by Rick O'Connor | Aug 27, 2021
For those who lived in the Pensacola Bay area 50 or so years ago, this question comes up from time to time. By scallop I am speaking of the bay scallop (Argopecten irradians), the one sought by so many scallopers then and now. This relatively small bivalve sits on beds of turtle grass, gazing with their ice blue eyes, filtering the water for plankton and avoiding numerous predators. They only live for a year, maybe two. They aggregate in relatively large groups and mass spawn. Releasing male gametes first, then female, fertilizing externally in the water column, to create the next generation.
Bay Scallop Argopecten iradians
http://myfwc.com/fishing/saltwater/recreational/bay-scallops/
These are unique bivalves in that they can swim… sort of. When conditions are not good, or a predator is detected, they can use their single adductor muscle to open and close the shells creating a current of expelling water that “pushes” them along and off the bottom. They were once found from Pensacola to Miami… but no longer. Scallops have become almost nondetectable in much of their historic range. Today they congregate in the Big Bend area of the state, and there they are heavily harvested.
What happened?
Well, if you look at the variety of causes for species decline around the globe habitat loss is usually at the top of the list. The habitat of the bay scallop are seagrass beds. There are many publications reporting the loss of seagrasses across the Gulf and Atlantic coast. Locally we know that the historic beds of the Pensacola Bay system have declined. We also know that some of those beds have shown some recovery in the last 20 years. But was the loss enough to cause the decline of the scallop?
Studies show that there is a strong association between seagrasses and scallops. The planktonic larva typically attached to grass blades a week or two after fertilization. This seems essential to reduce predation. Once they drop from the blades, vegetative cover is important for their survival. This suggests yes – any loss of seagrass could begin the loss of bay scallops.
What about water quality?
We do know that scallops need more saline brackish water – at (or above) 20 parts per thousand (20‰); 10‰ or less is lethal. Sea Grant is currently working with citizen scientists in Escambia County to monitor the salinity of area waters weekly. Though we do not believe the data is usable until we have 100 readings from each location, early numbers suggest that locations in Big Lagoon and Santa Rosa Sound are at 20‰ threshold. We do not know whether run-off engineering of the 1970s may have lowered the salinity to cause a die-off, and one would think (since they can swim) they would move to a better location. However, if salinities were low across much of their local range, and seagrasses were not available in areas where salinities were good, this could have a devasting impact on their numbers.
Then there is sedimentation. Studies show that young scallops (<20mm) that do not have seagrass to attach to settle on silty bottoms and their survival is very low. And then there are toxic metals, and other contaminants that scallops may have little tolerance for. It is known that juvenile scallops have a low tolerance for mercury.
Disease?
One study from the Tampa Bay area indicated that there was little loss of scallops due to disease and parasites.
And then there is overharvesting…
Scallops are mass spawners and there needs to be high numbers of adults near each other for reproduction to be successful. If people are taking too many, this can lead to more spaced adults and less chance of successful fertilization. This combined with environmental stressors probably did our populations in.
According to a publication from Sarasota Bay Estuary Program in 2010, populations of less than five scallops / 600m2 is considered collapsed. Sea Grant has been conducting volunteer scallop searches in the Pensacola Bay area for the last five years. In that time, we have found only one live scallop… we have collapsed. During the 2021 Scallop Search, 17 volunteers surveyed 4000m2 and found no live scallops. However, reports of live scallops outside of our surveys indicate they are still there. We will see what the future holds.
References
Castagna, Michael, Culture of the Bay Scallop, Argopecten irradians, in Virginia (1975). Marine Fisheries
Review, 37(1), 19-24.
https://scholarworks.wm.edu/vimsarticles/1200
Leverone, J.R. 1993. Environmental Requirements Assessment of the Bay Scallop
Argopecten Irradians Concentricus. Final Report. Tampa Bay Estuary Program. Pp.82.
Leverone, J.R., S.P. Geiger, S.P. Stephenson, and W.S. Arnold. 2010. Increase in Bay Scallop (Argopecten irradians) Populations Following Releases of Competent Larvae in Two West Florida Estuaries. Journal of Shellfish Research. Vol. 9, No. 2, pp. 395-406.
by Rick O'Connor | Aug 27, 2021
Six Rivers “Dirty Dozen” Invasive Species
Mimosa (Albizia julibrissin)
Define Invasive Species: must have all of the following –
- Is non-native to the area, in our case northwest Florida
- Introduced by humans, whether intentional or accidental
- Causing either an environmental or economic problem, possibly both
Define “Dirty Dozen” Species:
These are species that are well established within the CISMA and are considered, by members of the CISMA, to be one of the top 12 worst problems in our area.
Native Range:
Tropical Asia
Introduction:
Intentionally introduced into the United States in 1745 as an ornamental plant. It was popular due to its showy flowers.
EDDMapS currently list 18,546 records of this plant spread across the United States. The vast majority are from the southeastern U.S. 3,323 records are from Florida and 944 within the Six Rivers CISMA. It is most likely under reported.
Description:
This is a small trunked tree with an expanded canopy that reaches about 40 feet in height. It is easily identified by the compounds leaves that can have 20-60 leaflets per branch. The flowers are a brilliant pink and resemble poms-poms. The tree flowers in spring and early summer. Seed pods are present in winter. They are about six inches in length and are light brown in color.
Issues and Impacts:
The primary impact is direct competition with native species. Mimosa does very well in open areas and along the edges of disturbed forested areas. It produces numerous seeds and can take advantage of available native habitats.
Management:
Mechanical removal of saplings is recommended before the plant goes to seed. It is important to remove all roots when pulling by hand to reduce the chance of resprouting.
Chemical treatments (herbicides) will be needed if cutting trees. A 2% solution of glyphosate, or triclopyr, can be used but retreatments may be needed. Application will require a surfactant and contact with the leaves will be enough. 15% Garlon 4, or 100% Pathfinder II, on the bark covering an area of 2 feet can be effective. Trees with trunks larger than 3 inches in diameter may require re-treatment.
There are no known biological controls at this time.
For more information on this Dirty Dozen species, contact your local extension office.
References
Early Detection and Distribution Mapping System (EDDMapS)
https://www.eddmaps.org/
Six Rivers CISMA
https://www.floridainvasives.org/sixrivers/
University of Florida IFAS Assessment
https://assessment.ifas.ufl.edu/assessments/albizia-julibrissin/.
University of Florida Center for Aquatic and Invasive Plants
https://plants.ifas.ufl.edu/plant-directory/albizia-julibrissin/.
by Rick O'Connor | Aug 18, 2021
This is a famous fish. If you look back at the old tourism magazines of the early 20th century you will see a lot about tarpon fishing in Florida. As a matter of fact, some say that tarpon fishing was the beginning of the tourism industry in the state. Also known as “silver kings”, they put up a tremendous fight which anglers love, particularly on lighter tackle. It is a sport fish, not sought for food, so catch and release has been the rule for years. But those who seek them will tell you it is worth the fight even if you must release it.
Tarpon have been a popular fishing target for decades.
Photo: NOAA
Tarpon (Megalops atlantica) are large bodied, large scaled fish, with a deep blue back and silver sides. They are a large fish, reaching over 8 feet in length and up to 350 pounds. They tend to travel in schools and are often associated with other fish, such as snook2.
It has always been thought of as a “south Florida fish”. As mentioned, down there it is a popular fishing target for tourist and residents alike. Many charter captains specialize in catching the fish and they have been featured in fishing programs. But you do not hear about such things in the Florida panhandle. Hoese and Moore1, as well as the Florida Museum of Natural History2 both indicate that they are in fact in the Florida panhandle. As a matter of fact, this fish has few barriers and has the distribution of the classic “Carolina fish” group. That includes the entire eastern seaboard of the United States, the entire Gulf of Mexico, and the Caribbean1. The Florida Museum of Natural History indicates they are found on the opposite shores of the Atlantic Ocean and may have made their way through the Panama Canal to the Pacific shores of the canal. Within this range they are known to enter freshwater rivers. They seem to have few biogeographic barriers.
I grew up in the panhandle and remember hearing about them swimming in our area when I was younger. Fishermen said they would throw all sorts of bait at them. Artificial lures, live bait, cut bait, you name it – they tossed it… the tarpon never would take it. Catching one here was almost impossible. The flats fishing charter trips for tarpon in south Florida would not happen here. I remember once diving in Pensacola Bay near Ft. Pickens. We were looking for an old Volkswagen beetle that had been sunk years ago when at one point the water became very dark – almost like storm clouds had rolled in. When my buddy and I both looked up we saw a school of very large fish swimming above us. We were not sure what they were at first but as we slowly ascended, we realized they were tarpon. It was pretty amazing.
An interesting side note here. In 2020 tarpon were once again seen swimming around the Pensacola area but this time they WERE taking bait. There were several reports of tarpon caught off the Pensacola Fishing Pier and inside the bay. Why change over all this time? I am not sure.
The ladyfish (or skipjack) is the smaller cousin of the tarpon, but puts up a good fight as well.
Photo: University of Southern Mississippi
Tarpon belong to the family Elopidae which also includes another local fish known as the “ladyfish” or “skipjack” (Elops saurus). This is a much smaller fish reaching about 3 feet (and that would be a large ladyfish). The scales of this family member are much smaller, but the fight on hook and line is just as large. The characteristic that places these two fish into the same family (and these are the only two in this family) is the hard bony gular plate found between the right and left side of the lower jaw (in the “throat” area).
Like tarpon, it is not prized as a food fish but more of a game fish. It has the classic wide distribution of the “Carolina fish group” – the eastern seaboard of the United States, the Gulf of Mexico, down to Brazil. Like the tarpon, it is found in brackish conditions but is not mentioned in freshwater. Again, few biogeographic barriers for this fish.
Both members of this family provide anglers young and old with a lot of enjoyment.
1 Hoese, H.D., R.H. Moore. 1977. Fishes of the Gulf of Mexico; Texas, Louisiana, and Adjacent Waters. Texas A&M Press, College Station TX. Pp. 327.
2 Discover Fishes. Tarpon. Florida Museum of Natural History. https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/megalops-atlanticus/.
3 Discover Fishes. Ladyfish. Florida Museum of Natural History. https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/elops-saurus/.
by Rick O'Connor | Aug 11, 2021
EDRR Invasive Species
Green Mussel (Perna viridis)
This cluster of green mussels occupies space that could be occupied by bivavles like osyters.
Define Invasive Species: must have ALL of the following –
- Is non-native to the area, in our case northwest Florida
- Introduced by humans, whether intentional or accidental
- Causing either an environmental or economic problem, possibly both
Define EDRR Species: Early Detection Rapid Response. These are species that are either –
- Not currently in the area, in our case the Six Rivers Cooperative Invasive Species Management Area (CISMA), but a potential threat
- In the area but in small numbers and could be eradicated
Native Range:
Green mussels are native to the Indo-Pacific region extending from India to Southeast Asia.
Introduction:
Green mussels have been cultivated as an aquaculture product and were introduced to other parts of the world as such. They were first reported growing wild in the waters of the Caribbean in the 1990s reaching Venezuela by 1993. The first report in Florida was in the Tampa Bay region in 1999. They have been slowly dispersing south along Florida’s Gulf coast. In 2003 they were found on the Atlantic coast near Crescent Beach and the Jacksonville-St. Augustine area. That same year a few single specimens were collected off the coast of Georgia and by 2006 there were records in Charleston SC. There are only a couple records from the Florida panhandle. In 2008 a couple of specimens were reported in the Panama City area and one record in 2011 came from Perdido Key (this one may have been misidentified).
EDDMapS currently list 128 records of green mussels in the U.S. All 128 are from the state of Florida, though the USGS reports one from the state of Washington. There is only one record within the Six Rivers CISMA (that from Pensacola Bay region).
Description:
Mussels are sessile bivalves attached to the substrate using thin byssal threads. This is a large mussel, reaching lengths of 3-4” and some up to 6”. Its shell is not ribbed like our native ribbed mussel often found in salt marshes, but rather smooth and possesses a brilliant emerald green color. In larger/older individuals the green is found more on the margins of the shell with the rest taking on a brownish coloration. The inside of the shell resembles our native mussel in having a bluish iridescent coloration.
Issues and Impacts:
The primary issue with green mussels is fouling. Like zebra mussels, green mussels can foul boat bottoms, overgrow on marina pilings, and clog intake pipes for water treatment and power plant facilities. They can clog crab traps, shellfish aquaculture bags, and will displace native species such as oysters – making oyster restoration projects harder. There is evidence of predation by blue crab and sheepshead, but there does not seem to be enough predation to control populations where they are currently found.
Management:
First, check your boat hull and bilge water before trailering to another water body. It is recommended that you scrap the hull and empty your bilge on land so as not to provide any live material entering the waterways. Be sure you are removing at a location at the ramp where the animals, or even sections of the animals that may contain gametes, cannot reach the waterways during a rain event or other run-of situation.
Second, if found on a seawall or piling, use a paint scraper or flat shovel to remove from such. You want to collect AS MUCH MATERIAL AS YOU CAN into a 5-gallon bucket and remove from the water system. Again, any gamete material remaining could continue the population. At this point you can allow them to dry out and then dispose of.
Third, if in intake pipes there are several methods to remove but many are expensive and options depend on the system that is fouled. It is recommended that you contact your county extension office for advice.
In either case, it is important to report the record to EDDMapS – https://www.eddmaps.org/.
For more information on this EDRR species, contact your local extension office.
References
Dr. Shirley Baker, University of Florida, personal communication.
McGuire, M., J. Stevely. 2018. Invasive Species of Florida’s Coastal Waters: The Asian Green Mussel (Perna viridis). University of Florida IFAS Electronic Data Information System (EDIS). https://edis.ifas.ufl.edu/publication/SG094.
United States Geological Survey. Nonindigenous Aquatic Species Series. Green Mussel (Perna viridis). https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=110.
Early Detection and Distribution Mapping System (EDDMapS)
https://www.eddmaps.org/
Six Rivers CISMA
https://www.floridainvasives.org/sixrivers/
by Rick O'Connor | Aug 8, 2021
Like the ancient sturgeon, this is one strange prehistoric looking group of fish. I’ll say group of fish because there is more than one kind. For many, all gars are alligator gars. There is an alligator gar but there are others. Actually, the longnose gar may be seen more often than the alligator gar, but many do not know there is more than one kind.
Gars are freshwater fish, but several species have a high tolerance for saltwater. The alligator gar (Artactosteus spatula) has been reported from the Gulf of Mexico1. They are elongated, slow moving fish with extended snouts full of sharp teeth – very intimidating to look at. But swimming with gars in springs and rivers, I have found them to be oblivious to me. Snag one in a net however, and they will turn quickly and could do serious harm. While fishing my grandson had one come after his bait once and that was pretty exciting, but it is rare to catch them on hook and line. Many who fish for them do so with bow and arrow. Their skin is covered with tough ganoid scales. You really can’t scale them; you have to skin them.
Alligator Gar from the Escambia River.
Photo: North Escambia.com
In the book Fishes of the Gulf of Mexico, by Hoese and Moore, they list four species of gar in the northern Gulf. As the name suggests, the longnose gar (Lepisosteus osseus) has a long slender snout and has spots on the body. It is the one most often seen by people visiting our springs, rivers, and the one most often seen in our estuaries. It can reach a length of five feet3.
The famous alligator gar (Artactosteus spatula) has a shorter snout and spots are usually lacking. If they do have them, the are usually on the fins. This is a big boy – reaching lengths of nine feet and up to 100 pounds2. They are common in coastal estuaries and even the Gulf, though not encountered very often.
The spotted gar (L. oculatus) also has a short snout but has spots all over its body. It prefers the rivers and will enter estuaries only where the salinities are low. It is smaller at four feet4.
Spotted Gar.
Photo: University of Florida
The last panhandle gar is the shortnose gar (L. platostomus). This species too prefers rivers and may enter low salinity bays. It has a short snout and lacks spots.
There is a Florida gar (L. platyrhincus) not found in the panhandle but exists along the central and south Florida gulf coast. It seems to have replaced the spotted gar in this location5.
The biogeography of this group of fish is interesting in that it is an ancient like the sturgeon, it existed during a time period when much of Florida would have been underwater. The general range of gars is the entire eastern United States. They prefer slow moving rivers, or backwaters of faster rivers, and are common in springs. As mentioned, a few species will venture into saltwater and can be found around the Gulf of Mexico. But with several species there has obviously been some speciation over time.
The common longnose gar.
Photo: University of South Florida.
The longnose gars have one of the widest distributions within the group. They are found in most river systems across the eastern United States and all of Florida. It seems to have few barriers including saltwater.
Alligator gars have a similar distribution but seem to be restricted from the peninsula part of Florida. The Florida rivers where they are found are all in the panhandle and are all alluvial rivers – muddy and not tannic like the Suwannee. This could be due to required food that prefer alluvial rivers, pH (pH is lower in the tannic rivers), or something else. Though they did not disperse into central and south Florida, they did extend their range westward down into Mexico. And, as mentioned, have been reported in the open Gulf of Mexico.
Spotted gars follow a similar distribution to the alligator gar. Much of the Mississippi River basin, Florida panhandle, and west to Texas – but they are not found in peninsular Florida. Pre-dating the emergence of peninsular Florida from the sea, there was some barrier that prevented them from dispersing south when the landmass did appear.
A different species appeared in peninsular Florida along with the longnose gar – the Florida gar. It is found in central and south Florida and has dispersed a little north along the Atlantic coast to Georgia.
This is an interesting group of ancient fish. Some are commercially harvested and have suffered from human alterations of river systems. They are amazing to see.
1 Hoese, H.D., R.H. Moore. 1977. Fishes of the Gulf of Mexico; Texas, Louisiana, and Adjacent Waters. Texas A&M Press, College Station TX. Pp. 327.
2 Discover Fishes. Florida Museum of Natural History. Alligator Gar. https://www.floridamuseum.ufl.edu/discover-fish/florida-fishes-gallery/alligator-gar/.
3 Discover Fishes. Florida Museum of Natural History. Longnose Gar. https://www.floridamuseum.ufl.edu/discover-fish/florida-fishes-gallery/longnose-gar/.
4 Discover Fishes. Florida Museum of Natural History. Spotted Gar. https://www.floridamuseum.ufl.edu/discover-fish/florida-fishes-gallery/spotted-gar/.
5 Discover Fishes. Florida Museum of Natural History. Florida Gar. https://www.floridamuseum.ufl.edu/discover-fish/florida-fishes-gallery/florida-gar/.
