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Abundance Survey

divers underwater looking for scallops in seagrass

Bay scallop annual abundance surveys were started in 1994 in conjunction with the closure of both the commercial fishery and a large portion of traditional recreational fishing grounds. The initial intent was to determine which regions were most depleted and to monitor long-term trends as large scale, federally-funded restoration programs were conducted from the mid-1990’s through mid-2000’s.  The study showed bay scallop populations rebounded and much of the recreational fishery (Hernando, Citrus, and Levy Counties) was re-opened in 2002. Survey methods have evolved over the years but adapted bay scallop population surveys still occur in some parts of the state.

Recent FWRI studies show bay scallop populations are closely tied to environmental conditions such as salinity changes and harmful algal blooms. Populations are also strongly associated with seagrass health and the extent of seagrass cover. As seagrass habitat shrinks or expands and its quality improves or declines, proportional changes in scallop populations will follow over time. Therefore, when considering long-term scallop abundance, healthy and extensive seagrass meadows are a leading factor to having long-term healthy scallop populations.

Close view of a bay scallop underwater showing numerous blue eyes.

Bay scallops have very short life spans, 12-18 months in Florida. While the three main fishing grounds (St. Joseph Bay, Dixie-Taylor, and Citrus County) are generally stable enough to support a fishery, in any season or region high and low abundance can occur in back-to-back seasons or even persist over longer periods.  Bay scallop populations appear to fluctuate on broad 5–7-year cycles. Scallop populations may rebound from zero to high abundance or plummet from high abundance to low in one or two seasons, thus demonstrating the variability and resiliency of the species, but this also adds to vulnerability.  

The wide swings in the population make predicting future conditions based on preseason counts difficult. The sample design of the initial survey method would be adequate for long-lived species with more predictable trends, but is not sufficient to evaluate a highly variable, short-lived species.  Variability in the population was dependent on both natural conditions (such as red-tides, floods, droughts, hurricanes) as well as human dimensions (such as less fishing effort during a recession but more effort during the COVID Pandemic as people pursued outdoor activities).  Furthermore, the short-term variability of bay scallop populations makes timely changes to regulations very challenging as they must consider the impacts on the industries associated with the fishery (fishing and tourism). For these reasons, the pre-season survey has been discontinued for the foreseeable future.

Post season surveys may be a better way to monitor the population’s spawning stock along with indicators of habitat quality. While still challenging, the number of scallops remaining after the harvest season may be a better predictor of the following year’s crop as well as an indicator of long-term trends in regional populations. Over the next several years, FWRI will continue to analyze the environmental and habitat linkages in existing data sets to understand the importance of the ecosystem and stressors that affect the long-term viability of bay scallop populations.