Habitat Primer

The Importance of Coastal Habitats to Gamefish

This is the first in a series of articles about the ecology of coastal habitats in tropical and warm-temperate climates with a focus on the habitats that support many of the gamefish we pursue with a fly rod.  By warm-temperate I mean the coastal areas of the Gulf of Mexico and the southeast coast from Florida to the Carolinas.  As most of us know, coastal habitats are essential to the survival of many gamefish and the species they depend on for food.  What many don’t realize is just how intricately intertwined our favorite gamefish are with coastal habitats – in more ways than you might imagine. The food, shelter, salinity, and overall water quality of coastal habitats are some of the characteristics that make these areas so important to so many gamefish.  In this series I will discuss the importance of various coastal habitats to the numerous life stages of coastal gamefish, and in doing so provide an overview of why coastal habitats are so essential to gamefish survival.  In the process, I will discuss information that should help you become a more efficient and responsible angler.  As you might guess, the challenges confronting fish in coastal habitats are complex, and vary depending on the size and age of the fish. 

In this first article, I will paint a general picture of the life cycle of marine gamefish from conception to adulthood, and in this manner introduce many of the topics I will discuss in future articles. 

Life Stage Number 1

Most saltwater fish species fit three rather distinct ‘lifestyles’ into their relatively short lives.  Many saltwater fish, including most gamefish, reproduce through a behavior often called broadcast spawning – adult females and males (either as a pair or in groups) ‘broadcast’ (release) their eggs and sperm into the water, where fertilization takes place.  The fertilized eggs generally hatch within hours, and the tiny larvae start Lifestyle Number 1 (the larval stage) as plankton – small, free-floating individuals in the open ocean.  While this seems to be a risky approach to reproduction, females of many species can produce millions of eggs for a spawning period, so even though there is no parental care sheer numbers virtually ensure that some larvae make it home.

Although larvae of most species are able to swim, their swimming abilities are minimal, so they are unable to fight most currents and are transported wherever the currents take them.  Larvae of some species remain in coastal waters, while others may be transported out into the open ocean – where larvae spend their time depends on both a species’ requirements and luck.  The larvae live as zooplankton (animal plankton), eating small phytoplankton (plant plankton) and other zooplankton for periods of days to months, depending on the species.  For example, tarpon larvae are thought to spend 60 to 90 days, bonefish 41 - 71 days, but redfish larvae only about 17 days as plankton. 

Just so you don’t go searching for tiny versions of your favorite gamefish out in the open sea, most larvae are not only small (less than an inch), but look absolutely nothing like their parents.  Many are transparent, or nearly so (which is great camouflage in clear ocean water), some larvae have all kinds of spines and other protrusions for protection, and many aren’t even shaped like their parents.  In spite of their camouflage and long spines, more than 90% of larvae are eaten or die, but remember that 10%, or even just 1% of millions of original eggs and larvae is a substantial number.

Life Stage Number 2

At the end of the larval life stage, surviving larvae undergo a rapid and drastic transformation, changing from the clear, often spiny larvae to a form we would all recognize as a miniature fish, thus starting Lifestyle Number 2 – the juvenile stage.  At the same time the larvae are getting ready to transform into juveniles, they are searching for the right type of bottom habitat.  So if they were lucky enough to have survived the treacherous open ocean, the larvae must be lucky yet again – they must be near the right kind of bottom habitat at the time they are ready to start the juvenile life stage.  Depending on currents and how long they spent as plankton, these surviving larvae may end up close to their place of origin or far away – even on another island.

For some species, like tarpon, these new juveniles are miniature versions of the adults, and can be easily identified.  For other species, like amber jack, the juveniles have a different coloration than the adults, and change color, becoming more like adults, as they grow.

For many saltwater fish, and especially species I consider gamefish, coastal areas provide many of the habitats that are essential for the survival of juveniles.  Habitats important to juveniles are known as ‘nurseries’ in that they provide essential habitat for juveniles of many species of fish. These habitats are ‘essential’ because without these habitats few juveniles would survive.

Shallow coastal habitats such as seagrass beds, mangroves, marshes, estuaries and shorelines are heavily used by juvenile fish because these habitats provide the best food and shelter needed for the juvenile life stage.  For the purpose of this article, I will address two general types of coastal habitats that juvenile fish use as nurseries – those with plants and those without.

Shallow coastal areas provide two commodities important for supporting plant growth – high nutrient levels and sunlight.  Although plants, such as seagrasses, mangroves, and marsh plants, are not necessary for an area to support juvenile fish, plants do provide several advantages. First, by holding sediments together, plants keep the bottom and associated habitats intact, and the rooted plants then trap organic matter (which is food for crabs, shrimp, small fish, and other prey items for juvenile gamefish).  Second, plants are able to harness sunlight and nutrients into a form many prey species can use.  Third, plants create habitat structure and complexity, which provides shelter from predators for the juvenile fish. 

The combination of food and shelter create great habitat for many species, which results in a diverse community.  Juvenile gamefish are able to take advantage of this dual bounty of shelter from predators and abundant food to grow quickly.  And since juveniles face their greatest risk of predation during the first days in their nursery habitat, and since larger fish are less likely to get eaten by predators than smaller fish, the faster they can grow the better.

Coastal habitats without plants also support juvenile gamefish, though generally not as many as those areas with plants.  Often, these are areas that have high levels of nutrients but are too deep or too murky for sunlight to penetrate, so can’t support plant growth.  However, a variety of organisms that don’t need sunlight are able to take advantage of these areas and can provide habitat for juvenile fish.  Oyster reefs are examples of this type of coastal juvenile fish habitat.  Like plants, these structures provide shelter from predators and support communities of organisms that are food for juvenile fish. 

Coastal habitats without either plants or other habitat like oyster reefs support few juvenile gamefish.  Although there may be some organisms that inhabit these areas, such as worms and clams, there is little shelter for small fish. In general, survival of juvenile fish is higher in areas with complex shelter than in areas of open bottom, like sand or mud.

There are plenty of examples of coastal habitat use by juvenile gamefish.  Here is a partial list of just a few of the most preferred nursery habitats for many species: Bonefish, tarpon, and snook use shallow mangrove lagoons; on some Caribbean islands, juvenile permit can be found along shallow, grassy shorelines; small jacks of many species, like horse-eye jacks, are often found along shallow beachrock shores; juvenile barracuda are abundant among and around mangroves; and juvenile redfish may use seagrass in estuaries or cordgrass in wetlands.  It is important to note that not only juvenile gamefish use these areas as nurseries, but so do a host of other organisms – fish and otherwise.  For example, juvenile blue crabs are dependent on estuarine seagrass areas, and juveniles of numerous coral reef fish, like grunts, use seagrass and algae in lagoons.  The list of organisms that use coastal habitats as nurseries is large indeed, and in many cases it is these organisms that we attempt to imitate with our flies.

Life Stage Number 3

With these nutrient rich, diverse communities in coastal areas, you might ask – don’t large predatory fish know about all of this?  Of course, and that’s one reason large individuals of many gamefish are often accessible from shore – these shallow, rich habitats and the communities they support attract large fish within range of shore-bound fly anglers.  And this brings us to fish Lifestyle Number 3 – the adult stage. 

After surviving the gauntlet of the open ocean, and then escaping predators in their nursery habitats, the remaining juveniles grow to adulthood.  The transformation from juvenile to adult is not as rapid or drastic as from larvae to juvenile, and there tends to be some overlap in habitat and diet between juveniles and adults.  For some species, this juvenile-to-adult transition occurs within the same general area as the nursery, so juveniles and adults can be found together. For example, spotted seatrout use similar estuarine areas as juveniles and young adults.  For other species individuals gradually move from nursery areas to adult habitats.  For example juvenile and young adult tarpon often use mangrove lagoons while larger adults generally use more open areas and often undergo seasonal migrations.

Usually, a fish’s diet and behavior will change as it grows, allowing the fish to take advantage of different habitats and prey.  Spotted seatrout are a great example.  Juvenile and young adults tend to form large schools, while older fish adopt a more solitary existence.  Also, as spotted seatrout grow, they move from a diet of small mysid shrimps (the diet of juveniles) to increasingly larger shrimp species (as young adults), and eventually a more varied diet consisting of shrimp and fish (as older adults).  Red drum show a similar change in diet with age, subsisting on small crustaceans (shrimp and small crabs) as juveniles to a more varied adult diet of shrimp, larger crabs, and fish, but tend to school as both juveniles and adults. 

You’ve probably noticed seasonal changes in the abundance of your favorite gamefish in coastal waters, and maybe even changes in their diet.  While the reasons for this seasonality are many, such as temperature and spawning migrations, food availability is a major factor.  Juveniles of many of the organisms that use coastal habitats as nurseries are most abundant in spring and summer.  This is true even in the Caribbean, where abundance of juvenile fish is highest in summer months.  Gamefish and other predators may shift their diet and feeding locations to take advantage of this seasonal abundance of prey.

An experience I had on a recent summer trip in the Caribbean provides a vivid example.  I had just finished three weeks of intensive field work – counting juvenile fish on coral reefs and in lagoons while on SCUBA.  I had seen all the juvenile fish I cared to for a while.  I was taking a couple of days R&R before heading home, and on this particular day I was wading across a large sand flat in search of bonefish.  Out in the middle of this large sand flat I came across a broken down piece of old, dead mangrove that must have been washed onto the middle of the knee-deep flat in a storm.   The closest live mangroves were half a mile away along the shoreline. 

I slowly walked over to the old mangrove to see if it might hold some small snapper (the habitat provided by mangroves is important habitat for juvenile snapper).  As I reached the old mangrove I saw two torpedoes speed off – bonefish!  This really piqued my curiosity because I had never before seen bonefish so closely associated with structure, especially on a sand flat where I expected to see them cruising and feeding, but always on the move.  Once I was close enough to the mangrove, I saw why the bonefish were so attracted it.  There were hundreds of juvenile grunts huddled among and around the mangrove branches and roots, and by their size I figured they had made the transformation from larval to juvenile form about a month before.  The bonefish had found the jackpot, and were content to feed to their hearts’ content until tide, or an angler, forced them away.  An event like this would only happen in summer.

Fragile Habitats

We are fortunate that so many saltwater gamefish species requires coastal habitat.  Otherwise, we would have few options for fly fishing in saltwater.  Considering the importance of coastal habitats to at least two, and often three of the ‘Lifestyles’ of our most prized gamefish, you’d think it was a given that we protect these areas, but too often that is not the case.  Too many nutrients (such as may come from sewage or fertilizer), unchecked coastal development, erosion and sediment-laden runoff, and a host of other ills can make things tough for fish and other organisms in these coastal habitats.  If for no other reason than preservation of our fly fishing opportunities, we owe it to ourselves to make sure these areas remain viable habitats for our favorite gamefish.

In the next part of the series I will start to delve into the specific biological and ecological characteristics that make each coastal habitat attractive both as nurseries, and as feeding areas for adults.  Many of the issues I presented in this article will be revisited in more detail.  I will pay particular attention to the organisms that are preyed upon by our favorite gamefish, and their habitats.

Sidebar 1 – If readers are interested in pursuing these topics further on their own, the internet maybe a good place to start.  When doing a search, whether on the internet or at the library, you will get the best and most reliable information if you use the Latin nomenclature as your search keywords.  For example, use Sciaenops ocellatus, instead of redfish or red drum.  Kaplan’s Guide to Atlantic Coast Fishes is a good book to have for basic information, including the appropriate nomenclature.  Finally, your state fisheries agency likely has reports on various aspects of the biology of saltwater gamefish, including diet, habitat use, and seasonality.

Sidebar 2 – Seasonal variation in abundances of prey species (who are also going through their own life cycles) will result in diet shifts for many predatory fish species, and an observant angler can take advantage of this seasonality in selecting flies.  However, remember that every location will have its own nuances, so you will have to investigate your home waters to figure things out.  The following examples are only meant to demonstrate the importance of understanding seasonal changes in the diets of gamefish.  If you are traveling, a local shop may be able to give you tips, or you may want to hire a knowledgeable guide. 

While living on St. Croix, I discovered that small baitfish, known locally as ‘fry’, formed into dense spawning aggregations along the shores of protected coves in early April.  These large schools of fry attracted a host of predatory fish, including tarpon, bar jacks, and barracuda.  But most exciting was that bonefish often fed aggressively on these schools of fry, and were suckers for a white Crazy Charlie.  At other times of year, bonefish found in these same coves fed mostly on shrimp and crabs, so a tan Gotcha was the most productive fly.  In lagoons or flats lined by mangroves, during the summer bonefish will often feed opportunistically on juvenile grunts, which have a yellow hue, so a small yellow and white clouser may be worth a try.  In areas without habitat for juvenile fish, or where large schools of baitfish are not found, bonefish will feed almost exclusively on bottom organisms such as clams, crustaceans, and worms, and feed only occasionally on small fish.

Speckled seatrout also undergo seasonal shifts in diet that are important for an angler to know about.  For example, in Indian River, Florida, adult speckled seatrout feed mostly on shrimp in summer and early winter, but switch to a diet dominated by small fishes in late winter and early spring.  In the Virginia portion of Chesapeake Bay, speckled trout venture into shallow grass beds in the spring (May and into June) in search of juvenile and shedding adult blue crabs.  In contrast, the closely related red drum (both speckled trout and red drum are in the Drum family – Sciaenidae) has a diet similar to speckled trout (fish, shrimp, and crabs), but may have different diet preferences depending on location.  On Florida’s Gulf of Mexico coast, red drum prefer small fish such as menhaden and anchovies in winter and spring, and crabs and shrimp in summer and fall, while red drum along the coast of Mississippi prefer shrimp in winter, crabs in spring and summer, and small fish in the fall.