Publication Abstract

Role of environmental indices in determining the recruitment of the Bay of Biscay anchovy

By A. Uriarte, B.A. Roel, A. Borja, G. Allain and C.M. O'Brien

A review of the recent and potential use of the relationships between environmental indices and anchovy recruitment in the Bay of Biscay for modelling stock-recruitment (S-R) relationships and forecasting purposes of recruitment is presented. Borja et al. (1996, 1998) showed that for the period 1967-1996, oceanographic conditions caused by north-easterly winds of medium intensity in spring/summer in the Bay of Biscay are related to good levels of anchovy recruitment. The major oceanographic event linked to that wind regime is weak upwelling conditions. Allain et al. (2001) improved the previous relationship for the period 1987-1998 by simulating the oceanographic processes surrounding the life history of larvae, through a 3 dimensional hydrodynamic physical model. In addition to an upwelling index they retained a stratification breakdown index, which is associated to summer gales and impacts recruitment negatively. These two variables explained about 70 % of the recruitment inter-annual variability between 1986-1999. However the recruitments in the most recent years have led Borja's upwelling index to be not significant over the period 1987-2001 and have dropped the coefficient of determination of Allain's index to 50%, worsening its predictive power. Nevertheless, the spring-summer upwelling still seems to favour recruitment, while the negative role of the stratification breakdown seems to be corroborated by the likely bad recruitment occurring in 2001. Therefore this variable could be useful to identify bad recruitments scenarios for forecasting purposes. So far, the decision of the ICES Working Group on the Assessment of Mackerel, Horse Mackerel, Sardine and Anchovy [WGMHSA] to abandon the use of environmental indices for this species, after a failed prediction for the year 2000, seems to be judicious until a better modelling and/or understanding of the precision for forecasting is obtained. The inclusion of the environmental indices arising from the 3 dimensional hydrodynamic model in the modelling of S-R relationships results in a significant improvement over the models that do not include them.

Reference:

A. Uriarte, B.A. Roel, A. Borja, G. Allain and C.M. O'Brien.2002. Role of environmental indices in determining the recruitment of the Bay of Biscay anchovy. ICES CM 2002/O:25. 32p