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The Wrack

The Wrack is the Wells Reserve blog, our collective logbook on the web.

Rainbow Smelt in the York River

Posted by
Tyler Spillane
| May 15, 2017 | Filed under: Observations

The spring field season has begun with a 10-week study on migratory fish in the York River. We are collecting data for the Wild and Scenic Study Committee by using fyke nets to sample fish every day.

We started work in the beginning of April and in the first three weeks caught 2,598 fish, of which 1,228 were spawning rainbow smelt. We recorded the length, weight, and sex of each smelt caught, finding the average fish to be 6.1 inches long and weighing about 1 ounce. More than 87 percent of our catch was male. Males usually arrive first at spawning sites and wait for females. They can also travel up river to spawn more than once during the spawning cycle, while females will swim upstream and spawn in one high tide event.

While the presence of rainbow smelt in the York River has been known by locals for many years, this is one of the first studies showing large runs of smelt in the river. In comparison, a similar study done by the reserve in 2001 found only about 50 rainbow smelt, but that study started later in the season and likely missed a bulk of the run.

In addition to catching smelt, we are looking for their eggs so we can determine exactly where they are spawning.

Two images of rainbow smelt eggs adhered to stones in the York River.
Two images of rainbow smelt eggs adhered to stones in the York River.

Rainbow smelt look for upstream areas at the tidal interface, where the salt ocean water becomes fresh (head of tide). Smelt prefer to spawn in cool waters, typically in early spring, and at night. They seek out habitat with cobble and stones where their eggs will adhere to the rocks. Each female can lay 40,000 to 50,000 eggs at a spawning event. Once eggs are fertilized, they will hatch after 2 or 3 weeks, depending on water temperature. As we search for spawning evidence, we are glad to find clear eggs, which are live and fertilized, as opposed to white or opaque eggs, which are typically dead or unfertilized.

Now that the waters are warming, the rainbow smelt run is winding down. We expect to see brook trout, river herring, and sea lamprey migrations in the coming weeks.

Rainbow Smelt Status

Rainbow smelt are commercially and recreationally fished in the Gulf of Maine. Populations have declined due to barriers to stream access (such as roadways and dams), habitat loss and impairment, and decreases in water quality in spawning habitat. The decline has led the State of Maine to list smelt as a "Species of Greatest Conservation Need."

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