Abstract
Accurately estimating population sizes is often a critical component of fisheries research and management. Although there is a growing appreciation of the importance of small-scale salmon population dynamics to the stability of salmon stock-complexes, our understanding of these populations is constrained by a lack of efficient and cost-effective monitoring tools for streams. Weirs are expensive, labor intensive, and can disrupt natural fish movements. While conventional video systems avoid some of these shortcomings, they are expensive and require excessive amounts of labor to review footage for data collection. Here, we present a novel method for quantifying salmon in small streams (<15 m wide, <1 m deep) that uses both time-lapse photography and video in a model-based double sampling scheme. This method produces an escapement estimate nearly as accurate as a video-only approach, but with substantially less labor, money, and effort. It requires servicing only every 14 days, detects salmon 24 h/day, is inexpensive, and produces escapement estimates with confidence intervals. In addition to escapement estimation, we present a method for estimating in-stream salmon abundance across time, data needed by researchers interested in predator--prey interactions or nutrient subsidies. We combined daily salmon passage estimates with stream specific estimates of daily mortality developed using previously published data. To demonstrate proof of concept for these methods, we present results from two streams in southwest Kodiak Island, Alaska in which high densities of sockeye salmon spawn.
Highlights
The management, research, and conservation of salmonids requires accurate estimations of population sizes
We determined the salmon passage for the remaining hours by modelling the relationship between the subsample of hourly video counts and photo counts and using the model to predict salmon passage across the entire salmon run. We developed this method on two streams used by spawning sockeye salmon: Meadow and Southeast Creeks (Fig. 1A) in southwest Kodiak Island, Alaska
Researchers and managers increasingly acknowledge the important role of small salmon populations in generating stable returns for commercial fisheries and for supporting wildlife of high economic and commercial value (Schindler et al, 2010; Beacham et al, 2014)
Summary
The management, research, and conservation of salmonids requires accurate estimations of population sizes. Managers use salmon (Oncorhynchus spp.) escapement estimates (salmon remaining after harvest that enter freshwater to spawn) to develop stock-recruit curves and to improve management timing of fisheries. Researchers often need escapement data for studies involving productivity, nutrient subsidies, and predator–prey dynamics. We have good escapement data for many main-stem rivers used by migrating salmon, we have little escapement data at smaller scales, including small streams where many salmon spawn (Anadromous Waters Catalog, Alaska Department of Fish and Game). How to cite this article Deacy et al (2016), A time-lapse photography method for monitoring salmon (Oncorhynchus spp.) passage and abundance in streams.
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