Western Uusimaa/Järvi Hoi Anu Suonpää, Järvi Hoi kick-off, 9.5.2012
Association for Water and Environment of Western Uusimaa, Finland www.luvy.fi
Basic information Founded in 1975 Main office in Lohja 2 sideoffices Employees (2012) about 30 Researchers, field and laboratory staff, specialists etc. Operational area Karkkila Hanko Kirkkonummi
Operations Divided to non profit (3 %) and supporting and financing business operations (97 %) Non profit operations: - Advising, promotion, statements, seminars.. Business operations: - Environmental services - Laboratory services In addition Luvy works in projects either as a coordinator or as a partner
Järvi Hoi - target lakes in Western Uusimaa
Järvi Hoi/target lakes in Western Uusimaa
Lake Hiidenvesi The second largest lake of Uusimaa Large catchment area Lake area 30 km² : 935 km² Lakes 2 %, over 60 % forests ja 20-34 % farm land Soil: fine clay -> susceptible to erosion Paleolimnological studies have shown that because of the soil quality the lake is naturally eutrophic and clay- murky Main water discharge is from Rivers Vihtijoki and Vanjoki which are also eutrophic
Lake Hiidenvesi Lake area 30 km 2 Mean depth 4 m Max depth 33 m Mean retention time 9 kk Seperate basins which differ in morphology and water quality Ecological state satisfactory Highly eutrophic Large blue algae blooms High recreational value High population over 10 000 people lives in the area
What has been done? Lake Hiidenvesi restoration project in 1995- I-stage 1995-2005, focused on management fishing, the catch 717 565 kg in 1994-2004 II-stage 2005-2007 Management fishing ended and restoration focused on the external loading from the drainage basin III-stage Restoration project for 2008-2011 Drainage basin management The nutrient load from the drainage basin twice greater than the critical limit for nutrient loading (e.g. Marttila 2003, Saarijärvi and Sammalkorpi 2005) focus still on the management of the catchment area
Lake Hiidenvesi restoration project stage IV 2012- Main focus on the drainage basin management Large wetlands e.g. to close approximation from Lake Hiidenvesi small basins and wetlands Restoration of Lake Vanjärvi Buffer zones along the water course Chemical treatments to the hotspot areas (e.g. close to horse stables) Farm based water protection plans to the farms in the area Waste water treatment of scattered settlements Co-operation with other projects: producing new information of the lake area and the lake s ecosystem (e.g. Järvi Hoi) - Would management fishing be beneficial in Lake Hiidenvesi after all?
Why the management fishing ended in Lake Hiidenvesi? External loading twice greater than the critical limit main focus to reduce nutrient loading from the catchment area Management fishing (reducing internal loading) can not produce sustainable outcome because external loading is too high (e.g. Saarijärvi and Sammalkorpi 2005) There was no significant positive change on fish assemblages or water quality after 10 years of management fishing Complicated food web might have hindered the positive effects of biomanipulation
What happened? A trophic cascade.. When the planktovorous fishes are fished out.. Predatory invertebrate population density increases.. Which feeds on large zooplankton....the grazing pressure of phytoplankton decreases algal blooms appear
After management fishing: fish densities and biomass in > 5 m depth (test trawling and echo sounder study) in 2007 Smelt Perch White bream Bream Pikeperch Large blue bream Others Main fish density and biomass was smelt Malinen et al. 2007
Fish density in the shallow areas of Lake Hiidenvesi (test trawling and echo sounder study) in 2007 Malinen et al. 2007 Others Bleak Roach Small < 7 cm bream and white bream White bream Bream Perch Pikeperch Smelt
g/verkko kpl/verkko g/verkko kpl/verkko Lake area Mustionselkä in 2010: study of the ecological state of Lake Hiidevesi The biomass of the whole catch in 1997-2010 6000 5000 4000 3000 g/verkko kpl/verkko 300 250 200 150 The biomass of different species in 2010 2500 2000 1500 g/verkko kpl/verkko 100 80 60 2000 100 1000 40 1000 0 1997 1998 1999 2000 2001 2007 2010 Vuosi 50 0 500 0 Ahven Kuha Kiiski Särki Salakka Pasuri Lahna Sorva Sulkava 20 0 The egological state of fish stock in Lake area Mustionselkä has decreased below avarage below avarage/poor! Because of the the biomass of the catch per gill net has increased The biomass of cyprinid fish is still high 71 %! The biomass of predatory fish is 15 % Something should be done Sairanen 2010/Finnish Game and Fisheries Research
Management fishing in Lake Hiidenvesi in the future In the deep and large lake areas smelt is the main fish species feeds on phantom midge larvae should be avoided Management fishing needs to be targeted on the fish species which do not feed on large invertebrate predators Shallow lake areas of Mustionselkä and Nummelanselkä are possibilities for management fishing because the fish community is more diverse that in the deep lake areas Because of complicated food web a thorough study of the diet of the target fish species is mandatory before planning on starting management fishing
Conclusion possible benefits of management fishing in Lake Hiidenvesi Management fishing could increase recreational value of Lake Hiidenvesi Pikeperch is the most valued catch in Lake Hiidenvesi Management fishing reduces fish size (larger fish are removed) which produces possible prey for pikeperch increases the catch of pikeperch In addition with the catch the nutrients that would stay in the ecosystem and be available for the algae are removed