Baltic cod recruitment – the impact of climate variability on key processes

Large-scale climatic conditions prevailing over the central Baltic Sea resulted in declining salinity and oxygen concentrations in spawning areas of the eastern Baltic cod stock. These changes in hydrography reduced the reproductive success and, combined with high fishing pressure, caused a decline of the stock to the lowest level on record in the early 1990s. The present study aims at disentangling the interactions between reproductive effort and hydrographic forcing leading to variable recruitment. Based on identified key processes, stock dynamics is explained using updated environmental and life stage-specific abundance and production time-series. Declining salinities and oxygen concentrations caused high egg mortalities and indirectly increased egg predation by clupeid fish. Low recruitment, despite enhanced hydrographic conditions for egg survival in the mid-1990s, was due to food limitation for larvae, caused by the decline in the abundance of the copepod Pseudocalanus sp. The case of the eastern Baltic cod stock exemplifies the multitude effects climatic variability may have on a fish stock and underscores the importance of knowledge of these processes for understanding stock dynamics

High contrast panels and lights do not reduce bird bycatch in Baltic Sea gillnet fisheries

Bycatch is a cause of mortality among marine mammals, sea turtles, fish and birds. For some species this mortality may be sufficient to cause population declines. The Baltic Sea is a global ‘hotspot’ for bird bycatch in gillnet fisheries and is globally important for wintering sea ducks, but no technical solution has been found yet to reduce bird bycatch in gillnet fisheries in the Baltic. Here, we report on trials conducted in the Baltic Sea to test whether two different gillnet modifications with visual stimuli can effectively reduce bird bycatch while maintaining volume of fish caught. We conducted paired trials of two types of visual stimuli attached to nets: 1) high contrast monochrome net panels and 2) net lights (constant green and flashing white LED lights). We measured the amount of fish and birds caught in standard nets and those modified with the visual stimuli. Neither of the two most commonly caught species, Long- tailed Ducks (Clangula hyemalis) and Velvet Scoters (Melanitta fusca), were deterred from lethal encounters with nets by either black-and-white panels or by steady green or flashing white net lights. Long-tailed Ducks were caught in larger numbers in nets equipped with flashing white net lights than in unmodified nets at the same location. Catch rates of commercial fish were not affected by net lights or net panels placed within the nets. Hence, while the deterrents that we tested successfully maintained fish catch, they failed to reduce bird bycatch and are therefore ineffective. We discuss likely avenues for future investigation of bycatch mitigation methods for gillnet fisheries, including species and location response to net lights, managed fishery closures, above-water distraction of birds and gear switching. Keywords: Bycatch, Mitigation, Coastal gillnet fisheries, Sea duck, Seabird, Fisherie

The different uses of sea space in Polish Marine Areas: is conflict inevitable?

Seven major types of sea space use (Nature Protection Measures, Fisheries Exploitation, Geological Exploitation, Recreation, Large Infrastructures, Navigation, Military uses) in the Polish Marine Areas are presented in terms of how much space is used (km2) for each use and the degree of overlap among the different uses. The greatest degree of conflict is noted with regard to Nature Protection (which overlaps with 60% of the areas used for Recreation and Geological Exploitation), and Fisheries Exploitation (which overlaps with 60% of the areas used for Nature Protection, Recreation, Infrastructure and Navigation). On the other hand, Fisheries Exploitation areas are the least disturbed by other users, and its major competitor is Nature Protection, which claims 20% of the areas used by fisheries. A GIS-based map that illustrates the degree of conflict is included, and the authors suggest participatory management as the proper way to minimize conflicts over sea space use and to promote the effective protection of natural resources