|
|
|
{Page 8}
Department of Biology, Cameron University, Lawton, OK 73505
A total of 172 spotted gar (Lepisosteus oculatus) was collected from Lake Lawtonka in Comanche County, southwestern Oklahoma, during each spawning season between 6 May 1980 and 10 June 1982. Specimens were weighed, measured, sexed, and stomach contents examined. Total lengths ranged from 422 to 1030 mm and weights from 224 to 4311 g. Only 31 (18%) of the stomachs contained food. Fish constituted 68% and invertebrate organisms 32% of food recovered. Spawning extended from about mid-April to early June and typically occurred in water of 6 to 18 inches depth. Each large female gar was usually attended by 3 to 5 much smaller males.
| Introduction | Methods | Results and Discussion | References | Table of Contents | Home |
There is little information concerning the biology of Lepisosteus oculatus in Oklahoma. To counter this information void, this study was undertaken to identify specific prey items, evaluate sexual dimorphism in length and weight relationships, ascertain sex ratios, and record spawning behavior.
Spotted gar are abundant in Lake Lawtonka, being most conspicuous during spring, when large numbers congregate in the warm shallows to spawn. Dense beds of submerged and emergent vegetation (primarily Polygonum, Potamogeton, Myriophyllum, and Justicia) characterize these waters.
| Introduction | Methods | Results and Discussion | References | Table of Contents | Home |
Most gar were collected by bowfishing in well-vegetated water less than 18 inches deep, but five gar were taken by electroshocking. Polarized sunglasses enabled us to see below the water's surface. Gar were usually taken as they cruised the shallows, lay motionless near the surface, or were engaged in spawning. Initially, solid fiberglass fishing arrows were used, but we subsequently changed to hollow aluminum arrows with plastic fletchings because they were lighter, faster, and generally more effective. Bright shaft colors helped to avoid arrow loss. The shock of being impaled usually immobilized a fish. Each gar was weighed, measured, sexed, and its stomach removed, numbered, and preserved for later identification of contents. Tinsnips had to be used to cut through the body wall. Ovaries were distinguished from testes by their larger size, more granular consistency and by their more posterior location in the body cavity.
| Introduction | Methods | Results and Discussion | References | Table of Contents | Home |
We collected 54 females and 118 males, primarily because males were far more numerous. Stomachs of 141 (82%) of 172 gar contained no food. The high incidence of empty stomachs agrees with Hunt (1), who found empty stomachs in 76% of 448 spotted gar from Florida, and with Scott (2), who autopsied 89 longnose gar (L. osseus) in Indiana, 56% of which had empty stomachs. However, our results and those of Hunt (1) are in conflict with findings of Goodyear (3), who found empty stomachs in only 19% of 176 gar from Mississippi coastal waters, and Bonham (4), who found only 25% empty stomachs in 28 Texas spotted gar. The estuarine environment of the former study and the small sample size of the latter could explain the differences in results. In our gar (n = 31), 68% of the prey were fish and 16% each were crayfish and insects (Table 1). Advanced digestion precluded species identification except in two cases: a juvenile bluegill sunfish (Lepomis macrochirus) occurred in one stomach and a small drum (Aplodinotus grunniens) in another. Lengths of prey fishes varied from 40-290 mm and only 3 of 21 of them were 180 mm (7 in.) or longer. As can be seen in Table 1, there was a general trend for the larger gar to feed on bigger fishes. The only recognizable insects were coleopterans. Scott (2) also concluded that longnose gar are largely piscivorous in Indiana. A review of papers on food habits of spotted gar concluded that fish are the principal prey (5). The high number of empty stomachs seen in our data may be an artifact of sampling time since almost every fish taken in this study was collected in mid-afternoon. Other studies have indicated that feeding occurs princi-
{Page 9}
pally in early morning (5). If early morning feeding is the rule, rapid digestion would at least partially explain our high incidence of stomachs without food. Too, it is possible that feeding of gar slows or ceases altogether during the spawning period, and they may also be opportunistic (therefore sporadic) feeders as well. Perhaps some combination of these (and possibly other) variables is responsible for the disproportionatly large number of empty stomachs in our sample.
Female spotted gar weighed from 440 to 4311 g ( x¯= 1717) and their lengths ranged from 508 to 1030 mm ( = 729). Male weights varied from 224 to 2208 g ( = 472) and lengths from 422 to 809 mm ( = 508), although only 4 of 118 males exceeded 688 grams and only 2 were longer than 580 mm. Hancock (6) collected 14 spotted gar from Canton Lake in northwestern Oklahoma that ranged in length from 378-688 mm and 163 taken in Alabama by Swingle (7) measured from 152 to 737 mm. Data from the specimens were separated into nine weight classes of 500-g increments each, and seven length classes of 100 mm each. Largest numbers occurred in the lightest weight class (containing individuals weighing 500 g or less), and in the shortest length class (ranging from 501 to 600 mm; see Figs. 1 and 2). Males were nearly always lighter than females of comparable length and outnumbered females more than 2:1. Therefore, they dominate both the lightest weight class in Figure 1 and the shortest length class in Figure 2. The average female gar was 3.63 times as heavy and 1.43 times as long as an average male. Other authors (e.g., 6 and 7 above) have reported individual gar lengths, but without including the sex, therefore little or no comparable data are available.
By the third week in April (the earliest spawning date was 22 April 1981 and the latest was 10 June 1982), spotted gar had begun to spawn. In our study area, the most intense spawning activity occurred during mid-May. Typical spawning behavior was as follows: a large female, closely accompanied by 3 to 5 much smaller males, would swim slowly through the well-vegetated shallows.
{Page 10}
The apparent moment of egg deposition was denoted by her quick jerks, thrashing and concomitant splashing. Spawning was interrupted by the advent of cooler temperatures and turbid water resulting from spring rains.
This work was supported by a grant from Cameron University. We thank Mike England for his help in collecting specimens, James M. Finley and Shelly M. Granger for assistance with typing, and Joe Henson, Chief Lake Patrolman at Lake Lawtonka, for granting us permission to collect gar.
| Introduction | Methods | Results and Discussion | References | Table of Contents | Home |
1. B. P. HUNT, Trans. Am. Fish. Soc. 82:13-33 (1952).
2. W. SCOTT, Invest. Indiana Lakes Streams 1: 112-115 (1938).
3. C. P. GOODYEAR, Trans. Am. Fish. Soc. 96:296-300 (1967).
4. K. BONHAM, Trans. Am. Fish. Soc. 70:356-362 (1940).
5. K. D. CARLANDER, Handbook of freshwater fishery biology, Vol. 1, 3rd ed., Iowa State Univ. Press, Ames, 1969, p. 59.
6. H. M. HANCOCK, Oklahoma Fish & Game Council Proj. Rept., Pt. 2 (1955).
7. W. E. SWINGLE, Auburn Univ. Agric. Expt. Sta. Zool. Ent. Ser. Fish. 3 (1965).
