Penteriani V.,University of Oviedo |
Delgado M.M.,University of Helsinki |
Ivanc M.,Fisheries Research Institute of Slovenia
Italian Journal of Zoology | Year: 2015
Abstract: Skin spots play an essential role as a visual stimulus in the social behaviour of fishes, particularly in gregarious species. Several studies have demonstrated that the characteristics of some flank signals are used as conspicuous visual cues for different aspects of intraspecific communication, as well as shaping the interactions among individuals, and reflecting the features of individuals. Here, we analyse the spatial pattern of spots in the European grayling Thymallus thymallus(Actinopterygii, Salmonidae) (Linnaeus, 1758) (Salmonidae, subfamily Thymallinae), which are usually gregarious. Adult individuals are characterised by conspicuous black spots on their sides, generally restricted to the front half of the flank. By sampling 55 individuals in Slovenia, Croatia and Norway, we tested the possible influence of environmental factors (e.g. water velocity, water depth, position in the pool/stream) and/or individual characteristics (sex and length) on the characteristics and spatial pattern of graylings’ spots. Spottiness did not show any relationship with sex or body size, but the numbers of both spots and spotted lines appeared to be correlated with some physical properties of the river: more highly spotted graylings seemed to inhabit faster and deeper waters, and were positioned at the head of pools and streams. We suggested that in gregarious fish, spottiness may signal the status (e.g. quality and/or dominance) of individuals, which has a role in determining the spatial arrangement of individuals along the river bed and, consequently, within the group. © 2015, © 2015 Unione Zoologica Italiana.
Pengal P.,Fisheries Research Institute of Slovenia |
Jenic A.,Fisheries Research Institute of Slovenia |
Pajk N.,Fisheries Research Institute of Slovenia |
Toman M.J.,University of Ljubljana
Acta Adriatica | Year: 2013
Three types of multi-mesh benthic survey gillnets were tested for their performance in the uniform muddy bottom habitat of the Bay of Piran. We describe the compared methods, present their positive and negative aspects and suggest a sampling design that could be used with different research goals. The research sampling was performed in winter in the years from 2010 to 2012. The sampling site is situated close to a sea bass rearing fish farm in the Northern Adriatic Sea. With the Nordic 1.5 type nets 5 species were detected compared to the 23 and 20 species detected with the Adriatic 2.5 and 5.0 nets. In the Nordic 1.5 type nets only demersal species were caught and even for those a much greater sampling effort would be required to reach a representative sample. On the other hand, both the Adriatic type nets also caught benthopelagic and pelagic species, and a correlation between net height and size of fish in these two nets was detected. While both the Adriatic type nets proved successful in achieving a representative sample of fish assemblage, the Adriatic 2.5 nets performed better in terms of CPUE and as such also reached a better cost-benefit ratio.
A joint stock assessment for the anchovy stock of the northern and central Adriatic Sea: Comparison of two catch-at-age models [Evaluación conjunta de la población de la anchoa del Mar Adriático septentrional y central: Comparación entre dos métodos de dinámica poblacional]
Carpi P.,CNR Marine Science Institute |
Santojanni A.,CNR Marine Science Institute |
Donato F.,CNR Marine Science Institute |
Colella S.,CNR Marine Science Institute |
And 8 more authors.
Scientia Marina | Year: 2015
Anchovy (Engraulis encrasicolus, L.) is one of the most important commercial species of the northern and central Adriatic Sea, as well as one of the most productive fisheries in the whole Mediterranean. In the Adriatic Sea the stock of anchovy is shared between Italy, Croatia and Slovenia. A joint stock assessment was carried out using catch data from all the fleets for the time interval 1975-2009. Analyses were performed using estimates of natural mortality at age obtained by means of two different methods and two population dynamics methods based on the analysis of catch-at-age data: Laurec-Sheperd virtual population analysis (VPA) and integrated catch-at-age (ICA), both tuned to acoustic estimates of abundance. Gislason’s estimates for natural mortality appeared to be more realistic and were thus preferred for short-lived species. The general trend of biomass and fishing mortality is similar for the two models, highlighting the major collapse of the stock in 1987. Nevertheless, ICA has enough flexibility to combine all the data available without adding too much complexity in comparison with a VPA approach and seems to perform better in terms of the spawning stock biomass/recruitment relationship and diagnostics (i.e. the retrospective pattern). For the stock status, the exploitation rate from ICA is higher than the suggested threshold of 0.4 proposed by Patterson for small pelagic species. © 2015 CSIC.
Reproductive cycle and size at first sexual maturity of common pandora Pagellus erythrinus (Sparidae) from the Bay of Monastir (Tunisia, central Mediterranean) [Ciclo Riproduttivo e dimensioni alla prima Maturità sessuale di pagello fragolino Pagellus erythrinus (Sparidae) nella Baia di Monastir (Tunisia, Mediterraneo centrale)] [Reproduktivni ciklus in velikost ob prvi spolni zrelosti ribona Pagellus erythrinus (sparidae) v zalivu Monastir(Tunis, Osrednje Sredozemlje)]
Smida M.A.B.,Tunis el Manar University |
Hadhri N.,Tunis el Manar University |
Bolje A.,Fisheries Research Institute of Slovenia |
El Cafsi M.,Tunis el Manar University |
Fehri-Bedoui R.,Tunis el Manar University
Annales, Series Historia Naturalis | Year: 2014
This study, dealing with the reproduction of the common pandora, Pagellus erythrinus (Sparidae) from the Bay of Monastir, focussed 640 specimens collected from September 2011 to August 2012. These specimens were sampled monthly during landings of coastal fi sheries. Among the whole samples, 85 individuals were not sexually identifi ed. The sexed specimens were composed of 260 males (46.84 %) and 295 (53.15 %). The monthly sex ratio showed signifi cant differences between males and females. Females outnumbered males for sizes between 130 and 199 mm, while males outnumbered females from the 200 mm size up. Sexes combined, the length-weight relationship had a negative allometry. The reproduction period of the common pandora starts in April and ends in August. The gonadosomatic index (GSI) reaches the highest values in June for males and in July for females. Size at fi rst maturity (TL) occurred at 167.5 and 153.2 mm for males and females respectively.