248 
way, or poaching. Although it is. recog- 
nized that the population estimates and 
inventories of spawn at Ridge Lake are 
far from exact, it is believed that both 
have value because of a year-to-year uni- 
formity of technique used in gathering 
data. 
Table 10 shows the total numbers per 
acre of largemouth bass, bluegills, and 
other fish (mostly green sunfish and black 
Intinois NaruraAt History Survey BULLETIN 
Vol. 26, Art. 2 
of 6 inches in length are capable of 
spawning. Fish of this species 3 inches 
in length or longer may feed on bass fry. 
In 1941, at the time 100 bass of spawn- 
ing age were placed in Ridge Lake, the 
lake area was only about 9 acres, giving 
an assumed adult population of 11 bass 
per acre. The resulting spawn was the 
second largest recorded and the largest 
per acre: 38 broods estimated at 76,000 
Table 10.—Estimated numbers of largemouth bass, bluegills, and other fish per acre 
shortly prior to spawning time, and of largemouth bass fry at spawning time, for each of the 
years 1941-1951 at Ridge Lake. Calculations involving acreage were based on a water area 
of 18 acres except where stated otherwise. 
gs pay ps BLUEGILLS, OruHeR Fisu, Att Fisu, 
p sgh a PER ACRE Per Acre Per AcRE 
ER ACRE 
Pash 53 EsTIMATED 
YEAR Bass Fry, 
Ten Less Six Less Per AcrE 
tnches | Than "| ‘Inches! That) Tare | Small | Large: | sem 
Longer | Inches | Longer | Inches 
1941.....| ise tes as = ae ae 1 ee 8,444 
ASAD ORY, 24? 266 | — a 2 — 26 266 1,444 
1943 so04 i 64 \es104. 4 — - _- 6 104 1,000 
1944..... 57 33 — o= 29 15 86 48 56 
i ee 36 — | 3 — — 39 — 6,444 
19465.,(7:. 34 53 476 2,858 17 32 527 2,943 139 
{ee 22 a= 98 — — 120 — 2,056 
1948... Teed, aw? 299 | 1,120 16 4 392 | 1,196 
ge AOe ch) 28 = — — — 93 — 2,182 
Dh ee 42 31 58 2,878 20 56 120 2,965 
195027 32. 29 16° 36 — aw au 68 47 1,778 
? Calculations for this year based on actual water area (about 9 acres) at spawning time. 
2 Figure includes only 3 bass of spawning age per acre. 
® Calculations for this year based on actual water area (about 11 acres) during summer. 
* None less than 9 inches long. 
® None less than 8 inches long. 
® Warmouths only. 
bullheads) for each year, along with an 
estimate of the bass spawn per acre. Bass 
are separated into those of 10 inches in 
length or larger and those smaller; blue- 
gills into those of 6 inches in length or 
larger and those smaller. 
In a study of the relationship be- 
tween population density and spawning 
success, consideration should be given to 
the spawning and feeding habits of the 
species involved. 
In Illinois and other northern states, 
largemouth bass of 10 inches or more in 
length may not be capable of spawning 
unless they are at least 2 years old. Fish 
of this species larger than about 7 inches 
in length are usually not interested in 
food items as small as bass fry. Bluegills 
fry (8,444 per acre, table 10). The rel- 
atively sparse population of adult bass — 
had little or no interference with their — 
spawning. 
Forty of the bass placed in Ridge Lake 
in 1941 were recorded as being caught by 
fishermen after June, 1942, table 19. 
Seventeen were taken in the first drain- 
ing census, in 1943, table 4. So at least 
57 of the original Ridge Lake bass must 
have been present during the 1942 spawn- 
ing period (about 1.3 per cent of the bass 
taken in the 1943 draining census, table 
4). These 57 bass, plus a large number 
of “yearling” bass 5 to 11 inches in 
length, made up most of the 1942 popu- 
lation prior to spawning time; this popu-_ 
lation is calculated to have averaged 290 
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