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Mystery of the Missing Blue Crabs: Winter vs. Summer Young

Tuesday, June 25th, 2013

Republished with permission from the Blue Crab Blog. Check out the Blue Crab Blog for the latest news regarding Maryland’s favorite crustacean.

By Katie Sinclair, Guest Blogger and Intern at the Smithsonian Environmental Research Center
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The blue crab may be the most well-known denizen of the Chesapeake Bay, with the blue crab fishery one of the most productive in the region. From the late 1990s to mid-2000s, the blue crab population was in decline, with a near record low population of blue crabs recorded in 2008. The cause of this decline is not fully known, but is most likely a combination of overfishing, habitat loss, poor recruitment, and poor water quality.

Since new regulations on crab harvesting, particularly those restricting the harvest of mature females, were put in place in 2008, the population of blue crabs has increased significantly. However, a low number of juveniles were caught in the winter dredge this year, leading to a gloomy forecast for the number of harvestable blue crabs for the 2013 season.

During my summer internship at the Smithsonian Environmental Research Center (SERC), I want to investigate if this forecast is coming true. The winter dredge survey, an extensive bottom trawl survey that catches blue crabs overwintering at the bottom of the bay, is impressive for its scale and precision. The survey takes into account 3 different regions of the bay, and 1500 sites are surveyed. The data are used to calculate crab density and from that project overall crab abundance. The 2013 winter dredge survey found markedly lower numbers of juvenile crabs (crabs smaller than 2.4 in) than in previous years.  One of the key questions regarding the survey, however, is just how closely the observed winter population of juveniles correlates with the actual number of blue crabs that survive to the summer.

One of the main issues with using the juvenile index from the winter dredge survey to predict future abundance of adult blue crabs is that it does not take into account survivorship of juvenile crabs, which can vary widely from year to year. Blue crabs are competitive and cannibalistic, and a large proportion of juvenile blue crab mortality can be attributed to predation by blue crabs themselves. Using the juvenile index to predict future adult abundances does not take into consideration interactions between adult and juvenile blue crabs—a low number of juveniles could in fact be the result of increased predation pressure from the adult population. Longer term research conducted at SERC has indeed shown that mortality of juveniles is related to the density of adult crabs.

Over this summer, research will be conducted to determine how adult and juvenile abundances from the winter dredge survey correlate with the actual numbers of blue crabs observed in the summer. Crabs will be collected by net tows and their abundance and size will be recorded. Similar research conducted last summer showed that the high numbers of juvenile blue crabs found by the 2012 winter dredge survey had vanished by the summer.

Hopefully for crab-lovers, the future low abundance of crabs projected by the low juvenile index of the winter dredge survey will be found to be too low. Recruitment rates for blue crab are known to fluctuate wildly, and survivorship of larvae to juveniles depends on multiple factors: salinity, temperature, dissolved oxygen, and predation. The winter dredge report did show an increase in mature females, which suggests that management strategies designed to protect fecund females are in fact working.

Research done at SERC comparing crab abundance and mortality brings to light interesting questions regarding the overall dynamics of the blue crab populations. The comparison of observed crab abundance in the summer to the juvenile index from the winter dredge report will help us determine how accurate the juvenile crab index is at predicting future crab abundances. Studying the population dynamics of blue crabs can help us understand and preserve this valuable natural resource.

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Mangrove Tracking VII: Just Another Day at the Office

Monday, July 16th, 2012

by Nancy Shipley

Technician Lorae Simpson and intern Jake Bodart deep in the mangroves, assessing vegetation cover and substrate color. (Mayda Nathan)


It sometimes seems crazy to be climbing through mangrove stands and wading through large ponds to collect our data, but the sites we explore are chosen for a reason. That reason is two-fold: One, to ground truth satellite imagery so we can map historic and current mangrove distributions. Two, to document the plant communities in places dominated by mangroves, in places where mangrove encroachment is occurring, and in places where mangroves have not yet arrived.

By using satellite imagery from years past, we hope to determine how far mangrove communities have spread in the last few decades. To do this we have to first understand what individual plant species comprise the large areas of vegetation that we can see from the satellites.

That is where we come in, climbing through mangroves.

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Posted in Climate Change, Ecology, Grants, Interns, Invasive Species, Mangrove Tracking: Letters from the Field | Comments Off on Mangrove Tracking VII: Just Another Day at the Office

Mangrove Tracking VI: Attack of the Beetles

Thursday, July 5th, 2012

by Jake Bodart

Beetle tunnel. This Scolytid beetle has burrowed into a mangrove seedling and lain its larvae inside. (Jake Bodart)

In science not everything goes according to plan. For example, half of your project’s experimental units might die before you start.

In the back of the Smithsonian Research Station here in Ft. Pierce, the mangrove team has built an artificial pond (we call it Lake Simpson) to raise mangrove seedlings that will be used in experiments. However, when we arrived here last month, we noticed that about half of the red mangroves were turning black and dying. It was unclear at first whether these mangroves were dying directly as a result of the artificial habitat (was our pond too hot? Too salty? Not salty enough?), or if the pond was somehow making the mangroves more susceptible to pest insects. We know from other studies that predation by insects can cause a large amount of propagule and seedling mortality.

Upon closer inspection, we decided insects were the culprit. The evidence of insect predation: small bore holes and little piles of frass (chewed up/excreted parts of the plant, a.k.a. insect poop). We decided to sacrifice the seedlings that were clearly infested, and dissect them to see if there were any insects inside.

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Toughest Shellfish in the Sea?

Tuesday, January 24th, 2012

by Kristen Minogue

Blue mussels (Credit: Meriseal)

Some species can survive just about anywhere. Take blue mussels, a group of shellfish whose habitat stretches from the Arctic to the Mediterranean. Over the last several decades, biologists have thrown all kinds of tests at them – heat, cold, saltwater, freshwater, low oxygen. They’ve even tried drying them out. Almost nothing fazes these animals. For invasion scientists trying to figure out how far they could spread, that’s a scary prospect.
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Posted in Ecology, Fisheries, Interns, Invasive Species, Publications | 3 Responses »

How Plants (Occasionally) Escape the Food Chain

Friday, December 23rd, 2011

by Kristen Minogue

Leaf shredded by insects. Credit: Marina LaForgia


It’s a trick worthy of any spy thriller: to elude an enemy, hide among something it won’t notice. Or, to be extra safe, something it finds incredibly disgusting. It turns out the same strategy can work for plants that don’t want to get eaten. Sometimes.

For the last seven months, intern Marina LaForgia has kept tabs on tree saplings in more than a dozen different environments and watched the game of ecological survival play out. As she tracked their progress, she searched for an answer to a deceptively simple question: Is diversity good for plants? When it comes to the food chain, will hungry herbivores pass over tasty plants if they’re surrounded by less palatable ones?
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Posted in Ecology, Interns, Publications | 8 Responses »

The Satellite That Could Save the Coasts

Friday, September 16th, 2011

by Kristen Minogue

On a hot afternoon in July, a team of researchers sailing down Chesapeake Bay stumbled across a cluster of striped bass floating in the water. About a dozen of the iridescent black and silver fish bobbed at the surface near the ship’s bow. All of them were dead.

Scientists prepare to measure how light interacts with particles in the Bay. Credit: Carlos DelCastillo

The fish kill came out of a low-oxygen zone near Annapolis, just one symptom of the Bay’s declining health. Overflows of nutrients from farms and cities have fueled massive growths of algae that cut off light and oxygen to the Bay’s lower levels.

“There was a very quiet moment between everybody on the boat,” recalled Vienna Saccomanno, one of the Smithsonian research interns aboard when it was discovered. “You kind of knew what everyone was thinking, feeling empowered to continue with this research and hopefully contribute to prevention of this in our water system.”

The scientists on board weren’t there simply to document the Bay’s many ailments, however. They had joined the 10-day cruise to pave the way for a much larger goal: a geostationary satellite that could provide constant, detailed coverage of coastal health.
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Marshes, Microbes and the Other Blue Carbon

Tuesday, September 6th, 2011

by Kristen Minogue

Tidal marshes have long been lauded as carbon sinks for their ability to pull CO2 from the atmosphere and bury it in the soil, what scientists have taken to calling “blue carbon.” But wetlands are also notorious methane emitters. Now ecologists suspect that only a select few wetland types can reliably act as sinks, and that number may shrink as sea levels rise.

tidal wetland

The Kirkpatrick Marsh on SERC's campus in Edgewater, MD. Tidal wetlands both store and release greenhouse gases. Which will prevail as the planet warms is a question ecologists are still trying to answer. (Credit: Gary Peresta/SERC)

Scientists estimate wetlands are responsible for anywhere from 15 to 45 percent of all methane emissions – a wide range that makes predicting their role in climate change difficult. However, that role could prove critical in the years to come. Methane (CH4) is a far more potent greenhouse gas than carbon dioxide. Over the course of a century, a single gram of methane is roughly 25 times more powerful than a gram of CO2.
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Posted in Climate Change, Ecology, Interns, Publications | 2 Responses »

Intern Logs: A Soldier and a Scientist

Friday, August 19th, 2011

This summer the SERC interns had a unique addition to their ranks – Iraq veteran Kiel Edson, a former Marine finishing his last year of undergrad at California State University, Sacramento. In this edited Q&A, the 28-year-old shares thoughts on Iraq, SERC and the transition from soldier to researcher.

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After five years working as a Russian linguist for the Marines, 28-year-old Kiel Edson started college and discovered his passion for conservation biology. (Credit: Michael Tobias.)

What kind of work did you do for the Marines in Iraq?

E: I was part of a group of what’s called Signal Support Team. We basically go out onto missions off the base, closer to the main cities, and we collect intelligence on what’s happening within the city. And then anything relevant that we find, we basically just write-up in situation reports or intelligence reports and send them off to the commanders who are making decisions as to how to handle the situations in that city. We just tell them, hey, they know that you’re going to ambush, or they know about the convoy going through on Thursday, so that they can change the way that they operate to avoid taking casualties, or they know going in there’s going to be a firefight, so everybody’s prepared for it. It’s not a surprise.
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Posted in Ecology, Interns, Interviews, Invasive Species, Land Use | 1 Response »

Hunt for a Missing Nutrient

Wednesday, August 17th, 2011

by Kristen Minogue

Leviton

Intern Ginny Leviton (left) and Vienna Saccomanno sample groundwater from a drainage ditch, trying to pin down the exact spot where the nitrogen goes missing. (Credit: Tom Jordan)

The Choptank watershed has SERC researchers baffled. On the eastern shore of Chesapeake Bay, roughly a 75-minute drive from SERC, the groundwater flowing into the Choptank River passes through a cornfield – a likely source of nitrogen, a nutrient that can wreak havoc on the Bay’s ecosystem if it runs too high. But something is happening to the nitrogen here before it reaches the Bay. Nutrient ecologist Tom Jordan and his research team have spent the better part of a year trying to figure out what.
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Posted in Ecology, Fisheries, Interns, Land Use, Publications, Water Quality | 6 Responses »

Intern Logs: Witness to an Invasion

Tuesday, July 19th, 2011

snakehead students

Students on the SERC sampling team, with the 23-inch female snakehead fish they helped ensnare: Diana Sisson (intern), Alison Everett (visiting student), and Philip Choy (intern).

First-hand accounts of the snakehead capture from two interns on the seining survey.

It was around 3 p.m., and it was time to pull the last seine net of the day. We had been out on the water since 10 a.m., and we had already caught a few rarer species, including a stingray and a few juvenile Common Carp. Research biologists Eric Bah and Stacey Havard volunteered to pull what may be the seine of their career.
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Posted in Ecology, Interns, Invasive Species, Publications | 4 Responses »

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