Poredbena analiza značajki dvaju istraživačkih brodova za obavljanje eho-monitoringa sitne plave ribe

Acoustic surveys in the Adriatic Sea have been performed annually by the research vessels “Dallaporta” and “Bios”, equipped with SIMRAD echo-sounders (EK-500 and EK-60), and working with 38 kHz split-beam transducer (ES38B). Since the vessels have different characteristics and use different pelagic trawls for fish sampling, there is uncertainty regarding the comparability of the results obtained. In order to evaluate comparability of the results, a comparison between research vessels was performed. That included comparisons of vessels’ noise, acoustic data collection, and fish samples composition and size structure analyses. The noise generated by both vessels was sufficiently low to allow a single fish detection up to 200 m depth. Acoustic data collected by the two vessels showed similar trends, no significant differences in average SA-values, and highly significant correlation between SA-values. Therefore, unbiased acoustic data collected by vessels could be combined in future stock assessments. Concerning collection of fish samples, anchovy resulted as the most abundant species in the samples collected by both vessels even if size compositions of anchovy were significantly different.Eho-monitoring u jadranskome moru provodi se jednom godišnje korištenjem istraživačkih brodova “Dallaporta” i “bios”, opremljenih s ehosonderima SIMraD (ek-500 i ek-60), te pretvaračima podijeljenog snopa radnih frekvencija od 38 kHz (eS38b). Budući da ovi straživački brodovi imaju različite značajke, a koriste i različite pelagijske koće za uzorkovanje sitne plave ribe, postoje sumnje glede usporedivosti prikupljenih podataka. S ciljem procjene usporedivosti prikupljenih podataka, napravljena je usporedba u prikupljanju podataka ovim istraživačkim brodovima. Uspoređena je buka pojedinih brodova, prikupljanje akustičkih podataka, te usporedbe prikupljenih uzoraka riba s obzirom na sastav i strukturu uzoraka. utvrđeno je da buka koju proizvode oba broda je dovoljno niska da dozvoljava detekciju pojedinačnih riba do dubine od 200 m. Akustički podaci prikupljeni dvama istraživačim brodovima pokazuju slične trendove, bez značajnih razlika u srednjim Sa-vrijednostima i s vrlo značajnom povezanošću među njima. Potvrđeno je da se budućim procjenama ribljih naselja nepristrani akustički podaci ovih brodova mogu međusobno nadopunjavati. Glede prikupljanja uzoraka riba, došlo se do spoznaje da je inćun bio najzastupljenija vrsta u uzorcima koje su sakupila oba istraživačka broda iako je njihova veličinska struktura bila značajno različita

Klorirani spojevi u mišićnom tkivu riba iz istočnog Jadranskog mora: preliminarni podaci o zagađenosti i zdravstvenim rizicima

Levels of 17 polychlorinated biphenyl congeners (PCBs) and seven organochlorine pesticides (OCPs) were measured in the muscle tissue of 18 commercially important fish species from the eastern Adriatic Sea. PCBs [˂LOD-8,866 ng g-1 lipid weight (lw)] accounted for over 66 % of all analysed compounds. Their pattern was dominated by PCB-138 and PCB-153. DDE (14.2-649 ng g-1 lw) was the prevalent DDT isomer in all samples, suggesting no recent DDT input. β-, γ- and α-HCH and HCB were found in less than 50 % of samples. The analysed organic contaminants did not seem to bioaccumulate up the food web (trophic levels 3.0 to 4.5). Our findings show no risk of chronic (non-cancerous) effects on human health.Maseni udjeli 17 poliklorbifenila (PCB) i 7 organoklorovih pesticida (OCP) izmjereni su u mišićnom tkivu 18 komercijalno važnih ribljih vrsta iz istočnog Jadranskog mora. Maseni udjeli PCB-a (˂LOD do 8.866 ng g-1 masti) činili su više od 66 % svih analiziranih spojeva. U njihovu profilu PCB-138 i PCB-153 dominantni su kongeneri. DDE (14,2-649 ng g-1 masti), glavni izomer DDT-a, jedini je detektiran u svim uzorcima. U manje od 50 % analiziranih uzoraka nađeni su β-, γ- i α-HCH te HCB. U rasponu trofičkih razina analiziranih vrsta (3,0-4,5) nije bilo bioakumulacije organskih zagađivala u hranidbenom lancu. Rezultati procjene rizika za ljudsko zdravlje pokazali su da nema rizika od kroničnih (nekancerogenih) utjecaja na ljudsko zdravlje

Evaluación conjunta de la población de la anchoa del Mar Adriático septentrional y central: comparación entre dos métodos de dinámica poblacional

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.La anchoa (Engraulis encrasicolus, L.) es una de las especies comerciales más importantes del mar Adriático central y septentrional, a la vez que es una de las actividades pesqueras más productivas en todo el Mediterráneo. La población de anchoa en el mar Adriático es compartida por Croacia, Italia y Eslovenia: una evaluación conjunta de la población fue realizada usando los datos de captura de todas las flotas para el periodo 1975-2009. Se efectuaron análisis usando estimaciones de la mortalidad natural por edad obtenidos mediante dos métodos diferentes y dos métodos de dinámica poblacional basados en el análisis de datos de captura por edad: Análisis de Población Virtual (VPA) de Laurec-Sheperd y Análisis de Captura Integrada por Edad (ICA), ambos acordados en las estimaciones acústicas de la abundancia. Las estimaciones de mortalidad natural de Gislason aparentaban ser más realísticas y por lo tanto daba preferencia a especies de vida corta. La tendencia general de la biomasa y de la mortalidad por pesca es similar en los dos modelos, destacando la fuerte disminución de la población en 1987. Sin embargo, ICA permite una flexibilidad suficiente para combinar todos los datos disponibles sin agregar excesivas complejidades con respecto al enfoque VPA y aparenta un mejor desempeño en términos de relación de SSB-R y en términos of diagnósticos (por ejemplo: el patrón retrospectivo). En relación al estado de la población, la tasa de explotación del ICA es más alta que el umbral sugerido de 0.4 propuesto por Patterson para las especies de pequeños pelágicos

Distribution, diet and relationships of the invasive ctenophore Mnemiopsis leidyi with anchovies and zooplankton, in the northeastern Adriatic Sea

Blooms of invasive ctenophore Mnemiopsis leidyi can have massive consequences on fish stocks and marine food webs. The distribution, abundance and diet of this ctenophore were investigated in the northeastern (NE) Adriatic between 2016 and 2019. The abundance of M. leidyi was determined daily along the coast of Rovinj (Croatia), and its spatial distribution monitored by visual census from research vessels and by pelagic trawl during acoustic surveys in September of each year. Mesozooplankton samples were collected along the western coast of Istria by vertical tows from the bottom to the surface. Spatial distribution and abundance of anchovy (Engraulis encrasicolus) assemblages were determined by geo-referenced hydro-acoustic sampling using a scientific echosounder. Large swarms of M. leidyi covering several km2 were regularly reported between July and November extending up to 25 NM from the western coast of the Istrian peninsula and reaching maximum offshore densities of 270 individuals per m2. The abundance of anchovy in the areas where M. leidyi was present evidently decreased. The content of M. leidyi’s digestive tract and plankton samples consisted both mainly of cladocerans, copepods, pteropods, echinodermata and bivalvia larvae. Results indicate that M. leidyi may accumulate and increase its abundance in the stagnant and trophically rich areas of the northern Adriatic gyres, spreading to the surrounding larger areas with currents. We assume that M. leidyi presence correlates with a decrease in anchovy population due to competition for food (zooplankton). Our findings support the importance of implementing an international monitoring program throughout the Adriatic Sea and demonstrate the ability of current MEDIAS surveys to detect changes in the pelagic ecosystem throughout surveyed areas

Temporal and spatial genetic variation of Engraulis encrasicolus in the Adriatic Sea

Small pelagic fish play a key role in the marine ecosystem, controlling predator abundance and regulating primary production rates by foraging on plankton. Alterations induced at different ecological levels by fishing activities and/or environmental changes are affecting the reproductive success of several small pelagics, including European anchovy (Engraulis encrasicolus), which is a major target of Adriatic mid-water trawl and purse-seine fisheries. In this study, we evaluated short-term genetic changes of the species in the Adriatic Sea by applying molecular markers in samples of three generations of European anchovy. Thirteen polymorphic microsatellite markers and a mitochondrial gene were used in cohorts of adults and larvae, collected at three sites in the north-east, central, and southern Adriatic Sea in 2015. Furthermore, temporal, and spatial genetic variation was assessed by comparing the above dataset with a sample of adult anchovy collected in 2012 at three sites close to those sampled in 2015. Expected heterozygosity was higher in adults than in larvae, suggesting a loss of genetic diversity and uneven reproduction. In addition, a comparison of the two datasets demonstrated a change in the anchovy population structure from 2012 to 2015. In the reproductive event of 2015, this change led the two main genetic stocks described in the Adriatic Sea to merge into one. We suggest that the population structure of European anchovy in the north-eastern Adriatic may be influenced by changes in environmental parameters and by periodic alterations in the temporal pattern of population connectivity