On the dynamics of Sardina pilchardus: orbits of stability and environmental forcing

9 pages, 10 figuresThe dynamics of Sardina pilchardus in Iberian upwelling are examined. Spawning-stock biomass (SSB), recruitment (R), and production (R/SSB) data for the years 1978-2006 are analysed in relation to the upwelling index (UPW) and sea surface temperature (SST). The population oscillates in two relatively stable orbits (identified by multiresolution decomposition of the recruitment series) because the external forcing (UPW and SST) are the inverse of each other and the synchrony is lost between the two external variables, R and R/SSB as they shift towards steep, negative (depensatory) trends. Such mechanics may have induced recruitment failures and significant decreases in abundance of Iberian sardine. The relationships are assumed to validate a complex and dynamic continuum (multiple orbits of stability) and an alternative variable-carrying- capacity population model. Radial systems with two orbits of stability are proposed for the R/SSB and S/SSB (where S is the stock size) relationships. Results are discussed in relation to classical and alternative SR models to address stock rehabilitation and fishing mortality issues as the population shifts towards low recruitment and abundance, and critical factors to consider in developing exploitation strategies for systems with multiple orbits of stability are discussedThe paper is the product of ideas, discussions, and work carried out within the frameworks of three projects: a EUROCEANS concerted action on small pelagic fish (2008) at the Portuguese National Institute of Fisheries and Marine Research (IPIMAR); contract AGL2006-10448 drawn up to study fish/cephalopod dynamics off NW Africa and funded by the Ministry of Science and Innovation (MICINN) of the Spanish Government (2007–2009); and the ISTAM (Improve Scientific and Technical Advices for Fisheries Management) project (EU FP7, SSP-200n-022774; 2006-2008). Gary Sharp (Center for Climate/Ocean Resources Study, Salinas, CA, USA) and Serge Garcia (former head of FAO/FIRM) contributed with analysis and discussions on the theoretical framework proposed by Solari et al. (1997)Peer Reviewe