Fig. 10. — Ratio betwctn 

 standard length and body depth 

 in carp in 1963 from Hardin to 

 Morris. Note the change in 

 length-depth ratio at Beards- 

 town. ( Illinois Natural History 

 Survey data.) 



CARP 



RATIO OF STANDARD LENGTH TO BODY DEPTH 



BEARDSTOWN 

 MEREDOSIA . \ 



;2.60 

 270 

 ^2.80 

 ="2 90 

 ^3 00 



20 



tSSSSMESS 



THll I iroTHF SPRING VALLEY 



chillicothe , ottawa | 



peoriaX henry \utica 



PEKINu^^^^ 



ILA GRANGE POOLl 



11963 



80 



100 120 140 160 180 200 



MILES FROM MISSISSIPPI RIVER 



of fish life above Utica in the 1920's prevented Thomp- 

 son from extending his study as far upstream as we did 

 at the later date. The percentage of knothead carp 

 between Beardstown and the Peoria-Pekin area was 

 greater in 1963 than it was in 1926 and 1927, indicating 

 a greater pollution load in this stretch of the river. 

 Stating this another way, it appears that the pollutional 

 factors in the river responsible for this condition in carp 

 have not increased above the Peoria-Pekin area, but that 

 they have moved on downstream toward Beardstown 

 since Thompson's observations were made. 



The length-depth ratios of carp caught in oiu' 

 autumn 1963 Illinois River collections clearly indicate 

 a sharp distinction between specimens taken above and 

 below Beardstown (Fig. 10). Those below this city had 

 ratios less than 3. and above it the ratios were 3 or more. 

 \Vc suspect that this dift'erence may be due in part to 

 ihc elimination of fingernail clams abo\e Beardstown. 

 Slarrett & Paloiimpis (unpublished) have found these 

 mollusca regularly in the stomachs of carp collected in 

 the lower river. 



Carp in the niiddk- and upper river are subject to 

 lower dissolved oxygen conditions than those in the 

 lower river. It is possible that tlie life expectancy of the 

 fish above Beardstown is reduced because of periods of 

 stress resulting from oxygen deficiency. These two 

 factors — l(;ss of fingernail clams ]5lus low dissolved 

 oxygen — could explain the dearth of commercial-size 

 carp in the middle and up|)er reaches of ihc Illinois 

 River. 



Catfishes 



Black bullheads are still abundant in lh<' river, par- 

 ticularly in the middle and upper stretches. These fish, 

 together with carp, furnish most of the river fishing 

 for pole-and-linc fishermen from Morris downstream. 

 CMiaiincl catfish [Iclalurits jntnclalui) Iiave declined in 

 abundance in the river since 1899 as evidenced by the 

 following commercial fishing statistics: 241,000 pounds 

 in 1899 (Forbes & Richardson 1920:183). 105..5.54 

 jjounds in 19;')0 (Starrctt & Parr 1951:18), and about 



98,000 pounds in 1964 (Starrett, Lopinot. & Harth. 

 unpublished). Mc.st of the catfish are now taken in the 

 lower river. 



BufFalofishes 



The bufTalofishes of the genus Iclobius are now 

 found mainly in the middle and lower sections of the 

 river. Commercial catch statistics indicate that these 

 important fishes have declined in the past 65 years, with 

 the decline being the most rapid in the last 15. The 

 1964 commercial catch was only about half that of 

 1950. 



Crappies 



()ur data indicate very little change in crappie 

 (Pomoxis annularis and P. nigromaculatus) populations 

 in the lower river since 1 942. However, the decline in 

 the middle river has been alarming. A Natural History 

 Survey crew in 1942 (Thompson & Hansen, field notes) 

 caught six times more crappies in nets than we were able 

 to take by the same method in the middle river in 1964. 

 \X Bath, by electrofishing. we caught 14 cra|)pies pei 

 30 mimites of fishing in 1962, and only 4 in the same 

 time in 1964. We suspect that the drastic decline has 

 been due to the low oxygen conditions in association with 

 the low water levels of the past few years. 



Bluegill 



The bluegill (Lcpomb macrochirui) has declined in 

 out river collections even more than have the crappies. 

 The take of bluegills in our 1942 fishing in all pools was 

 33 times greater ih.ui in 1961. 



Largemouth Bass 



W'c have aliiaily meiuioiu'd the abundance of this 

 fish at the turn of the centui-y. Other than in a few 

 bottomlaml lakes, sport fishing foi- laigemouth bass is 

 now rare in the Illinois River. In 1962 we made a few 

 sizable collections from some parts of the middle and 

 lower river. In 19615 and 1964 our electrofishing catch 

 was substantially less in most parts of the river. The 

 decline has been related to pollution and the loss of 

 good habitat, as in the ease of other spot t fishes. 



17 



