ishing Southwest Florida Scallop Update

BRADENTON – Marine Scene readers might look at these numbers and lament that some of the numbers are down. But take heart! Bay scallops are essentially an annual crop (read more below) and naturally subject to wide fluctuations in abundance on an annual basis. This is why it is important to collect information over a number of years throughout southwest Florida.

Also, remember, these surveys are limited and can be imprecise in terms of sampling bay scallop abundance throughout an estuary. Scallop abundance can be “spotty” and unevenly distributed within a single bay. The important thing to note is that at least some scallops are being found year to year throughout southwest Florida. And, new restoration efforts are planned.

We monitor bay scallops in southwest Florida because they are an important species to both humans and the environment. When coastal waters are able to support bay scallops it is a sign of reasonably good water quality and seagrass conditions. Many volunteers participating in the search this year commented about how healthy the seagrass looked. Healthy seagrass is very important habitat for bay scallops, but it’s only part of the story.

Bay scallops are essentially an annual crop, completing their life cycle over the course of a year. In Florida, spawning typically occurs in the autumn. The free-floating larval stage lasts about two weeks, then the larvae settles out of the water to take the bottom-dwelling form we are familiar with. Scallops rapidly grow and mature in the spring and summer of the following year and then rapidly die after spawning. Predators take their toll and following spawning scallops are in a weakened condition and often become riddled with parasites. An 18-month old scallop is indeed a very, very old scallop. Hence the abundance of scallops in an area depends upon the success of the spawn, and the ability of larvae being transported by water currents to reach suitable seagrass habitat.

In addition to the scallop search, bay scallops are monitored throughout the year by counting recruiting scallops, referred to as
spat, the phase when scallops first settle on seagrass blades. Special collectors that mimic seagrass substrate are placed in the field and then periodically checked to see if small scallops have settled out of the water. These collectors are constructed of citrus bags filled with plastic mesh. See the photo below – they may not look like much, but they work.

These surveys are conducted by the Florida Fish and Wildlife Conservation Commission with support from partners, including the Florida Sea Grant Extension Program, and volunteers from St. Andrews Bay to the north, and Pine Island Bay to the south.Charlotte County volunteers under the direction of Sea Grant Extension Agent Betty Staugler are also monitoring scallops in cages at their docks. The caged scallops are part of a community restoration program where bay scallops are placed in areas to spawn, thus adding additional recruitment potential. Volunteers who have adopted the cages collect data monthly on their scallops. We use this information to determine the percent of survival and growth rate of the scallops.

Looking to the future
New restoration plans using hatchery-reared larvae are in the works for the later part of 2012 and 2013. Adult bay scallops (brood stock) were collected for hatchery spawning in late summer 2012. These adult scallops are then spawned and raised so they are ready to release and settle in seagrass beds. One release has already been conducted in Sarasota Bay. Others will follow, including locations in Charlotte Harbor. These restoration sites will be carefully monitored for some time to ensure that the released larvae result in adult scallops. One experiment conducted in Pine Island Sound years ago provided promising results. It should be noted that more releases on a larger scale will most definitely be needed if we are to stand a chance at restoring local bay scallop populations.

editor's note: This article is published courtesy of The Marine Scene: The Southwest Florida Sea Grant Newsletter