National Fisheries Institute

ABSTRACT Since 2004, a logbook study has been conducted with commercial fishers to generate yellow eel specific catch per unit effort (CPUE) data in the German part of the southern Baltic Sea. By the end of 2023, this data series covers a 20‐year period. Using a change point analysis, various shifts in the fyke net CPUE data series for under‐sized and legal‐sized yellow eels were detected, with increased mean monthly CPUEs within the last years. In contrast to the most recent recruitment trend, the CPUE data series indicate a slight increase of the yellow eel abundance in the study region. Possible causes contributing to this trend are discussed. Implications for the current debate on European eel conservation efforts are also highlighted.

Abstract. The objective of this study consists to conduct the first monitoring of seagrass meadows and two non-indigenous species (NIS) in the associated benthos (Bursatella leachii and Callinectes sapidus) as indicators of the Integrated Monitoring and Assessment Program (IMAP) in the Ramsar site of the Marchica lagoon located on the north-eastern coast of Morocco. This lagoon has been the focus of a succession of restoration actions since 2010 aimed at conserving its biodiversity and improving its environmental state. Thirty sampling stations were monitored during the 2022-2023 winter season to determine the spatial distribution of seagrass meadows and of two non-Indigenous species above mentioned. Our results showed the presence of two marine species Cymodocea nodosa, the most widespread species, and Zostera noltei. The spatial distribution revealed the presence of the species only on the borders of the lagoon and their absence in the central area. For NIS, the results showed 143 Callinectes sapidus and 45 Bursatella leachii in different sizes ranging from small to large. To protect the marine phanerogams in the Marchica lagoon, it is recommended to develop this preliminary study by a spatiotemporal survey considering a seasonal pattern (winter, spring, summer and autumn) and by monitoring others stations in order to examine the existence of other species of seagrass and identified the benthos associated. The results of field monitoring will be used for future seagrass monitoring using satellite remote sensing as recommended by IMAP guidelines.

The terrestrial aquaculture systems in Jeju Island have been increasingly threatened by the intrusion of deteriorated groundwater. In this study, we investigated spatiotemporal variations in hydrochemical properties and isotopic compositions (δ13CPOC, δ15NPN, δ15NNO3, and δ18ONO3) of influent waters from land-based fish farms to trace the sources of particulate organic matter (POM) and nitrate (NO₃⁻) pollution. During heavy summer precipitation (> 350 mm), hydrochemical and isotopic shifts revealed increased infiltration of terrestrial groundwater into fish farm systems. Based on discriminative isotopic values of POM and NO₃⁻ in aquaculture influents, source apportionment results after accumulated precipitation indicated that the contribution of anthropogenic POM (livestock; 39 ± 17%) was predominant than those of other sources (soil; 31 ± 16%, fertilizer; 24 ± 7%, septic waste; 6 ± 1%). In addition, the contribution of NO₃⁻ sources (soil; 67 ± 7%, livestock; 18 ± 10%, septic waste; 9 ± 4%, fertilizer; 5 ± 1%) were largely controlled by specific land-use types adjacent to aquaculture systems. These results suggest that variations in volcanic bedrock permeability and land-use patterns may lead to distinct infiltration pathways and delayed responses between the northern and southern sections of Jeju Island. Therefore, these findings demonstrated that legacy pollutants stored in both the unsaturated and saturated zones may continue to impair groundwater quality, thereby affecting aquaculture water quality, particularly during periods of accumulated precipitation. To effectively manage nutrient-driven degradation in aquaculture systems, we recommend integrating isotopic source-specific monitoring with hydrogeological zoning and the targeted pretreatment of saline groundwater. This approach can mitigate eutrophication risks and enhance the sustainability of fish farming operations in volcanic islands.

Moroccan coastal areas are becoming more and more exposed to hazards related to storms and sea level rise. The Sidi Moussa cliff, which is situated south of Salé, is a sensitive coastal sector regularly hit by marine flooding during extreme phenomena. This study will create a high-resolution Digital Terrain Model (DTM) of the area to better determine its morphological characteristics and its susceptibility to marine inundation. The topographic data were gathered by a differential Global Positioning System Real Time Kinematic (GPS-RTK) method. Indeed, the collected data have been treated in a geographic information system environment to generate the DTM and to conduct elevation analyses in detail. The obtained model will be a fundamental dataset for the future numerical simulation of coastal flooding and for the mapping of potentially flooded zones. This study will also offer, for the first time, a clear and detailed morphological expression of the Sidi Moussa cliff, for which no topographic data was previously available. A first look at the results shows a topography that appears irregular, where micro-reliefs and active erosion predominate, increasing the vulnerability of some sectors to wave overtopping during storms. The latter approach points out the contribution of high-resolution topographic data to the enhancement of coastal assessment and management.

We first began working on the propagation and rearing of the crucian carp ( Carassius carassius ) in 2002, when our initial stockings also took place. More intensive research started in 2007, focusing on issues related to the reproduction and rearing of the species under laboratory, semi-intensive, and pond farming conditions. Within induced spawning cycles, we examined the effects of egg treatment (Woynarovich solution combined with tannin treatment) and different incubation temperatures on reproductive parameters, as well as on embryo and larval development. In a series of larval rearing experiments, we compared various feeding strategies, including the use of commercially available feeds, live feed, and different combinations of both. We also determined the optimal weaning strategy to achieve optimal survival and growth for an economically feasible production. During intensive juvenile rearing (up to the one-summer-old stage), we carried out experiments to evaluate different feeding regimes, to determine optimal feed rations, and to assess the role of live feed supplementation in survival and growth, with special attention to the occurrence of deformities. In pond-based trials, we investigated the possibilities of monoculture rearing of crucian carp and co-rearing with tench ( Tinca tinca ) in nursery ponds and pond-cage systems. We also studied the development of restocked populations at the “ Umbra krameri ” species protection area. In a separate series of experiments, we monitored the migration patterns of tagged crucian carp in Lake Balaton. Additionally, we conducted morphometric comparisons of crucian carp, Prussian carp ( Carassius auratus gibelio ), and their hybrids, as well as population studies in habitats where all three genotypes occur. In the course of our work, we have so far restocked 150,000 individuals (larvae, juveniles, and sexually mature individuals. Our research is ongoing, with a special focus on developing rearing protocols and feeding strategies tailored to the species’ needs to support effective conservation and restocking programs.

Abstract This study provides the first culture-based survey of archaeal diversity in Moroccan Atlantic solar salterns (Oualidia and Khenifiss), using sediment samples collected across a gradient of moderate to extreme salinities (16.7–29.2% w/v) and slightly alkaline pH (7.4–7.5). A total of 67 representative strains were isolated, all belonging to the class Halobacteria. The community was dominated by the genus Halorubrum , with additional genera ( Haloarcula, Haloferax , Natrinema , Halobacterium , Halogeometricum , Halococcus , Halomicrobium , and Halostagnicola ) exhibiting site- and phase-specific distributions, likely influenced by salinity fluctuations, microhabitat availability, and harvesting stage. Phylogenetic analyses revealed several isolates with ≤ 98.65% 16S rRNA gene sequence similarity to known taxa, forming distinct clades and suggesting the presence of putatively novel species. Antagonism assays demonstrated widespread inhibitory activity among isolates, with Natrinema and Haloferax strains exhibiting the strongest antagonism against co-isolated haloarchaea, indicative of bioactive compound production (e.g., halocins, lanthipeptides, or halolysins). These results expand our understanding of haloarchaeal diversity in Atlantic salterns, underscoring their potential as reservoirs of extremophiles with biotechnological applications. Furthermore, this work highlights the necessity of integrating polyphasic and culture-independent approaches to resolve the taxonomy and chemical ecology of these dynamic hypersaline environments.

Developing species distribution models (SDMs) requires high‐quality species occurrence records. These records, stemming from various sources with different sampling procedures, are often archived in open‐access databases, making automated data quality checks inevitable. Temporal, geographic, and taxonomic quality checks are usually conducted in SDM workflows, but checking for records distant in environmental space, i.e. outliers, is often ignored. Here, we present ‘specleanr', an R package that contains 20 outlier detection methods (ODMs) that can be ensembled to identify potential outliers in environmental predictors. These methods are categorized into 1) species‐specific ecological range, 2) univariate, and 3) multivariate ODMs. All potential outliers flagged by the different methods are pooled to identify absolute outliers (records appearing in multiple methods). The local regression (LOESS) method is then used to automatically set a threshold that optimally identifies the absolute outliers. Additionally, clustering records into poor, fair, moderate, very strong, and perfect outliers, as well as non‐outliers, is possible based on each record's likelihood as a potential outlier, which allows expert assessment. We demonstrated the approach to 15 fish species from the Danube River Basin, including native, alien, threatened, and common species. We fitted SDMs using bioclimatic and hydromorphological parameters. We compared the model area under the curve (AUC) before and after outlier removal using three scenarios: 1) the LOESS method, 2) removing very strong outliers, and 3) removing perfect outliers. The results showed a significant improvement in the model AUC, with generally small to moderate effect sizes after outlier removal. ‘specleanr' is generalizable across taxonomic groups, data types, ecological realms, and geographic regions. Beyond SDMs, it can also be broadly used in general data analysis where outlier detection is essential. We provide detailed vignettes to support package use. ‘specleanr' offers a user‐friendly and reproducible approach for handling outliers in biogeographical modeling and general data analysis workflows.

This study was carried out to evaluate the nutritional compositions and microbial load of some frozen marine fish species sold in Kano State, Nigeria. A total of 81 samples comprising 27 each of Atlantic herring (Clupea harengus), Atlantic mackerel (Scomber scombrus) and Atlantic horse mackerel (Trachurus trachurus) were purchased from three sampling areas: Bichi, Dambatta and Gwarzo. They were analysed for proximate, mineral compositions, and microbial load using standard procedures. Results indicated that the highest crude protein content, 21.51% was recorded in T. trachurus from Dambatta, while the mineral composition revealed that C. harengus recorded the highest sodium content, 1.69 mg Kg-1, from Bichi. The highest free fatty acids 2.07 ± 0.18% was observed in T. trachurus from Gwarzo. The results of the microbial population elucidated that T. trachurus had the highest Salmonella spp. count of 4.22 x 106cfu g-1 from Dambatta. The Escherichia coli of 3.22 x 106cfu g-1 recorded in S. scombrus from Dambatta was the highest. All the microbial loads parameters were affected by the species, but not the collection station. The microbial load recorded in this study did not exceed the recommended limit of x106 to 107cfu g-1 of bacteria load safe for human consumption. The study therefore recommends T. trachurus as the best for consumption in the study area, due to its higher protein composition and the lowest microbial load.