Guest Writer Duncan Philpott shares his "deep dive" investigation of mouse fishing for brown trout.
What's the fuss about mouse fishing for brown trout?
People travel from all over the world to fish in New Zealand. It is easy to be excited about the gin-clear water, trophy trout and grand sense of adventure, yet there is one aspect of the fishing that even stirs the locals up into a frenzy...
Every few years the two islands in the South Pacific experience an angling phenomenon that blows your casual mayfly hatch right out of the water. Mice, in their thousands, take to the waterways and the ever opportunistic trout key in on them and feed, providing anglers with gripping, top-water, big-fly action!
I'm not on the menu, am I...?
Mouse fishing on different waters
Before we get into understanding the mouse "hatch" in more detail - let's see what this adrenalin-rush fishing looks like. The two main water-types to target are rivers and lakes...
Lake fishing for big "mouse-eating" New Zealand brown trout
Fishing tactics vary from stillwater to the river but one thing remains the same, you’re going to have the most success fishing at night. Proper precautions must be taken since fishing in the complete darkness complicates movement and presentation greatly! Check out this great overview in this video by the Manic Tackle Project (warning: contains stomach-contents footage!):
Lake fishing tactics:
In general, success can be had at any time of day but takes increase as the light level decreases. In a lake trout will patrol the margins looking for mice that have ventured in, torchlight can put trout off the feed so care must be taken.
Casts should be made out and along the margins.
Retrieve with moderate to slow retrieval speeds - mice don’t rival Michael Phelps when it comes to front crawl.
Calm weather can help trout detect the movement of your fly more easily. It is important to adopt strip setting (strip-strikes) since trout have been observed to slash at mice to drown them before eating them.
A normal trout hook-set, where you raise the rod, will remove your fly from hot-zone. That stops you benefiting from the highly likely repeat hits as the trout comes back to finish its meal.
Mouse fishing for brown trout on RIVERS
Leave it to BBC Earth to capture the thrill of the chase on a NZ river:
Stop Press: leave it to Mike Kirkpatrick to create a killer new "Mousing" Movie:
Mike's Movie "Insight" is available to rent or buy on the following link:
https://vimeo.com/ondemand/insightthetrophyquest/452682480
Note, we don't have any financial incentive arrangement with Mike or this film - it's just a perfect fit for this article.
Now, onto flowing water tactics...
River Fishing Tactics
Observations in New Zealand have yielded trout feeding on mice in the rapid, steep, beech tree-lined, headwaters of NZ rivers. In these circumstances, presenting a “drowned” rodent into plunge pool or pocket could prove productive (albeit a challenge in the darker hours!)
Casts can be made to the nearside bank, downstream and retrieved along the bank, or to the far bank and swung across the current.
Casting to features where mice may fall into the river or use as a crossing point also increases the chance of a take.
Rigging to go mouse fishing for brown trout
Tackle set up is nothing too out of the ordinary for chasing big browns. A 9ft 6wt rod loaded with a short-head, floating, fly line and short leader of 2x to help turn over the bulky mouse patterns. Trout aren’t particularly leader shy at night.
For a leader to fly knot a non-slip loop knot works well with broad monofilament and allows plenty of movement in the fly.
Here's a demonstration of how to use a perfection loop for this purpose by Orvis:
"Fly" Patterns for Mousing
The patterns themselves vary from size 1 to 6 hooks and a range of natural and synthetic materials. As long as it floats, creates a small wake and roughly satisfies the prey image it will draw plenty of attention.
Making the fly out of materials that will easily crush flat when eaten can really help to increase hook-up rates. More dense/rigid dressings can "bounce" out of the mouth when hit by a trout...
For the angler's benefit, using glow in the dark materials/indicators can aid with the challenges of fishing in complete darkness.
Here are some crushable examples:
The "Mickey" Mouse tied by Hans Stephenson at Dakota Angler & Outfitter
The "Trap Mouse" by Kyle Glass (Tying on Kast Gear Channel)
Understanding the Mouse Hatch in Detail
This phenomenon isn’t a random chance event, it is all due to the beech tree masting. Beech trees cover nearly a quarter of the total NZ landmass, approximately 6 million hectares, and while some of the trees flower and drop seeds every year, it is every 2-6 years that a masting occurs.
This is when all the beech trees produce seeds at a staggering rate with densities of up to 12,000 seeds per square metre recorded. Scientific research suggests that this happens when one summer is warmer than its preceding summer, this will then prime the beech trees to mast the following summer.
Beech masts on the ground. Photo: Jin Zan (CC by 3.0)
This abundance of seeds leads to a boom in insect life and this combined food source of seeds as well as insects lead to a plague of the non-native mouse.
How does this translate into "trout food"?
With abundant food for the mice, their populations explode. But how do they end up in the water as vulnerable pretty for trout? There are a couple of schools of thought...
One angle is that as more and more mice are born these mice become more competitive for the food and this can lead to the mice, which aren’t averse to swimming, to travel across the water in search of further food.
Secondly, the more mice there are, then the greater chance a mouse will accidentally end up in the water.
Trout are opportunistic feeders and some of them will key into this abundant food resource.
Not all trout do so though...
This is potentially due to the risk of wasted energy trying to change feeding habits from their normal productive food source.
It may also result from the few trout that DO key into the mice feed so prolifically that it prevents other trout from having the opportunity to recognise the new meal (not enough mice escape the few "locked in" trout)
Trout growth rate during mouse plagues
To give an idea of how prolific these trout can be, one trout, caught in the Nelson Lakes region was found to have 23 mice in its stomach!
The rate of growth of these trout can be astonishing. Mouse feeding trout caught often have stomachs and backs too big for their head (which hasn’t been able to keep up with the rapid weight gain). With a single protein-rich meal providing more nutrition than feeding repeatedly on nymphs or terrestrials, trout enjoy having to feed less often and expend less energy overall.
Simple biology of night fishing for "mousing" trout
Mice are most active at night and this coincides with confident feeding windows of big trout. Trout have been observed in lakes remaining dormant throughout the day while they digest their midnight feast of furry friends. These fish can double their weight in just a couple of months.
So if you’re in the hunt for a trophy brown then fishing mouse patterns, at night, during a plague of mice could be a good bet...
Other locations to try mouse fishing for brown trout (and other species?)
These tactics aren’t limited to New Zealand, in Alaska using mouse patterns is somewhat commonplace compared to the rest of the world. There are multiple times a year where “mousing” as they refer to it can be productive. These include high early-season flows where spate water can catch out unsuspecting rodents, as well as late-season when mouse activity increases and fish are wishing to gain winter weight.
In fact, as well as beech-masting, anywhere that there are grain crops next to rivers - there will be mice. There's a good chance that enough of those rodents end up in the water for trout to target them at times...
For the adventurous, the wilds of Russia (e.g. Kamchatka) have yielded excellent results for the fly fishing tourist too. While 2020 is forecast to be a monumental mast season, global travel isn’t the most certain topic right now...
However, these methods can be equally tried on your urban waterway close to home where Pike, Perch and Chub are known to take topwater presentations. Just make sure to include a wire trace if pike are on the cards - and don't be afraid to experiment. You might even find it productive to "level up" to rat-fishing for pike...
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