Monday, July 10, 2017

Horseshoe crab season 2017

By Beth Sullivan
There are some things you can rely on, events that happen at a certain time, under certain conditions, every single year. Some for hundreds or thousands and even millions of years.
One such occurrence is the arrival of the Horseshoe crabs along the sandy shores here, in the places we humans now call home. For millions of years, these ancient species have been pulled by the tides and phases of the moon, to seek mates and find their way to the safe coastal areas for spawning.
Certainly the shoreline has changed over that time. Sandy beaches have eroded, disappeared, and reappeared in new areas. Barrier beaches have been washed away, and islands have moved, literally. And new islands and sandbars have appeared in shallows along the edge of the sea. But what has not changed is the cycling of the moon, its constant pulling on the waters of the Earth, and the effect it has on the Horseshoe crabs which, as a species, has remained almost unchanged for many millions of years.
Gently sloping beaches and low surf areas are ideal for Horseshoe Crab nests.

Sandy Point has drifted over centuries, but continues to offer sanding nesting areas for Horseshoe Crabs

So, when we head out to Sandy Point and other local beaches to find and tag the Horseshoe crabs, we always anticipate that some things will not have changed.

Unusual year

This year was just an odd year for lots of reasons. The weather did not cooperate around the times of the full moon and new moon in May. Those are the times when the tides are most extreme and best for nesting crabs. It is not just that we humans don’t like going out in windy wet weather, but the crabs do not like it either. They do not like to come ashore when the surf is rough. A lot of freshwater-rain runoff into their favored nesting sites will also keep them away. So May really was a wash-out. I don’t know where they went, but they were not at all the places I expected them to be.
Too much surf can flip a crab or pair of crabs and expose them to predation.

The early full moon in June really wasn’t much better for conditions, but we paddled out to Sandy Point and cruised along the shore. In past years, the north side of the island would have been the most desirable stretch of sandy beach for nesting. We found a few pairs along that north shore, and a few more down toward the extreme eastern tip. But it was discouraging. We tagged about 15 that night, certainly not close to the dozens or hundreds of only a few years ago.
Each crab is assessed for size, condition, and gender. The tags are placed with a peg, into their shell, the carapace, in an area that will not impede their functioning. We make notations about certain physical characteristics including injuries or damage to shell, and also note all the “baggage” they carry: hitch-hikers that are mollusks of varying species and seaweeds. The tags bear a number that can then be tracked when they are recovered at a later date. When we look for crabs, we always note the “recaptures” and document their condition and tag number. It reveals interesting data.
Finding an old tag helps provide data on longevity and and travel patterns.

Once more we tried with the new moon phase at the end of June. Technically this should be the real high point. We have, in the past, counted over 1000 crabs jostling for space in the sand, jostling for mates, and jostling off competitors. But not this year.

End of June excitement

Three of us paddled out to the island. A bit of a wind and rolling waves made it interesting, but on the north side it was calm and quiet. We got caught in a sudden downpour but were rewarded by a spectacular rainbow and beautiful sunset. We noted more pairs of crabs, making their way to shore. Large females followed closely by their smaller mates.
The crabs often carry a lot of marine baggage. 
Tagged crabs are inspected closely for damage and condition. 

We were only allotted 50 tags for the whole season out on Sandy Point, and we used them up by the time we got to the eastern tip. And then the action started. Around the tip and out to the south side where the surf was a little rougher, we began to count more and more crabs. Singles, pairs, triples and even a few quads-one female with multiple males. We found several with older tags, and later investigation showed that some of them had been tagged more than three years ago, a couple right there on the island.
As we walked we counted: more than 100 more crabs, all participating in that ancient ritual, on that particular night. It was a far cry from that year of more than 1000. Something has changed. But for a smaller population, the moon still pulls them to this island. And something pulls us out to share in that ritual.
The adventure provides rainbows, sunsets and moon rise views.

Whatever pulls the crabs to Sandy Point, pulls us as well.

Photographs by Mike Charnetski, Rick Newton, and Beth Sullivan.

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