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
NL fish monitoring Wadden Sea
DFS survey & fyke Texel 2007
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
Fyke Texel 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
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?
The Wadden Sea in a wider perspective
n/ha 0 20 40 60 80 100 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 1970 1980 1990 2000 2010 stable fluctuating/poorly known Soldaat et al 2007
Total fish biomass
species
1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 0 10 20 30 0 10203040 biomass (kg/10000m2) 0 5 101520 0 20406080 0 5 10 15 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
Species guilds Marine juveniles Estuarine residents Catadromous/anadromous Marine seasonal migrants Marine advantageous
Species trends: marine juveniles
Species trends: residents
Species trends: residents
Species trends: residents
Species trends: residents
marine juveniles
estuarine residents
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 1970 1980 1990 2000 2010 1970 1980 1990 2000 2010 1970 1980 1990 2000 2010 region4 Ems-Dollard western Dutch Wadden Sea eastern Dutch Wadden Sea Dutch wadden coast southern Dutch coast
DFS CPUE Correlation fyke-dfs Western Wadden Sea Sept/Oct Species that occur in both series bib 6 R 2 0.469 4 2 0 dab 6 R 2 0.19 4 2 0 five-bearded rockling brill eel flounder R 2-0.015 R 2 0.214 cod eelpout herring R 2 0.08 R 2 0.173 6 R 2-3 4 2 0 plaice smelt R 2 0.02 sole R 2 0.117 6 R 2 0.064 4 2 0 sprat turbot R 2 0.054 whiting R 2 0.06 6 4 2 0 R 2-0.018 R 2-0.021 R 2 0.336 0.0 0.5 1.0 1.5 0.0 0.5 1.0 1.5 0.0 0.5 1.0 1.5 fyke CPUE
day number Phenology: fyke dab bull rout flounder plaice
number Phenology: fyke species presence species presence fyke sampling day number
day number Timing dab bull rout flounder plaice
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
mean length (cm) 1975 1980 1985 1990 1995 2000 2005 2010 1975 1980 1985 1990 1995 2000 2005 2010 1975 1980 1985 1990 1995 2000 2005 2010 1975 1980 1985 1990 1995 2000 2005 2010 1975 1980 1985 1990 1995 2000 2005 2010 1975 1980 1985 1990 1995 2000 2005 2010 4 6 8 10 5 10 15 7 8 910 12 5 6 7 8 9 10 5 10 15 10 12 14 16 18 2022242628 7 8 9 10 0 2 4 6 810 0 10 20 30 8 10 12 14 16 10 15 20 6 7 8 9 20 30 40 50 0 5 10 15 15 20 0 2 4 6 11 13 15 10 15 20 25 30 0 5 10 15 5 10 15 10 15 20 25 0 5 10 15 Size structure W Dutch Wadden sea Bib Brill Bull-rout Butterfish Cod Common dragonet Dab Eel Eelpout 5 10 15 Five-bearded rockling Flounder gobies sp Greater sand-eel Herring Hooknose pipefish sp Plaice sandeel sp Sea-snail Smelt Sole Sprat Tub gurnard Whiting
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
Climate change: growth potential plaice 1989 2002 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
fisheries
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
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
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
mean biomass (kg/10m2 Ems-Dollard western Dutch Wadden Sea eastern Dutch Wadden Sea Dutch wadden coast southern Dutch coast 1970 1980 1990 2000 2010 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