Trends in fish in the Wadden Sea and coastal waters

Transcription

1 Trends in fish in the Wadden Sea and coastal waters 8 January 2015, Hamburg, workshop conservation management fish populations in the Wadden Sea Ingrid Tulp, Henk van der Veer & Paddy Walker

2 NL fish monitoring Wadden Sea

3 DFS survey & fyke Texel 2007

4 Demersal Fish Survey IMARES since 1970 Sept/Oct: 1x a year ca 300 hauls aim: recruitment plaice and sole all fish and epibenthic species recorded shrimp trawl: 20 mm mesh size depth <20m in intertidal areas gullies>2m

5 Fyke Texel 6

6 Comparison schemes characteristic fyke DFS shrimp trawl carried out by NIOZ IMARES period >1966 >1970 frequency daily 1 per year timing spring and autumn Sept/Oct spatial coverage 1 site Wadden Sea+coast 300 hauls (120 Dutch Wadden Sea) effort per sample high (1 day) low (30 min) species caught demersal and pelagic demersal fish size caught all sizes small fish swim speed slow and fast slow origin fish local and migrating local

7 Questions fish in Wadden Sea Has total fish biomass changed? What is the species composition and has it changed? Do species belonging to different guilds show different developments? resident species vs marine juveniles Has timing changed in response to climate change? Has size structure changed?

8 The Wadden Sea in a wider perspective

9 n/ha Time series analysis Trendspotter Visser (2004) nonlinear trends classification of trends based on yearly change rates and the variation substantial de- or increase moderate de- or increase stable fluctuating/poorly known Soldaat et al 2007

10 Total fish biomass

11 species

12 biomass (kg/10000m2) Species composition (DFS) Ems-Dollard western Dutch Wadden Sea eastern Dutch Wadden Sea Sea Sea t plaice dab whiting gobies sp sole flounder bib bull rout herring cod smelt eelpout sea snail five-bearded rockling eel sandeel sp sprat hooknose Dutch wadden coast southern Dutch coast

13 Species guilds Marine juveniles Estuarine residents Catadromous/anadromous Marine seasonal migrants Marine advantageous

14 Species trends: marine juveniles

15 Species trends: residents

16 Species trends: residents

17 Species trends: residents

18 Species trends: residents

19 marine juveniles

20 estuarine residents

21 mean biomass (kg/10m2 Relative importance of areas plaice dab whiting gobies sp sole flounder bib bull rout herring cod smelt eelpout sea snail five-bearded rockling eel sandeel sp sprat hooknose region4 Ems-Dollard western Dutch Wadden Sea eastern Dutch Wadden Sea Dutch wadden coast southern Dutch coast

22 DFS CPUE Correlation fyke-dfs Western Wadden Sea Sept/Oct Species that occur in both series bib 6 R dab 6 R five-bearded rockling brill eel flounder R R cod eelpout herring R R R plaice smelt R sole R R sprat turbot R whiting R R R R fyke CPUE

23 day number Phenology: fyke dab bull rout flounder plaice

24 number Phenology: fyke species presence species presence fyke sampling day number

25 day number Timing dab bull rout flounder plaice

26 number Change in phenology? 30 species For species caught within fyke time frame 5 sp 1 sp 1 sp 1 sp fyke sampling day number

27 mean length (cm) Size structure W Dutch Wadden sea Bib Brill Bull-rout Butterfish Cod Common dragonet Dab Eel Eelpout Five-bearded rockling Flounder gobies sp Greater sand-eel Herring Hooknose pipefish sp Plaice sandeel sp Sea-snail Smelt Sole Sprat Tub gurnard Whiting

28 Drivers? climate: ability to cope with increased temperature decreased productivity fisheries: bycatch + potential effect via foodweb increasing predation pressure within Wadden Sea changing predation pressure outside Wadden Sea processes on North Sea habitat availability connectivity trends in catchability

29 Climate change: growth potential plaice plaice 1.5 cm plaice 20 cm Years with contrasting temperature and food productivity Bio-physiological model Growth potential plaice 40 cm Teal et al 2012

30 fisheries

31 conclusions strong negative trends in marine juveniles loss of older year classes plaice, dab, flounder, whiting changed distribution for several species no overall clear pattern in trends estuarine residents tidal basins within Wadden Sea show different trends in some species no overall clear phenology changes 2 monitoring schemes catch different parts of fish fauna pelagic fish/migratory fish still largely unexplored =>species-specific approach necessary to identify drivers and investigate mechanisms

32 Thanks to Loes Bolle (project leader DFS, IMARES) Hans Witte (NIOZ), Marcel de Vries, Andre Dijkman (IMARES) all field and data assistants NIOZ and IMARES crews of all research vessels 37

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34 birds vs fish birds fish population size international estimates SBB for commercial species census method (year round) counting fishing with unknown efficieny census transportation reproduction walking measure eggs and young expensive vessels not possible (not even known if a species reproduces in the area) migration ringing and tracking limited possibilities marking and tracking survival mark-recapture mark-recapture diet observation and faeces stomachs (of dead fish) habitat preferences research investment long tradition of Wadden Sea bird research known for many species known for few species DFS survey and fyke

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36 mean biomass (kg/10m2 Ems-Dollard western Dutch Wadden Sea eastern Dutch Wadden Sea Dutch wadden coast southern Dutch coast spec plaice dab whiting gobies sp sole flounder bib bull rout herring cod smelt eelpout sea snail five-bearded rockling eel sandeel sp sprat hooknose