Attack of the puny leaches


Have you ever noticed when looking into the water that fish tend to swim away and hide at first sight of you? If so then the following may interest you.

Ever since I was a young boy I was fascinated with fish and the watery world which they inhabited. Unfortunately the fish didn't share my fascination. Forty odd years later I found out why, and the answer may surprise you.

Curious, follow this link for the answer.

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One of the most curious scenes I have witnessed was on the headwaters of the Weweantic River in Carver Ma. It was August of 2002 and the Weweantic was extremely low due to drought and water withdrawals for the extensive cranberry bogs throughout its watershed. The stream was so low that it had become a series of shallow muddy pools separated by long muddy water less reaches. Although I began my trip in a kayak I soon found myself leaving it behind, finding it easier to hike up the muddy streambed.

Walking along through the soft mud of the streambed I was clearly not the only creature using this newly created footpath. Scattered throughout the mud were footprints left by all sorts of creatures, from the big broad prints of the great blue heron to the zig zagging scratches of tiny shrews. One track, or better yet trail was more peculiar than the rest. It looked as if someone had tied a large flat stone to a rope and dragged it along through the mud. In the rear part of the trail was a much thinner trail following behind the larger. Later, I laughed at myself for not recognizing this mysterious trail.

The creature that made it was no stranger. I had observed it countless times and in many different streams and ponds. However here out of its element, (or so I thought) its trail baffled me. Curiously I followed along the trail to a bend in the stream where I found a long shallow pool. Here I took note of another curiosity.

The river bank was quite steep through this pool. It was perhaps a three-foot vertical drop from the top of the stream bank down to the water line. The bank consisted of firm light brown mud. Along and above the waterline were shallow scalloped out depressions a foot across, six inches high and a foot deep in the center. Scattered among these larger holes were smaller holes. These looked similar to fiddler crab holes in the steep banks of a salt marsh stream. I had seen holes similar to both on other streams, but what made them was a mystery.

Walking further along the water became deeper. I hopped up on the bank to walk on the high ground for a bit. As I walked up around the bend, I caught sight of the mysterious trail maker. It was a snapping turtle, and there he sat on the edge of the stream at the water line. Normally a snapper on a small stream would be wary, but this one seemed quite oblivious as I approached to within ten feet of him.

The snapper was facing forward into the river bank. His head was buried in the mud as he feverishly clawed at the bank in a motion similar to that of a swimmer doing the breast stroke. As he dug, he pushed his head and body deeper into the hole he was digging. After about fifteen minutes of what appeared to be a frantic excavation he slowly backed out of the hole. He then dipped his head under water several times to wash off the large blob of mud that had accumulated on his head and face.

After he had cleaned the mud off his head, he sat very still at the entrance of his excavation site. Then very slowly he began paddling the bottom of the hole with his front feet. Several seconds later there was a splash as a small form skittered across the surface out of the hole. The turtleís head shot from its shell with amazing speed and accuracy, snapping the crayfish off the surface like a frog would snatch a bug with its tongue. After he crunched down the unfortunate crustacean, he resumed his paddling at the entrance of the hole, repeating his success again with another crayfish.

How often do snapping turtles hunt in this manner? I really donít know. However, holes such as these are fairly common sights along many of our small and mid-size streams during low flow periods. Now, I donít claim to be an expert in the affairs of snapping turtles or crayfish. However, it seems unlikely that this interaction I witnessed on the Weweantic was an isolated event. It seems more likely that this interaction was the result of the low flow conditions, which left the crayfish vulnerable and the snapper fat and happy. In fact judging by the abundance and diversity of the foot prints in the mud many animals such as wading birds, raccoons and mink were also living fat and happy, while creatures such as the crayfish, sunfish, perch, pickerel, bass and frogs were left vulnerable by the low water. It is also worth noting that crayfish, frogs and many fish have a natural capacity to reproduce and repopulate quite quickly compared to a snapping turtle which might live for fifty years or more.

On the Weweantic as with an increasing number of our streams, the extreme low flows were in part a result of excessive water withdrawals by humans. However extreme low flows do and always have occurred during drought even on streams and rivers which do not suffer from excessive withdrawals. Naturally occurring low flows and high flows have always stressed and challenged some species while benefiting others. This naturally occurring state of flux repeated over thousands of years is the very thing that has made our rivers and their dependant species so diverse and adaptable.

While it is disheartening and certainly a call to action when we see our streams drying up and flowing backwards. It is also a valuable learning opportunity, an open window into the ever changing, constantly fluctuating environment that is a river. By carefully observing low flows on streams which fluctuate naturally and those which human withdrawals have influenced, much can be learned about how abatable and resilient our stream ecosystems truly are. These observations and learning experiences are valuable tools in evaluating future river decisions, specifically in the area of dam removal decisions where more careful observation and less hyperbole would be welcome.

 

Spednic Lake alewives

 

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