Subtropical Seagrass

Tailing Redfish
The tide was so low I had to get out of my small aluminum skiff and push it over the sandbar.  As the boat slid off the sandbar into slightly deeper water, I jumped back on and slowly poled across the mirror-like water surface.  Tips of turtle grass blades poked into the air in scattered bunches.  The tide had just turned and was starting to flood, and I was hoping to find red drum feeding in the grassbed between the sandbar and the mangrove shoreline some 200 yards away.  With the morning sun at my back, I was able to make out the network of seagrass and open bottom.  Some areas were covered by large sections of dense turtle grass, and I could picture the flurry of activity among those grass blades as grass shrimp, snapping shrimp, gobies, brittle stars, mud crabs, and many other species moved about in search of food.  Other areas were expanses of open sandy bottom, and although a suite of animals also live in this habitat, many live within the sediment, making it appear less active above-ground than the seagrass.

I turned the boat with a quick sideways push of the pole and headed into my favorite section of the grassbed - a mixture of grass interspersed with open bottom.  The thick seagrass provided shelter and food for some of the red drum's favorite prey items.  The patches of open bottom and sparse seagrass provided areas where the feeding drum could more easily capture prey that ventured from the shelter of the seagrass to feed, and most importantly, gave me perfect opportunities to present my flies to feeding or cruising fish.  In these open or sparsely vegetated patches, the drum were more likely to see the fly, and the fly was less likely to get snagged on the grass.  Targeting these open areas also allowed me to use crab and shrimp flies that sank quickly to the bottom and could be moved ever so slightly with a short, quick strip B just like the real thing.   

Almost as soon as I'd turned the boat, I saw the reflection of the morning sun on the square copper tail of a red drum as it broke the water surface about 50 yards away.  As I gave a good shove to the push pole to send the boat moving toward the tailing fish, I saw another tail waving, this one much closer.  I quickly stowed the pole and grabbed my fly rod.  I threw a quick back cast and shot the fly toward the tailing fish.  The olive-colored crab fly plopped down in front of the fish just as the fish stopped tailing and was readying to move forward, a lucky break for me because the fish saw the fly as it dropped the 10 inches to the bottom.  The line jumped as the fish surged forward and took the fly, and with a strip-strike the fight was on. 

I repeated this scenario numerous times this past winter on some of my favorite flats in southwest Florida, some days with more success than others.  And as the water warms into summer, I use a similar strategy in search of snook and other gamefish on the flats.  By coupling knowledge about the important characteristics of seagrass as a source of shelter and food with information about seasonality of seagrass communities you should get more shots at fish.  Whether or not you actually catch the fish, well....

Seasonality of Shelter

Just as in the tropics, seagrass beds in the subtropics are an essential component of shallow coastal waters.  Seagrasses perform important ecological functions that have ramifications beyond the area they cover and provide essential habitat for many gamefish and their prey.  The basics of seagrass were covered in Part 2 of this series, so won't be repeated here. However, there are some characteristics of subtropical seagrass beds that are distinct from the tropics.  

The seagrasses you will encounter most often in the subtropics are Turtle Grass (Thalassia testudinum), Manatee Grass (Syringodium filiforme) and Shoal Grass (Halodule wrightii).  Other grasses are present in the subtropics, but are generally not as common as the three species just mentioned.  Turtle Grass is the most common grass throughout most of the subtropics, has the widest blades, and provides the greatest amount of shelter of the three common species of grass.  You will often find these grasses growing together in mixed beds, but you may also find areas with only one species of grass present.

In the tropics, seagrass grows throughout the year, with new blades replacing older blades that die, break off, or are covered by too many epiphytes or epibionts to survive.  In the subtropics, seagrasses usually go into a state of winter dormancy or extremely slow growth, or may even die back, in this case the blades will die and break off, with the plant material below the sediment remaining dormant until spring, when new shoots emerge.  Since grass blades are either not being replaced as they die or break off, or are disappearing altogether, you might think that grassbeds don't provide good shelter during winter months.  Fortunately, they do B in most locations the loss of seagrass blades isn=t so great that the grassbeds disappear, and as the seagrass slows or stops growth in late fall and winter, drift algae becomes more abundant, reaching its peak in late winter into early spring. 

Drift algae is kind of like the tumbleweed of the sea, being carried by currents and deposited in areas where the currents are no longer strong enough to carry the algae.  So, as the grassblades act as baffles to slow the current, they help to deposit drift algae.  As the drift algae grows through the winter, and is moved around by currents forced by strong winter winds, it often collects in depressions and along windward shorelines.  Sometimes there is so much drift algae that it carpets the bottom, and can be more than 2 feet deep.  Overall, I've found that areas with such thick accumulations of drift algae don't hold as many prey and don't make for the best fishing.  A good mixture of seagrass and algae seems to provide the best habitat during winter.

Seasonality of Seagrass Residents

As you might expect, most of the animals that reside in seagrass also use drift algae, so in a sense, the overall resident seagrass community doesn't change. Grass shrimp, pink or brown shrimp, pipefish, mud crabs, juvenile blue crabs, gobies, blennies, and brittle stars are present throughout the year and use both drift algae and seagrass, and all will be eaten by one species or another of gamefish.  However, these year-round communities living in grassbeds undergo subtle seasonal changes that may influence feeding patterns of some gamefish.  In winter, when many of the seasonally abundant prey species (mojarras - Family Gerreidae, pinfish - Lagodon rhomboides, croaker - Micropogonias undulatus) are absent or in low abundance, these resident prey species become even more important in the diets of gamefish.  Following are a few examples.

Mud crabs (often the Common Mud Crab, Panopeus herbstii) can be found throughout the year in seagrass beds in soft bottom, but can be especially abundant in clumps of drift algae during winter.  While sampling in grass beds this past February and March, I found a large number of large female mud crabs with eggs within drift algae.  Perhaps this is one reason why I found red drum feeding so intently in patches of drift algae.  In a couple of instances, while sampling a shallow grass bed from a small boat, I was able to drift over a red drum that had its snout buried deep into a clump of drift algae.  Neither fish noticed the presence of the boat until the boat was smack on top of the fish. Such intent feeding behavior may contribute to angler frustration in instances when a fish ignores a fly - it may be that the fish just never saw the fly.  When casting to tailing redfish feeding in grassbeds I try to cast the fly so it just about hits them on the head to be certain that they see the fly. 

Grass shrimp (Palaemonetes pugio) are a major prey item for speckled seatrout (other gamefish feed on grass shrimp as well).  Although grass shrimp are present in grass beds throughout the year, they show distinct seasonality in abundance; they are most abundant in summer, and least abundant in winter.  What=s more, you will find many of the females with eggs attached to their undersides in late winter/early spring, so you might want to tie a few of your grass shrimp fly patterns to reflect the presence of eggs on grass shrimp in early spring. 

Mullet are present in shallow waters of subtropical areas throughout the year, but they show distinct seasonal changes in size and abundance as well.  Adult mullet will gather in channels, cuts, and mouths of creeks in winter to spawn, and not long after you can find small juvenile mullet in shallow areas, including grass beds.  In late winter/early spring, these juvenile mullet will be small - an inch or two long - but by mid-spring when the tarpon arrive and the snook are on the flats, the juvenile mullet will be in the medium size class (4" - 8" long), so a medium size mullet fly is a good choice in spring.  In addition to snook and tarpon, red drum, crevalle jacks, and cobia will feed on these juvenile mullet. 

Warm Water Residents

Many other species that use grassbeds undergo more dynamic seasonal changes.  For example, juvenile croaker and mojarra first appear in shallow areas, including grass beds, in spring.  Juveniles of both species are almost all silver, and can be imitated with small (2" - 3") white deceivers or similar patterns.  Larger croaker are usually found in deeper areas of open bottom , but larger mojarras (3" - 4") can be found in open bottoms intermixed with seagrass throughout the summer.

One of the most interesting is the seasonal change in habitat use by pinfish (Lagodon rhomboides), an extremely important prey item in subtropical grassbeds B especially for snook.  Data from the Florida Marine Research Institute shows that pinfish are a major component of snook captured on seagrass.  In fact, snook sometimes take mouthfuls of seagrass as they grab the pinfish, so sometimes have pieces of seagrass in their stomachs along with the fish.

Pinfish are a very important species in seagrass.  Pinfish act as predators on small organisms that live on the grass blades and on the sediment, and they graze on the grass blades and epiphytes that grow on the grass blades.  In turn, pinfish are prey for numerous gamefish.  In this manner, pinfish act to harvest and transfer the energy of the seagrass beds to the larger predatory fish.

Pinfish show a distinct seasonality in size, abundance, and habitat use.  Pinfish larvae enter estuaries and other shallow areas with seagrass in the winter months (generally November through March) {see Part 1 of the series for a description of the life cycle of most marine fish}.  These larvae then transform into juveniles that are less than an inch long and look like miniature versions of adult pinfish.  While conducting a recent research project,  I found that these small juvenile pinfish prefer seagrass beds with drift algae, probably because the drift algae provides the necessary food (very small crustaceans called isopods and amphipods) and shelter.  Through performing several experiments I found the predation on these small pinfish was higher in seagrass without drift algae than in seagrass with algae.

Pinfish grow very quickly, so a fish that was less than an inch in March will be a couple of inches long by May.  As pinfish grow, they change their diet and behavior, lose their association with drift algae, and will forage throughout the seagrass beds.  So you will see a change in the average size of pinfish in seagrass beds: a lot of small fish in winter, a mixture of small to medium fish in late winter; medium to larger fish in late spring/summer; and the largest fish in early fall before the adults migrate to deeper water for winter.  Your fly selection should include a range of different sizes of flies to imitate pinfish through the seasons: I like yellow and white deceivers of 1" - 2" for winter; 1" - 3" for spring; 3" - 5" for summer and fall.             

Just like their prey, gamefish undergo seasonal changes in use of seagrass habitat.  For example, through the warmer months, snook may be found in patches of open bottom in the grass beds, either potholes (open areas that are deeper than the surrounding seagrass) or smaller  openings in the seagrass.  Although red drum can be caught in seagrass throughout the year, the sight of redfish tailing in grassbeds is most common in winter  months due to a combination of low tides and cooler temperatures.   Speckled trout are present in grass beds throughout the year, but they may change locations and depth depending on temperature, tide, availability of prey, and spawning (speckled trout spawn during the summer months).

Warming temperatures of spring bring a host of other gamefish onto grass beds in search of a meal.  Crevalle jacks will cruise the deeper grassbeds, and can be found along edges of shallow grassbeds.  Tarpon and cobia will also cruise the grass beds in search of prey.  I have seen large cobia feeding on blue crabs on a seagrass flat that was so shallow that the cobia's back was out of the water.  All of these gamefish will be feeding on the prey items discussed in this article.

Conservation 
Seagrass beds are under threat from a number of sources.  Sedimentation from coastal development can smother seagrass.  Too many nutrients from sewage, fertilizer runoff, and other sources, can cause algae blooms that decrease the clarity of the water, causing the seagrass to die due to lack of light.  Too many nutrients can also cause so many epiphytes to grow on the grass blades that the blades die.  These threats to seagrass are associated with various non-fishing human activities but they impact the seagrass that gamefish depend on, and should be of concern to anglers.. 

Perhaps one of the greatest threats to seagrass that can be directly addressed by anglers is destruction of seagrass due to boat propellers, called prop-scarring.  Caused by running the boat in water too shallow, so that the propeller digs a trough through the seagrass, prop-scarring is becoming a major problem to the overall health of seagrass in the subtropics.  This is a problem that can be solved to a great extent by boating anglers.  

Sidebar 1: During winter, snook often migrate into deep creeks to seek refuge from cold temperatures. Mangrove-lined creeks that empty onto seagrass flats can be good places to fish during warm spell in winter because snook will venture out of the creeks during warmer weather.   These flats are also good places in the spring when fish first start to migrate out of the creeks onto flats and toward their summer habitats.  The fish move along habitat corridors that extend from the creeks.  I prefer to anchor the boat and wade.  I start by fishing the deep hole that usually occurs at the end of the creek and the inner edge of the flat.  I then fish my way along the  shallow shoreline to either side of creek or pole the boat along a track parallel to the mangroves looking for snook sunning themselves in the open patches in the seagrass.

Sidebar 2: It is well worth the time and effort to snorkel the grass beds to get a fish-eye view of how the prey species use the habitat.  For example, this will give you an idea of how pinfish and mojarras zigzag through the grass blades, and how crabs and shrimp will crawl among the grass blades.  These observations will undoubtedly give you ideas for new fly patterns and strategies for how to fish these new flies.

Sidebar 3: Edges of grass beds, patches of open bottom in grass beds, and patches of sparse grass in otherwise thick grass beds are all good places to concentrate your fishing effort.  Overall, there are probably more species and more total numbers of prey items in the areas of thick grass, but the feeding efficiency of gamefish is higher in more open areas.  This is one reason why you will often find snook lying in wait in an open patch in the seagrass to ambush small fish, and why speckled trout will often hide among the grass blades near the edge of a seagrass bed and dart out into the open to grab a fly as it passes by.  These open areas also make the fly more visible and easire to fish, with fewer snags.

Sidebar 4: Favorite ways to fish flies that imitate pinfish B a white and yellow, high-bodied fly.  Flies for Saltwater, by Stewart and Allen has a couple of productive pinfish fly patterns. For juvenile pinfish, I like to strip the fly so it swims just above the drift algae, using short quick strips to give the fly a darting motion.  For larger pinfish, I cast over seagrass and along edges of grass beds, and use longer strips of the fly line.