eDNA Bread Crumbs Track Migrating Fish


New DNA sampling techniques have just established a benchmark for fisheries science -- the ability to determine the species type and abundance of migrating fish just by sampling water in a river.  The genetic bread crumbs that fish leave behind just by passing through a section of stream now are able to be used to gauge the size of migration runs and even the presence of different species moving with them.

Using DNA evidence found in the ambient environment -- a concept dubbed eDNA -- can now enable scientists to take census of fish and animal populations with an ease and accuracy never before available.

The technique was first applied in the Hudson and East Rivers of New York by researchers from Rockefeller University, and their analysis was detailed in the online scientific journal PLOS ONE.  As reported by UPI, the methodology showed, "the presence and absence of a variety of local fish species as they traversed the river.... (and) corresponded with migration patterns established by previous net surveys."

UPI coverage continued, "For the first time, we've successfully recorded a spring fish migration simply by conducting DNA tests on water samples," Rockefeller researcher Mark Stoeckle said in a news release. "

"If future research confirms that an index of species' abundance can be derived from naked DNA extracted from water, it could easily improve the rationality with which fish quotas are set, and the quality and reliability of their monitoring around the world," said Jesse Ausubel, director of Rockefeller's Program for the Human Environment.

Sockeye salmon (Oncorhynchus nerka); Canada

Sampling of genetic material has previously been conducted in river sediments as well.  Another well regarded scientific resource, Science Direct, hosts a study conducted in 2014 that showed the following correlations.

'¢ Fish eDNA was 8 — 1800 times more concentrated in sediment than water.

'¢ Fish eDNA remained detectable after more than 3 months in sediment but

not water.

'¢ Aqueous and sedimentary concentrations of fish eDNA were positively


'¢ Sedimentary eDNA may allow retrospective genetic monitoring of fish.


I did a short year-long stint working for the US Fish and Wildlife Service 40 years ago, conducting sample surveys of salmon and steelhead in Puget Sound and it's various river tributaries. Jaw tagging of adult salmon captured in salt water and micro tagging of juvenile fish in hatcheries on the Olympic Peninsula were part of an ongoing effort to quantify runs and escapement numbers.  While it provided the only real data fisheries managers had to work with, it was hard won and certainly had it's limitations.

New eDNA sampling techniques offer the ability to monitor and assess not only the strength of migrations, but could potentially be able to more accurately identify the presence and ratio of wild vs. hatchery fish in a given run, a holy grail dataset for environmental advocates wanting to engage legislators to effect policy regarding anadromous species.


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