The bigger picture: supplementing established monitoring surveys with knowledge on habitat-specific occurrence of fish in the Wadden Sea

Transcription

1 The bigger picture: supplementing established monitoring surveys with knowledge on habitat-specific occurrence of fish in the Wadden Sea Conservation Hydroacoustic management image of a of vendace fish populations school avoiding in a the Wadden Sea 8. & , trawl, Hamburg Schmidt, M. (29) Fish. Res. 96: Andreas Dänhardt University of Hamburg Institute for Hydrobiology and Fisheries Science

2 Outline Fish metrics: species richness, species composition (by guild), mean abundance, mean length, abundance trends Basic assumption: Catch per unit effort ~ population size Trends in fish abundance based on stow net surveys Seasonal comparison: monthly sampling in the Jade Bay, Spatial comparison: Jade Bay vs. Meldorf Bight, Fishes on an intertidal Pacific oyster/blue mussel-reef: A new habitat type for fish? Fishes in intertidal salt-marsh creeks Conclusions 1/21

3 Trends in fish abundance: Spatial and seasonal comparison Meldorf Bight Conger, Varel 7 km Luise, Beidenfleth Jade Bay 2/21

4 Trends in fish abundance: Seasonal comparison Sampling dates central Jade Bay April May June July August /7., 27./28. 2./ / , 22., 3. 7., / /6., 26./ /24. 1./ / /4., 22./ /2. 1./ /1. 6./7., 23./24. 2./ / /6., 26./ /25. 8./ / /6., 1./ /23. 2./ / / / /3.9. a flourishing time series on seasonal fish abundance patterns 3/21

5 Trends in fish abundance: Seasonal comparison Average cpue (n * 1 m -3 ) of Herring in the central Jade Bay by spring/summer month n * 1 m April June End May July August June Beginning /21

6 Trends in fish abundance: Seasonal comparison Selected priority species in the central Jade Bay April May* Beginning of June End of June July August Pelagic-anadromous species Twaite shad = = = = River lamprey Smelt = = Pelagic-marine species Herring Sprat = Anchovy = = Demersal species Plaice = = = = Sole = = Flounder = = Benthopelagic species Whiting = = = = Cod = = - * only 3 years available for May 5/21

7 5 Twaite shad Jade Bay Trends in fish abundance: Spatial comparison DÄNHARDT, A. & VORBERG, R. (212) Spatial and temporal variability of the Wadden Sea fish fauna against the background of the EU Marine Strategy Framework Directive Herring Meldorf Bight Concerted fishing campaigns in Schleswig-Holstein and Lower Saxony Jade Bay Meldorf Bight / / / n * 1 m Sprat Anchovy Smelt /

8 Trends in fish abundance: Spatial comparison =: no trend, / : increase/decline, ( )/( ): slightly increasing/declining, ±/ initially stable, later increasing. Overall trend: average across the 11 species shown ( / : -1/+1, ( )/( ); -,5/+,5, ±: Species Jade Bay Meldorf Bight Twaite shad =/ =/ Herring Sprat ( ) Anchovy = = Smelt ( ) Flounder = Plaice Sole = Whiting = Cod = River lamprey = Overall trend ( ) ( ) 7/21

9 Pacific oyster/mussel-reef Kaiserbalje 8/21

10 Pacific oyster/blue mussel-reef Kaiserbalje 9/21

11 May June September Common goby Plaice Sand goby Eelpout Herring Nilsson's pipefish Whiting Flounder Three-spined stickleback Sand smelt Twaite shad River lamprey Bib Spur-dog Dragonet Transparent goby Brill Grey gurnard Great sandeel Sea snail Horse mackerel Garfish Tope shark Montagu's sea snail Dab Red gurnard Anchovy Bull rout Sole Sprat Turbot Hooknose Smelt Surmullet Small sandeel Reef surface, n=988 Stow net, n=2927 Reef surface, n=116 Creeks, n= 873 Stow net, n=454 Reef surface, n=555 Creeks, n=533 Stow net, n= Relative share (%) /21

12 Pacific oyster/blue mussel-reef Kaiserbalje June reef surface_% (n=116) Common goby Plaice Sand goby Nilsson's pipefish Eelpout Flounder Three-spined stickleback Herring Red gurnard Sprat Hooknose Smelt June creeks_% (n=873) 11/21

13 Pacific oyster/blue mussel-reef Kaiserbalje September reef surface_% (n=555) Common goby Plaice Sand goby Nilsson's pipefish Eelpout Flounder Three-spined stickleback Herring Red gurnard Sprat Hooknose Smelt September creeks_% (n=533) 12/21

14 Relative share (%) Relative share (%) Pacific oyster/blue mussel-reef Kaiserbalje Plaice 35 3 June reef surface (%, n=17) June surrounding creeks (%, n=448) Photo: Dereck Haslam, the wildlife trust September reef surface (%, n=5) Standard length class (mm) September surrounding creeks (%, n=145) Standard length class (mm) 13/21

15 Fishes in intertidal salt-marsh creeks Stow net (August 211) < 1 km Fyke nets in intertidal salt-marsh creeks in Dieksanderkoog north October 21 May 211 June 211 August 211 Ship-based stow net in subtidal creek, Meldorf Bight 14/21

16 Absolute abundance per standardized haul Fishes in intertidal salt-marsh creeks: Seasonality Common goby North creek South creek North creek South creek Twaite Shad Herring North creek South creek - Marked seasonal patterns differing between species - Small-scale (between neighboring creeks!) differences in species-specific catch numbers - No stable patterns across years ( 214) 15/21

17 Fishes in intertidal salt-marsh creeks: Growth environment 1 m 16/21

18 Number of fish Habitat utilization patterns: Model cases Case 1: stationary species or small source, poor or no replenishment Case 2: mobile species, patchy source, random replenishment Number of hauls (chronological) Case 3: mobile species, rich source, directed replenishment 17/21

19 Number of fish Number of fish Habitat utilization patterns: Herring October 21 y = -4,8214x + 36,143 R² =,363 y = -4,357x + 22,857 R² =, South creek North creek y = 21,429x + 14,571 R² =,284 y = -7,357x + 67,857 R² =, Haul No (chronological) May 211 y = 4,2x - 34,222 R² =,5371 y = 19,83x - 8,8611 R² =, June 211 August y = -4,2143x + 26, R² =,5651 y = -1,3167x + 17,361 R² =, Haul No (chronological) 19/21

20 New research project: INTERaction of fish, plants, carbon and sediment: management and ecosystem functions of Wadden Sea salt marshes Funded by NIEDERSACHSEN SCHLESWIG-HOLSTEIN HAMBURG 2/21

21 Conclusions Supplementing established survey data with knowledge on habitat-specific occurrence patterns of fish in the Wadden Sea would help to cover typical elements of the WS-fish fauna currently not represented in the monitoringcatches Spatial and seasonal aspects need to be included in the interpretation of abundance trends Integrated analysis species by species, considering also other surveys and analyses along the ontogenetic pathway of the focal species (WFD monitoring transitional waters, stock assessment data North Sea) What do changes in the metrics mean? Studies on cause-effect relationships are required, monitoring data are not enough Specify the targets to make it easier to evaluate them Inventory of data, projects and knowledge and organized and extended cooperation, e. g. by a resurrected expert group on WS fish which close links to other WGs (e. g. ICES) 21/21

22 Thank you for your attention and stay curious