Subtropical Mangroves

Mangrove Basics
An important characteristic that the subtropicsshares with the tropics is that mangroves are an essential coastal habitat.  Throughout their range, mangroves are found in similar conditions – along low energy shorelines.  Shorelines that are consistently exposed to high energy from waves are not suitable for these plants.  In the tropics, this means you will find mangroves in lagoons, on flats where the large expanse of shallows protects the mangroves from wave energy, along shorelines that are protected from waves by coral reefs, and in estuaries.  In the subtropics of south Florida, mangroves are most common in estuaries and lagoons, on the leeward side of barrier islands, and in Florida Bay, which is an expansive, low wave-energy, shallow area.

An observant angler will note that the prop-roots of red mangroves perform the same important ecological functions in south Florida as they do in the Caribbean (see Part 3 in the series for a list of some of these irreplaceable functions).  The ecological function of most interest to anglers is the important habitat provided for countless species of fish and invertebrates.  In that respect, the information on mangroves in the tropics in Part 3 of this series should be helpful to anglers in south Florida as well.  However, upon close inspection important differences become evident.

One of the primary differences is in the group of organisms that grow on the red mangrove prop-roots (known collectively as a ‘fouling community’) in the subtropics.  In south Florida, oysters are a dominant part of the fouling community.  Although oysters are also present on prop-roots in the tropics, a large suite of other organisms (such as sponges) compete for space on the mangrove prop-roots in the tropics, which contributes to the lower abundance of oysters.  With many of these other organisms absent in the subtropics, oysters create the complexity of the prop-root surface that provides habitat for numerous small invertebrate species.  These small invertebrates are prey for larger invertebrates and small fishes, which, in turn, are preyed upon by gamefish. 

As you pole your boat or wade along a mangrove shoreline in south Florida, you have a good chance of surprising a blue crab in the middle of making a meal of one of these oysters.  While most of these blue crabs are large adults, juvenile blue crabs can sometimes be found along mangrove shorelines, especially if there is seagrass adjacent to the mangroves.  Speckled trout, red drum, and snook will all eat blue crabs.  Although for the most part the blue crabs you will see along the mangroves are too large to imitate with a fly, casting a crab fly to gamefish you site along the mangroves is still a good strategy because a juvenile crab lost along the mangroves may be too good for a gamefish to pass up.  And if a 17" trout is willing to tackle a 5" blue crab for a meal (I've pulled crabs this size out of speckled trout stomachs), a smaller version must be like popcorn.

Another major difference in the subtropics is that black mangroves (Avicennia germinans) are more likely to be encountered along fishable shorelines in the subtropics than in the tropics, at least in my experience.  Red mangroves are generally found in areas covered by water much or all of the time because the prop-roots provide greater elevation.  Prop-roots allow much of the plant to grow above the water, so the red mangroves out-compete other plant species in areas covered by water.

Black mangroves are usually found on the inland side of the red mangroves – in shallower water closer to the high tide line.  Black mangroves can be found without red mangroves as well – usually along shallow, often muddy shorelines, such as the protected, murky backwaters and creeks of an estuary or lagoon.  Instead of prop-roots, black mangroves have pencil-sized aerial roots (pneumatophores) that stick up vertically from the mud bottom – black mangroves look like trees that have tens or hundreds of these stick-like pneumatophores surrounding the area around the plant base.  This strategy allows the black mangrove roots to obtain oxygen while living in sediment that is naturally hypoxic (low in oxygen) and full of sulfur (the rotten egg smell of marsh muds).

Although pneumatophores are very successful adaptations that allow black mangroves to thrive in these tough environments, they don’t escape being covered at high tide and can’t tolerate long-term submersion like the prop-roots of red mangroves.  This is why black mangroves are found one step inland from red mangroves or in backwaters with a relatively minor tide range.

Because black mangroves don’t have large prop-root structures like red mangroves, they provide a different type of habitat – smaller in scale and less complex than prop-roots.  In addition, since the aerial roots are near the high tide line and often only submerged for part of the tidal cycle, they provide only limited shelter to the small fishes found along these shorelines.  A section of deeper water adjacent to a black mangrove shoreline can be a good place to look for gamefish feeding on the small baitfish huddled along the muddy shoreline at low tide.

Gamefish will often feed along edges of black mangroves at low tide because the fish and many of the invertebrates that use the roots as shelter during high tide are often concentrated along edges during low tide.  Most often, the areas adjacent to black mangroves are open bottom – either muddy or sandy sediment – which don’t provide much shelter.  Numerous species of killifish (Family Cyprinodontidae), Sailfin Molly (Poecilia latipinna), Mosquitofish (Gambusia affinis), and mojarras (Family Gerreidae) are common along black mangrove shorelines.

The killifishes, Molly, and Gambusia are brassy to dark in color, generally blunt-nosed, and somewhat cigar-shaped, so dark streamers of two to three inches are good for imitating these species.  The mojarras are silvery and a bit higher bodied than the killifishes and mollies, so light-colored deceivers of 3" or so are good bets. 

During high tide, fish such as red drum will often venture into flooded black mangrove roots to search for fiddler crabs and other prey items that inhabit the mud of the black mangrove roots.  Fiddler crabs (Family Ocypodidae), are commonly found in these areas – they make their burrows in the sediment just above the low water line. 

They generally come out to feed during low tides, but there can be enough activity at high tide to attract red drum.  Although the enlarged claw is the most notable characteristic of fiddler crabs, only the males have this appendage.  Females do not have an oversized claw, so when tying flies to imitate fiddler crabs, I suggest you concentrate more on matching the color and size of fiddler crabs than on imitating the oversized claw. 

Temperature and Tides
So far this article has focused on the fixed aspects of mangrove shorelines – the plants that make up these habitats and the potential prey items that are almost always present.  For example, killifish, mollies, and fiddler crabs are year-long residents of mangroves.  I will now shift gears to touch on some of the seasonal variation in what you can expect to encounter in subtropical mangrove habitats.

The first thing you will notice is that there are wet (summer) and dry (winter) seasons in the subtropics.  During the dry season, there is less fresh water flowing down rivers into the estuaries, so the salinity (salt concentration) of the estuaries increases.  In some years, the salinity can be nearly the level of the open ocean far into the estuaries and river mouths.  In the wet season, the salinity in the rivers and estuaries drops as more freshwater flowing from rivers and creeks mixes with the salt water from the ocean.  Although most of the species you will find in mangrove habitats in the subtropics can tolerate a wide range of salinities, overall distributions of some of these species will change.  For example, during a dry winter period, red drum might be found much farther up into an estuary than you would normally find them in summer, or might be more abundant in areas where you might not normally find them.  For example, this past winter I found some rather large red drum near a river mouth at the head of an estuary (as far from the Gulf of Mexico they could be before entering the river) – and part of the reason these fish were exploring this area was because the salinity was 25 (normal ocean salinity is around 35).  During the summer wet season, the salinity in this area will drop to less than 10, and these large red drum will head to higher salinity waters. 

Snook spawn in summer, and in order to spawn successfully snook need salinities greater than 20.  As the amount of freshwater coming out of rivers increases during the summer wet season, larger mature snook will migrate to areas closer to open ocean to spawn.  This may cause a sudden decrease in the number of large snook you see along a mangrove shoreline near the head of an estuary as the wet season progresses, and an increase of large snook near ocean passes.

Red drum are also a great example of seasonal changes in habitat use.  Winter is probably the best time to fish for tailing red drum in the subtropics.  Red drum can be found tailing in seagrass during winter for several reasons.  The two most important reasons are: (1) on average, tides are generally lower so access to mangroves is more limited than in summer; and (2) in winter the water is cooler, with sun warming the water on the shallow flats.  Since red drum, like other fishes, are cold-blooded, the warmer waters of the shallow flats are more desirable for them in winter. 

During summer, the water warms considerably, and although red drum can be found feeding in grass beds, you will often find red drum feeding in mangrove habitats as well.  The high daytime tides of summer make it possible for red drum to use the shade of the mangroves to find cooler water, and allow them access farther back into the red mangrove prop-roots and even into the flooded roots of black mangroves. 

Paddling my canoe along a mangrove shoreline at high tide, I was hoping to find snook cruising the mangrove fringe.  I heard a soft splash way up in the mangrove forest – not the ‘slurp-POP’ of a feeding snook, but a much softer sound.  I heard the sound again and was able to figure a direction, so I poked the bow of the canoe into the mangroves to take a look.  As my eyes adjusted to the dim light of the mangrove forest, I turned my head as I heard the soft splashing again to see a red drum tail waving among the pneumatophores of black mangroves, likely feeding on fiddler crabs.

It was pretty much impossible to get a fly to these fish, but it’s worth exploring these areas to  find small openings in the mangroves (mini-coves) that are close to areas with flooded black mangroves, or close to a spot where you can see or hear a red drum feeding.  If you are lucky, you might be able to intercept the fish as it moves along the shoreline.  Or, if you find areas where red drum are feeding in the flooded black mangroves at high tide, casting into the shadows of the red mangroves as the tide drops may fool a red drum that is resting in the shade. 

Expect numerous break-offs with this fishing technique because hooked fish will often head into mangrove prop-roots and cut your line.  A heavy bite tippet is a good idea for these conditions.  I like a relatively short leader (7') with 12 lb class tippet, and a bimini twist to a 20 lb shock tippet. Weedless flies are a must in this situation because of the mangrove roots and branches.

My favorite fly for casting into the mangrove shadows for red drum is a small (size 2) red and white or red and grizzly Sea-ducer because the fly will sink very slowly, which keeps the fly in the strike zone longer with only twitches to give the fly motion. 

Mangrove edges are also great places to find snook and even spotted seatrout and crevalle jacks during summer.  I use two approaches to fishing red mangrove shorelines.  The standard approach is to wade or to pole a boat some distance from the mangroves and cast into the shadows.  ‘Some distance’ means as far way as you can comfortably cast.  It is important to stay away from the mangroves to remain unseen by the fish.  As before, a weedless fly is a must.  And if you don’t occasionally snag a mangrove branch then you aren’t casting close enough to the prop-root habitat.  For this approach I generally use streamer patterns.  Snook are ambush predators, which means they are sitting in the shadows of the mangroves waiting for an unsuspecting prey fish to swim by, or for a school of resident silversides to move within striking distance.  This ambush strategy, plus their body shape, are probably why some people call snook ‘saltwater pike’.  Red drum will also take advantage of an unsuspecting fish, and crevalle jacks will cruise the mangrove edges chasing just about any small fish they can find.

A second approach is to wade or pole close to the mangroves and look for fish either cruising or resting in the strip of open bottom that is often between the mangrove shoreline and seagrass bed.   Or in the open-bottom potholes if seagrass grows all the way to the mangroves.  It is important that you see the fish from a long way off because they are more wary since they are lying on exposed bottom.  A long cast and good, soft presentation are also helpful. 
Since there is virtually no chance for these gamefish to ambush smaller fish in these open areas, I generally don’t use streamers.  Instead, I use shrimp and crab patterns, or small to medium clousers bounced along the bottom.  Resting fish may seem like they are asleep, so it may take a few casts – each one closer than the last – to move the fish, either to strike or to move away. 

Conservation
As in all of our coastal environments, the connectivity of healthy habitats is essential to the success of gamefish populations.  (See Part 1 of the series for an overview of the importance of multiple habitats to fish as they grow.)  For example, juvenile tarpon and snook require shallow, protected, low salinity areas during at least the first year of life, but must be able to move to somewhat deeper areas with higher salinity as they grow.  Eventually, adults use the various habitats provided by estuaries and the coastal ocean, but even adults have specific habitat requirements.  A fish’s chances of survival are much greater if it can move from one habitat to another without having to negotiate large inhospitable areas.  This is especially true for the juvenile and sub-adult stages of the life cycle, which is when these fish are in habitats that are under the greatest threat.  In addition, the close proximity of different habitats allows more varied feeding opportunities for the fish as well as access to shelter.  Plus, a mix of habitats usually provides better fishing – a mangrove shoreline next to seagrass provides different fishing opportunities from mangroves adjacent to mud bottom, for example.

Unfortunately, coastal habitats are under increasing stress, and poor quality habitats are bad news to the fishes that depend on them.  Despite some changes in environmental laws, development continues to eradicate important coastal, wetland, and estuarine habitats.  In many areas, only small sections of mangroves remain where once the entire shoreline was a continuous stretch of undisturbed mangrove habitat.  In other areas, poor water quality from too much sediment or pollution, or too much or too little freshwater due to channelization, has eradicated the seagrass, leaving only open bottom, or has altered the communities associated with mangrove prop-roots.  In addition, juveniles of some species, such as red drum, snook, and kingfish (Menticirrhus saxatilis) – also in the drum family, can be found along shallow, black and red mangrove shorelines in brackish water, which are often dredged for additional boat access.  Often, these destructive forces act in tandem, resulting in sparse coastal landscapes.  Fragmenting these important fish habitats into ever smaller, low-quality parcels will result in disaster for coastal gamefish, and is an outcome we should try our best to prevent. 

Sidebar 1 - The proximity of mangroves and seagrass provides a great situation for blue crabs, which require the shelter of thick seagrass as juveniles but can forage among the mangroves once larger.  In contrast, mangroves with mud adjacent are unlikely to harbor juvenile blue crabs, although adults may be present.  Connections between habitats such as this are important for anglers to notice because juvenile blue crabs are on the menu of numerous gamefish found in the subtropics, including snook and my favorite – red drum.  Given an opportunity to sight-fish for red drum along a mangrove shoreline lined by seagrass, I will often use my imitation of a juvenile blue crab.

Sidebar 2 - You may encounter a number of species of fiddler crabs (all of the genus Uca) in the subtropics – each species preferring a different type of sediment.  Don’t worry, you don’t have to be able to tell the difference between the species, or even know the types of sediments they prefer.  Instead, if you know that fiddler crabs dig burrows above the low water line in sandy or muddy bottoms of low energy environments, then you will know what to look for and what locations are likely best for using fiddler crab flies.  You should also know that fiddler crabs in the subtropics are pretty much the same shape and size, but that color varies.  Color varies among the species, but more important is that color varies depending on the location.  Generally, fiddler crabs will be brown to green (usually close to the color of the sediment where they live), with the oversized claw of the male a lighter color than the body, and a body approximately ½ inch across.

Sidebar 3 - Strategies for fishing mangrove edges change seasonally.  In winter, mangrove creeks (especially creeks with deep areas) are the best places to find snook.  Snook, a tropical species, are near the northern extent of their range in the subtropics, and can’t tolerate cold temperatures.  Snook find refuge in deeper waters of creeks sheltered from cold winter winds, and these are great places to find hungry snook in winter.  As the water warms in spring and into summer, many of the snook will move out of the creeks and will feed along mangrove shorelines and adjacent flats.  Although snook prefer to feed at dusk and into night, flies cast into the shadows of mangroves during the day will attract strikes from snook.  But even in summer don’t forget creeks.  Creeks are still good places to find snook during summer – they remain cool (but not cold) and are often well-shaded – especially creeks with current. 

Sidebar 4 - Low tide is often the best time to fish for snook along mangrove edges.  Near high tide, snook can hide way up under the mangrove branches, but as the water drops the snook are forced to leave this shelter.  Often, the fish will remain at the same spot – as close to the mangroves as the water depth will allow.  If you pole quietly along a shallow mangrove shoreline at low tide you may be surprised at how many snook are in this shallow water waiting for the rising tide to flood the mangroves again.

Sidebar 5 - Since black mangroves are often found in areas with murky water, getting your fly noticed is more important than using an exact imitation.  Flies with a lot of flash (like in a Crystal Crab), undulating motion (such as a marabou shrimp), noise (any pattern with a rattle incorporated in the design), or bright colors are all appropriate for these conditions.