Thursday, April 26, 2012

What's bad for lobsters is good for crabs?

Here's an interesting excerpt from a recent update on the Connecticut Blue Crab Population Habitat Study. It discusses alternating periods of blue crab and American lobster abundance.

Program reports are available upon request. Catch/observation reports 1-15 are also available.
For more information about New Haven Environmental Monitoring Initiative or for reports please contact Susan Weber, Sound School Adult Education and Outreach Program Coordinator – email to: susan.weber@new-haven.k12.ct.us.



Shellfishers May See First Blue Crabs

In April of 2010 members of the Guilford Shellfish Commission reported sightings of thousands of small blue crabs on shellfish beds off Guilford.  A warm winter had thought to increase small crab survival/populations and a couple of quick phone calls confirmed the Guilford observation.  A huge population of juvenile blue crabs was along the Connecticut beach fronts in creeks and coves in numbers such that no one could recall seeing before.  By June 1st (2010) small crabs were observed as far as east of Niantic Bay and by July 1st Connecticut was in the beginning of the best blue crab year since 1912.  What happened?  Well, the previous winters were relatively mild, and absent strong storms.  The 2007-2008 and 2010 will be remembered as some of the best recent Connecticut blue crab seasons.  Then, we had the winter of 2010-2011 with 76 inches of snow, bitter cold and tremendous record breaking spring floods and the 2011 crab year was much more modest, and overall blue crab abundance in the east fell sharply.  We had a 1950s winter and as in the 1950s and 1960s and following those type of winters we had a noticeable drop in blue crabs last year as compared to the 2010 season.  But Southern New England crabbers had seen this happen before.

What Connecticut has experienced the past two decades was similar to the end of The Great Heat in the late teens.  At the turn of the century northern blue crab populations soared most noticeably in Buzzards Bay, Narragansett Bay and Long Island Sound.  A huge upsurge in blue crab productivity then but as winters grew colder in the 1930s, 1940s and 1950s blue crab abundance dropped dramatically region wide.  A short passage in a report about the Westport River in Massachusetts details this concern about observations in blue crab abundance at the time.  The reference comes from a Massachusetts Board of Natural Resources Study (one of 23 such studies) titled A Study of the Marine Resources of the Westport River and this section appeared on page 39 of the report and mentions the decline in blue crabs.1

“The blue claw crab is a species which were formerly abundant the south shore of Massachusetts but has been declining in numbers for at least the last decade.  Such decline has also been observed in waters south of Massachusetts.  Jeffries (1966) noted that the blue crab began to decline in Rhode Island in the mid-1930’s and that by 1938 they had diminished to the point that it was no longer profitable to fish for them commercially.  The cause of the decline of this crab in our waters is unknown.  Many fishermen along the shore have expressed the belief that the loss of blue claw crabs- also fiddler crabs (Uca spp.) is due to the careless use of pesticides in coastal areas.  While it is certainly possible that pesticides have had a detrimental effect upon crab populations no conclusive evidence has been documented in this regards.”

What fishery regulators didn’t understand at the time is that as the climate grew colder it favored lobster habitats – kelp cobblestone forests and red macro algae populations grew while the huge eelgrass meadows (1880-1920) were uprooted by storms which now more frequently occurred following decades of heat and few storms.  The colder winters most likely greatly reduced blue crab populations.  To the crabbers of the 1960s and 1970s the blue crabbing resembled nothing like former years or crabbing experiences as young people in Connecticut.  Those observations from the Westport River in Massachusetts (1967) were largely correct, blue crab populations greatly diminished during this period as it became a colder and more storm filled period.  Thousands of acres of cobblestones however were exposed along beach fronts, cleaned and with tumbled by hurricanes, and came to have kelp forests that were often in the same habitat areas as eelgrass meadows occurred decades before.

What was better habitat conditions for the blue crabs (heat and quiet) was not so good for lobsters – which in our area needed that critical stage four kelp/cobblestone habitat.  When the blue crab populations surged at the turn of the century Southern New England lobster populations crashed.  All the Southern New England lobster stocks were impacted.  Rhode Island even closed for a portion of the 1905 year, its fishery to lobstering.  Today we see that same dynamic – blue crab populations have surged (2010 was the best blue crab year since 1912 according to historic Fulton fish reports) while our lobster population has shrunk to its lowest levels since 1905.  Today much of that shallow water kelp/cobblestone habitat has failed – it is gone, disappeared and lobster recruitment is now at extremely low levels.  Blue Crab populations however have benefited from the warmer winters and heavy sets of Mya, the soft shell clam.  The presence of

1 Much thanks goes to Director Bruce Carlisle of the Massachusetts Coastal Zone Management Office for making this entire set of marine resource publications available to The Sound School and students researching fisheries histories.
eelgrass in some coves also may also have helped – but it is those sandy/shelly areas that are thought to hold the first megalops stage.  That is why shellfishers may be the first ones to see the results of a successful megalops set from last fall – the big unknown is of course is the effect of Tropical Storm Irene – those shallow near shore areas got quite a cultivation event and the unusual Halloween Blizzard, could have caused a large megalops mortality – we just won’t know for a few more weeks.

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