Sunday, June 20, 2010

Fish Ladder Tour

To wrap up my short series on spring wildlife, let me tell you about a tour of the Exeter, NH, USA fish ladder on a Saturday in early June.

NH Fish & Game operates fish ladders in area rivers so that anadromous fish can return from the ocean to fresh water to spawn. (For more fish pictures and maps, see this Fish & Game PDF.)

Netting herring in the Squamscott River

The area where the Squamscott River becomes the Exeter River has been dammed for hundreds of years. There were sawmills here almost as soon as Europeans arrived.

Below the dams, there's a gradual rise with small waterfalls. This area is where the majority of the herring harvested in the Great Bay Region are collected.

Only about 5% of the migrating herring use the fish ladder, but 80% of harvest is here because it's an easy place to capture fish with a net.

Herring are used for bait, primarily for catching striped bass or lobster.

Fish swim upstream to get to fresh water

Fish that migrate from the ocean to spawn in the fresh water of the Exeter River:
  • River herring (bluebacked herring)
  • Alewives
  • American Shad (only 10 - 30 per year)
  • Sea Lamprey

Fish & Game people on the fish ladder
The gulls are hunting for fish too!

Fish look for swift current, so the ladder produces swift current like a water fall. The flat portions are resting pools for the fish ascending the ladder. This ladder was built in 1970's

On the Exeter River, Fish & Game counts the fish by hand daily since the numbers of fish are so low.

At the fish ladder in Newmarket, 32,000 herring and alewives ascended the ladder by June 4. In the Cocheco River in Dover, 30,000 fish had ascended the ladder by June 4. In Exeter, only approximately 40 herring will use the ladder all year.

As part of the annual fish ladder tour, you can volunteer to visit all of the fish ladders in the Seacoast region and net and release fish with Fish & Game personnel.

Fish ladder and bridge

Many of the towns surrounding Great Bay were founded at a waterfall, so the water power could be used to build mills (sawmills and grist mills at first). The dams constructed at these town sites are obstacles to fish that must migrate upstream past the waterfall to reach fresh water. Below the waterfall, the rivers are still subject to tides and are salt or brackish water.


This particular herring was about 4-5 years old. Herring live up to 9 years. They do not die after they spawn.

To determine the precise age of a fish, you can check the growth rings on scales. Under a microscope, constricted growth rings indicate winter. (Fish grow more slowly in the winter, just like trees.)

Juvenile herring stay in fresh water for the summer, then head out to sea until it's time for them to spawn when they return to a freshwater river.


Lamprey are an old species. They have no bones in their jaws. This lamprey was very strong and wriggled away from the Fish & Game handler. It immediately suctioned onto the side of the bucket at his feet, a common reaction for a lamprey.

Young lamprey live in river substrate for 7-10 years as filter feeders. Then they go to the ocean for about 10 years. When they return to freshwater to spawn, they die during that spawning run. Females actually re-absorb internal organs during their spawning run for maximum egg production.

The Great Lakes are overpopulated with sea lampreys

Two lampreys attached to a rock at the Pickpocket Dam

Despite flooding in New Hampshire in March, by now the water flow is fairly low. Several miles upstream from the fish ladder is a second dam. Because the water flow is so low, the lampreys cannot get above this dam.

To round out my wildlife update, I'm happy to say that the phoebes are nesting again, incubating their second clutch on the back of our house.

The barred owl family seems to have moved on. We had a few sightings of two owls near each other, and heard some calls at night last week. For this whole week we haven't seen or heard the owls. It was a magical spring watching owls every day!


Beatrice P. Boyd said...

Thanks so much for the post about fish spawning which I have forwarded to Grenville. He is more the naturalist than myself, but I do like being outdoors and photographinc nature - all types. Glad to see the phoebes have returned.

Lois Evensen said...

What fascinating information and images. Thank you so very much. I learn so much out here in blog land.

Delighted Hands said...

I appreciated the virtual tour-did you ever think about being a guide yourself?! You would be a great one!

LA said...

I didn't realize that the fish ladders were used on the East Coast...I usually associate them with the Northwest! This was very interesting!

Julie said...

What a pretty location! And great information!

Anonymous said...

Sue, thank you for the tour and for all your lovely posts with the beautiful pictures. They lift up one's spirit.


Theresa said...

Wonderful! I had no idea. I'm wishing I had known more about fish ladders while I lived around there. DANG! They do have them here in the west for the salmon, and lots of battling over them too in some parts.
How fun with the Phoebes doing a second clutch. The owls might have moved on to teach their fledglings hunting skills or they may have depleted the area raising babies. I bet they'll be back though. Maybe next year or later in the season.

Janet said...

Very interesting info and photos. Thanks.