While most anglers can attest to having fish die in warm water, particularly after long fights, or too much time in the net after deep hooks, most of the lore around fishing in warm water comes from very few limited studies or empirical evidence only. In this post we are going to take a look at where this idea started and the actual data surround the topic.
Summer Musky Fishing
Most anglers have it almost beaten into them that fishing for musky in water >80 F is just as bad as killing them. While we aren't saying that warm water isn't a factor or that there is no additional risk to fish mortality we do think its best to understand why you are doing something if you are going to do it. While studies conducted can have data that show or arrive at a particular conclusion it is important to look at it from the viewpoint of anglers and not as a scientist because the context at which you look at data can change the conclusions; or at least how you respond to them. From our own members professional experience in engineering there is a big difference between an "increased risk" and a significant risk. As an example with exaggerated numbers to help illustrate this point if 1 in 1000 caught fish die in water temperatures less than 80 F and there is a 1000% increase in mortality from caught fish in water temperatures over 80 F we are still only talking 10 fish in 1000 or 1% of total caught fish. While saying there is a 1000% increase in likelihood of mortality is true, overall the mortality rate is still not significant enough that we as anglers should be worrying about it; especially when there are other factors that are more significant and in our control.
Warm Water Musky Fishing
Some of the main questions surrounding this concept which we hope to answer by looking through the studies conducted include:
Why is it not 80 not 75? How did this become the threshold
What if the temperature stays at 78-79 is 1 degree going to make a difference?
What if this is the first day the temp gets to 80 or the first day it drops below 80 are we still ok?
Is warm water a greater factor than poor handling? Is 80 really the limit for warm water?
If you handle properly in 80 degree is it still worse than handling poorly in 60 degree water?
What if theres a thermocline or cold water spring nearby?
And most importantly if this is really such a guarantee why have the biology experts at natural resource & fisheries departments not closed the season in August?
We may never know the exact answers to these questions but if we are going to make decisions based on studies that have been performed we should at least read and understand how they arrived at the conclusions we are basing our decisions around. Let's take a look at all the published studies we can find and see if the data/conclusions agree with the musky community that musky are more likely to die when caught in warm water compared to other times of the year, compared to musky that aren't caught, and if this increase is signifiant compared to more controllable factors like fish handling practices.
For future reference when it comes to ability for esox species to tolerate warm water are as follows:
Musky Fishing Hot Weather: The Origin - 2013
Released in the 2013 July/August issue of Muskie Magazine by E. Heyob suggests not fishing for musky once surface temperatures exceed 80 F at first light. We were unable to find a copy of this article to understand how this conclusion was arrived at other than empirical evidence. As well, the question of why was 80 F picked as the barrier still seems unclear but has been used as a barrier in all future studies, likely as a result of this article being promoted around the musky community. We assume this is the extreme end of temperatures a lot of smaller, shallow, popular musky waters got to once August hit. It is important to note that C&R fishing and proper fish handling techniques were still relatively new concepts (only a few decades old) compared to the history of musky fishing where all fish were harvested as trophies. Muskie Magazine is also based in southern United States where there are many smaller, shallower, musky waters, so the idea works as a good rule of thumb to pass along to anglers but doesn't apply as well to anglers in the northern reaches of musky populations or on Canadian Shield type bodies of water where water temperatures barely reach 80 F and there are cold water sources easily accessible.
If anyone has a copy of this article we would love to take a look to understand the history around this topic fully. Between 2013 & 2021 there were no formal scientific studies completed and published that could validate this claim and as such not fishing in water above 80 F has become an unwritten rule in the musky community despite not having a scientific basis of proof. Since 2021, there have been multiple studies around the topic with plenty of data to interpret.
Musky Catch and Release Mortality Study James River - 2021
This study is completed in the James River in Virginia. The James River is a shallow water system where thermal refuge is not available. While the study does throw out some numbers to suggest that angling in warm water does in fact increase musky mortality there is little explanation and statistical significance of the results due to the small sample sizes, uncontrolled factors of significance, crude calculation methods, and exclusion of key data for comparison.
In the study 39 tagged fish were located in 2020 and 46 tagged fish in 2021. Before the warm water period 5 fish died in 2020 and 5 in 2021 (one was harvested and should be removed from consideration). The study states that warm water leads to higher mortality simply because of 12 caught fish (7 in 2020, 5 in 2021) during the warm water period 4 died after release (33%). This is in comparison to 4 fish which died during the same period but were not caught (4/(39+46-12-11) = 6.5%).
While this does suggest catching musky increases the likelihood of mortality there are a few issues with this analysis when it comes to discussing warm water in particular:
The people catching and releasing these fish were also local volunteer anglers so there is no way to ensure handling of all fish were the same. Are we sure the cause of the deaths in this study is due to warm water and not long handling as a primary factor?
With only 12 fish being considered each death holds a much higher significance level than a larger study would. If we consider that even one fish was improperly handled leading to its death (as the 2020 update suggests) rather than warm water the crude analysis would drop the value from 33 to 25 or 27% depending if you discount the fish entirely or assume it would have lived with proper handling. Previous studies on the impact of fish handling suggest that amongst anglers almost 17% are killed by poor handling. This relatively matches the results of this study which would suggest warm water isn't a significant factor in comparison to handling practices. An excerpt from the linked study:
"The impact of mortality caused by catch-and-release practices is often underestimated by both anglers and fishery managers. From a review of 118 catch-and-release studies (Appendix 1), which, in total, involved over 120,000 fish, the average mortality associated with catch-and-release angling was 16.2%. Thus, while many anglers may assume that by practising catch-and-release they are having no impact on the fish population, a significant number of released fish may die. Additionally, many anglers will continue to fish after they have caught their limit under the premise that they will release all further fish caught, however they often do not take into consideration the number of fish which will inadvertently be killed as a result of this practice."
The study doesn't compare to catch and release at other periods of the year. This would help to eliminate poor handling as a primary factor but also give actual evidence to the claim that angling in warm water increases the odds that musky will suffer from mortality. As anglers we all know in any water temperature there is a risk of mortality.
There is no comparison or discussion to the 10 fish which were not caught and died prior to warm water periods. This information alone contradicts the study's claims as significantly more fish died in the cold water period of natural causes than ones caught and handled in the warm water period.
Our Conclusion: The results of this study neither confirm or reject the idea that angling in warm water poses a greater risk of mortality to musky than other times of the year due to the gaps in the study. While it is a good starting point and the data helps to highlight the link between proper fish handling and mortality, as well as establish natural mortality rates, more data and tighter controls are needed to make definitive statements. Another study was planned to occur in Stonewall Jackson Lake where thermal refuge was available in warm water months.
Catch and Release Mortality Study Stonewall Jackson Lake
Unfortunately, the full study from this project is not available to the public at this time. Despite trying to locate the results of the study only a few informal sources are available. The study in Stonewall Jackson Lake was completed co-currently with the James River study. stonewall Jackson Lake stratifies in the summer months and has thermal refuge available for musky unlike the James River. Based on the information that is available a few key points can be understood.
In the 2020 update it states of the 10 fish caught, one died from poor handling and bait location, 2 did not move after release and were assumed dead, while 7 others were mobile. Based on the 2020 update the mortality rate from caught fish should be closer to 22% (2 of 9) which is much closer to the values of average fish handling.
From the linked press release the final data supposedly shows only 10% of angled musky in warm water suffered mortality. This suggests that as long as thermal refuge is available anglers do not need to worry about angling in warm waters. This value is lower than the average mortality rate of angled fish discussed previously.
There is also discussion not just about the days temperature but the temperature of the days before and after a catch. Although no conclusions can be drawn this suggests more research is needed.
Hot Weather Musky Fishing Mortality Study - 2023
This study collected 102 adult musky and stocked them in experimental ponds. 53 fish not caught during the study and used as controls. The caught fish were examined post release.
The study is set up in a way which directly addresses the issues we mentioned with the previous study and is specific to understanding musky C&R mortality in warm water (25 C+ / 77 F+).
Unlike the previous studies looked at this one does a great job at considering multiple factors and realistic scenarios encountered in angling as outlined by their methods below:
"Upon setting the hook, a timer was started and the fish was netted as quickly as possible, as is typically done by Muskellunge anglers. Fight time (s) was recorded as the time it took to reel in the fish, and the timer was stopped once the fish was captured in the net. Once landed, the fish was kept in the water for dehooking and processing. Hooking location(s) was identified as the mouth, gills, esophagus, and/or tongue, and hooks were removed with long needle-nosed pliers. Because there are multiple points per lure, fish were often hooked in multiple locations. In these instances, the primary hooking location was used in analyses. Primary hooking location was defined as the “weight-bearing” location, or the location in which the most force was exerted on the fish as it was reeled in. If unhooking times exceeded 2 min, then the hooks were cut below the barb with handheld bolt cutters. The fish was then scanned for its PIT tag and recorded for individual identification. Net time (s) was recorded as the time from initial landing until the fish was removed from the net for the admiration period. Because Muskellunge are highly prized, many anglers hold them out of water for pictures and admiration. To emulate this, each fish was held out of water for 30 s in a horizontal orientation to simulate how an angler would take a picture or admire the catch."
The high level conclusions of the study state "mortality was greater for angled fish (30.0%) than for control fish (11.3%) during warm water periods". However, the results are quite telling as ponds with certain characteristics had 0% mortality while others had over 40% from catch and release activities! The study concluded fight time is a poor predictor of mortality but net time is a good predictor of mortality.
In short, if there is a thermocline or cold water source available the fish will survive even if surface temperatures are above 25 C (77 F). It is only the shallow water systems where the temperature is warm everywhere that this becomes an issue. This means many bodies of water and areas on larger bodies of water like the great lakes or Georgian Bay are completely safe to fish all summer without additional risk to musky as long as proper handling is practiced. At the same time many of the control fish deaths occurred in the same pond where there were no recorded deaths from catch & release highlighting that death of fish is inevitable with angler intervention or not. If we look at this single pond in particular 5 of the fish died without being caught while none of the caught fish died. This would suggest a control mortality rate of 25%! Perhaps these fish were not caught as they were already in too poor of health to feed or they were captured from sites differing drastically from the experimental pond leading to their death which the study does make note of.
Removing the above mentioned pond from the results the control mortality rate drops to 2% and the C&R mortality rate was up to 43% in some of these ponds (all shallow water systems with no thermal refuge). These results show a much more clear correlation that warm water musky fishing in shallow water systems without thermal refuge putting musky at increased risk of mortality from angling. 43% is a significant number of deaths for caught fish.
The study also determined that that mortality was strongly associated with the 5-day cumulative total temperature, suggesting that the temperatures experienced by fish prior to and after the angling event can affect the probability of mortality. So, from the perspective of anglers in shallow water systems without thermal refuge the first day the water hits 25 C (77 F) or the first day after it drops below don't put you in the clear. As well, a standing temperature of even 25 C (77 F) for 5 days will also put musky at greater risk for mortality if caught and at a rate which is significant for anglers (25%)! Based on the figure below in, in order to achieve a catch and release mortality rate that is not significant for anglers (<8%) the 5 day cumulative temperatures should be less than 120 C or daily average 24 C / 75 F.
"The West Virginia ponds experienced the highest C&R mortality (42.9%), the lowest CPUE (0.03 fish/h in 2020; 0.15 fish/h in 2021), and the highest water temperatures. In contrast, the Wisconsin pond exhibited the lowest C&R mortality (0%) and the highest CPUE (0.28 fish/h) and developed a distinct thermocline (Figure 3)."
Our Conclusions: This study is very well conducted and offers insights that are directly applicable to anglers as well as biologists. Not only does it answer most of the questions within the musky community raised at the start of this post but it also abolishes the long standing idea that fishing in water above 80 F is a poor choice. In fact, it lowers this temperature to 75 F unless the water body has thermal refuge available.
Summer Musky Fishing Tips - From Scientific Data
Based on the assessment of the above mentioned studies in this blog post we would put forth the tips below for summer musky fishing in the future.
The body of water being fished makes a big difference
If thermal refuge is available (like many canadian shield lakes or deep bodies of water) anglers do not need to worry about mortality of fish due to warm waters
In shallow bodies of water with no thermal refuge anglers should avoid fishing in stable water temperatures above 24 C / 75 F as the risk increases significantly above this point.
Proper handling remains a significant factor for reducing musky mortality & becomes especially important in warmer waters
Stay open minded and challenge conventional ideas until you have a solid understanding of why you are making decisions
To learn how you can undertand, find, target, and catch mor musky be sure to take our Musky Fishing Course at the link below:
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