Subtask 3.3. Biological sampling (HCMR, IFREMER, HCMR, IEO, CNR-Ancona, CNR-Sicily)

1. Subtask 3.3. Biological sampling (HCMR, IFREMER, HCMR, IEO, CNR-Ancona, CNR-Sicily)

2. The target of the task was to investigate: • The difference in sampling between daytime and nighttime • Dimensions of the approach • Species composition • Length composition Examine differences in terms of: • Year (survey-or season) • Area • In Addition • Trawl efficiency compared between Day – Night • Sensitivity analysis

3. SAMPLING Aegean Sea: 22 pair groups – 4 experimental Adriatic Sea: 8 pair groups – All experimental Sicily Channel: 2 pair groups – All experimental Gulf of Lions: 1 pair group Iberian coast: 1 pair group – All experimental

4. SURVEY Group 2 Group 2 Group 1 The analysis scheme Day Night Day Day Night Night Hauls 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6

5. DIVERSITY • In Aegean Sea • The following indices were estimated and compared • Species richness (Margalef) • Shannon-Wiener diversity (H) • J-eveness indices • Simpson’s 1-L • All pair comparisons between Day and Night in groups from the same area, as well as by year, indicated. No difference of bio-diversity indices between Day and Night

6. Sardine - groups From 24 comparisons 10 cases: Day > Night 3 cases: Night > Day 11 cases: No difference Length composition 1. Pair -groups Anchovy - groups From 26 comparisons 13 cases: Day > Night 7 cases: Night > Day 6 cases: No difference

7. Sardine - Year From 16 comparisons 7 cases: Day > Night 1 cases: Night > Day 8 cases: No difference Length composition 2. Surveys Anchovy - Year From 14 comparisons 8 cases: Day > Night 3 cases: Night > Day 3 cases: No difference

8. Although in about half of the cases no differences were estimated Day Length > Night Length was more frequent. Question: Is it something systematic or random Paired-Sample Comparison Analysis Mean min, max, range Standard skewness Standard kurtosis • ND • ND • ND • ND • ND • ND

9. Trawl efficiency during dayand night (Doray et al. 2009) • We used the available trawl data that have simultaneously been insonified.Monospecific:13 D (9 anchovy), 23 N (16 anchovy) • The fish nautical area scattering coefficients (NASCs) estimated using elementary sampling units (ESUs) 500 m.Values of fish NASC were then summed over the depth range sampled by the pelagic trawl. 5 meters above and below the trawl • Catch data transformed to equivalent acoustic data, equivalent NASC σbs =10TS/10, The σbs used were -71.2 db anchovy and -72.6 db sardine. • The value of NASC(t) recorded on board; station t is a reasonable estimate of the true density of fish encountered along the trawl trackENASCs(t)= Q [NASC (t)]b ; Q is the trawl efficiency • Hauls by Day and Night were analysed separately, as well as the monospecific hauls of anchovy

10. Nighttime estimates differ from daytime, • Nighttime presented trawl efficiency close to 1; • while the trawl efficiency seem to be random during the day.

11. Sensitivity analysis

12. Conclusions • No significant differences were estimated in species composition • Paired-Sample Comparison Analysis indicated no difference in the mean length between day and night • The analysis of the trawl efficiency indicated that the trawling during night seem to be more efficient than day. Further investigation - targeted experiments • Sensitivity analysis indicated a possible under- or overestimation of the biomass comparable to an error of 0.5db in the b20 coefficient. • Results of the present study imply that a more flexible strategy could be adapted depending on the needs of each acoustic survey. • Daytime sampling can be combined with night time sampling reducing the survey time. Night time sampling seems to provide a more unbiased length frequency distribution, while the day time sampling is necessary to identify associations.