Acoustic assessment and distribution of anchovy and sardine juveniles in the ICES Subdivision IXa South during the ECOCÁDIZ-RECLUTAS 1009 Spanish Survey (October-November 2009).

Abstract

ECOCÁDIZ‐RECLUTAS 1009 survey is the first attempt by the IEO of acoustically assessing the abundance of anchovy and sardine juveniles in their main recruitment areas off the Gulf of Cádiz. The survey was conducted between 26th October and 5th November 2009 onboard the Spanish R/V Emma Bardán. In order to achieve a better sampling coverage of juveniles, the acoustic sampling grid was more intensive (4 nm‐spaced transects) than the adopted one in conventional surveys. Unfortunately, the initially planned survey area limits and the ship‐time available (17 transects over waters shallower than 50 m depth between Tavira and Chipiona, and 11 days) showed both insufficient due to a deeper bathymetric distribution of anchovy juveniles than expected and the sucession of a series of unforeseen problems which led to drastically reduce the actual sampled area to only 6 transects from the easternmost zone. Acoustic estimates from this last area are available for anchovy (2 771 t, 524 million fish), sardine (25 167 t, 500 millions), chub mackerel (17 627 t, 152 millions) and Mediterranean horse‐mackerel (17 005 t, 159 millions). The abundance and biomass of age 0 anchovies in the surveyed area were estimated at 2 588 t and 510 million fish, respectively, i.e. 93% and 97% of the total estimated anchovy biomass and abundance. Sardine estimates were not age‐structured but the abundance and biomass of juveniles smaller than 17 cm were estimated at 3 382 t and 130 millions, 13% and 26% of the total estimated species’ biomass and abundance. An approximate evaluation of the impact of the incomplete coverage of the anchovy juvenile distribution during the survey was carried out by comparison of our data with the resulting yields and location of positive fishing stations from a groundfish survey carried out just after the present survey.