Alewives are in the Clupeidae or Herring family, which includes seven species found here in Maine; two kinds of shad, sea herring, blue back herring, men haiden, thread herring and alewives. Several of these herring species stay at sea and do not come inland to breed, a few others, including the alewives do. Alewives are planktivorous fish, meaning they feed entirely on plankton, microscopic organisms suspended in the water column. Planktonic crustaceans make up the bulk of their diet. They make their way up coastal watersheds in New England during the spring, arriving on Cape Cod and southern New England in April, and Maine in May. It is thought that they spend most of their time in schools off shore, and wait to come up into fresh water until the fresh water discharged into the ocean warms to some critical temperature threshold, signaling inland conditions appropriate for spawning. If you cut open an alewife heading up stream you will see where its priorities lie. Most of its body is designed by evolution for propulsion, its just muscle and bone. Lots of bone in fact, like its bigger cousin Shad, alewives are especially bony fish, and seem to have an extra whole set of ribs on the bottom half of their bodies. Where there isn’t muscle there is a small internal cavity where the all the non head associated organs are found. In a female alewife heading up stream, this cavity is filled almost entirely with roe, two large sacs of eggs that she will release when she reaches the slack water of the pond or lake at the head of the stream. The males release their milt or sperm at the same time and the eggs are fertilized externally, and stick to any surface underwater. Once spawned, the extremely thin adults head back down the stream to the ocean. They are thin because not only have they essentially emptied out their body cavities of their reproductive material, they also don’t eat on this spawning migration. Once they get back down into brackish water, they resume eating with a vengeance, and if conditions are good, rapidly gain weight. Like all of the Atlantic anadromous fish we see in Maine, alewives don’t necessarily die after spawning like west coast salmon do. They can return to the same stream again the next year to spawn (most likely in fact, the same stream they were born in).
Every source you read about alewives talks about how they tie marine and freshwater ecosystems together, moving nutrients in and out of lakes and ponds, and how they are an important food sources for so many species of other fish and birds. Its like their job is to get eaten. And this is the first clue about how to see alewives. Look for hungry birds, lots of them. This spring I was driving home one late afternoon, passing by a tidal stream with a small fringing salt marsh that leads up to a pond, when I noticed two juvenile eagles at the waters edge. I got excited and stopped the car, and as I looked closer, I noticed another eagle in the tree line. As I looked further, I saw at least ten eagles, adults and juveniles congregated along this small stretch of stream, all waiting. I didn’t go down to the stream to see if there were fish, because I didn’t want to disturb this amazing conclave of eagles, but I imagine the fish were not far. I did managed to see alewives at the outlet of another local pond, they were trapped on the upstream side of a gate that was designed to keep them from attempting to go up the main outlet channel that leads to an impassable old dam, and to direct them to the fish run channel that circumvents the dam structure. I think that the fish I saw had gone up the fish run, but then came back down over the dam on their way down stream and found them selves trapped behind the gate. We opened the gate temporarily to let these fish through, as well as flush out the bodies of the ones that had died waiting. And this year I got brave and followed the hand written sign posted a few miles from my home to the house where an old timer sells the smoked alewives he dipped netted by hand.
So, I’m getting closer. I have yet to see the full expression of the spring alewife migration, but I am just an aspirant in the discipline of fish knowing. I think it will take years to learn what I need to know, which is as it should be. A creature of the water, mysterious and hard to see, can’t be, shouldn’t be known so easily, with so little work or patience or humility. That is the lesson everyone who hopes to catch fish must learn eventually, and every one who hopes to see them too.