Temporal development of Baltic coastal fish communities and key species in Vinö

 

	Author: Jens Olsson

 

Return to main indicator fact sheet

Key Message

Temperature and secchi depth are important for the structure of coastal fish communities. In the waters at Vinö monitoring area, these parameters show no significant trends during the monitoring period.

Several coastal fish indicators have, however, changed significantly with time. The total biomass decreased during the monitoring period. This pattern is driven by the peak catch in 1995, and strongly influenced by the biomass of the key species perch which shows a similar pattern with decreasing catches with time. Reduced biomass in turn indicates decreased productivity, recruitment and/or growth of the fish stock.

In the Vinö monitoring area the mean length of perch decreased during the monitoring period, indicating a transition towards smaller individuals. This could be a result of decreased recruitment, extensive size selective mortality and/or decreased growth rate of perch. A decrease in any of these variables has negative effects on the biomass, something plausibly explaining the pattern observed here.

Background and oceanographic information

Vinö, in the Misterhult archipelago, belongs to the continuous archipelago of the Swedish east coast. The bedrock consists of granite. Vinö have, since 1995, been used as a reference area to Mönsterås Bruk. It is a sheltered area with connection with the open sea through deep furrows. No outflow from streams or brooks of important size exists in the area.

 

Figure 1. Temperature and Secchi depth in Vinö between 1995 and 2007. None of the indicators show significant trends during the monitoring period.

 

Local pressure

Vinö represents a region with very limited impact of local discharge.

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 species, divided into freshwater, marine and migratory species, at Vinö monitoring area. No trends were detected for either of the indicators during the monitoring period, but there is an almost significant positive trend for the total number of species which thus has a tendency to increase with time. 21 different species have been caught in the area during the monitoring period.

 

Total biomass

 

Figure 3. Total biomass (mean per station in kg) at Vinö monitoring area. Total biomass fluctuates strongly between years and shows a negative trend during the monitoring period. This indicates decreased growth and/or recruitment of the fish community. Total biomass are, however, strongly affected by the development of the key species perch (see below biomass of key species indicators), suggesting that not all species are experiencing decreased recruitment. Worth considering is however that the peak catch in 1995 is driving the negative trend of this indicator. 

Species diversity

 

Figure 4. Shannon-Wiener diversity index at Vinö monitoring area. No significant trends were detected for the index during the period, suggesting no change in diversity.

 

Slope of size spectrum

 

Figure 5. Slope of size spectrum of all species at Vinö monitoring area. Decreased values indicate an increase of larger individuals in the fish community, which inturn indicate low fishing pressure and/or increased growth rate and productivity. This indicator shows no significant trend during the monitoring period.

 

Key species indicators

  The key species at Vinö monitoring area is perch, a warm water, freshwater species.

Species biomass

 

Figure 6. Perch biomass (mean per station in kg) at Vinö monitoring area. Perch biomass fluctuates between years and shows an almost significant and negative trend during the monitoring period. This indicator strongly affects the total biomass which also shows a similar development. Decreased perch biomass in turn suggests decreased growth and/or recruitment of the perch population at Vinö. Worth considering is however that the peak catch in 1995 is driving the negative trend of this indicator.

 

Mean length

 

Figure 7. Mean length of perch at Vinö monitoring area. This indicator decreased during the monitoring period. Mean length in perch reflects the length distribution in the fish stock. The decrease could be due to variation in recruitment, extensive size selective mortality and changes in individual growth rates.

 

Slope of size spectrum

 

Figure 8. Slope of size spectrum of Perch at Vinö monitoring area. This indicator shows no significant trend during the monitoring period. Slope of size spectrum reflects the length distribution of the fish community.

Methods used

 

Fishing with coastal survey nets (mesh sizes 17, 21, 25 33 and 50 mm from knot to knot) at eight stations was annually performed. The stations were repeatedly fished for six nights in early August.

References

Andersson, J. 1998. Kustfisk och fiske vid svenska Östersjökusten. Fiskeriverket Information 1:1998, s. 1–44.

Links

Swedish Board of Fisheries, Nationell och regional fiskövervakning.

 

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: 2008-09-24