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Author Topic: Megalops Report #3 July 20, 2017 Tim Visel  (Read 381 times)
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« on: August 10, 2017, 02:18:19 PM »

The Search for Megalops
“You do not need to be a Scientist to Report”
Megalops Report #3 July 20, 2017
View all Megalops, Environment and Habitat History Posts on The Blue Crab Forum™
Tim Visel, The Sound School, New Haven, CT  06519

•   Early Season Reports – Rivers, Salt Ponds and Coves
•   Maine’s Lobster Megalops Set Shows Possible Decline
•   Warning to Blue Crabbers

•   Early Season Reports

Some very large blue crabs are being caught in areas that crabs have overwintered – deep holes that contain Sapropel.  I often write about Sapropel and sulfide bottoms in heat but in cold, the oxygen makes these bottoms suitable for overwintering blue crabs, eels and terrapins. In fact, some blue crabs may have a black sulfide stain early in spring as they emerge from hibernation. In cool temperatures, oxygen reduces sulfide formation and blue crabs can burrow in.  The deep holes and dredged channels appear to hold the most crabs now, shallows are subject to winter ice and the open shore subject to storm moralities.  Uncovered blue crabs in the winter are very susceptible to predation, so they go where most fish will not, Sapropel, a marine compost that “leaks” sulfide that allows blue crabs to be safe from predators.  It is these protected inshore areas where blue crabs are compressed and that here again had the best early season catches. Blue crabbers who fish from boats and can find these deep holes have had the best catches to date.

In general the best catches - 2 to 4 crabs/hour have been in these deep saline holes or near them 4 to 6 crabs/hour. Crabs have not experienced large habitat coverage here – or have moved that much into the shallows.  The water temperature is still a little cooler than average and if crabbers want to see what a different water temperature will do just review the Blue Crab Forum™ post of April 23, 2012. 
In some recent years, large crabs were feeding as early as April 17th  in the lower Connecticut River,  however in 2015, they did not “arrive” at all (Special Report #2, September 1, 2015).   At Clinton Harbor, in talking to some experienced blue crabbers a few years ago, I heard that the “normal” arrival time for blue crabs at the Clinton Harbor mouth was around July 15th.  I think that the blue crabs were present in the upper reaches of this estuary much earlier, but just moved down river as temperatures warmed.  Last year I had several reports from the Hammonasset River that large numbers of hard shell male blue crabs were far above the Route 1 Bridge on the Hammonasset River, almost all the way up to the fresh water interface.  As the summer progressed, crabbing improved between the Route 1 Bridge and the lower river; by July, crabbing increased at the Cedar Island area, but nothing like the catches between 2009 and 2013.
We may find some answers to these overwintering questions in the CT River.  Here freshwater spring floods (ice melt) are thought to eliminate blue crabs in many areas (except in those dredged areas that “hold” salt water). This year catches in them at the mouth of the Connecticut River improved after June 15th, a difference of 60 days which is huge to our habitat quality for Connecticut blue crab reproductive capacity. That is why Megalops drift from southern areas is so much a part of our blue crabs habitat quality history. As we had a series of mild winters which advanced the timing of our Megalops set to much earlier in the summer, perhaps even to “our spring.”  In July of 2011 we had three waves of sets – some crabbers may recall the size breakouts then from catch reports.  The changes in the Megalops set is key to our blue crab fishery. More recently, they have been much later, or none at all.
Look for adult crabs to “spread out” into the shallows leaving dense concentrations from winter in the next few weeks.

•   Maine’s Lobster Megalops Set Shows Decline

One of the reasons I attended the Maine’s Fishermen’s Forum in Rockland, Maine in 2016 was to hear about a reported Megalops lobster set failure. Another reason was to access some recent drift surveys analysis of larval spatial sets along Maine’s coast. Wind direction and intensity is now linked to blue crab Megalops drift to our south, but largely confirmed by studies to our north in Maine. (See Bai  Li et al. 2015, University of Maine, Orono North American Journal of Fisheries Management 35 pg 942-957. “Evolution of Effectiveness of Fixed Station Sampling for Monitoring American Lobster Settlement.” The future of the blue crab in our area is the Megalops set, and that may depend on wind direction.

The oyster industry also questioned the absence of extensive oyster reefs on the Long Island North Shore, but extensive along the Connecticut shore, and especially in the western communities they thrived. They calculated that by June 15,th the time of the first oyster set wave (a so-called second wave occurs mid-August to the middle of September, frequently termed the fall or “late set”, according to John Volk, then Connecticut Aquaculture Division Chief had recorded these two waves in 1981), wind directions had changed to prevailing southwest and had blown oyster larvae against Connecticut’s shore and not New York’s (Personal Communication with George McNeil. T Visel 1980s). A study of Blue Mussel larvae largely confirmed the wind drift theory- blue mussel larvae once it left Maine’s coast and entered the Gulf of Maine and had little chance of return to the shallows. From time to time during colder periods, Connecticut has held a bottom mussel set. The Long Island Sound mussel set of June 2009 was the heaviest mussel set I had ever observed (lobster pots on Madison reef were covered in blue mussels). Wind and current is also being looked at as the source of Connecticut’s Blue Crab Megalops; in fact did not come from the female sponge crabs in Long Island Sound in the early 1990s.

In 2008 (and perhaps before that?), we did see female sponge crabs in large numbers in the estuaries, and complete reproductive cycles. Bridgeport and New Haven harbors had prevailing southerly winds, but that declined in 2013 when it became sharply colder. The 2011 Megalops waves were intense and reports of The Search for Megalops started in 2010, had recorded them in 2011; we had three distinct Megalops waves.  (See Megalops Report July 2011, Blue Crab Forum™). Recent colder winters and a more northerly winds is through now to delayed a Connecticut Megalops set into the late fall and perhaps drifted out too deep to make the salt marshes before frost. This time the winds had changed to the Northwest, perhaps blowing blue crab Megalops into more offshore waters and deeper waters.  Most of the blue crabs ended up in deep water consumed by record numbers of Black Sea Bass (Megalops # 10, October 2, 2013) and Megalops # 4, October 7, 2014).  I then looked at habitat capacity.  In 2008-09, I contacted several organizations in Maine regarding habitat capacity for lobsters – the recruitment into the Maine lobster fishery was approaching 2 to 3 times heritage levels, while blue crabbing was steadily improving in Connecticut.  Because habitat quantity is fixed (artificial reef programs excluded), carrying capacity can only be from increasing habitat quality, expansion of previous unsuitable habitat or from changing natural prey/predator relationships, all in some way related to climate.  Maine’s waters for a century have been described as “cold water limiting”- that is, lobsters could grow faster then, but water then temperatures did not allow it.  (It was a slower growing lobster to reach ”legal size” than Connecticut.)  I had watched northern lobsters grown in glass aquaria in 1973-74 while attending the Florida Institute of Technology (eventually became the Harbor Branch Oceanographic Institute). In very warm water, lobsters (northern) reached legal size in about 30 months. A critical factor than was lobsters would cut themselves during the molting process and quickly bleed to death. 

This rapid growth happened here – blue crabs grew quickly in the 2010s, but summer heat also increased blue crab mortality incident to the recreational fishery. I witnessed multiple buckets – sometimes tubs of hot seawater and dead, dying crabs, some so spoiled,  you already could get a whiff of ammonia (dead lobsters and blue crabs spoil very quickly) coming from them. My son  Willard put his old lobster banding tool to good use and on these hot days took a lobster band and held the claw to the shell, a “knuckle bander,” as he termed it, and reduced post bucket catch mortality to almost zero. (Blue Crab Forum™, August 9, 2012).  I tried to educate as many new blue crabbers as I could, to keep crabs cool and moist, no water, but still saw thousands of wasted blue crabs. One catch (evening) was about 600 crabs, but most were dead, which made counting easy at the Essex Town Dock.  The truth of the matter is that large numbers of first time blue crabbers were unfamiliar with handling (on one occasion my tee-shirt was used a quick bandage at Essex for a new crabber at the town dock who tried to “pet” two or three rusty hard shell crabs) or keeping them alive. A cooler with ice packs and moist cloth (like dishcloths) have found to be the best to keeping blue crabs alive for the day until home cooking.

•   Megalops Study Key to Population Cycles - Southern New England Lobster Stocks May Give Clues
At some point, fishery managers will need to adjust lobster management models that reflect primary recruitment drivers and one not based just upon fishing effort. But this includes other fisheries as well. Traditional management models strived to protect sufficient habitat capacity, but falter when that and reproductive capacity combined has little value – you can have lots of reproductive capacity but if none survives,  it is of little value, the same is true about habitat, you can have large amounts but if it is of so little quality or degraded that previous management options holds little chance of success.  If we cannot rebuild fisheries by reproductive capacity, and faced with declined or diminished habitat quality very few options remain. They include predator/prey relationships and habitat capacity- building perhaps new blue crab “ponds”.  One of the options not explored is changes in habitat capacity (also termed carrying capacity) and here the lobster industry, which made some strides in the 1960s but then that effort ended. Some of the first research was conducted in Boothbay Harbor, Maine with circular pipes in an artificial lobster reef deployment.  Researchers found that lobsters much preferred these round openings to reefs- about six times as much. Rubble reefs (mostly chipped concrete) was found to hold stage four Megalops but carrying capacity studies did not continue to calibrate for age or density.  Of all these management actions the habitat capacity/quality succession aspects held the most
promise (my opinion)because they could respond to energy (work) – such as the production of seed oyster beds or the protection of seed clams from predators (hard shell –soft shell clams).  Here the work extends or enhances habitat quality while husbandry culture practices often enhance habitat carrying capacity such as in agriculture by pest management. These habitat/prey reduction options are compounded by environmental policies that often discourage work (bottom disturbance) in subtidal areas. The protection of seed is most critical to the shellfish harvests but this also requires work such as predator protection nets and predator control, habitat modification, and habitat mitigation at times (cultch planting on bay bottoms to obtain seed oysters for example).

The lobster fishery is a case study in habitat carrying capacity; the enhancement of the use of new metal lobster traps has in many respects enhanced carrying capacity (feeds shorts). The number of small lobsters has increased in northern areas, but this has happened as a major lobster predator, codfish, is at historic low levels.  The codfish it ‘seems’ that nature was able to provide incredible abundance, then suddenly may take that away? So many times in the historical literature you see a great set of clams or oysters  only a few years later subject to increased clam or oyster predators such as starfish or crabs especially now the green crab. With blue crabs, it seems to be in our area  that black sea bass is the chief predator next to striped bass. Both increase in response to warmer temperatures and few storms, such as the blue crab. The Megalops sets for lobsters are currently under study and could provide key climate cycle information of wind direction in the near future.

•   Eelgrass/Sapropel Linked to Finfish/Shellfish Disease: Warning to Blue Crabbers

I put out a warning the past two years about hot/Sapropel deposits; organic matter in hot sun can generate heat (compost deposits, such as leaves composting, for example can reach 140 degrees). Vibrio growths thrive under SAV (HAB cysts) and in Sapropel as part of a long term habitat succession process. Fin rot/shell disease appears in Sapropel deposits and is continually associated with Vibrio bacteria.  In a review of high mortalities in commercial soft shell crab shedding systems of Louisiana and warmer waters, found shell disease (Vibrio chitinolytic and Vibrio bacteria in 37 of 96 of the blue crab hemolymph (blood) tested. Rogers, et al – January 2015- “Disease, parasite and commensal prevalence for blue crab Callinectes sapidus at shedding facilities in Louisiana, USA).”
It seems for the blue crab habitat quality disease has also a cycle signal – heat for long periods or cold for the same. Colder periods have far less disease, especially shell disease. In the lobster fisheries, history shell disease first appeared in the early 1970s off New York but much earlier in 1937 at Nova Scotia (shell disease in Lobster-  Aqua info Canada- In lobster pounds with “Soft organic bottoms”.
And much earlier, a link appears to be warm water and the presence of organic matter and HAB cysts/species  (the media host or food for bacteria) which may have become Sapropel or taken Sapropelic characteristics – low oxygen bacteria, higher amounts of vibrio and sulfur reducing (SRB) bacteria.  Blue crabs should be aware of this vibrio/Sapropel relationship as found in the Blue Crab Forum™ Environment/Conservation posts.

To learn more about Sapropel (Black Mayonnaise) deposits, Dr. John Trefry of the Florida Institute of Technology has posted an excellent presentation about changes in habitats titled, “Running Amuck: Our Six Decade Legacy To The Indian River Lagoon.”  It describes sulfide and ammonia generation from these organic deposits in heat the same shallows where blue crabs live and is well worth a look, my view.
All blue crab observations and habitat reports are very important, thank you for any reports. I respond to all emails at [email protected].

See you at the docks,
Blue Chip


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