Date of Award

Spring 5-5-2023

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Wildlife Ecology and Wildlife Conservation

Advisor

Joseph Zydlewski

Second Committee Member

Stephen Coghlan

Third Committee Member

Christina Murphy

Abstract

The Gulf of Maine Distinct Population Segment of Atlantic Salmon has suffered from habitat loss and exploitation over the last century. Hatchery supplementation has prevented the extirpation of the species, but stocking methods represent tradeoffs between survival, domestication, and logistics. Egg planting, the use of eyed embryos, maximizes natural rearing opportunities which can be important for adaptation. This method, however, is logistically demanding and requires significant labor over large spatial, but short temporal, scales dictated by the ontogeny of the fish. However, the survival and dispersal behavior of Atlantic Salmon fry immediately after emergence from eggs planted in artificial nests is poorly characterized. To address these uncertainties, we assessed spatial distribution of fry from egg planting among habitats of differing quality in three rivers in Maine (Narraguagus, Pleasant, and Machias). The dispersal of post-emergent fry planted as eyed eggs during the winters of 2019 and 2020 was observed during the first year of growth across several, two-kilometer reaches. There was little observed difference in abundance within reaches for each drainage, indicating substantial movements post-emergence for some individuals. There were differences in abundance for reaches within drainages that corresponded to qualitative mean habitat scores derived from habitat suitability indices, with greater densities in habitat with greater scores. Higher densities were observed closer to planting sites with density diminishing with distance away from planting sites. Larger fish were found further from planting locations. Size was greater in more thermally suitable reaches, but density was not affected by water temperatures.

These observed dispersal patterns of post-emergent fry were then applied to a suite of scenarios developed from a range of egg numbers and possible stocking locations to identify optimal combinations of stocking inputs and stocking locations of varying habitat quality that contribute to optimal Young of the Year (YOY) recruitment. These scenarios were then compared using Production Possibility Frontiers to identify the scenarios producing the greatest YOY recruitment. A model with total sites and total YOY production indicates the optimal egg planting scenario is to plant 4,000,000 eggs across 91 planting locations resulting in 55,301 YOY salmon. But when including a distance penalty to account for logistical constraints, the optimal scenario shifted to planting 2,000,000 eggs among 6 planting locations resulting in a total of 29,062 YOY. The benefit of not penalizing distance is that eggs are planted into more rearing habitat resulting in higher YOY production. However, logistically this may not be feasible given time constraints. Thus, identifying optimal planting locations within the constraints of a distance penalty maximizes YOY production in a more realistic framework.

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