(including WG7 - Spawning and nursery habitat quality dynamics, WG8 - Spawning habitat dimensions and location and WG6 - Daily growth and zooplankton)

Theme representatives: D. Checkley and C. Roy

The focus of Theme 3 is comparisons between systems to identify how small pelagic fishes adapt their reproductive strategies to the various kinds of physical forcing and mesoscale features of their habitat, and how such systems constrain fish productivity. A central hypothesis is that changes in productivity are caused by changes in the temporal and spatial dimensions of the spawning habitat, as well as its location and quality. A major component of Theme 3 is based on the use of CUFES for mapping egg distributions and to achieve a quantitative description of the spatio-temporal dynamics of spawning. The use of hydrodynamic models coupled with NPZD and IBM models is also a central focus, in order to investigate the links between environment variability, spawning, and recruitment success. Ecosystems are compared to separate physical forcing from stock-dependent effects on spawning and recruitment selection and to examine the extent to which productivity is limited by space and time variation in spawning habitat.

Activities related to Theme 3 have a wide geographical range and cover the Humboldt, Benguela, and California Current Systems and the Bay of Biscay. A SPACC/IDYLE/ENVIFISH workshop held in Cape Town (September 2001) focused on spatial approaches of the dynamics of coastal pelagic resources and their environment in upwelling areas (see GLOBEC Newsletter, April 2002). The meeting aimed at synthesizing the state of the art concerning recent theoretical achievements, analysis techniques and modeling tools used for the integration of spatial structures in the study of the dynamics of marine populations and their environments. The outcome was published in GLOBEC Report 16 (Van der Lingen et al., 2002). On-going CUFES sampling is currently taking place in California (16 cruises 1996-2002), Mexico (10 cruises 2000-2002), Peru (5 crusies 1999-2001) and Chile (4 cruises 1999-2001), thanks to IAI funding. CUFES is also used by South Africa (Benguela), Spain and France (Bay of Biscay), and Canada (East Coast). The automation of detection and counting of fish eggs in CUFES in real-time by use of machine vision is nearing completion.

A workshop and meeting on characterizing and comparing the spawning habitats of small, pelagic fish was held in Concepcion, Chile 12-16 January 2004. The meeting also addressed the use of daily egg production method to assess the spawning biomass of small, pelagic fish.