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  • Writer's pictureNew Wave Fishing Academy

Delayed Mortality

Updated: Dec 16, 2023

Over the past few months we have noticed a huge uptick in social media comments / posts shaming improper holds on big fish. While this is great that so many anglers are becoming more aware of proper handling techniques the comments often aren't about educating and more about belittling the poster and claiming they killed the fish; due to a vertical hold for instance. See below as an example of such a hold:

giant georgian bay pike

While we will push conservation and proper handling as much as possible at the end of the day fish are a public resource and individuals are legally entitled to keep most of these fish if they wanted. We have enough experience with catching big fish to know that these fish are often at the end of their life anyways and can die just from the stress of the fight even when proper handling is practiced. Anglers must realize that the act of fishing itself has risks for the fish associated with it and the potential for fish to die. If that is their biggest concern the best thing they can do is not fish at all.

However, this is not a possibility for most of us. We are HOOKED but this got us thinking. Is delayed mortality really as big of a problem that social media would make it out to be? Sure if you are dropping fish, keeping them out of the water for extended periods of time, or injuring their gills than these fish are at a big risk for delayed morality but is an improper hold for a quick photo really risky enough to worry about?

Before going any further let's take a minute to clarify some terms. Delayed mortality is the term coined to fish that do not die when released but shortly after release as a result of their injuries (angler caused, the fight, or other). These fish may even swim away appearing to be healthy but still succumb to their injuries. This could be hours, or even days after release so there is no way of knowing for the angler. To top it off most fish sink to bottom when they die. However, this is part of the ecosystem lifecycle and won't go to waste. Scavengers such as fly larvae, sucker or carp fish, catfish, turtles, and crustaceans will all eat up this easy meal.

A number of factors are commonly known to increase fish mortality including barotrauma, water temperature (oxygen), duration of fight, time out of water, and fish handling practices, not to mention that each species has a different resilience level to stressors.

A study conducted in 2005 showed results that the average mortality rate of multiple fish species caught and released was 18% with the hooking location being the most important mortality factor. Other significant mortality factors were related to hooking location including use of live bait, the act of removing deep hooked fish, type of hook (circle vs J) but also included barotrauma, water temperatures, and handling times. While the average mortality rate varied greatly between species the type of hold was not mentioned as being a significant contributor rather the time the fish was out of water and damage to their protective slime layer being the concern when mentioning fish handling.

A study from 1997 in Oaklahoma tracked the mortality of bass after release from a tournament (when the culture cared less about fish health and gear, handling practices, and livewell technology is not what it is today). The study noted that previous work in this field throughout 1970's showed mortality rates as high as 60% post release. Following the introduction of the now current guidelines for tournament fish handling this study was completed during numerous tournaments in 1995 and 1996.

In 1995 up to 4% were observed dead when brought to weigh in by anglers and total mortality average of 2.9% in spring but 33% in summer. The study also looked at if angler used continuous or non-continuous aeration in the livewell and sorted the fish into groups from low or high dissolved oxygen in livewells for comparison. Fish which came from well oxygenated livewells had a mortality rate of 28% while those from poorly oxygenated livewells 42%.

In 1996 average mortalities were recorded closer to 15% for each tournament studied. At one event where the guidelines were not followed 65% of fish ended up dead. 53% of dead fish were found at the bottom of nets and would not float to the surface until 4 or 5 days had passed. This giving scavengers plenty of time to eat before showing signs of delayed mortality to the average person on the lake.

A study on muskie specifically compared caught to un-caught muskie and found that caught muskie had a mortality rate of 32% compared to 9% for uncaught in the same period. This study utilized angling best practices and an out of water horizontal hold to further match the stressors a caught fish would go through in the wild. The catch and release mortality was 32% overall but spiked to 44% when looking at fish caught in water >25 C (77 F), and only 14% in water 19-25C (66-77 F). Fish during this same time period which were not caught had an observed mortality at 9.4%. Aside from this the most important note from the study is that fish kept in nets for 60 seconds before release was observed at 11% and reached 72% if the fish was in the net for 5 minutes. Keep in mind this is in the net in the water. For the experienced angler this is an easy feat to release a fish that quickly but for those that are unprepared it becomes much more difficult. The study also notes that there was only one gill hooked fish in the study and so poorly hooked fish or fish hooked in bad locations would only increase the disparity between caught and un-caught morality.

So, what does this all mean?

The studies discussed above clearly show the impact that simply catching fish have on their survival. Just catching a musky (and using best practices) increased its chances of mortality by almost 4 times compared to environmental stressors! As an avid angler these numbers seem very high and are concerning to read about. Fortunately, through the use of proper gear, fish care, and handling techniques the impact of delayed mortality can be reduced considerably and it is up to all anglers (beginner or new) to promote these practices for the health of our fisheries. Does a vertical hold mean that the fish is going to die? There is no data to support this currently; But, those that perform vertical holds are also likely those that are unaware of general good practices or take more time to release the fish which can lead to a significant increase in delayed mortality potential as outlined in the studies.

Long story short; it's important to take care of our fish and to teach other anglers how they can do the same. Should anglers be shamed for doing a wrong hold? No. Does this kill the fish? There isn't specific data on this but even doing everything right according to current best practices there is still a good chance at killing it. Given vertical holds only add to the potential for injury of the fish we recommend not doing it whenever possible.

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