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Sunday, May 13, 2012

The Osprey Files: Herring!

May is a bountiful time of year for portions of Maine's Osprey population. A few rivers still host annual runs of herring (aka alewives) that come in from the sea to go to their spawning grounds in freshwater lakes and streams. Hatched in fresh water, alewives spend several years in the ocean before returning to their natal stream to spawn. This is Maine's equivalent to the salmon runs of the Pacific Coast of North America.

And like the salmon runs on the Pacific, the alewife population has suffered greatly. Most of the rivers that hosted runs in the past no longer have alewives returning yearly - some due to dams that the fish cannot scale, others to overfishing and pollution. And for the dams that do have fish ladders, most of the ladders are old, crumbling, and are not very easy for the fish to climb. The last I saw, only 5 rivers and streams (out of several hundred) in Maine had predictable, yearly, alewife runs.

A few streams still have healthy populations though, and it's these streams that, I hope, will provide the foundation for the return of the alewives. In the meantime, Osprey, Herring Gull, Bald Eagles, and other wildlife depend on these remaining runs to help raise their young.

Herring Gulls - waiting for the Alewives


I spent the last couple of days volunteering with an alewife counting project near my home in the Midcoast of Maine. I'll admit that I volunteered not only to help with the fish restoration project but to be in one of the best places in the US to watch Osprey actively fishing.

The stream didn't disappoint!

The alewives come in on a high tide when the stream temperature is warm - above 58 deg F seems to be best. Fish are cold blooded so if the water temperature is too cold, they are sluggish and have a tough time swimming upstream.

Alewives - the start of the run


The area was devoid of Osprey during the low tide but as the tide came in, several birds flew over to check out the stream.

Osprey checking out the river


I'm not exactly sure what they were looking for - could the Osprey sight individual fish from 100 or more feet above the water? Were they looking for fish rises or other activity? I'm not exactly sure, but I do know that as soon as the run started in earnest, the area was inundated with hungry Osprey!

As the tide rose and the alewives came in, the fish were packed so tightly that the surface of the water was turbulent with fins and splashing fish. The submerged entrance to the fish ladder was black with the backs of alewives - a very good sign! Onlookers were anxiously watching the fish ladder from the top of the dam, cheering the fish on as they passed step after step.

On Friday I counted at least 18 individual fish catches by Osprey in the 1 hour I stayed after max tide. On Saturday the count was 16. I left only because the high tide was in the evening and the shadowed lighting was just too dark for photography - but shadowed water seemed to help the Osprey sight fish so they kept fishing after I left.

Some of the raptors perched on branches that overhung favorite fishing holes. They would watch the water, head bobbing back and forth trying to spot a fish. Once a fish was in their sights they leapt off their perch, slamming into the water feet first, then flying out again with a fish in their talons.

Osprey watching the water from a favorite branch



When the favorite perches filled, arriving Osprey had to hunt from on-the-wing. They flew in low and slow, face into the wind (upstream), hovering over the fishing hole. If they didn't see a likely target they circled off and came back around again for another try. As the alewife run progressed, more and more Osprey chose this method to spot a fish.


A few Bald Eagles flew past during the height of the Osprey fishing-frenzy, but the Eagles didn't fish for themselves. Their tactic was to wait on a nearby branch until an Osprey caught a fish. As soon as the Osprey flew away with the fish, the Eagle would launch itself off its branch and chase down the smaller raptor. The Eagle would then harass the Osprey by diving at it until the smaller bird released its fish, at which point the Eagle would grab the fish out of the air and fly off. The poor Osprey would them turn around and go back to the river for another fish.



Watching these beautiful birds in their fishing frenzy was one of the most amazing things I've witnessed here in Maine. Over two days and 34 catches that I witnessed, only once did I see an Osprey dive and miss a fish. Pretty good success rate!

For more information on Alewives, visit:

http://www.fws.gov/GOMCP/pdfs/alewife%20fact%20sheet.pdf


All photos and text copyright Nancy Rynes, 2012. You may link to this article, but do not copy any content without my permission.

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