Coregonus hoyi is endemic to the Great Lakes basin of North America where it inhabited all lakes except Lake Erie. This species was probably extirpated from Lakes Ontario and Nipigon and is threatened in Lake Michigan and declining in Lakes Superior and Huron.

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Great Lakes basin; but not in Lake Erie. Possibly extirpated from Lake Ontario and Lake Nipigon.

Coloration is silvery with some pink and purple iridescence, with a greenish tinge above lateral line and a silvery white ventral surface (Downs et al, 1998). These fish are distinctly laterally compressed with greatest body depth in front of dorsal fin. Coregonus hoyi has a long head and small eye, snout short or pointed with terminal mouth, lower jaw protruding past upper jaw with distinct tubercle, and a maxillary extending posteriorly to below the anterior portion of the eye. Gill raker number 37-50. A small dorsal adipose fin is present. The following is a characterizatin of the fins: dorsal 1, rays 9-11; caudal fin distinctly forked; anal rays 11-12; pelvic rays 11; pectoral rays 15-16. The scales are cycloid. It has 55-57 vertebrae. Females reach a slightly larger size than males (Crossman and Scott, 1973).

Average mass: 227 g.

Average length: 23 cm.

Other Physical Features: ectothermic ; bilateral symmetry

Sexual Dimorphism: female larger

Length: 30 cm

• Freshwater

Bloaters exist in both pelagic and benthic regions of deep, freshwater lakes. During the day Coregonus hoyi is found on or near the bottom, but it moves upwards in the water column at night. Bloaters are most abundant between 40 and 110 m, but have rarely been reported as shallow as 10 m and as deep as 180 m.

Range depth: 10 to 180 m.

Average depth: 40-110 m.

Habitat Regions: freshwater

Aquatic Biomes: pelagic ; benthic ; lakes and ponds

Habitat Type: Freshwater

Comments: Large lakes, usually at depths of about 30-190 m. Larvae in Lake Michigan often are near the bottom at about 100 m (Scott and Crossman 1973). Spawns over all sorts of bottoms usually at about 50-100 m (Becker 1983).

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Coregonus hoyi is primarily a pelagic feeder, with occasional bottom feeding, but habits and diet appear to be variable between bodies of water. Analysis of stomach contents revealed primarily Mysis relicta and Pontoporeia affinis, both near bottom dwelling plankton. Copepods dominated some stomachs, indicating pelagic feeding. Fish eggs and fingernail clams were also found in some stomachs. Vertical migration on an individual basis is hypothesised to be driven by migration of invertebrates in the water column (TeWinkel and Fleischer, 1999). High potential feeding rates at cold temperatures allow bloaters to feed and grow during the winter when many competitors are inactive. Increased activity at cold temperatures also allows the bloater to take advantage of high early spring zooplankton abundance which its competitors cannot do.

Foods eaten: Mysis relicta, Pontoporeia affinis, Cyclops bicuspidatus, Diaptomu, copepods, fish eggs, fingernail clams 

Animal Foods: eggs; mollusks; aquatic crustaceans; zooplankton

Primary Diet: carnivore (Eats eggs, Eats non-insect arthropods); planktivore

Comments: Eats mainly crustaceans, including zooplankton and crustaceans on or near bottom (Becker 1983). Benthic feeding is more common now than in past, probably due to competitive interactions with alewife (Crowder 1984).

Coregonus hoyi is a deep water planktivore that provides an important trophic link between zooplankton and top predators. After initial population declines due to competition with and predation by introduced alewives and rainbow smelt, C. hoyi populations increased greatly in response to alewife and smelt predation by introduced Pacific salmonids. This change in fish community resulted in a shift in dominance from epi- and metalimnetic planktivores (alewife) to a hypolimnetic benthivore (bloater). This can affect the abundance of prey for pescivores, prey abundance for the forage fish, and possibly water clarity and primary production.

Historically, the main predator of Coregonus hoyi has been the lake trout (Salvelinus namaycush). After parasitic sea lampreys decimated the lake trout populations in the Great Lakes, introduced Pacific salmonids have become the dominant predators of C. hoyi. Populations can also be limited by competition and predation from alewives.

Coregonus hoyi is heavily parasitized, with common parasites including: Botriochocephalidae, Nematoda, Trematoda, Cestoda, Acanthocephala 

Known Predators:

• lake trout (Salvelinus namaycush)
• "salmons, salmonids, and trouts (Salmonidae)"
• alewives (Alosa pseudoharengus)

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 1 - 5

Comments: Evidently remains only in the three largest of the Great Lakes.

Unknown

Comments: Still abundant in lakes Superior, Michigan, and Huron (Evers 1994:309).

Coregonus hoyi remains in the larval state for aproximately 24 days with a length range of 8.6-14.9 mm. Larvae are most frequently located near the bottom at depths between 90 and 110 m in water with temperatures not exceeding 4.7 degrees C. Mature C. hoyi reach lengths of 200-250 cm, with size and growth rate variable between lakes.

Development - Life Cycle: metamorphosis

Females have a lifespan of 10 to 11 years, and reach a slightly larger size than males, which live to an age of 9 years.

Range lifespan

Status: wild: 9 to 11 years.

Average lifespan

Status: captivity: 10 years.

Spawning generally takes place in February and March, but some spawning occurs throughout the year as indicated by observations of ripe, nearly ripe, and spent male and females in almost all months. Spawning occurs over almost all bottom types at a depth between 36 and 90 m. Egg production ranges from 3000 to 12000 per female, with larger females producing more eggs than smaller individuals. The average number of eggs per ounce of fish is 1241 with little variation. The eggs are relatively large with an average diameter of 1.95 mm.

Breeding season: February -March

Range number of offspring: 3000 to 12000 eggs.

Average number of offspring: 7500.00.

Key Reproductive Features: seasonal breeding ; sexual ; fertilization (External )

There is no parental care in this species.

Parental Investment: no parental involvement

Spawns mostly in fall and winter but probably also at other seasons as well. Eggs hatch in about 4 months. Sexually mature in 2-3 years (Becker 1983, Smith 1985).

• Needs updating

Overfishing of other species of ciscoes has reduced populations, and shifted more pressure to Coregonus hoyi. Unchecked, this additional fishing effort could devastate Coregonus hoyi populations, as it has done to other ciscoe species. The bloater is not currently given special status under the Endangered Species Act. The IUCN classifies Coregonus hoyi as vulnerable. Fluctuations in the populations of bloaters have been inversely related to the introduced alewive, which competes for resources. Stocking of pacific salmonids in order to control alewive populations has allowed the Lake Michigan Coregonus hoyi population to rise from an estimated 4,000 metric tons in 1974 to 300,000 metric tons in 1987.

US Migratory Bird Act: no special status

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

IUCN Red List of Threatened Species: vulnerable

Canada

Rounded National Status Rank: N4 - Apparently Secure

United States

Rounded National Status Rank: N4 - Apparently Secure

Rounded Global Status Rank: G4 - Apparently Secure

Reasons: Formerly occurred in Lake Nipigon and all of the Great Lakes except Lake Erie; now evidently extirpated in lakes Ontario and Nipigon and declining in lakes Superior and Huron; introduced alewife (food competitor) apparently contributed to the decline.

Degree of Threat: B : Moderately threatened throughout its range, communities provide natural resources that when exploited alter the composition and structure of the community over the long-term, but are apparently recoverable

Comments: Alewife introductions may cause population declines.

Global Protection: Unknown whether any occurrences are appropriately protected and managed

Bloaters have no known negative impact on people.

Coregonus hoyi is an important component in the diet of larger salmonid species. Many of these salmonids are very valuable as gamefish, bringing economic benefit to the waters they inhabit. As the larger ciscoes have been depleted through overfishing, the smaller Coregonus hoyi has become an increasingly important component of commercial catches. Commercial catches of Coregonus hoyi, like other ciscoes are primarily smoked and distributed for human consumption.

Positive Impacts: food

Comments: Populations outside Great Lakes drainage, formerly included in C. HOYI, now are assigned to C. ARTEDII or C. ZENITHICUS (Scott and Crossman 1973).