The Eastern Hemlock: Guardian of Brook Trout

If you've ever walked or fly fished along a New England trout stream, you've probably noticed the dense shade of some large evergreen trees along the banks. At first glance, they look like spruce or fir, but those species generally grow only at high altitudes. These special trees, guardians of trout streams, are Eastern Hemlocks.

A hemlock-lined stream in western Massachusetts

Hemlocks prefer areas that are cool, shady, and moist, conditions met perfectly in the ravines formed by many small trout streams. Here the hemlocks grow, slowly but surely, for hundreds of years, ultimately reaching over 100 feet in the air with trunks over 5 feet in diameter. The dense needles of these mature trees provides shade year round - even on the brightest days it's surprisingly dark in a hemlock grove. This shade shields our trout streams from the warmth of the sun, helping to prevent temperatures from rising to levels lethal to brook trout.

Range of Eastern Hemlock

Unfortunately, hemlocks are currently under threat. The hemlock wooly adelgid is a parasitic insect species native to Japan. While its name may conjure up images of prehistoric beasts, it is formidable in its own right. It attaches to the base of a hemlock needle, then slowly robs the tree of its sap, ultimately leading to death. If you turn over a hemlock branch in Massachusetts, you're likely to see an adelgid on nearly every needle.

The adelgids are the puffy white balls on each needle

As of right now, the most significant threat the adelgid poses is to hemlocks in the Southern Appalachians. Because it's native to a relatively moderate maritime climate in Japan, it can't survive extreme cold, so it hasn't spread much farther north than southern New England...yet. As the climate grows warmer, the adelgid will likely be able to spread northward. I've never seen any in the White mountains, but it's all over the hemlocks in my town near the MA/NH border. The cold winter of 2014/15 probably reduced the population to some degree, but this past winter was too warm to do much damage, so they could be farther north than ever before.

A brook trout caught in shade of hemlocks

Fortunately, there is some hope. A study in the southern Appalachians found that while the death of hemlocks greatly increased the amount of light falling on headwater streams, temperatures in these streams were correlated more with proximity to groundwater sources than light levels (Study Here - it's behind a paywall, but the conclusions are in the abstract). That means the brook trout should be able to survive, but as the climate continues to warm every little bit of shade could make a difference. The adelgid has also been subject to intensive research in recent years, and new control methods, including introduction of predatory beetles and application of pesticides, have shown some promise in reducing the population.

While it looks like trout will make it through regardless of what happens to the hemlock, I hope at least some hemlocks will survive. Even if the trout don't need the shade, there's nothing quite like fishing in a hemlock-forested ravine.

Geology and the Trout Stream

The other day I was talking with Will from Flies, Fat Tires, and Family about a small wild trout stream we both fish. We both noticed that the fish there are bigger and more numerous than in similar streams, and Will mentioned that a friend from the MA Division of Fisheries and Wildlife told him electroshocking confirmed these observations.

A nice brook trout from the stream in question

A quick look at the Massachusetts Coldwater Fishery Resource List will tell you that there are a lot of wild trout streams in Massachusetts - over 1,200, in fact. But not all 1,200 have fish like the stream Will and I like. You might think that the best streams are those with the most pristine watersheds, but that isn't always true. This stream is fairly close to Boston, yet it is far more productive than several streams I've fished further west.

So why is this stream so much better? The answer is, at least in part, geology.

Bedrock and Acid Rain

Bedrock is the layer of rock that lies underneath soil, sand, and other deposits on the surface. If you've explored the White Mountains of New Hampshire, you've probably seen the granite bedrock jutting out from the thin mountain soil.

So how does bedrock affect a trout stream? Groundwater, which contributes a significant portion of the flow of most wild trout streams, flows over and through bedrock on its way to the stream. As it flows, it dissolves some of the rock, changing the chemical content of the water. For trout, the most important consequence of this chemical change is acidity.

Different trout species have different tolerances to acidity, with Brook Trout being the most tolerant and Rainbow Trout the least. But the direct effects of acidity on the trout are not the most significant influence on productivity, rather it is the effects on their food supply that translate to the quality of the stream. Most aquatic insects prefer water in the neutral to slightly basic range (pH ~7-8), and crustaceans, such as scuds and sowbugs, require basic conditions to prevent their shells from dissolving. This means that all other things being equal, a more basic trout stream will have more food, and therefore more/bigger trout than an acidic stream.

Precipitation is naturally mildly acidic (pH < 7), but in areas with significant industrial pollution (basically all of the Northeast and Great Lakes) it can be significantly worse. As this precipitation flows into the ground, the acid is neutralized by basic ions dissolved from the rock. The only problem is, when it comes to neutralizing acid, not all rocks are created equal.

Granite, which makes up most of the bedrock in New England, has very little capacity to buffer acid, so our streams tend to be more acidic, and therefore less fertile. The White Mountains are a perfect example - the fish are small and almost all wild fish are brook trout, rather than the less acid-tolerant browns and rainbows. A good counter-example would be the streams of the Driftless area of Wisconsin or the spring creeks of Pennsylvania - the bedrock there is limestone, which has an exceptionally high buffering capacity. This results in highly fertile streams with tons of insects and trout populations exceeding 10,000 fish per mile.

Applying Geology to find a Productive Trout Stream

There are many other types of bedrock besides granite and limestone, each with a different degree of buffering capacity. It can be a little difficult to figure out how a given type of bedrock will influence acidity, so the best things to look for are actual measurements of pH from the stream of interest.

For Massachusetts, a great source of data is the Acid Rain Monitoring Project run by UMass. They have pH data for most streams in the state dating back several decades.

When you look at the data, keep in mind the date of the measurement - nearly every stream will be relatively acidic in late winter and early spring when the snow is melting. Generally, streams with good buffering capacity will run between 6.5 and 8 in summer and fall. If a stream is lower than 6.5 in summer, it's probably somewhat sterile.

If you can't find any pH data for a stream, take a look at a Bedrock Geology map and identify the type of bedrock underlying the stream. Try a Google search for "X bedrock buffering capacity" or "X bedrock acidity". There are an unbelievable number of categories and subcategories of bedrock, so you might not get a definitive answer short of asking a Geologist.

For Massachusetts, the three main types of bedrock with good buffering capacity are Carbonate Rocks (royal blue on the map below), Calcpelite (sky blue), and Calcgranofels (lavender). Find a stream in one of these areas, and the fishing is likely to be pretty good.

Bedrock Geology of Massachusetts - from MA OLIVER

Conclusion

Keep in mind that there are many factors that influence the productivity of a trout stream. A stream flowing over limestone will generally be better than a stream flowing over granite, but there's more to trout fishing than productivity. If granite streams were never fun, no one would fish in the White Mountains, but obviously that's not the case. So as you explore new trout streams this spring, consider geology - just don't forget to consider everything else that makes for a great day on the water!

See also: Aquifers: Saviors of Suburban Trout Streams

Speed Up or Slow Down?: Some Thoughts on Fishing Speed

One element of fly fishing I've always found difficult is determining the amount of time to spend before moving to a new spot. Sometimes I feel I'm going too fast, while other times I feel I'm going too slow. Over time I've noted of some of the fishing situations that lead to those feelings in attempt to improve my approach in the future.

Trout

Trout are the fish I target most often, so let's begin with trout fishing.

When to Speed Up 

A stream fit for fast fishing

I've found it important to move fast when fishing small, high-gradient streams. The food supply in these streams tends to be the limiting factor in trout density. Because trout densities are low, each pool will likely have only one or two trout, and fish will tend to be in the best habitat - deep pools, undercut banks, and other areas with a lot of cover. This means you should fish faster, as trout will tend to be spread out. Skip over the less desirable habitat and head straight to the nice pools.

Once you get to the fish, another reason to speed up becomes apparent. Again due to the low food supply in these streams, fish are typically eager to strike a fly. If you make more than a couple casts to an area without a strike, the trout there are probably either spooked or not present at all.

I made the mistake of moving too slow when I started fishing small streams - I would try to get a perfect drift in every likely-looking part of the stream, but the few fish I caught were almost always on one of my first few casts. I soon realized that the fish in these streams didn't care if I got a perfect drift. I started moving quickly and subsequently started catching a lot more fish. The one thing to be careful of when moving fast is not to let the fish see you. Luckily, most streams where moving fast is helpful are high gradient enough that trout can't easily see what is going on around them.

When to Slow Down

A stream fit for slow fishing

On larger, lower gradient streams, I've found that slowing down is often a good idea. These streams tend to be more productive, so trout densities are much higher. The trout also become more selective, as they have more foods to choose from and don't have to eat everything they see to survive.

This means that trout will care a lot more about drift and fly selection, so it's worth staying in a spot for longer, especially if you're confident there are fish there. The trout in these streams can also see you a lot better in the flat water, so it's important to move slowly so as to not spook them. Lastly, low gradient streams tend to have a lot of sediment, so quick movement could ruin the fishing downstream.

When I fish in the Driftless I have to remind myself to slow down. I always catch more fish when i slow down, but it can be hard for me to get over my urge to move faster.

Bass

Bass tend to be solitary and bite relatively quickly if they are interested, so they should be fished similarly to small streams. Because most bass lakes are hard to access from shore, a boat is ideal to quickly move between spots.

Panfish

Panfish, on the other hand, usually live in schools, so I usually try to find the best spot and stay there. I'll move if I get bored and want to explore, but otherwise I'll typically stay in one spot.

Aquifers: Saviors of Suburban Trout Streams

What are Aquifers?

Aquifers are large pools of groundwater close to the surface. The temperature of this groundwater is roughly equal to the mean annual air temperature and changes little over the course of the year. Most of the wild trout in Eastern and Central Massachusetts rely on these groundwater inputs to survive.

Unfortunately, suburbanization is a major threat to trout streams. Impervious surfaces like lawns and paved areas cause warm rainwater to run directly into streams, rather than soaking into the ground where it can cool down. This can raise water temperatures to levels lethal for trout. Luckily, many of our wild trout streams flow over aquifers, which contribute enough cold groundwater to buffer the effects of runoff. The springs also have the added bonus of keeping temperatures slightly warmer in the winter. I find that the spring-influenced suburban streams fish better in the winter than the more pristine streams in the western part of the state.

Lots of impervious surfaces = no wild trout in my town

How to Find Spring-influenced Streams

As usual, MA OLIVER is a great resource. It provides a map layer called "Aquifers by Yield Green Shades", which is in the "Aquifers" folder, which itself is in the "Physical Resources" folder. This map is pretty self explanatory - green shaded areas are aquifers, with darker shades of green representing those with a higher yield (more water).

You can combine this with the Coldwater Fisheries layer (also in the "Physical Resources" folder) to see which trout streams flow through aquifers. You'll notice that many of the remaining coldwater fisheries in Eastern MA pass through aquifers.

There are also smaller aquifers that aren't listed on the map. Look for areas with large sand and gravel deposits. These are common in large river valleys, especially those, such as the Nashua and Connecticut valleys, that were previously covered by glacial lakes. Groundwater can easily flow between sand and gravel particles, so these areas tend to have springs where streams pass through.

Another tell-tale sign of spring-influence is a small watershed. While freestone streams depend entirely on water that falls as precipitation within the watershed, spring-fed streams are composed of both ground and surface water. This means that a spring fed stream can have the same volume of water in a much smaller watershed. If you see a decent-sized, perennial stream with a small watershed, it's likely it has springs.

A spring given away by melted snow

You can also look for springs as you are fishing. In the winter look for areas where significant amounts of snow have melted. You'll also sometimes see green vegetation in the water near springs long after other plants have died off. Sometimes you can see water seeping into the stream from the bank - this is especially common in areas where a stream cuts into a steep hillside. My theory is that the water table is slightly higher in the hill, and the erosion from the stream allows some of that water to "leak" out into the stream. Individual springs are good spots to fish in the winter, when fish will seek out the warmer water, but leave them alone when water temperatures get dangerously warm - trout will seek these spots as thermal refugia.

Green plants in a spring during winter

The spring from the above picture is in the bottom right corner of this picture - note the melted snow

How to be a Wild Trout Detective: Part I

Finding wild trout streams can be difficult. Anglers are notoriously tight-lipped about their favorite spots, so you won't find much first-hand fishing information available online. Most of the time you just have to get out and explore. Fortunately, there is plenty of publicly available data that can help you find the most promising streams before hitting the road.

Tools of the Trade:

Here are the programs/websites I use frequently to find trout:

Caltopo: This is a mapping with topographic maps covering the entirety of the US. It's especially convenient because you can overlay different map types with the menu in the top right corner of the screen. I usually use Google Hybrid as a base layer with USGS 7.5' Topos on top. You can also save maps marking stream locations to your Google account.

Google Maps: Although Caltopo can display Google Maps imagery, it has a less refined search feature, so Google Maps is still convenient for finding streams by name. Street View can also be useful in locating access points. 

Bing Maps: Bing Maps has a birdseye view that provides a more detailed look at the surroundings of  a stream than satellite imagery.

MA OLIVER: This site displays public GIS data on an interactive map. OLIVER is MA-specific, but I think some other states have similar sites. Search for "(insert state here) GIS" and see what you can find. If not, the useful GIS data is likely available in other, albeit less convenient, forms.

USGS Water Data: Few trout streams have USGS gauges, but those that do can be helpful in determining the size/temperature of nearby streams.

Fish Surveys: This data can be a bit difficult to locate, but it is probably the most useful. After all, there's no better way to determine a stream has trout than to look at electroshocking data. In MA this is available in the form of Water Quality Assessments. I'm not sure where to find this data for other states, but a google search for "(insert state) fish surveys" or "(insert state) electroshocking" should turn up some results.

Water Chemistry Data: I usually check water chemistry data last. Good water chemistry doesn't guarantee a stream will have trout, but it's useful to determine stream productivity after confirming trout presence. For MA I use the UMass Acid Rain Monitoring Project. As with fish surveys, this data is likely available in some form for other states, but it will take some research to find it.

Getting Started

So we know that there's tons of data available to help find wild trout.

Now what?

I like to divide my search into two phases: Stream Identification and Quality Determination.

Stream Identification

This is exactly what it sounds like: identifying streams that contain wild trout. My first step is to Google "(insert state) wild trout". Many state Fish and Game agencies document wild trout streams publicly, especially in states with relatively few streams. Even if there is no official information, this search will often lead you to news about wild trout. Oftentimes local newspapers will write public-interest pieces when TU and/or other conservation groups do work on trout streams.

If a Google search is unproductive, check out WildTroutStreams. They compile publicly available info on trout for all states with wild trout populations. For some states this means a list of streams; for others, like MA, it will lead you to fish surveys. Regardless of the detail of available info, it should point you in the right direction.

After a simple search and a look at WildTroutStreams, it's time to flex your "Google-Fu". Many people don't know about Google's advanced search functions. Here is a good summary sheet of the features - though you don't need to use all of these. You can use these search features both to find new streams and to learn more about wild trout streams you've already identified.

The feature I use most frequently is quotation marks to search for an exact word or phrase. For example:

wild trout 

Will get a lot of results that just happen to have both "wild" and "trout" on the same page.

"wild trout"

Will only get results where the two words were mentioned together.

Another useful search feature is the specific site search.

If you insert:

site:www.inserthere.com 

into your search, you will only get results from www.inserthere.com.

Putting these features together makes Google a powerful tool. Say you come across a blog or forum where people occasionally mention wild trout streams in your area. Rather than reading through post by post, you can search:

site:www.someflyfishingblog.com "wild trout" massachusetts

This will allow you to quickly scan through all the posts relevant to wild trout in MA.

Keep in mind that while advanced Google searches are useful in initial Stream Identification, they are not limited to this role. These search techniques will come in handy in future sections of this guide.

Stream Documentation

As you identify more and more streams, it can get tough to keep track of them all. Once you've accumulated a few potential streams, it's useful to compile a list in one place. I prefer to use a mapping program, as it allows me to see the distance between streams and the distance from home.

I use CalTopo. As I mentioned above, this site is great for displaying multiple map layers, but here we I'll focus on markers. First, you need an account. I linked mine to my Google account, but you can also link to a Yahoo account. 

Here's an overview of Caltopo:

Once you're logged in and familiarized with the use of CalTopo, you can start marking streams. The easiest way is to right click on the spot you wish to mark, then select "New" and then "Marker". You should see a window like this:

Here you can name your marker, add comments (I usually put down what species I know/think are there and why I think it should have good fishing), and change the marker style/color if you wish. I usually stick to the dot markers, but sometimes I change the color to indicate different species.

It won't be long before your map looks like this:

End of Part I.

Part II coming soon!

Weather and Trout

Most anglers agree that weather has an impact on trout fishing, What they tend not to agree on is how weather impacts trout fishing. Weather is complex and difficult to predict, as is trout behavior, but I’ll try to be as scientific as possible in this post.

Water Temperature

Water temperature is likely the most important environmental influence on trout behavior. For a good description of the ways water temperature affects trout, check out this blog post: Link, but for this discussion all you need to know is that trout feed most actively between 40-65 F and begin to suffer potentially lethal stress at 70 F.

So, how does weather affect water temperature?

Several factors come into play. The first, and most obvious, is air temperature. Air that is warmer than the water will warm it and air that is colder than the water will cool it. But air temperature is not the most important factor.

The transfer of heat between air and water is slow and can only take place at the waters surface. Sunlight plays a larger role in warming the water in streams, as it directly warms the water and stream bottom. This is why shade is vital to keep water temperatures below lethal levels in trout streams in warmer climates.

When planning a outing, it’s important to pay attention to both air temperature and sunlight. In winter, when water temperatures are cold, a sunny day can give trout the boost they need to feed. Daytime air temperature is less important than sun in winter, but it can pay to check the low temperature for the day before. Although warmer high temperatures are generally better for fishing, a cold night can cool the stream enough to negate the effects of the daytime temperature. For example, a day with a high of 32 following a nightly low of 30 will probably be more productive than a day with a high of 40 and a low of 20.

In the summer the sun can raise temperatures to dangerous levels, so poorly shaded streams should be avoided on sunny days, or at least at midday. High air temperatures can also cause temperature problems, but this is likely unless the day is unseasonably warm.

Feeding Activity

Different weather conditions can lead to wildly different feeding patterns in trout. For this discussion, I’ll consider three general conditions: Sunny, Overcast, and Rainy.

Sunny Days

The brighter the day, the more visible everything is. This means that both trout and their food sources are at higher risk of predation and are therefore less active. It also lets trout see your flies, line, and shadows more easily, increasing the risk of spooking a fish. That’s not to say it’s impossible to catch fish on a sunny day. Focus on riffled areas, where trout are less visible from above, and you’ll likely find fish.

Overcast Days

Overcast days are ideal for fishing. Trout are more active, and many insects are more likely to hatch. You also won’t cast a shadow, so the risk of spooking fish is much lower. The only exception is in winter, when water temperatures are often too low on cloudy days.

Rainy Days

If you can stand being outside, rainy days are even better than overcast days. All of the advantages of overcast days still apply, and the rain adds further benefits. Rain breaks up the surface of the water, making it more difficult for the fish to see you. This is great on flat spring creeks where fish usually won’t let you get close enough to cast without spooking. Rain also washes terrestrials into the stream, which results in active fish. The only potential downside of rain is that it can raise water levels to unfishable levels.

The last element of weather to which I pay attention is wind. It can be a bit of a wildcard. Although wind can break up the surface of the water and blow terrestrials into the water, it also makes casting difficult. Personally, I feel the negatives outweigh the positives on days with wind over 10 mph, but his is my last consideration.

Hopefully this helps in planning future trips!

An Underrated "Hatch"

Photo Credit : D. Garding

I first discovered the importance of inchworms in trout fishing last May. I was fishing a sea-run brook trout stream where the trout take streamers almost exclusively. On this particular day, however, I didn’t get a single strike on my go-to brookie streamer, the Mickey Finn. I decided to try a black wooly bugger instead.

I cast the wooly bugger into a pool and it was met with a sudden rise.

Too sudden.

The Wooly Bugger’s magic lies in the lifelike motion of its marabou tail. But this fish struck long before it would have had time to see any motion in the tail. I got the fish in, still confused as to why the trout struck so quickly, but happy to catch a fish. After all, it doesn’t matter to me why a fish strikes.

When I looked into its mouth to remove the fly, it immediately became clear why the trout struck on the surface. Three bright green inchworms were lodged in its throat.

Photo Credit: David Illig

For the next two weeks I paid close attention to inch worms every time I fished. I noticed a few characteristics that make inchworms good flies to try:

Where there’s one, there are many

Inchworms are the caterpillars of Geometer Moths, a widely distributed family containing over 35,000 species. These caterpillars congregate on their preferred tree species, so you’ll typically find many individuals in a small area.

They’re clumsy

Inchworms often fall out of trees. When they fall, they suspend themselves on a thin piece of silk, but they don’t seem to have the strength to pull themselves back up. This means you will often see an inch worm drop slowly towards the surface of the water from an overhanging branch. The fish can see this too, so they have plenty of time to set up below the falling worm and wait for it to hit the water. I’ve even seen a bluegill clear the water to grab an inchworm that hadn’t yet hit the surface.

They float

Inch worms float high on the surface, and I’ve never seen one drift long enough to sink without being eaten. Everyone likes fishing dries, and with inch worms active in the middle of the day, there is a rare opportunity for midday dry fly fishing.

For some reason, inchworm flies are not common. Maybe its because they’re considered “Junk Flies” like eggs and San Juan worms, or maybe people just don’t realize trout eat them. Whatever the reason, a lot of people are missing out. My black wooly bugger worked, but it isn’t the best imitation and likely wouldn’t work on selective fish. After that outing I bought some greenie weenies, and they worked, but they don’t float and most fish were taking worms from the surface. If any fly-tiers want to come up with their own pattern, I think a floating foam fly would work perfectly.

Last year the inchworms were peaking in MA in mid-may, but this year’s long winter might push that back a few weeks. Be on the lookout for these little green guys this spring and you might find a great day of fishing!