Pacific Lamprey’s Big Year

While South Fork of the Lamprey River does not roll off the tongue with same ease as South Fork of the Eel, it would be a more accurate name for our local waterway, especially this year when it is enjoying an abundance related to the high pre-drought water flows of a few years back. Older than the dinosaurs, a delicacy to native tribes, and a fussy architect to boot, the Pacific Lamprey is integral to the complex web of life involving endemic and introduced fish species in the inaccurately named Eel.

River otter enjoying a pacific lamprey. Photo by Talia Rose

The renewed abundance of this very old fish is like a happily singing canary in the mine here on the North Coast when the news about so many of our local fish is grim. Because of its role in the food chain, return of the lamprey may be good news for other fish species.

Evolving 450 million years ago around the same time as sturgeon and shark, the lamprey spends most of its life as an ammocoete, or larva, after hatching in fresh water streams. The small, worm-like larvae burrow into the rocky river bottom and filter-feed on detritus and micro-organisms.

After 2-7 years, the ammocoetes undergo a metamorphosis lasting several months and then journey out to sea as adults, growing up to 30 inches long, where they feed by attaching their jawless mouthparts onto fish and other vertebrates, drawing blood and other body fluids without killing the host.

After 1-3 years at sea, lamprey return to fresh water streams where the female may spend a week or more preparing her “redd” or egg repository, arranging rocks on the stream bed to her precise specifications before depositing up to 100,000 eggs which are later fertilized by the male.

Juvenile Pacific lamprey, or ammocoete. Photo from Wikicommons

Like most anadromous fish in the Eel, the adult lampreys die after spawning, bringing a huge quantity of nutrients into the Eel River food chain. Unlike Pacific salmon species, it is suspected that lamprey do not necessarily return to the same river in which they were born.

The fact that they are so abundant in the Eel these days could be a very good sign for our river. The Pacific Lamprey is in decline in most of the Pacific Northwest and elsewhere in California due to pollution and flow diversion, and may be choosing the Eel because of its health relative to other waterways.

According to Patrick Higgins, local fish biologist and Managing Director of the Eel River Recovery Project, our lamprey are going through a resurgence that is part cyclical, but also may indicate that a healthy balance of fish species is returning to the watershed.

“My hypothesis is that the lamprey are doing better because the Pikeminnow population is depressed,” says Higgins. The invasive Pikeminnow, introduced to the Eel system in about 1979, has taken a toll on the lamprey by feeding on the ammocoetes. “About 20% of the Pikeminnow diet was lamprey ammocoetes when diet studies were done in the late 90s. River Otters appear to be suppressing Pikeminnow through intensive predation, which is likely to have caused a resurgence of lamprey,” says Higgins. [Note: Some scientists have expressed serious reservations about the theory that the Pikeminnow population is suppressed. As one of the commenters says below, “[Lamprey] returns were also very strong to the Klamath and especially to the South Fork Trinity both of which do not have pike minnow. This indicates more of a region-wide resurgence.]

The weather may also play a part in the lamprey resurgence as wet years have typically enabled the downstream migrating ammocoetes to maneuver more successfully past the Pikeminnow in the greater volume of water and increased turbidity. “This is the third year of high abundance of lamprey, which indicates good brood production in 2005-2007; therefore, runs are likely to continue strong for the next several years as a result of high spring flows through 2012,” said Higgins. It remains to be seen how the next cycle from 2020-2024 will reflect the low water times of that drought.

Another factor contributing to renewed lamprey productivity is the recovery of gravel beds in the Eel system. With much of the sand and silt deposited during the 1964 flood now washed to the ocean, there is more suitable clean gravel for lamprey redds. Lamprey, unable to jump like the salmonids, attach their mouths to rocky surfaces to shuttle upstream against the current. This same attachment function allows the parent lamprey to move rocks around precisely, creating an ideal nursery for the eggs.

Keith Parker, Yurok tribal member and Humboldt State University graduate student, has been working on genetic diversity of Pacific Lamprey in the nearby Klamath River. Local tribes have long used lamprey as a nutrient-dense food that helps them get through the lean times when salmon are scarce. Lamprey have nearly 5 times the lipid content of salmon, making them a high energy food source. Because the primitive fish is a poor swimmer that hugs the edges of streams where it can attach its mouth when needed in order to make progress, it is harvested from the shore with an eel hook, a short pole with a wire hook at one end.

Osprey with lamprey catch. Photo by Talia Rose

“Lamprey is what fed our people when there were no salmon,” says Parker. He adds that a healthy abundance of lamprey benefits the entire riparian ecosystem. Like all fish who die in the river after spawning, their corpses deposit rich marine nutrients that contribute to the health of flora and fauna throughout the system. “Core samples of redwood trees taken in the upper reaches of Redwood Creek show marine-derived phosphorus, most likely deposited by lamprey, who account for the largest bio-mass in the Klamath system.”

According to Parker, an abundance of lamprey also benefits the salmonids because “they are the preferred meal for seals and sea lions, being easier to catch than fish, and less challenging to consume because of their soft cartilaginous skeleton.” When seals and sea have fewer lamprey to take, they take more salmon.

Lamprey numbers have declined since the 60’s. One study counted 380,000 lamprey crossing over the Columbia River’s Bonneville Dam in 1969. That number was down to 11,000 in 2011.

“By building anadromy barriers,” says Parker, “we have blocked the return of energy upstream.” Parker’s current research seeks to identify a correlation between lamprey size and travel distance in the several north coast river systems which will be used to aid the recovery of lamprey throughout its once extensive range.

When a critical species such as the Pacific Lamprey rebounds as it has over the past few years, it is hoped that because of the role it plays in the web of local life, other species will be boosted by its numbers.

Article by: Ann Constantino

Published: June 18, 2017 by Redheaded Blackbelt

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