Recruitment Processes Program Contributions to the Lower Trophic Level and Modeling Components of the Gulf of Alaska Integrated Ecosystem Research Program
Figure 6. Seasonal variation in abundance and distribution of Pacific cod larvae from ichthyoplankton collections (1971, 1977-2009) by the Recruitment Processes Program in the western Gulf of Alaska; half monthly mean abundance (+standard error) weighted by year in 60-cm Bongo Net samples (a), weighted mean abundance in 20-km2 grid squares in the area sampled during the second half of April (b), first half of May (c), and second half of May (d).
The lower trophic level (LTL) component of the Gulf of Alaska Integrated Ecosystem Research Program (GOA-IERP) is focusing on the investigation of early life history dynamics and recruitment of five target species of groundfish: walleye pollock, Pacific cod, arrowtooth flounder, sablefish, and Pacific ocean perch. Compilation, analysis, and interpretation of ichthyoplankton surveys pertaining to these species from three decades of sampling in the western GOA by the Recruitment Processes and EcoFOCI Programs has commenced as part of the GOA-IERP retrospective analysis of this time series.
Annual patterns of abundance and seasonal progression in distribution of eggs (pelagic spawners) and larvae at various ontogenetic stages are being compiled and analyzed (Fig. 6). A time-series of abundance for late spring (1981-2009) is available and will be used to investigate relationships between species larval abundance and environmental variables. Links between the species and the variables will contribute to a mechanistic understanding of environmental forcing on early life history aspects of recruitment processes among these species in the GOA ecosystem. Synthesis of the historical ichthyoplankton data will also provide species-specific life history parameters for egg and larval stages that will be used in the development of individual based models (IBM) for each of the GOA-IERP focal species.
Figure 7. Conceptual model for Pacific cod early life history as it will be represented in the individual based model. Shown are the individual life stages and some of the processes that Pacific cod eggs, larvae and juveniles go through over time and as they change in depth and size. Eggs are spawned between February and July on the bottom in rocky areas with emergent vegetation, and rise to near surface waters as yolk-sac larvae. Feeding larvae begin diel migration after caudal fin development begins at 10-17 mm standard length (SL) and settle into nursery areas characterized by depth and emergent vegetation (kelp, eelgrass).
The modeling component of GOA-IERP includes the development and application of a vertically integrated suite of models from the Regional Ocean Modeling System (ROMS) hydrodynamic model, a Nutrient-Phytoplankton-Zooplankton (NPZ) model, five IBMs, one for each focal species (Fig. 7), and an upper trophic level model.
Recruitment Processes personnel are involved in coordinating the modeling work and will have responsibility for construction and integration of several of the IBMs into the GOA Program. This suite of models is intended to integrate information from the historical databases and the field and lab components of GOA-IERP, and to trace the effects of climate and environmental forcing through the ecosystem, from upper ocean and atmospheric physics through plankton to larval and juvenile fish. This knowledge can then be applied to questions about how best to manage our groundfish fisheries under a changing climate scenario.
