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The aim of the Workshop on Stickleback and Round Goby in the Baltic Sea (WKSTARGATE) was to update, summarize and synthesize the current knowledge of both species with respect to their ecology and potential use in fisheries. Ongoing projects were presented in the mornings of the first two days to inform participants about current research in the respective countries (Annex 5). The group discussed ecological aspects that are relevant to fisheries, such as distribution and abundances, feeding ecology and behaviour. So far, no dedicated monitoring exists for either of the species. However, the Baltic International Acoustic Survey (BIAS), coordinated by ICES, has been used to estimate abundances and biomasses of pelagic stickleback in offshore areas across the Baltic, while the availability and quality of coastal data differs between countries, but is generally scarce. Even less current abundance information is available for round goby. It is only available for areas where it is already commercially exploited like Latvia. Most studies on the ecological impact of these species focus on trophic interactions, and its resulting competition. It became clear, that these ecological impacts depend on the abundance of the species and that the effects therefore vary on a temporal and spatial scale. Estimating the ecological impact of a stickleback or round goby fishery is therefore very speculative without reliable abundance data, why the group decided to describe the known impact of the species on the ecosystem. Landings of round goby increased significantly in Latvia during the last years, while stickleback landings decreased over the last five decades but most recently show a slight increase. A targeted round goby fishery exists in Latvian waters, while the stickleback is solely taken as bycatch in all Baltic countries. Both fisheries are currently unmanaged and, with the exception of round goby fishery in Latvia, unregulated. In Latvia the round goby fishery

Competitive interactions between marine mammals and fisheries represent some of the most complex challenges in marine resource management worldwide. The development of commercial fisheries and recovering marine mammal populations have contributed to a decrease in fish availability. Whilst ecosystem-based fisheries management (EBFM) can counteract this decrease, achieving the EBFM objectives faces certain major obstacles including insufficient or unreliable data, inapplicable assessment models, as well as inadequate management decisions that do not account for fisheries-induced morphological alterations (FIMA) and marine mammal management. Despite a body of evidence addressing various aspects of marine mammal-fisheries competition, little is known about the effects of marine mammal-fisheries biological interactions affecting the fish viability and food web stability. We review the research on marine mammal-fisheries competitive biological interactions (hereafter biological competition) by focussing on (1) the prerequisites for marine mammal-fisheries biological competition and the relevant methodologies to explore them and (2) recent studies revealing the implications of FIMA and trophic interactions for the biological competition. We also discuss the implications of FIMA, eco-evolutionary feedback and prey-predator dynamics for EBFM implementation in contemporary harvested ecosystems. Our main findings reveal a lack of data about marine mammals’ prey choice and selectivity, the need for better representation of marine mammals in modelling approaches and lastly, the necessity for additional research linking FIMA, trophic interactions and the EBFM objectives. To conclude, interdisciplinary approaches may serve to link all of the efforts needed to effectively and holistically support the implementation of EBFM.

There is a rising concern involving the impact of modern fisheries on the dynamics and viability of the exploited fish populations. The increasing fishing pressure has been recorded to cause declines in age and size at maturation in variety of marine fish species. In this study I have aimed to detect heritable phenotypic changes of the European hake (Merluccius merluccius) under the currently prevailing fishing intensity. Using dataset of 64 individual-based growth parameters of the studied species and an individual-based simulation, which incorporates quantitative genetics, ecological processes and biological characteristics, I have simulated ecological and evolutionary dynamics of hake. Species` phenotypic traits were observed through three different scenarios which showed significant ecological consequences for hake population under the current fishing strategies but detected no evolutionary changes in life-history traits, e.g. growth and age and size at maturation. Even though, the current fishing intensity does not appear to select for a specific life-history type, the ecological impact observed under under the current fishing practices can pose a severe risk through direct population declines., Popular science summary Is the European hake “shrinking” under the current fishing practices? Did you know that the current fishing practices have caused significant declines in body size of many exploited fishing stocks? This effect of fishing management has become one of the major threats for commercially exploited fish species and it can have severe negative consequences for the offspring of the species as well as the ecosystem`s stability. As the demand for fish grows, the fishing gear, such as fishing nets, become more effective in harvesting older and bigger fish since they are the most valuable fish on the market. By removing these individuals, there is more food and space for smaller fish to grow and feed. This will eventually lead for the smaller ones to grow faster and achieve sexual maturity earlier than it occurs in populations not experiencing the pressure by fisheries. As the fish matures earlier and at a smaller size, so does their offspring become smaller and such biological characteristics can become heritable over time. In the long run, these changes induced by fishing intensity, can cause higher variations in the population dynamics and, in the end, lead to population collapse. Following this theory, I have investigated the state of European hake (Merluccius merluccius) stocks across geographic areas in order to detect whether current fishing practices are causing heritable changes in size and age at maturation. For this purpose, I have simulated fish populations and exposed them to three different scenarios which allowed me to compare the effects of: (a) non-fishing conditions, (b) fishing with and (c) without evolutionary processes. Opposite of our expectations, the overall results of the simulations show a biologically nonsignificant decline in size and age at maturation for the European hake. However, the ecological impact of fisheries shows drastic drop in biomass and recruitment. In other words, the results of the study suggest that either t