2019 Juvenile Coho Population Smaller Than Expected

Biologists estimate that 8,978 juvenile coho were living in the mainstem of Olema Creek and that 1,594 were living in Redwood Creek at the time of their surveys in August and September. NPS / Jessica Weinberg McClosky

February 2020 - Summer juvenile salmonid monitoring has revealed that the juvenile coho population was smaller than expected on both Olema and Redwood Creeks given the substantial spawning activity seen during the winter of 2018-2019. Possible reasons for lower survival rates include the major storm events that occured in February of 2019. Although it is not uncommon to have large storms in February, the size of these storms combined with the later timing after redd deposition likely resulted in substantial coho redd (nest) scour and/or emergent coho fry mortality. In particular, one storm in late February resulted in a flood on Olema Creek of a magnitude that typically occurs just once every 15-20 years.

Biologists estimate that 8,978 juvenile coho were living in the mainstem of Olema Creek at the time of the surveys there in September. Redwood Creek surveys took place in August, and yielded an estimated population size of 1,594 juvenile coho. Despite the low juvenile coho population estimates, summer 2019 juvenile steelhead totals were the highest since surveys began in 2009. For more details on these monitoring results, and how they compare to past seasons, check out the newly released Summer 2019 Juvenile Coho & Steelhead Monitoring Summary.

Next month, salmonid monitoring teams will install downstream migrant traps in Olema and Redwoods Creeks to capture these juvenile coho as they make their way to the ocean. They hope to get a measure of the young fishes’ overall health and determine how many of those observed during the summer were able to survive through the winter.

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