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The alewives are here, and just in time!
The value of these fish as a food source cannot be underestimated. They make their journey up the rivers of Maine just at the end of a tedious hard winter which have drained the local species of their protein reserves. Mammals are carrying the next generation, and birds are courting and building nests. Some, like eagles, are already trying to feed their young. And like magic, millions upon millions of bite sized food sources flood our waterways on their journey to their spawning grounds, where they will serve as food to fish and others higher up on the food chain within the rivers in which they temporarily reside.
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These incredible little fish fight their way up full blown rapids on their journey to calmer waters. Alewives are a diadromous species, meaning that they will migrate between fresh and salt waters to complete their life cycles. They will flood the waterways in the spring, travelling up snow melted streams to get to the ponds where they will lay up to 300,000 eggs! These eggs also serve as a valuable food source to the local species, but those that survive will hatch in a few days and remain in their freshwater habitat for several months, before migrating back to the ocean where they will spend the next 3-4 years - growing to the size of about 12 inches, before returning to their natal streams.
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Only the lucky, however, will survive all legs of this perilous journey. Throngs of cormorants fish the streams for them, sometimes diving in groups to flush the panicked fish into the mouth of a neighboring bird. Cormorants are very in need of calories at this time of year, since they are in the process of nest building and courting. These fish strengthen the winter-weakened adults to prepare them for the trials of raising young.
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Eagles chicks have already largely hatched, and adults are looking for food to feed their young. As massive and impressive as these birds are, they often spend as much time stealing fish from other birds as they do fishing. In fact, they will chase osprey for miles trying to get them to drop fish, rather than catch their own. This young eagle was very hopeful someone else would catch him breakfast. He poked around in the rapids but seemed reluctant to get his feet wet. Ultimately, he took a fish from a merganser - although it didn't seem to meet his standards, and he promptly dropped it again.
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Seals congregate in large numbers around the schools of alewives. They have either already pupped - or will soon - and very much need the calories to feed their new and delicate young families. Watching them fish is comical, with plenty of lounging, rolling, and chasing being interspersed with the hard work of eating.

The migration and fishing frenzy will continue for a few weeks, progressing from south to north up the coast. As the alewives migrate, the fish tend to become smaller - and so the hunters need more of them to fill their needs. Once they disperse into the calmer lakes and ponds, the fishing becomes more challenging for the birds and mammals, but the food sources shift to the resident fish within the lakes until the alewives return to the ocean - continuing to feed the bounty of life there. And the circle continues until they return next spring.......
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Along with the influx of alewives comes the (sometimes unwanted!) influx of insects! Next time you are cursing the mosquitos or blackflies - think of all the animals that are surviving on them as a protein source. Sit back and enjoy the feeding pattern of the Black and White warbler -- this one seemed to specialize on arachnids - having caught several while I watched!