ALBERT

Description: The relationship between fisheries and marine spatial planning (MSP) is still widely unsettled. While several scientific studies highlight the strong relation between fisheries and MSP, as well as ways in which fisheries could be included in MSP, the actual integration of fisheries into MSP often fails. In this article, we review the state of the art and latest progress in research on various challenges in the integration of fisheries into MSP. The reviewed studies address a wide range of integration challenges, starting with techniques to analyse where fishermen actually fish, assessing the drivers for fishermen's behaviour, seasonal dynamics and long-term spatial changes of commercial fish species under various anthropogenic pressures along their successive life stages, the effects of spatial competition on fisheries and projections on those spaces that might become important fishing areas in the future, and finally, examining how fisheries could benefit from MSP. This paper gives an overview of the latest developments on concepts, tools, and methods. It becomes apparent that the spatial and temporal dynamics of fish and fisheries, as well as the definition of spatial preferences, remain major challenges, but that an integration of fisheries is already possible today

Description: Highlights • Records of hard-bottom communities show regional differences in community dynamics. • Regionally, signs of regime shift were detected. • Shift can be explained by the decline of the foundation species Mytilus sp. • Modelling process revealed three environmental variables explaining the decline. • Regional differences in larval dispersal could explain contrary Mytilus recoveries. Abstract Ecological processes modulate ecosystem functioning and services. Foundation species are those exerting intense control on such processes as both their existence and loss have profound implications on the structure of ecological communities. For the distinction between random fluctuations and directional regime shifts in community composition, long-term records are of strategic need. In this study we present the monitoring of benthic hard-bottom communities over 11 years along seven stations in the SW Baltic Sea. Regional differences were found between the communities of Kiel and Lübeck bights, with the former area displaying signs of regime shift. The decline and near disappearance of the foundational species Mytilus edulis from settlement panels deployed in Kiel Bight correlated with three environmental variables: sea surface temperature, water current speed and chlorophyll a concentration. Thus, low spring temperatures, in some cases reinforced by local maxima of chlorophyll a, correlated with reduced recruitment of Mytilus. Moreover, regional differences of larval dispersal and population connectivity could explain the rapid recovery after disturbance of the mussel populations in Lübeck Bight in contrast to Kiel Bight. Our findings underscore the relevance of long-term monitoring programmes to detect the interactive impacts of global climatic and regional environmental drivers.

Description: Highlights: • Designing spawning closures requires consideration of the mechanisms through which the closures can affect the fish stocks. • Small area closures may have unintended negative effects to the stocks due to fishing effort reallocation. • Closures covering most of the stock distribution are more robust to gaps in biological knowledge than small area closures. Abstract: Fisheries management measures often include spatio-temporal closures during the spawning period of the fish with an overarching aim of improving the stock status. The different mechanisms how a spawning closure potentially can influence the stock are often not explicitly considered when designing such closures. In this paper, we review and synthesize the available data and knowledge on potential effects of the implemented spawning closures on cod in the Baltic Sea. The Baltic cod example represents a relatively data rich case, which allows demonstrating how a closure might affect different parameters of stock status via different mechanisms, including potential unintended negative effects. We conclude that designing relatively small area closures appropriately is highly complex and data demanding, and may involve tradeoffs between positive and negative impacts on the stock. Seasonal closures covering most of the stock distribution during the spawning time are more robust to data limitations, and less likely to be counterproductive if suboptimally designed.

Description: The period of larval drift into a suitable nursery area is considered to be of great significance for recruitment variability in flatfish. Here, a hydrodynamic model coupled with a Lagrangian particle tracking technique was utilized to study the drift from the first feeding larval stage until time of settlement of Central and Eastern Baltic flounder (Platichthys flesus), originating from spawning in the Baltic Sea deep basins, the Arkona- and Bornholm basin (central Baltic Sea), and the Gdansk deep and Gotland basin (eastern Baltic Sea). We examined the spatio-temporal dynamics of the probability to settle in preferred nursery habitat by detailed drift model simulations. The study suggests that the majority of larvae (89% and 74% for Central- and Eastern Baltic flounder, respectively) drift towards coastal areas and settle at metamorphosis ≤20 km from a sandy habitat enabling further migration to a preferred nursery area, i.e. larval drift seems not to be a major bottleneck in recruitment of flounder spawning in the Baltic Sea deep basins. The drift model results suggest that Central Baltic flounder utilize nursery areas mainly in the central and western Baltic, and in the Kattegat, whereas Eastern Baltic flounder mainly utilize the coast in the central and eastern Baltic. Thus, the two stock components seem to use different nursery areas following settlement. Further, in accordance with the “nursery size hypothesis”, the model demonstrates that larvae from the Bornholm basin, utilizing areas with extensive distribution of preferred nursery habitat, display the highest relative successful transport to nursery grounds until settling (72% of successfully settled larvae), suggesting that spawning in the Bornholm Basin is of great importance for stock recruitment of deep basin spawning Baltic flounder.

Description: Highlights: • Recruitment indicator: egg survival probability vs. “reproductive volume concept”. • Traditional sampling methodology unable to resolve spatial egg distributions. • Predominance of self-sustaining stock components and low connectivity. • Egg buoyancy and topographic features: limitation of cod egg transport. • Sedimentation as a new mortality source of eastern Baltic cod eggs. Abstract: In the highly variable environment of the Baltic Sea two genetically distinct cod stocks exist, one west of the island of Bornholm, which is referred to as the western stock, and one to the east of Bornholm, the eastern stock. A hydrodynamic model combined with a Lagrangian particle tracking technique was utilised to provide spatially and temporally resolved long-term information on environmentally-related (i) spawning habitat size, (ii) egg/yolk-sac larval survival, (iii) separation of causes of mortality, and (iv) connectivity between spawning areas of eastern Baltic cod. Simulations were performed to quantify processes generating heterogeneity in spatial distribution of cod eggs and yolk sac larvae up to the first-feeding stage. The spatial extent of cod eggs represented as virtual drifters is primarily determined by oxygen and salinity conditions at spawning, which define the habitat requirement to which cod’s physiology is suited for egg development. The highest habitat suitability occurred in the Bornholm Basin, followed by the Gdansk Deep, while relatively low habitat suitability was obtained for the Arkona and the Gotland Basin. During drift egg and yolk sac larval survival is to a large extent affected by sedimentation. Eggs initially released in the western spawning grounds (Arkona and Bornholm Basin) were more affected by sedimentation than those released in the eastern spawning grounds (Gdansk Deep and Gotland Basin). Highest relative survival of eastern Baltic cod eggs occurred in the Bornholm Basin, with a pronounced decrease towards the Gdansk Deep and the Gotland Basin. Relatively low survival rates in the Gdansk Deep and in the Gotland Basin were attributable to oxygen-dependent mortality. Low oxygen content had almost no impact on survival in the Arkona Basin. For all spawning areas temperature dependent mortality was only evident after severe winters. Egg buoyancy in relation to topographic features like bottom sills and strong bottom slopes could appear as a barrier for the transport of Baltic cod eggs and yolk sac larvae and could potentially limit the connectivity of Baltic cod early life stages between the different basins in the western and eastern Baltic Sea. The possibility of an eastward directed transport up to the first-feeding larval stage exists only for eggs and yolk sac larvae at high buoyancy levels, suggesting that dispersal of early life stages between these spawning areas is limited.

Description: Highlights: • Model output indicates high connectivity between the eastern Baltic cod nursery grounds. • Variability of spatial juvenile distribution patterns affected by flow dynamics. • Trend of simulated occupied juvenile cod habitat have been declining over the last decades. • Condition of juveniles suggests density-dependence due to hypoxia-related decrease in suitable habitat. • Baltic cod recruitment indicator: habitat availability for juvenile settlement as a factor for recruitment. Abstract: In this study the drift of eastern Baltic cod larvae and juveniles spawned within the historical eastern Baltic cod spawning grounds was investigated by detailed drift model simulations for the years 1971–2010, to examine the spatio-temporal dynamics of environmental suitability in the nursery areas of juvenile cod settlement. The results of the long-term model scenario runs, where juvenile cod were treated as simulated passively drifting particles, enabled us to find strong indications for long-term variations of settlement and potentially the reproduction success of the historically important eastern Baltic cod nursery grounds. Only low proportions of juveniles hatched in the Arkona Basin and in the Gotland Basin were able to settle in their respective spawning ground. Ocean currents were either unfavorable for the juveniles to reach suitable habitats or transported the juveniles to nursery grounds of neighboring subdivisions. Juveniles which hatched in the Bornholm Basin were most widely dispersed and showed the highest settlement probability, while the second highest settlement probability and horizontal dispersal was observed for juveniles originating from the Gdansk Deep. In a long-term perspective, wind-driven transport of larvae/juveniles positively affected the settlement success predominately in the Bornholm Basin and in the Bay of Gdansk. The Bornholm Basin has the potential to contribute on average 54% and the Bay of Gdansk 11% to the production of juveniles in the Baltic Sea. Furthermore, transport of juveniles surviving to the age of settlement with origin in the Bornholm Basin contributed on average 13 and 11% to the total settlement in the Arkona Basin and in the Gdansk Deep, respectively. The time-series of the simulated occupied juvenile cod habitat in the Bornholm Basin and in the Gdansk Deep showed a similar declining trend as the Fulton’s K condition factor of demersal 1-group cod, which may confirm the importance of oxygen-dependent habitat availability and its effect on density dependence as a process relevant for recruitment success.