Coho Otolith Project

Juanes Lab, University of Victoria

Determining the causes and consequences of vateritic otoliths in wild and hatchery-reared Coho Salmon (Oncorhynchus kisutch) in British Columbia, Canada

Project Overview

The Coho Otolith Project, led by PhD candidate Leigh Gaffney at the Juanes Lab, University of Victoria, is designed to address significant challenges in salmon welfare and conservation efforts. Collaborating with the Goldstream Community Hatchery, British Columbia Conservation Foundation, Pacific Salmon Foundation, and Fisheries and Oceans Canada, this research initiative aims to uncover the causes and consequences of vateritic otolith formation in hatchery-reared Coho Salmon. Vateritic otoliths, which are abnormal and occur much more frequently in hatchery-reared salmon than in their wild counterparts, have been shown to impact salmon's sensory abilities and may reduce their survival. By examining various hatchery environmental factors, the project seeks to identify specific practices that lead to the development of these abnormal otoliths. Additionally, we ‘re undertaking large-scale sampling of otoliths from Coho Salmon across multiple hatchery facilities surrounding the Strait of Georgia, covering various rearing years, life stages (smolts and adults), and genetically distinct stocks in order to determine how widespread the issue of increased vateritic otolith formation is.

What is an otolith?

Otoliths, similar to ear bones in mammals, are vital sensory structures in the inner ears of teleost fish, crucial for hearing and balance. Healthy otoliths are composed of aragonite, a polymorph of calcium carbonate, however otoliths can also include an abnormal polymorph called vaterite. While vateritic otoliths are rare in natural-origin salmon, occurring in less than 10% of individuals, they are common in hatchery-reared salmon, affecting 50-80% of these fish. Vaterite makes otoliths larger, less dense, more brittle, and more irregularly shaped compared to their aragonitic counterparts. The formation of vaterite is irreversible and is thought to be influenced by environmental differences between wild and hatchery settings. The specific functional impacts and mechanisms of vaterite deposition in hatchery-reared salmon are still not fully understood.

Aragonitic otolith from an adult coho salmon

Three "types" of otolith pairs (1. aragonitic pair, 2. asymmetrical vateritic pair, 3. symmetrical vateritic pair)

Vateritic otolith from an adult coho salmon

Hatchery-rearing Trials at Goldstream Hatchery

We are examining various parameters in the hatchery environment that might influence vaterite formation, such as:

water flow direction
feed composition
environmental enrichment (including the addition of plants, natural substrate, and structures for hiding)
tank biodensity

If we can successfully link hatchery-rearing practices to decreased vateritic otolith development, we will be able to recommend rearing practices that help reduce these abnormalities in the future.

Marine and Stream Survival

While understanding the causes of vateritic otolith formation is crucial, it is equally important to determine the impacts this abnormality may have on the survival of these fish once released into the wild.

Coho Salmon rely on their hearing to navigate their environment, locate suitable habitats, and detect potential predators. If hearing is compromised, it may lead to severe consequences for the survival of these fish. To investigate whether vateritic otoliths influence the stream and marine survival of hatchery-reared Coho Salmon, we PIT-tagged a subsample of fish from our hatchery-rearing trials and installed an antenna array in the Goldstream River estuary to collect survival data on the out-migrating smolts and returning adults. PIT tags, which are inserted into the body cavity of the fish, serve as individual bar codes that allow us to track individuals as they leave the river as juveniles and return years later to spawn as adults.

Behaviour Study

To investigate how compromised hearing may lead to lower survival rates, we also conducted laboratory experiments using predator sounds (Pacific Harbour Seal growls, a top predator of Coho Salmon), boat noises (anthropogenic noise), and ambient river sound playbacks. This experiment aimed to determine whether Coho Salmon juveniles with vateritic otoliths exhibit different behavioural reactions to these sounds compared to fish with aragonitic otoliths.

Importance

Our research is the first of its kind to investigate the causes and consequences of vateritic otoliths in Pacific salmon. Our efforts will provide hatchery managers and stakeholders with crucial insights into the effectiveness of current hatchery-rearing practices and guide modifications to reduce vateritic otolith formation in Coho Salmon juveniles. Determining the impact of vateritic otoliths on marine survival and predator-avoidance behaviours is essential for improving the success rates of hatchery restoration efforts and conserving salmon stocks within the Strait of Georgia and worldwide.