Tuesday, July 23, 2013

2013 Connecticut Blue Crab Special Report #3

From Tim Visel of "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

Special Program Report #3

July 23, 2013

The 2013 Blue Crab Year


  • Blue Crabs Massing at Entrance to Connecticut River
  • Crabbing Soars in Eastern CT Coves
  • Western CT Crabbers Seek Answers About Habitat Concerns

Blue Crabs Massing at Entrance to Connecticut River

Reports continue to come in about a very large population of 3 to 4 inch crabs massing on the west side of the lower Connecticut River – Old Saybrook area.

These crabs have at times made dock fishing impossible (loss of bait). Reports from trappers also in some lower river regions and Old Lyme rivers (lower) now report hundreds of 3 to 4 inch crabs while crabbing. As the salt water wedge continues to build look for these crabs to advance up the river. The tidal wedge is building strength and excepting any new rainfalls should be in Essex in five days. Blue crabs did appear on July 4 at Essex only to be pushed south again after heavy rains. The first sublegal crab I observed was caught in Essex again on July 20th.

These immature crabs should move up the Connecticut River at night (at least that has been the pattern) in the next few days.  Reports of 3 to 4 inch crabs have also greatly increased from shore areas Guilford to Westbrook (Clinton Harbor especially).

No discernable “wave” movements along the coast however have been detected as of today, July 23rd.

Crabbing Soars in Eastern CT Coves

Crabbing continues to improve in eastern Connecticut as reports indicate good to excellent catches in nearly all the coves, including Bakers, Alewife, Jordan, and Masons Island.  Excellent high tide catches from handliners, low tide night time dippers with flashlights. Still, no reports for the Pawcatuck River or Thames River: these areas tend to follow the shallow warmer water Eastern CT coves.

Western Connecticut Crabbers Seek Answers About Habitat Concerns

Several Western Connecticut crabbers have asked about signs and symptoms of a habitat failure for blue crabs. I know of no such research underway at present but two indicators of a very much changed ecology and habitat would indicate Sapropel or oatmeal – large new accumulations of organic matter, usually brown leaves as a dominant source material. Bottom samples may be black underneath this brown surface layer but the leaf stems remain intact for one to two years (personal observations) and thick growths mats of sea lettuce (Ulva lactuca) can also be in close proximity.

What to look for:

1) New thick green mats of sea lettuce; sea lettuce has been known since the middle 1980s to emit toxic substances that could kill blue crab Megalops (Johnson and Welsh, 1985) sometimes in a matter of minutes. Thick mats of decaying sea lettuce mats have occurred worldwide and once dead, released so much hydrogen sulfide fumes it overwhelmed beach walkers in Europe.  

In France large amounts of Ulva lactura rotted and emitted large quantities of hydrogen sulfide gas with tragic results killing school children who had volunteered to help with cleanup efforts (2009).

China has just recently experienced a sea lettuce bloom the size of Connecticut!  Sea lettuce is now also linked to natural biocides. When eelgrass populations declined in the 1930s Brant (geese) switched to eating sea lettuce which led to a report by the US Fish & Wildlife that hunters complained bitterly that Brant that fed on sea lettuce tasted terrible.  (US Fish & Wildlife Service, Department of the Interior:  Waterfowl Tomorrow US GPO 1964 page 145-146) Brant eventually faced with starvation and on a poor food substitute Ulva, had to change their migratory routes.

In a 1980s experiment at the University of Connecticut and a paper published later in the Journal of Experimental Marine Biology and Ecology details the toxic impacts of Sea lettuce upon blue crab Megalops in low oxygen conditions. (Detrimental effects of Ulva lactuca exudates and low oxygen on estuarine crab larvae Journal of Experimental Marine Biology and Ecology Vol. 90 #1, 1985.)

Blue crab areas with sudden or much larger sea lettuce populations are now suspected in a regional western CT blue crab habitat failure.  Increases in sea lettuce in good (pre July 2011) crabbing areas have been reported.

2) Increased Sapropel and Hydrogen Sulfide gas discharges from leaf rot. Look for previous harder firm bottoms now soft and filled with rotting leaves, stems, bark and grasses. When disturbed, these deposits emit a slight sulfur odor (matchstick smell).  If these deposits have putrefied, than intense hydrogen sulfide (rotten eggs) smells are possible.  If areas are low in oxygen bottom organic matter continues to rot, releasing streams of gas bubbles to the surface. This is a very bad sign for crab habitat as it shows depleted respiration in low oxygen conditions. At low tides on hot days with little current, these bubbles will appear to rise or stream off the bottom.  In the summer these bubbles tend to be hydrogen sulfide, in winter and with greater oxygen in the water, methane.

Several Baldwin Bridge crabbers over the weekend experienced these conditions briefly, so it’s just not a Western CT concern, at slack water, low tide, crabbers noticed bubbles coming to the surface (crabbing was terrible) at this time, perplexed, I explained it was gas given off by rotting leaves below, and threw a box wing wall crab trap slowly pulled in to the dock contained about six black oak leaves in the trap indicating a leafy rotting bottom. When the tide changed and salt water with more oxygen hit the pier, crabbing quickly improved and bubbles disappeared.

In the west, look for these bubbles, at low slack water, their presence could signal a habitat “failure” for blue crabs.

A larger report will follow on Western CT habitat histories.

Thank you for your recent emails.

Tim Visel

Email your blue crab reports to: tim.visel@new-haven.k12.ct.us

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 susan.weber@new-haven.k12.ct.us

The Sound School is a Regional High School Agriculture Science and Technology Center enrolling students from 23 participating Connecticut communities.

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