April Estuary Sightings

Despite a string of sunny, spring-like days, much of our wild, native landscape shows very little change from winter to spring. The first signs seem to be limited to our swamps, where red maple flower buds are beginning to open and the huge, bright green leaves of skunk cabbage are unfurling.

The most noticeable greening seems to be the assortment of grasses adorning our roadsides. This was not the case for our most productive and largest grasslands, those found in our salt marsh ecosystem.

Signs of green in the marsh grasses at Accabonac Harbor last week were hidden below last year’s yellow-brown leaves, and tiny at that. Two of the ubiquitous creatures of the salt marsh, the fiddler crabs and the mud snail, were still tucked out of sight in their winter quarters.

Yet, something had clearly changed. It was the congregation of piscivores that has signaled the arrival of spring in the marsh and estuary. All five osprey nests visible from Louse Point were active. Adults were busy sprucing up nests, and in the case of the northern Wood Tick Island nest, it appeared that a threesome was vying for nesting rights.

A great egret seemed to be resting in the lee of Wood Tick, perhaps awaiting a change in the tide when it would have better luck stalking mummichogs and striped killifish in the shallows of the flooded marsh.

Red-breasted mergansers, common loons, and double-crested cormorants plied the deeper water found in the boat channel and inlet. The mergansers and loons swam at the surface, dipping the heads into the water and peering intently for suitable prey below before diving.

Two harbor seals joined them, and a large number of herring and great black-backed gulls wheeled overhead, the latter occasionally plunge diving like a gannet into what must have been a school of fish that attracted all this attention.

A type of river herring called alewives are in the midst of their annual spring spawning run. I’m not aware that Accabonac supports a run, but perhaps a small school makes its way up into the harbor’s freshwater reaches at Pussys Pond to spawn. There are also reports of Atlantic menhaden (aka bunker) making their way back into the bays from wintering grounds to the south and offshore.

One of the gulls managed to capture a fish, and for a few moments as it struggled to get it down its gullet, I got a quick look at its prey: a 7- to 8-inch-long, silvery fish that seemed a bit small for an alewife and was more likely part of a school of menhaden.

Even as full-sized (8- to 12-inch-long) adults, menhaden feed on tiny plankton particles that they filter out of the water column by way of their net-like gill rakers. Our shallow bays and harbors are first to warm up in spring and produce copious amounts of plankton.

It’s been interesting to monitor the bay and ocean water temperature over the year as part of the informal cold water swim group called the Chill Squad. Despite a few nights of freezing temperatures in early April, our shallow bays have warmed up and for the past week have been registering 50 degrees Fahrenheit. This warming seems to be the effect of the sun’s ray shining through the very clear bay water and warming the dark bottom mud, that then radiates the sun’s energy back up into the water column.

Water temperature in the 48-54 degree range sets a few things in motion. One, as mentioned previously, is the alewife spawning run. The other is the spawning cycle of the Atlantic silversides, a 4-inch-long, slim, silvery fish that is also known as spearing and sand smelt. Both species also time their spawning with the tidal cycle. The alewives ride an incoming tide up to their freshwater spawning grounds, while the silversides move into the flooded salt marsh at a new or full moon high tide, and spawn in the shallow water among the marsh grasses. The latter is done during daylight hours, and since the eggs are laid during the peak of the tidal cycle they spend a fair bit of time incubating among the wet peat and thatch — out of the water — at low tide.

The Atlantic silversides is a very prolific fish and an important prey species in the diet of many commercially valuable finfish, as well as many seabirds. It also serves an important role in transporting an incredible biomass of fish generated by the estuary over the summer months to the ocean pelagic zone as it migrates in huge schools during the fall.