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The research proposes the integration of a live fish sorting device that will allow a relevant proportion of undersized fish that currently die during hauling to survive healthy and return to the sea. Adjustment of fishing gear and appropriate sardine catch size selection methods could reduce the proportion of juveniles of these species in the catch. The selected fish were at different stages of gonadal maturity and were assigned to age group 1. It is recommended that the small pelagic fish selector be further developed to improve its performance for even better selection of undersized individuals.

Eating fish has known benefits for human health, especially for heart function and lowering the risk of obesity in adults whereas during pregnancy it is necessary for child neurodevelopment as an important source of omega-3 fatty acids, fat-soluble vitamins and various essential elements.[1] However, toxic trace elements that accumulate in fish meat, primarily Hg, are a potential risk for adverse health effects. Guidelines on fish consumption for sensitive population groups, such as women during reproductive period and children have been to date focused on large, predatory fish species and widely vary among countries. We evaluated the effect of fish body length on the levels of essential (Mn, Cu, Zn, Se) and toxic elements (Hg, Cd, Pb, As) in edible muscle tissue of wild European hake (Merluccius merluccius) that is the most commonly consumed fish species in Croatian population.[2] Fish specimens were collected between 2016 and 2021. They were caught by pelagic trawl net at several locations in the eastern part of the Adriatic Sea (n = 11 ; within EU project MEDIAS) and bought at fish market in Zagreb (n = 17). The samples of skinless dorsal muscle tissue were freeze dried and homogenised in the mixer mill using tungsten balls (Retsch, Germany). Approximately 0.25 g of sample was then wet digested in a high-pressure microwave system UltraClave IV (Milestone, Italy). Multielement analysis was performed using 7500cx ICP-MS (Agilent Technologies, Japan) and accuracy of the method was checked using commercially available certified reference materials IAEA 407 fish homogenate and ERM BB422 fish muscle. Concentrations of measured elements were (range, mg/kg wet wt): 0.08-0.61 for Mn ; 0.08-0.36 for Cu ; 2.4-5.1 for Zn ; 0.24-0.48 for Se ; 4.5-25 for As ; 0.05-0.97 for Hg, and (range, µg/kg wet wt) 0.03-0.89 for Cd ; 0.08-9.9 for Pb. Calculated molar ratio of Se:Hg and Se health benefit value were on average 8.1 and 3.9, respectively, indicating benefits for human nutrition. Fish specimens were categorized by fork length into three groups (G):11.0-20.9 cm (G1), 21.0-30.9 cm (G2), and 31.0-50.0 cm (G3). In G3 vs. G1 were approximately 3-fold higher Hg and 1.2-fold lower both Cu and Zn levels. Only the longest specimen of 50 cm had concentration 0.97 mg Hg/kg, which exceeded the EU regulatory limit for Hg in fish meat (0.50 mg Hg/kg). Correlations between fish length and element concentrations were positive for Hg (rs=0.65, p

Commission Decision of 25 February 2016 setting up a Scientific, Technical and Economic Committee for Fisheries, C(2016) 1084, OJ C 74, 26.2.2016, p. 4–10. The Commission may consult the group on any matter relating to marine and fisheries biology, fishing gear technology, fisheries economics, fisheries governance, ecosystem effects of fisheries, aquaculture or similar disciplines. Within a management strategy evaluation harvest control rules were tuned and robustness tested for the anchovy and sardine stocks in the Adriatic Sea. This investigation was done in support of GFCM and a continuation of the preliminary report (EWG 21-adhoc-02). For the sardine stock no meaningful MSE could be conducted. For the anchovy stock two HCRs were identified to be achieving the management targets and being robust. European Commission Published Non Refereed

Mnemiopsis leidyi distribution, abundance and diet were investigated in the North-eastern Adriatic from summer 2017 to summer 2018. The abundance of zooplankton and anchovies in the areas where M. leidyi was present showed a drastic decrease. The diet of M.leidyi consisted of all the zooplankton taxa found in the surrounding waters with a preference towards larger zooplankton and bivalvia larvae.

The rapid identification of escaped farmed fish presents a challenge in the management of escapee scenarios due to phenotypic plasticity which enables them to respond adaptively to environmental change by modifying their behaviour and physiology. Rogdakis et al. (2002) demonstrated that hatchery – released gilthead seabream can gain wild morphotype after 6 to 7 months in wild habitats as a result of exposure to natural abiotic and biotic factors. Thus, the aim of the present study is to assess characteristics for morphological differentiation from wild and farmed gilthead seabream populations. Gathered morphometric data can then be used to form a database for enhancing the detection sensitivity of morphological tools in future farmed – escapee identification in wild populations.

This study analyses the size-age structure of bluefin tuna (BFT) juveniles captured by Croatian purse seine fleet in the central Adriatic in 2016 by applying the available age-length key (ALK) of spine radius. The results indicated a relatively normal size distribution for BFT captured in central Adriatic during purse seine BFT campaign in 2016, with a large mode of fish from 75 to 85 cm that appear to belong to the age 2 class. There is a predictable and stable relationship in the size-age grouping of BFT tuna captured in the central Adriatic. Considering that the majority of BFT juveniles spend their first years feeding together with a significant degree of size homogenization, the observed schooling pattern may facilitate legal purse seine fishing for caging in Adriatic.

The levels of essential macro- and trace elements (K, Na, S, Mg, Ca, Fe, Cu, Zn, Mn, Se) were determined in edible tissue of eight fish species typical for Croatian coastal area diet: chub mackerel, Atlantic horse mackerel, European anchovy, and European pilchard (oily fish) and bogue, blotched picarel, European hake, and red mullet (lean fish). All samples (in total n=323) were collected in the eastern Adriatic Sea during 2014. After freeze- drying and homogenization, samples were wet digested and analyzed by ICP-MS. The results showed lower S and higher K, Mg, Zn, Fe and Cu levels in oily than in lean fish, with the highest levels in pilchards, indicating that besides omega-3 fatty acids, small oily fish is also a valuable source of essential trace elements and a healthy food choice.

The study evaluated levels of essential (Fe, Cu, Zn, Se) and toxic (Pb, Cd, Hg) trace elements in the edible tissue of three commonly consumed fish species in coastal Croatia: the oily fish European anchovy (Engraulis encrasicolus ; n=90) and sardine (Sardina pilchardus ; n=59), and lean demersal fish red mullet (Mullus barbatus ; n=64). Samples were collected in the coastal and open waters of the eastern Adriatic Sea at 11-13 locations for each of the species. Composite samples of muscles were freeze-dried, homogenised and digested before analysis. Inductively coupled plasma mass spectrometry (Agilent 7500cx ICP-MS) was used for multielement analysis. Oily fish species had 3-4 times higher levels of essential elements Fe, Cu and Zn in comparison to the lean fish. Levels of Se ranged as follows (mg kg-1 wet wt): anchovy 0.27-0.37 ; sardine 0.66-1.1 ; red mullet 0.35-0.73. Ranges of Hg concentrations (mg kg-1 wet wt) for these fish species were: anchovy 0.02-0.13 ; sardine 0.05-0.14 ; red mullet 0.18- 4.1. Toxic metal levels in all three species were below the maximum permissible values set by EU Commission Regulation, with the exception of one red mullet sample with an Hg concentration of 4.1 mg kg-1 wet wt. The presented results are valuable for the assessment of nutritional and toxic metal intake via seafood in the Croatian population, especially for women of reproductive age and children, vulnerable population groups for toxic effects of common environmental pollutants including metals.

Bluefin tuna farming, as a capture-based aquaculture activity, where fish captured mainly by purse seines are transferred into rearing cages for growing purposes, created a problem in collection of accurate catch-at-size data, having negative effect on quality of ICCAT Task 2 statistics. Use of stereoscopic camera system has been proposed as a possible solution to overcome this problem (ICCAT Rec. 12-03), as a tool that can improve quality and accuracy of Task 1 catch data and Task 2 size data, and therefore contribute to collection of catch-at-size data needed for bluefin tuna stock assessment. Some of first experiences of using stereoscopic camera system at Croatian bluefin tuna farms are described in this paper.

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.

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 [

Acoustic investigation of the part of the mixed carbonate-siliciclastic Adriatic Shelf was conducted in order to test a 38kHz quantitative split-beam echosounder, usually used as tool in acoustic surveys on pelagic fish. The seabed sediment data were ground-truthed by 38 grab samples. Spatial distribution of the calculated mean volume backscattering coefficient has revealed a strong similarity with existing seabed sediment textural maps, alowing us to use this echosounder as suitable for seabed characterization.

Caging practices of live bluefin tuna (Thunnus thynnus) captured by purse seines for fattening and/or farming purposes, become an important fishery based aquaculture practice. However, it has been observed that this practice include uncertainties about number and size of seed fish captured and stocked into growth out floating cages, and also problems in collection of purse seine catch-at-size data. To solve this problem, ICCAT made recommendation (Rec. 10-04) asking all contracting parties to use stereoscopic cameras in order to assess initial capture-at-size information of the live fish placed in the fattening and/or farming cages. Its usefulness has been studied in the Adriatic Sea area, where mostly small bluefin tuna have been used as seed fish for eventual farming purposes. Underwater stereoscopic camera system together with an appropriate image analysing software was used to determine individual fish lengths, eventually used to calculate tuna weights using given length-weight relationship. Number of fish has been obtained by direct counting of specimens on slow-motion video records (frame-by-frame) made during fish transfer from transporting cage into anchored growing cage. It has been observed that weight estimates may vary according to length-weight relationship chosen, as well as due to different individual fish positions or camera motions. Difficulties in assessment of fish numbers by direct counting have been observed, mainly due to fast swimming and schooling behaviour of small tunas. The quality of images recorded was also an important factor for eventual analyses. Therefore, with aim to ensure good image quality, use of white background, a rigid frame to fix camera at appropriate distance from fish and good lightning conditions (i.e. avoid camera use at dawn and dusk) is needed.

Identification of the potential habitat of European anchovy (Engraulis encrasicolus) at different life stages in relation to environmental conditions is an interesting subject from both ecological and management points of view. For this purpose, acoustic data from different seasons and different parts of the Mediterranean Sea along with satellite environmental and bathymetry data were modelled using generalized additive models. Similarly, egg distribution data from summer ichthyoplankton surveys were used to model potential spawning habitat. Selected models were used to produce maps presenting the probability of anchovy presence (adults, juveniles and eggs) in the entire Mediterranean basin, as a measure of habitat adequacy. Bottom depth and sea surface chlorophyll concentration were the variables found important in all models. Potential anchovy habitats were located over the continental shelf for all life stages examined. An expansion of the potential habitat from the peak spawning (early summer) to the late spawning season (early autumn) was observed. However, the most suitable areas for the presence of anchovy spawners seem to maintain the same size between seasons. Potential juvenile habitats were associated with highly productive inshore waters, being less extended and closer to coast during winter than late autumn. Potential spawning habitat in June and July based on ichthyoplankton surveys overlapped but were wider in extent compared with adult potential habitat from acoustics in the same season. Similarities and dissimilarities between the anchovy habitats as well as comparisons with sardine habitats in the oligotrophic Mediterranean Sea and other ecosystems with higher productivity are discussed.

The spawning behavior of captive Bluefin Tuna (Thunnus thynnus) was observed in cages at an Adriatic facility in summer 2011. Approximately 20, 000 eggs were collected from cages and transferred to a land-based nursery, with an estimated fertilization success rate of 80%. Eggs were spherical with a diameter of 1, 035.06 ± 20.16 μm and were pelagic with a single oil globule (227.63 ± 8.07 μm). Newly hatched larvae (3.08 ± 0.14 mm total length) followed scombrid larval development: melanophores were scattered over the body, head, notochord, and yolk, except finfold ; eye pigmentation was observed 1.5 days posthatch, pectoral fins started to appear, and two-thirds of the yolk sac were absorbed ; the mouth developed at 2.5 days posthatch, and larvae began feeding upon enriched rotifers. After mortalities occurred in the nursery (5 days posthatch), DNA was extracted from a sample of larvae. An 890 base pair fragment of the mitochondrial partial control region was amplified and sequenced to genetically confirm fish species identity. Based on multiple sequence alignment, larval sequences showed no ambiguities to the T. thynnus mitochondrial control region, thereby confirming spontaneous spawning in captivity. Although such an event has previously been reported in the Mediterranean, this is the first report supported by both morphological and genetic data.

Historical and recent size composition of bluefin tune caught in the Adriatic Sea by the purse seine were analised and compared. Among the fish being captured, the domination of juveniles was noticed in both periods analysed. Among them, two-year-old specimens of bluefin tuna were the most abundant. The findings presented in this paper confirm that the minimum size regulations under ICCAT (Rec. 08-05) are well defined for purse seine fisheries targeting bluefin tuna for subsequent farming in the Adriatic Sea.

A stereoscopic camera AQ100 was used in 16 transferring events during which fish were stocked into 9 cages located at three bluefin tuna farms in the Croatia. Aiming to test the accuracy of the fish length obtained by stereoscopic camera, 112 fish were randomly sampled from the cages, measured for fork length (FL in cm) and total weight (WT in kg), then placed into the sea for subsequent measurement. The tuna filmed with stereoscopic camera and on board measured with caliper ranged from 73.5 to 97.0 cm in FL with an average of 78.75 ± 3.6 cm, and 8.0 to 17.6 kg in total weight with an average of 9.57 ± 1.5 kg. Length-weight relationships were compared among measured and estimated ones. Different levels of errors were considered to get insight into the accuracy of estimates of FL and WT. Obtained differences between estimates and direct measurements as well as calculated errors in length-weight relationships are encouraging in making a reliable, non invasive measurement of length frequency distribution of the wild bluefin tuna catch.