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Recovery Strategy for Paddlefish (Polyodon spathula) in Canada (Proposed)
Feasibility of Recovery
Recovery feasibility is determined according to four criteria outlined in Government of Canada (2006):
- Are individuals capable of reproduction currently available to improve the population growth rate or population abundance?
Yes. Although the paddlefish is extirpated from the Great Lakes, they are still found throughout the United States and its populations are supplemented by hatcheries. Artificial propagation using individuals from extant American populations could be undertaken to re-establish Canadian populations, if deemed appropriate.
- Is sufficient suitable habitat available to support the species or could it be made available through habitat management or restoration?
No. Disagreement exists as to whether Great Lakes paddlefish records represent resident populations or vagrants from the Ohio River and/or Mississippi River. Paddlefish are highly mobile and undertake extensive movements often associated with spawning. Spawning migrations of more than 300 km are common in one Missouri population (Russell 1986), and, in another study, one tagged paddlefish was recaptured almost 2000 km downstream (Rosen et al. 1982). A report of paddlefish in Lake Michigan, although the record was felt to be improbable, was suggested by Greene (1935; cited in Becker 1983) to be the result of the fish entering the lake through the Chicago Canal. Hubbs et al. (2004) identified a number of natural (floodwaters that connected Mississippi River and Great Lakes basin headwaters) and man-made connections to the Great Lakes (canals built in the early 1800s to join Lake Erie and Ohio River, and Mississippi River to Lake Michigan) that have served to change fish species distributions. Further, Cavender (1987) suggested that the lack of paddlefish remains from archeological excavations in northern Ohio was evidence of it being either exceedingly rare in Lake Erie or introduced after the European colonization. Trautman (1957) favoured a pre-Columbian invasion, with a small relict population in Lake Erie present before the canal building.
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. Therefore, recovery actions for habitat management or restoration for this species would not be appropriate.
- Can significant threats to the species or its habitat be avoided or mitigated through recovery actions?
No. In other parts of its range, the paddlefish has declined as a result of destruction of spawning grounds, exploitation, dam construction, river channelization, dewatering of rivers and pollution (Carlson and Bonislawsky 1981). Trautman (1957) speculated that its extirpation could have resulted from dams on Lake Erie tributaries blocking upstream spawning migrations and/or destroying its spawning habitat. Alternatively, Becker (1983) felt the Great Lakes populations of paddlefish were encountered on their way to natural extirpation. It is not known why paddlefish disappeared from Canada. Therefore, it is not feasible to identify associated recovery actions to address threats to species recovery.
- Do the necessary recovery techniques exist and are they demonstrated to be effective?
Yes. Techniques to artificially propagate paddlefish exist (Mims 2001). Stocking of fingerlings is being used in a number of jurisdictions in the United States to supplement existing stocks where natural recruitment is insufficient to maintain populations, or to recover populations at the periphery of its native range (Graham 1997).
Regulation of river flows by dams during spring can disrupt paddlefish spawning by altering river temperatures and discharge necessary to trigger spawning. Dams can also impede upstream migrations to spawning areas (Jennings and Zigler 2000). Discharge below dams could be manipulated to more closely resemble the natural spring hydrograph. Habitat suitability curves presented in Crance (1987) provide guidance for making such adjustments. Dams that represent migration barriers to upstream spawning areas could be either removed or fitted with fish passage structures. The efficacy of fish passage structures is, however, unknown for paddlefish (Jennings and Zigler 2000).
Improvements to water quality in non-wadeable Ohio rivers have also been associated with greater abundance and distribution of paddlefish (Yoder et al. 2005).
However, if the four individuals found in Canada represent vagrants, recovery techniques should not be employed for this species.
In conclusion, it has been determined that recovery of the paddlefish in Canada is not feasible as only four individuals have ever been found in Canada. There is no evidence that there were ever any reproducing populations in Canada, and it is likely the four individuals collected in the Canadian Great Lakes in the late 1800's and early 1900's represented vagrants from the United States.
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