| Summary: | Chapter 2 Population dynamics of forage fish species are typically characterized by extreme fluctuations. Therefore, diversity in forage fish communities creates a portfolio effect, whereby the stability of marine ecosystems is increased by sustaining their role in transferring energy between lower and higher trophic levels, a key ecosystem process. The objective of this chapter was to investigate whether inter-annual trends in abundance, distribution, and biometrics (length, mass, condition) were synchronized in key forage fish species, sand lance Ammodytes spp and capelin Mallotus villosus, across the southeastern Newfoundland Shelf during the spring using a 20-year (1996-2015) bottom-trawl dataset. I also investigated whether species-specific distribution and biometrics were influenced by abundance. Sand lance length, mass and condition decreased with increasing abundance, suggesting density-dependence, but distribution did not expand with abundance. In contrast, capelin length and mass did not decrease with increasing abundance, nor did distribution. Inter-annual variation in abundance, distribution and biometrics were not synchronized in capelin and sand lance, possibly due to species occupying different regions at different life stages. Indeed, capelin were distributed farther north and more inshore than sand lance, possibly because capelin migrate inshore to spawn during the spring and sand lance are resident in the shallower waters of the Grand Banks. These findings support the collapsed state of the Newfoundland capelin population and the lack of predator release at the meso-predator trophic level after the overfishing of a top predator, Atlantic cod, Gadus morhua, in the early 1990s. Overall, this study increased the knowledge of forage fish population dynamics on the Newfoundland Shelf, specifically the understudied sand lance Ammodytes species. Chapter 3 Non-spawning fish select habitat based on many abiotic and biotic factors. Although prey and predator densities are important biotic factors, many ...
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