Beyond fishing in the Newfoundland and Labrador marine shelf ecosystem: the roles of climate and environment in affecting change

Mullowney, Darrell (2016) Beyond fishing in the Newfoundland and Labrador marine shelf ecosystem: the roles of climate and environment in affecting change. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The primary objective of this thesis is to identify and investigate important climatic and bottom-up processes affecting the marine shelf ecosystem off southern Labrador and eastern Newfoundland (Northwest Atlantic Fisheries Organization Divisions 2J3KLNO). The analyses are intended to extend the breadth of understanding for important ecosystem processes beyond the well-established impacts from overfishing. Knowledge gained from research on key commercial species is intended to address how ecological phenomena have affected the fisheries in recent decades and may be driving present changes in the ecosystem. Apart from advancing and informing science, the information presented is intended to benefit a wide audience of industry stakeholders including governments, harvesters, processors, and environmental interest groups. Four research chapters are chronologically themed from the collapse of northern cod (Gadus morhua) in the late 1980s / early 1990s, to the delayed recovery of capelin (Mallotus villosus) and cod, to factors presently affecting the decline of snow crab (Chionoecetes opilio). The first two research chapters examine the impacts of temperature and diet in affecting physiological growth and performance of juvenile and adult northern cod during and following stock collapse. The third research chapter focuses on factors affecting the low abundance of capelin since an abrupt decline in the early 1990s, while the final research chapter reviews top-down and bottom-up processes contributing to the rise and fall of snow crab. Collectively, these works contribute to improved understanding of some of the most important ecosystem processes influencing Newfoundland and Labrador fisheries. Temperature and food limitation were found to have a large impact on the Newfoundland and Labrador marine shelf ecosystem. Both factors either directly or indirectly regulated the productivity of each examined species. Recent warming coupled with increases in zooplankton abundance and an improving match between capelin spawning times and the spring bloom are shown to be supporting increasing abundances of capelin and by extension cod. Meanwhile, warming has directly led to a decline in snow crab productivity. Overall, the results suggest the Newfoundland and Labrador Shelf ecosystem is experiencing a shift in structure and forcing from being predominately bottom-up over the past two decades to a more balanced state wherein both bottom-up and top-down forcing are prevalent. To address concerns of management, advice based on the present findings is provided and putative future directions of the ecosystem, fisheries, and climate are discussed.

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