 |
|
|
|
|
|
|
|
|
|
|
 |
|
|
| |
September 2003, Vol. 13, No. 5 | Return to Table of Contents
DNA Evidence Could Spark Changes in Fisheries Management
MBL investigators study genes of squid to learn more about populations and mating behavior
Close on the heels of two major efforts to characterize the geographic “neighborhoods” of marine animals, a discovery by a team of researchers at the Marine Biological Laboratory is showing once again that the creatures that live below that seemingly unending, uniform surface of water have a more sophisticated sense of place—and themselves—than previously believed. The management of the major squid fishery in the Northeast may never be the same, and it may turn out that other commercially important fisheries need different management as well.
 Fishery managers have long assumed that the squid Loligo, which live in the waters from Virginia to Cape Cod, are part of one interbreeding population. If this were true, heavily-fished squid in one area would be replaced by squid migrating from other, less intensely fished areas, and the population would remain healthily diverse. Yet fishery managers also had some indirect evidence of squid populations that did not interbreed. In an attempt to settle this matter, a team of MBL researchers examined DNA from squid sampled in five inshore summer spawning locations and three winter habitats off the continental shelf. “What we found was simply shocking,” says Roger Hanlon, director of the Marine Resources Center at the MBL, who led the research.
“In our wildest dreams, we thought we might find two or three stocks,” he says. Instead, they found five-a different genetic stock in each of the five summer spawning grounds they sampled.
This finding suggests both that the fishery might need to be managed differently, and that there might be more than five distinct populations of squid plying the currents.
Even more surprising, Hanlon says, was the realization that while squid spawn with their own stock in the summer, they then mix-without spawning-in the deep warm waters off the continental shelf when they overwinter. “They may swim with each other on those long trips,” Hanlon says, “but they are not interbreeding.” All told, some squid may travel a distance of 600 kilometers.
The distinct genetic populations are made of individuals that belong to the same species, Loligo pealeii, and so could mate, but they do not. That means to be effectively managed, they have to be considered as distinct populations, says Hanlon. They will have to be considered as different genetic stocks, even if they look and taste the same.
The squids’ newly recognized abilities to recognize members of their own stock, to navigate to the inshore location where other members of their own stock spawn, and the reason for spawning only with their own stock all remain mysteries. They almost certainly use their sense of smell, Hanlon says, and likely use their ability to sense polarized light to keep track of the sun, to help them navigate the hundreds of miles required to travel from winter to summer grounds. ”They may use their nose, and figure out that Cape Cod smells differently than Long Island,” he adds.
The work also highlights the intriguing possibility that the squid return to their natal spawning grounds, which, if true, would prove the first example of that behavior by a marine invertebrate. The other marine animals known for this rare behavior are salmon, eels, turtles, and weakfish.
For each of the five spawning areas sampled, geneticists determined that the squid were distinct from the squid in all other areas. Yet each of the three winter grounds proved to have a mix of those five stocks. One stock was found in all three offshore sites sampled, while others were found in only one. One southern offshore site contained squid from all five distinct stocks.
Similar to the way in which all humans share a large proportion of their genes with all other people, squid share a large chunk of their DNA. By looking at the differences in DNA between the sampled squid, however, the researchers identified the different populations, identified by genes common within a population but different between the distinct populations.
Because most squid taken from the ocean are caught in the winter grounds, and because in these locations the squid stocks are intermingled, there may need to be a substantial shift in the management of this fishery. A fleet could, Hanlon says, remove what seems a reasonable number of squid from a winter fishing ground based on the total number of squid there, but in doing so seriously debilitate a particular genetic stock in the process.
Fisheries managers estimate that the squid are being fished at their limit. The discovery that the squid do not all interbreed suggests that the current level of pressure might mean the demise of one or more stocks. Because the squid live for only about a year, the lack of interbreeding means that stocks could be lost quickly. “With intensive fishing, you could, hypothetically, wipe out one stock within a year,” says Hanlon.
Beyond changes in the numbers of squid caught, the findings also suggest that particular spawning grounds may need to be protected to ensure the future of certain stocks, which may mate nowhere else. “We have to consider the idea of protecting some areas for spawning habitats if a sustainable fishery is to be maintained,” says Hanlon.
The management of the 30-million-dollar-plus squid fishery matters to more than just those who like their calamari and those willing to find it for them. Squid are also a major food source in the marine food chain, Hanlon says, and a collapse in squid populations could mean damage to recovery in other major fisheries, such as cod, halibut and haddock.
The research highlights the mysteries that remain about the large-brained, socially complex squid. “We don’t know how they manage to navigate such distances to mate,” says Hanlon. “The squid know what they are doing, but we have much to learn about their life cycle and habits.”
Future research will include sampling the squid in multiple locations simultaneously, and comparing seasonal results to similar seasons in different years. Hanlon also plans to take another look to see if there are more stocks than the five discovered so far.
“We found a different stock in each of the five places we looked,” he says. “Who knows what we will find when we look in seven or more?” The surprising results of this work have Hanlon eyeing other marine species, such as cod, for the application of powerful molecular genetic tools.
“It helps a good deal to understand some of these basic truths about a species before you can manage it effectively,” said Hanlon. “In many ways, despite having fished these waters for centuries, humans are still quite ignorant about many marine animals.”
— Jonathan Talbot
|
|
|
|
|
|
|
