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