SATS Saithe Acoustic Trawl Survey Combining acoustic and

SATS - Saithe Acoustic Trawl Survey Combining acoustic and bottom trawl data to improve estimates for spawning stock biomass of North Sea saithe (Pollachius virens) Matthias Schaber 1, Holger Haslob 1, Jennifer A. Devine 2, Gavin J. Macaulay 2 1 Thünen Institute of Sea Fisheries, 2 Institute of Marine Research/Havforskningsinstituttet M. Schaber, H. Haslob, J. A. Devine & G. J. Macaulay ICES Annual Science Conference Hamburg, 29. 3. 2018

Background / Rationale Saithe (Pollachius virens) ICES Category 1 stock, fishing pressure is below FMSY, Fpa, Flim, spawning stock size is above MSY Btrigger, Bpa, Blim (ICES 2018) Uncertainty in the assessment of North Sea saithe due to highly uncertain and fluctuating fisheries independent survey indices (ICES, WGNSSK Report 2017) • Insufficient spawning stock containment • IBTS not able to resolve highly patchy distribution of saithe schools, because only two tows per ICES statistical rectangle, not covering full depth distribution • Fluctuations in Q 1 survey indices seem unrelated to stock size Page 2 26. 09. 2018 M. Schaber, H. Haslob, J. A. Devine & G. J. Macaulay ICES Annual Science Conference

Background / Rationale Commercial annual saithe landings (2013 -2015) FRA, NOR, GER (ICES 2016) Page 3 26. 09. 2018 M. Schaber, H. Haslob, J. A. Devine & G. J. Macaulay ICES Annual Science Conference

Background / Rationale AIM: Fishery independent saithe SSB index in Q 1 • Spawning stock most accessible in Q 1 Saithe form aggregations Initially thought to be less movement of spawning component Stock containment thought to be highest in Q 1 • Joint international survey (Norway & Germany): Norwegian Survey since 2012 SATS Saithe Acoustic Trawl Survey: Trials in 2017 (and 2018) Germany joined in 2018 Page 4 26. 09. 2018 M. Schaber, H. Haslob, J. A. Devine & G. J. Macaulay ICES Annual Science Conference

Survey design Position data (VMS) of German fishing vessels targeting saithe (landings data) engaged in fishing (speed) for Q 1 (20122016) + SATS 2018 Survey Strata covered by FRV „G. O. Sars“ (NOR) and „Walther Herwig III“ (GER). Page 5 26. 09. 2018 M. Schaber, H. Haslob, J. A. Devine & G. J. Macaulay ICES Annual Science Conference

Survey coverage SATS 2018: Transects realized, strata covered and hauls conducted Continuous recording of acoustic data (EK 80 GOS, EK 60 WHIII), trial acquisition of EK 80 broadband acoustic data. Page 6 26. 09. 2018 M. Schaber, H. Haslob, J. A. Devine & G. J. Macaulay ICES Annual Science Conference

Demersal fish NASC distribution SATS 2018: Categorized demersal fish (DFI) NASC values measured. Page 7 26. 09. 2018 M. Schaber, H. Haslob, J. A. Devine & G. J. Macaulay ICES Annual Science Conference

Saithe CPUE SATS 2018: Saithe (Pollachius virens) CPUE per tow type/tow category Page 8 26. 09. 2018 M. Schaber, H. Haslob, J. A. Devine & G. J. Macaulay ICES Annual Science Conference

Exemplary Echograms WH 414 Haul 12 (38 k. Hz, CW). Targeted Tow R 941 kg Saithe Page 9 26. 09. 2018 33 kg Cod 11 kg Haddock M. Schaber, H. Haslob, J. A. Devine & G. J. Macaulay ICES Annual Science Conference Blue Whiting, Velvet Belly Shark, Krill

Exemplary Echograms WH 414 Haul 20 (38 k. Hz, CW), Targeted Tow R 192 kg Saithe Page 10 26. 09. 2018 17 kg Cod 3 kg Haddock M. Schaber, H. Haslob, J. A. Devine & G. J. Macaulay ICES Annual Science Conference 3 kg Whiting

Exemplary Echograms GOS (38 k. Hz, CW), Blind Tow B Ca. 1000 kg Saithe Page 11 26. 09. 2018 M. Schaber, H. Haslob, J. A. Devine & G. J. Macaulay ICES Annual Science Conference

Exemplary Echograms GOS (38 k. Hz, CW), Targeted Tow R, pelagic trawl Pure “pelagic” saithe Page 12 26. 09. 2018 M. Schaber, H. Haslob, J. A. Devine & G. J. Macaulay ICES Annual Science Conference

Exemplary Echograms GOS (38 k. Hz, FM), Targeted Tow R 510 kg Saithe Page 13 26. 09. 2018 M. Schaber, H. Haslob, J. A. Devine & G. J. Macaulay ICES Annual Science Conference

Conclusions from preliminary data evaluation Challenges & problems to address: Interpretation of echograms/allocation of species or categories: patchy aggregations of saithe shoals highly diverse species composition in near bottom layers with varying contribution of large gadid fishes (Lauffenburger et al. (2016) “masking” of saithe from Norway pout, herring, blue whiting etc. saithe in the acoustic dead zone? (Kotwicki et al. 2013; 2015) improve resolution (large gadoids) with FM data? General: Evaluate combination of bottom trawl/CPUE abundance indices and acoustically derived indices Page 14 26. 09. 2018 M. Schaber, H. Haslob, J. A. Devine & G. J. Macaulay ICES Annual Science Conference

matthias. schaber@thuenen. de Page 15 26. 09. 2018 M. Schaber, H. Haslob, J. A. Devine & G. J. Macaulay ICES Annual Science Conference