Fish Mortality and Angling Methods – Fly Fishing Versus Spin Fishing
by Don Jellyman
Some time ago I inadvertently became involved in a spirited discussion about the merits of ﬂy ﬁshing versus spin ﬁshing. Fish Mortality and Angling Methods.
One of the most vocal claims of the ﬂy anglers was that spinning lures with treble hooks were much more damaging to ﬁsh than were ﬂies. Hence, undersized ﬁsh caught by spinning and then released would have a much higher mortality rate than would equivalent ﬂy-caught ﬁsh.
As I was in danger of becoming the meat-in-the-sandwich in the discussion, I professed my ignorance but determined to do some investigation. I have since collected eight North American scientiﬁc papers (1970-1986) on this and related topics and the following information is gleaned from those sources.
The concept of no-kill (catch and release) trout ﬁsheries is widely established in North America. It obviously works, as evidenced by the fact that in part of Yellowstone River, USA, cutthroat trout are caught an average of 9.7 times per year (see Freshwater Catch 32). Similarly, in parts of Colorado, 50-75% of all trout in catch and release areas have visible hooking scars. So, is one method of capture to be preferred over another?
Interestingly, the consensus in the ﬁve studies which dealt with hooking mortality was that there is no signiﬁcant difference between ﬁsh caught by ﬂy, lure (spinner), or worms – provided that the bait was not swallowed. Further, there are no differences between barbed and barbless ﬂies and single and treble hooks.
For example, from a sample of 570 cutthroat trout, mortalities by ﬁshing method within 10 days of capture were: barbed ﬂy 4.0%, barbless fly 3.3%, barbed treble 2.7%, barbless treble 6.0%, worm not swallowed 8.2%, worm swallowed 73.0%. controls (electric-ﬁshed) 4.8%. The obvious ‘misﬁt’ in these results is for swallowed worms.
A study of landlocked Atlantic salmon also gave a ﬁgure of 73% mortality within l4 days for deeply hooked ﬁsh; if the hook was removed only 10% survived, while if the trace was cut and the hook was left in, 43% survived. An analysis of hook penetration of treble hooks showed that 74% of all ﬁsh caught had only one hook penetrating, 22% had two hooks, and 4% had all three hooks. For the majority of ﬁsh caught then, a treble hook acts similarly to a single one.
Stress and Fish Mortality
Getting caught is obviously a stressful experience for ﬁsh. Biologists have investigated ‘stress’ in relation to ﬁsh size, spawning and non-spawning condition, water temperature, and the length of time the ﬁsh are played before landing. Stress has been variously measured as the mortality rate, or as physiological stress as seen in blood chemistry.
Overall, the results from these investigations are more variable than those from the hooking experiments, mainly because different degrees of exhaustion were induced. For example, two similar but separate studies on rainbow trout gave 87% and 7% mortality respectively.
However, various studies have shown the following:
- Physiological stress is greater in hatchery ﬁsh than in wild ﬁsh and is also greater in larger than in smaller ﬁsh. Up to three days are required for blood chemistry to equilibrate.
- Higher mortalities occur at higher temperatures.
- An experiment on playing time for cutthroat trout showed no differences in mortality for ﬁsh played for 5 minutes or 10 minutes. In another study on cutthroat trout, where ﬁsh were played until unable to maintain their normal attitude in the water, mortality over 30 days varied from 0-9% according to temperature.
- Reproductively mature cutthroat trout were found to be as equally resistant to hooking and handling as were non-mature ﬁsh.
Mortality also varies with species but comparisons between experiments are diﬁicult because of differences in technique. Two studies. however, included both brown and rainbow trout and in both studies the mortality rate for rainbows was several times greater than for browns.
So what does all this mean for the New Zealand angler?
There is no evidence that mortalities of spinner-caught ﬁsh are any greater than ﬂy-caught ﬁsh. Similarly, whether the hooks are barbed or barbless makes no difference. except that ﬁsh caught on barbless hooks could presumably be returned more quickly to the water. From the point of view of hooking mortality, there is no basis for reserving reaches of waterways as ‘ﬂy only’.
As rainbow trout are more vigorous ﬁghters than brown trout, the mortality of released rainbow trout will exceed that of browns, and increasing temperatures will accentuate this trend.
Deeply hooked ﬁsh, or ﬁsh which bleed profusely, especially from the gills, will almost invariably die if released.
Tips to reduce fish mortality
So angler, if you want to return that ﬁsh, don’t play it to complete exhaustion; make sure your hands are yet before handling it; hold ﬁrmly but don’t squeeze and don‘t hold it through the gills; return it gently and if it can’t maintain its own position hold its head into the current until it can if in a lake it may be necessary to ‘swim’ the ﬁsh by walking along with it, but don’t do it in the warm shallow margins.
Let’s not fool ourselves, wild trout have substantial recuperative powers and survive some horrendous injuries – eel and shag bites, missing eyes, misshapen jaws, deformed ﬁns, and so on. They also withstand the rigours of an environment which may change within hours from a gentle ﬂow to a raging ﬂood. Still, trout are not indestructible. The old gift-shop maxim comes to mind “handle with care”.
This article first appeared in Freshwater Catch, April 1988, No 35. At that time, Don Jellyman was a scientist with MAFFish at Christchurch.
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