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Reproductive ecology and habitats of deep spawning Kokanee and Sockeye Salmon Oncorhynchus nerka

University of British Columbia

Understanding a species’ life history and habitat requirements are fundamental to conservation and successful resource management. Sockeye Salmon Oncorhynchus nerka are a highly valued fish species that exhibit astonishing life history variability; yet, despite their management importance and diversity, there are wide declines in productivity and many populations are at risk. Within Alouette Lake, British Columbia, are two ecotypes of O. nerka (the anadromous form, herein Sockeye Salmon; and the nonanadromous form, Kokanee), and both spawn anomalously deep within the lake. The objective of my thesis was to study the reproductive behaviour and habitats of deep spawning Sockeye Salmon and Kokanee, including reviewing potential habitat availability within Alouette Lake to support Sockeye Salmon restoration objectives. Using repeated gill net and remote operated vehicle surveys focused on the more abundant form, Kokanee (assuming Sockeye Salmon would behave similarly), I found that spawning behaviour was similar to other populations; this included protandry, large-scale movement patterns in males, some early arriving females, and nest excavation in a variety of lake bed types. Notable exceptions were the spawning depths (10-105 m), extended spawning period (2-3 months), and lack of floating carcasses that occurs in other deep spawning populations. Location data from Kokanee gill net surveys and Sockeye Salmon telemetry studies were combined with topographic and substrate information to develop Maxent habitat suitability models tested over a range of settings. Models predicted that suitable spawning habitat was available throughout the Alouette Lake at a magnitude that should not limit Sockeye Salmon restoration. Models for both ecotypes predicted stronger links to topographic variables than to substrate, but substrate was more important for predicting Kokanee spawning habitat. Moreover, ecological niche similarity tests showed significant differentiation between the two ecotypes. Innate differences between Sockeye Salmon and Kokanee and their mating preferences, as well as interactions between ground water and surface water movement that was detected (via a data logger mooring) may be associated with the variability in observed habitat use and model predictions. Together, these findings further our understanding of reproductive behaviour and habitats in deep spawning O. nerka populations and have important management implications.

Text

2019-09-27

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/71796

Forestry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/