Phenology and growth of rainbow smelt (Osmerus mordax) in Lake Melville, Labrador, under increasing pressure from climate change and anthropogenic activities

Sutton, Jordan (2022) Phenology and growth of rainbow smelt (Osmerus mordax) in Lake Melville, Labrador, under increasing pressure from climate change and anthropogenic activities. Masters thesis, Memorial University of Newfoundland.

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Abstract

The rainbow smelt (Osmerus mordax) is the most abundant and widespread forage fish residing within the Lake Melville estuary, Labrador, and plays a key role in the upcycling of energy from lower trophic levels to top predators. Rainbow smelt is an abundant prey for a myriad of animals, such as salmonids, gadids, flatfish, birds, and marine mammals, and is one of the preferred wild-caught fishes for subsistence and recreational fisheries in the region. The phenology, including spawning, of rainbow smelt is attuned to the hydrography of the Lake Melville estuary. For example, both spawning and hatching periods coincide with increased water temperature in the spring. With the completion of a new hydroelectric dam in Lake Melville’s main tributary, the Churchill River, a modification to the natural flow regime of freshwater into the estuary is expected. Following the demand for electricity, the Churchill River will likely experience lower than normal runoffs in the spring and summer and higher than normal flows in the fall and winter, when demand for power is higher. Modifications in the inflow of freshwater in Lake Melville can result in temperature variations and change the timing of ice formation and break-up as well as the total duration of ice cover within the estuary. Such changes to the natural flow and hydrography can impact the life history of rainbow smelt, especially given that Lake Melville is at the northern limit of the distribution range of the species. Here, I examine the period of spawning and hatching, and variation in abundance of larvae in relation to temperature and salinity. Additionally, I document larval growth as well as the age structure, growth, and maturation of adult rainbow smelt in an effort to understand how the new hydroelectric facility and a changing climate may impact rainbow smelt phenology. Larval growth rate is up to 3.33 times faster than that of more southern regions, while the spawning season and hatching period occurred later, which is hypothesized as being a result of the shorter growth season prevailing at high latitudes. In contrast to early life iii stages, our findings confirm that adult rainbow smelt grow slower, mature later, and live longer in northern populations compared to southern populations, which is likely due to lower metabolic rate in colder waters prevailing at high latitudes. This thesis contributes to the relative scarcity of information on the life history processes of rainbow smelt in this region. These gaps in basic life history information hinder data-driven management decisions on population status and vulnerability. Additionally, this study provides important baseline information which can be referenced in future studies examining the impact of hydroelectric dam operation on the life history of rainbow smelt and, in turn, ecosystem health due to the species’ ecological importance.

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