Florida's state shell at higher risk of extinction than previously
thought

Date:
April 6, 2022
Source:
University of South Florida (USF Innovation)
Summary:
Unregulated commercial harvesting and recreational live collection
are pushing Florida horse conch populations closer to collapse.



FULL STORY ==========================================================================
The Florida horse conch population -- one of the world's largest
invertebrate animals -- is shrinking. Established in 1969 as the Florida
state shell with a record length of two feet, it has become symbolic
of Florida's natural resources and widely used in advertising for the
state's tourism industry. But unregulated commercial harvesting and recreational live collection are pushing populations closer to collapse.


========================================================================== According to a study led by the University of South Florida, the average lifespan of a Florida horse conch is between eight and 10 years, and
it doesn't start reproducing until about age six, giving birth to up
to 28,000 offspring each year. This is a dramatic shift from previous
belief that a horse conch could live for half a century -- meaning far
fewer offspring are born to replace those removed as a result of harvest
or natural causes.

The interdisciplinary research team, which includes the Florida Fish and Wildlife Conservation Commission (FWC) and current and former USF graduate students, also found that the largest Florida horse conch is no more than
16 years old. The two-foot shell is on display at the Bailey-Matthews
National Shell Museum in Sanibel. The team's results, published in PLOS
ONE, were based on analyses of museum specimens, reducing harm to an
already fragile population if they removed shells from the wild.

To estimate horse conch ages, researchers analyzed chemical bands in
the shell, which track water temperature as the snail grows and can
be counted like tree rings to measure the passage of time. Unlike tree
rings, which are visible, the chemical bands can only be determined by geochemical analysis.

The team was also able to determine the horse conch's amount of growth
each year by wrapping string around each coil and then straightening
and measuring the string. They found females grow rapidly each year of
their lives, whereas males slow down early and mature at a much smaller
size. Researchers determined that female horse conchs start laying eggs
at about age six, based on spikes in shell carbon levels.

"Our research shows that horse conch reproduction is less likely to keep
pace with intense harvest than previously thought," said lead author Greg Herbert, associate professor from the USF School of Geosciences. "Horse
conch populations are important. They create habitat for other species
by leaving empty shells of dead prey around for fish, crabs and other
animals to use as homes. They also contribute to the unique experience
that we have in Florida of being able to go to the beach and seeing one
of the largest seashells in the world at the water's edge." Data from
FWC shows that there has been a steady population decline since the
mid-1990s. Commercial fishermen reported a peak count of 14,511 Florida
horse conchs in 1996, followed by 6,124 in 2000, 1,461 in 2015 and just
67 in 2020.

"We still know very little about how many horse conchs exist and
where their preferred habitats or what their optimal environmental
conditions are," said co-author Stephen Geiger, research scientist at the
FWC. "Because we have no dedicated funding for more than 1,500 species of mollusks found in the waters that surround Florida, we continue to seek
grants that enable us to study their biological traits, including those
that will help managers decide if some species are in need of better protection." The shells that were studied were collected from the Dry Tortugas, Vaca Key, Sanibel Island and Cape Romano. Researchers say the
further north you go, the smaller the Florida horse conch, possibly due
to overexploited fisheries and recreational collecting.


========================================================================== Story Source: Materials provided by University_of_South_Florida_(USF_Innovation). Note: Content may be edited
for style and length.


========================================================================== Related Multimedia:
* Horse_conch ========================================================================== Journal Reference:
1. Gregory S. Herbert, Stephen P. Geiger, Stephen G. Hesterberg, Nicole
Seiden, Jaime A. Rogers, Ryan M. Harke, Martin Sala, Kaydee
J. West, Ethan A. Goddard. Age and growth of one of the world's
largest carnivorous gastropods, the Florida Horse Conch,
Triplofusus giganteus (Kiener, 1840), a target of unregulated,
intense harvest. PLOS ONE, 2022; 17 (4): e0265095 DOI:
10.1371/journal.pone.0265095 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220406160508.htm

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