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COSEWIC Assessment and Update Status Report on the Margined Madtom (Noturus insignis) in Canada

Technical Summary

Distribution

Extent of occurrence in Canada:

43 500 km²

Extent of occurrence in North America:

280 000 km²

Area of occupancy in Canada:

120 km²

Area of occupancy in North America:

unknown

Population Information

Total number of individuals captured in Canada prior to 1990:

49

Total number of individuals captured in Canada 1990 to 2000:

64+

Generation Time:

2 years

Population Trend:

increasing

Number of sub-populations in Canada:

10 (captured in 10 separate waterbodies)

Is the population fragmented?

Yes, disjunct population inferred from the lack of connectivity amongst the Muskoka, Lanark, Hull, Gatineau and Papineau county waterbodies and the separation between the Canadian and American distributions.

Number of individuals in each subpopulation (range):

1-24 (number of individuals captured from one sampling location)

Number of extant sites in Canada:

10

Number of historic sites from which species has been extirpated in Canada:

0

Does the species undergo fluctuations?

Yes, inferred from the different number of individuals captured when some sites were resampled in subsequent years.

Threats

The margined madtom is influenced by habitat change. Literature records detail the specific habitat requirements of this species although recent captures in the Muskoka Lakes suggest that this species may have a wider tolerance than first reported. Any activity that eliminates riffle areas or slows water flow may limit their population size (Coad 1986). These fish are intolerant of silt covering the rocky substrate (Coad 1986). Siltation may be caused by natural erosion, agricultural or urban development. Low numbers of individuals and a limited amount of suitable habitat restrict the population size and distribution of the margined madtom, which is at the northern limit of its range in Canada. The collection of specimens may also have contributed to the depletion of populations already low in numbers.

Rescue Potential

Does this species exist outside of Canada?

Yes

Is immigration known or possible?

Yes, immigration is plausible as nearest U.S. site in New York is 130 km away from Canadian site in Gatineau Park Quebec. Individuals may have been transferred to new locations by anglers using this species as bait.

Would individuals from the nearest foreign population be adapted to survive in Canada?

Yes

Would sufficient suitable habitat be available for immigrants?

Yes

Assessment of Status

Low numbers of individuals, limited habitat, disjunct distributions, and fluctuating population sizes may affect the continued survival of the margined madtom in Canada. Noturus insignis was captured in increasing numbers at all historic sites and at several new locations suggesting stable or possibly increasing population sizes, although the new records of capture may be the result of increased and more rigorous sampling efforts or recent introductions. Also, the possibility of broader habitat tolerances than once thought indicates that the habitat preferences of this species may be less restrictive. It is also possible that the number of individuals appeared to fluctuate due to the difficulty with capturing specimens with inappropriate gear. If there are no adverse changes to the margined madtom’s habitat, species numbers should remain stable. Given these considerations, the status of the margined madtom could be downlisted, but it should not be de-listed since few mature individuals have been captured and there are no records of juveniles or breeding from Canadian waters.