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di・a・ry: A book in which one keeps a record of events and experiences. (Oxford Dictionary)
riv・er di・a・ry: A bank on the river that collects debris as the tide recedes, leaving a record of events and experiences of the river. (Salvatore’s Dictionary)
According to the definition of a River Diary above, most freshwater rivers don’t have a diary because most freshwater rivers don’t have a tide. Tides are for saltwater rivers. But every so often, conditions are just right to produce a freshwater tidal river. Such is the case for Herring Brook, the small freshwater river behind my house. As such, the river bank acts as a river diary, collecting the debris that washes up at high tide, leaving me with a record of the events and experiences of the river when the tide recedes.
Herring Brook flows into a larger river, the North River, that eventually empties into the ocean. The portion of the river abutting my property is 14 miles upstream, yet because the elevation of the surrounding land is so low, when the tide rises in the ocean, it pushes the freshwater back upstream. This causes the water level in Herring Brook to rise. Then, when the tide at the ocean recedes, the freshwater in the river once again flows downstream and the water level drops. Twice a day, the water rises, covering the bank, and twice a day it recedes, dropping its debris on the bank, leaving a record of the events and experiences of the river for me to read.
So what does my river diary have to tell me? It tells me of the animal life on the river. I have found evidence of animals using the river - ducks, turkeys, herons, muskrat, otter, mink, deer and others.
I also learn about the human events that have happened on the river in the form of fishing lines, shotgun shells, beer cans and other such treasures.
My river diary keeps a record of the changing seasons by collecting flowers in the spring, seeds in the summer and fallen leaves in the autumn.
Every once in a while, my river diary leaves me an entry of an event that happened at a considerable distance away, an event that leaves me wondering how it came to rest on my bank. Such was the case when I found a mermaids purse left high and dry on the bank.
The mermaids purse is the egg case of a skate - in this case, the Little Skate. What was so surprising about finding this egg case on my bank is that the Little Skate is a saltwater fish. It lives in the ocean, not in freshwater rivers.
The Little Skate lives in shallow waters, from the shoreline to 300 feet. Eggs are laid two at a time, usually on a sandy bottom. The eggs have sticky filaments that help them adhere to the substrate, keeping them in place until the skate has hatched. A golden-brown color when first laid, the case turns black after it has washed up on the beach and dried out. If the skate is lucky, it hatched successfully before being washed up on the beach. If not, it didn’t.
So here is what my river diary tells me: at some earlier date, a Little Skate laid a pair of egg cases just off shore of the North River. At least one of these successfully hatched a baby skate. I can tell this because there is a slit at one end of the egg case. This is the exit hole made by the baby skate. If there was no slit in the dried egg case, it would indicate that the baby skate never hatched, and died within the case.
Heavy wave action, most likely from a storm, dislodged the egg case from the ocean bottom and an incoming tide carried it up the North River. Floating back and forth with the changing of the tides, it eventually made its way into Herring Brook where it came to rest on my bank.
I enjoy reading my river diary every time I stop by the bank of the river. It keeps me up to date on what is happening.. However, every so often I find an entry that I can’t interpret. This is when the real fun begins, because now I have a challenge. It is time to do a little research to see if I can figure out what I have found.
My skate egg case presented me with just such a mystery. The mystery is not the egg case, but what was attached to the egg case. In the pictures below, you can see some seed-like structures. These are not part of the egg case. At the present time, I have no idea what they are. But, if I find out, they will make another backyard biology story.