Lepomis gulosus (Cuvier, 1829)
Basis for Listing
The Warmouth (Lepomis gulosus) is at the northern edge of its range in the Mississippi River in the southeast corner of Minnesota (The Blufflands Subsection). Populations appear stable in Pools 5A, 6, 8 and 9, but the species is never abundant. In Pool 8, from 1990-2011, surveys sampled 456 specimens; however, annual tallies ranged from 6-54 individuals and averaged 21.7 per year. The annual number of localities ranged from 2-23 and averaged 8.9 per year (LTRMP 2013).
From 2006-2008, the Warmouth was one of several rare species targeted in a DNR State Wildlife Grant Program survey of the Mississippi River from the Coon Rapids Dam (Anoka County) to the Iowa border. However, only five specimens were collected in Pool 5a and three in Pool 9 (Schmidt and Proulx 2009). Additional, albeit unusual, distributions elsewhere in the state include Big Ole and East lakes (Itasca County), though the species has not been reported from the latter locality since 1982. Both occurrences are assumed to be the result of DNR fish rescue efforts, probably prior to 1960 (McInerny, in preparation). The species apparently is extirpated in Lake Jefferson (Le Sueur County), where specimens have not been collected since 1956.
The species peripheral and restricted distribution in Minnesota, possible extirpation of one population, and prevalent low abundance prompted listing the Warmouth a special concern species in Minnesota in 2013.
The Warmouth is a medium-sized sunfish, which, as adults, are typically 12.5-20 cm (4.9-7.9 in.) total length but may reach a maximum of 25 cm (9.8 in.). Flanks and dorsal fin are mottled or spotted, it has 39-43 scales in lateral series (in Minnesota), anal fin has 3 spines, pectoral fins are moderately long and rounded, mouth is large (upper jaw extending to middle of eye or beyond) and has a tooth patch in the middle of the tongue, gill cover flap is dark, with a light margin, and there are 9-12 moderately long thin primary gill rakers on the first arch (Lyons et al. 2006).
In Wisconsin, the Warmouth is found in turbid lakes, ponds, sluggish streams, and ditches with dense aquatic vegetation and substrates of mud, sand, or gravel (Becker 1983). In Pool 8 of the Mississippi River, the Warmouth prefers backwaters, where it has been sampled 124 times at depths of 0.4-2.2 m (1.3-7.2 ft.) over substrates of silt and clay and velocities of 0.01-0.12 m/s (0.03-0.39 ft./s). It was also found in impounded areas 33 times, side channel borders (18), tailwaters of dams (14), and main channel borders (6) (LTRMP 2013).
Biology / Life History
The age of sexual maturity is unknown in Minnesota. However, given that size, rather than age, is a greater factor influencing maturity, age and size data indicate that it's likely this species matures at 2-3 years in Minnesota (McInerny, in preparation). Elsewhere, the Warmouth reaches sexual maturity at 7.5-15.2 cm (3-6 in.) total length (McInerny, in preparation). Lifespan is at least 6 years. In Illinois, spawning can begin as early as the second week in May, when water temperatures near 21° C (70° F), peaks in early June, declines in early July, but may continue into August. Males guard the nest, but the species is generally not a colonial nester, which is contrary to other sunfish (Lepomis spp.). Nests are typically constructed at depths of 0.6-0.8 m (2.0-2.6 ft.) in substrates of silt, detritus, or rubble and near cover, such as boulders, root wads, and vegetation. Eggs hatch in 34.5 hours at 25-26.4° C (77-79.5° F). Warmouth hybrids have been reported, resulting from crosses with other Lepomis spp. (Becker 1983).
Conservation / Management
Research needs include a life history study and habitat assessments to determine factors limiting the species distribution and abundance.
Conservation Efforts in Minnesota
Warmouth habitats are protected within the boundaries of the Upper Mississippi River National Wildlife and Fish Refuge. The recent inception of Minnesota’s Clean Water Legacy Program will eventually yield benefits to the species' habitats through sediment load reductions.