The present study provides updated information on the occurrence, abundance and biomass distribution patterns and length frequencies of Merluccius merluccius in the Mediterranean Sea, by analysing a ...time series of data from the Mediterranean International Trawl Surveys (MEDITS) from 1994 to 2015. The highest values of abundance and biomass were observed in the Sardinian Seas. The use of a generalized additive model, in which standardized biomass indices (kg km–2) were analysed as a function of environmental variables, explained how ecological factors could affect the spatio-temporal distribution of European hake biomass in the basin. High biomass levels predicted by the model were observed especially at 200 m depth and between 14°C and 18°C, highlighting the preference of the species for colder waters. A strong reduction of biomass was observed since the year 2009, probably due to the strengthening of the seasonal thermocline that had greatly reduced the availability of food. The general decrease in biomass of several stocks of anchovy and sardine, preys of European hake, might be indirectly connected to the decreasing biomass detected in the present study. The length analysis shows median values lower than 200 mm total length of most of the investigated areas.
The Mediterranean Sea shows a trend of increasing temperature and decreasing productivity from the western to the eastern basin. In this work we investigate whether this trend is reflected in the ...cephalopod assemblages found throughout the Mediterranean. Data obtained with bottom trawl surveys carried out during the last 22 years by EU Mediterranean countries were used. In addition to analysing spatial differences in cephalopod assemblages, we also analysed putative temporal changes during the last two decades. For this purpose, the basin was spatially divided into bioregions, the trawling grounds were subdivided into depth strata, and the dataset was split into two time series of 11 years each. All analyses were done using PRIMER software. The species richness did not vary with the longitudinal gradient, though in most bioregions it showed a mild decrease with depth before plummeting in the deepest waters. Cluster analysis revealed four different bathymetric assemblages in all bioregions. Despite the contrasting conditions between basins and the claims of biodiversity loss, our study revealed that spatial and temporal differences during the last two decades were restricted to changes in the relative abundance of species from a common pool of species inhabiting the whole Mediterranean.
Most studies on European hake focus on the recruitment process and nursery areas, whereas the information is comparatively limited on the ecology of the juvenile stage (ca. second year of life)—the ...one most exploited by the Mediterranean trawl fisheries. Using information of the MEDITS programme, we provide a spatial and temporal assessment of the influence of body size and growth on hake survival from recruits (age 0) to juveniles (age 1), along with the impact of surface temperature and chlorophyll variability. At a biogeographic scale, size-dependent survival is supported, with areas with higher mean length of recruits and juveniles yielding higher survival. A similar pattern was observed at interannual level in some western Mediterranean areas, also mediated by a density-dependent effect on growth. However, the most recurrent inter-annual pattern was a negative effect of size on survival, which could be attributed to potential ontogenetic changes in catchability and underrepresentation of intra-annual recruitment pulses that are seasonally inaccessible to the MEDITS survey. Results also evidence that survival in the Alboran and Adriatic seas is dependent on the primary production variability, and that Corsica and Sardinia could be potential feeding grounds receiving juveniles from neighbouring areas. The present study reveals the importance of size- and growth-dependent survival in the juvenile stage of European hake in the Mediterranean Sea.
Although integrated multi-trophic aquaculture (IMTA) is recognized as a strategy to control and minimize the impact of fish farming on the marine environment, there are still many unknowns when it ...comes to this type of farming. This paper presents the results of research on the growth of European flat oysters in IMTA and monoculture systems. Growth was monitored at three different sites: near fish cages, 100 m from fish cages, and in a monoculture system, during an 18-month experiment. The highest mortality occurred at the site near the fish cages. At the end of the experiment, all monitored individuals reach commercial size, except for four individuals at the site near the fish cages. There were statistically significant differences in oyster growth with respect to site and period. At the site near the fish cages, oyster growth was significantly lower compared to the growth at the two other sites. The most intense growth of oysters occurred during the spring and early summer period. Our results indicate that the production cycle of oysters in integrated aquaculture and monoculture is quite similar and that sites directly adjacent to fish cages should be avoided for oyster farming.
The knowledge of small‐scale fisheries (SSFs) is important to develop management policies and mitigate the competition for marine resources. However, spatially explicit information is often ...unavailable at the regional and subregional scale. We designed and tested a novel participatory approach to map the SSF fishing effort using the Mediterranean sea as a case study. We applied the approach in eight countries (Albania, Croatia, Italy, Libya, Malta, Montenegro, Slovenia and Tunisia) characterized by different cultural, social, political and ecological features. The results provided quantitative and spatially explicit information on fishing operations on a fine‐scale resolution, contributing to overcome the pragmatic and budgetary constraints that to date have prevented an accurate assessment of SSFs worldwide. This novel participatory approach is inspired by the principles of governance, adaptive management, cross‐national cooperation and spatial planning, thus supporting the ecosystem approach to fisheries and has the potential to provide a useful complement to traditional assessments.
Montenegro has limited data on biological and population parameters of glass eel e.g. accurate time and the number of migration waves, condition, rate of survival, recruitment success, etc. Since the ...early 1980s, the occurrence of glass eels in European waters has decreased significantly. ...after almost 25 years the first research was conducted on glass eel in the river Bojana (Montenegro). Data of the Fulton's condition factor (CF) of the analyzed specimens was calculated from the W (g) and TL (cm) using the formula according to Fulton (1904). Since the number of registered individuals in 2021 did not meet the statistically valid number of individuals for making relevant conclusions about their condition and quality, their basic biometric characteristics will be presented since these are the first findings and descriptions of these individuals after almost 25 years, and a more detailed analysis was done on a sample from 2022. In Europe, glass eels enter estuaries mostly from October to April/May (Elie, 1979). Since Montenegro has limited data on biological and population parameters of glass eels for almost 25 years the first research was conducted on glass eels in the river Bojana (Montenegro).
The otolith morphology, biometry and otolith size and fish length relationship of three demersal fish species: red mullet Mullus barbatus, common pandora Pagellus erythrinus and hake Merluccius ...merluccius were examined. Based on otoliths relative sizes P. erythrinus and M. merluccius have Large otoliths, while M. barbatus has Small sagittal otoliths. The relationships between otolith variables and fish somatic growth were described by a linear function. All relationships were statistically highly significant (p<0.001). Otolith length (OL) was found to be the
variable most strongly related to fish size, with 61.2 – 95.3 % of the variability, while otolith weight had the lowest coefficient of determination (r2). No differences were found neither between left and right otoliths, nor between male and female otoliths in these relationships. For all species studied the relationships of otolith length, height and weight against total fish length were all found to have positive allometry, indicating that the accretion of otoliths is relatively faster than increase in fish body size. The shape indices of form factor (FF), roundness (RD), aspect ratio (AR), circularity (C), rectangularity (R) and ellipticity (E) were calculated and the relationships between otolith length (OL) and shape indices were determined.
Ispitana je morfologija otolita, biometrija i
odnos veličine otolita i duljine tri pridnene vrste riba: trlja
Mullus barbatus
, arbun
Pagellus erythrinus
i oslić
Merluccius merluccius
. Na temelju
relativnih veličina otolita
P. erythrinus
i
M. merluccius
imaju velike otolite,
dok
M. barbatus
ima male sagitalne
otolite. Odnosi između varijabli otolita i somatskog rasta riba opisani su
linearnom funkcijom. Svi odnosi bili su statistički visoko značajni
(p<0,001). Utvrđeno je da je duljina otolita (OL) pokazuje najveću
povezanost s veličinom ribe, sa 61,2 – 95,3 % varijabilnosti, dok je masa
otolita imala najniži koeficijent determinacije (r2). Nisu pronađene razlike ni između lijevog i
desnog otolita, niti između muških i ženskih otolita u tim odnosima. Za sve
proučavane vrste utvrđeno je da odnosi duljine, visine i mase otolita u odnosu
na ukupnu duljinu ribe imaju pozitivnu alometriju, što ukazuje da je
nakupljanje otolita relativno brže od povećanja duljine tijela ribe. Izračunati
su indeksi oblika faktora forme (FF), zaobljenosti (RD),
omjera stranica (AR), kružnosti (C), pravokutnosti (R) i
eliptičnosti (E) te su izračunati odnosi između duljine otolita (OL) i indeksa
oblika.
The structure and composition of Mediterranean biodiversity has changed significantly. So far, in Montenegrin coastal waters, nine new non-native species have been recorded: Tylosurus acus ...imperialis, Caranx crysos, Siganus luridus, Fistularia commersonii, Stephanolepis diaspros, Sphoeroides pachygaster, Lagocephalus sceleratus, Callinectes sapidus and Farfantepanaeus aztecus. Allochthonous species are starting to compete for food and space and leading to habitat degradation, socio-economic impacts and can hybridise with the native species. Natural factors and human activities have enabled the arrival of non-native species into the Adriatic Sea. Four of the species are Lessepsian immigrants, which arrived via the Suez Canal, but five others were introduced from the Atlantic Ocean, through the Strait of Gibraltar. Analysis using the Marine Fish Invasiveness Screening Kit (MFISK), Aquatic Invasiveness Screening Kit (AS-ISK) and Receiver operating characteristic (ROC) showed a calibration threshold of 22.5 for MFISK, a BRA (Basic Risk Assessment) score of 34 and a CCA (Climate Change Assessment) score of 46. A measure of the accuracy of the calibration analysis is the area under the ROC curve (AUC). Two species were characterised as non-invasive: Tylosurus acus imperialis and Caranx crysos, but five others were characterised as invasive and covered by the categories from moderate to high-risk.
Struktura i sastav bioraznolikosti Sredozemlja značajno su se promijenili. Do sada je u crnogorskom primorju zabilježeno devet novih ne-nativnih vrsta: Tylosurus acus imperialis, Caranx crysos, Siganus luridus, Fistularia commersonii, Stephanolepis diaspros, Sphoeroides pachygaster, Lagocephalus sceleratus, Callinectes sapidus i Farfantepanaeus aztecus. Alohtone vrste počinju se natjecati za hranu i prostor i dovode do degradacije staništa, socio-ekonomskih učinaka i mogu hibridizirati s autohtonim vrstama. Prirodni čimbenici i ljudske aktivnosti omogućili su dolazak ne-nativnih vrsta u Jadransko more. Četiri vrste su lesepsijski imigranti, koji su stigli preko Sueskog kanala, ali pet drugih uneseno je iz Atlantskog oceana, kroz Gibraltarski tjesnac. Analiza korištenjem programa MFISK (Marine Fish Invasiveness Screening Kit), AS-ISK (Aquatic Invasiveness Screening Kit) i ROC (Receiver operating characteristic) pokazala je prag kalibracije od 22,5 za MFISK, BRA (Basic Risk Assessment)) rezultat od 34 i CCA (Climate Change Assessment) ocjenu od 46. Mjera točnosti kalibracijske analize je površina ispod ROC krivulje (AUC). Dvije vrste okarakterizirane su kao neinvazivne: Tylosurus acus imperialis i Caranx crysos, no pet drugih okarakterizirano je kao invazivno i obuhvaćeno kategorijama od umjerenog do visokog rizika.
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