Temporal development of the coastal fish community in Kaitvesi (Finland), Archipelago Sea

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1 Temporal development of the coastal fish community in Kaitvesi (Finland), Archipelago Sea Authors: Raisa Kääriä, Outi Heikinheimo, Jens Olsson and Eevi Suleva Key Message In the Kaitvesi area there were no clear temporal trends in any of the indicators nor in the background information. The monitoring time is quite short, from year 2005 to year The majority of the indicators assessed have, however, relatively high values during the last two years. Background and oceanographic information The Kaitvesi monitoring area is situated in a sheltered inner Arcipelago about 15 kilometers southeast from Turku. The catchment area is sparsely populated and agricultural land dominates the area. The depth in the area is mainly below 10 meters and the bottom consists mainly of mud and clay. The nutrient content in the surface water is at an eutrophic level, the phosphorus content during June August is generally μg/l and the nitrogen concentration between μg/l. There have been no trends in nutrient concentrations since (Figure 1). The salinity in the monitoring area varies between 5-6 PSU. The secci depth has been m during the monitoring period The temperature has only been observed during the fish monitoring periods, and there has not been no change in the variable over time (Figure 1).

2 Figure 1. Temporal development in variables potentially affecting the state of fish communities in the Kaitvesi area (Temperature and secci depth are the mean values measured during fish monitoring each year). The nutrient concentrations have been measured near the monitoring area at one meters depth (mean of the values in June September; data from the Finnish Environment Institute). No trend can be seen in the variables. Results and assessment The indicators used below and their relevance for conveying developments in the environment are derived from HELCOM (2012), and described in the main indicator fact sheet on Temporal development of Baltic coastal fish communities and key species. Overall state Monitoring data cover the period There were no clear temporal trends in any of the indicators, but the majority of the indicators assessed have relatively high values during the last two years. In 2005 the species Diversity was relatively high, whereas the Trophic Level was low. During the following years ( ) the Diversity decreased and the Trophic level increased. In 2010 and 2011 all size and abundance related indicators had relatively higher values than in previous years. In 2010 Mean Maximum Length and Large Individuals, Marine Species and Piscivore Abundance were relatively high, whereas in 2011 the diversity got higher again as did Total Abundance, Cyprinids, Nonpiscivores, Perch Abundance and Large Perch. Figure 2. Result of an analysis of all indicators together for the Kativesi area (PCA, years ). The black line connects the years in a chronological order. The blue lines show the indicators mainly characterizing the different years, by pointing in the direction of that year. Long vectors indicate a strong relationship between the indicator and the years studied. Only the first two ordination axes of the PCA is presented, the first axis (PC-1) explained 54,6% of the total variation observed in the data set, and the second axis (PC-2) explained 24,7%.

3 Species composition Total Abundance Figure 3. Temporal development of the Total Abundance (CPUE) in the Kaitvesi area. There is no clear trend in the indicator values. Total Abundance in the Kaitvesi area is strongly affected by changes in Perch, Roach and White bream abundance. The indicator is used as an index of the size of the standing stock. Increased abundance indicates increased nutritional conditions and production potential. Perch Abundance Figure 4. Temporal development of the Perch (> 12 cm) Abundance (CPUE) in the Kaitvesi area. There is no overall temporal trend for the indicator. The abundance of Perch is quite low in the area. The indicator is strongly affected by changes in year class strengths and is used as an index of the size of the standing stock of the species. In the long term, increased abundance or perch indicates increased nutrition conditions, high summer temperatures and production potential.

4 Cyprinids Figure 5. Temporal development of Cyprinids (CPUE) in the Kaitvesi area. There is no clear trend in the indicator values. Cyprinids is an indicator of the abundance of species from the carp family, and is influenced by prevailing nutrient and temperature conditions. Increased cyprinid abundance indicates increased nutritional conditions, production potential and water temperatures. Freshwater Species Figure 6. Temporal development of Freshwater Species (CPUE) in the Kaitvesi area. There is no clear temporal trend in this indicator. Freshwater Species is strongly affected by changes in the abundance of Perch and species from the carp family. The indicator responses to changes in prevailing nutrient and temperature conditions. Increased abundance of freshwater species indicates increased nutritional conditions, increased water temperatures, habitat quality and lowered salinity levels.

5 Marine Species Figure 7. Temporal development of Marine Species (CPUE) in the Kaitvesi area. There is inter-annual variation in the indicator values which are overall very low. The indicator is sensitive to events of upwelling of cold and saline water. Marine Species indicator in the Kaitvesi area is dependent on the occurrence of mainly herring. Decreased abundance of marine species indicates lowered salinity levels and increased water temperature. Size structure Large Individuals Figure 8. Temporal development of Large Individuals (CPUE) in the Kaitvesi area. There is inter-annual variation in the indicator values. Large Individuals is an indicator of Perch, Pike and Pikeperch, but also large cyprinid species like common bream. In the Kaitvesi area Pikeperch was the most numerous species of large individuals ( 30 cm). The indicator is dependent on the temperature conditions and fishing pressure, but to lesser extent also by nutrient status. Decreased values of this indicator are associated with decreased water temperature, increased fishing pressure and decreased nutrient conditions.

6 Mean Maximum Length Figure 9. Temporal development of Mean Maximum Length (cm) in the Kaitvesi area. There is no temporal trend in this indicator. Mean Maximum Length is an indicator of the size structure in the fish community, and is a measure of the relative abundances of large and small species in the community. As such it also to some extent considers recruitment of different species. The indicator is dependent on the temperature conditions and fishing pressure, but to a lesser extent also on the nutrient status. Increased values of this indicator are associated with increased water temperature, decreased fishing pressure and increased nutrient conditions. Mean Length Perch Figure 10. Temporal development of Mean Length Perch (cm) in the Kaitvesi area. There is no temporal trend in this indicator. Mean Length Perch is an indicator of the demographic characters and size structure in the key species Perch. The indicator is affected by variation in recruitment, extensive size selective fishing and changed individual growth rate. As such it is dependent on the temperature conditions and fishing pressure. Increased values of this indicator are associated with increased water temperature and lower fishing pressure.

7 Trophic structure Mean Trophic Level Figure 11. Temporal development of Mean Trophic Level in the Kaitvesi area. The indicator shows inter-annual variation. Mean Trophic Level reflects the trophic status of the fish community, where increasing values indicate that a higher proportion of species are at higher trophic levels, e.g., piscivorous fish and/or lower levels of the plankton and benthos feeding species. In Kaitvesi the highest value of Mean Trophic Level index in the year 2010 occurs with also highest value in the Piscivore Abundance. Lowest values of the Mean Trophic Level index are associated with the highest values in the Cyprinids indicator. Generally, the indicator is influenced by fishing pressure and nutrient levels. Piscivore Abundance Figure 12. Temporal development of Piscivore Abundance (CPUE) in the Kaitvesi area. There is inter-annual variation in this indicator. Piscivore Abundance reflects the abundance of piscivorous fish in the community and as such also its trophic status. Compared to Brunskär, Helsinki and Tvärminne abundance of piscivores seems to be quite low but this may have something to do with the Total Abundance index also being quite low. Generally, Piscivore Abundance indicator has a positive response to decreased fishing pressure.

8 Species diversity Diversity Figure 13. Temporal development of Diversity (Shannon Wiener Diversity Index) in the Kaitvesi area. There is no trend in this indicator. The Shannon-Wiener index reflects the species richness and equitability of the community. Decreasing values indicate community changing towards few dominating species and a small number of species. Calculations are based on the biomass proportion of each species. Methods used The area was monitored using Nordic coastal multi mesh gillnet (mesh sizes 10, 12, 15, 19, 24, 30, 38, 48 and 60 mm from knot to knot) in randomly selected stations, divided into four depth intervals. The stations are monitored annually in the beginning of September (Table 1). Table 1. Monitoring time and the amount of stations yearly. fishing time stations Acknowledgements The monitoring in Kaitvesi has been financed by Turku University of Applied Sciences, the municipalities of Kaarina, Turku and Parainen, the fisheries organizations Airisto-Velkua, Parainen and Paimionselkä and the Promotional Fund for Fisheries ( Centre for Economic Development, Transport and the Environment for Southwest Finland). References Finnish Environmental Institute OIVA - the environmental and geographical information service for experts, HELCOM Indicator based assessment of coastal fish community status in the Baltic Sea Balt. Sea Environ. Proc. No. 131B.

9 For reference purposes, please cite this Baltic Sea environment fact sheet as follows: [Author's name(s)], [Year]. [Baltic Sea environment fact sheet title]. HELCOM Baltic Sea Environment Fact Sheets. Online. [Date Viewed], Last updated: 26 September 2013