly mobile predator capable of rapidly swimming more than five meters to capture its prey. S. saurus maintains a territory through agonistic interactions, and also interacts non-agonistically with heterospecifics such as Bothus podas maderensis.
- Feeding habits of the lizardfish Synodus saurus (Linnaeus, 1758) (Actinopterygii: Synodontidae), from the AzoresPublication . Barreiros, João P.; Sousa, Luis; Soares, Marta S. C.The feeding habits of the lizardfish Synodus saurus were study in the Azores archipelago, north-eastern Atlantic. Factors examined were diet composition, prey importance, season, fish size, feeding strategy and prey orientation in the oesophagus. The stomach contents of 308 specimens were collected and analyzed between March and November 2000. Synodus saurus is common in Azorean water. Though it prefers small gregarious pelagic fish, it also feeds on epibenthic and benthic prey. We found the following prey in its diet: 9 families of teleostean fishes (Carangidae, clupeidae, Cynoglossidae, Gobiidae, Labridae, Myctophidae, Spaidae, Spyraenidae and Synodontidae), two families of crustaceans (Cymothoidae and Scyllaridae) and one of cephalopods (Loliginidae). The European pilchard, Sardina pilchardus was the commonest prey. The diet of the lizardfish varies with the season, showing the greatest diversity (given by the Shannon-Wiener index) in October. There is a significant correlation with the sea temperature. The size of the predator is not correlated to the size of its prey. However, we observed a positive correlation between the size o the positive correlation between the size of the predator and the quantity of food in its stomach. The orientation of the prey in the oesophagus may partly depend on the predator’s size. However, analysis of the stomach contents provided no information on the selection of prey.
- Preliminary notes on the reproductive biology of the lizardfish, Synodus saurus (Actynopterygii: Synodontidae) in the AzoresPublication . Sousa, Luis; Barreiros, João P.; Soares, Marta S. C.; Hostim-Silva, Maurício; Santos, Ricardo S.Between March and November 2000, 307 specimens of the lizardfish Synodus saurus (Linnaeus 1758) were captured on several coastal areas of Terceira Island, Azores. This species is an important coastal epibenthic predator. Although common, its biology, namely its reproduction, is virtually unknown. During the study period, 206 females (155 mm to 460 mm TL) and 101 males (269 mm to 290 mm TL), were captured. Sex ratio was 2:1 with more males in June. Gonados-somatic Index (GSI) for females and males attained its maximum values during Spring and Summer, showing that these are the most intensive reproduction periods. Hepato-somatic Index (HSI) suggests that this species may well recur on body reserves for energy metabolization in gonad development. Nevertheless, more studies are necessary in order to confirm this assumption. Ovarian histology, presenting different oocytarian phases, indicates that this species has an asynchronous posture. The male increment of June, associated to higher GSI values, suggests that this could represent a moment of intense competition for females, within the studied area.