Science Friday: How does catch and release affect steelhead?

Written by Nick Chambers

Today we review a study on the impacts of catch and release angling on wild steelhead in the Bulkley River, the largest tributary to British Columbia’s legendary Skeena system. Conducted by Will Twardek and several others, this study looked into the effects of catch and release, air exposure and fight time on behavior and survival to spawning.

The study took place during the fall of 2016. Anglers landed 129 steelhead using a variety of methods, including swung flies, spinners and rubber worms using fly, spin and centerpin rods. Of these, 92 fish were caught on fly rods while 23 were caught on spin and centerpin methods. Once a fish was hooked researchers would time the duration of the fight, note the landing method (tailing vs. netting), hooking location, how difficult the hook was to remove, and water temperature.

Of the 129 wild steelhead caught, a subset of 45 fish were also evaluated to understand the effects of air exposure on blood chemistry and responsiveness. Immediately upon capture these fish were exposed to air for either 0, 10 or 30 seconds. A blood sample was then taken to measure peak lactate, elevated glucose levels and pH. The measurements taken from fish caught by anglers were then compared against a baseline of blood chemistry measurements taken from fish at a trap downstream of the study area. The fish in the trap were exposed to minimal handling and were not subject to the physical effects of a fight so their blood chemistry was assumed to be that of a rested fish.

An additional method the researchers used to determine the level of exhaustion from the fight was to time the fish’s ability to turn itself right side up when flipped over. Salmonids have a natural reflex to right themselves and the researchers timed the righting reflex of angled fish, using a cutoff of 3 seconds to determine if the reflex was impaired.

What did they find? Some interesting results.

First, fish that had been exposed to air for either 10 or 30 seconds had a significantly slower righting reflex than fish that had not been air exposed at all. Surprisingly, none of the other variables the authors measured had an effect on the righting reflex — including fight time or water temperature.

Furthermore, fish that failed to right themselves within the three second window had significantly more downstream movement after release than fish that were able to “pass” the righting test. This means that exposing fish to air after they are exhausted from a fight does impair their near-term recovery ability. Fortunately, however, after two weeks there was no significant difference in movement between air-exposed and non-air exposed groups.

Second, blood lactate and glucose levels were elevated in angled fish, but these factors did not seem to impact their behavior or survival. Steelhead swim long distances often passing waterfalls or other major barriers so they are probably well adapted to physical stresses and able to recover relatively quickly.

In other words, these guys could put Michael Phelps to shame. So it makes sense they can withstand short bursts of intensive exercise without significant long-term physiological effects.

Third, steelhead that were caught and then landed with a net had significantly lower blood glucose levels than fish that had been tail grabbed, yet there was no difference in relation to fight time. This means use of a net was not helpful because it reduced the length of the fight, but most likely because it reduced the stress in a struggling fish. Think of how difficult it can be to work a fish into knee-deep water and then tail it.

Lastly, water temperature at time of capture was positively correlated with blood lactate. Warmer water meant more lactate buildup, while the opposite relationship was observed with pH. This suggests that stress levels were actually lower when water temperatures were warmer.

Of course, the Bulkley does not see the high water temperatures that we deal with in many of our steelhead fisheries in the Northwest and this variable did not have a strong correlation with angling-related mortality as has been seen in other studies conducted in warmer water. Nonetheless, the relationship of catch and release mortality with high water temperatures has been well established and we should all pay heed when water temperatures approach or exceed 70ºF.

One of the biggest questions for many anglers — and for fisheries managers — is how many caught and released wild steelhead will survive and spawn. One unique aspect of this study addressed this question, by attaching radio telemetry tags to 68 fish from various air exposure groups. This allowed the researchers to track their movements through the spring spawning season to ascertain the long term survival of released steelhead.

In this study, 95.5% of tagged steelhead survived to 3 days and 94% survived to two weeks. This is consistent with the range of estimated catch and release mortalities at similar temperatures and with similar gear types from other studies. Over the long-term, there was a 10.5% overwinter mortality and an estimated pre-spawn mortality of 15%. Again, these numbers were consistent with previous studies in the Skeena system.

One should not infer from these results that 100% of the fish would survive to spawn in the absence of contact with sport anglers. The study focused on summer steelhead, which spend many months in freshwater and should have a higher natural freshwater mortality rate than their winter and spring returning counterparts (they have to survive otters, mink, and other predators, in addition to any natural disease or genetic issues that may arise). And, similar over winter mortality rates have been observed in other summer steelhead populations, so it can’t necessarily be correlated with angling. Just because an adult makes it into the river, and survives an encounter with anglers, does not necessarily mean it will survive to spawn.

This study shows that catch and release mortality on steelhead is pretty darn low when anglers use the types of gear employed in this study. However, it does have short-term effects on steelhead physiology. And the study’s results suggest that air exposure may elevate those short-term negative effects, even if exposed for relatively brief periods. Fortunately, those effects did not appear to be long-lasting (although air exposure has been implicated in reducing reproductive success in Atlantic Salmon; this study did not look into that specific impact).

The findings and implications of science often change as new studies are published. But the results of this study are largely consistent with those of other, similar studies — and the basic take-away for anglers is simple: reduce fight time and air exposure as much as possible. For anglers who really care about steelhead, there is no excuse anymore, if there ever was. When catch and release fishing, keep ‘em wet.

LINK (via: Wild Steelheaders United)