ALBERT

Description: Highlights: • Egg production methods have been used for assessing the Eastern Baltic cod stock. • The analysis contributed to the re-establishment of an analytical assessment for the stock. • Annual and daily egg production methods gave similar results. • Results confirmed trends from trawl surveys, questioned earlier because of potential change in catchability. • Several biological processes impact on absolute spawning stock estimates and research needs are identified to improve these. Abstract: Egg production methods (EPM) provide fishery independent estimates of spawning stock sizes and dynamics of fish populations. Such methods are commonly used for short-lived pelagic species, less so for demersal fish such as cod. In this paper, we apply EPMs on cod in the eastern Baltic Sea, using a long time series of ichthyoplankton data. Stock assessment of Eastern Baltic cod has been challenged due to changing productivity of the stock invalidating some of the standard procedures, e.g. age determination and input variables, e.g. natural mortality. We demonstrate that EPMs, based on other data and assumptions than standard stock assessments, provide useful information on stock status and dynamics. We apply both the annual and daily egg production methods, which yielded similar results and were in line with stock trends derived from bottom trawl surveys. However, the EPM based spawning stock estimates were consistently lower compared to results from the latest analytical stock assessment. We identified processes introducing uncertainties in EPM estimates and their effects on the resulting estimates, and conclude that they mainly affect the absolute estimates but less the relative trends in stock dynamics. Therefore, we consider that EPMs are useful for providing relative indices for stock assessment purposes, with the Eastern Baltic cod being the first case where such indices are included in an official stock assessment of a demersal gadoid species. We also identify knowledge gaps in order to be able to derive absolute stock size estimates from EPMs in the future.

Description: Food webs are central entities mediating processes and external pressures in marine ecosystems. They are essential to understand and predict ecosystem dynamics and provision of ecosystem services. Paradoxically, utilization of food web knowledge in marine environmental conservation and resource management is limited. To better understand the use of knowledge and barriers to incorporation in management, we assess its application related to the management of eutrophication, chemical contamination, fish stocks, and non-indigenous species. We focus on the Baltic, a severely impacted, but also intensely studied and actively managed semi-enclosed sea. Our assessment shows food web processes playing a central role in all four areas, but application varies strongly, from formalized integration in management decisions, to support in selecting indicators and setting threshold values, to informal knowledge explaining ecosystem dynamics and management performance. Barriers for integration are complexity of involved ecological processes and that management frameworks are not designed to handle such information. We provide a categorization of the multi-faceted uses of food web knowledge and benefits of future incorporation in management, especially moving towards ecosystem-based approaches as guiding principle in present marine policies and directives. We close with perspectives on research needs to support this move considering global and regional change.

Description: Food webs are central entities mediating processes and external pressures in marine ecosystems. They are essential to understand and predict ecosystem dynamics and provision of ecosystem services. Paradoxically, utilization of food web knowledge in marine environmental conservation and resource management is limited. To better understand the use of knowledge and barriers to incorporation in management, we assess its application related to the management of eutrophication, chemical contamination, fish stocks, and non-indigenous species. We focus on the Baltic, a severely impacted, but also intensely studied and actively managed semi-enclosed sea. Our assessment shows food web processes playing a central role in all four areas, but application varies strongly, from formalized integration in management decisions, to support in selecting indicators and setting threshold values, to informal knowledge explaining ecosystem dynamics and management performance. Barriers for integration are complexity of involved ecological processes and that management frameworks are not designed to handle such information. We provide a categorization of the multi-faceted uses of food web knowledge and benefits of future incorporation in management, especially moving towards ecosystem-based approaches as guiding principle in present marine policies and directives. We close with perspectives on research needs to support this move considering global and regional change.