Fishing for Answers

Quantifying the best handling practices for trout
– Dr. Steven Cooke, Carleton University

The Fish Ecology and Conservation Physiology (FECP) Laboratory at Carleton University is committed to ensuring that recreational fisheries are sustainable and to that end they work with a variety of partners to improve the science and practice of catch-and-release.  Core to the Kenauk brand is providing clients with a true “wilderness” experience – private access to entire lakes in a pristine setting where the fish are plentiful.  Beyond limiting fishing effort on lakes (i.e., clients “book” a specific lake and associated cottage and boat for a period of time), much of the Kenauk reserve is managed under a catch-and-release framework (i.e., fish are released after capture).  Nonetheless, Kenauk must engage in extensive and costly stocking efforts to maintain fishing quality which implies that there is some level of post-release fishing mortality.  Assuming that catch-and-release mortality occurs (at some unknown level) it is necessary to quantify that mortality to inform stocking practices and to identify opportunities for reducing catch-and-release mortality such that the need for costly stocking could be reduced.  

With funding support from NSERC (NSERC Engage Grant funded in May 2015) we will generate the necessary biological knowledge for the industry partner to ensure long-term viability of their recreational fisheries using defensible research methods.  The project will involve the capture of trout between spring and early fall to understand how water temperature (which changes seasonally) and fish condition (which also changes seasonally) influence catch-and-release outcomes.  Fish would be captured using common gear used by clients including lures (spinners/spoons) and flies with either barbed or barbless hooks.  Fish will be fought and handled for various periods of time to reflect a diversity of angler expertise.  Details on species, water temperature, gear type, fish size, hook location, bleeding, and fish vitality (assessed with a reflex impairment technique) will be recorded and fish will be temporarily marked (with an external tag) and held for 48 hrs in lake net pens to evaluate mortality rate.  Data will be incorporated into a model to identify the factors that influence mortality and reflex impairment which will identify opportunities for reducing mortality and sublethal impacts.  We will also identify seasonal thresholds for air exposure which are necessary to share with anglers.  The mortality estimate will inform models that will determine the extent to which stocking is needed to maintain fishing quality.

A follow up project was also conducted investigating temperature-dependent responses to catch-and-release angling in Rainbow Trout (Oncorhynchus mykiss). Catch-and-release angling (C&R) is an emerging conservation technique that focuses on returning fish to their environment following capture. These fish are assumed to return to their normal behaviour; however, we know this is not the case. Following a fisheries interaction, fish may experience stress and become impaired. This impairment can manifest as compromised decision making, inability to avoid predation, inability to seek refuge or in extreme cases, fish may also perish. The goal of this project is to determine the influence of surface water temperature on post-release behavioural impairments in angled Rainbow Trout, and to investigate the use of holding devices that are designed to facilitate recovery. The project aims to provide anglers with the knowledge to make handling-related decisions that maximize the survival of released fish. To accomplish this, two primary research questions were investigated: (1) What is the influence of surface water temperature, fight time, and air exposure on post-release recovery? And (2) When is it beneficial for anglers to assist fish in their recovery after an angling event, and what methods are the most beneficial?

Results Summary:
– Trout experience the most substantial behavioural changes such as equilibrium loss when water temperatures exceed 22°C.
– Deeply hooked fish have high mortality rates – barbless hooks can help reduce dehooking time.
– Assisted recovery is only beneficial when the water used in the recovery tank is significantly colder than surface water temperatures.
– At the height of summer water temperatures (25°C +), holding fish in a recovery box or cooler for 3 minutes using 18°C water significantly decreased equilibrium impairments upon release.