Too hot? Too cold? Or just right?

Man in waders adjusting a small instrument in the middle of a stream in Maine

NOAA Fisheries biologist Graham Goulette retrieves and downloads a temperature logger from the Narraguagus River in Downeast Maine. Photo by NOAA/NEFSC

Hi – I’m Graham Goulette.  As a member of the Atlantic Salmon Ecosystem and Research Team out of the NOAA Fisheries Maine Field Station in Orono, I maintain a series of temperature loggers deployed in juvenile Atlantic salmon rearing habitat as part of a statewide effort in Maine to monitor stream temperature. Collecting stream temperature may seem mundane, but sometimes it’s little tasks like this that provide significant contributions to much larger projects further down the road.

Temperature is important for all livings things, especially fish. They are ectothermic — which means they rely on their environment to manage their body temperature.  Different species tolerate different temperatures, however, Atlantic salmon and other cold-water species require cooler temperatures in order to survive. We focus on the endangered population of Atlantic salmon found in the Gulf of Maine and the watersheds where they can live.

Juvenile salmon underwater, resting on rocky, sunlit bottom of a stream in Maine

Juvenile Atlantic salmon resting in a gravel patch on the bottom of a cold- water stream near a logger site. Photo by NOAA/NEFSC

We place temperature loggers in streams so we can monitor temperatures in these important habitats throughout the time juveniles are developing. The loggers are collecting data that form a record of temperatures over time, one that has multiple purposes.

Laptop connected to downloaded temperature data displays results.

Temperature data retrieved from the logger is uploaded to a laptop from a waterproof shuttle. The data are displayed to ensure proper collection and re-deployment of the logger before leaving the site. Photo by NOAA/NEFSC

For instance, in drought years like the summer of 2016, we can see how warm the water was in certain rearing areas for juvenile salmon, an indicator of whether conditions were good, or not so good, for juvenile salmon survival.  We know that at 22.5 oC, juvenile salmon stop growing.  If they are in 27.8 oC water for seven days, none survive. On the lower temperature end, at 3.8 oC they stop eating.  So stream temperature data from these rearing habitats are important for running growth rate models and can also provide an early glimpse into likely survival rates for juveniles in a given year.

Our temperature data are also contributed to a much broader stream temperature database. Data from federal and state agencies as well as universities and non-governmental organizations across the Northeastern U.S. from multiple collection efforts are shared, reducing duplication of effort.  This collaboration allows for a much larger geographical distribution of temperature collection than a single entity could tackle.

The entire database supports SHEDS — Spatial Hydro-Ecological Decision System – a data visualization and decision-support tool.  Among other things, SHEDS feeds a model that predicts daily mean water temperatures.  Forecasting stream temperatures is important for identifying where salmonids will find cool water refugia in the future. Have a look at the SHEDS public data viewer – search on NOAA as the agency and you’ll see what I have been up to this summer!

Salmon team and predators ready for Spring on the Penobscot


This is the computer readout from our two frequency echosounders.  The water surface and bottom are thick red lines, the specks in between the lines are likely fish. Photo by NOAA/NEFSC/NEST

Another beautiful spring day in Maine means that salmon biologists are busy in the field.  Since our last post, we’ve been waiting for the warmth of spring to arrive, bringing with it the sea-run fish migrations.  Last Friday we conducted one of our biweekly fish surveys of the Penobscot Estuary.  We used single frequency echosounders, also known as “fish finders”, to measure the amount of fish in the water column as we cruised through the estuary.  Generally this technique is called “hydroacoustics,”and uses sound waves to record what types of objects are in the water.  In our case we are using it to identify fish in the water.

For the past five years, we have made the same cruise along the Penobscot Estuary and are accumulating the data from echosounders which translate into the number of fish.  This allows us to describe patterns of fish abundance.  Many of these fish are sea-run species that make a migration inland during the spring.

Why is this important? Because one aspect of our research is understanding the dynamics of Atlantic salmon smolt survival as they migrate from rivers to the ocean.  Previous studies have shown that predators are a big factor. This survey is designed to figure out where predators such as large fish, cormorants, and seals congregate relative to their prey – namely, fish.  While the echosounders are counting fish, we observe the birds or mammals that we see, record their species, number, and behavior (feeding or resting).  Describing the overlapping distributions of predators and prey is the first step in understanding the complex ecological interactions that salmon are part of as they migrate to sea.


A pair of loons looking for a meal in the freshwater portion of the Penobscot River estuary. Photo by NOAA/NEFSC/NEST



A harbor seal sits on a haul-out ledge. The Penobscot Estuary survey records the number and location of any marine mammals encountered to help in determining areas of potentially high predation for Atlantic salmon smolts as they migrate the estuary. Photo by NOAA/NEFSC/NEST


Roosting double crested cormorants. These birds are exceptional fishers that eat migrating Atlantic salmon smolts in Maine Rivers.  Photo by NOAA/NEFSC/NEST

In this survey our nice day turn unsettled when Northwest winds instigated a small craft advisory for the area.  Luckily for us we were already north of the more exposed areas of the survey and could safely continue on our mission.  We saw a number of cormorants and seals but they were mostly at roosting and haul-out areas.


Justin Stevens, contract NOAA Fisheries biologist, navigating the Penobscot Estuary during a fish survey using hydroacoustics. The weather looks nice but mid-survey a small craft advisory was issued for the general area and this is the face of a boat operator scowling at the news.


The number of fish counted with the echosounder was less than we have seen in previous years by this time, but water temperatures are still around 10°C (50°F) so we probably are not close to the peak of the fish migration.  My gut tells me that things will be changing soon given we have started to have some sunny days with temperatures in the 80s.  One thing that is guaranteed, things will be different next time we are out.


The NOAA Fisheries Northeast Salmon Team

Penobscot River, Maine





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