Paddlefish (Polyodon spathula) COSEWIC assessment and status report: chapter 5
Habitat
Habitat requirements
There is little or no information on paddlefish habitat preferences in Canada. Paddlefish specimens collected from Canada at the turn of the 20th century were taken from inshore areas of the Great Lakes or from moderately large tributary rivers of the Great Lakes (Halkett 1913; Parker 1988).
In the U.S., paddlefish are reported from large slow-moving waters of the Mississippi, Missouri and Ohio River system (Pflieger 1975; Becker 1983; Rosen et al. 1982; Parker 1988; Etnier and Starnes 1993; NatureServe 2007). There, the habitats preferred by paddlefish are seasonally variable, and directly linked to food supply (they are invertebrate filter feeders), and flow rates (Southall and Hubert 1984). During the spring spawning period, paddlefish were found to congregate below dams and in tailwater areas. Spawning in the Missouri river occurs in fast, shallow water over gravel bars (Stancil et al. 2002). At other times of the year they utilized main channel borders, backwater areas and areas with reduced current at water depths in excess of 1.5 m (Rosen et al. 1982; Burkhead and Jenkins 1991). These reduced current velocities ranged from 0 to 30 cm/sec (Southall and Hubert 1984; Moen et al. 1992; Jennings and Zigler 2000). In late fall, they may move to deeper areas (>3 m) to overwinter (Rosen et al. 1982; Crance 1987). They are known to congregate in small areas below structures such as sandbars, protected bays, bridge supports and eddies in the tailwaters below dams. When such structures are unavailable to provide refuge from high current velocities, they may select nearshore habitat with low current velocities (Southall and Hubert 1984; Moen et al. 1992; Jennings and Zigler 2000).
It is possible to rear paddlefish in large impoundments, but paddlefish must have access to large, free-flowing rivers for successful spawning (Russell et al. 1980; Russell 1983). Spawning needs include water temperatures of 16°C, clean gravel substrate for egg attachment, and increased water flow to trigger spawning (Russell 1983).
Trends
Trends in paddlefish habitat quality in the Great Lakes are similar to those affecting lake sturgeon (see Dick et al. 2006). Many of the structures that may have blocked upstream migration around the turn of the 20th century are still present or have been replaced by other structures that also block migration. The rate of habitat change is unknown. Site-specific modification to migratory routes may benefit U.S. populations, but would not impact the status of this species in Canada. In the U.S., barriers to migration and loss of suitable spawning habitat have been identified as causes of range fragmentation.
The importance of habitat loss to paddlefish populations is not well documented; the loss of habitat was considered far less important than overfishing in their decline (Parker 1988; NatureServe 2007). In fact, many of the populations were reduced to remnant status prior to major environmental perturbations affecting paddlefish habitat.
Habitat destruction and river modification are the most obvious changes affecting paddlefish distribution and abundance. Construction and operation of dams on mainstem streams have had severe impacts. Dams eliminated traditional spawning sites (paddlefish can live in reservoirs but need streams for spawning), interrupted natural spawning migrations, altered water flow regimes, dewatered streams, and eliminated backwater areas that were important as nursery and feeding areas (see Graham 1997; Pflieger 1997). Dams have curtailed the long-range movements that may be required to maintain populations (Dillard et al. 1986). It is likely that structural changes in big river systems have adversely affected most of the species’s original habitat (Sparrowe 1986).
Protection/ownership
Paddlefish habitat may be protected by the Canadian Environmental Assessment Act, Canadian Environmental Protection Act, Federal Fisheries Act, Canada Water Act, Ontario Environmental Protection Act, Ontario Environmental Assessment Act, Ontario Planning Act, Ontario Lakes and Rivers Improvement Act, and Ontario Water Resources Act. Although specific, direct protection is not offered through such legislation, protection is afforded through protection of wetlands and habitats. Most of the lands adjacent to the known occurrences were privately owned.