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Temporal development of Baltic coastal fish communities and key species in Hiiumaa
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Key Message
In the Hiiumaa monitoring area temperature and Secchi depth have not changed, both parameters show no significant trends during 1991-2007 (Figure1.). No significant trends were observed also in community and species level during the period of investigation. New alien species Prussian carp has appeared in Hiiumaa area.
Background and oceanographic information
The Hiiumaa monitoring area is located in the Sea of Straits in western Estonia southeast from island Hiiumaa. Section one is sheltered. Water depth seldom exceeds 3 m. The bottom consists mainly of mud and clay. Section two is more exposed area with water depths up to 7 meters. The bottom is sandy and stony. The salinity in the surface water is 4-6 PSU in both sections.
Figure1. Mean temperature and Secchi depth in the monitoring area at Hiiumaa (both sections). No significant trends occurred during the period. As the area is shallow the water transparency depends a lot on the wind direction and velocity.
Local pressure
The area of southeastern Hiiumaa is sparsely populated and industries are absent. The area is located inside the nature reserve. Fishing effort was very high in 1990s, but has decreased a lot during the last five years. There is a large population of great cormorants in the area. Investigations showed that establishment of a cormorant colony not far from Hiiumaa monitoring area excluded the normal functioning of historically very important spawning grounds for roach and other freshwater species. That area no more can create recruitment effect to adjacent fisheries.
Results and assessment
The indicators used below and their relevance for conveying developments in the environment are described in the main indicator fact sheet on Temporal development of Baltic coastal fish communities and key species.
Community indicators
Number of species
Figure 2. Number of freshwater, marine, migratory and alien fish species at Hiiumaa section 1 and 2. The species number in section 1 was inscrutably smaller during the early nineties compared to section 2 and later period. During the last years alien species Prussian carp has become more common also in Hiiumaa waters but its abundance is still small compared to some other Estonian coastal areas.
Total biomass
Figure 3. Total biomass (weight per unit of effort, mean per station in kg) in the monitoring area at Hiiumaa. The total biomass showed high values in some stations in section 2 during the early nineties but the trends are not significant for the whole study period of 1992-2007.
Species diversity
Figure 4. Shannon Wiener diversity index in the monitoring area at Hiiumaa. No significant trends occurred during the study period.
Slope of size spectrum
Figure 5. Slope of the size spectrum in the monitoring area at Hiiumaa. No significant trend occurred during the study period.
Average trophic level of catch
Figure 6. Average trophic level of catch in the monitoring area at Hiiumaa. No significant trends occurred during the study period. Small values during mid 1990s are explained by the low abundance of perch in the fish community.
Key species indicators
Species biomass
Figure 7. Perch biomass (weight per unit of effort, mean per station in kg) in the monitoring area at Hiiumaa. No significant trends occurred during the study period.
Mean age
Figure 8. Geometrical mean length of perch in the monitoring area at Hiiumaa. No significant trends occurred during the study period.
Slope of size spectrum
Figure 9. Slope of size spectrum of perch in the monitoring area at Hiiumaa. No significant trends occurred during the study period.
Methods used
Fishing with coastal net series (mesh sizes 17, 21.5, 25, 30) at twelve stations was annually performed. The stations were repeatedly fished for six times in early August.
Links
Return to main indicator fact sheet
For reference purposes, please cite this indicator fact sheet as follows:
[Author’s name(s)], [Year]. [Indicator Fact Sheet title]. HELCOM Indicator Fact Sheets 2007. Online. [Date Viewed], http://www.helcom.fi/environment2/ifs/en_GB/cover/.
Last updated: 14.05.2008