As commercial and recreational landings of Florida’s spiny lobsters continue to remain below historical levels, new findings about the lobster’s ecology are helping guide management strategies to benefit future populations and the fishing industry.
Spiny lobsters are one of the largest commercial fisheries in Florida, and one of the most economically valuable in the Caribbean. In the five years leading up to 2001, commercial fishermen in Florida landed an average of nearly 7 million pounds of spiny lobsters each year, worth on average more than $28 million dockside.
And then, landings dropped off sharply. For the past 10 years, commercial landings have averaged just 4 million pounds each year, generating about $20 million dockside.
A virus contributes to the decline
Don Behringer, a marine ecologist at the University of Florida, has been studying the effects of the lethal PaV1 virus that has been killing juvenile lobsters and potentially hurting the commercial and recreational fisheries. Behringer, in fact, discovered the virus while sampling juvenile lobster populations in the Florida Keys in 1999.
The virus, the first identified for any lobster in the world, has since been reported in Mexico, Belize, Cuba, St. Croix, and St. Kitts, and is suspected to be widespread in the Caribbean. Behringer’s ongoing research continues to study the transmission of the virus — how it is spread between individuals in the population as well as on a larger scale throughout the Caribbean.
Recently, Behringer used Florida Sea Grant funding to determine how lobster traps, the primary means of capture by the commercial fishery in Florida, could impede trap function or contribute to the prevalence of PaV1.
“We asked if current practices in the fishery compromise lobster resistance to infection, increase disease transmission rates, or if the presence of infected lobsters affects the capture efficiency of traps,” Behringer said.
“We knew that the fishing industry and the Florida Fish and Wildlife Conservation Commission would benefit by using the results to manage the fishery with respect to PaV1 infection dynamics.”
Indirect impacts on juvenile lobster survival
One of Behringer’s primary objectives in the study was to determine if a trapped lobster carrying the PaV1 virus would attract other lobsters in the trap, or if healthy lobsters could detect the diseased lobster and avoid the trap.
Traps exploit the “gregarious,” or social nature of young and adult lobsters, because they typically contain other lobsters, but are impenetrable to most predators. In the natural environment, Behringer says, this behavior affects the ability of young lobsters to survive into adulthood.
“Lobsters view traps as nothing more than a shelter from which only the larger lobsters cannot escape,” Behringer said. “Small, under-sized lobsters are capable of moving freely into and out of the traps, but we were unsure about trap use between healthy and diseased lobsters.”
Behringer’s previous research had shown that healthy lobsters were able to detect and avoid lobsters infected with the PaV1 virus, most likely through a chemical cue. (Recent findings confirm this.) With the assistance of local commercial fishermen, the research team deployed traps containing either a diseased or a healthy lobster. Then, a week later, they pulled the traps to see how they functioned.
“Indeed, traps with diseased lobsters attracted significantly fewer lobsters,” Behringer said, indicating that a trap into which a PaV1-infected lobster has moved will attract fewer lobsters than those containing only healthy lobsters.
“This avoidance may reduce infection risk, but it also means potentially lower landings for those traps. Furthermore, because healthy lobsters avoid taking shelter with a diseased lobser, it could increase their risk from predators.”
New research directions
Behringer’s research also looked at the effect of temperature on the infection.
Experiments found that lobsters held in the lab in high-temperature seawater and exposed to PaV1 developed active and more intense infections much more quickly than those held at lower temperatures. The finding could become important given rising temperatures in the global oceans.
“High temperature, even in small increments, often results in stress that can increase the susceptibility of organisms to infection and potentially alter the time course of infection,” Behringer said. “In future projects we’re going to test if water temperature may affect disease susceptibility and infection progress.”
Behringer was also recently funded by the National Science Foundation for a multi-year, $1.4 million grant to study the dynamics of the PaV1 virus throughout the Caribbean-wide range of the spiny lobster.
The findings will continue to provide fishermen and fisheries managers with a better understanding of how the deadly PaV1 disease spreads in spiny lobsters, which they then hope to use to implement management plans that reduce the impact of the disease.