1. SPANISH ACOUSTIC SURVEYS: ANALYSIS OF THE FISH PELAGIC COMMUNITY M. Iglesias, M.B. Santos, C. Porteiro, M. Bernal, F. Ramos, D. Oñate, A. Giráldez, E. Nogueira, N. Díaz, P. Tugores, G.J Pierce & J. Miquel

2. The Ecosystem Approach requires joined-up thinking in fisheries, building from traditional framework of target species up to communities, populations, ecosystems, and the interaction with humans. In Spain, acoustic research surveys have traditionally been used to evaluate and monitor the population of commercially important pelagic fish species such as sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus). These surveys have been carried out annually both in the Mediterranean and Atlantic coasts since the 1980s collecting acoustic and hydrographic data and lately also information on distribution and abundance of top predators.

3. Four acoustic surveys are carried out annually in Spain, covering the shelf (20 to 200 m). PELACUS spring, which was developed to estimate the spawning stock biomass (SSB) of sardine in northern waters (since 1986).

4. Four acoustic surveys are carried out annually in Spain, covering the shelf (20 to 200 m). PELACUS spring, which was developed to estimate the spawning stock biomass (SSB) of sardine in northern waters (since 1986). ECOCADIZ which started in 2004 to monitor SSB of anchovy in the Gulf of Cadiz

5. Four acoustic surveys are carried out annually in Spain, covering the shelf (20 to 200 m). PELACUS spring, which was developed to estimate the spawning stock biomass (SSB) of sardine in northern waters. ECOCADIZ which started in 2004 to monitor SSB of anchovy in the Gulf of Cadiz PELACUS autumn which started in 2006 to obtain an index of the anchovy juvenile stock in the Bay of Biscay.

6. Four acoustic surveys are carried out annually in Spain, covering the shelf (20 to 200 m). PELACUS spring, which was developed to estimate the spawning stock biomass (SSB) of sardine in northern waters (since 1990). ECOCADIZ which started in 2004 to monitor SSB of anchovy in the Gulf of Cadiz. PELACUS autumn which started in 2006 to obtain an index of the anchovy juvenile stock in the Bay of Biscay. ECOMED, which was implemented to obtain a recruitment index for anchovy in Mediterranean waters (since 1990).

7. Material and Methods Acoustic and biological sampling - R/V Thalassa (northern waters) and Cornide de Saavedra (Gulf of Cadiz and Mediterranean). - Echo-sounder at 38 kHz, calibrated prior to each survey (Foote et al., 1987). - Complementary frequencies (18, 70, 120 and 200 kHz). Transects perpendicular to the coast and evenly spaced (4 – 8 nm), constant speed (10 knots) from dusk till dawn. -Pelagic trawls at daytime (Cantabrian coast and Gulf of Cadiz) or at night (Mediterranean).

8. Material and Methods Data processing Acoustic data is post-processed using SonarData Echoview©. Fish density integrated by nm and expressed in NASC (m2 x nm 2) (MacLennan et al., 2002). Energy split into species following their proportions in the trawls. Length frequency distributions are obtained for all fish species in the trawl. Length-weight relationships are obtained for the main pelagic species.

9. Material and Methods Complementary data Sampling of fish communities (trawl stations) Hydrography and hydrodynamics (rosettes and CTD) Ichthyoplankton (Continuous Underwater Fish Egg Sampler) and Visual censuses of top predators (marine mammals and seabirds).

10. Results There has been a decline in both abundance and distribution area of sardine in the Cantabrian Sea... 2007 2006 2005 2004 2003

11. Results...and anchovy in Northern Mediterranean (Tramontana region). 20032004200520062007

12. Results Results from the 2007 surveys, when all main fish species were evaluated acoustically, show that the most abundant species were: - sardine (Sp), mackerel (Ss) and horse mackerel (Tt) in the northern waters - anchovy (Ee), sardine and chub mackerel (Sc) in the Gulf of Cadiz -sardine, anchovy, Mediterranean horse mackerel (Tm) and bogue (Bb) in the Mediterranean.

13. Results The lowest fish biomass per squared nautical mile was estimated for the Mediterranean. In the Mediterranean, where the longer time series exists, there have been changes in the relative proportion of target/non-target species in the survey. The Simpson´s index indicates that species have become more evenly distributed.

14. Discussion Acoustic surveys constitute ideal platforms for the integrated monitoring of pelagic communities and ecosystems. Data on abundance, distribution and behavior of pelagic species can be collected systematically and geo-referenced, at the same temporal and spatial scales as environmental data. Historically, surveys monitored changes in abundance of commercially important species. By collecting data on other components of the community we can monitor changes at community level. Fishing removes important amounts of small pelagic fish in Spanish waters and this selective removal of species and in many cases size-classes can cause changes in pelagic community structure and functioning (Pauly et al., 1998). As we have shown, some of these changes have already taken place in the abundance and distribution of some species both in northern and Mediterranean Spanish waters, and the influence of fishing and environmental changes should be assessed.

15. Discussion In the Mediterranean, an oligotrophic environment, pelagic species are becoming more evenly distributed and there is a substantial reduction in total biomass. Parallel changes can be observed in fisheries landings. Total fish landings have decreased but number of exploited species is on the increase. An increase in evenness implies a higher diversity, higher diversity in an exploited ecosystem can be explained by the Intermediate Disturbance Hypothesis (Huston, 1994) which states that disturbance (e.g. exploitation) prevents competitive exclusion and therefore systems at intermediate levels of disturbance possess highest diversity.

16. Future work - Historical analysis of long time series of acoustic data to obtain estimates of non-target species. - Study the temporal and spatial dynamics of non-target species. - Explore alternative biodiversity indexes and other ecosystem metrics to monitor changes at ecosystem level in Spanish waters. - Application of hydrodynamics - Nutrient Phytoplankton Zooplankton - fish community coupled models to disentangle the effects of climate variability and fisheries on the community. Acknowledgements We would like to thank all the crew and participants in the surveys.