Wednesday, June 19, 2013

Mystery of the Missing Blue Crabs: How Does The Winter Juvenile Blue Crab Index Compare to the Observed Summer Population?

By Katie Sinclair, Guest Blogger and  Intern at the Smithsonian Environmental Research Center

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. 

Monday, June 17, 2013

2013 Connecticut Blue Crab Report #3

From Tim Visel at The Search for Megalops:

The Sound School – The ISSP and
Capstone Project Proposal
Building a Network of Citizen Monitors
The Connecticut Blue Crab Population
Habitat Study 2010-2015
You Do Not Need To Be A Scientist To Report! 

The Search for Megalops
Program Report #3
June 12, 2013

The 2013 Blue Crab Year

  • A Lack of Small Crabs - Continued Concerns
  • The 2013 Crab Year – A Slow Start
  • A Habitat Reversal is Possible
  • Western Crabbers’ Reports
Lack of Small Crabs – Continued Concerns 

Some of the early spring reports include observations of large mostly male crabs. Rivers included with large crabs: Branford; Lost Lake, Guilford; Rt. 146; East River; Hammonasset and lower CT River. No reports east of Old Lyme and no western reports except several checks and rechecks of the Saugatuck River, no crabs observed.  Crabs have been observed actively feeding, but many of the lower Connecticut River reports mention silt laden waters and strong currents, not the best blue crabbing conditions. 

One good size catch of crabs was made in the lower CT Old Lyme section but catches ranged from 2 to 4 crabs/hour, but that is based on just a few very early reports. 

Water temperatures have recently taken a jump up, especially in the shallows but eastern CT usually runs 3 to 5 weeks after the west, again cooler ocean temperatures. A strong salt water wedge is yet to materialize in the Connecticut River.

Teachers at the Sound School have seen just a few blue crabs near our docks, not nearly the same quantity as last year. 

The word around the waterfront is that crabbers are waiting and hoping for positive signs now. 

See you at the docks, 

Tim Visel 

2013 Crab Year – A Slow Start

With most of the central areas now reporting some surviving adults (nearly all males) catches continue to be light except for a couple of good catches in the lower Old Lyme - Connecticut River estuary. The Black Hall – Lieutenant River systems seem to be able to hold a significant over-wintering blue crab population- (flooding has been less) but these areas were some of the first to report in 2010 and 2012. What is apparent is the lack of 2 – 3 inch crabs as reports do not mention them. It is thought that the 2 – 3 inch size is most vulnerable to habitat events, and is consistent with the first Chesapeake Bay reports (Chesapeake Bay crabbers now face harvest restrictions).  The first reports in 2010 and 2012 came from municipal shellfish commissions who reported huge numbers of 1.5” to 2.5” crabs over or adjacent to shellfish beds. 

It seems early reports of 2 inch crabs were precursor to some outstanding blue crab seasons that did not occur as yet this season, nor reports of the one- inch category, the growth of the August Megalops set that was photographed last August by Sound School teacher Steven Joseph and his son Kelly of Branford.  That Megalops set was huge, and if coast-wide, produced billions of 1 inch crabs. Hurricane Sandy and the cold winter add to the survival concerns. 

While it is much too early to predict the outcome of the entire 2013 blue crab year, the three previous indicators of good years (2007, 2010, 2012) have not arrived, large numbers of surviving adults in April and reports of small crabs in May over shallow water shellfish beds. The next timeline is June 15 to 30th, the appearance of a possible delayed Megalops set- which should be the size of a nickel by then. 

Look to see these first “star” blue crabs in small mesh minnow seines mixed in with silversides by the 4th of July.  They like the creeks and shelly bottoms as hiding is the rule of order for several more weeks.  Small crabs are easy prey for a host of predator species and the one most noteworthy is the Sea Robin which hunts along tide rips between sand bars on open beachfronts. Smooth sand and featureless bottoms (no structure) provide little protection from these predators which have mouths that resemble the early steam shovels. A sea robin caught off Hammonasset Beach in June 2010 contained pieces of small blue crabs.  Reports of huge populations of small crabs are often from shellfish beds or creek bottoms with pieces of shell. 

The shallow areas containing bivalve shell (Tom’s Creek Study in Madison) and creeks in general seem to show the first small crabs. It is these areas that in early spring provide the most predator protection from full salinity predators other than other blue crabs. Tom’s Creek will soon be sampled with a minnow seine to determine if any small blue crabs are present.

A Habitat Reversal is Possible

 Several questions have come in regarding the habitat reversal concept and the difference between distinct habitat periods.  One of the interesting features of this research is that the year to year changes are sometimes small – differences only become apparent over much longer terms.  It is not an instant process, from the very cold 1870s the Narragansett Bay deep water bay scallop fisheries continued until the late 1880s and early 1890s.  Only after decades of low storm activity and higher temperatures did these deep water bay scallop habitats reverse from red algae to eelgrass and bay scallop habitat quality turned strongly negative.  Although the climate started to moderate in 1880 it wasn’t until 1898 that massive habitat shifts occurred – most noticeable in the southern New England lobster fishery – to blue crabs and bay scallops to oysters, hard shell clams (quahogs) to soft shell clams (steamers). It seems if habitat quality has two basic parameters – too hot or too cold. The 2008 year for example, was a poor one for the Chesapeake Bay blue crab fishery, and reports include two potential hydrogen sulfide toxic events, (high heat habitat failure). These events are called jubilees – a combination of low oxygen and anaerobic sulfur reduction processes that drive adult crabs out of the water. Those events are large and noticeable, yet small but significant changes over time do not often attract attention and largely go unnoticed.

If the winters on average stay cooler and storms continue to wash away acidic Sapropel deposits (a black sulfur smelling organic compost locally called black mayonnaise) estuarine soils will become more alkaline we may see a habitat reversal in two decades, so it’s not so much a light switch impact – it takes decades for a habitat reversal to occur.  It may be however, possible to check this process. Native Americans may have left us a “habitat history” in their shell heaps of discarded bivalve shells centuries ago.  I have sent some notices out to some colleagues in the archeological field to reexamine some reports regarding Native American shell heaps (middens)  in New England – including looking for blue crab claw points and dominance of bay scallop/quahog to oyster and soft shell clams.   

Some early reports do indicate that at certain levels the dominance (abundance perhaps) changes and the most significant difference is the absence or presence of bay scallop shells.  Bay Scallop shells may signify time periods of much cold and stormier periods.  Oysters like relatively warm and quiet periods.  Hard shell and soft shell clams set heaviest after storms (soil recultivation) biggest sets for quahogs in cold, soft shells in heat.  Oysters it seems appear on both sides of layered deep dark organic matter from a midden examination in Maine at the turn of the century (see Harold Cassner 1985).  It is thought now that layers of carbon rich compost are deposited during long periods of extended heat – lowering the pH of marine soils eliminating bivalve sets.  Similar type core layering has been found in studies here in Connecticut.  (Paddon 1994) (Paddon  2002).[1]  The deep acidic nitrogen rich Sapropel deposits could signify a habitat reversal which then favored blue crabs – much as our present day observations.  Following decades of prolonged heat and absence significant coastal energy events (until recently) many of Connecticut’s coves have deep accumulations of Sapropel.  Fishers started to notice this change which then gathered the attention of some early estuarine researchers.  John Clint Hammond – a retired oyster grower on Cape Cod noticed the increase of “marine compost” on bay bottoms in the late 1970s.  We would often talk about this excess vegetation which would rot and turn black in the hot summer sun.  He sent me a newspaper article shortly after I left a position with the University of Massachusetts with a short note – “It’s happening.”  What Mr. Hammond was concerned about a regional habitat failure and at New York Fishermen forums 1980 – 1982 – groups of eastern Long Island baymen from Peconic and Great South Bay described the same precise habitat changes of winter flounder and bay scallop habitats, mentioning more soft bottom Sapropel. I have sent requests off to the State of Massachusetts to see if the increase of blue crabs followed an increase in Sapropel deposits often containing eelgrass.  Previously hard bottoms often containing estuarine bivalve shell now appeared softer and accumulating plant matter in the 1980s.  Baymen in eastern Long Island were already noticing the habitat reversal before the middle 1980s.  It seems that these soft organic deposits (Sapropel) provide an important over wintering habitat for blue crabs.  A period of storms could possibly wash deposits away especially if the energy pattern storm frequency increased for years.  A colder and stormier pattern could them turn habitat quality from positive to negative.  That happened in the 1950s and 1960s.  What did a habitat reversal look like, fishers had described it perfectly since the mid 1970s as energy levels declined and temperatures began the rise and the 1984 Cape Cod article describes it here – the one that John “Clint” Hammond mailed to me from Cape Cod. The article mentions oxygen depletion but the visual clues describe the reversal or habitat changes. Sapropel is often termed “sulfurous bottom muck.”  Warmer water holds less oxygen than cold, so fishers and coastal residents seem to notice these conditions in late summer.

“Scientists seek input on oxygen depletion

UPTON, N.Y. – Marine scientists at Brookhaven National Laboratory are conducting a research study dealing with oxygen depletion of salt water along the mid-Atlantic coast, from North Carolina to Maine.

They would like to receive first-hand reports from shore residents and others who are familiar enough with a body of salt water to recognize some of the unusual or abnormal things that occur as a result of oxygen depletion. The study deals with salt water only in coastal areas or in estuaries, not with fresh water.

The scientists are interested in information on the following things, particularly if they have occurred since 1970; fish kills, red tides, algae blooms or scums, unusual smells (especially sulfurous bottom mud), the disappearance of “regular” marine life (fish, plants or birds), and the appearance of “new” marine life.

The results of the research study will be important to people who live in coastal areas because oxygen depletion can destroy marine resources, particularly fish and shellfish.

Anyone who can contribute information is invited to write or call Terry Whitledge, Ocean Science Division, Brookhaven National laboratory, Upton, NY. 21677”

Rekeyed by Susan Weber, Sound School, June 5, 2013 – Printed with permission of the Cape Cod Times 

By 1984 the signs of a regional habitat reversal were recognized and perfectly described in 1984 article only a decade after the warm up began in 1974 and energy levels (storm activity declined). How did fishers measure energy loss and temperature increases, as flushing (energy) and heat often as stagnation. Stagnant waters in high heat would be lethal to marine “valued” fish and shellfish species including blue crabs. Sapropel would then shed hydrogen sulfide or the infamous rotten egg odors.

1974 is the beginning of the second “Great Heat” here within a century. Studies conducted after 1974 would not include that the 1950s period of much colder temperatures and powerful storms. That is the great value of long term studies they can “see” past short term events.  Historical fisheries surveys should look at the last century, not just a few decades.

Western Crabbers’ Reports 

I do appreciate the reports from crabbers who still report after the 2011 western CT die off. The reports mention a few crabs but nothing like 2010 or the first half of 2011 seasons. 

If the Megalops set survived they should have plenty of habitat, space and feed as the current adult blue crab population is at low levels, they do not need to compete with large masses of adults because there just aren’t any.  A good population of 1 to 2 inch crabs could mean a good fall season, but that size will need to appear by the end of July. 

For the most part the western reports are grim with little or no sightings, despite frequent checks. It would be good to hear some positive news, but it’s been almost two years and questions have been asked if in fact the habitats are now reversing in western CT. 

It is a good question and historically those habitats that tended to reverse first, reverse the “first” back again. It was western Connecticut that reported the first high density lobster die offs and the first to report increased blue crab populations. It would seem plausible that those first habitat areas to reverse could do so again. 

It is a long term and slow process and cultivation by hurricanes can certainly speed habitat reversals since post Irene/Sandy evidence of that has already happened in some areas. 

In some of the eastern coves and bay bottoms after all these damaging storms, vast accumulations of organic muck (Sapropel) are gone, some areas contain “new” sands and shell fragments as if the bottom was churned, as it most likely was. Reports have come in to Connecticut Bait & Tackle shops this spring that such areas now contain small winter flounder. That is one of the major problems with habitat quality, by the time enhanced fishery levels are reported, it could be years or decades since the “habitat reversing event” happened and little connection then made. If these small winter flounder live to legal size will people recall the habitat conditions years ago that made it possible?  In 1938 The Great New England Hurricane raked New England’s coast with destructive storm surges and powerful waves. The marine soils in many coves and bays were “washed clean” by this energy and acid bearing organics compost deposits removed, it was simply lifted up off the bottom and washed away. The remaining marine soil now rinsed of organic “high heat” acids became more alkaline. I’m certain that predator species were also removed, but the hard clam sets that followed four to five years later were extraordinary; they (Rhode Island hard shell clam sets were huge), the storms continued into the 1950s and hard shell clam sets improved but little connection was made to these cultivation events when Rhode Island hard clam production peaked in the 1960s. At the same time Quahog clam sets were improving, the habitat conditions for blue crabs were now turning sharply negative. As the cold and energy levels increased, blue crab abundance declined. At no time in Connecticut’s environmental fisheries history have I found lobster and blue crabs to be extremely abundant at the same time.
And some of the first fishers to notice this habitat reversal four decades ago were from Niantic Bay CT and the Peconic Bay and Great South Bay, New York. There small boat fishers were keen observers of the habitats from which they derived a livelihood. These habitats were important and noteworthy even if it was just visual observations (softer bottoms) and likely the only long term terrestrial observation process similar is some Connecticut pond and lake associations.  As Connecticut’s forest canopy returned watershed small bodies of water filled in with windblown leaves which composted in high heat releasing nutrients for pond weed growth. Eventually when faced with this “habitat succession” change, the bottom filled with soft organics and they were dredged. Some of the first intensively studied dredged/restoration fresh water projects were done in Clarks’ Pond in Hamden CT which now forms the edge of Quinnipiac University.                                                                                                                     There is much literature available about this habitat succession process and often the “dredged material” had value as potting soil. It was basically “wet compost”. In the marine environment and in low oxygen conditions this composting also occurs (Sapropel). It is the Sapropel that is now linked with improving blue crab habitats and shares a direct climate and energy habitat succession connection.  It is also the same Sapropel that has been so damaging to bay scallop and winter flounder habitats.
However, all habitat reversals in the past were connected to increases and decreases in energy (storm) levels, whether it was the huge sets of soft-shell clams after the Portland Gale of 1898 or those heavy hard-shell clam sets after the Hurricane of 1938, habitat quality appears to have a direct “energy link”.  And, for those who follow the weather our recent very early tropical storm Andrea followed the NAO storm track mentioned in Report #1 (March 26, 2013). 
All blue crab observations are important.
Email your blue crab reports to:
Every observation is valuable as we learn more about our blue crab population. 
The Search for Megalops is part of a Project Shellfish/Finfish Student/Citizen Monitoring Effort Supported by a 2005 grant to The Sound School from the National Fish and Wildlife Foundation grant #2005-0191-001.
Program reports are available upon request. For more information about New Haven Environmental Monitoring Initiative or for reports please contact Susan Weber, Sound School Adult Education and Outreach Program Coordinator at
The Sound School is a Regional High School Agriculture Science and Technology Center enrolling students from 23 participating Connecticut communities.

[1] Patton, PC. Rates of sediment accumulation in coastal coves on Fisher’s Island Sound, Long Island Sound research Fund # CWF-310-8, 2002, see core examinations.
Patton, PC. Post-glacial stratigraphy and cakes of sediment accumulation in these small Connecticut coves; Long Island Sound Research Fund #CWF-266-R, 1994; see core examinations.

Thursday, June 6, 2013

Support American Crabbers, Eat Local Crabs

The recent warm weather has me thinking about eating crabs. I like to support local crabbers (watermen here in Maryland) whenever I can, but it's not always easy to find out where crab meat comes from. It is not uncommon for crab meat to come from other US East Coast states or from Venezuela. At least these are truly blue crabs of the same species Callinectes sapidus that we have in Chesapeake Bay. It is more common to find crab meat from different species in Asia or elsewhere served as "Maryland Style" crab. If you are in Maryland and want to be sure your crabs are from local sources, look for this True Blue label at your favorite restaurant. Local crab meat may often cost a little more, but it's likely to taste much better! To find out more, visit or read this article from the Washington Post. If you know of similar programs in other states, let me know so I can highlight them here.