I've been in conversation with a fellow member of the FMZ 18 Council who is a post doctoral fellow at Carleton. It appears the "Science" is NOT settled on fatal temperatures for trout. Most of my concern has been on our local stocked Rainbows. I admit it, I'm a trout bum. I love to catch Rainbow Trout. Pound for pound, they give the best fight, jump the highest, pull the hardest. A close second is SM Bass. I've been concerned about the dangers of warm temperatures on trout. The biologist's textbook bible, "Freshwater Fish of Canada", states that the "fatal" temperature of Rainbows is 24C or 75F. And that is why for the last few years, I have switched over to SM Bass fishing come July and continue through to September when I go trout hunting again until hard water. It appears that the "science" contained in the textbook is a bit out of date and research is continuing, interestingly enough, right here at Carleton U. under Steven Cooke (also a member of the FMZ 18 Council). The Council is meeting with various stakeholders to determine new policy and regulations and give recommendations to the Ministry. I fish for trout mainly in FMZ 15 but they are not having a Council. I suspect that whatever we decide will impact their area as well as the Ministry is keen on simplifying regulations.
I have a few biology contacts across the country and I am awaiting responses. Since the textbook appears to be unreliable and the internet even more so, I'm assuming that researcher's comments are closer to the mark. One researcher I'm keen to hear from out west is on how long we can keep fish out of water. My memory of our conversation is that more than 30 seconds causes permanent gill damage but don't quote me at this point. That email is in one of my many dead computers. Some of the more famous trout fishers (other than myself) like Brian Chan and Phil Rowley have given me figures like 7 or 15 seconds out of water as a max.
Rather than paraphrasing Nick's comments, I'll paste them directly. In the first one I expressed interest in stress as a factor.
"I agree that stress can be a killer across the animal kingdom. At the same time, catch and release has proved to be effective across a range of species and conditions (when fishes are handled properly). In terms of fish being caught several times in a season, that could have effects on growth rate, but this type of stress has short-term effects. Unless the fish was severely injured, the effects of that stress would only last a few hours to days at most. Being caught multiple times wouldn't likely lead to cumulative stress, though it could perhaps slow growth a tad."
In this exchange, I was concerned about Catch and Release (C&R) for Lake Trout in warm temperatures from depth for slot determination but also in terms of other trout. Baratrauma, is the stress of unequal pressure between the inside and outside of the fish, ie, "bends". Many people believe that trout, especially Lakers, can easily equalize pressure through their air bladder. That apparently is not true, and especially in the case of Rainbows which rocket from depth when caught.
"I don't think anyone has a good handle on how deleterious catch and release angling can be. It all depends on the situation- sometimes survival can approach 100%, other times mortality rates can be very high. Changes in temperature can be stressful to the fish, as can the energy spent fighting. Add to that handling (which carries the potential for a wide variety of stressors and injuries), and in some cases barotrauma. Overall, these factors tend to be cumulative- (but) for example, exposing a fish to warmer temperatures might not have a major effect if it is not handled much and released quickly."
Here was my first inquiry on temperatures. BTW, FCC costs around $120 which is why I don't have one.
"FFC is a fantastic textbook - the authors give a lot more information than just basic biology, including etymology (the history of where fishes' names came from) and a section for each fish on relation to man, which generally involves how they taste. Fatal temperatures aren't quite as cut and dry as that. Rainbow trout can certainly survive more than a few seconds (probably hours, even days) at 25C, but prolonged exposure will lead to stress and eventually death. Higher temperatures will lead to this occurring faster- at 35C, rainbow trout would probably be dead in less than half an hour. Even at 23C though, rainbow trout would experience stress and lower growth rates because their metabolism isn't as efficient outside their optimum temperature range. As for other trout, they range considerably. I don't know exact numbers off the top of my head but lake trout would be in the 12-15 C range, whereas brown trout might be in the 25-30C range. "
There are many factors to consider when practicing C&R for trout. When surface temperatures are ideal around 11C (52F) then one doesn't need to be too concerned. However, when the water warms, one should get that trout in as fast as possible, keep it in the water, and get it on its way ASAP. If you are going to fish for trout in the summer, make sure to bring along your canvas creel. You might have something unintended for the bar-b-que. Another concern is slime removal. Even a small skin area of slime removed through over-handling and rough nets will cause fungus growth and eventual death. Use soft rubber nets and keep it in the water. Don't fish deeper than 10 meters at any time just to be safe. The research on baratrauma is ongoing.