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What’s up with walleye?
BY Kirsten Nikel
ON August 4, 2018
You may have heard that walleye have been stocked in Hamilton Harbour over the past few years, but what are those fish doing now? What does this mean for the harbour? Stocking walleye is one of the ways that people are trying to restore fish communities and improve the health of the harbour, but it isn’t the only part of the story.
 
Having a self-sustaining population of walleye in Hamilton Harbour is a goal of scientists, community members, and sport fishermen alike. Walleye (Sander vitreus) are a top predator and a popular sport fish. They used to be abundant in Hamilton Harbour; the harbour and Cootes Paradise were cold- and warm-water spawning ground for fishes, respectively (Boston et al., 2016). However, decades of industry, pollution, and habitat loss led to massive changes in the fish community (Boston et al., 2016). Walleye and other top-predator populations collapsed, and the fish community shifted to more pollution-tolerant species, such as brown bullhead, white perch, and invasive species including the common carp and round goby (Boston et al., 2016). 

Because of all this ecosystem damage, Hamilton Harbour was listed as an Area of Concern by the International Joint Commission in 1985, and a Remedial Action Plan (RAP) was developed in order to improve the harbour’s health (Boston et al., 2016). Some of the impairments outlined by the RAP include the degradation of fish populations and loss of fish and wildlife habitat (HHRAP, 2012). Actions that have been taken to help combat these impairments include walleye stocking and habitat reconstruction. Walleye stocking first occurred in the mid 1990s, and was then resumed in 2012 with the stocking of 100,000 fingerlings into the harbour (Ontario MNRF, 2015). Now, these stocked fish are reaching maturity, and Hamilton anglers are excited to be catching walleye in their own backyard (Ontario MNRF, 2015). Walleye caught in the harbour in winter 2018 ranged in size upward of 15 inches (McNeil, 2018)!

Keeping track of fish community structure and top-predator biomass is very important in monitoring restoration efforts. One way of monitoring fish populations is by using the Index of Biotic Integrity (IBI; Boston et al., 2016). The IBI combines the effects of fish community composition, water quality, habitat supply, and piscivore species into one score (Boston et al., 2016). The goal for Hamilton Harbour is an IBI of 55-60, and progress is slowly being made towards this goal from an IBI of around 30 in 1988 (HHRAP, 2012). Another way that scientists are assessing fish populations is by measuring the percent of piscivore (fish-eating) fishes. A healthy fish community has over 20% top predators (Hoyle et al., 2012). Luckily, the numbers in the harbour seem to be moving upwards, especially since the walleye fingerlings that have been stocked in the harbour are doing well (Boston et al., 2016). In 2013, piscivores made up around 10-15% of the biomass at sites where habitat restoration had been done (Boston et al., 2016).

To improve fish habitat, shoals have been constructed along the northeast corner of the harbour in hopes that walleye will use these areas to spawn (HHRAP, 2012). In 2015, biotelemetry work started in order to monitor the movements and habitat preferences of walleye in the harbour (Brooks et al., 2017). Sexually mature walleye were tagged with transmitters and depth sensors. Fixed receivers were distributed throughout the harbour, and when a fish passes by a receiver, it records the individual fish’s location and depth (Brooks et al., 2017). So far, the data from this project have shown that the stocked walleye are living in the harbour for most of the year, and are spending a lot of time around the reconstructed shoals (Brooks et al., 2017). Only time will tell if they use them to spawn and successfully reproduce, creating a self-sustaining population of walleye right here in Hamilton Harbour.

References:
  1. Boston, C.M. et al., 2016. The fish community of Hamilton Harbour, Lake Ontario: Status, stressors, and remediation over 25 years. Aquatic Ecosystem Health & Management, 19(2), pp.206–218.
  2. Brooks, J.L. et al., 2017. Use of Fish Telemetry in Rehabilitation Planning, Management, and Monitoring in Areas of Concern in the Laurentian Great Lakes. Environmental Management, 60(6), pp.1139–1154. 
  3. Hoyle, J.A. et al., 2012. Fish community structure in the Bay of Quinte, Lake Ontario: The influence of nutrient levels and invasive species. Aquatic Ecosystem Health and Management, 15(4), pp.370–384.
  4. HHRAP, 2012. Summary of 2012 Hamilton Harbour RAP Stakeholder Forum Decisions. Hamilton Harbour Remedial Action Plan (HHRAP) Beneficial Uses.
  5. McNeil, M. 2018. Hamilton Harbour turning into sport fishing haven with return of walleye. Toronto Star, 14 Feb 2018. 
  6. Ontario Ministry of Natural Resources and Forestry (Ontario MNRF)., 2015. Lake Ontario Fish Communities and Fisheries: 2014 Annual Report of the Lake Ontario Management Unit. Ontario Ministry of Natural Resources and Forestry, Picton, Ontario, Canada. 
Author Bio - Kirsten Nikel
BARC Summer Intern
BARC Summer Intern

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