Captive Rearing Strategies Could Impact Lake Sturgeon Recovery Success

by guest contributor Derek Smith

Flowing between the kitschy, Bavarian-style architecture of Frankenmuth, Michigan is the Cass River, where biologists released 104 young lake sturgeon in September 2022. Before releasing them, the biologists equipped the sturgeon with tracking and identification devices to follow the fish’s movements and survival after their release. That knowledge is critical to assess the success of sturgeon release events because there is no guarantee the sturgeon will remain where they are released.

A small lake sturgeon being held in a person's hands.
A young lake sturgeon being released into the Cass River. The fish will leave the river after its first year, but scientists are hoping that they return when they are old enough to spawn. Photo courtesy Derek Smith.

Once numerous in North American freshwaters, lake sturgeon are considered globally endangered due in part to severe overfishing in the late 1800s and early 1900s and are absent from many rivers where they historically lived, such as the Saginaw River and its tributaries, including the Cass River. According to US Fish and Wildlife Service biologist Justin Chiotti, the goal of releasing captive-raised sturgeon is to “restore historic populations to self-sustaining levels.”

But sturgeon don’t hunker down in one place. After one year, many sturgeon leave their birth rivers to live in lakes, bays, and river mouths. When they reach sexual maturity between twelve and twenty-seven years later, the sturgeon return to their natal waters, which are better suited to spawning. There, fertilized eggs and larval fish take shelter from predators between the rock crevices in cobblestone substrate and thrive on the fast-flowing, oxygen-rich water.

How sturgeon navigate back to their rivers of origin is still largely unknown, but scientists think that larval sturgeon imprint to chemical signatures in their natal waters. Later in life, the sturgeon “sniff” their way back to their natal rivers to spawn by following those chemical queues.

Imprinting captive-reared sturgeon to rivers where they are now extirpated presents a challenge to conservation biologists When sturgeon are not raised in the waters in which biologists plan to restore self-sustaining populations, the re-introduced fish might not imprint to the historic habitat, potentially reducing the return rates when the fish are old enough to spawn. ,

A lake sturgeon fish hatchery in Genoa, WI. Photo courtesy Derek Smith.

Stream-side rearing facilities could be the solution to the imprinting challenge. At these facilities, biologists raise sturgeon directly in the river water where the sturgeon will be released. The Toledo Zoo has one such facility along the Maumee River, where they have been raising fish for release into the Maumee River since 2018. Similar facilities are located in Michigan, such as the Black River facility run by Michigan State University and the Big Manistee River facility run by the Little River Band of Ottawa Indians.

According to Matt Cross, the Toledo Zoo’s Conservation Coordinator,“the idea with the stream-side facility is that the fish will pick up on the different chemical cues from the river, which they will use to return to the river to spawn.” By raising sturgeon in the waters to which they will later be released, the Zoo’s biologists are increasing the chances that the sturgeon are in the river water during the developmental stage when imprinting occurs, which Cross says is “a big question mark.”

But the stream-side facilities are costly and have water quality issues that off-site hatchery facilities optimized to grow large amounts of fish are better equipped to manage. The National Fish Hatchery in Genoa, Wisconsin is one such facility. There, U.S. Fish & Wildlife biologists rear sturgeon from eggs in Genoa well water. The facility raises hundreds to thousands of sturgeon for release into rivers each year, but there is a chance that hatchery-raised fish miss the crucial period at which imprinting occurs before they are large enough to be released. The unknown timing of when sturgeon can imprint to rivers obscures the relative effectiveness of these two rearing strategies.

Larval lake sturgeon swim around a tank filled with well water at the Genoa National Fish Hatchery. Biologists refer to the fish at this age as “free-living embryos” because they still have a yolk sac that provides all their nutrition. Photo courtesy Derek Smith.

According to Cross, “it’s a cost-benefit problem.” If sturgeon raised in well water still reliably return to the rivers where they are released, the large number of fish raised at the Genoa Hatchery could be a boon to sturgeon conservation across the Great Lakes region. On the other hand, if the hatchery-raised sturgeon wander, additional streamside facilities may prove necessary to re-introduce self-sustaining sturgeon populations to target rivers. The Cass River, for example, lacks a stream-side rearing facility and may potentially benefit from one.

To better assess the costs and benefits of each rearing strategy, biologists at the Toledo Zoo, US Fish and Wildlife Service, Ohio Division of Wildlife, Michigan State University, and the University of Toledo will test whether the two rearing-strategies impact how sturgeon return to rivers. In the summer of 2022, the biologists collected eggs and sperm from the same spawning adults in the St. Clair River, where healthy, self-sustaining populations exist today. Fertilized eggs were created by mixing sperm and egg, then half of the eggs were raised at the Genoa Hatchery while the other half were raised at the Toledo Zoo’s stream-side facility.

Once the fish were fingerling size, the biologists equipped them with PIT tags. The tags are similar to the microchips implanted into pet dogs and cats and encode an identification number linked to information about where an individual fish was released and in which facility it was raised. Whenever a released sturgeon is recaptured, scanning its PIT tag will allow biologists to identify how many fish from each rearing facility returned to the Maumee River to spawn

Both institutions have partnered to release sturgeon into the Maumee River in this manner since 2018, so the oldest fish released in this program are only 4 years old. The team must wait until the first of the released sturgeon mature eight to twenty-three years from now before they get their answers.

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Michigan Nature Monday: Poweshiek skipperling

One of the rarest butterflies, the Poweshiek skipperling, is truly on the brink of extinction. Once abundant in the tall prairie grasslands and the prairie fens of several states and provinces in the upper Midwest, the tiny butterfly is now found only in a handful of sites in Manitoba and northern Oakland County, including an MNA nature sanctuary. Loss of habitat and other factors contributed to a decades-long—and now a relatively recent and rapid—population decline that has scientists scratching their heads and worried about what their disappearance may mean for other pollinators.

The globally endangered Poweshiek is now so rare that only 100 individual butterflies were counted in a 2021 census. Recovery plans—aided by an international partnership that includes MNA—call for captive breeding efforts to headstart individuals and increase survival to adulthood in order to build a reserve population that can be reintroduced to the wild. The Minnesota Zoo, John Ball Zoo in Grand Rapids, Michigan State University’s Haddad Lab, and the Michigan Nature Association are specifically collaborating within the Poweshiek Skipperling International Partnership to annually produce more individuals for wild releases in 2022 and beyond in what is known as ex situ or “offsite” conservation.

Poweshiek skipperling photo by Cale Nordmeyer, Minnesota Zoo

MNA is proud to protect habitat critical for the Poweshiek skipperling’s survival, and to be part of the important partnership that is working to save this species from extinction. We look forward to continuing participation in this partnership effort to increase the Poweshiek skipperling population in the wild in the coming years.

Learn more about our conservation work and how you can contribute at michigannature.org.

Life on the Brink: Endangered Butterfly Gets a Helping Hand

Michigan nature is so full of wonder that… Some of the rarest species can be found here.


Once common across much of the Midwest, now one of the rarest butterflies—the globally endangered Poweshiek skipperling—exists in only a handful of locations in Manitoba (Canada) and northern Oakland County, including at an MNA nature sanctuary. Over the course of just a few decades, the population of Poweshieks has crashed, for reasons mostly unknown (see Plight of the Poweshiek story map here). In the most recent surveys in 2021 and 2022, the number of wild Poweshiek skipperlings surveyed in the field has continued to decline.

Poweshiek skipperling. Photo by Cale Nordmeyer, Minnesota Zoo.


An international partnership that includes MNA, is working to better understand the reasons for the Poweshiek decline, and provide habitat and ex-situ (off-site) and captive rearing efforts to assist with recovery.


One such recovery effort involves partners at the Minnesota Zoo, John Ball Zoo, and the Haddad Lab at Michigan State University. The research partners have been collecting Poweshiek skipperling eggs for a captive-rearing program to help the species recover. And last month, 12 captive-reared Poweshiek butterflies were released at MNA’s nature sanctuary—representing a milestone for MNA and hope for future generations of Poweshiek in the wild. In all, a few dozen butterflies were released this year in the program, with hundreds more eggs laid. These eggs will overwinter in the rearing facility at John Ball Zoo, for breeding and release next year.

Dave Pavlik, a research assistant at the Haddad Lab, places a Poweshiek skipperling caterpillar into a special enclosure at John Ball Zoo. Photo by Lauren Ross.


In May, John Ball Zoo held a ribbon-cutting ceremony for the opening of a second hoop house for the Poweshiek skipperling, more than doubling the capacity of the rearing program. “This is more than just a ray of hope. This is a giant leap forward,” explained Nick Haddad, who leads the Haddad Lab at Michigan State University’s Kellogg Biological Station.

Dave Pavlik, a research assistant at the Haddad Lab, releases a captive-reared Poweshiek skipperling butterfly on a Black-eyed susan. Photo by Lauren Ross.


MNA is proud to protect habitat critical for the Poweshiek skipperling’s survival, and to be part of the important partnership that is working to save this species from extinction. MNA looks forward to continuing participation in this partnership effort to increase the Poweshiek skipperling population in the wild in the coming years.

Ten Years After Major Wildfire, Swamp Lakes Moose Refuge Sees Remarkable Recovery

On June 15, 2012 after burning more than 21,000 acres including part of MNA’s Swamp Lakes Moose Refuge Nature Sanctuary in Luce County, the Duck Lake Fire was officially contained. Now, 10 years later, we are taking a look at what has changed at this sanctuary as a result of the fire.

The sanctuary derives its name from the surrounding area known as the Swamp Lakes which is of significant importance as a large block of wildlife habitat. This area is known to be frequented by moose, gray wolf, pine marten, and numerous other species of wildlife requiring a landscape intermingled with forests and wetlands.

The forest here is dominated by Jack and Red Pines which, once mature, create a dormant understory of easily burning materials—a critical part of the Jack Pine life cycle as their cones will not release seeds except under the extreme heat of fire.

But the Jack Pine isn’t the only benefactor of wildfire. As William Rapai wrote in the July/August issue of Jack Pine Warbler, “Only days after the fire was brought under control, bark beetles moved in to eat the damaged trees. And where there are insects, there are insect-eating birds—including the Black-backed Woodpecker, a species of special concern in Michigan… That woodpecker species is associated with burned areas because one of its primary foods—the bark beetle—attacks trees damaged by fire.”

Water levels in many of the affected areas were very low for the season as seen in this photo from the Swamp Lakes Moose Refuge Nature Sanctuary taken one month after the fire. MNA Archives.

Other species that were observed returning to or newly entering the area shortly after the fire were white-tailed deer, black bear, snowshoe hare, and gray wolf.

Beaver are common to the area, and have been able to expand their territory without human intervention in the years since the fire. At Swamp Lakes Moose Refuge, beaver activity has restored the wetlands and allowed much regrowth to occur.

Possibly the most significant result of the fire is the potential for thousands of acres of new habitat for the Kirtland’s Warbler, which prefer nesting in young (5-20 years old) Jack Pine forests. These formerly endangered neotropical migrants have experienced population recovery after many years of habitat management efforts in the northern Lower Peninsula. While MNA does not have record of Kirtland’s Warbler at the Swamp Lake Moose Refuge Nature Sanctuary, the existence of young Jack Pines in the nearby forest gives hope for future populations.

Not all areas are expected to see the same recovery. Fire suppression efforts resulted in a significant amount of leaf litter and dead wood accumulating in the path of the fire, allowing the fire to burn much hotter and longer (nearly a month) than the soil is able to tolerate. “In some places, the Duck Lake Fire destroyed all the organic matter and microorganisms for some depth,” wrote William Rapai, “Particularly damaging will be the loss of the mycorrhizal fungus that is critical in the lifecycle of many species. The fungus has a symbiotic relationship with plants, helping them to absorb nurtients.”

Live at Swamp Lakes Moose Refuge Nature Sanctuary is abundant as seen in this photo taken from the same location as the photo above, in June 2022. Many beaver inhabit the area, as indicated by the beaver lodge at center. Photo by Andrew Bacon.

A month after the fire, early indications were that the natural communities within Swamp Lakes Moose Refuge would recover without restoration efforts. Given the sanctuary’s wetland composition, the fire has proved beneficial, thinning out the canopy and allowing other plants like bracken fern, blueberry, and leatherleaf to regenerate. MNA will continue to monitor nature’s recovery from the fire and the landscape changes through the years.