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Pacific herring (Clupea pallasii) trophodynamics and fisheries in the Northeast Pacific Ocean

University of British Columbia

Pacific herring is a common North Pacific forage fish targeted by commercial, aboriginal, and subsistence fisheries. Recent declines in several Northeast Pacific herring stocks have caused concern among scientists, management agencies, and aboriginal peoples. This dissertation investigates the trophodynamics of herring in Northeast Pacific ecosystems and their effects on fisheries management. Its main hypothesis is that herring interacts strongly with both predators and prey, with some interactions governed by top- down and others by bottom-up control. Chapter 1 presents a set of high-resolution, mass- balanced ecosystem models representing waters surrounding Haida Gwaii, an archipelago off northern British Columbia, Canada. These three models provide a dynamic simulation platform and indicate strong interactions between herring and its predators and prey, as well as notable changes in local ecosystem structure across the 20th century, largely due to fishing and whaling. Chapter 2 reveals whale depletion and recovery trajectories off Haida Gwaii, and the historical and current role of whales as consumers, using surplus production and ecosystem models, respectively. Dynamic ecosystem simulations suggest that whale recovery could exert top-down effects on herring and other prey, with indirect trophic impacts on competing predators and ecosystem composition. Chapter 3 employs management strategy evaluation, combined with ecosystem simulations, to comparatively evaluate potential impacts of herring depletion and fisheries management strategies on dependent predators and ecosystem structure. The results suggest sharp tradeoffs between herring and many predator biomasses on the one hand and high, stable herring catches on the other, as well as potential compromise solutions. Chapter 4 investigates the potential positive effects of high adult herring energy content on the trophic role of herring using energy-balanced ecosystem models, reformulated from their mass-balanced counterparts using a novel methodology. Both static and dynamic analyses conducted in these models indicate that elevated energy content increases the dependence of numerous predators on herring. It may thus be concluded that herring, while belonging to a diverse forage fish guild, nevertheless exercises a key role in Northeast Pacific ecosystems as a trophic node connecting zooplankton to higher predators. Many of these depend on herring to support healthy populations, stimulating management tradeoffs for commercial herring fisheries.

Text; Dataset

2019-03-13

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/68682

Resource Management and Environmental Studies

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/