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From the Mississippi basin to the Hudson Bay, the lake sturgeon (Acipenser fulvescens) is making its recovery after nearly becoming extinct at the beginning of the twentieth century from overharvesting. This prehistoric and long-lived fish is a great emblem of the Great Lakes region and is also an integral component of the Great Lakes ecosystems. Learn more about the sturgeon's past decline and current trends, as well as the ongoing concerns and conservation success stories of one of the Great Lakes region's oldest indigenous species.

Overview

Lake sturgeon (Acipenser fulvescens) are the largest indigenous fish found in the Great Lakes Basin and represent an important biological component of the Great Lakes fish community that can serve as an indicator of the overall Great Lakes’ ecosystem’s health and diversity.1 Lake sturgeon populations have been greatly impacted since the late 1800s, with almost all populations dramatically reduced or extirpated as a result of overfishing, habitat loss, dam construction and pollution.

 

Current Range & Status

Lake sturgeon are found within the Great Lakes Basin, the Mississippi River and Hudson Bay, and are considered either threatened or endangered by 19 of the 20 states within its original U.S. range.2 Lake sturgeon are also protected in the Canadian waters of the Great Lakes with closed seasons, size limits, creel limits and gear restrictions. These ancient fish have existed for 136 million years (the Upper Cretaceous period), a time when dinosaurs thrived, and have lived in the Great Lakes since the last glaciation formed the lakes around 10,000 years ago. Within the Great Lakes Basin, only 5 rivers have a spawning run of 200 or more adults and only one river exceeds the minimal viable population spawning run target of 350 adults.3

 

Description

Lake sturgeon can reach lengths of more than eight feet with weights of over 200 pounds.411 Their bodies are heavy and torpedo-shaped, with young sturgeon being angular (5-sided), but adults being rounded. Lake sturgeon do not have scales, but instead host “armor” in the form of boney, shell-shaped plates, or scutes, arranged in five rows – two on each side and one along the back running the length of the body. The scutes come to a peak with a sharp-pointed spur, but as fish age, the scutes smooth out. Head of a young lake sturgeon, with barbels and mouth visible.Lake sturgeon have long tapering snouts that get shorter and blunter with age, and four barbels (whisker-like tactile organs that help them locate food) on the lower snout, a lower lip with two lobes, and spiracles (respiratory vents just forward of the gills). With no teeth, lake sturgeon rely on protruding their tubular mouths to suck up food along with silt, gravel and other bottom materials; debris is later expelled through the gills. Lake sturgeon have a short, stout, partly naked caudal peduncle (narrow part of the fish’s body to which the tail fin is attached), and the upper lobe of their tail fins are pointed without threadlike extensions (as some other sturgeon species possess). Young sturgeon are gray or brown dorsally (on their backs) with dusky dorsal and lateral blotches, while adults tend to be gray to olive dorsally and white ventrally (on their stomachs).

 

Habitat

Lake sturgeon were historically abundant throughout the Great Lakes and were a dominant component of the nearshore benthivore (bottom feeding) fish community, with populations estimated in the millions in each of the Great Lakes.5 Sturgeon inhabit large river and lake systems and can be considered a nearshore, warmwater species with water temperature and depth preferences of the low 50s to mid-60s F and 15-30 feet, respectively. As benthivores, lake sturgeon feed on small invertebrates like crayfish, clams, snails, leeches and insect larvae. With the introduction of invasive zebra and quagga mussels in the Great Lakes, some believe lake sturgeon may benefit from additional food sources. Sturgeon spawn in shallow (1-15’ deep) swift-moving stream and river rapids, as well as in wave action over clean gravel shoals, rocky ledges and around rocky islands. Scientists know little about the seasonal movements of lake sturgeon; while some adult lake sturgeon may remain in a small territory during the summer months, others move long distances.

 

Life History & Reproductive Biology

Female sturgeon reach sexual maturity at between 14 and 33 years of age, though most often between ages 24-26, and can live 80 to 150 years.6 Male sturgeon typically live about 55 years and reach sexual maturity at 8 to 12 years of age, though can take up to 22 years.  Female lake sturgeon spawn once every 4 to 9 years, while males spawn every 2 to 7 years.  As a result of these interrupted spawning cycles, only 10-20% of adult lake sturgeon spawn within a given season. Spawning typically occurs between April and June when water temperatures reach 53-64F, though in the warm spring of 2012, sturgeon began spawning in mid-March.  Lake sturgeon exhibit homing behavior in which adult fish return to the streams in which they were born, often migrating great distances up rivers in spring.

Spawning lake sturgeon

Male sturgeon reach spawning sites before females, often cruising the spawning area in groups of more than eight fish, and are frequently so close to the bank they can easily be captured.7 As soon as a ripe female enters the group, spawning begins with several males attending her by swimming alongside her in the same direction, usually against the current. Once spawning occurs, one or more males vibrate simultaneously alongside a female, with the average spawning act lasting only 5 seconds. Spawning activity for one female may last from 5 to 8 hours, but may take a day or more. Males release milt (sperm) at the same time a female extrudes anywhere from 50,000 to 700,000 black, highly adhesive eggs.  Hatching time is determined by water temperature, with hatching occurring after about 8 days in temperatures of 55-57F, while it may take as little as 5 days at warmer temperatures in the low 60s. Within 12 to 14 days of hatching, the fry (newly hatched fish) are one inch long and have fully developed mouths and barbels.

Several states including Michigan and Wisconsin sponsor efforts to protect sturgeon during their spawning period because the fish are vulnerable to poaching while in shallow waters and oblivious to human activity.8 Variously known as “Sturgeon Guard” and “Sturgeon Patrol,” these efforts are coordinated by state Departments of Natural Resources, and enlist the help of hundreds of volunteers to monitor spawning sites 24 hours a day while the fish are present.

Historic photo of a lake sturgeon

 

Reasons for Decline

Most early information about Great Lakes lake sturgeon populations comes from commercial harvest data.9 Prior to 1850, commercial fishermen considered lake sturgeon a nuisance and the fish’s slaughter was widespread. Later, as the economic importance of the species was recognized, lake sturgeon became a huge component of the commercial fishing industry. Between 1879 and 1900, over 4 million pounds of lake sturgeon were harvested annually on average in the Great Lakes, though in 1885, 8.6 million pounds were caught. By 1900, heavy fishing had decimated lake sturgeon populations and little is known about the species status through most of the 20th century.

Lake sturgeon visible below a dam

In addition to the widespread commercial overexploitation of the species, habitat loss and degradation hastened the lake sturgeon’s decline. Tens of thousands of dams were installed on Great Lakes tributaries during the 20th century, and these structures continue to block lake sturgeon from reaching their historic spawning grounds. Additionally, extensive deforestation and agriculture produced heavy erosion and siltation that covered spawning gravel within Great Lakes tributary streams and rivers.10 Pollution from nutrient and contaminant-loaded runoff further harmed the species, and researchers have documented low hatching success and larval deformities among populations in polluted streams.

Today, only remnant populations remain in many tributaries lake sturgeon historically used, while many more historic tributaries had their sturgeon populations extirpated long ago. Since lake sturgeon take many years to reach sexual maturity, and even then only spawn a few times each decade, the species’ reproductive biology further complicates recovery.11  However, lake sturgeon populations throughout the Great Lakes appear to be recovering, albeit very slowly over multiple generations. Recent scientific research finds age-class structure within populations and increasing numbers of juvenile sightings, which indicates natural reproduction is occurring.

 

Pressing Conservation Concerns

Numerous lake sturgeon management plans identify a need for accumulating additional biological information on sturgeon. Wisconsin’s Lake Sturgeon Management Plan calls for a comprehensive understanding of lake sturgeon biology, population dynamics, habitat needs, movement and migration patterns, water quality requirements, fisheries interactions, and the short and long-term effects of human-induced impacts.12 Additionally, the report finds a lack of population level information for the majority of the state’s river systems, and calls for greater information in order to set biologically sound population goals; it further calls for the development of standardized collection techniques for population, reintroduction, catch and harvest assessments. The report also indicates more needs to be known about the species’ early life history requirements for successful recruitment, as well as the seasonal habitats the species requires so restoration opportunities can be identified and guided.

Since the vast majority of historic lake sturgeon spawning runs are blocked by dams, the species’ distribution has been dramatically altered. The Wisconsin management plan goes on to say that for lake sturgeon to exist and flourish, it is critical to provide passage opportunities at dams, reduce the occurrence and intensity of unnatural water level fluctuations, and sustain or improve river habitats and wetlands conducive to reproduction, growth and survival.13

 

Recovery Activities

According to the Great Lakes Restoration Initiative (GLRI), over 40 partnerships exist throughout the Great Lakes to conserve, protect and enhance lake sturgeon populations through numerous cooperative efforts.14 GLRI funding hopes to accelerate sturgeon rehabilitation in the basin through on-the-ground habitat enhancement and restoration projects including restoring fish passage to historical spawning areas, as well as supporting the rearing, stocking and assessment of sturgeon populations. GLRI funding will also support a coordinated, multi-agency investigation of environmental contaminants in sturgeon and will improve evaluation and prioritization of habitat restoration projects.

Of the 26 tributaries that currently support sturgeon in the Great Lakes, 16 will benefit from either installation of stream-side rearing facilities to enhance recruitment, or habitat enhancement through the GLRI.15 As a result of GLRI-enhanced sturgeon management and rehabilitation efforts, a basin-wide total of 25,000 fingerling lake sturgeon will be stocked to enhance existing small but remnant populations. A boosted stocking effort through FY2014 is expected to promote lake sturgeon spawning success and push populations toward self-sustaining levels. Habitat assessment and enhancement projects will be implemented on 20 existing sturgeon streams, and fish passage will be provided on two barriers that limit sturgeon access to upstream habitat.

In addition to the GLRI efforts detailed above, other major efforts call for developing proper flow management at dams (e.g., run-of-river mode) to benefit sturgeon and other tributary species, requiring all hydroelectric facilities to provide enough flow to allow completion of each lake sturgeon life stage in bypassed and natural river channels, and requiring provisions for fish passage during FERC re-licensing of tributary dams.16

Lake sturgeon eggs and juvenile fish raised as part of restoration efforts at a streamside rearing unit