Rapport nr 149: Bedömning av faktorer som påverkar abborrens (Perca fluviatilis) tillväxt och födoval I Marsund/Bovik och Kumlinge I Ålands skärgård
RAMSTEDT, R. (2018)
RAMSTEDT, R.
Åbo Akademi, Husö biologiska station
2018
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Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:978-952-12-3748-5
https://urn.fi/URN:ISBN:978-952-12-3748-5
Tiivistelmä
This study was conducted during the summer of 2017. The study focused on the growth and diet of Eurasian perch (Perca fluviatilis) in two separate areas in the Åland Islands. The bays of Marsund/Bovik lie in the transition zone between the middle and outer archipelago in the northwestern part of the Åland islands. The other study area, Kumlinge, is positioned in the outer archipelago in the eastern part of the Åland Islands. 45 stations in Marsund/Bovik and Kumlinge, respectively, were visited during test fishing and mapping of the bottom habitats, using the drop-video technique. The stations were divided into four depth intervals (0-3 m, 3-6 m, 6-10 m, >10 m). In addition, 10 stations per area were randomly selected for benthic fauna sampling and measurement of environmental conditions. Otoliths were used to determine the age of perch and stomachs were collected for stomach-content analysis.
The fish catches showed that perch was the most abundant species at both areas. The perch abundance was almost twice as high in Kumlinge compared to Marsund/Bovik. Marsund/Bovik was also characterized by a large roach population but in Kumlinge there were almost no roach caught at all. The growth of perch was faster in Kumlinge in contrast to Marsund/Bovik, but there were no major differences between any age-classes.
The diet of perch varied between the areas. Perch in Marsund/Bovik ate more fish than macroinvertebrates compared to Kumlinge where the relative amount of macroinvertebrates in the diet was higher. The relative abundance of different fish species/groups and macroinvertebrates showed that the diet of perch in Kumlinge was dominated by a few species/groups of fish and especially invertebrates in contrast to Marsund/Bovik where the relative proportion of different groups was more even in the diet. All in all the perch preyed mostly on macroinvertebrates that occurred in a relatively small proportion of the total abundance and biomass of the benthic community (e.g. crustaceans).
The benthic fauna had a higher biomass and abundance in Kumlinge at all depth intervals except >10 m compared to Marsund/Bovik. The most abundant macroinvertebrates at both sites were the Hydrobia-snail and the Macoma balthica-clam, the relative biomass was dominated by M. balthica-clams and other bivalves.
Vegetation cover on the bottom varied between the sites. At Marsund/Bovik roughly one third of the bottom had some kind of vegetation when the vegetation cover was almost two thirds in Kumlinge. The diversity of habitat types was also higher at Kumlinge.
The differences in growth and diet of perch between the two areas are probably caused by a sum of factors acting together. Perch in Marsund/Bovik most likely experience competition from roach, degraded feeding conditions because of poor light conditions, scarce vegetation and benthic fauna. On the other hand the warmer and less saline coastal waters at Marsund/Bovik fits better perch than the colder and more saline waters at Kumlinge in the outer archipelago. Perch in Kumlinge do possibly compete with each other but the good feeding conditions including transparent waters, a rich benthic fauna and habitat diversity contribute to a faster growth of perch compared to Marsund/Bovik
The fish catches showed that perch was the most abundant species at both areas. The perch abundance was almost twice as high in Kumlinge compared to Marsund/Bovik. Marsund/Bovik was also characterized by a large roach population but in Kumlinge there were almost no roach caught at all. The growth of perch was faster in Kumlinge in contrast to Marsund/Bovik, but there were no major differences between any age-classes.
The diet of perch varied between the areas. Perch in Marsund/Bovik ate more fish than macroinvertebrates compared to Kumlinge where the relative amount of macroinvertebrates in the diet was higher. The relative abundance of different fish species/groups and macroinvertebrates showed that the diet of perch in Kumlinge was dominated by a few species/groups of fish and especially invertebrates in contrast to Marsund/Bovik where the relative proportion of different groups was more even in the diet. All in all the perch preyed mostly on macroinvertebrates that occurred in a relatively small proportion of the total abundance and biomass of the benthic community (e.g. crustaceans).
The benthic fauna had a higher biomass and abundance in Kumlinge at all depth intervals except >10 m compared to Marsund/Bovik. The most abundant macroinvertebrates at both sites were the Hydrobia-snail and the Macoma balthica-clam, the relative biomass was dominated by M. balthica-clams and other bivalves.
Vegetation cover on the bottom varied between the sites. At Marsund/Bovik roughly one third of the bottom had some kind of vegetation when the vegetation cover was almost two thirds in Kumlinge. The diversity of habitat types was also higher at Kumlinge.
The differences in growth and diet of perch between the two areas are probably caused by a sum of factors acting together. Perch in Marsund/Bovik most likely experience competition from roach, degraded feeding conditions because of poor light conditions, scarce vegetation and benthic fauna. On the other hand the warmer and less saline coastal waters at Marsund/Bovik fits better perch than the colder and more saline waters at Kumlinge in the outer archipelago. Perch in Kumlinge do possibly compete with each other but the good feeding conditions including transparent waters, a rich benthic fauna and habitat diversity contribute to a faster growth of perch compared to Marsund/Bovik