Alcott unlocks the mysteries of Wellfleet herring
Provincetown Banner
By Doug Karlson
Banner Correspondent
Posted May. 6, 2016 at 9:31 AM
WELLFLEET — Derrick Alcott, a graduate student at UMass-Amherst, likes slogging through the marshes of Wellfleet.
He’s working on his doctoral dissertation on the migration of spawning herring, who face numerous challenges in their annual journey from saltwater to fresh — everything from hungry snapping turtles to physical barriers like road crossings and dikes.
Alcott says he chose the topic because he’s interested in subjects like fish biology, the physics of water flow and the interactions of different organisms. He also likes working in the field, and applying complex analytics.
“Being able to work with all those things is what really drew me to the project,” Alcott says.
So from March through July, seven days a week, he gets up and goes into the field to study Wellfleet’s herring. This is his third season. He’s learned a lot about Wellfleet herring and has developed several hypotheses that he’s in the process of testing.
This year has seen an unusual herring run, he says.
“This year was weird in two ways,” says Alcott. First, probably owing to the warm winter, the fish showed up “crazy early,” in mid-March. That’s a month earlier than previous years. Then, due to the subsequent cold snap and snow, the run stopped. Eventually the fish returned, and now it appears that the run is larger than usual. But Alcott suspects that the cold weather has now resulted in more herring arriving in a more condensed time frame.
In his research so far, he’s made one overarching observation: every time a fish approaches a structure, such as a dike, it stops. “They go back and forth, back and forth, before they cross the barrier.”
He’s also observed that fish that show up early, in mid-April, seem to be more likely to make it to the spawning grounds and survive to return to the ocean.
He thinks the reason is that the pressure from predators is not as great early in the season. Also, unlike salmon, herring come back every year. Alcott has a theory that older fish come back earlier. “They have it figured out.”
Striped bass, the main predator downstream as the herring enter the run, are less abundant in April, too. Upstream the main predators seem to be raccoons, snapping turtles and possibly river herring. Early in the season, Alcott theorizes, these predators haven’t yet figured out the best spots to hunt. “But later in the season they’re hitting them pretty hard,” says Alcott.
Alcott discovered that snapping turtles eat a lot of herring. In the ponds they can’t catch them. But at the choke points, look out. Snapping turtles position themselves inside the culverts, narrow concrete pipes that allow water to flow under roads, and stay there all day.
“All of a sudden it gets a whole lot easier when a herring has to swim right over its head,” Alcott says. “It’s basically a feeding tube.”
Alcott uses PITs (passive integrated tags) to track the movements of the herring. The tags are similar to EZ Pass technology and the digital inserts people use to find cats and dogs. He has detectors set up all along the herring run, including at all road crossings and at the entrance to spawning grounds. He’s discovered one area between Route 6 and Old King’s Highway, near Black Pond, where the herring disappear. To better understand this mysterious disappearance, he searched the area with a scanner, but found only one tag.
“They’ve almost certainly been eaten by predators,” said Alcott. He suspects that the fish are eaten at a place where the river gets very shallow and narrow, just upstream of Black Pond. “Raccoons appear to be the biggest culprit.”
Alcott is excited about the current efforts to restore the Herring River estuary.
“The salt marsh is one of the most productive ecosystems on the planet, up there with tropical rain forests and coral reefs,” he says.
He looks forward to the rich ecosystem that will result.]]>