Sand lance (Ammodytes spp) on the Newfoundland Shelf: habitat selection, diel behaviour, and synchrony of dynamics with other forage fish

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 species also have specific abiotic habitat requirements. Sand lance (Ammodytes spp) lack a swim bladder and, thus, require sandy substrate for burrowing when not actively feeding to avoid predation and reduce energy expenditure. Although sand lance species in other regions show diel shifts in feeding in the water column and burrowing in seabed substrate, diel patterns for species in the Northwest Atlantic remain unknown. The objectives of this chapter were to investigate sand lance habitat characteristics and diel behaviour during July-August 2013-2021 on the northeast Newfoundland coast. Integrating camera surveys, sediment grabs, and hydroacoustics, I found sand lance were associated with 0.5-4 mm seabed grain sizes that were < 11˚C (typically ~2˚C). Acoustic sand lance biomass was higher during the morning and afternoon but decreased throughout the day and evening, while densities in sediment grabs simultaneously increased later in the afternoon and evening and buried fish more commonly had non-empty stomachs in the evening. These findings suggest that sand lance were feeding in the water column during the day and burrowed later in the day once stomachs were full. Diel patterns were size-dependent, with more smaller sand lance (<150 mm) caught in sediments throughout the day but primarily only larger sand lance (>150 mm) caught in sediments throughout the night. Findings suggest sand lance species in the Northwest Atlantic exhibit similar habitat requirements and diel patterns to those in other regions. Overall, this study provided a better understanding of Ammodytes distribution, abundance, density, biomass, diel behaviour and habitat selection in coastal Newfoundland.

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