Trout in the grass, Understanding SAV

Submerged aquatic vegetation (SAV) is important to the coastal ecosystem, and it’s a great place to find and catch speckled trout. Learn more here.

When inshore anglers talk about grass, they are either cursing the plants that are stealing time away from their fishing or heaping praise on the plants that attract their favorite gamefish species. 

In the latter case, the plants are aquatic grass or more specifically, submerged aquatic vegetation (SAV). There is good reason to talk about it, beyond its ability to foul our hooks, because it is one of the richest aquatic habitats found in inshore waters. SAV holds a plethora of baitfish species, from mullet, killifish and silversides, to juveniles of larger species such as spotted sea trout and crustaceans such as crabs and shrimp. 

For inshore anglers, the list of aquatic species above encompasses much of what speckled trout and redfish feed on, so it’s no wonder that during parts of the year grass beds are a fishing heaven.

Jerkbaits, twitchbaits and topwater plugs can be fished above submerged grass very effectively.

When to look in the grass 

In April, speckled trout are found in shallow waters, including flats along channels, medium-sized lakes and the edges of bays. They have not begun to move to higher-salinity waters on the outside to begin the spawn. Where these shallow waters are also home to SAV, anglers are more likely to find trout, redfish and bass, which are there to feed on the plentiful bait. This productive grass habitat can also be found along the edges of channels like the MRGO. Knowing where to find and how to fish the grass will improve your fishing success. 

Adult speckled trout are most often found around grass beds during the spring and fall. As the water warms in March and April, trout will move into areas with flooded grass beds to forage because of the abundance of food and access to cover from predators. Similarly, in September and October, trout leaving the sounds where they have been spawning will appear around the grass beds of large, inshore water bodies. Again, grass beds provide excellent feeding and cover habitat until the beds begin to die back as the hours of sunlight decline. 

Speckled trout love to feed around grass beds because of the food that it holds: baitfish and crustacaens.

How to fish grass beds

The most-productive time to fish over grass is when the water completely covers grass, such as on rising tides and high-tide periods, and when the water is relatively still. With at least a foot of water above the SAV, anglers are able to work lures effectively without continuously snagging, but more important, the flooded grass lets trout and redfish cruise over or through the top of the grass, which is an effective feeding behavior. Marsh bass also frequent grass, but they often ambush from stationary positions inside the grass bed, so high water is less important when choosing when to target them in grass beds. 

My most-productive techniques for fishing flooded grass are a shallow-running jerkbait or twitchbait, a topwater bait or a popping cork. For instance, the Matrix Shad RipShad and the Rapala Shadow Rap are excellent jerkbaits for this purpose. They are both shallow-running baits that will make a ruckus while skimming the tops of the vegetation. When fishing a popping cork over grass, I like to keep the leader at a length where the swimbait will hang among the tops of the leaves. Either paddletails or shrimp imitations have worked well for me. 

Eel grass is a prominent SAV in Louisiana’s coastal waters; small fish use it as cover and predators as feeding grounds.

Types of grass

The most-ecologically productive SAV beds, according to the research work done is American eelgrass. Eelgrass provides an especially rich habitat because it covers the bottom with a mat of thin leaves that smaller fish and crustaceans can use for cover from larger species such as speckled trout, redfish and sheepshead. Despite the cover, eelgrass beds still allow larger species to cruise the tops and perimeter of the beds and grab bait should it wander too far from the protective cover. 

Another common SAV in Louisiana is widgeon grass, which provides a more-productive habitat than mud bottom but is not as ecologically productive as eelgrass. The widgeon grass bed structure is taller and less dense than eelgrass, because it has stalks with branching small leaves attached to the stalks. This provides less cover for small fish than eelgrass but much more cover than a bare, mud bottom. The widgeon grass also holds sediment in place, which improves local water quality and makes that part of the bed more attractive for predators. 

SAVs are categorized across the estuary gradient by marsh zones, and eelgrass is found in the intermediate marsh zone, which has salinity in the 3.0 to 10 ppt range. Widgeon grass can be found from intermediate to brackish zones with 10 to 20 ppt of salinity, and even in some saline zone areas where salinity is greater than 20 ppt. Its greater tolerance for salinity allows widgeon grass to thrive over more of the Mississippi River estuary than eelgrass.

Trout numbers have dropped in Louisiana waters as SAV coverage has dipped and habitat has been degraded.

The decline in grass beds

Eelgrass dominated the SAV varieties in Lake Pontchartrain in the 1950s, but by 2000, it had lost 50% of its distribution in the basin. Currently, eelgrass in Lake Pontchartrain is mostly found on the north shore and in patches elsewhere, such as the area around Irish Bayou. In the 1950s, eelgrass heavily populated the south shore of Lake Pontchartrain as well but is now largely absent from that area. 

Due in part to the completion of the Mississippi River Gulf Outlet (MRGO) channel in 1965, eelgrass distribution in Lake Pontchartrain has declined, largely replaced by widgeon grass. The MRGO allowed high-salinity water direct entry into Lake Pontchartrain. 

All grass species have seen a decline since the 1950s. While eelgrass was impacted by salinity increases, all species of SAV were negatively impacted by municipal and agricultural runoff and storms. Researchers recorded a 90% decrease in SAVs from 1950 to 1985. A 74% decline in grass in Lake Pontchartrain is attributed just due to damage from Hurricane Andrew in 1992.

 The loss of SAV is another, less-visible symptom of the devastating habitat loss in coastal Louisiana, and it’s worth noting that the speckled trout stock has also decreased in similar magnitude over the same period of time. 

Grass growth factors 

The flourishing of SAVs is dependent on protection from high salinity, high turbidity, and excessive wave energy. Natural turbidity due to tidal flow and normal weather activity is decreased by the presence of SAV, but conversely, hurricanes, marshland loss, and the dumping of Mississippi River water into Lake Pontchartrain can overwhelm the SAV with turbidity, blocking out the sun and creating excessive drag on the leaves, leading to plant damage. 

An ever increasing loss of marshland is followed by the creation of open water, and that will increase wave energy in areas where SAV historically exists. Eelgrass is more tolerant than widgeon grass to wave energy, which is a beneficial characteristic where marsh erosion is being fought, so the widespread replacement of eelgrass with widgeon grass is less effective at combating marsh erosion. 

This chart shows distribution of aquatic vegetation along Louisiana’s coastal area.

Why care about grass? 

Marshland loss is believed to be a significant reason for the decline in Louisiana’s speckled trout stock and, conversely, the restoration of marshland carries hope for a pathway to restoring the trout. However, research shows that SAV beds are far-more ecologically productive than mud bottoms, so restoration of SAV alongside land restoration should be a faster pathway to speckled trout stock enhancement. 

Research in Lake Pontchartrain showed that while adult speckled trout can be found across all types of bottom structure during the year, SAV is critical to the survival of trout larva and juveniles. This research has been duplicated in other Gulf states, including Florida. 

Expanding SAV coverage as a primary driver for promoting both inshore fisheries and water quality is a practice of management authorities in other regions such as the Chesapeake Bay and parts of Florida, including Tampa Bay. These areas are achieving a growth in SAV through conservation, environment changes and even SAV planting. Since SAV also improves water quality and sediment stability, expansion of SAV beds could be the bridge that links costal restoration and speckled trout stock restoration in Louisiana. Knowing suitable areas for SAV growth is critical to any SAV restoration plan, and scientists at LSU have already created a model that would help coastal restoration managers determine where to target restoration activities for expansion of SAV. 

Increasing SAV

Increasing SAV in Louisiana will require improvements to other aspects of the inshore waters. While our inshore area covers more than a half-million acres, the area suitable for SAV growth is decreasing. Suitableness is negatively impacted by highly variable salinity, blown-out marsh where wave energy directly impacts the potential SAV areas, and high turbidity.

Ironically, high turbidity is partly the result of a lack of SAV to stabilize marsh sediment. The best SAV for locking down the sediment despite the wave energy from eroded marsh is eelgrass. However, eelgrass must have salinity controlled to the intermediate zone of 3 to 10 ppt, so expansion of eelgrass beds requires a more controlled salinity gradient from the fresh marsh zone to the saline marsh zone. 

The Louisiana Department of Wildlife and Fisheries, which manages fisheries stocks, has only harvest controls to manage the health of the stock, but coastal-restoration plan managers may well hold the most-effective key to bringing about the change anglers want. Encouraging costal restoration managers to design in SAV expansion when developing their action plans is one of the most-productive lobbying efforts for anglers and fishery conservation organizations to grow the speckled trout stock in Louisiana.

About Jon Miller 61 Articles
Jon Miller is an engineer, lifetime fisherman, and host of the YouTube channel Jon Miller Fishing.