The daily egg production method: A valid tool for application to European hake in the Bay of Biscay?

The purpose of the present study is to investigate the relevant parameters, and associated uncertainties, in order to apply the daily egg production method (DEPM) to European hake in the Bay of Biscay from data obtained during the triennial egg surveys. The work carried out in this study is a considerable improvement on the previous preliminary attempts at a DEPM approach made in 1997-2001. Moreover, most of the parameters investigated in this study and required for DEPM are actually known. In contrast, to precisely estimate both the planktonic egg production and the adult fecundity parameters (i.e. to reduce the variance associated with those estimates) adjustment of the current sampling strategy and techniques is required. The present study concluded that the DEPM is potentially applicable to this stock. However, the triennial egg surveys sampling design is not considered an optimal sampling platform to carry out northern hake egg production estimation and thus, the sampling strategy should be adapted for the spawning behaviour of hake. In addition, this paper presents estimates of hake adult biomass using the DEPM in the Bay of Biscay. Hake SSB exhibited a fivefold decrease from approximately 49,000 tons (CV=0.565) to 9500 tons (CV=0.910) between 1995 and 1998. Thereafter, it increased to 35,500 tons (CV=0.574) in 2001 before decreasing again to around 24,000 tons (CV=0.595) in 2004. In general, the DEPM-based spawning stock biomass (SSB) estimates follow similar trends to those estimated by the virtual population analysis (VPA). (C) 2009 Elsevier B.V. All rights reserved.