Long-term changes in spatial overlap between interacting cod and flounder in the Baltic Sea

The strength of interspecific competition and predator-prey interactions depends on the area of co-occurrence of the interacting species. Therefore, it is necessary to quantify the changes in the spatial overlap of trophically connected species to understand the outcomes of species interactions. In the Baltic Sea, the interplay between cod and flounder has previously been neglected. In this study, we use four decades of data on cod and flounder distributions covering the southern and central Baltic Sea to: (1) model and map the changes in the distributions of the two species using generalized additive models; (2) quantify the temporal changes in the potential competitive and predator-prey interactions between them using spatial overlap indices; (3) relate these changes in overlap to the known dynamics of the different cod and flounder populations in the Baltic Sea. Competition overlap has continuously increased for cod, from the beginning of the time-series. This is a possible cause of the observed decline in feeding levels and body condition of small and intermediate sized cod. Flounder overlap with large cod instead has decreased substantially, suggesting a predation release of flounder, potentially triggering its increase in abundance and distribution range observed in the last decades

The Third Workshop on Population of the RDBES Data Model (WKRDB-POP3)

The aims of this workshop were to explain the data model developed for the commercial fisheries Regional Database and Estimation System (RDBES), assist in populating it with real data for the second test data call for the RDBES, and encourage participants to take part in ongoing testing of the RDBES data submission system. This report documents the progress that participants have done to prepare their institutes for future use of the RDBES system. Some issues with data conversion have been identified and are documented in this report. None of the identified issues are thought to be serious impediments to moving forward with the RDBES development according to the roadmap decided by the Steering Committee of the Regional Fisheries Database in 2020. The RDBES Core Group (the group of people developing the RDBES data model) and ICES Data Centre will look at the results of this workshop and either respond to individual questions or adapt the data model and documentation as required. The workshop concluded and reported before the deadline of the test data call. For a complete test of the data model, all participants were encouraged to complete the data call. A report on the degree of completion of the data call may be expected from WGRDBESGOV which convenes after the data call deadline

Data from: Spatial contraction of demersal fish populations in a large marine ecosystem

Aim: The interdependencies between trophic interactions, environmental factors and anthropogenic forcing determine how species distributions change over time. Large changes in species distributions have occurred as a result of climate change. The objective of this study was to analyse how the spatial distribution of cod and flounder have changed in the Baltic Sea during the past four decades characterized by large hydrological changes. Location: Baltic Sea Taxon: Cod (Gadus morhua) and flounder (Platichthys flesus) Methods: Catch per unit of effort (CPUE) data for adult and juvenile cod and for adult flounder were modelled using Delta-Generalized additive models including environmental and geographical variables between 1979 and 2016. From the annual CPUE predictions for each species, yearly distribution maps and depth distribution curves were obtained. Mean depth and the depth range were estimated to provide an indication on preferred depth and habitat occupancy. Results: Adult and juvenile cod showed a contraction in their distribution in the southern areas of the Baltic Sea. Flounder, instead, showed an expansion in its distribution with an increase in abundance in the northern areas. The depth distributions showed a progressive shift of the mean depth of occurrence towards shallower waters for adult cod and flounder and towards deeper waters for juvenile cod, as well as a contraction of the species depth ranges, evident mainly from the late 1980s. Main conclusions: Our study illustrates large changes in the spatial distribution of cod and flounder in the Baltic Sea. The changes in depth distribution occurred from the late 1980s are probably due to a combination of expanded areas of hypoxia in deep waters and an increase in predation risk in shallow waters. The net effect of these changes is an increased spatial overlap between life stages and species, which may amplify cod cannibalism and the interaction strength between cod and flounder

Data_cod_flounder

Adult cod, juvenile cod and flounder CPUE data (in grams). The datasets contain also the associated bottom temperature, salinity and oxygen concentration of each haul as well as the latitude and longitude in decimal degrees

Data from: Spatial contraction of demersal fish populations in a large marine ecosystem

Aim: The interdependencies between trophic interactions, environmental factors and anthropogenic forcing determine how species distributions change over time. Large changes in species distributions have occurred as a result of climate change. The objective of this study was to analyse how the spatial distribution of cod and flounder have changed in the Baltic Sea during the past four decades characterized by large hydrological changes. Location: Baltic Sea Taxon: Cod (Gadus morhua) and flounder (Platichthys flesus) Methods: Catch per unit of effort (CPUE) data for adult and juvenile cod and for adult flounder were modelled using Delta-Generalized additive models including environmental and geographical variables between 1979 and 2016. From the annual CPUE predictions for each species, yearly distribution maps and depth distribution curves were obtained. Mean depth and the depth range were estimated to provide an indication on preferred depth and habitat occupancy. Results: Adult and juvenile cod showed a contraction in their distribution in the southern areas of the Baltic Sea. Flounder, instead, showed an expansion in its distribution with an increase in abundance in the northern areas. The depth distributions showed a progressive shift of the mean depth of occurrence towards shallower waters for adult cod and flounder and towards deeper waters for juvenile cod, as well as a contraction of the species depth ranges, evident mainly from the late 1980s. Main conclusions: Our study illustrates large changes in the spatial distribution of cod and flounder in the Baltic Sea. The changes in depth distribution occurred from the late 1980s are probably due to a combination of expanded areas of hypoxia in deep waters and an increase in predation risk in shallow waters. The net effect of these changes is an increased spatial overlap between life stages and species, which may amplify cod cannibalism and the interaction strength between cod and flounder

Third Workshop on Population of the RDBES Data Model report

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