I have to admit, the title of this article really caught my attention, "Can smartphones kill Trout? Mortality of memorable-sized Bull Trout (Salvelinus confluentus) after photo-releases?" The paper comes from our neighbors to the North - well, and quite a bit West - Alberta, Canada.
If you are not familiar with Bull Trout, they are a char, a Salvelinus species like our native Brook Trout (S. fontinalis) and Lake Trout (S. namaycush). They are a fish that occurs West of the Continental Divide. Historically, they were considered to be Dolly Varden (S. malma) and have only been recognized as a separate species since 1980. In the United States, they are a threatened species and are a bit more secure in Canada but are generally not common anywhere. In large part, this is because they are predators with the ability to grow very large and few large predators are very common. They are well known for attacking Cutthroat Trout (Oncorhynchus clarkii) and other trout when attached to anglers' lines. Thus, they are the streamer angler's dream fish - about as close to muskie fishing as a trout stream will provide.
Back to the article...the abstract is a big attention grabber, among other things, the authors' write:
We found that handling time and air exposure of large bull trout subjected to photography and measurement was long (112 s) and associated post-release mortality was high (10 dead / 30fish; 33 % after 24 h observation). Immediate release mortality was also high (3 dead / 20 fish; 15 %).
I have to say that the 112 second (1 minute, 52 seconds) average handling time - NEARLY 2 MINUTES! - shocked me. Now, it was an experiment and they had a procedure to handle fish in what they thought was rather typical of how large fish get handled. Fish were photographed twice and then measured. That seems pretty reasonable to me and what a trophy - likely a once in a lifetime fish - experiences. But it was an experimental treatment and not necessarily indicative of how anglers handle trout. For example, anglers might be somewhat more observant and careful in handling fish compared to an experimental procedure. They might reduce handling time, not take the photograph or measurement when the fish is looking stressed. Or maybe not?
After reading the article, the mortalities were hardly surprising. Not only that, the minimum time that a trophy Bull Trout spend out of the water to be photographed was 75 seconds - 1 and a quarter minutes - and the maximum was nearly 3 minutes (162 seconds). While the mortalities were not unexpected, they were eye opening. Instant mortality of one-third is a huge number - and this is only after 1 day. Delayed mortality over the next couple of days would add to the 24 hour mortality which was 33%. I think that the most damning piece of evidence here is that 10 of the 30 (33%) fish that were photographed, measured, and released died prior to release whereas only 3 of the 30 (10%) fish that were immediately released died. In any case, large fishes are going to die at a higher rate because of the fight they put up - but they die at a much higher rate if they are handled after capture.
Figure 1 from the paper by Joubert et al. (2020) shows how much larger the fish from their study were MUCH larger than your average Bull Trout. And as it turned out, they died at a MUCH higher rate due to, umm, there is no polite way to put this, narcissism. The real "take home" messages from this study are twofold for me. First, mortality of large - PB, memorable, trophy, etc. - fish was extraordinarily high. Second, this is quite unsustaintable and I fear will have implications on closing catch and release fishing for rare fishes like Bull Trout.
Some mortality is unavoidable, however when mortality is much higher for the largest of fishes, that is a significant problem. Large Bull Trout died at much higher rates than did smaller trout which means that large fish - the rarest of the rare - are disproportionately affected. The "least expendable" of the fishes are killed at much higher rates - this is an issue.
I know you are thinking, "But I would never do this" - and I am not sure I agree, I think that good and informed anglers can and do things like this. I can't tell you how many times I have heard, "Well, it swam away just fine" - a very out of sight, out of mind statement. I say this because I know I have done it and had them swim away, or so I thought. The only fishermen that have not accidentally killed a fish are those that harvest everything they catch and those that have not not caught many fish. It happens to all of us, myself included. Fish get hooked in a bad spot - the eyes and brain in particular - or they swallow it deep and there is not much that can be done. It happens - I am not and will not argue that, but what I will argue is there is acceptable - by chance and bad luck - mortality and unacceptable mortality due to poor handling of fishes, particularly for our own vanity.
What I found most striking about this paper was the fact that mortality was disproportionately high for the largest and rarest of Bull Trout. In some ways, this is hardly surprising. That is, large fish are likely to experience greater stress from the fight which puts them in a weakened position. And they are more likely to experience greater handling - for revival but also photos and measurements. This, of course, has the potential to greatly affect a species that is rarely in high densities - like Bull Trout. With the effect being most significantly focused on the largest of fishes, typically those that contribute most significantly to the spawn, there is a possibility of a long-term effect. The authors write:
The combination of mortality from prolonged handling, immediate release, and illegal harvest is a cumulative C&R-related cryptic mortality that may have population-level effects in high-effort sport fisheries.
Being rather Wisconsin and Midwest-centric, my mind went to what the effects are here. Here in the Driftless, this unintended mortality is not an issue at the population level - at least not in most streams. Our streams tend to have high density populations and C&R mortality is typically compensatory, not additive. It is, of course, pretty significant to the individual fish and significant to the size structure of a stream if mortality is happening to our largest and rarest of trout. Maybe a more important comparison is to muskellunge, another low density, top predator. Certainly dedicated musky anglers are better at handling these fishes than is your average angler. And their low catchability makes it more difficult for anglers to have a population-level effect on their populations through catch and release mortality (Bauerlien et al. 2022). But I do have to assume there is some effect of catch and release mortality and poor fish handling in some musky fisheries.
Some other thoughts...A pretty significant note here is that the researchers measured handling time and not just time out of water, though they are certainly correlated. The lesson from this paper, I think, is that of "cryptic mortality" that is essentially unknowable for any specific fishery. Unknowns make it difficult for fisheries managers.
My Thoughts on the Fish Handling Debate
I certainly see both sides here. The "toughness" of trout is somewhere between the online crowd that thinks any fish out of water is a dead fish and the crowd that thinks every fish that swims away is "just fine". I fairly regularly cringe at some of the fish handling I see online - particularly fish placed on the ground or the snow, fingers in gills, or the old death grip. At the same time, the keyboard warriors rather coarse and terse online handling of the situation is certainly not helpful and probably counterproductive. It is always difficult to critique someone online without looking like an asshole - and based on what I have seen online, few have threaded that needle successfully.
Learning to handle fish takes some experiences and some giving a shit about the fish over your photo. The problem is that most fish "swim away just fine" and mortality is cryptic - you do not know if fish died after you released them. This means lessons are not easily learned for many anglers because they simply never see the effects of their poor fish handling. And few lessons are likely learned when other anglers berate poor fish handling online. The best is to hope that anglers are contentious and think about doing what they can to minimize handling time, particularly the time out of the water. I doubt it has much impact but maybe blog posts and social media posts will at make some anglers think about handling fish in ways that reduce mortality, particularly when that better than average fish comes along which is probably the place anglers can have the greatest effect. Or maybe not...
In the Driftless, a little extra catch and release mortality is not going to change the fishery in a notable way on most streams. However, if the effect is greater on the larger trout, trout we have some evidence are also more likely to be kept; C&R mortality could further affect size structure. So at least give it a bit of thought, plan ahead and keep a fish in the water, in a net and wet. If you must take a photo, plan ahead and get everything in place before taking the fish out of the water. I do think if we are going to catch and release trout, we owe it to them to treat them with respect and make all reasonable accommodations to increase the likelihood that the fish swims away.
The article was pretty eye opening in how we can can an effect on larger trout in a population and is, at the very least, worthy of some thought no matter what your view on "grin and grips" and fish handling may be.
Literature Cited
Bauerlien, C. J., Crane, D. P., Smith, S., Palmer, G., Young, T., Goetz, D. B., ... & Hartman, K. (2022). Low catchability limits the effect of warm-water catch-and-release mortality on muskellunge. Fisheries Research, 254, 106434.