Causes of spatial and temporal trends in species richness and abundance? Niels Daan Pensioner Wageningen IMARES
Climate change: a hot issue
Recent success stories of southerly species... Beare et al. 24 Engelse poon Striped Mul Recruitment at age 1 (millions) North Sea cod 1 9 8 7 6 5 4 3 2 1 1945 195 1955 196 1965 197 1975 198 1985 199 1995 2... as well as current failure of a northerly species
Axiomatic conclusion: Effects of climate change! But: - A priori selection of examples? - Correlations do not imply a causal relationship - How would the response mechanism work?
Hypothesis If there are effects of climate change, northerly and southerly species should decrease and increase, respectively Two parameters: (1) Species richness (2) Species abundance Biogeographic regions (after Ekman, 1953)
NORTHERLY SPECIES SOUTHERLY SPECIES Artediellus atlanticus Pleuronectes platessa Aphia minuta Pomatochistus spp. Cyclopterus lumpus Pollachius virens Argentina sphyraena Raja clavata Hippoglossoides platessoi Raja batis Arnoglossus imperialis Raja montagui Hippoglossus hippoglossus Raniceps raninus Arnoglossus laterna Raja naevus Liparis liparis Rhinonemus cimbrius Aspitrigla cuculus Scophthalmus rhombus Lumpenus lampretaeformis Sebastes viviparus Atherina presbyter Scyliorhinus canicula Raja radiata Spinachia spinachia Buglossidium luteum Solea vulgaris Triglops murrayi Taurulus bubalis Callionymus lyra Sprattus sprattus Anarhichas lupus Trisopterus esmarki Callionymus maculatus Symphodus melops Glyptocephalus cynoglossu Zeugopterus punctatus Callionymus reticulatus Trachinus draco Myoxocephalus scorpius Zoarces viviparus Chelon labrosus Trachurus trachurus Pholis gunnellus Ciliata mustela Crystallogobius linearis Trigla lucerna Agonus cataphractus Galeorhinus galeus Ctenolabrus rupestris Trisopterus luscus Belone belone Lophius piscatorius Dicentrarchus labrax Capros aper Brosme brosme Platichthys flesus Diplecogaster bimaculata Dasyatis pastinaca Ciliata septentrionalis Pollachius pollachius Echiichthys vipera Liza aurata Clupea harengus Psetta maxima Engraulis encrasicolus Lophius budegassa Echiodon drummondi Scomber scombrus Eutrigla gurnardus Merluccius merluccius Entelurus aequoraeus Squalus acanthias Gaidropsurus vulgaris Pagellus erythrinus Gadus morhua Trisopterus minutus Gobius niger Phycis blennoides Limanda limanda Labrus bergylta Raja brachyura Liparis montagui Labrus mixtus Raja circularis Melanogrammus aeglefinus Lepidorhombus whiffiagoni Raja undulata Micrenophrys lilljeborgi Lesueurigobius friesii Sardina pilchardus Microstomus kitt Merlangius merlangus Scyliorhinus stellaris Molva molva Microchirus variegatus Solea lascaris Osmerus eperlanus Mullus surmuletus Spondyliosoma cantharus Phrynorhombus norvegicus Mustelus spp. Trigloporus lastoviza Phrynorhombus regius Myxine glutinosa Zeus faber
IBTS International Bottom Trawl Survey 61 6 59 58 57 56 55 54 53 52 51 5 Estimated average # of species in 2 hls 1. to 3. 3. to 7. 7. to 13. 13. to 25. 25. to 1.1-4 -3-2 -1 1 2 3 4 5 6 7 8 9 1 11 12 Participation by 8 countries Standardized since 1977 DATRAS data base ICES 3-4 hauls annually Species specific catchability: Species identification often questionable Spatial and temporal effort variable 15 hauls 17 species : 49 Northerly, 58 southerly 61 6 59 58 57 56 55 # Species recorded Affected by # hauls: Correction necessary 54 53 52 51 5 Estimated average # of species in 2 hls 2. to 18. 18. to 25. 25. to 31. 31. to 39. 39. to 64. -4-3 -2-1 1 2 3 4 5 6 7 8 9 1 11 12 SPECIES RICHNESS
# Species recorded after 1.. n hauls (based upon 2 Monte Carlo simulations) Nsp 6 5 4 3 2 1 1 2 3 4 5 6 7 8 hls Loglinear increase: no asymptote! Slopes and intercepts vary by location Relative index determined by arbitrary choice of n (2) Nsp 6 5 4 3 2 1 1 1 1 n hls 44F3-23- 43F3-11- 41F2-22- 43F2-22- 43F4-21- 42F2-22- 42F4-12- 43F5-32- 42F4-22- 43F3-22- 38F2-22- 41F2-12- 42E8-31- 42F3-22- 43F4-22- 45F2-22- 41F1-12- 41F4-22- 48F2-22- 4F1-13- 41F3-32- 44F2-22- 46F2-22- 46F1-22- 4F4-22- 41F3-22- 42F5-12- 39F-13-44F4-11- 36F7-13- 43F2-23- 45F3-11- 4F4-13- 48F1-22- 37F7-11- 38F2-31- 39F2-13- 44F3-22- 38F3-22- 39F4-32- 38F3-21- 42E9-21- 38F1-12- 39F4-22- 4E9-23- 4F3-22- 43F6-12- 45F2-32- 44F3-23- 43F3-11- 41F2-22- 43F2-22- 43F4-21- 42F2-22- 42F4-12- 43F5-32- 42F4-22- 43F3-22- 38F2-22- 41F2-12- 42E8-31- 42F3-22- 43F4-22- 45F2-22- 41F1-12- 41F4-22- 48F2-22- 4F1-13- 41F3-32- 44F2-22- 46F2-22- 46F1-22- 4F4-22- 41F3-22- 42F5-12- 39F-13-44F4-11- 36F7-13- 43F2-23- 45F3-11- 4F4-13- 48F1-22- 37F7-11- 38F2-31- 39F2-13- 44F3-22- 38F3-22- 39F4-32- 38F3-21- 42E9-21- 38F1-12- 39F4-22- 4E9-23- 4F3-22- 43F6-12- 45F2-32- SPECIES RICHNESS
Spatial variation in diversity (Average # species recorded after 2 hauls) 61 6 Diversity higher along borders Central North Sea relatively poor 59 58 57 56 55 54 53 52 51 5 Estimated average # of species in 2 hls 1.8 to 27.6 27.6 to 31.6 31.6 to 35.3 35.3 to 39.1 39.1 to 55.9-4 -3-2 -1 1 2 3 4 5 6 7 8 9 1 11 12 SPECIES RICHNESS
Species richness for the two groups separately 61 61 6 6 59 59 58 58 57 57 56 56 55 55 54 54 53 53 52 52 51 5 Estimated average # of species in 2 hls 6.2 to 16.5 16.5 to 18.5 18.5 to 2.8 2.8 to 23.3 23.3 to 34.3 51 5 Estimated average # of species in 2 hls 1. to 9. 9. to 12.2 12.2 to 14.8 14.8 to 18.2 18.2 to 33.3-4 -3-2 -1 1 2 3 4 5 6 7 8 9 1 11 12 Northerly species -4-3 -2-1 1 2 3 4 5 6 7 8 9 1 11 12 Southerly species SPECIES RICHNESS
Relationship with environmental factors -5-3 -1 1 3 5 7 9 11 13 61 61 59 59 57 57 55 55 53 53 51 Summer Bottom Temperature 1997-22 49 49-5 -3-1 1 3 5 7 9 11 13 51 Fronts Bottom T (ICES) Depth 61 61 N S 6 6 59 59 58 58 57 57 56 56 55 55 54 54 53 53 52 52 SPECIES RICHNESS 51 5 Estimated average # of species in 2 hls 6.2 to 16.5 16.5 to 18.5 18.5 to 2.8 2.8 to 23.3 23.3 to 34.3-4 -3-2 -1 1 2 3 4 5 6 7 8 9 1 11 12 51 5 Estimated average # of species in 2 hls 1. to 9. 9. to 12.2 12.2 to 14.8 14.8 to 18.2 18.2 to 33.3-4 -3-2 -1 1 2 3 4 5 6 7 8 9 1 11 12
Temporal trends? ( Same trick: # species after 3 hauls) 1 9 8 7 6 5 4 3 2 1 1 2 3 4 1 9 8 7 6 5 4 3 2 1 1 1 1 1 SPECIES RICHNESS
Trends total North Sea and by area Smoothed in threes Nr of species after 3 hls 1 9 8 7 6 5 4 3 2 1 Total Nort Sea all_sp northern southern Nr of species after 3 hls 1 9 8 7 6 5 4 3 Southern North Sea 2 1 1975 1985 1995 25 Nr of species after 3 hls 1 9 8 7 6 5 4 3 Northern North Sea 2 1 1975 1985 1995 25 61 6 59 58 57 56 55 Nr of species after 3 hls 1 9 8 7 6 5 4 3 Skagerrak/Kattegat 2 1 1975 1985 1995 25 54 1975 1985 1995 25 53 52 51 Estimated average # of species in 2 hls 1. to 9. 9. to 12.2 5 12.2 to 14.8 14.8 to 18.2 18.2 to 33.3 All trends significant! N & S not significantly different! -4-3 -2-1 1 2 3 4 5 6 7 8 9 1 11 12 SPECIES RICHNESS
Standardized indices by species,1,5,,2,15,1,5, Agonus cataphractus 1975 198 1985 199 1995 2 25 Entelurus aequoraeus 1975 198 1985 199 1995 2 25 hooknose snake pipefish little weever solenette,25,2,15,1,5,,2,15,1,5, Buglossidium luteum 1975 198 1985 199 1995 2 25 Echiichtys vipera 1975 198 1985 199 1995 2 25,1 Gadus morhua,2,15 Trisopterus luscus N,5, 1975 198 1985 199 1995 2 25 cod bib,1,5, 1975 198 1985 199 1995 2 25 S NUMERIC TRENDS
Mean trends in abundance 1, Northerly Southerly More species increased than decreased, independent of origin 1, Southerly species have increased steeper than northerly species,1 1977 1982 1987 1992 1997 22 NUMERIC TRENDS
Average trend in standardised catch per hour of species of different biogeographic origin (corrected for differences in catch rates among species) 3.5 3. index nphr 2.5 2. 1.5 1..5 41 Lusitanian-Boreal sp. 28 Boreal sp. 9 Boreal-Lusitanian sp. More species of all origin have increased than declined Southerly species (LU+LB) have on average increased steeper than northerly species (BO+BL) 16 Lusitanian sp.. 197 1975 198 1985 199 1995 2 25
Anomalies in the Fair Isle Current Northern North Sea Temperature Anomaly Salinity Anomaly 1.5 1..5. -.5-1. -1.5 197 198 199 2 Year.2.1. -.1 -.2 197 198 199 2 Year Nr of species after 3 hls 1, 1 9 8 7 6 5 4 3 2 1 1975 1985 1995 25 1,,1 Northerly Southerly 1977 1982 1987 1992 1997 22 NUMERIC TRENDS
Anomalies in the southern North Sea # species after 3 hls 1 8 6 4 2 Southern North Sea 1975 1985 1995 25 1, Northerly Southerly 1, Ferry at 52 o N,1 1977 1982 1987 1992 1997 22
Average surface temperature High Low Low High winter summer SPECIES RICHNESS
Size compositions Daan et al., 25 IJMS Mean weight N by size class N by ln(lmax) class 1. IBTS 1, <2 2-3 a. 1, a. Gemiddeld gewicht per vis.1.1.1 BTS DYFS cpue (N per h) 1, 3-4 4-5 >5 relative change in ln cpue (N) 1,,1 <3 3-4 4-5. 1977 1982 1987 1992 1997,1 1977 1982 1987 1992 1997, >5 2. 1.5 Roundfish All MSVPA 3: 2 cm 4: 55 cm 5: 148 cm 1..5 Exploitation rate. 1963 1968 1973 1978 1983 1988 1993 1998 OTHER CHANGES IN FISH COMMUNITY
An Alternative Interpretation These changes are all artefacts of improved sampling and better species identification!!! 25 2 Den 25 2 Eng 25 2 GFR 25 2 Sco 15 15 15 15 1 1 1 1 5 5 5 5 1965 197 1975 198 1985 199 1995 2 25 1965 197 1975 198 1985 199 1995 2 25 1965 197 1975 198 1985 199 1995 2 25 1965 197 1975 198 1985 199 1995 2 25 25 2 Fra 25 2 Ned 25 2 Nor 25 2 Swe 15 15 15 15 1 1 1 1 5 5 5 5 1965 197 1975 198 1985 199 1995 2 25 1965 197 1975 198 1985 199 1995 2 25 1965 197 1975 198 1985 199 1995 2 25 1965 197 1975 198 1985 199 1995 2 25 Mean # species per haul by country compared with overall trend
Conclusions Species richness has increased despite overexploitation or climate change. Both southerly and northerly species have increased in abundance, both in terms of # species and numerically. Southerly species have increased steeper. Climate change does not provide a satisfactory explanation, although it may have contributed. The mechanism still has to be elucidated: how would these species now that it has become warmer up north? Simultaneous changes in size composition better explained by overexploitation: better survival of juvenile fish and small species by released predation pressure (Daan et al., 25). But the last word has not yet been said!