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WKACUGEO

WKACUGEO. Case Study: North Aegean Sea. M. Giannoulaki, A. Machias, K. Tsagarakis, M.M. Pyrounaki. WKACUGEO Palma de Mallorca 20-21 November 2010. Northern Aegean Sea survey. Sampling period 2003-2006, 2008 Season: June-July Target species: anchovy & sardine

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WKACUGEO

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  1. WKACUGEO Case Study: North Aegean Sea M. Giannoulaki, A. Machias, K. Tsagarakis, M.M. Pyrounaki WKACUGEO Palma de Mallorca 20-21 November 2010

  2. Northern Aegean Sea survey • Sampling period 2003-2006, 2008 • Season: June-July • Target species: anchovy & sardine • Life stage: adults, spawning period concerning anchovy • 25-30 days required to cover the entire area North Aegean Sea WKACUGEO Palma de Mallorca 20-21 November 2010

  3. Northern Aegean Sea survey • Split Beam Biosonics DTX echosounder at 38 kHz • Parallel transects perpendicular to bathymetry, zig zag in gulfs • 10 nm inter-transect distance • Daytime echo collection • 25-30 days required to cover the entire area • 9 000 NM2/ 31.000 Km2 • EDSU was 1 nm WKACUGEO Palma de Mallorca 20-21 November 2010

  4. Echo traces are interpreted based on: • haul catches and • past experience of echogram analysis and echo trace characteristic shape Adult Sardine during June in Aegean Sea Adults Anchovy during June in Aegean Sea Sardine Juveniles during June in Aegean Sea

  5. Hauls held for a) echo traces identification and b) biological sampling purposes WKACUGEO Palma de Mallorca 20-21 November 2010

  6. 102 CTD stations are held within a predetermined grid of 10 nmi distance. Vertical profiles up to 100m depth of: • Temperature, • Salinity, • Fluorescence, • Oxygen, • Photosynthetic Active Radiation • WP2: Zooplankton & Ichthyoplankton samples are obtained WKACUGEO Palma de Mallorca 20-21 November 2010

  7. Sardine Anchovy Data to be analysed • Anchovy NASC per 1 nmi • Sardine NASC per 1 nmi • Period 2003-2006, 2008 • Latitude and Longitude WKACUGEO Palma de Mallorca 20-21 November 2010

  8. Log transformed Sardine Anchovy WKACUGEO Palma de Mallorca 20-21 November 2010

  9. Anchovy Maximum abundance 2005: 32000 tn 2006: 62000 tn 2003: 48000 tn 2008: 68000 tn

  10. Sardine 2008: 39000 tn 2004: 14000 tn 2003: 55000 tn

  11. Other sources of error… • Echogram analysis : e.g. School marks assigned into species • Haul sampling: how representative could it be? • TS applied WKACUGEO Palma de Mallorca 20-21 November 2010

  12. HCMR work on geostatistical analysis • Software used: EVA2, RGeoS, Surfer for krigging and mapping • Total NASC values (2003-2008) • NASC values of anchovy and sardine (2003-2008) • Intrinsic variograms calculated per year and subarea • range, sill and nugget estimations are available • geometric anisotropy examined WKACUGEO Palma de Mallorca 20-21 November 2010

  13. Geostatistical analysis initial results • Practically what we have done is stratifying the area into homogeneously sampled areas and checked for the spatial structure to each stratum • East Thracian Sea • West Thracian Sea • Thermaikos gulf • North Evoikos gulf WKACUGEO Palma de Mallorca 20-21 November 2010

  14. Problems raised during analysis, Technical Issues for discussion Transformations • Logarithmic transformation or not? What are the implications for kriging and survey estimates? • or raw data and cutting off extreme values? • Anisotropy: what is the effect? How influential can be on variance estimates? RGeos • Automatic fit of variogram but especially in cases where few data points are available it should also take into account weighting by the number of pairs • Very easily can result into total nugget with the automatic way • Fit variogram manually sometimes can perform better

  15. Geostatistical analysis with EVA2 Thracian Sea • Anchovy, ln(NASC+1) West Thracian WKACUGEO Palma de Mallorca 20-21 November 2010

  16. Geostatistical analysis applied with RGeoS Anchovy, NASC but cutting off extreme values Thracian Sea West Thracian

  17. Sardine, ln(NASC+1) Thracian Sea West Thracian WKACUGEO Palma de Mallorca 20-21 November 2010

  18. Sardine, NASC but cuting off extreme values Thracian Sea West Thracian

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