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Dr. Mark Bertness, Brown University – Sport Fishing and Marsh Die-Off

In today’s Academic Minute, Dr. Mark Bertness of Brown University reveals how sport fishing is damaging marshes along Cape Cod.

Mark Bertness is the Robert P. Brown Professor of Biology and chair of the Department of Ecology and Evolutionary Biology at Brown University where his lab’s research is focused on marine coastal ecology and conservation. His current project is examining the causes and consequences of salt marsh die-off in coastal New England. He earned his Ph.D. at the University of Maryland.

About Dr. Bertness

Dr. Mark Bertness, Brown University – Sport Fish and Marsh Die-Off

The potentially strong impact of grazers on salt marshes is a difficult concept for ecologists because marshes were long thought to be exclusively controlled by physical factors. But marsh die-offs can be the indirect consequence of human activities. A depletion of predators can leave herbivores uncontrolled, leading to marsh die-off and collapse. We’ve seen this most recently on Cape Cod, where it’s caused by recreational fishing.

Marsh die-off is important because salt marshes are economically one of the most valuable natural habitats on the planet in terms of the societal services they supply. First reported in 2004, Cape Cod die-offs were first attributed to climate change and sea-level rise. Our experimental work, however, has unambiguously attributed die-off to runaway herbivory by the native, nocturnal purple marsh crab, Sesarma reticulatum.

Cordgrass transplanted into die-off areas are eaten in a couple of weeks, unless protected from Sesarma by cages. In 2008 50% of marsh creek banks had severe die-off and historical reconstruction revealed that die-off areas have been growing in size for 35 years. Most remarkably, contemporary survey data and historical reconstructions revealed that die-offs occur exclusively at marshes exposed to heavy recreational fishing pressure. 

Recreational fishing efficiently targets top predators, and can severely deplete populations wherever boat slips, moorings and boat ramps allow angler access.  The buildup of fishing infrastructure after WW II and skyrocketing Cape Cod summer populations have left many Cape marshes decimated.

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