Bay Scallops – Current Research Projects

POPULATION MONITORING

To assess the status of bay scallops in Florida waters, Fish and Wildlife Research Institute (FWRI) scientists conduct adult population surveys during June of each year at various sites along Florida's west coast. Survey sites include Pine Island Sound, Sarasota Bay, Tampa Bay, the nearshore waters of Pasco and Hernando counties, coastal waters in the vicinity of the Homosassa and Crystal rivers, the Steinhatchee area, the St. Marks area, St. Joseph Bay, and St. Andrews Bay.

An FWRI biologist searchesthe  seagrass and algae for bay scallops.

At each site 300-meter transect surveys are conducted at 20 stations. A pair of SCUBA divers conducts each transect survey; each counts all of the scallops found within one meter on their side of the transect line. Thus, all scallops within a 600-meter squared (m²) area at each station are counted, resulting in a sample area of 12,000 m² at each site. Surveys have been conducted since 1994 at most sites.

Using the results of transect surveys, the following criteria are applied to determine the health of a local scallop population:

1) Abundance: In a healthy scallop population, mean population density, or average population density, generally exceeds 25 scallops per a 600 m² transect. Mean population density below five scallops per transect is considered a collapsed population. Mean density between 5 and 25 scallops per transect is considered a transitional population.

2) Distribution: Scallops should be widely distributed throughout the sample area. While sampling 20 stations at each study site we expect to recover scallops from a minimum of 10 of those stations. High distribution throughout the study site indicates a more healthy population.

Shell height is measured using  underwater slates.

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.

Divers measure the first 30 scallops at each station within each site to determine the average size of the population. Estimates can be compared between years and sites to determine if populations are maturing at different rates.

JUVENILE MONITORING

In addition to monitoring the local adult populations, FWRI scientists are also interested in monitoring bay scallops that are recruiting to the population. Most recruits come from the local adult population, but some recruits may have been from larvae that were delivered from distant populations by ocean currents. In order to study the recruitment of bay scallops to local estuaries, a simple but effective procedure is used.

Collectors, or traps used to attract scallops, consisting of citrus bags stuffed with black mesh are tied to a block and float array (left) and deployed in the nearshore, grassy habitats around Florida's Gulf coast. These collectors simulate grass blades, and any juvenile bay scallops, called "spat," that are settling out of the water column land on the mesh and attach using small fibers called byssal threads.

The collectors are allowed to be submerged for approximately eight weeks and are then retrieved and processed in the FWRI mollusc lab. Any scallops found on the collectors are counted and then the data is standardized by dividing the count by the number of days that the collector was in the water.

Recruitment rates can then be compared from local populations to determine timing of spawning events, as well as a secondary evaluation of the health of the estuary. If there are plenty of adults available for reproduction, but the number of recruits is limited, then a different form of restoration may be required to boost the local bay scallop population.

RESTORATION

A diver cleaning scallops in a  restoration cage.

Previous funded bay scallop restoration projects include a National Oceanic and Atmospheric Administration grant from 1997 - 2002 which targeted the scallop populations between Anclote and Crystal River; two Saltonstahl-Kennedy grants for the period from 2002 to 2005 which continued targeting the near-shore waters of Pasco through Citrus counties, as well as Tampa and Sarasota bays. These funded projects used juvenile bay scallops raised in either a University of South Florida hatchery or by Bay Shellfish, Inc. which were then planted in wire cages attached to the seafloor. Scientists monitored the scallops monthly and recorded growth, mortality, and reproductive processes.

Due to the cost associated with the cage-style approach to restoration, FWRI scientists shifted to a more energy efficient form of scallop restoration, larval releases. An Ocean Trust Grant, and collaborative grants in association with Mote Marine Lab, and Sanibel-Captiva Conservation Foundation funded a local aquaculture facility to spawn and raise scallops to the ready-to-set stage. These pedivelgiers were released into large containment enclosures deployed in select local depleted estuaries (left).

Current restoration efforts are funded by a small grant from the Pinellas County Environmental Fund and also rely on the participation of local agencies and volunteers. FWRI scientists deploy recruitment collectors in Tampa Bay, Sarasota Bay, and St. Andrews Bay and then process the collectors in real time on research vessels. Any spat found are placed in mesh bags and raised off FWRI docks in Bayboro Harbor.

During this early stage of our restoration efforts, FWRI volunteers and interns diligently clean the mesh bags and scallops by removing fouling organisms such as barnacles, tunicates, and oysters (left). These fouling animals may prevent the scallop from opening its shells, limiting the amount of food the scallop can ingest and possibly stunting its growth.

Raising the scallops generally takes 3-4 months. Once scallops have grown to 30 millimeters (mm) (just over one inch) they are either placed in cages hung off of residential docks (right) within the target restoration area, or are released directly into local seagrass beds. Monitoring scallops in cages not only allows scientists to track optimal growth in different areas, it also protects the scallops from any predators that they would normally encounter.