Trophic modeling of Eastern Boundary Current Systems: a review and prospectus for solving the “Peruvian Puzzle”

Abstract

Eastern Boundary Current systems (EBCSs) are among the most productive fishing areas in the world. High primary and secondary productivity supports a large biomass of small planktivorous pelagic fish, “small pelagics”, which are important drivers of production to the entire system whereby they can influence both higher and lower trophic levels. Environmental variability causes changes in plankton (food) quality and quantity, which can affect population sizes, distribution and domi-nance among small pelagics. This variability combined with impacts from the fishery complicate the development of management strategies. Consequently, much recent work has been in the development of multispecies trophic models to better understand interdependencies and system dynamics. Despite similarities in extent, structure and primary productivity between EBCSs, the Peruvian system greatly differs from the others in the magnitude of fish catches, due mainly to the incredible production of the anchovy Engraulis ringens. This paper reviews literature concerning EBCSs dynamics and the state-of-the-art in the trophic modeling of EBCSs. The objective is to critically analyze the potential of this approach for system understanding and management and to adapt existing steady-state models of the Peruvian system for use in (future) dynamic simulations. A guideline for the construction of trophodynamic models is presented taking into account the important trophic and environmental interactions. In consideration of the importance of small pelagics for the system dynamics, emphasis is placed on developing appropriate model compartmentalization and spatial delineation that facilitates dynamic simulations. Methods of model validation to historical changes are presented to support hypotheses concerning EBCS dynamics and as a critical step to the development of predictive models. Finally, the identification of direct model links to easily obtainable abiotic parameters is emphasized to add practicality to the model as a predictive tool.

Comparative Food Web Analysis of Two Peruvian Bay Systems Along a Latitudinal Gradient: Resource Use and the Environmental Envelope

“…All values of production and consumption (P/B and Q/B) were estimated from literature, using mainly the FishBase online repository (Froese and Pauly(eds), 2000), published models that use similar species or functional groups under similar conditions, and empirical models from Thomas Brey's "Population Dynamics in Benthic Invertebrates Virtual Handbook" (Brey, 2001). Some values were guessed estimated based on previous models of the study areas (Taylor and Wolff, 2007;Tam et al, 2008;Taylor et al, 2008a,b;Kluger et al, 2016). Even though IMARPE performs regular stomach content studies for some species along the coast, specific diet composition studies from within the two bays are inexistent.…”

“…The upwelling off Peru is particularly strong because the system has several distinct characteristics, such as the almost constant blow of equatorward winds and its closeness to the equator (Bakun and Weeks, 2008;Chavez et al, 2008). These characteristics generate apt conditions for sustained production of phyto-and zooplankton that favor Small pelagic fish but also support higher trophic species of coastal and oceanic food webs (Taylor and Wolff, 2007;Bakun and Weeks, 2008;Chavez et al, 2008;Belmadani et al, 2012;Echevin et al, 2014). The northern boundary of the NHCUS adjoins the warmer and less productive waters of the Pacific Central-American Large Marine Ecosystem (Heileman, 2009;Heileman et al, 2009), creating a transition area that roughly extends from 3-6 • S under normal conditions (Tarazona and Arntz, 2001;Graco et al, 2007;Heileman et al, 2009).…”

“…The high levels of primary production generated within the NHCUS lead to the decay and precipitation of organic matter down to a poorly ventilated and highly shallow Oxygen Minimum Zone (OMZ). This layer acts as a barrier that concentrates many pelagic and benthic species toward the surface and shallow areas (Taylor and Wolff, 2007;Chavez et al, 2008;Guevara-Carrasco and Bertrand(eds), 2017). The Peruvian upwelling system is substantially affected by the El Niño Southern Oscillation (ENSO) at interannual timescales, especially during its warm El Niño (EN) phase.…”

“…The Peruvian upwelling system is substantially affected by the El Niño Southern Oscillation (ENSO) at interannual timescales, especially during its warm El Niño (EN) phase. It generates dramatic oceanographic and atmospheric changes that result in heavy rains in the north coast and the "tropicalization" of typical upwelling areas off central and southern Peru (Graco et al, 2007;Heileman et al, 2009;Espinoza-Morriberón et al, 2019), leading to latitudinal changes in species composition due to mortality and migration (Tarazona and Arntz, 2001;Taylor and Wolff, 2007). Besides supporting one of the largest single-species industrial fisheries worldwide, i.e., anchovy Engraulis ringens, the NHCUS also sustains several other coastal and littoral fish and shellfish of economic importance.…”