Finally, so many fish! Are they late?

They’re back! River herring are returning at super high rates to Upper Mystic Lake in their annual migration up the Mystic River to spawn.

 Compared to last year, this big arrival of fish seems late. Our video system estimates that 160,000 fish have passed as of today, May 22.  In 2018, nearly that many fish had arrived by May 9--thirteen days earlier.  

 Why the two-week difference?

 Here’s one possible factor: It has been a cold spring. Plants in my garden are certainly flowering and leafing out late compared to last year. 

 And water in the Mystic Lakes has stayed colder, longer. By May 8, 2018, mean daily water temperature was already above 17 degrees C, and 100,000 fish had climbed the fish ladder.  In 2019, the lake did not reach 17C until May 21, which is also the day the estimated total had reached 100,000-fish mark.

So one hypothesis is that colder water has delayed this year’s migration upstream.  We know that fish respond to temperature cues in many contexts.  Time will shed more light.  Stay tuned! 

 In any case, we expect many fish in the next few weeks, so help us count!  Join us at www.mysticherring.org, and contribute to our crowd-sourced citizen science project.  Everything we know about this fish run comes from volunteer effort (either on-line or in-person).  Thank you.  And happy counting.

2018 Cumulative Est. Fish Count by Date

2019 Cumulative Est. Fish Count by Date