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A review on small pelagic TS; anchovy ( Engraulis encrasicolus ): preliminary results.

A review on small pelagic TS; anchovy ( Engraulis encrasicolus ): preliminary results. M. Iglesias, J.Miquel, F. Ramos. Introduction.

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A review on small pelagic TS; anchovy ( Engraulis encrasicolus ): preliminary results.

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  1. A review on small pelagic TS; anchovy (Engraulis encrasicolus): preliminary results. M. Iglesias, J.Miquel, F. Ramos

  2. Introduction • The acoustic target strength (TS) is an important metric in fisheries and plankton acoustics to inform on fish characteristics and to convert the acoustic energy in biomass units. • TS = 20 log L + b20 • σbs = 10TS/10

  3. In the last WGACEGG 2005: • A revision was done on Target Strength used by every Institution (IPIMAR, IEO, AZTI and IFREMER). • It was recommended to check literature to explore the most suitable TS relationship that could be used for the two target species: Sardina pilchardus and Engraulis encrasicolus.

  4. Target strengths (b20) adopted by Institutions (WGACEGG05)

  5. Target strengths (b20) adopted by Institutions

  6. Report of the Planning Group for pelagic acoustic surveys in ICES sub-areas VIII and IX (A Coruña, 30-31 January 1998). * This correspond to a relationship in which log L is multiplied by 21.8.

  7. Report of the Planning Group for pelagic acoustic surveys in ICES sub-areas VIII and IX (A Coruña, 30-31 January 1998). * This correspond to a relationship in which log L is multiplied by 21.8.

  8. Sardine (S. pilchardus) & anchovy (E. encrasicolus) TS: references. • -72.6 (IEO, AZTI): Degnbolet al., 1985. Herring TS (Clupeaharengus). • -71.2: TS of small pelagics (Diner & Marchand, 1995; ICES, 1997).

  9. Mackerel (Scomber scombrus) TS: references. • -82 dB (Ifremer & Ipimar): PG 1998. • -84.9 dB (IEO): Edwards et al., 1984, recommended by the PGAAM (Anon. 2002). • -88 dB (Azti): Clay & Castonguay, 1996. • There are 6 dB difference between TS.

  10. Anchovy (Engraulis encrasicolus): preliminary results.

  11. EcoCádiz acoustic survey 0606 • EcoCádiz acoustic survey is carried out in the Gulf of Cadiz (Spain and Portugal areas). • Principal pelagic species detected are anchovy, sardine and chub mackerel. • Fishing trawls are conducted to identify echo traces at day time during tracks. • In the last survey (June 2006) 3 fishing stations were carried out at night in areas were abundant anchovy was detected in order to get data on the anchovy TS.

  12. Acoustic sampling with: • Echosounder EK500 (38 kHZ, split beam transducer). • SonarData Echoview software: split-beam method for single target echo detections. • Trawl sampling: • pelagic trawl, vertical opening 20 m. • Speed: 3-4 knots.

  13. Fishing trawls at night • Trawl haul 16: • Nº of individuals: • Anchovy: 2284 (92%). Mode: 12 cm. • Sardine: 116. Mode: 17 cm. • Chub mackerel: 46. Mode: 22 cm. • Mackerel: 29. Mode: 22 cm. • Trawl haul 21: • Nº of individuals: • Anchovy: 176 (43%). Mode: 12 cm. • Chub mackerel: 58. Mode: 22 cm. • Mackerel: 153. Mode: 22 cm. • Trawl haul 22: • Nº of individuals: • Anchovy: 4594 (82%). Mode: 10 cm. • Sardine: 505. Mode: 17 cm. • Chub mackerel: 128. Mode: 21.5 cm. • Mackerel: 75. Mode: 31.5 cm. • Horse mackerel: 38. Mode: 17.5 • Others: 246.

  14. Preliminary results • TS = 20 log L - b20 • b20 = TS - 20 log L • Haul 16: b20 = -77.21 • Haul 21: b20 = -76.15 • Haul 22: b20 = -75.02

  15. References • The TS used for anchovy comes from herring and “small pelagics”. • There was a TS for Engrauliscapensis, South Africa: Barangeet al., 1996, ICES Journal of Marine Science, 53: 225-232. • E. capensis = E. encrasicolus. • b20 = -76.1.

  16. Conclussions • There is a necessity of standardize species TS if results must be compared or compiled. • Ideal: to determine TS “in situ”: sardine and anchovy. • If not, to use TS of these species calculated in other areas (like South Africa????).

  17. Then, the question is which TS for anchovy? • -71.2 dB • -72.6 dB • -76.1 dB ????????????

  18. EcoCádiz 2004: estimation with different TS for anchovy.

  19. EcoCádiz 2006: estimation with different TS for anchovy.

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