Why community-scale analyses?

1. Analysis of climate & fishing effects on the fish community structure of the Bay of BiscayFabian BLANCHARD, Jean BOUCHER & Jean-Charles POULARDIFREMER

2. Why community-scale analyses? • Increasing evidences of climate effects on marine biota as on numerous fish populations are brought. A huge diversity of effects are observed according to species and areas and many ecological processes are probably involved. • Amplitude and strength of the changes observed on commercial species is of concern for the fisheries management particularly in the framework of an ecosystem based approach where production of the commercial species as well as the well-being of the non commercial ones must be preserved.

3. Ecology and population dynamics knowledge is necessary but operationnally impossible for all the species (about fifty fish species landed by the french fleet). General rules driving the observed biological changes may exist for groups a species. These general rules are investigated by the mean of macroecology & community ecology approaches. • The knowledge of these general rules is a prealable, to assess the fishing effects.

4. (OSPAR, 2000) (OSPAR, 2000) (OSPAR, 2000) Biogeography of the Bay of Biscay In the waters of the Biscay continental shelf, boreal species at the southern edge of their range meet transition species typical of the Bay and sub-tropical species at the northern edge of their range. In such ecotone, it is thought that species may answer fasly to small shifts in climate

5. Planque et al., 2003 Klyashtorin et al., 2000 COADS data set Increase of summer bottom temperature at 200m depth in the Bay of Biscay

6. Hypothesis 'Climate envelopes' theory may be used to analyse climate effects on an exploited fish communityEcologists & biogeographers currently attempt to predict the future distribution of species by climate mapping based on the attractively simple idea that range & abundance are determined first & foremost by the physiological tolerances of individual organisms. Optimal conditions are thought to be found in the middle of the range where the abundances may then raise the maximal values.Knowing present climatic patterns, present distributions & predictions about future climates, species ranges are assumed to simply follow shifts in their characteristic 'climate envelopes'.

7. At the scale of the eastern atlantic continental shelves, latitude is correlated to temperature. Sea Surface Temperature (LEVITUS) Then the latitudinal distribution of the species may be used to infer their climate envelope considering the optimal conditions at the midpoint of the latitudinal distribution.

8. Abundance According to these hypothesis we have the following variations of abundance within the latitudinal range of a theoretical subtropical (in red), a transition (in green) and a boreal species (blue).

9. ValidationIf these assumptions hold true, a multispecies negative relationship between local abundance in a given ecosystem and the distance between this ecosystem and the midpoint of the latitudinal range may be observed.

10. Abundance Distance Abundance

11. Abundance Distance Abundance Sub-tropical species Knowing predictions about future climates, for example warming trend, species ranges are assumed to simply follow northward shifts in their characteristic 'climate envelopes' as in the following case of a theoretical subtropical species

12. Abundance Distance Abundance And for a theoretical boreal one

13. Abundance Distance Abundance And for a theoretical boreal one

14. However, there are many debate around these assumptions because species distribution may not depend only on climate conditions but also on other abiotic and biotic conditions. In the particular case of fish communities exploited by fisheries, the fishing effects may act as a counfounding factor.Consequently, the existence of barriers to migrations, the existence of suitable habitats, and of different competitors/predator/preys in different locations may prevent species from linear shifts in distribution.

15. Abundance Distance Abundance In fact, the existence of particular other abiotic and biotic local conditions for some species may induce some variability around the relationship The existence of this relationship is investigated for the fish community of the Bay of Biscay as well as the abundance increase of subtropical species & the abundance decrease of the boreal ones.

16. Large scale continuous biological observations are used from the groundfish surveys EVHOE carried out with the R/V Thalassa in 1973 and annually from 1987 to 2002. A subset of 87 species (commercial and non commercial ones) sampled over the whole time period is chosen

17. I II III Merlangius Micromesistius merlangus Merluccius Sardina poutassou Capros Trisopterus Lophius merluccius pilchardus aper minutus piscatorius Engraulis encrasicholus Trisopterus Scomber luscus Trachurus trachurus scombrus I – species at southern edge of their latitudinal range in the Bay of Biscay, boreal species, potentially unfavoured by warming II – Mid-point of the latitudinal range in the Bay of Biscay, transition species, no strong effects of warming III – species at the northern edge of their range, subtropical species, potentially favoured by warming in the Bay of Biscay Latitudinal range and midpoint of the fish species observed in the Bay of Biscay

18. Abundance Distance RESULTS : multispecies relationship between local abundance in the Bay of Biscay and distance between the Bay and the midpoint of the latitudinal range Temperature deviation is calculated rather than latitudinal distance as it is a more direct measure of the climatic conditions: difference between the mean temperature of the Bay and the mean temperature of the midpoint of the latitudinal distribution of the species. It is then devided by the temperature range encountered within the distribution area to avoid the effect of different ranges between species Mean species abundance is calculated for the time period from 1987 to 1990 in order to avoid temporal variations effects in the relationship.

19. Temp deviation are in average greater for subtropical species than for boreal ones so that because of the shape of the relationship, a decrease of deviations induced by warming for subtropical species will imply an increase of abundance while an increase of deviation for boreal & transition species will not have effect on abundance.

20. Temporal variations of the total abundance of species for the 3 groups in the Bay of Biscay As expected from the relationship, the only significant temporal trend is for sub-tropical species.

21. Photo by V. Ticina (IZOR, Croatia). Increase in summer temperature (breeding season) at the bottom (200m depth) in the Bay of Biscay Exponential increase of a subtropical species abundance Capros aper in the Bay of Biscay

22. Perspectives : towards an analysis of climate & fishing effects • Klyashtorin et al. have brougth evidences that the temporal variations of the fish stock production match the temporal variations of global climatic indices (i.e. the atmospheric clirculation index ACI, temperatures anomalies…). Periodic oscillations of the indices are observed as well as an increasing temperature trend. • A predictive model of production is built up accounting for these climatic changes. • Two groups of species are defined as they are respectively correlated positively to the ACI and other indices or negatively.

23. On the Bay of Biscay scale, one may apply the positive correlation to the so-called subtropical species and the negative to boreal and transition one. Then the lack of fit may be imputed to fishing effect. Simultaneous long term changes in climate & Atlantic & Biscay fishery landings : transition and boreal species simultaneous long term changes in climate and Atlantic fishery landings cod landings ACI meridional 1.5 herring landings sea bass landings 1 hake landings ACI WE 0.5 ACI Index Hake 0 Sea bass Relative biomass -0.5 North Sea cod -1 -1.5 North Sea herring -2 L. piscat -2.5 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 Years

24. simultaneous long term changes in climate and Biscay fish species sea bass landings Sea bass 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 Simultaneous long term changes in climate & Atlantic & Biscay fishery landings : subtropical species Anchovy Capros aper L. Budegassa Sea bass

25. The results confirm the climate effects on population dynamics (harvested ones and not). Consistently with the climate envelope theory : • the abundances in the Bay change according to the distances from their biogeographic center. Particularly sub-tropical species abundance have increased during the last decade. • This hypothesis is also supported for the harvested stocks : the biomass increase with warming for the species defined here as subtropical ones and the biomass decrease for the species defined as transition or boreal ones. Next step is to explain the deviations in the relationship between biomass and climate indices analysing recruitment and fishing mortality patterns.