When visiting and exploring seagrass beds, most are hoping, and expecting, to see fish. As we have seen in this series, there are a lot of creatures that can be found living within a seagrass meadow, but it is the fish that get our attention and what we talk most about afterwards.
According to Hoese and Moore’s Fishes of the Gulf of Mexico; Texas, Louisiana, and Adjacent Waters, there are 497 species of fish found in the Gulf of Mexico. In my surveys of Pensacola Bay over the years, I have logged 101 of those in the estuary. I am sure there are more, but I can confirm there are at least those. Many spend all or part of their time in our seagrasses. As you seine or snorkel in the grassbeds you will notice most of them are very small. Much of this is due to the fact that the seagrasses are nursery areas for many species, and it is the young that we find here. But many are also small as adults, and the grass provides food and shelter for them. There are far too many to mention in an article like this, but let’s look at some of them.
Sardines and Anchovies
As you snorkel through the grass, or even look at it from a boat or dock, you see numerous silver colored baitfish flashing as they dart in and out of the grass. There are all sorts of silver baitfish in the seagrasses with sardines and anchovies being two of them. In my experience seining for fish, they appear to be seasonal. I did not capture them all year but when I did, I would capture a lot. These species are famous for being the ones in small tins that people consume, though there is no fishery for them here locally. Anchovies have also been considered an indicator species; their presence suggests good water quality.
Also known as silversides and glass minnows, these are one of the most common fish collected in seine nets. They are abundant year-round and are an important food source for many of the larger predators living here. Small and transparent, you do not see them while snorkeling. Their huge presence is only discovered when you pull a seine net through the grass. There are several species of them, but they are not easily identified and more often are just logged as “silversides”. They are an important member of the seagrass community.
Seahorses and Pipefish
These two fish are highly specialized for living in seagrasses. They look like grass and move very little making them hard to detect. Like silverside minnows, it is rare to see them while snorkeling but make their presence known when seining. Their bodies are covered in armor-like scales, and they have tubed mouths for “vacuuming” small invertebrates from the water column. They are very slow swimmers and have to avoid detection by blending in with the environment. And yes, it is the males that carry the eggs in their brood pouches. These are amazing fish and always bring excitement when they are captured in the net. There are two species of seahorses and seven species of pipefish found in our waters.
Often called “bull minnows” by anglers, these small fish are, at times, very abundant. There are seven species of killifish in our bays but the Gulf Killifish, Longnose Killifish, and the Bayou Killifish are the ones we most often collected.
These are common, frequently seen, fish swimming at the surface of the water. Long and needle-shaped, these fish have long snouts full of sharp teeth indicating they are one of the predators of this system. There are four species of them, and they are not easy to tell apart. They are harmless to humans unless you capture them in your net at which time they will try to bite.
Another very common fish found year-round here. This species are the ones famous for jumping while you are fishing, paddling, or just watching from the beach. Those who do not visit the Gulf coast often always ask “I just saw a fish jump!” and the reply from a local (without even looking up to see what it was) will reply “It’s a mullet”. These schooling fish can get pretty large (average length is 30 inches) and it is common to see fishermen out with their cast nets trying to catch a few. It is a popular food fish for those along the Gulf coast. Mullet fries, with beans and grits, are a way of life here. The fish are easily seen swimming and darting over the grass as you paddle by, and their young are found seasonally in seine nets. They are bottom feeders, feeding mostly on algae from the grass blades. There are actually two species, the white and the striped mullet. The striped mullet, also known as the black mullet, is the one most often sold in the seafood markets.
Drums and Croakers
With 18 species within this family, this is the largest family of inshore fish in the Gulf. Growing up along the panhandle people learn quickly about croakers. Back in the day when gill nets were used to harvest mullet, croakers were a common catch as well, and often consumed. Today they are still sought by some shore-based anglers and juveniles are common in seine nets. The species I most often captured were the spot and Atlantic croaker. Spot croakers were common year-round, Atlantic croakers were more seasonal.
Drums are larger members of this family. There are several species more associated with sandy bottoms and the shoreline of the Gulf, many of these are called whiting, but the red drum (redfish) and black drum can be found in the grassbeds. Redfish are particularly common here and one of the reasons many anglers get out of bed in the morning. They are very popular sportfish across the region. Black drums are not found as often, and like being around pilings and structures that offer certain foods they prefer. Both species can get quite large. Redfish average 5 feet while black drums can reach an average of 3 feet.
All of the fish in this family are famous for their “croaking” “drum” sounds they make using their swim bladder, and it is rare not to capture at least one kind in a seine net.
Spotted Seatrout; Speckled Trout; “Specks”
There is no “trout family” in the fish world. Most freshwater trout are members of the salmon family while the marine versions are members of the drum/croaker family. This is the case with the famous speckled trout – or speck. There are white trout and silver seatrout in this family, and all are sought after by anglers, but it is the speckled trout that is most associated with seagrasses, most sought after by anglers, and is one of the top predators in this system. They reach an average length of 4 feet.
Pinfish and Sheepshead
From my experience both snorkeling and seining the grasses, I would say – hands down – that pinfish is the most common species found in our grasses. For many young anglers this is the first fish they ever catch. You can see them easily while snorkeling and they are the most numerous species in the nets throughout the year. Their huge numbers play an important role in the food web of this system. Feeding on a variety of small invertebrates in and around the grass blades, pinfish are a large part of the diet of the larger sportfish we target. Throwing cast nets and dropping pinfish traps is popular with anglers to collect this abundant baitfish for their life bait fishing efforts. They are called pinfish because of the sharp spines in their dorsal fins. These are also the fish that nip at your ankles while you are standing still in the water.
Sheepsheads are larger members of the porgy family (the ones these two species belong to). As adults sheepsheads prefer hard structure where they can use their incisors to chip away at barnacles and other shellfish, but they are sometimes found roaming the grassbeds and their young will spend their growing years hiding and feeding in the grass.
When first captured in the seine net, pigfish are often confused with pinfish – they look very similar. But a closer look at the striping/spotted pattern on their sides, and the position of their mouth, you realize you have something different. Being members of the grunt family, they also “croak” like croakers and drums – hence their common name “pigfish” – due to the grunting sounds. This helps with identifying which fish you have. Though common in the grasses, I did not catch these as frequently as pinfish and they were not as abundant.
This is a common silver baitfish that resembles the pinfish and is frequently collected in our seine nets. The mojarra is in a different family than pinfish. They lack sharp spines and incisor teeth, rather they have a sort of “vacuum” like mouth which they use to suck small invertebrates from the sand.
This is a popular sport and commercial fish from the wrecks and reefs of the Gulf of Mexico. But gags begin their lives in the seagrass beds, and we have collected medium sized individuals in our seine nets. This underscores the importance of these grassbeds to the fisheries so many love. We need to protect these systems from our activity both on land and in the water.
Another popular group with anglers, many species of jacks use these grasses as their nurseries. We most often collected juvenile lookdowns, pompano, and crevalle in our nets. At times we caught a small member of the family called a leatherjacket. These were seasonal and associated with breeding. Once again, underscoring the importance of having healthy seagrasses.
One of the creeper looking fish in the seagrass community is the Gulf toadfish (also known as the oyster dog). This monstrous looking bottom fish lives in burrows scattered around the grassbeds where they lie in wait to ambush prey. Their large mouths and sharp teeth can grab a variety of creatures, including the human finger. At times small toadfish will move into an empty can or bottle discarded by people instead of a burrow where they grow to a size they can no longer escape. It is said there may be a mild venom associated with their bite. Though no one has ever died, or been sent to the hospital, due their bite, it is painful and should be avoided.
Yes, barracuda can be found in seagrasses. But in our case, these have all been juveniles. There are three species of them, and they are not easy to tell apart. They also appeared to be seasonal in our collections. We never found them high numbers, usually one or two in a seine. But they are present.
This is another medium sized, sharp toothed, bottom dwelling predator of the grassbed community. There are seven species of them, and all have that “snake” “lizard” look to them having many sharp canine teeth. They spend their time buried in the sand waiting to ambush potential prey. Snorkelers may see them as they dart away tossing up sand when we get too close. I rarely see them snorkeling but occasionally capture them in the seine net to the delight of the students assisting.
Blennies and Gobies
These are very small fish that are almost impossible to find while snorkeling but are often collected in the seine net. They resemble the freshwater darters and, lacking a swim bladder, spend their time on the bottom. There are many species associated with rocks and artificial reefs but there are some who call the seagrasses home. They use their incisor teeth to feed on small invertebrates in and on the grasses. Being territorial, they can give a little nip to your hand. Gobies differ from blennies in that their two pelvic fins are fused together to form a sort of “cup” or “sucker disk”.
Another one of the more popular fish with students who help me seine. Everyone loves to see them inflate with either water or air into a “balloon” to make it very difficult for predators to consume them. There are eight species of puffers in the Gulf of Mexico, five of them have been captured in our seines. Most are small with little “bumps” on their bodies instead of spines. But there is the Burrfish, who is a member of a different family that is medium sized, has spines, and is very common in the grassbeds.
Our grassbeds are full of a small cousin to the triggerfish – the planehead filefish. Like triggerfish, filefish have a thick sharp spine that is found at the front of the dorsal fin – called a “trigger” on the triggerfish. The planehead filefish is a small species (nine inches average length), green to brown in color, and very common in the grassbeds; though you will probably not see one unless you catch it in a net.
Flounders and Soles
A favorite food fish for many locals, flounders spend a lot of time buried in the sand near grassbeds to ambush prey. Born with a typical fish design, early in development one of their eyes will move to the other side of the head, giving them two eyes on one side. By doing this, they have increased their binocular vision, improving their ability to judge accurate distance of the prey, and making hunting easier. They lose color on the side where the eye has left and have chromatophores (cells) on the side where the eyes are that, like octopus and squid, allow them to change colors and blend in. In our part of the Gulf, if the eyes move to the left side of the head, they are called flounders. If they move to the right, they are called soles. Soles in our part of the Gulf of small not of much interest to anglers. One small species is often collected by shrimpers who feed them to hogs. This sole can “cup” their body in defense making like a suction cup and they do this in the throat of the hogs sometimes killing them. They are called “hogchokers”. Flounders on the other hand are very popular with anglers. Some fish for them using rod and reel, others prefer gigging them at night using lanterns. There are 17 species of flounder, some reaching lengths of three feet.
Tonguefish are small flat fish with eyes on one side of their heads like flounder. They differ than that their tails come to a point and there is no caudal fin present, as there is in flounders. As mentioned, they are small – ranging from 3 to 8 inches in length. The Blackcheek tonguefish is particularly common in our grassbeds. But like so many, you will not see it unless you catch it in a net.
This is a very popular gamefish from south Florida associated with several habitats including grassbeds. Due to a process some call “tropicalization” – the movement of tropical species north due to climate change – snook are now, albeit in small numbers, reported in the Florida panhandle. This is a new species you may see while exploring or fishing out there.
There are many more species of fish found in our grassbeds we could talk about, but we will end it here. As we mentioned in the beginning, this is a group of animals that many come to the beach to find. Whether for fun or for food, finding fish makes for a good day. See how many different species you can find.
As I write this article it is mid spring, and the rays are bedding on the edges of our seagrass beds. The most common species seen is the Atlantic Stingray (Dasyatis sabina). They are often found in the sandy areas near the grass where they bury in the sand to ambush potential prey. This time of year, their numbers increase as the females are preparing to releasee their young in summer. Mating occurs in early spring and the females will deliver live young1.
According to Hoese and Moore2, there are eight families and 18 species of rays and skates found in the Gulf of Mexico. These are cartilaginous fish found in the same class as sharks but differ in that their gills slits are on the ventral side (bottom) of the body and their pectoral fins begin before the gill slits do on the side of the head. Most are depressed (top to bottom) and appear like pancakes, but not all of them. Sawfish and guitarfish appear more like sharks than rays.
Of the 18 species listed, seven can be found in the estuaries and may be associated with nearby seagrass beds. Two are species of sawfish, which are rare in our bays these days.
There are two members of the eagle ray family, the cownose ray and the eagle ray, which can be found in our bays. These resemble manta rays but differ in that they lack the characteristic “horns” of the manta (often called the Devil Ray because of them) and they do possess a bard on their tail, which manta’s do not. These are more pelagic rays spending their time swimming in the water column and hunting for buried food.
The butterfly ray does resemble butterflies in shape having wide “wing-like” fins and a very small tail. It behaves similar to stingrays burying in the sand and ambushing smaller prey.
Two of the more familiar stingrays are found in our grassbeds, the Atlantic Stingray and the Southern Stingray. The Atlantic Stingray’s disk is more round in shape while the Southern Stingray’s is more angular shaped. The Southern Stingray is larger (disk width about five feet, Atlantic disk width is about two feet) and prefers estuaries with higher salinity. The Atlantic Stingray is very common and can tolerate freshwater, thus is common throughout the bay.
Stingrays are notorious for their venomous bards and painful stings. They actually try to avoid humans and are frequently spooked by our activity fleeing as soon as they can. However, there are times when people accidentally step on one buried in the sand, or hiding in the grass at which time they will flip their whip-like tail up and over to drive their barb into your foot forcing you to move it – and you do move it – while you yell and scream. The ray then will swim away and can regrow a new barb.
The bard is a modified tooth. It is serrated on each side and there is a thin sac of venom along the flat side of the barb. When it penetrates your foot there is pain enough there. But the natural reaction of your body to an open wound is to close it, this reaction can pop the venom sac and release the toxin. The chemistry of the toxin is not life threatening to humans but is very painful. This experience is something you do want to avoid.
Like their shark cousins, rays do have rows of small teeth which they use to crush small invertebrates including shelled mollusks. They lie in the sand to ambush prey moving in and out of the seagrass beds. They possess two spiracles on the top of their heads which provide water to the gills when they are lying on the seafloor or buried in it.
Like sharks, males can be identified by the two claspers associated with the anal fin and the females usually have two uteri where the young develop. In skates, and some other rays, the young are deposited into the environment within a hardened egg case often called a “mermaids purse”. We see these washed ashore in the beach wrack. Young stingrays usually develop within the female and are born “live” in summer.
Though there is fear of this animal from some seagrass explorers they are a small threat unless you step on one. To avoid this, when in and around the sandy areas of a grassbed, move your feet in what we call the “stingray shuffle”. This is sliding your feet across the surface of the sand instead of stepping. The pressure generated from this movement can be detected by the ray several feet away and they will immediately move away.
Despite the fear, they are amazing creatures and play an important role in the overall health of the grassbed community.
1 Snelson, F.F., Williams-Hooper, S.E., Schmid, T.H. 1988. Reproduction and Ecology of the Atlantic Stingray, Dasyatis sabina, in Florida Coastal Lagoons. Copeia. Vol. 1988, No. 3 (Aug 1988). Pp. 729-739.
2 Hoese, H.D., Moore, R.H. 1977. Fishes of the Gulf of Mexico; Texas, Louisiana, and Adjacent Waters. Texas A&M University Presse. College Station TX. Pp. 327.
The Emerald Coast Open Lionfish Tournament May 20-21, 2023, at HarborWalk Village in Destin, FL, is gearing up to tackle a pressing ecological challenge while showcasing the power of sport to make a positive impact. This unique tournament, held along the picturesque shores of the Emerald Coast, focuses on combating the invasive lionfish population in the region’s waters.
Lionfish, native to the Indo-Pacific region, have become a significant threat to the delicate balance of marine ecosystems in the Gulf of Mexico. With their voracious appetite and rapid reproduction, these invasive species pose a grave danger to native marine life. The Emerald Coast Open Lionfish Tournament aims to address this issue by encouraging divers and fishermen to actively hunt and remove lionfish from the waters.
Participants in the tournament will compete to catch the most lionfish, utilizing their skills in underwater navigation, spearfishing, and conservation. Sponsors provide cash and prizes for multiple categories including most caught, largest and smallest lionfish. The event provides an exciting platform for experienced divers and newcomers alike to contribute to the preservation of the marine environment.
Beyond the ecological significance, the tournament also offers a thrilling experience for both participants and spectators. Divers equipped with their spears dive into the depths, searching for lionfish while showcasing their prowess and bravery. The tournament fosters a sense of camaraderie and shared purpose among the participants, creating a community dedicated to the cause of protecting marine ecosystems.
In addition to the competitive aspect, the Emerald Coast Open Lionfish Tournament promotes education and awareness about the invasive species. Participants and attendees have the opportunity to learn about the impact of lionfish on local marine life and explore sustainable solutions to combat the issue at the free Lionfish Awareness Festival from 10:00-5:00 each day. Sign up to volunteer at the event if you want to join the fun. The week prior to the tournament is dedicated to Lionfish restaurant week where local restaurants practice the “eat ‘um to beat ‘um” philosophy and cook up the tasty fish using a variety of innovative recipes.
The Emerald Coast Open Lionfish Tournament 2023 represents a unique fusion of sport, environmental conservation, and community engagement. By bringing together individuals passionate about marine conservation, this event serves as a powerful catalyst for change and a shining example of how sport can contribute to the preservation of our natural world. Learn more at https://emeraldcoastopen.com.
This fish is a classic example of why scientists use scientific names. There are numerous common names for this species and multiple ones even in the Gulf region. Ling, Cabio, Lemonfish, Cubby Yew, Black kingfish, Black salmon, Crabeater, and Sergeant fish to name a few. The Cajun name for the fish is Limon – possibly where the name Lemonfish came from. Based on the references, Cobia seems to be the most accepted name, but Ling is often used here along the Florida panhandle. Again, this is a great example of why scientists use scientific names when writing or speaking about species. There is less chance for confusion. I say less because at times the scientific names change as well, and some confusion can still occur.
The scientific name for this fish is Rachycentron canadum. The genus name refers to the sharp spines of the first dorsal fin, which are sharp. The species name may refer to Canada. It is a common practice to give a species the name of the area/location in which it was first described. But it seems that Carlos Linnaeus, the biologist who first described it, used a specimen from the Carolinas to do so. So, not sure why the name was given4. It is the only North American fish in the family Rachycentridae and its closest relative are the remoras of the shark sucker family.
Some state that cobia have only one dorsal fin, but in fact they have two. The first is a series of 7-9 spines spaced with no membrane connecting. They are small, sharp, and somewhat embedded into the body. This is very similar to how the remoras and shark suckers first dorsal spines work, albeit remora’s first dorsal is softer. Cobia have a low depressed head that gives them the appearance of a shark when viewed from the side. It is often confused with sharks because they can get quite large – an average of five feet in length and up to 100 pounds in weight. The small juveniles resemble remora quite a bit. They are darker in color with pronounced lighter colored lateral stripes and their caudal fin (tail) is more lancelet and less lunate than the adults.
Biogeographically they are listed as worldwide, albeit tropical to subtropical – they do not like cold water. In the United States they are found all along the east and Gulf coast, but are absent from the west coast – again, a dislike for cold water. The literature states that there are two population stocks of cobia here. The Atlantic group and the Gulf of Mexico group all head south towards the Florida Keys for winter. However, breeding appears to take place in the northern parts of their range and so no genetics are exchanged while the two groups co-exist in the Keys. If this is the case, and it seems to be, there is a reproductive barrier, or behavioral barrier, that could, over time, isolate these two groups long enough that the gene pools could become different enough that attempts to breed between the groups would not produce viable offspring. If this were the case then they could be listed as subspecies, possibly the Atlantic and Gulf Cobia. But this has not happened. There are also studies that suggest in the Gulf there may be isolated groups. One comment is that there are cobia along Florida’s Gulf coast that migrate inshore and offshore but do not make the run to the Keys and back4. There are also studies that show a similar behavior with a group over near Texas. Obviously, there is a lot of work to be done on the movement and genetics of these possible subgroups to completely understand the biogeography of this animal. And don’t forget, there are cobia along the European/African coast of the Atlantic as well as the Indian and western Pacific.
But migrate they do. The “Ling Run”, as it known in the Pensacola area, is something many anglers wait for early in the year. We even have some local bait and tackle shops monitoring water temperature to announce when the run will begin. When water temperatures warm to 67°F it is time. Local anglers flock the Gulf side piers and head out on their boats with high ling towers to search for them. At the beginning of the ling run I have seen the inshore Gulf of Mexico littered with hundreds of boats covering the surface like small dots as far as you can see. One boat I remember was about 20 feet long and had precariously placed a large step ladder in the center as a “ling tower”. The angler was perched at the top of the ladder, holding on in the chop, searching the waters for his target.
Cobia will travel alone or in groups of up to 100 and are often attracted to objects in the water. Flotsam like Sargassum weed, or marine debris are places that anglers focus on. They are known to shadow sharks, manta rays, and sea turtles. I know anglers when they see a sea turtle begin throwing bait in that direction in hopes that a cobia is nearby. To the west of us in Alabama they seem to visit the offshore gas rigs and are attracted to the fishing piers many communities have extending into the Gulf – hence the large crowds of non-boating anglers visiting them during the run. Many anglers are known to drop FADs (Fish Attracting Devices) into the water to attract cobia, though these are not allowed during cobia/ling tournaments – which also pop up across the panhandle during the run.
Despite this apparent heavy fishing pressure, it is considered a sustainable fishery. Cobia mature at an early age, 2 years for males and 3 for females – and they live for about 12 years. They mass spawn in the northern waters. A typical season will find females breeding 15-20 times and producing 400,000 – 2,000,000 per spawn event. There is no evidence that this fishery is overfished, and there is commercial fishery for them as well. Due to their quick growth rates, large size, and high-quality flesh, there is interest in offshore aquaculture of this species.
It is an amazing fish. One of the best fish sandwiches I have ever had was a fresh ling sandwich. It is also a very interesting species from a biographical point. Enjoy the next “Ling Run” along the panhandle – or “cobia run”, or “lemonfish run”, which ever you wish to call it.
“Bluefish!” … “It’s just a school of bluefish!” So yelled the lifeguard in Jaws II when Chief Brody had mistaken a school of bluefish for the rogue great white shark that was plaguing the town. He would not have been the first to mistake these large schools for a larger fish, particularly a predatory shark, but as some know, bluefish are quite predatory themselves.
Bluefish Image: University of South Florida
Growing up along the Florida panhandle we heard little about this species. We had heard stories of large bluefish schooling along the Atlantic coast killing prey with their razor-sharp teeth and, at times, biting humans. But not much was mentioned about them swimming along our shores. But they do, and I have caught some.
Bluefish are one of several in a group Hoese and Moore refer to as “mackerel-like fish” in Fishes of the Gulf of Mexico. They differ in that they lack the finlets found along the dorsal and ventral sides of the mackerel body and mackerels lack scales having a smoother skin. Bluefish are the only members of the family Pomatomidae. They can reach three feet in length and up to 30 pounds. They travel in large schools viciously feeding on just about anything they can catch and seem to really like menhaden. They move inshore for feeding and protection from larger ocean predators but do move offshore for breeding.
Bluefish landed from the Gulf of Mexico are much smaller than their Atlantic cousins, rarely weighing in more than three pounds. They do have a deep blue-green color to them and thin caudal peduncle and forked tail giving them the resemblance of a mackerel or jack. Some say they are bit too oily to eat while others enjoy them quite a bit. There is a commercial fishery for them in Florida and, as you would expect, it is a larger fishery along the east coast. Most of the panhandle counties have had commercial landings, albeit small ones.
Biogeographically, the blue fish are found all along the Atlantic seaboard and into the Gulf of Mexico. It is listed as worldwide but seems to be absent from the Caribbean and other tropical seas. This could be due to a distaste of warmer waters, or the lack of their prey targets.
They are an interesting and less known fish in our region. Swimming in a school of them should be done with caution, there are reports of nips and bites from these voracious predators.
This began with a call from one of my volunteers who was checking salinity at Shoreline Park. She reported the salinity, but also reported to smell of dead fish – though she could not see them. I visited Shoreline Park the following day on another project and could smell it as well. There was a large amount of dead seagrass washed ashore from a recent storm and I thought this may be the cause of the smell because I did not see the dead fish either.
When I got home, I checked the FWC fish kill database. It reported a redfish kill in Pensacola Bay. It is unusual to see a kill of only one species. Many times, these are releases from fishing activity, particularly bait, and thought this must be the case – FWC did not mention the cause. I let the volunteer know and asked to keep an eye out.
I reported this to the Escambia County Division of Marine Resources to (a) let them know, and (b) to find out if they had any idea of cause. They replied that the location was incorrect. The kill was actually near Galvez Landing on Innerarity Point. He (Robert Turpin) had visited the site and did find any dead fish. I have a lot of volunteers over that way so asked each to take a look. They did not see any dead fish. I asked them to keep an eye out and collect a dead fish if they saw one for testing. Often when a large fish kill occurs, and it is only one species, the suspect cause is disease. Tissue samples could confirm this.
And then came another call.
This time it was from one of our Master Naturalist who lives on the eastern shore of Mobile Bay. He wanted to know what was up with all of the dead redfish along the shore of the bay. He sent photos and his beach was littered with them. I reached out to Mississippi/Alabama Sea Grant to see if they knew what was going on. They had heard about the situation and knew the Alabama Department of Natural Resources was collecting samples. The Gulf Islands National Seashore then reported large numbers of dead redfish along the National Shores property in Mississippi, something was up.
Dead redfish on the eastern shore of Mobile Bay. Photo: Jimbo Meador
I eventually got word from Dr. Marcus Drymon at the Dauphin Island Sea Lab. They had a team working on this. Their team reported that stratification of the Gulf had created a hypoxic (low dissolved oxygen) layer on the bottom and the male “bull redfish” had gathered for breeding and died.
So, we are back to our title – what is stratification and how did this cause the fish kill?
Stratification is the layering of the water. Less dense water will sit atop the more dense. Water temperature or salinity can cause this density difference and layering. Colder and/or saltier water is denser and will form the bottom layer. If you have high winds, it will mix the water and the stratification disappears. Tides and currents can affect this as well.
What they believe happened recently was excessive amounts of rainfall created a large layer of freshwater to move from Mobile Bay into the open Gulf. The combination of tides and wind allowed a stratified layer to form. The oxygen that marine life uses is dissolved into the water at the surface and referred to as dissolved oxygen (DO). If the system is stratified, then the oxygen dissolved at the surface will not reach the bottom and hypoxia (low DO) can happen. They this is what happen. It just so happens that the large male redfish (bull reds) had congregated just offshore for breeding. They are more sensitive to low DO than the smaller females and any juveniles. So, the males died. To answer the question as to why other fish did not die (what you typically see in a DO related fish kill) – the numbers were not mentioned by there was one reference to 4.0 ppm. This is the high threshold of hypoxia. Many fish can tolerate at this concentration, but the male redfish could not.
So, that is what we think happened. The perfect storm of the demise of a group of male redfish just off of Mobile, and the carcasses drifted to other locations.