Spotted gar

Spotted gar
Spotted gar, Lepisosteus oculatus
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Lepisosteiformes
Family: Lepisosteidae
Genus: Lepisosteus
Species: L. oculatus
Binomial name
Lepisosteus oculatus
Winchell, 1864

The spotted gar (Lepisosteus oculatus) is a primitive freshwater fish of the family Lepisosteidae, native to North America from the Lake Erie and southern Lake Michigan drainages south through the Mississippi River basin to Gulf Slope drainages, from lower Apalachicola River in Florida to Nueces River in Texas, USA. It has a profusion of dark spots on its body, head, and fins. Spotted gar are long and have an elongated mouth with many teeth used to eat other fish and crustaceans. They grow to 0.61–0.91 metres (2–3 ft) in length and weigh 1.8–2.7 kilograms (4–6 lb) on average, making it the smallest of the gars. The name Lepisosteus is Greek for "bony scale". Habitat for spotted gar is clear pools of shallow water in creeks, rivers, and lakes.

Description

Gar larva at 22 days, stained for cartilage (blue) and bone (red)

The spotted gar Lepisosteus oculatus is a part of the gar family (Lepisosteidae). They are notable for being one of the few extant fish species with ganoid scales. They have been known to hybridize with (and look similar to) Florida gar. It occurs in quiet, clear pools and backwaters of lowland creeks, small to large rivers, oxbow lakes, swamps, and sloughs. It occasionally enters brackish waters. The fish is a voracious predator, feeding on various kinds of fishes and crustaceans. The lifespan for L. oculatus varies between males and females. The maximum lifespan for a gar is 18 years. Males mature at the age of two or three, whereas females mature at three or four years old.[1] Females on average are known to be larger and live longer than the males. Females also have less annual mortality rates.[1]

Distribution

The spotted gar is native to North America and its current range is from southern Ontario to the west from the Nueces River in Texas east to the northern coast of the Gulf of Mexico and southeast to the lower Apalachicola River in Florida. The gar population is small in the north and is being threatened in Lake Erie by the destruction of their habitat and pollution. The gar is more common in the southern waters like the Mississippi River basin from southern Minnesota to Alabama and western Florida. Historical records indicate the spotted gar resided in the Thames and Sydenham Rivers in Ontario, Canada. Also, the fish was once common in Illinois in the Green and Illinois Rivers to the swamps in Union County; though sporadic, the population has dwindled in these water systems because of the loss of specific habitat they need to live, clear pools with aquatic vegetation.

Ecology

A diet study of the spotted gar reported the diet of a spotted gar consists of four species of fish; golden topminnow, warmouth, bluegill, and spotted sunfish, which adds to 18.1% of total food volume in the stomach, while 57.5% of the stomach content was shrimp.[2] Other invertebrates filled the remaining 23.6% of the stomach. Gar are also known to eat insect larvae and algae. Herbivorous fish eat the algae and zooplankton, and then herbivorous invertebrates are eaten by gar. Another food chain would be algae are eaten by herbivorous invertebrates and other carnivorous fish eat them, then they are eaten by the gar.[2] Gar do not have many predators, only carnivorous fish would eat them, mainly at an early life stage. Gar are a main predator in the aquatic food chain in lakes and rivers. The fish would compete with other carnivorous fish such as the bowfin (Amia calva). In one study, most spotted gar were shoreline oriented, preferred submerged branches as cover, and avoided areas of exposed bank.[3] During a flood pulse, a floodplain provides habitat for spawning and nursery habitat for gar eggs. Movement rates were higher during the summer than during the fall and winter, and rates were greater at night than at dawn during both seasons. The temperature greatly affects their moving rates and their ability to range their home turf. When the water is warmer during the spring and summer, they travel more often than during the cold seasons. Spotted gars eat 70% of their food intake at night compared to dusk and dawn.[3] Abiotic factors that affect the spotted gar by humans include destruction of habitat and increased sedimentation in the water. In 2002, the Louisiana Department of Environmental Quality, Office of Water Resources, in coordination with the US Environmental Protection Agency, took fish tissue samples in the Lower Mississippi River to test for heavy metals and organic compounds.[4] Spotted gar was found to be a cancer risk with high concentrations of heavy metals and organic compounds.[4]

Life history

Spotted gar spawn in the spring in April, May, and June, or when the water temperature is between 21.0 and 26.0 °C (69.8 and 78.8 °F), depending on the location. Gar spawn in shallow water with abundant vegetation and cover. The spawning season occurs from April to May. A female can have multiple mating partners and the female is usually larger than the males with which it is mating. The number of eggs the female lays can vary up to about 20,000 eggs, but on average about 13,000 eggs are laid. They lay their eggs on leaves of aquatic plants. The eggs are green in color and have an adhesive coating to keep them attached to aquatic vegetation. After 10 to 14 days, the eggs hatch. At this stage, the gar are most vulnerable. Also, shallow water is preferred, about 0–1 m in depth.[5][6] Males mature at the age of two or three, whereas females mature at three or four years old. The male’s average lifespan is 8 years and the female’s average lifespan is 10 years. Females have lower annual mortality rates.[6] The maximum lifespan for a gar is 18 years.

Current management

Today, humans are affecting this fish species by destroying habitat and aquatic vegetation, and creating sedimentation in the waters of North America. Waste and chemical drainage into lakes and rivers causes chemical buildup and contamination of the water. Consequently, the water becomes murkier and causes predatory fish to have high mercury levels or accumulate carcinogenic compounds into their bodies.[7] Spotted gar desire clear pools of water, and anthropogenic factors can decrease their survivability. This species is not on the U.S. Fish and Wildlife Service federally endangered species list, although in some northern states it is on special concern lists. In Canada, the fish is designated as threatened by the Committee on the Status of endangered wildlife in Canada. For Canadian waters the spotted gar is protected by the Species at Risk Act and the federal Fisheries Act. The Habitat Stewardship Program for Species at Risk works to protect the spotted gar and its habitat. Current management plans for spotted gar include: increasing water quality, minimizing or avoiding pollution, analyzing contaminated samples.[8] The most important biological decline of the species is habitat destruction.

References

  1. ↑ 1.0 1.1 Murie DJ, Parkyn DC, Nico LG, et al. (2009). Age, differential growth and mortality rates in unexploited populations of Florida gar, an apex predator in the Florida Everglades. Fisheries Management and Ecology. 16:315-322.
  2. ↑ 2.0 2.1 Hunt, Burton. (1953). Food Relationships Between Florida Spotted Gar and Other Organisms in the Tamiami Canal, Dade County, Florida. Transactions of the American Fisheries Society. 82:13-33.
  3. ↑ 3.0 3.1 Snedden, G. (1999). Diet and seasonal patterns of spotted gar movement and habitat use in the lower Atchafalaya River basin, Louisiana. Transactions of the American Fisheries Society. 128:144-154.
  4. ↑ 4.0 4.1 Watanabe, Karen. 2003. "Fish tissue quality in the lower Mississippi River and health risks from fish consumption." Science of The Total Environment. 302.1-3:109-126.
  5. ↑ DFO. (2010). Recovery Potential Assessment of Spotted Gar (Lepisosteus oculatus) in Canada. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2010/047.
  6. ↑ 6.0 6.1 Alfaro RM, Gonzalez CA, Ferrara Am. (2008). Gar biology and culture: status and prospects. Aquaculture Research 39:748-763.
  7. ↑ Hayer, Cari-Ann. (2008). Influence of Gravel Mining and Other Factors on Detection Probabilities of Coastal Plain Fishes in the Mobile River Basin, Alabama. Transactions of the American Fisheries Society 137: 1606-1620.
  8. ↑ Brim, M.S., D. Bateman, R. Jarvis. (2000). Environmental Contaminants Evaluation of St. Joseph Bay, Florida. Publication No. PCFO-EC-00-01. U.S. Fish and Wildlife Service, Panama City Field Office, Panama City, Florida. Vol 1 - Vol 2.

Further reading

External links

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