FWRI scientists have been studying bay scallops since 1992. Learn about some of these research projects.
An FWRI biologist searches for bay scallops.
To assess the status of bay scallops in Florida waters, Fish and Wildlife Research Institute (FWRI) scientists conduct adult population surveys each June along the state's west coast. Researchers monitor 10 sites from Pine Island Sound to St. Andrew Bay. At nine of the 10 sites, they survey 20 stations – 10 at the other site – located in seagrass beds in depths up to 10 feet. At each station, researchers deploy a 300-meter (984.3 feet) weighted transect line. Two divers – one on either side of the line – each count all scallops within a meter-wide (3.3 feet) area along the line, for a total survey area of 600 square meters (1,968.5 square feet).
Divers measure the first 30 scallops at each station to determine the average size of the population. Researchers compare estimates between years and sites to determine if bay scallop populations are maturing at different rates. Using the results of transect surveys, researchers can determine the health of a local scallop population based on the following criteria.
A diver measures the shell
height of a live scallop.
1) Abundance: Researchers assess the health of a local population based on the average number of scallops in a survey area. Populations fall into one of four classifications: collapsed, average of 0-5 scallops; vulnerable, average of 5-25 scallops; stable, average of 25-50 scallops; or sustainable, average of 50 or more scallops.
2) Distribution: Healthy scallop populations are widely distributed throughout seagrass beds. For each local population, researchers sample 20 stations and calculate the distribution of sustainable stations, which is the percentage of stations with 50 or more scallops. They then classify distribution as sparse, less than 25 percent; patchy, 25-50 percent; or dense, more than 50 percent. Sites with dense distributions generally have higher numbers of scallops from year to year.
3) Resilience: Even healthy scallop populations fluctuate in abundance from year to year, but a healthy population should recover from a low point within one or two years.
In addition to monitoring the local adult populations, scientists study juvenile bay scallops as they recruit to, or settle into, the population. Most juveniles come from the local population where they were spawned, but some come from distant populations, relocated by the ocean currents. To study the recruitment of bay scallops to local populations, scientists use a simple but effective method.
They anchor citrus bags stuffed with black mesh to a block (pictured left) to collect juveniles. The collectors are deployed every month in the nearshore, grassy habitats found along Florida’s Gulf coast. They simulate grass blades, and juvenile bay scallops, called spat, settle out of the water column and attach to collectors using small fibers called byssal threads.
Researchers leave the collectors underwater for eight weeks. The location of each is marked by a surface float. They then retrieve the collectors and take them to the lab for processing. Researchers count any scallops found on the collectors. They standardize data by dividing that count by the number of days the collector was in the water.
Researchers then average the counts from each collector to determine the recruitment rate for each deployment period. Scientists use average recruitment rates to compare local populations, determine timing of spawning events and evaluate the health of a population over time.
A diver counting scallops
planted in a cage.
Previous bay scallop restoration efforts included two projects along Florida’s west coast. From 1997 to 2002, researchers targeted scallop populations between the Anclote River in north Pinellas County and Crystal River in Citrus County. In another project from 2002 to 2005, they continued targeting scallops in the nearshore waters between the two rivers while adding restoration efforts in Tampa and Sarasota bays.
In each project, researchers used juvenile bay scallops raised by a University of South Florida hatchery or by Bay Shellfish, Inc. They planted the scallops in wire cages anchored to the seafloor. Scientists then monitored the scallops monthly and recorded growth, death and reproduction.
Because of the amount of labor and high costs associated with wire-cage restoration, FWRI scientists shifted to a more low-maintenance method – larval releases. Since 2005, restoration programs have relied on an aquaculture facility in Palmetto, Florida to spawn and raise scallops through their early developmental stages. Within 10 to 14 days, they reach the pediveliger stage – the point at which scallop larvae are ready to settle out of the water and attach to seagrass blades.
During a larval release, researchers place the pediveligers into large containment enclosures (left) or release them directly into the seagrass. Released scallops that survive to adulthood will increase the number of spawning scallops in the population. More spawning scallops will produce a higher number of larvae, which helps boost the number of scallops in future generations.