Improving whitefish (sik) reproduction with habitat restorations?

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1 Improving whitefish (sik) reproduction with habitat restorations? Lari Veneranta Natural Resources Institute Finland (Luke) Vaasa

2 Whitefish catches in Finland Bothnian Sea, sea-spawning Whitefish, total catch in professional fishing catch, tonnes 1600 Gulf of Finland Bothnian Sea Archipelago Sea Bothnian Bay Bothnian Bay, sea-spawning 0 Both the catches and catchability have gone down Less whitefish in waters Seals make fishing difficult

3 Perho å, whitefish catch of spawning stock Stockings Damming, power plants Draining Dredging of rapids Data: Dan Vikström

4 Stockings have been used to improve catches Stockings were started already in 1930s Whitefish stocking with one summer old fish started in the change of 1970s and 1980s The annual stockings are m larvae and 4-8 m one summer old whitefish Most of stockings are done with migratory whitefish, only a small part is sea-spawning ecotype. Stockings have kept the whitefish fishing profitable

5 Whitefish / Torne älv Catches depend on stockings Average size depends on intensity of gillnet fishing

6 Natural reproduction in rivers Number of larvae In rivers were mapped, and Larvae were observed in 664 sites 30 rivers have verified natural reproduction Also dammed or constructed

7 Sea-spawning ecotype Reproduction has decreased south from Quark Increased coastal eutrophication and changes in winter iceconditions Stock status in the Bothnian Bay still good Vanhatalo et al. 2012; Veneranta et al. 2013

8 Algal coverage effects on larval occurrence Clean sand bottom Without algae Algal growth on sand bottom With algal coverage Bottom structure

9 Whitefish egg, eutrophication and sedimentation Müller 1992 Whitefish egg Sediment

10 Identification of spawning sites?

11 Reproduction areas as a basis for fish stocks Larval area V a s a 600 km Spawning area

12 Even a small reproduction area can produce a fish stock of vast area!

13 Restoration of spawning grounds? What kind of bottom? Type of river flow? Water quality? Extent of areas? Methods to identify spawning grounds are needed Fabricius & Lindroth 1954

14 Spawning area identification 1 Bottom structure side scan sonar 3 Egg sampling with pump 2 Image interpretation / sampling stratification 4 Identifiation of spawning locations

15 Kokemäenjoki 24 27th November

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17 Sea-spawning whitefish in Vaasa archipelago Gillnet fishing sites Egg pumping site

18 Egg pumping / early test Exposed shallow point, prone to water currents Gravel between boulders, depth 1.5 m.

19 Possibilities for artificial reproduction areas? Great Lakes example

20 The sea is so vast practical possibilities for restorations Process to enhance whitefish reproduction areas Test fishing or telemetry of target species at spawning time Side scan sonar, mapping of bottom structure Egg sampling at spawning area Identification of bottom structure / underwater photography Identification and modelling of spawning locations Definition of restoration possibilities and usefullness Testing of restoration methodology in limited areas (funding???) 1. Site selection 2. Transport of suitable sediment 3. Stocking of eggs or larvae 4. Follow-up of larval production / spawners 5. Evaluation of process

21 Thank you!