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Home Interpreting the Data HRECOS Stories HRECOS Stories Immature American Eels Are Riding the Tides

Immature American Eels Are Riding the Tides

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A dwindling eel population has beckoned the help of kids and adults who splash around in streams with hands-full of eels.

 

Assessing the health of the eel population is the goal of the Hudson River American Eel Research Project, a citizen science program run by the NYSDEC Hudson River Estuary Program, the National Estuarine Research Reserve, and the NYS Water Resource Institute at Cornell.

 

The American Eel (Anguilla rostrata) begins its life in the Sargasso Sea. The immature eels, called “glass eels,” migrate across the ocean to the coastline of the Eastern U.S. and push their way up our rivers and streams. The eels stay here for decades before returning to the ocean as fully grown “silver eels.”

 

Unfortunately, American Eel populations are declining. This may be the result of overfishing, habitat loss, disease transmitted by non-native fish, changes in ocean-atmosphere conditions in the Sargasso Sea, or perhaps dioxin pollution. The purpose of the Hudson River American Eel Program is to learn more about the environmental conditions that affect eel migration in order to improve management strategies.

 

A volunteer with the Hudson River American Eel Resear Project holds up a bag of immature Glass Eeels.

Every day during the spring migration, glass eels are captured and counted in seven tributaries to the Hudson River. This is a huge undertaking requiring hundreds of hours. Thanks to the help of volunteers, many hands make light work and a large amount of data is collected.

 

One finding from last year’s study was that more glass eels were caught during new or full moons. New and Full moons occur when the moon, sun, and Earth are in perfect alignment. The gravitational pull of the sun and moon tug in tandem on ocean waters creating the largest tides, called spring tides. Glass eels take advantage of this big push and ride the tides further up stream.


This year, the program coordinator was puzzled when there was no observed correlation between eel catch and new or full moons. Peaks in glass eel numbers were observed before and after but fewer eels were caught during full or new moons.  

 

Eels are riding the tides! As daily high water levels increase, more eels were caught in Hudson River tributaries. Displayed above is the eel catch from FallKill Creek versus water level data from the HRECOS station at Norrie Point.

The highest water levels are not always observed during new or full moons. Other factors, such as rain events or topography, affect the tides as well as the lunar cycle.

 

Water level data from the HRECOS station at Norrie Point, eight miles to the north of the Fall Kill Stream sampling site, show a mismatch between maximum tide level and the lunar cycle. During April, for example, the highest water levels were observed before and after but not during the new moon. This was confirmed by water level data collected at the U.S. Geological Survey's station five miles to the south of the sampling site.

 

Using the HRECOS and U.S. Geological Survey water level data, we can observe that the number of eels caught did increase with rising high water levels this season even though the peaks did not correspond with full or new moons.

 

We are excited to join the efforts of the Hudson River American Eel Research Project. Collaborating scientists are already examining other parameters measured by the HRECOS and USGS stations to try and puzzle out other abiotic factors which may be influencing eel migration. To learn more about this program, visit the Hudson River American Eel Research Project homepage.

 

If you are interested in examining and exploring this data for yourself, you may download the Excel file I used to process this data by clicking here: Data for this HRECOS Story.

 


 

 

Last Updated on Monday, 02 November 2009 12:09