Subtropical Oyster Bars and Sand Bars

Salaries for marine biologists generally aren't the best, but the following account provides testimony to the advantages that 'fringe benefits' can bring to the career.  Not long ago I was conducting research on some of the fish living in seagrass beds.  Mid-morning, I finished sampling the first grass bed of the day, so loaded the sampling gear into the skiff and headed toward the next sampling location.  I slowly made my way off the grass bed, and then put the boat up on plane as I reached deeper, open water.  After 5 minutes of travel over a glass-calm surface I approached the sandbar that separated another grass bed from deep water.  (From reading previous articles on seagrass (Part 2 and Part 6 in this series) you'll remember that seagrass grows best in shallow areas protected from heavy wave action and strong current.)

As I approached the sandbar I could see the sandy bottom rise quickly toward the surface.  Small patches of sparse seagrass dotted the outer side of the sandbar.  I pulled back on the throttle, and as the boat settled back into the water  I saw what looked like moving patches of seagrass.  A pod of manatees was cruising south along the bottom on the outer edge of the bar.  I put the boat in neutral and watched as the manatees passed by.  Then I saw movement out of the corner of my eye.  With a quick glance I saw the movement was made by a set of fins.  I stood on the bow deck for a better view B cobia!  Five of them!  They were cruising the outer edge of the sandbar hoping the manatees would stop to feed and stir up something to eat, or hoping to use the manatees as cover in order to get close to unwary baitfish. 

I was too close to the fish to get in a cast without spooking them, so after they passed I started the engine and traveled in a wide arc to get ahead of the traveling herd.  I stopped the boat at the edge of the sandbar about 50 yards ahead of the cruising manatees and set up for a cast to the fish.  The seven manatees swam by in single file.  The five cobia followed, tightly grouped, as if they were the caboose in a long manatee train.

As the last manatee passed the boat, I made a cast to the lead fish in the group of five.  The fly had barely hit the water when the second fish sprinted forward and inhaled the fly.  I set the hook, and after a few head shakes the fish was off and running.  The fish suddenly stopped after a 30 yard run and again shook its head from side to side.  The hook popped loose, and the line went slack.  The now free cobia turned and hastily swam south to rejoin the other four fish who had not skipped a beat in their trailing of the manatee train. 

I restarted the engine and steered the boat in a wide arc - the small wake made by the school of cobia was an easy mark.  Again, I set up on the edge of the sandbar and waited.  Once again the manatee train passed.  Once again I cast the fly behind the tail end of the last manatee.  As the five cobia approached I gave the fly a twitch, and then a small strip.  This time all five of the fish surged forward, and the lead fish took the fly.

The thrashing of the hooked fish set the other cobia into a brief frenzy before they regrouped and headed south at double speed to rejoin the manatee train.  After a couple of short runs the hooked fish realized it was alone and sped off in pursuit of the group.  As backing peeled off the reel I started the engine to follow, and caught up just as the fish rejoined the group and slowed its run.  I floated southward, now the new caboose on the manatee-cobia train, slowly regaining line.  A few minutes later I had the fish in hand, a fat fish 36" long. 

Although this may seem like a once-in-a-lifetime experience, I've had numerous similar experiences (without manatees) fishing the outer edges of sandbars by boat and wading.  Crevalle jacks, snook, tarpon, speckled trout, red drum, juvenile blacktip sharks, and ladyfish are the other species I've encountered along the edges of sandbars in the subtropics.  Oyster bars can provide similar opportunities.  Crevalle jacks, red drum, snook, and sheepshead are some of the species you'll find along the edges of oyster bars in subtropical estuaries.

Sandbars and oyster bars have a very important characteristic in common - they are both associated with current.  Find an oyster bar or a sandbar and you've found a place that is exposed to current consistently during a part or all of a tidal cycle.  In general, both types of bars will be oriented across rather than along the dominant current.  Overall, most bars exposed to tidal currents will experience the strongest currents on the outgoing tide, although there are certainly exceptions. Sandbars are the results of currents - whether the currents result from waves or tides.  Strong currents have enough energy to carry sediments considerable distances, whether the sediments were swept off the bottom or were washed off the land.  Sandbars occur in areas where the currents slow enough that the sediments fall to the bottom.  Places this may occur include where opposing currents meet, such as where incoming ocean currents meet outgoing river currents in estuaries, where currents that flowed strongly through a constricted area (an inlet or cut, for example) are dispersed over a large open area, and where waves lose energy as they approach land or shallows (like a beach) and crash onto themselves.  Sandbars exposed to wave-induced currents will usually be parallel to the waves with the deepest water on the side opposite the direction that the waves approach.

In contrast, oyster bars aren't the result of currents, but oysters do need current to survive.  Oysters are filter feeders (they filter plankton and particles out of the water they pump through their gills), so need a constant supply of new water to bring them food.  The currents of incoming and outgoing tides bring new food for oysters.

Oysters also need a hard surface to attach themselves to, so once one oyster becomes established, new spat (oyster larvae that are settling out of the water column - see Part 1 of the series for a review of marine organism life cycles) are quick to attach themselves to the established oysters.  This is the manner in which oyster reefs grow. 

Once sandbars and oyster bars are large enough, they can exert an influence on water flow by deflecting and channeling currents.  The abrupt changes in currents help to create areas with shallow and deeper habitats immediately adjacent to each other.  In this fashion, sandbars and oyster bars help to create additional habitats for gamefish and their prey. 

When bars deflect currents, they sometimes create a current eddy on the upcurrent side of the bar - usually an area of slow, swirling water.  Baitfish that are drifting downstream can get confused by these slowly whirling currents and may collect here.  I like to approach these upcurrent eddies from the upstream side and cast streamers to the edges of the eddy where the swirling water meets the downstream flowing current.  I always cast to these upcurrent eddies from as far away as possible and still make good casts.  Casting across the current and letting the fly swing into the slow water of the eddy is another good strategy.

I've found that gamefish holding on upcurrent sides of bars are more wary than their counterparts on the down-current sides of bars.  Perhaps the fish on the down-current sides of bars can't see or hear anglers approaching from upstream, while the fish on the upcurrent side of the bar can.  Whatever the reason, make your casts to the upcurrent eddies from a distance before moving close to the bar.

Once I've fished the edges to my satisfaction, I always try a few casts with a sinking fly (like a clouser minnow) to the slower water along the front of the bar.  This area often contains the deepest hole and can hold large fish in its depths.  I once cast a fly into such a hole a dozen times before finally getting a strike from a 'gator' speckled trout.  Of course, I've cast a dozen times into similar holes without such a result, but I think it's worth the extra effort. 

As currents race around the ends or over the tops of sandbars and oyster bars, they dislodge and wash away sediments, creating deeper holes.  The best locations to look for deeper holes will vary depending on the depth of water where the bar is located and the bar's configuration.  On bars located in shallow water that have little water flow over the top, you are likely to find deeper holes on the ends of the bar or in the cuts between adjacent bars.  These holes aren't necessarily large, but they often hold fish. 

My favorite series of oyster bars lie in knee-deep water along the edge of a grass bed.  Incoming tidal currents have carved small sand potholes about 5 feet across at the ends of the bars.  Despite the small size of the deep areas, I've seen as many as 6 snook laying in a single pothole on an incoming tide. 

In contrast, bars that have strong water flow over the top will often have deep holes on the down-current side of the bar.  These holes are best fished when water is flowing strongly enough to sweep small fish and other prey over the top of the bar.  This includes prey that are being swept downstream, such as silversides, and organisms that live on the oyster bar, such as shrimp, crabs, and small fish that are dislodged by the strong currents.

Fish these areas just as you would a stream.  My favorite approach is to cast across and just upcurrent of the bar and let the fly wash over the bar and swing through the rear of the eddy.  I start by casting to the area nearest to me and make my casts progressively longer until I've sufficiently covered the hole. 

Transient Prey
You have many choices when it comes to choosing an appropriate fly for fishing sandbars and oyster bars.  The first step toward simplifying things a bit is to split potential gamefish prey into two categories - transients and residents. 

Transient species are prey species that can be found near bars at certain tides, or even as long as a season, but aren=t always present.  This group of species is generally what we are imitating when we cast baitfish imitations into currents that sweep past and over bars.  Silversides (Family Atherinidae), anchovies (Family Engraulidae), and herrings (Family Clupeidae) are the most common members of this group.  The baitfish species that gamefish key on varies with location and time of year.

In my experience, the best time of year to cast and swing baitfish imitations across sandbars and oyster bars is in the late summer and fall.  Late summer is when these species are in greatest abundance, and fall is when the migratory baitfish species begin to leave the estuaries and migrate to winter locations.  The abundance and migration of baitfish combine to make these species a common diet item for gamefish in late summer and fall.  Drifting flies into the holes around sandbars and oyster bars can bring in a grab-bag of gamefish, including crevalle jack, speckled trout, and red drum, on successive casts.  This is one reason that when you drift a size 1 clouser minnow over an oyster bar on an outgoing tide the snook that sees the fly might mistake it for a silverside lost in the currents.

Baitfish can also be found schooled against the shallow edges of sandbars and oyster bars as they search for shelter in the shallow waters of the bars.  The proximity of deeper water allows gamefish to approach the bars and, unfortunately for the baitfish, the shallow bar can be an easy place for gamefish to corral and feed on the  baitfish.  When gamefish are focusing on baitfish schooled along sandbars and oyster bars, catching fish doesn't require much more than being there.

I recently came upon a school of large red drum that was cruising through a grass bed at the beginning of the incoming tide.  The grass bed was exposed to currents from mangrove creeks that drained on the outgoing tide, so there were numerous small oyster bars scattered around the grass bed.  As the marauding school of red drum came upon each small oyster bar, their pace quickened and they pushed a large bow-wake.  The water then exploded as the red drum attacked the small schools of scaled sardines that were trying to hide in the shallow water surrounding the oyster bars.  I was able to get in front of the school of red drum three times and hooked three large fish, landing two, using a white deceiver.  It didn't take much more than me being in the right place at the right time, knowing the red drum were keying on the baitfish that were hiding along the oyster bars.

Oyster Bar Residents

Although sandbars and oyster bars are associated with current, the currents are not always strong enough or the water is not deep enough to fish these areas like you might fish structure in a stream, and currents are non-existent at slack high or low tides.  Or perhaps the bars were formed when strong current flowed through the area but for some reason the currents are no longer as strong.  In these cases, you are likely to find gamefish feeding along the edges of the bars on a rising tide, on top of submerged bars at high tide, and resting in the deeper holes between bars at low tide.  For example, in tidal areas red drum will take advantage of higher tides to feed on the tops of oyster bars that are not accessible for most of the tidal cycle and either rest or continue feeding in the deeper holes around the bars during low tides.

In these situations, gamefish will feed mostly on the resident group of prey species.  A typical oyster bar in a subtropical estuary will have half a dozen small fish species - mostly gobies (Family Gobiidae) and blennies (Family Blenniidae), with some killifish (Family Cyprinidae) - that are medium to dark brown in color and small (perhaps one to three inches long).  Muddler minnow variations are perfect imitations of these small fishes.  Crabs are the most abundant crustacean, and are favorites of red drum and speckled trout.  The shamefaced crab, blue crab , mud crab, and porcelain crab are most abundant.  A small (size 2 or 1), dark colored crab fly in olive or brown is a decent imitation of any of these crab species.  Snapping shrimp are also common on oyster bars, and are a favorite of red drum.  Snapping shrimp are generally slow moving, dark in color, and can be up to 2 inches long but are usually smaller.

(Sandbars have fewer resident species, resulting in gamefish presence for relatively brief periods centered around tides and currents.  Depending on the location of the sandbar, you may find killifish, mojarra, mullet, and blue crabs in the shallow protected areas.)

Mixed Habitats
Finally, the different types of habitats (seagrass and sand, oysters and seagrass, oysters and mud bottom) that surround sandbars and oyster bars increases the diversity of prey that a gamefish might encounter.  As you will remember from the previous articles in this series, each habitat provides different opportunities and challenges to gamefish, so the mixture of habitats can make for some interesting fishing.  By combining the information contained in the articles on subtropical seagrass and mangroves with this article, you can be well prepared for fishing in these areas.

The proximity of deep-water and shallow-water habitats attracted the cobia to the sandbar and the snook and speckled trout to the holes next to the bars.  And the mix of habitats around oyster bars gave the red drum an opportunity to cruise in the safety of the seagrass bed and feed on the schools of scaled sardines hiding in the shallows of the oyster bars.  In each case, the proximity of different habitats provided the gamefish advantages over a single habitat type.  A prudent angler can also take advantage of these areas to find more gamefish.

Oyster bars that are made up of live oysters support larger communities of resident species than oyster bars made up of dead shell, so are better feeding place for gamefish.  There are numerous threats to oysters that can potentially impact fishing.  Too much sediment can bury oysters.  Too many nutrients can cause plankton blooms that create hypoxia (low oxygen) or anoxia (no oxygen) that last for long enough periods that oysters die.  Too much wave energy - like boat wakes along a channel - in estuaries that are normally protected from frequent wave energy can also kill oysters, as can too much physical disturbance from tonging, dredging, and frequent boat groundings.

Sandbars and oyster bars influence current patterns, so changing their location, size, or orientation can have unpredictable impacts on currents that will effect fish habitats.  In many areas sandbars are always changing shape, size, and orientation in response to currents, waves, and storms.  This is a natural process that is essential to the maintenance of sandbar habitats.  Interrupting the flow of sediments and sandbars causes unpredictable problems that impact fishes and prey. For example, currents may become stronger and carve deep holes in the bottom or wipe out areas of seagrass that were protected by a removed bar.  Or currents may be blocked, creating a stagnant area behind an altered bar that holds few prey and gamefish. 

Sidebar 1- Many of the flies you use for fishing oyster bar habitats should be either weedless or ride hook point up.  Most of the resident prey species on oyster bars use the oyster shells for shelter, and usually don't venture above the bottom.  To fish these flies naturally, you'll have to get the fly near the bottom, which can result in hooking oysters rather than fish if your flies are not weedless.

Sidebar 2 - I prefer floating lines for fishing oyster bars because a sinking line can get snagged on the shallow part of the bar.  If I am fishing a deeper hole next to an oyster bar I prefer to use a sinking fly (e.g., clouser) and a slow retrieve to get fly deeper. 

Sidebar 3 - Water around oyster bars and sandbars can be turbid when currents or waves are strong enough to dislodge sediment from the bottom.  In such conditions, flies with rattles can be productive.  I often use a snapping shrimp pattern with a rattle when fishing in muddy areas around oyster bars.

Sidebar 4 - Although you don't often hear about the practice, it can be very productive to sight-fish along sandbars and even long oyster bars.  I like to pole my boat along the shallowest part of bar I can and, with the sun at my back, search for fish along the deeper edge next to the bar.  The highest part of the bar will also give you a sight-fishing advantage if you are wading.