Keep the Magic Going

Cold Water Fish Species are Canaries in the Coal Mine for Climate Change

The Ducktrap River

Along the shore of Penobscot Bay in Midcoast Maine there is a Shangri-La for cold water fish species. It is a place of beauty and natural bounty that has been known to the Penobscot indigenous people since the Neolithic period. Legend states that Vikings arrived centuries before Captain John Smith landed in 1614. It became a site for colonial mills and early shipbuilding activity in America. However, this story is not about the past. It is about climate change and the impact today on native fish.

Located in midcoast Maine

For over 10,000 years, following the retreat of  Laurentide Ice Sheet, sea run fish have populated the Ducktrap.

This river is their maternity ward and nursery. Here is where they mate, deposit eggs, and where their fry hatch. As rivers go, with only a nine mile flow and fed from three ponds, the Ducktrap barely registers on the radar. Few roads cross the river so you must look carefully to find it, but in hidden waters of those nine miles there is aquatic magic.

In the spring thousands of alewives return from the Gulf of Maine to the three Ducktrap headwater spawning ponds. In the fall the river becomes crowded with very active two-way traffic. This is when Atlantic Salmon and sea run brook trout, known locally as "salters", return to build their redds in the gravel bottom. At this same time their are juvenile alewives, Atlantic Salmon smolts, and a great number of wild brook trout all gathering in the lower river to make their tidal journey into the sea. These events are as nuanced as a choreographed ballet, with each species playing a specific role.

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Hydrology

The Ducktrap is a spate river, closer in character to the small streams of Scotland than to the rivers of North America. Its rate of flow rises and falls dramatically based on rainfall.  In summer months the flow drops.  Long sections of its river bottom are composed of fine gravel deposited by ancient glaciers.  The river waters are ice cold in the winter, only warming in the summer.  This river does not provide a favorable habitat for year-round cold water fish species. The warm water forces cold water fish to seek the colder waters in the small tributaries or the sea. The Ducktrap is relatively free of natural predators due to dense overhead foliage.

The river provides a food rich environment where sea run fish can spawn and mature.

In dry summers the flows can drop substantially.

The river often freezes solid in winter.

Spring rains and warming waters trigger the start of a new cycle.

Autumn needs rain producing low pressure systems to provide flows for spawning Atlantic Salmon and Salters

Sea Run Fish

Alewives

Alewives (Alosa pseudoharengus) are an anadromous species of herring found in North America.  They live in the sea but return to freshwater lakes and ponds to spawn.  Thousands of alewives return to the Ducktrap each year to spawn in the three feeder ponds.  Alewives provide nutrients throughout the food web to small insects as well as top predators such as eagles and coyotes.

These fish enter the Ducktrap in May. Their migration is triggered by a combination of tidal activity and water temperature variation.

After negotiating barriers to passage such as water falls and beaver dams, alewives pause to regroup before heading upstream to the ponds.

Salters

"Salters" or sea run brook trout are diadromous fish that move between fresh and salt water.  The reasons for this evolutionary adaptation are thought to be their needs for food and thermal refuge.  

When first returning to freshwater from the sea, salters appear heavier in girth are more silver in color.

Though they quickly regain their natural darker defensive colors once back in fresh water.

Like snowflakes, no two wild brook trout appear to be the same.

Atlantic Salmon

Atlantic Salmon return to the fine clean gravel beds of the Ducktrap to spawn in the fall.  They often return to precisely the same location in the river where they were born in order to deposit and fertilize their eggs.  The fertilized eggs will remain in the gravel redd over the winter and will hatch in the spring. 

The fry will remain in the river for two years as parr,  subsequently developing into smolts before returning to sea. 

 After two or more years at sea, they will school up with other Gulf of Maine salmon off the coast of Greenland. Those salmon who survive the trials of the open ocean will return to the Ducktrap to repeat this life cycle.

Conservation

Through the foresight, generosity, and hard work of over a dozen community-based, government, and academic organizations, more than 85% of the Ducktrap River watershed is now under protective easement managed by the Coastal Mountains Land Trust.  CMLT actively manages and monitors the watershed for invasive plants and insects such as Japanese Knotweed and Hemlock woolly Adelgid. The current survival of its native fish populations is a testament to these extraordinary conservation efforts.

The Georges River Chapter of Trout Unlimited (GRTU), was previously known as the Ducktrap Chapter. Our chapter has long been involved in promoting the protection and conservation of the Ducktrap River.  Our work includes land remediation and road culvert replacement.  Beginning in 2022, in response to threats from climate change, GRTU initiated a fresh multi-year conservation program for the Ducktrap.

This initiative involves working with The State of Maine and NGO conservation groups to develop and deploy signage and educational materials along with an automated smartphone based Ducktrap Angler Survey Application.

In 2023 our efforts expanded into a robust science-based species identification and water temperature monitoring project.  This project is in coordination with the Maine Department of Inland Fisheries and Wildlife and the Maine Department of Marine Resources. This year GRTU conducted the first ever Environmental DNA (eDNA) study of the Ducktrap River.  Water samples  were collected from 14 discrete locations within the watershed: the main stem, several tributaries, and the pond outlets.  Each sample was frozen and shipped to the University of Maine eDNA laboratory for analysis. The samples were tested for six fish species:   Native Atlantic Salmon and Brook Trout, along with invasive species of Largemouth Bass, Smallmouth Bass, Black Crappie, and Northern Pike.  

eDNA Study Results

eDNA used to determine the presence of Native and Invasive Species

All fish "shed" their DNA into the aquatic environment. Water samples where carefully collected and analyzed to determine which species are present.

Native Atlantic salmon (Salmo salar) and Brook trout (Salvelinus fontinalis) were both detected.

Invasive Smallmouth bass (Micropterus dolomieu), Largemouth bass (Micropterus salmoides), and Black crappie (Pomoxis nigromaculatus) where also detected.

Invasive Northern pike (Esox lucius) have not been detected.

Following map shows detection locations within the watershed.

eDNA results showing Native and Invasive Fish

Water Temperature Results

Since the early 1980s, the rate of warming in the Gulf of Maine has been more than triple that of the world's oceans; 0.86 degrees F versus 0.27 degrees F.

In 2006 the Maine Department of Environmental Protection conducted a summer water temperature study of the Ducktrap River watershed.

Classification of streams to support cold water fish based on temperature in degrees celsius.

The larger streams without ponds and all of the smaller streams were found to be good sources of cold water to the mainstem. Streams with headwater ponds were relative sources of warm water. The conservation of cold water sources is extremely important. Land conservation is critical in order to preserve these cold water sources.

GRTU 2023 Summer water temperature study shows the mainstem and tributaries from feeder ponds warm to stressful levels for cold water fish in the summer months. However the smaller tributaries continue to be a life preserving source of cold water for Atlantic Salmon and Brook Trout.

Call to Action

The original native residents of the Ducktrap River, Atlantic Salmon and Brook Trout, now have new neighbors. In their evolutionary past our native fish did not compete against other species of fish for food, nor were they preyed upon by invasive fish. Largemouth bass, Smallmouth bass, and Black Crappie have entered the river from illegal stocking in the feeder ponds.  The river water is now warm enough to accommodate the survival of these invasives because the river's main stem heats up in summer months. The native cold water fish are forced to seek thermal refuge in a few spring fed tributaries and seeps or they must enter the sea.

Don’t let the magic end on our watch!

Support climate change mitigation efforts in your community.

Report illegal fish stocking to the warden service.

Support habitat restoration efforts such as the replacement of defective road culverts that restrict native fish passage to thermal refugia.

Support fishery regulatory changes in order to encourage the removal of invasive species.

Support local cold water fisheries advocates such as GRTU.

About this Story

This report was produced by the Georges River Chapter of Trout Unlimited. Guidance for the eDNA study was provided by the Maine Department of Inland Fisheries and Wildlife and the Maine Department of Marine Resources. eDNA analysis performed by the University of Maine eDNA CORE Facility.

eDNA Data

TU eDNA Detection Report, August 10, 2023

Water Temperature Data

Ducktrap River Tributary Study, Maine Department of Environmental Protection, January, 2007 and GRTU Study September, 2023

Photos

Tim Shaw, Patrick Gallagher

Classification of streams to support cold water fish based on temperature in degrees celsius.