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Location: New Haven/Madison/Essex

PostPosted: Thu Aug 04, 2016 7:30 am    Post subject: Search for Megalops #3 - Blue Crab - Tim Visel Reply with quote

The Sound School Regional Vocational Aquaculture Center
The Search for Megalops Special Report #3
“You do not need to be a scientist to report”
Timothy C. Visel
June 1, 2016, 2016

• Cool Water as Oxygen Saturation Remains High
• Small Crabs in Most Estuaries
• Jonah Crab Megalops Mix in Northern Areas
• The Blue Crab Cycle?

Cool Water Oxygen Saturation Remains High- A Cool Habitat Spring
The very cool spring has overshadowed the opening of the Connecticut Blue Crab season – waters remain cooler, but habitat refuge areas, those found mostly in dredged river channels show that blue crabs made it safely past the hibernation period. Some late March reports from shell fishers mentioned the bottom (oyster beds) were just alive with small fish and crabs. The lower portions of tidal rivers show the greatest numbers of some older, larger crabs.
With some mild March days, water temperatures quickly warmed to the middle 40°F, then paused and then dropped a couple of degrees as a very cool weather pattern settled in. Early May saw temperatures in the 30°F range with some records from the 1870s set or matched. The 1870s were very cold in New England and set the stage for the habitat reversals of the 1890s when it was then very hot.
Cool but not cold has been good for the bottom dwelling organisms this year. Habitats have stabilized and have sufficient oxygen reduction processes. With so much dissolved oxygen, sulfur reducing bacteria should be only in deep organics now, not on the surface, as high oxygen levels favor the “good bacteria” those that recycle organic matter into the “cold water” nitrogen cycle.
It is the cool water bacteria that takes the very toxic ammonia and turns into nitrate which is the nutrient base for the nutritious algae that shellfish consume after a cold period. Cool (but not cold) water holds more oxygen so shallow seas such as Long Island Sound cool off quicker and oxygen requiring life rebounds faster. The oxygen saturation level remains high at 10 milligrams per liter. Blue crabs have adjusted to these temperature extremes living in the estuaries where water temperatures can be in the 40°Fs to the 90°Fs in the summer. But even the blue crab Megalops is even more resilient. They can “hibernate,” waiting for environmental conditions that favor maturation, something I did not know until a few years ago. While good oxygen levels are desired cooler water also delays blue crab shedding and sponge development. Blue crabs hold on northern estuary habitats may be declining and successful Megalops sets (early summer) may now come from only southern areas.
We just have not had the kind of Megalops activity, blue crab recruitment seen in 2010 and 2011 that made the 2012 and 2013 seasons here, truly ones to remember. Watch those areas that have deep sub tidal and warmer habitats to hold the largest number of blue crabs this summer. They are at the lower ends of tidal rivers often near or adjacent to dredged areas.
See you at the docks,
Blue Chip
Shallow Waters Show Early Changes in Crab Population
Small estuaries contain a broad range of microhabitats – extremely shallow to semi saline waters. The tidal range dictates now salty high tide and at low tide how fresh. Many Connecticut crabbers have noticed that during draughts – low rainfalls, lower Connecticut River flows allows the salt water wedge to bring blue crabs far inland to Deep River, even Chester, CT, while heavy spring floods can eradicate any overwintering blue crabs. Organisms that live in estuaries are uniquely able to survive in these extremes and the blue crab is especially adapted to them. In extreme heat when sulfur reducing bacteria (not oxygen requiring) produce sulfides, they can even walk out as in the blue crab jubilees. That has happened here in Niantic River-- (Crabs Pick Land Over Niantic- Jamie Muro, August 7, 2009) and a century ago, a more famous 1898 Narragansett lobster die-off described in IMEP Newsletter #15 Part 1 on The Blue Crab Forum. ™ Fishing, eeling, oystering thread, April 12, 2014. Extreme heat has been as damaging as extreme cold – cooler water rich in oxygen has been good for sea life. In fact it is great. When waters cool or heat rapidly fishers’ report the changes, some species seem to go away, others return, some after a long absence.
The Connecticut Halibut Fleet, for example, soon moved north as the climate warmed and Long Island Sound became hot, in the 1800s. The fleet following the habitat population changes from here all the way to the Davis Straight by Greenland. One observation during this period speaks to different climate at the time describing ours as “sweltering heat.”
But, more importantly was why our halibut vessels were in the Davis Straights at all; over time the fish simply had moved north in cooler waters. In colder times here, halibut had moved south making them accessible to fishing fleets in southern New England. In the 1870s, it was cold again here and Halibut fisheries moved south as well. It is the very cold times that blue crabs are scarce here, but in 1880-1920 and 1972-2012 (hot cycles) they were abundant.
Jonah Crabs Move to the Shallows And Mix In
One of the things we can do is watch those crabs who do better in colder water such as green, Jonah and rock crabs. At one time the most prevalent crabs in New Haven Harbor were the Rock crabs not the Blue Crabs (see EC #11, April 28, 2016,The Blue Crab Forum™)
Since 2002 the population of Jonah crab has soared followed by an increase in landings of southern New England. The Jonah Crab catch in New England has soared since 2002 with Massachusetts landings from 1 million pounds to 7 million (2012), Rhode Island from negligible landings in 2002 to almost 3.5 million pounds in 2012 (see the Jonah Crab fishery April 14, 2014, a briefing for the Atlantic States Marine Fisheries Commission Gulf of Maine Research Institute). Several factors can alter the populations of crabs but some reports mention a mixing of small Jonah crabs into the shallows. As this species is a cool – cold water habitat crab, it is thought that colder temperatures may have helped the Megalops and recruitment in offshore waters. Recreational crabbers may find Jonah crabs may mix into the blue crab habitats in early spring.
In more northern areas, some Jonah crab Megalops has already mixed into the shallows. If waters remain cool, Jonah crab may continues to increase here and become part of the recreational crab catches. In the early 1980s, I conducted some adult education classes at the Massachusetts Maritime Academy and during breaks, I would walk the Cape Cod Canal. Here crab fishers with box traps were catching Jonah not blue crabs, in fact they were preferred with some rock crabs in the catch well. If temperatures remain cool, inshore crabbers may see more Jonah and rock crabs. in areas that just a few years ago produced good numbers of blue crabs are now in the catch as well. Maine has also experienced a green crab explosion since 2011 and with some brutal cold winters has impacted soft shell clam fishery there, to such a point, green crab mortality has reached all the soft shell clams in some clam flats as recent reports mention no survivors in heavy green crab areas. The green crab or “shore crabs,” however, are considered in many areas of Europe “ the best crab” to consume; they are in fact, “edible”.
I have eaten Jonah Crab, (it is very good) rock crab and spider crab, (Blue Crab Forum™ Other Crabs thread May 20, 2014). I have never tried green crab, but it does reach edible sizes here as in the North Sea. There it is still harvested as an edible commercial species in Europe – in fact, it is part of a soft-shell fishery in the lagoon of Venice, Italy since the 17th century (The Oxford Companion to Food, 2014.). The Food and Agriculture (FAO) of the United States (Mediterranean Coastal lagoons) reports on green crab soft shell shedding operations in Venice since the 1600s. Local fishers discovered how to recognize those green crabs about to shed termed, “moleche”. The crabbers are known as “molecanti” and sort soft green crabs into three divisions; those about to shed “spiontani” or those who will shed in a few weeks (boni) and “matti,” those who will not shed, Green crabs close to shedding are placed in wood pens (called “Vieri”), very much like old wood lobsters cars with spaced lath to allow water circulation. These are placed in shallow water and from March to June, both females and males, and September to December (males only) are the shedding seasons. .They are hauled and checked for shedders termed “muta”. A recent article mentions that moleche fishers obtain about $50 / pound for soft shell green crab. Soft shell green crab became a popular food dish into Europe North and Baltic Seas, but an organized shedding system has existed in Venice for hundreds of years. I found a recent report that a delegation from Prince Edward Island is going to Italy to investigate this green crab fishery. We have had large green crabs occur here at least as large as those described in European fisheries.
In the 1960s for example, the Waterford/East Lyme shellfish Commission had an active green crab trapping program to protect young bay scallops. The green crabs lived in the deeper eelgrass meadows (its premier habitat type) and heavily predated small bay scallops as they reached a large size.). Questions have been raised recently about eelgrass and green crab habitats – a close connection is seen in Northern Europe Evidence is also increasing by genotype identification that our eelgrass strains may not be “ours” at all but those from the North Sea. I suspect what John “Clint” Hammond also suspected on Cape Cod in the early 1980s was that both the green crab and eelgrass arrived here perhaps together, eelgrass as packing and green crab as an edible crab with the first European fishers – as it was an edible crab and one that had a “shelf life” if packed carefully packed in seaweed to keep “gills” moist; it could survive for longer periods. Eelgrass was available and likely used to pack crabs (and oysters) for transit to our shores.
Today the green crab in Europe is still the favorite in some areas as witnessed here myself – green crabbing not for bait but for food. The green crabs in the Niantic River grow to enormous sizes (Niantic River, personal observations), and according to one green crabber I spoke with a few years ago, the best green crabbing (edible size) is early in the morning over eelgrass beds. I am going to try to capture some of these green crab giants and give them a try – I will report out, but several recipes for the green crabs are now on the Internet, mostly from Europe.
The Blue Crab Cycle?
This year should see the remaining 2011 and 2012 Megalops sets; these should be very large crabs now at or near the end of their life spans. The catches this spring reflect that – large numbers of older, larger crabs in tidal rivers. We did have Megalops and post star crabs appear in 2013 and 2014 but they were late in the season and heavily predated by Black Sea Bass. An early set is what blue crabbers need, a set that appears by July 15, and is able to reach the three inch size, for the fall, even legal size by late October. Cool waters could delay the set to later lower survival rates then, and also subject to offshore winds of fall that tended to move these small crabs into offshore waters. In 2013, 2014 summer temperatures would create the warm south westerly’s that tend to move any blue crab Megalops against our coast and bring these small stages deep into the salt marshes, mosquito ditches and pools and away from those offshore predators. More and more researchers are looking at the impacts of wind, moving larval stages towards the shore or out into deeper waters for abundance, clues even perhaps for Megalops survival. Maine, for example has lost its inshore Megalops lobster sets for two years now. It has appeared in offshore areas and some feel it was from cold and the impact of strong offshore Northwesterly winds just blew the larval stages offshore. Some lobster Megalops studies are currently underway in Maine, looking at these important environmental factors.
.Some important considerations for this blue crab season:
1. Did a large female sponge crab population release eggs that survived Megalops dormant period last year?
2. Have the last three years Megalops sets occurred later in the fall and ended up in deeper water, victim to enormous Black Sea Bass predation.
3. Were the 2013 waters so cold as to reduce blue crab populations in areas that seemed to hold so many crabs in 2010-2012?
Thank you again for all the positive comments last year, everyone have a great and safe Blue Crab season. All Blue Crab observations are important – thank you for sending them.
I respond to all emails at tim.visel@new-haven.k12.ct.us
See you at the Docks.
Blue Chip
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