Mate Šantić

Diet and feeding strategy of thornback ray Raja clavata

The diet and feeding strategy of thornback ray Raja clavata, from the eastern-central Adriatic Sea, were investigated. Stomach contents of 428 specimens, total length (L(T)) of 14·0-75·1 cm, were collected from commercial bottom trawls. The prey items identified in the stomachs belong to eight major groups: Cephalopoda, Polychaeta, Stomatopoda, Decapoda (Natantia and Reptantia), Mysidacea, Isopoda, Amphipoda and Teleostei. Decapods were the most important prey (index of relative important, %I(RI) ,= 72·8) followed by teleosts (%I(RI) = 20·4), whereas other prey groups were only occasionally ingested. Small-sized individuals (<25 cm L(T)) fed primarily on small crustaceans (mysids and amphipods), whereas large-sized specimens consumed larger prey, such as decapods, cephalopods and teleosts. Diet composition showed little seasonal variation; decapods were the most important prey in all seasons. There was high dietary similarity between sampling locations. The percentage of empty stomachs did not differ significantly among size classes and seasons. In terms of composition by species, the diet of R. clavata was characterized by a variety of rare or unimportant prey. As a result, R. clavata could be considered a generalist predator.

Feeding habits of small-spotted catshark (Scyliorhinus canicula Linnaeus, 1758) from the eastern central Adriatic Sea

Abstract The feeding habits of small-spotted catshark, Scyliorhinus canicula, from the central Adriatic Sea, were investigated with respect to fish size, season and sampling location. Stomach contents of 1200 specimens, collected at monthly intervals (January to December 2010), were analysed. The prey items identified in the stomachs belonged to eight major groups: Cephalopoda, Polychaeta, Stomatopoda, Decapoda, Mysidacea, Euphausiacea, Amphipoda and Teleostei. Decapods were the most important ingested prey in all seasons, for medium sized fish (22–38 cm TL). Euphausiids and mysids constituted the main prey items of small fish (<22 cm TL) while teleosts dominated the stomach contents of larger specimens (>38 cm TL). Two decapods, Alpheus glaber (%IRI = 5.1) and Solenocera membranacea (%IRI = 3.0), were the most numerous prey items identified to species level. The mean weight of stomach contents (relative to predator size) increased significantly for fish larger than 30 cm TL, while the mean number of prey items did not differ significantly among size-classes. The percentage of empty stomachs showed a monthly variation with a maximal occurrence in February (48.0%) and a minimal in August (9.0%). The lowest feeding frequency could be related to low sea temperatures during the winter. The small-spotted catshark could be considered a generalistic predator.

Feeding habits of brown ray (Raja miraletus Linnaeus, 1758) from the eastern central Adriatic Sea

Abstract The feeding habits of brown ray Raja miraletus from the eastern central Adriatic Sea were investigated. The stomach contents of 418 specimens, total length (TL) of 13.5–40.0 cm, collected from commercial bottom trawls from January to December 2010 were analysed. The prey items identified in the stomachs belong to six major groups: Decapoda (Natantia and Reptantia), Mysidacea, Teleostei, Cephalopoda, Amphipoda and Polychaeta. Decapods were the most important prey (%IRI=88.2), whereas other prey groups were only occasionally ingested. Fish size was the most important factor affecting diet. According to the observed ontogenetic shift, small-sized individuals (<20 cm TL) fed primarily on small crustaceans (mysids and amphipods), whereas large-sized specimens consumed bigger prey, such as decapods, cephalopods and teleosts. Diet composition showed low seasonal variation: decapods were the most important ingested prey in all seasons. There was high dietary similarity between sampling locations. The percentage of empty stomachs did not differ significantly among size-classes and seasons. In terms of species composition, the diet of the brown ray was characterized by a variety of rare or less important prey. As a result, the brown ray could be considered to be a generalist predator.

AGE, GROWTH AND MORTALITY OF POOR COD (TRISOPTERUS MINUTUS L.) FROM THE EASTERN ADRIATIC SEA

The age, growth and mortality parameters for poor cod, Trisopterus minutus, from the eastern Adriatic were analyzed. Samples were collected monthly from January to December 2009 on a random basis, with a total of 1200 specimens analyzed (885 females and 315 males). The values of parameter b (the exponent of the arithmetic form of length-weight relationships) of males (2.97), females (3.01) and total sample (2.99) indicated isometric growth. Fish aged 1-6 years were present in the samples, including a high proportion of 2-year-old individuals. The oldest female was estimated to be 6 years old, while the oldest male was 5. The von Bertalanffy growth parameters were L¥ = 26.81, K = 0.186, and to = 1.41 for males ; L¥ = 29.5, K = 0.197, and to = 1.33 for females ; L¥ = 28.76, K = 0.194, and to = 1.34 for all specimens. This study revealed that poor cod is a relatively slow-growing fish with intensive growth during the first two years of life. Total and natural mortality were Z = 1.01 year–1 and M = 0.50 year–1, respectively. The exploitation rate, E = 0.50, revealed a high fishing pressure on the stock in the studied area.

Monitoring DNA damage in Mytilus galloprovincialis from the Kaštela Bay in Croatia

The Kaštela Bay (Croatia) is known, by the use of Fast micromethod, as an area with the highest level of genotoxic agents along the Adriatic Sea. The genotoxic impacts in Kastela Bay and the neighbouring Trogir Bay using micronucleus test and Comet assay with mussel (Mytilus galloprovincialis) haemocytes were assesed during 2003 and 2004. This location received effluents from various industries (brewery, cement plant, etc.), ports (oil and general port), the Split shipyard, Vranjic shipworks along with domestic sewage and agricultural discharge that enters the bay without any treatment. In the meantime, a lot of industries were closed and the input of pollutants were discontinued. The tested mussels from the 2003–2004 confirmed that mussels from Kaštela Bay were affected by genotoxic contaminants. The aim of our study was to assess genotoxic impacts on Mytilus galloprovincialis in the same area after six years using Comet Assay test. Our survey showed decreses of genotoxic damage on mussel haemocytes.

Shell Characteristics of Land Snail Eobania vermiculata (Müller, 1774) (Helicidae) from Croatia

Abstract. The land snail genus Eobania P. Hesse, 1913 in Croatia consists of four taxa: Eobania vermiculata vermiculata (O.F. Müller, 1774), E. v. pelagosana (Westerlund, 1894), E. v. figarole (Rensch, 1928) and E. v. kamenensis Berberović, 1963. Only E. v. vermiculata and E. v. pelagosana have been included in this study. The mean shell diameters (D) of the 13 samples ranged from 19.99 mm (sample from the island of Sušac) to 31.78 mm (Šibenik, seaside) and the mean shell height (H) from 17.31 mm (Sušac) to 25.66 mm (Island of Šolta). Shell morphology confirms that all island populations are smaller with examples of nanism on outside islands of Palagruža and Sušac. However, molecular analysis (16S rDNA and COI sequence data) showed no significant differences between the South Adriatic population from the mainland and islands, thus providing no molecular evidence for classification of a single E. vermiculata species into separate subspecies within the investigated area. The observed differences might possibly be attributed to ecological influences. The population with the largest average shell size was approximately 1.5x larger than the population with the smallest average size.

Shell Characteristics of Land SnailEobania vermiculata(Müller, 1774) (Helicidae) from Croatia

Abstract. The land snail genus Eobania P. Hesse, 1913 in Croatia consists of four taxa: Eobania vermiculata vermiculata (O.F. Müller, 1774), E. v. pelagosana (Westerlund, 1894), E. v. figarole (Rensch, 1928) and E. v. kamenensis Berberović, 1963. Only E. v. vermiculata and E. v. pelagosana have been included in this study. The mean shell diameters (D) of the 13 samples ranged from 19.99 mm (sample from the island of Sušac) to 31.78 mm (Šibenik, seaside) and the mean shell height (H) from 17.31 mm (Sušac) to 25.66 mm (Island of Šolta). Shell morphology confirms that all island populations are smaller with examples of nanism on outside islands of Palagruža and Sušac. However, molecular analysis (16S rDNA and COI sequence data) showed no significant differences between the South Adriatic population from the mainland and islands, thus providing no molecular evidence for classification of a single E. vermiculata species into separate subspecies within the investigated area. The observed differences might possibly be attributed to ecological influences. The population with the largest average shell size was approximately 1.5x larger than the population with the smallest average size.

CONDITION AND LENGTH-WEIGHT RELATIONSHIP OF THE HORSE MACKEREL (TRACHURUS TRACHURUS L.) AND THE MEDITERRANEAN HORSE MACKEREL (TRACHURUS MEDITERRANEUS L.) FROM THE EASTERN ADRIATIC SEA

The length-weight relationship and variation of condition factor in relation to the total length (TL) of Trachurus trachurus (Linnaeus, 1758) and Trachurus mediterraneus (Steindachner, 1868) were studied. Samples were collected in the eastern Adriatic Sea using bottom-trawl during 2008 and 2009. The b values for males, females and total sample showed that the growth of T. trachurus was isometric, i.e. equal in length and weight. The growth of the males and females of T. mediterraneus was positively allometric while the total sample (males, female and immature) showed isometric growth. The condition factor was calculated indicating the smallest values in immature specimens. The highest values of condition factor for males and females of both species were observed in the range of TL from 16 to 19 cm and 31 to 33 cm, respec- tively.

Community Structure of Aquatic Insects in the Karstic Jadro River in Croatia

Abstract This study focused on the aquatic insect community in the longitudinal gradient and temporal scales of the Jadro River. The river was sampled for a period of ten years (2000– 2010), four times per year through the various seasons, along the river course. Sampling stations were selected in the upper, middle, and downstream parts of the river. A total of 21,852 specimens of aquatic insects belonging to six orders were obtained. The species determination confirmed 27 different species in the river. The data were analyzed by the multivariate methodologies of correspondence analysis and cluster analysis (unweighted pair group method with arithmetic mean) using the similarity index of Morosita for all ten years. Canonical correspondence analysis was applied to the data to check which of the mesured physicochemical variables significantly explained community variation. According to those data, significant variables for the upper station were water temperature and dissolved oxygen, and chlorides was the significant variable for the lower stations.

The shell characteristics of land snail Eobania vermiculata (Muller, 1774)from Croatia

Abstract. The land snail genus Eobania P. Hesse, 1913 in Croatia consists of four taxa: Eobania vermiculata vermiculata (O.F. Müller, 1774), E. v. pelagosana (Westerlund, 1894), E. v. figarole (Rensch, 1928) and E. v. kamenensis Berberović, 1963. Only E. v. vermiculata and E. v. pelagosana have been included in this study. The mean shell diameters (D) of the 13 samples ranged from 19.99 mm (sample from the island of Sušac) to 31.78 mm (Šibenik, seaside) and the mean shell height (H) from 17.31 mm (Sušac) to 25.66 mm (Island of Šolta). Shell morphology confirms that all island populations are smaller with examples of nanism on outside islands of Palagruža and Sušac. However, molecular analysis (16S rDNA and COI sequence data) showed no significant differences between the South Adriatic population from the mainland and islands, thus providing no molecular evidence for classification of a single E. vermiculata species into separate subspecies within the investigated area. The observed differences might possibly be attributed to ecological influences. The population with the largest average shell size was approximately 1.5x larger than the population with the smallest average size.