Fisheries

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DNA Detects Two Hidden Oysters in Panama

Thursday, May 21st, 2015

by Monaca Noble and Katrina Lohan

Image: Oysters and other life grow on dock pilings at the Smithsonian Tropical Research Institute (Credit: Kristina Hill-Spanik)

Oysters and other life grow on dock pilings at the Smithsonian Tropical Research Institute in Panama
(Kristina Hill-Spanik)

A robin is a robin. It isn’t often confused with other birds. But some marine organisms are very difficult to identify because they look similar, too similar even for taxonomists trained to detect differences. Oysters are like this.

Oyster shells come in all shapes and sizes. As oysters fight for space and battle to survive in tough environments, their shells can change appearance based on conditions where they live. This makes it very hard to distinguish similar-looking species. Using DNA, we can identify these difficult species and provide new insights into their distribution, ecology, and ranges—insights not possible using shell morphology alone. In Panama, this DNA detective work led to two surprising discoveries.

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Oyster Disease Thrives in Nightly Dead Zones

Wednesday, February 11th, 2015

by Kristen Minogue

Image: Slides of oysters suffering different Dermo intensities as the parasite multiplies, from healthy (left) to severely infected (right). (Credit: SERC Marine Ecology Lab)

Slides of oysters suffering different Dermo intensities as the parasite multiplies, from healthy (left) to severely infected (right). (SERC Marine Ecology Lab)

In shallow waters around the world, where nutrient pollution runs high, oxygen levels can plummet to nearly zero at night. Oysters living in these zones are far more likely to pick up the lethal Dermo disease, a team of scientists from the Smithsonian Environmental Research Center discovered in a new study published Wednesday.

Oxygen loss in the shallows is a global phenomenon, but it is not nearly as well known as the dead zones of the deep. Unlike deep-water dead zones, which can persist for months, oxygen in shallow waters swings in day-night cycles, called diel-cycling hypoxia. In nature it works like this: When algae photosynthesize during the day, they release oxygen into the water. But at night, when photosynthesis stops, plants and animals continue to respire and take oxygen from the water, causing dissolved oxygen to drop. Nutrient pollution, because it fuels massive algal blooms, can make the cycle even more drastic. The resulting lack of oxygen can cripple the oysters’ ability to fight off the parasite Perkinsus marinus that causes Dermo and slowly takes over their bodies.

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Not Your Everyday Martha Stewart Glue Sticks

Friday, December 19th, 2014

by Heather Soulen, research technician

When I mention that we use “glue sticks” at the Smithsonian Environmental Research Center to help answer research questions about wetland ecology, I get looks of confusion and amusement. People often think I am using:

Glue Sticks (Credit: Heather Soulen/SERC) or GlueGun (Credit: Heather Soulen/SERC)

But, what I really mean is that I use these:

+ +

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Saving the River Herring: Don’t Let the Good Die Young

Wednesday, November 26th, 2014

by Kristen Minogue

Image: Alewives, a species of River Herring. (Credit: Geoffrey Gilmour-Taylor)

Alewives, one of two species of River Herring in Chesapeake Bay. (Geoffrey Gilmour-Taylor)

It’s no secret that River Herring are in trouble. There was a time, back in the 1950s, when Maryland fishermen regularly pulled in 4 million pounds or more a year of the silver fish. Then something mysterious happened. Herring harvests generally fluctuate from year to year. But in the 1970s, they fell and never came back up. For the last four decades, commercial fishermen in Maryland have been lucky to catch a few hundred thousand a year. Now they catch none.

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Oysters and the Chesapeake’s Jellyfish Wars

Tuesday, September 30th, 2014

Image: Jellyfish Chrysaora quinquecirrha (Credit: Lori Davias)

Jellyfish Chrysaora quinquecirrha (Lori Davias)

by Kristen Minogue

Every summer, the food web in Chesapeake Bay gets jostled around as two plankton-eating predators jockey for power: comb jellies and jellyfish. Most smaller species don’t have a stake in the battle—both predators eat zooplankton and fish eggs, after all. But for young oyster larvae, the victor could make the difference between being protected civilians or collateral damage.

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Banishing the Ghosts on the Bay Floor

Tuesday, August 12th, 2014

by Kristen Minogue

Image: A ghost pot pulled out of Chesapeake Bay. (Credit: Michael Reid/Southern Maryland Newspapers)

A ghost pot pulled out of Chesapeake Bay. (Michael Reid/Southern Maryland Newspapers)


Every year, thousands of crab pots disappear, their lines snapped by violent storms or severed by the propellers of passing boats. Cut off from the buoys that once marked their presence, they become “ghost pots,” lost at the bottom of the Chesapeake.

But ghost pots aren’t dead pots. They’re still quite capable of trapping crabs, including mature females undergoing their spawning migration. And with no one to retrieve them, crabs too large to escape are condemned to a slow death by starvation. This often has the eerie effect of luring even more animals to their demise, says Laura Patrick, aquatic ecologist at the Smithsonian Environmental Research Center (SERC).

“The crabs are just going in and they’re dying,” Patrick says. “And one of the problems is that the dead animals that are in there can be bait for new crabs to come in. So it’s kind of a self-baiting pot.”

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Virtual crabs could help real recovery

Friday, August 8th, 2014

by Sarah Hansen

Image: Julie Sepanik holds up a large male blue crab caught in the Rhode River. (Credit: SERC)

Julie Sepanik holds up a large male blue crab caught in the Rhode River. (SERC)

No one disputes that blue crab numbers in Chesapeake Bay are low.  There is much discussion, however, about what to do to fix the problem.  Smithsonian Environmental Research Center intern Julie Sepanik is working with SERC postdoctoral fellow Matt Ogburn to develop a computer model that will help improve our understanding of blue crab population dynamics in the Bay. The model works to identify where female crabs mature in the Bay and track their migration to lower Bay spawning areas. Ultimately, they hope the model will help inform decisions about preserving habitat and restoring the population.

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Blue Crabs Need (More Than) A Few Good Men

Thursday, July 24th, 2014

by Kristen Minogue

Photo: Male blue crabs can mate with multiple females. But with fewer men to go around, their female partners are left with less sperm to reproduce. (Credit: SERC)

Male blue crabs can mate with multiple females. But with fewer men to go around, their female partners are left with less sperm to reproduce. (SERC)

The practice of selectively fishing male blue crabs in the Chesapeake—intended to give females a chance to reproduce—may have a hidden cost. A Bay without enough males could reduce the number of offspring females produce, ecologists at the Smithsonian Environmental Research Center found in a paper published in the July issue of Marine Ecology Progress Series.

Maryland and Virginia began reducing the harvest of female crabs by commercial and recreational watermen in 2008, the year officials declared the blue crab fishery a federal disaster. Since then, the crabs have shown signs of a shaky recovery. But a lasting comeback hinges on females producing enough offspring to sustain the population.

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Thousands of Tags Could Unearth Clues to Saving Blue Crabs

Tuesday, July 8th, 2014

by Kristen Minogue

Photo: Technician Laura Patrick holds up a blue crab caught in the Rhode River. (Credit: SERC)

Technician Laura Patrick holds up a blue crab caught in the Rhode River. (SERC)

This summer and fall, biologists at the Smithsonian Environmental Research Center are looking to tag 10,000 blue crabs in Chesapeake Bay. They’re pursuing the project in spite of the two-year slump the crabs have suffered in the latest reports of the Chesapeake Bay Stock Assessment Committee. They’re hoping some of those crabs will help answer two unresolved questions on the path to recovery: the role of recreational crabbing, and the struggling population of adult females.

Every year watermen on Chesapeake Bay haul in between 40 and 110 million pounds of blue crabs on trotlines or in crab pots. The vast majority come from commercial watermen who rely on the crustaceans for their livelihoods. But recreational crabbers also take their share, and today no one knows exactly how large or small that share is.

“We really have very little idea how big the recreational fishery is now,” says Matt Ogburn, a postdoc at SERC’s Fish and Invertebrate Ecology Lab.  Click to continue »

Curiouser and Curiouser: A Motor at the Front?

Tuesday, February 18th, 2014

by Heather Soulen

A Chesapeake Bay NOAA mullet skiff. Note the moter near the bow. (SERC)

A Chesapeake Bay NOAA mullet skiff. Note the motor near the bow. (SERC)

With its motor located near the bow (front) of the boat, the modern-day mullet skiff could have been a character in Lewis Carroll’s novel “Alice’s Adventures in Wonderland.” Similar to the unpunctual rabbit, vanishing cat and hookah smoking caterpillar, it seems illogical…or does it?

Commercial mullet fishing in 1955. (Monts de Oca, C. Morris courtesy of State Archives of Florida)

Commercial mullet fishing in 1955. (Monts de Oca, C. Morris courtesy of State Archives of Florida)

In the early 1900s, the mullet skiff was originally designed for use in the commercial mullet fishery of the south. Popular for its simple construction, flat-bottom dory style hull with vee entry, and rounded stern (back) design, the mullet skiff was ideal for operating in shallow waters while carrying heavy loads of fish. However, during Prohibition, entrepreneurs souped up their mullet skiffs with straight-8 engines (precursor V8s) to run rum from the Bahamas and Cuba to the states. Since then, many mullet skiffs have undergone less scandalous modifications and have evolved to have an outboard motor in a well near the bow.

Why place a motor here? For three important reasons: 1) It places the motor higher in the water for maneuvering in shallow water, 2) it leaves the stern (back) open to work a net, and 3) it eliminates the risk of net entanglement in the propeller. So, with “the wrong end in front,” the mullet skiff was the perfect choice for the near-shore predator study our field crew conducted this summer throughout the Chesapeake Bay.

Predators of the Not-So-Deep

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