Episode 050: Frostfish

You can download and/or listen to the audio of this episode here!

Transcript 12/22/18:

A fish turns its head and travels upstream. It is joined by another and a school forms and swims upstream to ancestral spawning grounds. Eggs on current, eggs on stream-bottom. Young hatch, young grow, young travel back to sea. Welcome to The Nature of Phenology where we share the cycles and seasons of the outdoors. I’m your host, Hazel Stark, and this episode was written by Joe Horn.

The winter solstice: the darkest day of the year. We wake up to a dark world and watch, often in dismay, as the sun sets early in the middle of the afternoon. Just eight hours and forty-eight minutes of calmingly dim sunlight illuminating the frosty forest around me today. Often for us humans, dark cold days encourage relaxation and stillness. It is a good time of year to hunker down next to a blazing woodstove to darn one’s holey socks, knit a few more rows on that bulky soon-to-be sweater, catch up on a dense novel, or eagerly tie fishing fly after fishing fly in hopeful preparation for next year’s fishing season. But catching up on neglected projects isn’t in the cards for one single-minded native fish species that is currently ascending our icy coastal streams: Atlantic tomcod.

For those of you with a fondness for feasting on fine fish, you are probably quite familiar with various members of the cod family, which scientists refer to as the Gadidae. These gadiformes include many of the common firm, white-fleshed saltwater fish that one can find at a local monger like cod, haddock, pollock, red hake, white hake, and silver hake. Those among us that are ice fisher-folk might also be well acquainted with the cusk, or burbot, which is the only freshwater gadiform. But the tomcod live a life both in the salt and freshwater of our coastal waterways.

Tomcod rarely venture far from shore, staying mostly in eelgrass beds and rocky bays at water depths of only a few fathoms. The color and pattern of these fish naturally match the colors of their surroundings, being anywhere from yellow to olive or brown and speckled all over to blend into their surroundings. Unlike so many fish that spawn in either the spring or fall, tomcod are right now in our darkest days ascending our coastal rivers, streams, and brooks in search of freshwater spawning grounds. In addition to their odd seasonal selection, they also run from the ocean into freshwater making them something of an anadromous anomaly among their gadiform kin. Like most sea-run fish, they will often wait until a rising tide to make a push upstream to conserve energy and ensure there is adequate water for passage. When the female tomcod expel their eggs in fresh or slightly brackish waters, they sink to the bottom and will rest there for nearly a month until the eggs hatch and extremely tiny young emerge to begin their downstream migration to the briny bays along our coast where they will grow up.


Tomcod spawning peaks precisely around the solstice once hard frosts or decidedly frozen weather is the norm and our creeks transition from warm, to cool, to frigid. This solstice spawning behavior has earned them the catchy nickname “frostfish.” But our Québécois neighbors to the north also refer to the tomcod as “poissons des chenaux,” or “fish of the channel,” in reference to the fish’s fondness and abundance in coastal waterways.

Unfortunately, pollution during the early to mid-20th century resulted in a widespread decline in the populations of these fish all across New England and a complete collapse of the commercial fisheries. But because of their relatively small size of about 9-12 inches long and their low importance in our modern food system, modern research on these fish has been scarce and scientists do not have a good sense of their current populations. They speculate that the species has rebounded some but may remain extirpated from some areas.

In the past, however, tomcod was a key component to coastal communities making it through the harsh Maine winter. The fish were either caught on line and hook, speared through gaps between tidal ice slabs, or were caught in traps during their solstice run. Like all members of the cod family, these frostfish were added to chowders, baked in cream, or simply breaded and fried, but could also be salted to preserve them for long storage.

So as you are hunkered down under blankets near woodstoves, you can think fondly of the intrepid tomcod as they ascend up our tidal creeks, rivers, and streams on today’s rising tide, often under slabs of salty ice.

You can find a link to the full transcript of this show as well as references, contact information, and accompanying photos by visiting archives.weru.org. You can also listen to or download our features or subscribe to podcasts. Theme music was by a pileated woodpecker, made available by the US Fish and Wildlife Service. Thanks for listening and please join us next week for another dive into The Nature of Phenology.


Stewart, L. L., & Auster, P. J. (n.d.). Species Profiles: Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates (North Atlantic): Atlantic Tomcod. Retrieved November 19, 2018, from https://www.nwrc.usgs.gov/wdb/pub/species_profiles/82_11-076.pdf

Wondering where Episodes 001-033 are? Find out here.


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