Environmental conditions experienced by marine fish eggs, larvae and juveniles are critical for recruitment into the spawning population, thereby influencing patterns in population fluctuations and year-class strength. Marine fish typically show a type III survivorship curve, where the most vulnerable stage occurs early in life. Capelin (Mallotus villosus) is a small, short-lived (3-6 years) forage fish species that occupies an important middle trophic position in the food web. In the 1980-1990s, capelin population collapses occurred in the three commercial fisheries in Iceland, the Barents Sea, and Newfoundland and Labrador. The Newfoundland population is the only one that has not shown any recovery in the subsequent three decades.

The aims of this thesis were to:

1. Determine habitat- and bay-specific larval densities (as a proxy of site quality) (Ch.1)
2. Investigate environmental drivers (prey, predators) of larval densities and condition (Ch.2)
3. Determine the influence of ambient water chemistry on larval otolith chemistry (Ch.3)
4. Investigate connectivity among bays using otolith chemical signatures (Ch.4)

In Chapter 1, I found consistent trends in the timing of spawning and annual larval densities in two northeastern Newfoundland bays (Trinity Bay and Notre Dame Bay (NDB)), suggesting coast-wide interannual trends in recruitment. Intertidal and subtidal habitats within NDB were of similar quality based on temperature, egg density, proportion of dead eggs, and larval densities. In Chapter 2, emergent larval densities were correlated with prey biomass, but not predator biomass or temperature, suggesting that larvae are emerging into a favourable prey environment but not necessarily into low predator abundances. Higher variation in larval length and condition was observed between years, with less variation between intertidal and subtidal habitats. In Chapter 3, I found that the concentrations of some non-essential elements increased in capelin embryonic otoliths with increasing environmental concentrations (i.e., strontium), while others do not (i.e., barium). Lastly, in Chapter 4, I found distinct otolith chemistry signatures in recently hatched capelin larvae from five bays throughout coastal Newfoundland that could be classified with high success. Overall, this research is important for the management of the Newfoundland capelin stock to ensure the survival of this critical species.