Understanding Inshore Spoils and Oyster Reefs
The Kitchen in the Bay (Part 1 of a series)
When the intracoastal waterway (ICW) was excavated through each bay, sound, and inlet along the Gulf and Atlantic coast, they left the excavated material to the side of the canal that was cut. This material is referred to as spoil.
Why do the spoils attract speckled trout, redfish, and flounder? In the sediment that was excavated were very dense clays and gravel (mostly iron or calcium nodules as pea to golf ball sized gravel). The gravel, along with the stiff clay substrate, is just hard enough to allow oyster larvae (referred to as spat) to set and form oyster reefs, or at a minimum scattered oyster clumps. These reefs and scattered shell reef fragments create structure for the spotted sea trout, redfish, and flounder to relate to and create what I refer to as the kitchen in the bay.
Oyster reefs are tremendous resources for the bays and estuaries. Here is what happens at a mid bay live oyster reef. The oysters spawn monthly during the summer, typically starting by June in most bays. Ok, great, but what does that have to do with anything? ... The spawn, from the eggs to the milt, feeds the bottom of the food chain and microorganisms. Those micro organisms and their decomposition then feed bait fish and crabs which in the end feed our trout, reds, drum, and a host of other species. The reefs are the proverbial kitchen in the bay, and everyone loves to hang out and snack in the kitchen right?
The oysters are also filter feeders and clean the water of the bay of pollutants, so they also provide an environmental benefit beyond feeding the bait. The oysters actually feed on plankton, but take up large amounts of phytoplankton as well in the process. Oysters consume nitrogen containing compounds and thus can remove much phytoplankton from the water and thereby reduce turbidity in the water. Also, reducing the phytoplankton in the water reduces the competition for dissolved oxygen, which leaving more oxygen for the fish. USGS.
The spoil side-cast material was typically left in piles in deeper open water so it causes increased tidal and wind driven current and turbulence which mixes oxygen into the water column, sweeps bait fish, shrimp, etc. to predators and provides structure.
Structure gives predator species several things. First, it provides a roughened bottom surface that causes water speed to slow at the boundary of the rough texture due to water turbulence, thus giving the fish a refuge from fighting strong current. Second, the structure provides something for the fish to relate to and ambush bait from, and third, it gives them a narrowed space to trap the bait against. A rise from the bay floor causes the water column to be smaller and thus give the prey has less room to flee. What’s easier… playing tag on a football field or in a room the size of a kitchen?
Oysters can form on any hard clay, old spent or reclaimed oyster shell, other living oysters, wood, steel, rock, caliche well pad material etc. The spoils aren't the only places to find oyster reefs and scattered oyster reefs fragments. Well pads, mid bay jetties, historic bridge abutments or fragments from old roads and their construction can provide the needed substrate for starting oyster reef as well as historic areas where oysters naturally occur in mid bay areas. Additionally, most states have an oyster reef reestablishment program where they collect discarded oyster shell from commercial oyster establishments and replace that discard shell in areas of the bays that would make good habitat for oyster spat to connect on and grow into reef.
So, how do you find all these reefs and structure? Most maps of the bays will have some information relating to large reefs. Any mid bay hump or ridge will likely have oysters at the cause of creating the hump or ridge. Look for any excavated shipping or waterway area to have left spoil ridges (NOTE: be careful of wakes and currents from barges and ships as fishing near shipping or waterway spoils can be dangerous or sometimes fatal if care is not taken. Large wakes and shallow waters can capsize vessels). Look for wells in the bays (look for surface structures that look like something that might be related to petrochemical industry). Almost all of them have well pads made of caliche or crushed limestone gravel placed at the bottom of them in a house to half acre sized square-ish area and thus create substrate for oyster. However, you’ll want to focus on live reef. What? I thought you just told me that it forms all over? Well, not exactly.
Reefs form anywhere there is suitable hard substrate, but in order for a reef to stay alive and spawn it must reside in the area of the bay with the proper salinity for oyster growth and reduction of parasites that would kill the oysters. When I first started shooting the footage for the TroutSupport.com DVD’s I was lucky enough to meet and interview Dr. Sammy Ray in Galveston. In the interview, he said “oysters have numerous parasites that kill them and thus kill the reef”. One is a parasite referred to as the oyster drill (Urosalpinx cinerea), which is a predatory saltwater snail that can make a hole in the oysters shell and insert it’s proboscis to eat and thus kill the oyster. There is some data that indicates that the parasite’s distribution is somewhat controlled by major freshwater inflows. However, it appears the oyster drill can adapt for short lengths of time as long as the salinity change is gradual. According to Dr. Sammy Ray what seems to be true is the higher populations of oyster parasites, including the drill, typically require higher levels of salinity. Thus areas of bays having high salinity, and hyper saline lagoons, have less, and sometimes, no live reef at all. In some bays that have shifts in salinities, some wet weather years there will be live reef while some draughty years the reef will die due to the parasite abundance.
On the low salinity range, oysters require a salinity of at least 10 part per thousand (ppt) to survive. They can survive temporarily in lowered salinities below 10 ppt, which explains why we see them all the way up tidal creeks, but require at least 10 ppt to open, feed, and live (USGS). Back to our discussion of parasites or pests, brackish water clam species do use oyster as substrate to form on and attach to and in the best years of clam production, clams can cover or encrust and kill or at a minimum hinder the expansion of oyster reef.
In general you’ll find higher concentration of live oyster reef in areas of the bay that are at least some distance away from the Gulf and Atlantic inlets to allow some mixing of fresh water and thus reduce the amount of parasites. On the lower salinity or freshwater inflow side you’ll generally find a higher concentration of live oyster reef some distance away from inflows in order to allow for some salt water to mix into the water. Basically, the majority of live oyster reefs are found in the middle somewhere between the fresh and saltwater inflows.
Now, we all have maps and a friend or two that says he’s got a secret reef that is a honey hole for speckled trout or red drum. There may be some reefs that hold more schools more consistently but let us look at reef formation and destruction over a season. First of all, according to Dr. Sammy Ray, as long as there is suitable substrate to attach to it only takes about 3 months for an entire new reef to form from spat. That’s a significant growth rate to essentially have a new speckled trout and redfish…let’s call it a “honey hole”…be created and more than likely this will be somewhere in 3 to 8 feet of water. More than likely none of us will ever know exactly where this new reef forms and it probably won’t be on any map, it’s just somewhere in the middle of the bay where there’s enough hard particles for the spat to form on and 3 months ago it wasn’t even there. On the same note, an oyster boat can rake a reef area to nothing more than fragments in a matter of days… secret honeyhole reef could be gone that fast.
Some bay maps may get you close to the right area where oyster reefs or scattered shell on spoil may exist. However, you will want to learn how to read the water to know where the fish are on any particular day. The fish will tell you where they want to be on any given day and they will move also depending on tide direction and speed. I am suggesting that you let the fish tell you where they are by looking for bait, slicks, and birds in any area that you think might have oyster reefs or scattered mud/shell mix.
Speckled trout, or spotted sea trout, will be found in various locations on the reef depending on the season, water temperature, and oxygen level. Generally speckled trout will be found more shallow in spring and fall, and deeper in summer. Redfish will typically be shallower in “waste” deep or less depth of water, but not always. We will talk more on redfish later in the series. Flounder will be found on the shelf of channels and at the edge of the reef; they typically won’t lie directly on oysters themselves but can be found in small pockets or mud between the oysters.
Our TroutSupport.com DVD “Find the Fish – Catch a Limit- LimitSTi” was created specifically to help bay fisherman find and catch more and bigger speckled trout from Late April - November. As we approach summer and the water begins to warm the speckled trout and redfish will slowly begin to move to the deeper part of the water column taking up residence near these deep oyster reefs and we’ll begin to see consistent fishing reports, just as it has been every summer...The reports will say “…limits or near limits of speckled trout caught "keying on slicks and active bait".
The DVD allows you to see what the guides are looking for on the water to weed out unproductive water; you'll see specifically what to look for after finding schools of baitfish (we have all found herds of bait- what do you look for inside the school of bait to know which where the fish are?); In the DVD we use detailed motion graphics and computer models show how to work slicks in every wind and tide condition; and use birds in unique ways (were talking about what species to use and NOT use to key you in to finding feeding fish and more; this goes beyond gulls and terns).
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