The Small Pelagic Fish and Climate Change (SPACC) program was created to facilitate research on the dynamics of populations of small pelagic fish, including anchovy and sardine. These populations exhibit large variations in size, extent, and production on the scale of decades. At times, anchovy and sardine alternate in abundance. Collectively, small pelagic fish often occupy a central role in the food web they occur in, often described as a wasp-waist ecosystem. Humans are an integral part of those ecosystems. Variability of populations of small pelagic fish is believed to be due primarily to variations in climate and fishing, but the mechanisms of these relations remain unknown in most cases. It is also uncertain whether these ecosystems alternate between states, e.g. regimes, and whether inherent variability may limit our ability to predict their future states. The fisheries for populations of small pelagic fish are increasingly global in nature. While the global catch of small pelagic fish constitutes approximately one quarter of the world fish catch and has been relatively constant during the past several decades, the catch of individual taxa and stocks varies much more. The management of these fisheries will be challenged by increasing demand for human consumption and mariculture in light of their finite and variable production, importance within the ecosystem, and unprecedented climate change, and will depend on both science and governance. We recommend continued, global research on climate change effects on small pelagic fish, and its periodic assessment for use by decision makers.
Small pelagic fish are termed “wasp-waist” species as they dominate mid trophic levels and comprise relatively few species but attain large abundances that can vary drastically in size. They have been found to exert top-down control on their prey species and bottom-up control on their predators and, in this way, appear to induce unsuspected ecosystem dynamics. Largely based on model results, this chapter explores these effects and associated dynamics, not only illustrating the importance of small pelagic fish in structuring marine ecosystems, but also revealing the consistency of the role of small pelagic fish across various upwelling systems in which they play key roles. The Northern and Southern Benguela, Southern Humboldt, South Catalan Sea and North and Central Adriatic Sea ecosystems are compared in terms of the importance and role of small pelagic fish using information gained from landings and ecological models. Trophic level of the catch, the Fishing-in-Balance (FiB) index and the ratio of pelagic:demersal fish are calculated from reported landings. Sums of all flows to detritus are compared across modelled ecosystems. Models of the Southern Benguela, Southern Humboldt and South Catalan Sea are used to perform two simulations: (1) closure of fisheries on small pelagic fish and (2) collapse of small pelagic fish stocks, to further explore the roles of small pelagic fish in the dynamics of these ecosystems.
Tracking pelagic:demersal fish catch and biomass ratios over time is a means of detecting collapses in the small pelagic fish stocks, and comparing these ratios across ecosystems highlights the greater importance of small pelagic fish in the Humboldt compared to other ecosystems.
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