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Montana Field Guide

Montana Field Guides

Shortnose Gar - Lepisosteus platostomus

Species of Concern
Native Species

Global Rank: G5
State Rank: S3
(see State Rank Reason below)

Agency Status
USFWS:
USFS:
BLM:
FWP SWAP: SGCN1


 

External Links





State Rank Reason (see State Rank above)
The Shortnose Gar is currently ranked as S3 in Montana. The previous rank of S1 was revised to S3 due to recent observations upstream of known populations on the Missouri river into the Milk River and 70 miles upstream into the Yellowstone River.
  • Details on Status Ranking and Review
    Shortnose Gar (Lepisosteus platostomus) Conservation Status Review
    Review Date = 07/16/2017
    View State Conservation Rank Criteria
    Population Size

    ScoreU - Unknown

    CommentUnreliable estimates can be derived from sparse sample data and could be a significant underestimate, since this species is rarely targeted in routine fishery surveys. Data deficient!

    Area of Occupancy

    CommentLinear Range was calculated to be a liberal 456 km (286 river miles) of predicted occupied river extent based on MFISH river miles calculations associated with surveys, while conservative estimates of actual suitable river habitat is likely half this (143 river miles). Scores either way within the LD range.

    Length of Occupancy

    ScoreLD - 200-1,000 km (about 125-620 miles)

    Long-term Trend

    ScoreE - Relatively Stable (±25% change)

    CommentEven though they have been impacted by Fort Peck dam. Due to their habitat requirements, they have probably been pretty stable in terms of available habitat since the arrival of Europeans- within +/-25%.

    Short-term Trend

    ScoreE - Stable. Population, range, area occupied, and/or number or condition of occurrences unchanged or remaining within ±10% fluctuation

    CommentWe decided upon a stable trend, because, although we acknowledge loses of occupied river miles due to dams and diversions, this is encompassed within the 10% variability allowed. We encourage more monitoring of sites, especially in suitable habitat areas between the Yellowstone confluence and Fort Peck Dam. Monitoring and distribution in the Yellowstone River is increased at a number of sites.

    Threats

    ScoreF - Widespread, low-severity threat. Threat is of low severity but affects (or would affect) most or a significant portion of the population or area.

    CommentDiversion dams, dams, pollution, oil spills and introduced species (predation by Smallmouth Bass and Northern Pike on juvenile gar in particular) all represent threats.

    SeverityLow - Low but nontrivial reduction of species population or reversible degradation or reduction of habitat in area affected, with recovery expected in 10-50 years.

    ScopeModerate - 20-60% of total population or area affected

    CommentShortnose Gar range overlaps with dams and diversions. Introduction of Northern Pike may have had an effect on some suitable habitats areas.

    ImmediacyHigh - Threat is operational (happening now) or imminent (within a year).

    Intrinsic Vulnerability

    CommentRank factor not assessed, although we would lean towards “Not Intrinsically Vulnerable”.

    Environmental Specificity

    ScoreC - Moderate. Generalist. Broad-scale or diverse (general) habitat(s) or other abiotic and/or biotic factors are used or required by the species but some key requirements are scarce in the generalized range of the species within the area of interest.

    CommentWe decided that the Shortnose Gar is a broad-scale or diverse habitat generalist or other abiotic and/or biotic factors are used or required by the species, but some key requirements (slow, stagnant areas) are scarce in the generalized range of the species within the area of interest. They seem to handle a variety of turbidities, substrates, and water temperature fluctuations as long as slow, stagnant areas can be found.

    Raw Conservation Status Score

    Score 3.5 + (-0.25) (area occupancy+ pop) + 0.0 (environmental specificity) + 0.0 (short-term trend) + 0.0 (threats) = 3.25

 
General Description
The gar family has only one representative in Montana, the Shortnose Gar. This fish is native to Montana and has been previously found at only one location--the dredge ponds below Fort Peck Reservoir. But more recent collections (2010-2015) have reported this species in the the Milk and the Yellowstone Rivers. Because of its restricted distribution and limited population size, it has been named a Montana state Fish of Special Concern. Gars are predaceous. They are spring, broadcast spawners. They have several unusual features including rectangular scales found only in primitive fishes, and a gas bladder that can function like a lung. All fish have gas bladders, which they use to regulate their buoyancy, but the gas bladder of a gar can extract the oxygen from air that is swallowed. Consequently, gars can survive in waters that have very little oxygen where most other fish would perish. Gar eggs are poisonous to humans.

For a comprehensive review of the ecology, conservation status, threats, and management of this and other Montana fish species of concern, please see Montana Chapter of the American Fisheries Society Species of Concern Status Reviews.

Diagnostic Characteristics
This prehistoric-appearing fish is cylindrically shaped, with an elongated bony head and snout containing one row of sharp, conical teeth. The dorsal fin is located well posterior and the pectoral and pelvic fins have no spots (Marshall 1966). The skin is covered with diamond shaped ganoid scales arranged in oblique rows, providing a very protective surface armor (Moyle 1993). Scales number 60 to 64 along the lateral line. Color varies from brownish or olive-green on the dorsal surface lightening to yellow on the sides and white on the belly (Holton and Johnson 1996). Young gar less than 10 inches in length process a black stripe along the midline. Shortnose Gar may reach a size and weight of about 31 inches and about 3.5 pounds (Montana AFS Species Status Account).

Species Range
Montana Range

Year-round

Western Hemisphere Range

 


Range Comments
The shortnose gar is widely distributed throughout North America within the Missouri and Mississippi River system. However, its distribution within Montana was initially thought to be very limited with occurrences being documented primarily in the Missouri River dredge cuts downstream of Fort Peck dam (Brown 1971). But other more recent documented observations of shortnose gar in Montana are from specimens collected on the Yellowstone River ~70 miles upstream to intake and ~10 miles upstream into the Milk River.

Observations in Montana Natural Heritage Program Database
Number of Observations: 24

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density

Recency

 

(Observations spanning multiple months or years are excluded from time charts)



Migration
Shortnose gar are not known to migrate for spawning purposes.

Habitat
Shortnose Gar are typically found in large rivers, quiet pools, backwaters, and oxbow lakes. It has a higher tolerance to turbid water than the other four gar species found in North America (Montana AFS Species Status Account).

They are found in dredge cuts below Fort Peck Dam (Holton 2003).

Food Habits
The diet of the Shortnose Gar is primarily composed of fish. However, crayfish and insects are also utilized (Brown 1971). Young gar are known to feed on small insects and zooplankton, with fish entering the diet when gar are 1.25 inches in length. Gar is known as fierce predators of smaller fish using ambush as a primary hunting technique (Moyle 1993, Montana AFS Species Status Account).

Ecology
Due to their limited distribution, little is know about shortnose gar within Montana. Shortnose gar are typically found in large rivers, quiet pools, backwaters, and oxbow lakes. They have a higher tolerance to turbid water than the other four gar species found in North America. Gar also have the unique ability to supply a high vascularized swim bladder with supplemental oxygen by engaging in a behavior of "breaking" where air is gulped at the surface.

Reproductive Characteristics
Shortnose Gar become sexually mature at three years of age and typically spawn in May or June as water temperatures reach the mid 60s (Brown 1971). Adhesive eggs are deposited in quiet, shallow water over aquatic plants or other submerged objects. A sticky, gelatinous adhesive holds clumps of yellowish-green eggs to the vegetation for 8 to 9 days whereupon hatching occurs (Montana AFS Species Status Account).

The young lead solitary lives floating near the surface (Brown 1971).

Management
Due to low numbers and poor quality flesh, the Shortnose Gar is not considered a sport fish in Montana (Montana AFS Species Status Account).

References
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Citation for data on this website:
Shortnose Gar — Lepisosteus platostomus.  Montana Field Guide.  .  Retrieved on , from