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Background

 

In Canada, the past occurrence of paddlefish (Polyodon spathula) is known only from four individuals collected from the Great Lakes basin, the most recent in 1917. However, some authorities question the validity of Canadian records, as authentication of the records has proven difficult (Parker 1987, 1988, COSEWIC 2000).  In the United States, the paddlefish was never common in the Great Lakes; it was known with certainty only from Lake Erie, where there were at least two well-authenticated records, both before 1910 (Van Meter and Trautman 1970, NatureServe 2006).  It has been extirpated from Maryland, Michigan and New York, which are all peripheral to the species range and never represented a significant portion of it’s distribution (NatureServe 2006).  Currently, the paddlefish is considered extirpated from the American Great Lakes basin.  Canada never represented a significant part of its distribution. 

Disagreement exists as to whether the Canadian Great Lakes paddlefish records represent an historic resident population or were vagrants from the Ohio River and/or Mississippi River.  Becker (1983) felt that the Great Lakes populations of paddlefish were encountered on their way to natural extirpation.  The 1987 Committee on the Status of Endangered Wildlife in Canada (COSEWIC) paddlefish status report states that the Canadian records represent a relict population; however, under current COSEWIC guidelines, it is likely that the species would be termed a vagrant, as there is no evidence of natural reproduction occurring in Canada.

Paddlefish was designated as Extirpated by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 1987 and this designation was re-confirmed in 2000 using the same information as the 1987 designation.  The International Union for the Conservation of Nature considers Paddlefish to be Vulnerable, and its American Fisheries Society Status is Special Concern.

1.1 Species Assessment Information from COSEWIC

Common Name: paddlefish Scientific

Name: Polyodon spathula

COSEWIC Status: Extirpated

COSEWIC Reason for designation: Last reported in Canada in 1917, the 1987 COSEWIC report on the species suggested the paddlefish was lost due to exploitation and habitat degradation.

Canadian Occurrence: Formerly Ontario COSEWIC

Status History: Last recorded in Canada in 1917. Designated Extirpated in April 1987. Status re-examined and confirmed in May 2000. May 2000 assessment based on new quantitative criteria applied to information from the existing 1987 status report.

1.2 Description

The following description is adapted from Trautman (1981) and Becker (1983).  The paddlefish (Figure 1) is a large, primitive fish with a typical specimen having an average total length of 0.5-1.2 m and weighing 0.9-9 kg.  Larger individuals can attain lengths of 2 m and weights of more than 80 kg.  The paddlefish has a long, paddle-shaped snout which is approximately 1/3 the length of the fish, and a very long, pointed, opercular flap that nearly reaches the pelvic fin.  It has no scales aside from a few rhomboid scales on the tail.  Colouring is gray to blue-black dorsally and laterally and whitish ventrally.  The urogenital papilla is somewhat raised in males while in females it is more flattened and softer.    

paddlefish

Figure 1. Paddlefish (Polyodon spathula) (photo by B. Cudmore (DFO), 2006)

1.3 Populations and Distribution

Distribution:

GlobalRange: In the United States, the paddlefish occurs in larger rivers throughout 22 eastern and central states (NatureServe 2006) (Figure 2).  It occurs in Alabama, Arkansas, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Minnesota, Mississippi, Missouri, Montana, Nebraska, North Dakota, Ohio, Oklahoma, South Dakota, Tennessee, Texas, Virginia, West Virginia and Wisconsin.  It has been extirpated from Michigan, New York and Pennsylvania.  It is unclear whether populations remain in North Carolina where it was found historically. 

North american distribution of paddlefish

Figure 2. North American distribution of paddlefish (information from Page and Burr 1991).

CanadianRange:Very few Canadian records of paddlefish exist (Figure 3).  The only records are from the late 1800s and early 1900s, when individuals were collected from Lake Huron, near Sarnia (two specimens), the Spanish River, Georgian Bay (one specimen), and in Lake Helen on the Nipigon River (one specimen) (Halkett 1913).  However, authentication of these records has proven difficult and some authorities question the validity of Canadian records (Parker 1987, 1988, COSEWIC 2000).  The last record of paddlefish in Canada is from 1917.

Canadian records of paddlefishRecords of Paddlefish in Canada

Figure 3. Canadian records of paddlefish (from Mandrak and Crossman 1992).

Percent of Global Range in Canada: This figure is unknown; however, it is likely less than 1% as very few specimens were ever collected in Canada and it would have been at the northern edge of its range.

Population Size and Status:

Global Population Size and Status: The population size of the paddlefish in the United States is unknown but is believed to range from 2500 to more than a million individuals (NatureServe 2006). 

Table 1. Canadian and American national and sub-national natural heritage status ranks for paddlefish (NatureServe 2006).
Canada(NX)Ontario (SX)
United States(N4)Alabama (S3), Arkansas (S2?), Illinois (S2S3), Indiana (S3), Iowa (S3), Kansas (S3), Kentucky (S4), Louisiana (S3), Michigan (SX), Minnesota (S2), Mississippi (S3), Missouri (S3), Montana (S1S2), Nebraska (S2), New York (SX), North Carolina (SH), North Dakota (SNR), Ohio (S2), Oklahoma (S1S2), Pennsylvania (SX), South Dakota (S4), Tennessee (S3), Texas (S3), Virginia (S1), West Virginia (S1), Wisconsin (S2?)

Canadian Population Size and Status:In Canada, the paddlefish has been designated as Presumed Extirpated nationally (NX) and provincially (SX) by NatureServe, as no specimens have been collected since 1917.  It has also been designated as Extirpated by the Ontario Ministry of Natural Resources.

Nationally Significant Populations:  As very few paddlefish specimens were ever collected in Canada, it is unknown whether they were part of a larger population or strays that made their way into the Great Lakes basin through canals.  As such there are no nationally significant populations in Canada.

1.4  Needs of Paddlefish         

1.4.1 Habitat and Biological Needs

Historically Occupied Habitat: Paddlefish specimens collected in Canada at the turn of the century were captured from the inshore areas of the Great Lakes or from moderately large tributaries of the Great Lakes (Halkett 1913).  Two specimens were collected from Lake Huron, near Sarnia, Ontario; one specimen was taken from the Spanish River, Georgian Bay; and one specimen was captured in Lake Helen, Nipigon River (Halkett 1913).  Habitat data are not available for these capture locations.   

In the United States, adult paddlefish inhabit the slow waters of medium to large rivers, channels, oxbows, impoundments, backwaters and river-margin lakes (Becker 1983, Parker 1988, Etnier and Starnes 1993, NatureServe 2006).  In un-impounded, un-channelized rivers, adult paddlefish can be found downstream of submerged sandbars, typically at depths of 2 – 3 m, during late spring through early fall.  Sandbars reduce the current velocity directly downstream.  Preferred velocities in this situation range from 0 to 30 cm/s.  From late fall through early spring, adult paddlefish are found in deeper waters (i.e. > 3 m) (Rosen et al. 1982, Crance 1987).  Preferred substrates are unknown but the species has been reported over mud bottoms (Becker 1983).  In regulated rivers, paddlefish congregate in small areas below structures such as sandbars, protected bays, dikes, bridge supports, and eddies in the tailwaters below dams where velocities are less than 0.3 m/sec (Southall and Hubert 1984, Moen et al. 1992, Jennings and Zigler 2000).  When these structures are unavailable to provide refuge from high current conditions, paddlefish select nearshore habitats with low current velocities (Rosen 1976; cited in Jennings and Zigler 2000).

Currently Occupied Habitat: Currently there are no known occupied habitats in Canada.

Habitat Trends:  The few records of capture from the Great Lakes provide little or no information regarding the characteristics of habitats historically utilized by Great Lakes populations of paddlefish.  Without knowing specifically the habitats occupied in the Great Lakes, it is not possible to identify trends in paddlefish habitat.  

Habitat Protection/Ownership:  Paddlefish habitat is protected under the general fish habitat provisions of the federal Fisheries Act.  The paddlefish and/or its habitat is also protected under Ontario’s Lakes and Rivers Improvement Act, Environmental Protection Act, Environmental Assessment Act and Water Resources Act

General Biology:  Nothing is known regarding the biology of the paddlefish in Canada and all available information comes from populations in the United States.  Paddlefish spawn in the spring, usually during April and May, when water temperatures range from approximately 10-17°C (Purkett 1961, Wallus 1986, Lein and DeVries 1998).  Spawning is preceded by an upstream migration to the vicinity of the spawning areas where the fish congregate in deep areas of the river (Purkett 1961, Pasch et al. 1980).  Large increases in water velocity trigger paddlefish to move into spawning areas and spawning is triggered by increased water flow (Purkett 1961, Pasch et al. 1980, Jennings and Zigler 2000).  Optimal water velocities range from 60 – 140 cm/s (Crance 1987).  Paddlefish spawn over gravel bars and other hard surfaces such as rock and rip/rap, in areas with enough current to keep eggs free from silt (Pasch et al. 1980, Wallus 1986).  Reported water depths at spawning locations range from 2 – 12 m, but optimal depths probably range from approximately 3 – 6 m (Crance 1987).  In Missouri, spawning occurred after water levels rose 2.7 m and water temperatures were 16.1°C.  Eggs become adhesive upon fertilization and immediately stick to the clean gravel substrate (Purkett 1961).  Hatching occurs in seven days or less at 18.3°C – 21.1°C (Purkett 1961).  After hatching, larval paddlefish begin swimming continuously from bottom to surface, resting only when gliding back to the bottom.  This behaviour helps remove the larvae from the receding waters of temporarily flooded spawning sites (Wallus 1986).  Current velocities of 30 – 122 cm/s are required to transport newly hatched larvae to nursery habitats.  Velocities in nursery habitats are generally low, allowing larvae to feed without expending large amounts of energy (Crance 1987).

1.4.2 Ecological Role

Paddlefish primarily feed on zooplankton and occasionally consume small insects, insect larvae and small fishes (Jennings and Zigler 2000).  Walleye (Sander vitreus) and sauger (S. canadensis) can be significant predators on young paddlefish in American reservoirs (Mero et al. 1994).

1.4.3 Limiting Factors

Population growth is limited by late sexual maturity and intermittent spawning by females.  Paddlefish require a long period of time to become sexually mature, which is estimated at 7 years for males and 9-10, possibly up to 12, years for females (Parker 1987, 1988, NatureServe 2006).  While male fish are able to spawn each year, several studies suggest that females require 2 to 5 years to develop mature ova before spawning again (Jennings and Zigler 2000).

In the spring, spawning is generally preceded by an upstream migration (sometimes over extremely long distances) to the spawning area.  Successful migration to spawning habitats and initiation of spawning is dependent on barrier-free migration routes and specific water temperatures and flow levels.  Paddlefish recruitment is therefore vulnerable to natural and man-made changes to these factors.

1.5 Threats

Specific factors that were a threat to any paddlefish individuals in Canada are unknown.  In the United States, the primary factors responsible for changes in distribution and abundance of paddlefish across its range are: destruction of spawning grounds; blockage of movements by dams; channelization and elimination of backwater areas; dewatering of streams; industrial pollution and over-harvest (Carlson and Bonislawsky 1981).  Trautman (1957) speculated that its extirpation from Lake Erie could have resulted from dams on tributaries blocking upstream spawning migrations and/or destroying its spawning habitat.  

1.7 Knowledge Gaps

Unresolved Issues: It is unclear whether populations of paddlefish ever existed in Canada.  Disagreement remains as to whether the four Canadian paddlefish records from the Great Lakes represent resident populations or vagrants from the Ohio River and/or Mississippi River.  If Canadian records of paddlefish represent vagrants from the Ohio River or Mississippi River basins, then paddlefish populations and associated habitats never existed in Canadian waters.  It is important to remember that the data used for the COSEWIC designation is over twenty years old and the species was designated as Extirpated prior to the implementation of SARA.  COSEWIC’s Operating and Procedures Manual is now more explicit about potential vagrancy of species, and therefore more guidance is provided to consider this species.  It is likely paddlefish would not be eligible for assessment by COSEWIC as there is no evidence of natural reproduction in Canada.  Therefore, it is recommended that further study be conducted to confirm paddlefish vagrancy in Canada.

Threat Clarification Research Requirements: Specific reasons as to why the paddlefish disappeared from Canada (if populations ever existed here) are unknown.