Fate of hatchery-reared juvenile Nechako white sturgeon (Acipenser transmontanus): Assessment of predation by river otters (Lontra canadensis)

Abstract

Predation of fish raised and released as part of conservation aquaculture programs can pose a threat to the recovery of endangered populations. Therefore, understanding the impact of specific predators is important to inform these programs. In central British Columbia, a conservation aquaculture program exists for the endangered Nechako white sturgeon (Acipenser transmontanus). In Chapter 1, I provide evidence that river otters (Lontra canadensis) are a notable predator of these released sturgeon through the collection of over 500 sturgeon PIT tags from river otter latrine sites and finding sturgeon radio tags in suspected otter feeding sites. In Chapter 2, I used the collection of additional PIT tags to estimate the extent of predation and to identify spatial and temporal patterns in the predation. My results suggest a confirmed minimum of 3.9% of released sturgeon were consumed by otters, however, I also identify several factors that suggest this number is much higher. Predation hotspots were identified and varied depending on release year and location, and predation evidently decreased with a shift to low release numbers and fewer sturgeon being present in the river. In Chapter 3, I present the results of laboratory experiments I performed that revealed an inability of naïve juvenile white sturgeon to be conditioned to recognize otters as a threat using conspecific alarm cues. However, spatial avoidance was identified as an important anti-predator response and suggestions are provided to improve future experiments. My findings specifically inform the recovery of the Nechako white sturgeon, however, may also be informative where other populations of sturgeon and otters coexist. Additionally, as this predator-prey interaction was previously unstudied, my results contribute to a growing knowledge of sturgeon predators.