1,721,076 research outputs found
Struttura e risorse trofiche della associazione ittica del margine della piattaforma continentale tirrenica.
No full textLe aree di nursery nel contesto degli ecosistemi marini: aspetti funzionali, metodi di studio e prospettive gestionali
No full textIn questo studio si sintetizzano i principali aspetti scientifici inerenti l'identificazione e valutazione del ruolo svolto dalle aree di reclutamento per la produttività delle popolazioni ittiche. Vengono presentati e discussi i risultati di diversi casi di studio con l'obiettivo di definire un framework metodologico applicabile in Mediterraneo
Sforzo di pesca, catture e gestione dello stock di nasello (Merluccius merluccius) in un'area del Tirreno centrale
No full textRhythms of feeding activity and food consumption of two mediterranean burrowing fish: Gnathophis mystax (Delaroche) and Chlopsis bicolor Rafinesque.
No full textData on the food consumption, feeding activity and periodicity of two burrowing fish, the congrid eel Gnathophis mystax (Delaroche, 1809) and the false moray Chlopsis bicolor Rafinesque, 1810 are presented. In all, 455 specimens were collected by bottom trawl in the central Mediterranean Sea at depths ranging from 140 to 160 m during four 24-h day-night sampling cycles. The diet of G. mystax and C. bicolor was investigated by means of stomach content analysis. Diet varied significantly with length and maturity stage. During ontogenetic development G. mystax occupied different trophic levels: diet shifted from amphipods, predominantly in the smaller congrid eels [ 30 cm TL). Before the transition to the icthyophagous phase, the congrid eel showed a more generalistic foraging behaviour where decapods (Solenocera membranacea, Parapenaeus longirostris, Alpheus glaber), cephalopods (Sepiola spp. and Alloteuthis media), benthic (Gobiidae, Callionymus maculatus, Arnoglossus laterna) and benthopelagic fish (Argentina sphyraena) dominated the diet. Smaller C. bicolor (< 25 cm TL) fed primarily on amphipods and cephalopods; bigger specimens fed also on decapods both natantian (A. glaber, Processa canaliculata) and reptantian (Medorippe lanata, Goneplax rhomboides). Daily ration values, computed from the Eggers method, ranged from 2.48% to 2.99% wet body weight for C. bicolor and G. mystax, respectively. Diel patterns in stomach fullness and the trophic niche overlap between the two species were also discussed
Settlement evidence of the Mediterranean parrotfish Sparisoma cretense (Teleostei: Scaridae) in the Central Tyrrhenian Sea (Giglio Island, Italy)
Full text linkNew data are reported on the Mediterranean parrotfish Sparisoma cretense in the coastal waters of Giglio Islands (North Tyrrhenian Sea). Using visual census strip transects, we documented the occurrence of both adult and sub-adult individuals, providing evidence on the existence of an established population of this species, 26 years after its first record in the same location. The potential of this warm adapted fish to further expand its distribution across the Mediterranean coasts is raised and discussed
Growth and mortality of exploited Sardina pilchardus (Walbaum) larvae along the western coasts of Italy
No full textA special type of fishery legally performed in winter to catch pilchard larvae (according to the Italian legislation still in force) has been investigated along distinct coastal areas of Italy to evaluate its environmental impact. This study shows that Sardina pilchardus larvae and juveniles numerically account for _99% of the total catch obtained during the official fishing season approximately falling in January 15–March 15.
Our estimates obtained during winter 1997 on natural mortality of the sardine larvae show that at least 40% of the individuals would even die in unexploited fry shoals. Otolith readings and analysis of modal progression give an average growth rate of 0.36 mm per day for larvae in the 20–45 mm size range at 13 8C water temperature
Valutazione del ruolo degli habitat per il successo del reclutamento del nasello (Merluccius merluccius) del Mar Tirreno.
No full textBiology, spatial distribution and population dynamics of Lepidotrigla cavillone (Pisces: Triglidae) in the Central Tyrrhenian Sea
No full textSpecimens of Lepidotrigla cavillone (the large-scaled gurnard) were collected in the Central Tyrrhenian Sea during trawl surveys carried out in April-May and September 1985, 1986, 1987, 1994, and in October 1995. The species was fished between 30 and 200 m depth. A significant size-depth relationship (p < 0.001), was observed for juveniles (S.L. < 7 cm) and adults: the former migrated deeper from the coastal nursery, at the end of the first year of life; the latter moved shallower toward the spawning grounds at 60-100 m depth. Principal Component Analysis, indicated gonadal development as the main factor affecting L. cavillone depth-size relationships. Mature females were observed with significantly higher abundance (p < 0.001) at depth of 80-100 m. Large-scaled gurnards accomplished more than half of their growth during the first two years. Reduction of growth coincided with attainment of sexual maturity. An increase of the mesh size towards the legal size may bring the age at first capture from 1.5 years up to the age of first maturity (second year) improving current Y/R
Growth and reproduction of Xyrichthys novacula (Pisces : Labridae) in the Mediterranean Sea
No full textMediterranean razorfish, Xyrichthys novacula, were collected between July and December in a sandy bay of Ponza Island (Central Mediterranean Sea) to investigate the effects of reproduction and growth patterns on sexual inversion processes and haremic territoriality The minimum body size of males decreased from 17 cm in July to 15 cm (T.L.) in October as a consequence of the sexual inversion after reproduction. Females showed a reproductive peak in August using both the Holden and Rait scale and the gonodosomatic index. The gonads of males were small, on average only 0.14% of total body weight. The proportion of body weight devoted to gonads did not change with male size. This is probably a consequence of the haremic mating system of the species which reduces sperm competition between males. A new coloration phase for females was introduced in addition to the three already described in the literature. Individuals of each age class are characterised by different coloration patterns. This chromatic feature of the species allows dominant males to recognize the age of females and consequently to choose during harem formation the older and larger specimens able to produce a larger number of offspring
Day-night variations in the demersal nekton assemblage on the Mediterranean shelf-break
No full textThe composition of the demersal nekton assemblage inhabiting the Mediterranean shelf-break of west-central Italy was examined to investigate the diel variation in species composition and abundance. Fish were obtained during four 24-h sampling periods that represented the four annual seasons. Thirty-two hauls (eight in each season) were conducted in a shelf-break area at 140-160 m depth. The density of fish, crustaceans, and decapods exhibited differences on short- and long-term time scales: Multidimensional scaling suggested that season and light intensity may be important factors influencing fish assemblage composition. At the diel scale two main assemblages separating nocturnal and diurnal hauls were identified. The typical assemblage structure of shelf-break bottoms was represented during daylight by species such as Merluccius merluccius, Capros aper, Serranus hepatus, Macroramphosus scolopax and Trisopterus minutus capelanus. At night, the assemblage showed a drastic change due to the increase of small nektobenthic species, Argentina sphyraena and Glossanodon leioglossus, together with cave-dwelling fish (Gnathophis mystax, Chlopsis bicolor, Nettastoma melanurum) and nektobenthic crustaceans (i.e., Parapenaeus longirostris and Solenocera membranacea). The above-mentioned differences in species composition may be related to changes in vertical distribution for trophic needs (M. Merluccius) and/or in the shoal structure (A. sphyraena and G. leioglossus). The lack of data on the pattern of trawl catchability of Mediterranean species during the day may lead to an inaccurate estimation of species abundance when only diurnal trawl survey data are used
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