What led up to bucket-driving, plankton-sorting students was an academic interest
in lobster larval transport and unanswered questions about connections between
inshore and offshore lobster populations—and the notion that such research may have management implications for the fishery. Cohen's
former boss at Harvard, population geneticist Steve Palumbi, along with Cohen,
secured Sea Grant support to put their ideas to the test.
"South of Cape Cod, the traditional lobster fishery was inshore. Increasingly," says Cohen, "it has become an offshore fishery. Are there connections between these populations? We know something about [the region's] currents and winds, and we know that population mixing is occurring at both larval and adult stages, but we haven't quantified that mixing. Genetics will help us do that."
Comparing the genetics of lobster larvae from one area—a source area—and testing whether larvae can be identified and tracked, are two of the project's goals, says Cohen. These goals will test the viability of one fisheries management approach: designated no-take areas. This management tool, designed to protect source populations, is currently in place for groundfish populations like cod, haddock, and flounder. Cohen wonders if management areas make sense, given what information is known—and can be learned—about lobster populations.
To test no-take areas as a management tool, Cohen and her colleagues looked to New Bedford Harbor as a de facto no-take area. The harbor, designated a Superfund site in 1982, is closed to fishing. Based on anecdotal information from fishermen and conversations with Bruce Estrella, biologist for the Massachusetts Division of Marine Fisheries, the presence of egg-bearing females and reproductive adult lobsters is a good indication that larvae are being released from New Bedford Harbor.
Cohen, with the help of East Coast fishers, charter boat operators, and fishery managers, collected nearly 3,000 early- and late-stage larval lobsters from an inshore area ranging from New Bedford Harbor to Point Judith, Rhode Island. Adult lobsters were collected from the same areas, and additional onshore and offshore locations from Hudson Canyon north to offshore Georges Bank and inshore Gulf of Maine.
Back in San Francisco, the West Coast contingent is busy preparing the samples for extraction and genotyping. "We'll be grinding them furiously for the next while here to get the genetics done," says Cohen. That work—begun at Harvard and now taking place at SFSU's Romberg Tiburon Center for Environmental Studies—involves development of single copy nuclear loci, a type of genetic marker that can often be used for multiple species.
Cohen explains that, while some genes are considered neutral, other genes— "genes under selection"—are influenced by the organism's environment. This project will look at both.
"The markers we've made use of so far are relatively less varying," says Cohen, "but they are readily available. The point [of this effort] is to use the latest tools to make quantitative estimates of the amount of mixing between lobsters from different populations. We're looking for markers that evolve quickly, and we're looking for ones that evolve by different mutational mechanisms," explains Cohen. "Ideally," she says, "our markers will pick up the subtle differences between inshore and offshore lobsters, and possible differences between local larval populations."
Cohen says that their genetics work should help answer questions like "how genetically similar are the first-stage and late-stage larvae? Are the larvae hanging out in the same area or can they also be found in southern locales? Do the late-stage larvae look like inshore adults or adjacent offshore adults, or do they look like lobsters from distant areas?"
If they find that the populations are not connected, it makes sense to manage them separately, says Cohen. However, their preliminary data make the populations look very connected, suggesting they should be managed together. "Fishing in one place has an impact on another place; not only in coastal areas, but offshore as well," she says.
Cohen cites anecdotal and published reports of adult lobsters migrating inshore and offshore. "Fishers and researchers have seen lines of adult lobsters moving inshore. Is this gender-biased? Do reproductive females move inshore to release larvae? feed? become reproductive?" asks Cohen. "One can't make assumptions about what percentage of the population is represented by these observations, or the reproductive contribution made by these individuals, or even if they really stay inshore to release their eggs or if they go back offshore first."
This is where genetic tools could help to quantify the information, offers Cohen. "If you get answers from one region, you can use it to make suggestions for other regions—if you know the hydrography and reproductive biology of the region. If we can provide genetic tools, they will be useful at a variety of spatial scales, across and within the region."
Cohen is optimistic about the direction of the project and its usefulness for lobster fishery managers, but acknowledges the frustration she has encountered from those tired of "waiting for the science." She admits that genetics work takes a long time. And, at a time when the fishery is categorized as over-fished, yet open to increased fishing effort, one can't help wonder: how long can the fishery wait for answers? When pressed, Cohen is quick to point out the alternative: what she calls "data-less conservation management," or the "don't wait; do it now" approach. "During this project, the fishery has seen increasing pressure," she says. "The implications of this work will be even more important."