NARRAGANSETT — Finding a remedy for a shell disease that has reduced the lobster population, and introducing methods to improve the environment for quahogs and to better manage that fishery were two of the research projects discussed Thursday by University of Rhode Island graduates at the Bay Informed discussion series sponsored by Rhode Island Sea Grant. The monthly talks take place at URI’s Bay Campus.
Melissa Hoffman studies shell disease in Rhode Island lobsters and Conor McManus has studied quahog populations, reproduction and larval transport.
Hoffman offered some intriguing facts about the American lobster, the species caught in Rhode Island. They molt often when they’re young and less as they age. It takes seven years for a lobster to grow to legal catch size, and female lobsters hold their eggs for nine months after fertilization. And yes, lobsters can re-grow their claws.
“If a predator has one of their claws or it’s stuck in a rock, they have a stress response inside them that actually allows them to detach their claw from their body,” Hoffman said.
Lobster is culturally and economically significant to Rhode Islanders, and the decline in the catch over recent years is a major cause for concern.
Hoffman explained that overfishing is not the cause of the depletion of Rhode Island’s lobster population. Factors contributing to the decline in southern New England are rising seawater temperatures, which drive lobsters to seek colder waters in Maine and Canada, shell disease, and pollutants such as oil from oil spills and other chemicals. Warmer water is also encouraging the proliferation of fish species like scup, also known as porgy, which are believed to eat young lobsters.
But it is shell disease, known as epizootic shell disease, that is the primary focus of Hoffman’s work.
The factor or factors causing shell disease are unclear, but the bacteria produce dark lesions on lobster shells, making the lobsters undesirable for market and also preventing them from molting. Approximately 30 percent of Rhode Island lobsters have the disease and up to 70 percent of reproductive females are infected.
“It doesn’t always directly kill the lobster but sometimes the lesions will get so bad they will get through to their tissue, so when they try to molt their shell will basically get stuck and then they’re left vulnerable,” Hoffman said.
From 1990 to 1995, before the appearance of the disease, lobster landings in Rhode Island were 6.5 million pounds, with a value of $20 million. Following the onset of the disease, landings from 2010 to 2015 were 2.5 million pounds with a value of $12 million.
Hoffman is now working with probiotics, live microorganisms that she adds to her lobster tanks for experimental purposes.
“I’m just trying to see if using probiotic treatments could have any sort of beneficial impact on the state of the disease,” she said. “This was a research question that was brought to the University of Rhode Island by lobstermen.”
McManus presented an overview of the state’s quahog fishery, which generates an average of $5.5 million a year and employs more than 600 active shell fishermen. Quahogging waters in Rhode Island are divided into designated areas, which McManus and others usually survey every two years using hydraulic dredges that scoop up the sediment and the clams living in it so the clams can be counted.
“We have a map of Narragansett Bay with areas that we call tagging areas and it helps us track where quahogs come from when they go to a dealer,” McManus said. “When a quahogger goes out and fishes for quahogs, he’ll actually label what area he was in when he or she got it. This gets reported to the dealers. It helps us to understand the spatial side of the fishery, where removals are coming from.”
The goal of the management plan is to maximize the harvest without depleting the population.
“What we’re trying to do is implement regulations that allow for a nice sweet spot between the most that can be removed while also allowing for a population that will keep re-populating itself,” McManus said.
Regulations include size and catch limits and the opening or closing of certain areas depending on the season or if pollutants are washed into the bay during a heavy rainfall.
“With quahogs, unlike a lot of other fisheries that we manage here in Rhode Island, you’ve got the complexity of water quality as well as trying to maintain the stock status,” McManus said.
Several factors affect quahog abundance: the type of sediment they’re living in, the area designation and whether there is a lot of harvest, the time of year the sampling takes place, and the availability of food — microscopic plants known as phytoplankton.
Some shell fishermen have complained that since 2005, when waste water treatment plants began removing nitrogen from effluent, the bay has become too clean, and there isn’t enough phytoplankton for the organisms that eat it.
“We’re trying to figure out how nutrient reductions for Narragansett Bay will influence the quahog population,” McManus said. “We’ve seen changes in various types of nutrients in the water, nitrogen, phosphorus and so the question is, if nutrients are what supports phytoplankton and phytoplankton’s the major food for quahogs, do we think there might be a change in either quahog abundance or growth?”
The Bay Informed discussions take place the third Thursday of every month, and public participation is welcome. More information can be found at: https://web.uri.edu/chowder-marching/bay-informed/