Another fish migration season starts on the Penobscot River

When I tell someone I work for NOAA, they ask what the weather is going to be.  When I clarify I work with Fisheries, they assume I work with groundfish.  But when I explain I work with sea-run fish that need both the ocean and rivers to complete their life-cycle, for example the endangered Atlantic Salmon, they are often hearing a story for the first time.  This post will be one in a series this spring to help inform folks about what sea-run fish are and why NOAA fisheries studies them.

For me, spring means the melting of snow and break-up of ice in rivers allowing sea-run fish to begin their migration inland to spawn.  Monitoring these migrations is a large part of the work done at NOAA’s Maine Field Station and something I have done for the past 16 seasons as a fisheries biologist in Maine.  Today (April 28) was the first day of our estuary fish survey, which encompasses the sea-run fish migration period that runs from April to November.  Our study goal is to measure the timing and abundance of the 12 sea-run fish species within the Penobscot River Estuary, a system with a long history of abundant runs of salmon, shad, smelt, river herring but currently struggling to maintain the small fraction that remain today.  We use two types of gear, acoustics that I will talk about in later posts, and a mid-water trawl which is the feature today.

At the start of the day, we were greeted by a familiar face as we walk onto the docks. Josh, a local lobsterman from Isleboro, is contracted with NOAA Fisheries and provides use of his boat and estuary expertise to assist us in conducting our research. Also joining us was a fellow researcher, Eric Brunsdon, with the Atlantic Salmon Federation located out of Saint Andrews, Canada. He was interested in learning about our data collection methods with hopes to bring this knowledge back to Canada to conduct similar studies. To us, collecting quality data are fundamental, but the people we work with, and the ability to share our techniques with other researchers, are just as important.

Maine salmon work in the Penobscot 2017

Justin Stevens (left), contract NOAA Fisheries biologist, discusses sampling and gear methods with Eric Brunsdon (right), biologist with the Atlantic Salmon Federation. Photo by Sarah Bailey, NOAA Fisheries.

Our objective as we start the day was to verify the sonar survey conducted the previous day, which revealed few fish in the estuary – typical for early spring when the water is cold and migrations are just beginning.  We planned on conducting 8 tows within our study area but are always at the mercy of the tide and river conditions.  Here in the Penobscot River Estuary, the combination of a 15 feet tidal range and a river draining two-thirds of the state results in water velocities that vary minute by minute and determine what sampling we can complete.  Our first few tows provided little excitement with only a couple juvenile Atlantic and Blueback Herring, typical when water temperatures are around 6°C (43°F) .


A typical catch for the Penobscot Estuary during early spring: few fish including blueback herring (Alosa aestivalis), nearly translucent Atlantic Herring (Clupea harengus), and the ctenophore or ‘Sea Gooseberry’ (Pleurobrachia pileus). Photo credit: Sarah Bailey, NOAA Fisheries.

The day was not without a hiccup, when a tow came up with flounder and a tear in the net. This indicates the strong currents sunk our net to the bottom.  After a quick net repair and moving locations, we were able to get the remaining tows in for the day.  The most exciting haul of the day was a catch of Rainbow smelt and Atlantic tomcod in the midst of their spawning run.  Rainbow smelt are a sea-run species that were once a favorite for New England anglers from Connecticut to Maine but have experienced declines in abundance with the only strong runs left today in Eastern Maine including here in the Penobscot.  Although today was relatively quiet capturing hundreds of fish, in a few short weeks we hope to see these numbers increase to thousands per tow as the sea-run migration unfolds.

three small fish next to ruleron cutting board

We measure adult rainbow smelt before releasing them to continue their spawning cycle. Any local angler would be happy to have a pail of these for a fish fry dinner tonight!! Photo credit: Sarah Bailey, NOAA Fisheries.


The closest thing to a groundfish we handle here at NOAA Fisheries’ Maine Field Station is the sea-run Atlantic tomcod (Microgadus tomcod).  It is a miniature relative of the iconic Atlantic cod, also called a “frost fish” as they can be seen spawning in the still icy brooks along the estuaries of the Northeast U.S. and Canada. Photo credit: Sarah Bailey, NOAA Fisheries.

More to come as the season progresses….

Justin Stevens
Fisheries Biologist
NOAA/Northeast Fisheries Science Center (NEFSC)
Maine Field Station
Orono, Maine

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