DEPM and Acoustic joint surveys applied to sardine and other pelagic fish

2014-04-14 (IPMA)

DEPM and Acoustic joint surveys applied to sardine and other pelagic fish

The R/V Noruega is currently at sea carrying out a survey during which for the first time, two methods will be applied simultaneously – the DEPM (Daily Egg Production Method) and the Acoustic surveying. The objective of both methods is the estimation of the biomass of sardine (DEPM and acoustic) and of other pelagic fish species (Acoustic) used in stocks assessment, and this joint survey aims at comparing the results obtained by the two methodologies.

Surveying takes place off the Portuguese coast (from Caminha to Vila Real de Santo Antonio) and in the Spanish waters of the Gulf of Cadiz, along a predefined number of transects perpendicular to the coast. The survey is funded by the National Programme for Biological Sampling (PNAB/DCF).

In order to estimate the spawning stock biomass of sardine, the DEPM requires that the survey covers the whole spawning area of the species. For the method to be applied, 1) plankton samples (with CalVET net) and environmental data (CTD profiles) are collected to be used in the estimation of the spawning area and egg production., and 2) fishing trawls are carried out to obtain fish samples used in the calculation of several adult parameters (female mean weight, sex ratio, batch fecundity and daily spawning fraction). These fish are complemented by samples provided by the purse seine commercial fleet, which, together with Docapesca, have always and readily collaborated with IPMA in the acquisition of these samples and data.

The Acoustic surveying methodology is based on the echointegration (sum) of pelagic fish schools carried out by a scientific hydroacoustic echosounder, along a predefined number of transects which cover the whole distribution area of sardine and of other pelagic fish over the Portuguese continental shelf (down to 200 m depth). During the survey, fishing trawls are also carried out, for echo traces ground truthing and in order to obtain data on several biological parameters required for the application of the acoustic method (length frequency distribution, length/weight relation ship, age, sex, sexual maturity stage, and fat content).

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