Bull 14 article IV STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION DIVISION OF THE NATURAL HISTORY SURVEY STEPHEN A . FORBES. Chief Vol. XIV. BULLETIN Article IV. Changes in the Bottom and Shore Fauna of the Middle Illinois River and its Con­ necting Lakes since 1913 - 1915 as a Result of the Increase, South- ward, ·of Sewage Pollution BY ROBERT E. RICHARDSON PRINTED BY AUTHORITY OF THE ST ATE O F ILLINOIS URBANA, ILLINOIS December, 1921 STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION W. H. H. MILLER, D irector BOARD OF NATURAL RESOURCES AND CONSERVATION W. H. H. MILLER, Chairman WILLIAM TRELEASE, Biology JORN M . COULTER, Forestry ROLLIN D. SALISBURY, Geology WILLIAM A. NOYES, Ohernistry JOHN w. ALVORD, Engineering KENDRIC C. DABcocrr Representing the President of the University of Illi­ nois THE NATURAL HISTORY SURVEY DIVISION STEPHEN A. FORBES, Chief SCHNEPF & BARNES, PRINTERS SPRINGFIELD. I'LL. 1921 55188-1200 ARTICLE IV.-Changes in the Bottom and Shore Fauna of the Middle Illin,ois River and its Connecting Lakes since I9IJ-I9I5 as a Result of the Increase, Southward, of Sewage Pollution.. BY ROBERT E. RICHARDSON. The following short account of the principal changes that have oc­ curred both in the composition and abundanc~ of the small bottom-inver­ tebrate fauna of the Illinois River system between Chillicothe and Brown­ ing since 1913-1915-these points being re pectively 146.5 and 229.5 miles below the mouth of the Chicago River-is based on hauls made in July, August, and September, 1920, with the Petersen quantitative bot­ tom-sampler at seventy-one stations in the river and Peoria Lake between Chillicothe and the head of Grand Island, and at twenty-five stations in five of the more important bottom-land lakes in the neighborhood of Havana. "\Vhile the composition of the small bottom-fauna was apparent­ ly normal as far north as Chillicothe in 1915,* the 1920 data herein pre­ sented disclose conspicuous changes since that time both throughout the northernmost and southernmost portions of the section of river system studied, these including sweeping reductions in numbers and poundage of the till surviving groups of small bottom-animals, total obliteration of numerous families and species, and_. in the range covered above Havana, the intrusion in large numbers of new pollutional or tolerant forms. If, as is approximately correct, we assume that Chillicothe marked about the upper limit of wholesome conditions in the bottom muds in 19.15, then the added river mileage that is shown to have been more or less seriously damaged since that time figures out at not less than eighty, and represents an average southward encroachment of pollution amounting to fully six­ teen miles per year for each year of the five. Valuations of the small bottom-animals have been made in the same manner as for the 1915 material reported upon in the paper ju t cited. Valuable assistance in working up the Chironomidae of the collections of this year, as well as in the elucidation of older data for comparison, has been given by Dr. C. P. Alexander and Mr. J. R. Malloch. • The Small Bottom and Shore Fauna of the Middle and Lower Illinois River and Its Connecting Lakes, Chillicothe to Grafton: its valuation; its Sources of Food Supply; and its Relation to the Fishery. By R. E. Richardson. Bul. Nat. Hist. Survey, Vol. 13, Art. XVI. 1921. • • 34 SYNOPTIC LIST OF DREDGING STATIO s, ILLINOIS RIVER AND 0 N ECTING LAKES, JULY-SEPTEMBER, 1920 1. ILLINOIS RIVER AND PEORIA LA.KE, CHILLICOTHE TO WESLEY MILE 146.5- MILE 167.8 BELOW LAKE MI HIGAN Upper lake, Chillicothe to Spring Bay, Mile 146.5-153.2 Middle lake, Mossville to Al Fresco Park, Mile 154.9-159.3 Peoria Narrows, Mile 161.0 Lower l ake, Straw-board Mill to Liberty St., Mile 161.7-164.2 Peoria and Pekin Union Railway Bridge, Mile 166.4 Total Channel I 4--7 feet. 11-3 feet. 3 3 1 8 1 16 4 4 1 3 1 13 1 1 0 4 0 6 Total 8 8 2 15 2 35 2. ILLINOIS RIVER, LIVERPOOL TO 1.5 MILE BELOW HEAD OF GRA 'D ISLAND MILE 199.0- MII.E 215 BEL-OW LAKE MI HIGAN Liverpool to Havana, Mile 199.0~207.0 2 miles below Havana to 1.5 miles below head of Grand Island, Mile 209 .0-215.0 Total Channel 7 11 18 4-7 feet. / 1-3 feet. Total 7 0 14 8 3 22 15 3 36 35 3. ILLINOIS VALLEY LAKES , LIVERPOOL TO 3.5 MILE ABOVE BROW NING MILE 199.0-Mrr..E 226 BELOW LAKE MICHIGAN Lakes north of Havana, Mile 199.0-207.0 Liverpool Lake Dogfish Lake Thompson Lake Quiver Lake Lakes south of Havana, Mile 224.0-226.0 Stewart Lake All mud bottom, Depths, 2-6 ft. 5 3t 3 4* 5 15 • In Quiver Lake fh·e additional co llect ions were made in the deep channel cut by the wash from Quiver Creek and in the sandy-muddy zone near the east beach. The Illinois River and Peoria Lake, Chillicothe to Wesley (Mile 146.5-167.8 below Lake Michigan) At all o.f the thirty-five lake and river stations between Chillicothe and We ley where bottom dredgings were made in 1920, there was evidence in some form or other of deteriorating change since 1915. The various tests and observations made both in 1920 and five to even year earl ier had regard chiefly to the physical condition, appearance, and odor of the muds; the composition and abundancf' of the small bottom- and shore-fauna ; and the kinds, amount and distribution of the coarse aquatic veo-etation. W hile sharply drawn comparisons are not easy in the first group of item , bubbling and more or les foul odors having been noted at some stations between Peoria and Chillicothe in 1915, in the second item­ ization we have to do with the disappearance since that year f whole families and numerous genera and species of mall bottom-animals, as well as with the entrance in their place, in several instances, of new pollu­ tional forms; and in the la t, with the practically complete di appearance of a rich aquatic vegetation which formerly covered several square miles of shall ow-lake territory at low water, along with the similarly complete rxtingui hment of a previously very rich shore- and weed-fauna. The mud taken at the eight tati n in the "upper lake,' between Chillicothe and Spring Bay, were all strong in odor, and bubbling "as abundant, when the mud was stirred in all depth-zone . Both in the channel at Rome and Spring Bay and in the open lake oppo ite Rome a peculiarly spongy and foul-smelling mud was lifted by th· dr ·dg- . The e arnples showed a texture not unlike fre hly ri en bread. and gave out a distinct blubbering sound on being pressed with th hand as th y lav 3G in the tray. Some improvement in odor and less bubbling was noted in samples taken well toward the east edge of the upper lake. In the middle lake, opposite Mossville, the mud from the channel was spongy with gas, and in the channel of this lake as far south as Al Fresco Park, a mile and a half above Peoria Narrows, odors were foul and trong. ·on iderably less bubblina and milder odor were noted at the shallower-water stations in this ection of Peoria Lake. In the lower lake, opposite and . below the principal ~ewers of the bu ines and re iden c di ·tricts of Lhe city of Peoria. all dredgings were made in the center or to the eastward of th.e steamboat channel and were for the most part out of the way of the worst of the local pollution. At our station in the lake, neither in the main channel nor in the shallower water eastward were odors so bad as at upper-lake stations, although bubbling wa abundant in whatever d pth the dredae wa let down. At all stations, both in this and in the upper and middle lake it wa noted that all dead shells of snails were badly blackened or otherwi e di - colored. The principal changes in the bottom fauna in this 18-mile section since 1915 may be summarized under three heads: (1) disappearance of most species and g-enera and of everal families of small Mollusca, along with important average decrease in numbers of the more tolerant forms still surviving; ( 2) enormous increase in larval midges ( Chironomidae), with invasion of several more or less distinctly pollutional species, and similar or even greater increase in sludge-worms (Tubificidae) ; and (3) disappearance throuO'hout Peoria Lake, except immediately along shore or in the short, half-mile, stretch of swifter water in Peoria Nar­ rows, of all "other insects'* (Ephemeridae, Odonata, Phryganeidae, Corixidae, etc.), as well as of planarians and leeche , . mphipoda, Isop­ oda, sponge , and Bryozoa. Although in 1913-1915 at least fifteen or sixteen pecies of snails, representing no less than eight families, were readily taken in the lake and river channel between Chillicothe and Peoria, but four species, repre­ senting three familie . were found in the same ran e in July and August, 1920. The three principal surviving kinds (Campeloma subsolidum, Pleurocera species, and Musculiuni transversum) were tho e found by u farthest north-and hence mo t tolerant of foul water and bottom­ in the upper Illinois in 1912, the first-named species occurring as far n rth that year as Starved Rock, and the last as far north a Mar­ "eilles. Two of the formerly abundant species of Viviparidae (Vivip­ ara contectoides and Liopla .• 1: subcari11,ata), two species of Valvata, two Amnicolas, three or four species of Physidae and Planorbinae, a species of ncylus, and at least three species of Sphaeriidae eem to have dis­ appeared altogether from the muds between 1915 and 1920. • Understood in text and tables following to mean other insects than Chiro­ nom!dae. SN.\IL FAUNA"° OF BO'rTOM Muns, CilllLICOTHI•: 1'o Foo·r o,,, P1, on1A LAKii:, 1913-1915 TO 1920 l. Sprcies surviving in 1920, and thelr aistrib1ttion. 1. Viviparidae .. 1. Campeloma subsolidum ........ East side lake, opposite Rome; channel and 4-7 feet, lower lake. 2. Pleuroceridae 2. Pleurocera sp .................. Channel of lower lake only. 3. Sphaeriidae .. 3. Musculium transversum ........ Iloth zones, upper lake; shallower zone, middle lake; chan- nel, lower lake. . , 4. Sphaerium stamineum ......... Channel, lower lake, one occurrence . [I. Spcc'ies co1nnion or abundant in 1913-1915, b1tt not found in 1920, and clistrib1ttion in former period. 1. Viviparidae .. 1. Vivipara subpurpurea .......... Lower lake only. " 2. V. contectoides ..... ............ Abundant in both zones, Chillicothe to Peoria. 3. Lioplax subcarinata ............ Common to abundant, principally in channel. 2. Amnicolidae 4. Amn icola emarginata ........... Common locally. " 5. Somatogyrus sp ................ Upper lake only . . 3. Valvatidae ... 6. Valvata bicarinata ............. Common outside of channel. " 7. V. tricarinata .................. Common outside of channel. 4. Physidae. . . . 8-9. Physa spp .................. Common in shallower zones. u. Planorbinae 10-11. Planorbis spp .. .. ..... ..... Common in shallower zones. 6. Sphaeriidae 12. Sphaerium stria tin um .. ... ..... Lower lake only. " 13. Musculium jayanum ........ .... Scattered occurrences. " 14. Pisidium sp ......... . ... ...... Common. 7. Ancylidae ... 15. Ancylus sp, ........ ........... Common on shells of Unionidae. • Nomfln~lature that of l•'. C. Baker, in "A Catalogue of the Mollusca of Illinois," Bul. Ill. State Lab. Nat. Hist., Vol. 7. Art. _\'II. Sept., 1906. c,., ~ 3 Even the surviving snails showed in 1920 great reduction in average numbers and weight since 1915 in nearly all portions of the area studied. The extent to which they had shrunken in the different depth-zones of the upper, middle, and lower lake is shown in the comparative valuation tables appended, and it will be sufficient here to note that whereas in 1915 the weight of the combined Gastropoda and Sphaeriidae in Peoria Lake collections made up from over 85 to over 99 per cent. of the total edible matter in the average haul, the snails in 1920, except in the short swift stretch through Peoria Narrows and in a few collections in the channel of the lower lake, weighed on the average less or only a little more than did the sludge-worm or midge larvae, and made up, in fact, only from 2 to 15 per cent. of the average catch under the new dispensation. The Viviparidae and Pleuroceridae in 1920 were found only in the channel and 4- -foot zone of the lower lake, opposite Peoria and in the 1-3-foot zone, on the east side in the Rome- fos ville section. The single surviving species of Sphaeriidae ( J1/J usculium transvers11111 ) showed a visibly wider distribution than the large Gastropoda. and it "vas some­ what of a surprise to us to take the largest hauls of thi stoutly tolerant little shell amona the sludge-worms and larval midges of the filthy chan-· nel-bottom between Chillicothe and the foot of the upper lake. Sx TL F AUNA OF BOTTO'.\f M D , HlLLI OTIIE TO FOOT OF P EORIA LAKE, 1915 .AND 1920 1 . A verage nmnber v er squa:r e yard , 1nain groups I I Channel \ 4-7-ft. zone I 1-3-ft. zone 1915 1920 1915 1920 1915 1920 Upper lake 111 0 32 0 10 24 Viviparidae and Middle lake 19 0 28 0 7 0 Pleuroceridae Lower lake 134 63 153 8 50 0 Upper lake 152 112 204 24 12 24 Sphaeriidae Middle lake 91 0 116 3 277 12 Lower lake 5 6 97 0 30 0 Upper lake 6 0 3 0 32 0 Amnicolidae, Lower lake 0 0 12 0 12 0 Valvatidae, etc Middle lake 0 0 70 0 40 0 39 2. Average ii:eight, 111.ain grO'Ups, pounds per acre, shells deducted - -- Channel 4-7-ft. zone 1-3-ft. zone 1915 1920 1915 1920 1915 --- Upper lake 317 0 87 0 50 Viviparidae and Middle lake 26 0 57 0 18 Pleuroceridae Lower lake 391 110 446 24 174 Upper lake 76 56 88 12 6 Sphaeriidae l\Iicldle lake 43 0 54 1 66 Lower lake 3 3 28 0 1 pper la ke 0.8 0 0.1 0 .5 Amnicolidae, Valvatidae, Middle lake 0 0 1.7 0 0.6 etc. Lower lake 0 0 27.4 0 8.6 3. Average weight of total snails and per cent. decrease, 191 ii to 1920 1915 1920 Per cent. decrease Channel 394 56 85.7 'Upper lake 4-7 ft. 175 12 93.1 1-3 ft. 64 84 31.2* bannel 69 0 100.0 Middle lake 4-7 ft. 113 1 99.1 1-3 ft. 6 6 93.0 -~-- 'hannel 394 113 71.3 Lower Jake 4-7 ft. 501 24 95.2 1-3 ft. 184 0 100.0 • Increase. 1920 72 0 0 12 6 0 0 0 0 40 4- Percentage, by weight, of average total hauls contributed by snails I Channel 1915 1920 4-7-ft. zone I 1-3-ft. zone 1915 1920 1915 1920 ------ Upper lake Middle lake Lower lake 99.4 93.2 98.8 13.6 95.1 0 91.1 55.1 98.8 6.6 85.3 1.8 89.5 15.3 95.3 91.1 12.5 0 The change in compo ition and abundance of the chironomid pop­ ulation of the bottom mud in this ection of the river ince 1915 are perhap even more inter ting and significant than tho e of the small M llusca. including, as they do, the appearance of several new and more or le pollutional speci , the di appearance of a number of formerly common or abundant cleaner-water forms and an almo t ixty-fold multiplication in weight of the average chironomid contribution to hauls since 1915. Unusually tolerant or pollutional species that have come into Peoria Lake since 1915 seem to be everal in number, and include Chiro110/ll11s plw1ws11s Linn. C. 111at1trns Joh. C. freq11ens Joh. and a variety of the fir t-named pecie . Chiro110111us p!u 111os11s L. ha before 1 een recorded by writers in Europe as a specie common in foul mud . It wa taken by us in 1920 in large numbers all the way from Chillicothe to the foot of Peoria Lake, both in the chann 1 and in the shallower zone . and al o occurred in moderate numbers in the ga y river-muds eight mile above Havana. It was not found by Malloch in 191 or 1. 13 collection from either above or below Peoria, but appears to have been pre ent in the badly foul d bed of the Des Plaine River at Lockport in the autumn of 1911, as indicated by a provisional determination by Mr. ha . . Hart. Chirono1w1s 111aturns Joh. and C. freq11cns Joh. are here listed a pecies capable of maintaining themselves in polluted muds becau e of their oc­ currence in 1920 in abundance in the Illinois River oppo ite Peoria, and because of the absence of definite record of them from clean mud, I e­ where-either in the Illinois River or other waters. Three more or le tolerant or pollutional p cie , Ta11_1,p11s dyari Coq., Chiro11011111s decants Joh., and C. crassica11dat11s J\Iall.. may be Ii ted as hold-over from 1913-1915, when, a in 1920, they wer common in collections from some tation opposite or above Peoria. \Ve note that C. derorus was the comrnone t pecie of this family found by \Ve ton and Turner in the contaminated bottom of the Cowee et River in 1916, just below the drain of the city of Brockton, Ma . Ta11ypus dyari oq. wa found by Malloch some years ago to frequent a badly polluted local 4:1 ditch in Illinoi . and wa taken by u in 1912 in the wor·t fouled portion of the Illinoi River between Morri and Marseille . thotwh not north­ ward of tho e place . 1 one of the three l eci wa f und by us either in 1 }l20 or in 1n3 _outh of Peoria; and th la t one namecl. n - where at all except at Peoria. The li t of larval midge- pecie that have dropped out of thi. ~ cti< n of the Illinois River since 1915 include at lea ·t four, of which Lut one, hiro11011111s ll'11ta11s F .. is known d finitely to do badly in the pre ence f pollution and to have been common in thi section during or before 1915. Thi pecies was common to abundant in 1913-191.- both in the river and in the lakes all the way from Peoria Lake to Havana, but ha now - apparently disappeared altogether from the lake and from the greater portion of it old river-range. pecie of apparently rather indiff rent habit as indicated by their distribution in this s ction and above and be­ low six or seven years ago, but that failed to appear in Peorja Lake col­ lection in rnzo. are two in number-C. lobifcrus ay and C. 'zriridicollis V. d. \V. MIDGE LARVAE ( CHlRONOl\'llDAE* ) OF BOTTOM M u m, OF ILLINOIS RIVER AN Jl P F.ORTA LAKE, CHILLICOTHE TO WESLEY, 1913-1914 TO 1920- JULY-OCTOilEH. 1. Poll-utional or tolerant svecies that have come in since 1918- 1,1. Chironomus plumosus L ... .. Des Plaines River, Lockport, 1911, Hart. .Common, 1920, Chillicothe to Peoria, and Havana to Liverpool. C. plumosus L. , var ... ..... .. . ........... .. .. . ...... ........ ... ...... Common, 1920, lower Peoria Lake, but not south of Peoria. C. maturus Joh ...... .. ...... ..................... . ...... . ....... ... i· Common, 1920, lower Peoria Lake, but not south of Peoria. C. frequens Joh ....... . .. . .. . . .. ................. . .................. ·;- Common. 1920, lower Peoria Lake, but not south of Peoria. 2. Tolerant or indifferent species comm on both 1913-14 ancl 1920. Tanypus dyari Coq .. .. ... .. Peoria. 1913; Morris to Marseilles, 1912 .. Common, Chillicothe· to Peoria Narrows, Chironomus decorus Joh .... Common at Peoria and present at Havana, 1913 1920. ommon at Chillicothe and in upper Peoria Lake, 1920. C. crassicaudatus Mall ...... Adults taken by Hart at Peoria, 1914 .. .. Common in lower Peoria Lake, 1920. 3. Tolerant or incUfferent svecies that have dropped ou,t s in ce 1918-14- Chironomus lobiferus Say ... Commou, 1912- 13, Havana to Peoria and north to Depue. C. viridicollis v. cl . W ....... Common, 1912- 13, Havana to Peoria and north to Mar seilles. 4- Cleaner-water svecies. or s1iecies of doitbtful position, that llcwe clroppecl. out sincf' 1913-1,1• Chironomus nigricans Joh .. Peoria Narrows, 1913. C. tentans F ................ Cornmon, Havana to Peoria. 1913- 15. Cricotopus sp ........ .... .. . Peoria, 1913. Orthocladius sp ........ ..... Peoria, 1913. • It will be noted that this list and other lists bf C'hiroi.om idae following are compl e te . eith e r for 1!120 or 1913-15, only so far as they concern more or less definitely dc Lcrmine1l s pec ies; sever a l species of unce rtHin pos ition. both peri­ ods, iire omitted. t Adults and pupal ex u viae. ~ l'O 43 The vast increa e in number and weight of midge larvae in the muds of Peoria Lake between 1915 and 1920, the comparison being of July-September collections for both periods, goes far in some portions of the range toward making up the losses in the small Mollusca. \Vhile the average number of young midges taken to the square yard between Chillicothe and the foot of the Jake was less than 10 in the summer of 1915 in 1920 it had risen for the whole lake to 31 ; while in the channel and 4-7-ft. zone of the upper lake, between Chillicothe and pring Bay, numbers per yard were 121(5 and 554. Again, while in 1915 the greate t _ weight per acre figured for Chironomidae in a subdivi ion of Peoria Lake (the 4-7-ft. zone of the middle lake) was only pound , and the averaae for all zones and all subdivisions in 1915 was only 1.4 pound . in 1920 the average weight had risen in the channel and 4-7-ft. zone of the upper lake to 182 and 128 pounds respectively, and for all ubdivi ions and all zones to 83.3 pounds, or 59.5 times the average valuation figure of 1!)15. \Vhen we compare. the weight of the Chironomidae with the ·weight of the average total haul we find that the largest catches in Peoria Lake in ] 915 ran less than 6 per cent. Chironomidae, most of the collection , in fact, running less than 3 per cent. In 1920, on the other hand, we finri the Chironomidae making up from 21 to 42 per cent. of the average total \\'eight of collections in the channel between Chillicothe and Peoria, and from 70 to 96 per cent. in the 1-3-ft. and 4-7-ft. zones. Mro E LARYAE ( I-Imo~ ?IIIDAE) OF BOTTO:\! M D ' CHILLICOTHE TO FOOT OF PEORIA LAKEj, 1915 AND 1920 1. Nmnber and weight per unit of bottorn area --- Channel 4-7-ft. zone I 1- 3-ft. zone 1915 1920 1915 1920 1915 1 pper lake ~ 1216 13 554 12 Average No. per sq. :.\fiddle lake 10 36 21 201 6 yard Lower lake 0 244 0 332 0 - - - l'pper lake 0 •) ... 1"2 4.2 12 2 Average pounds l\1iddle lake 1.5 5 7 51 3 per acre Lower lake 0 86 0 132 0 Average weight per acre, all channel collections, 1920, 89.2 lbs. " " " all 4-7-ft.-zone collections, 1920, 1 1.0 lbs. ·• " all 1-3-ft.-zone colle ti ns, 1920, 27.6 lhs . Average weight per acre, all collections, all zones, 1920, 83.3 lb . Average weight per acre, all collections, all zon s, 1916, 1.4 lbs. 1920 0 84 198 0 42 24 ,! P r Pntage, by w ight. of averng total hauls contributecl by Chi1·ono1nidae hannel I 4-7-ft. zone 1-3-ft. zone Upper lake Middle lake Lower lake 1915 1920 1915 1920 1915 1920 0.08 2.0 0 44.2 2.2 20.8 5.7 41.9 0 71.1 2.6 96.2 3.4 84.7 0 ·O 87.5 82.7 lliuch a have the Judge-worm . the larYae of the midg have in­ crea ed in the past five years in Peoria Lake f rorn an averaecies present in 1913-15 b1it not Yound in 19'20, and, cli~tr-ib1ition in former period. 1. Viviparidae 1. Lioplax subcarinata Scattered occurrences. .. 2. Vivipara contectoides Common locally. " 3. V. subpurpurea Scattered occurrences. 2. Pleuroceridae 4. Goniobasis sp. Rare. 3. Amnicolidae 5. Amnicola emarginata Small uumbers locally. " 6. Amnicola sp. Common locally in shallower zones. 4. Sphaeriidae 7. Sphaerium staruineum Rare. 5. Ancylidae S. Ancylus sp. Not uncommon on live or dead shells. • To 1.5 miles l)elow h ead of Grand Island, 1920; to head of Grand Island, 1915. 0t 0t 56 Further evidence of a mixed status or condition of the bottom fauna in this portion of the river is furnished in the lists and figures of Chiro­ nomidae. In the first place, we note that while midge-larvae have in- ·creased greatly here since 1915, in spite of the disappearance the while of half a dozen formerly common species of clean-bottom habit, yet no distinctly pollutional species has invaded this section since 1915, and only two forms of wide range or doubtful preference (Chironomtts lobiferu,s Say and a species very close to C. decorus Joh.) are new here since the 1913-1915 period. Further, it will be noted that more than half of the increase in weight-valuation of Chironomidae in the river below Havana in the five years preceding 1920 is not due to these two newly introduced tolerant forms, if indeed they are both so, but follows from the multipli­ cation here recently of three of the large larvae of clean-bottom habit which were common to abundant in the lakes above Havana in and before 1915, but which have since been exterminated in that range, with the ex­ ception of Quiver Lake. These three species ( C. tentans F., C. ferrugi­ neovittatus Zett., and Procladi·us concinnus Coq.) occurred in good num­ bers in 1920 in this section of the river wherever there was mud and the sharp reversal in their distribution, from lake and backwater above Havana to river below Havana, seems to lend some support to the sup­ position that their recent appearance and rapid multiplication in their new range is in some manner connected with their disappearance from the old one. MIDGE LARYAE ( CHI.RONO:MIDAE) OF BOTTOM Muns OF ILLINOIS RIVER BELOW HAVANA,* 1913-14 TO 1920-JULY-OCTOBER 1. 'l'oTerant species or species of doubtful preference that have come in since 1913-14. Chironomus lobiferus Say. Present, 1920. C. sp. near clecorus Joh., No. 2. Abundant, 1920. 2. Cleaner-water species that have dropped out since 1913-14 . Palpomyia longipennis Lw, Present in 1913-14. Tanypus monilis L. Present in 1913-14. Chironomus dux Joh. Present in 1913-14. C. digitatus Mall. Present !n 1913-14. Cricotopus trifasciatus Panz. Present in 1913-14. Cricotopus sp. Present in 1913-14. S. Cleaner-water svecies that have coine in since 1913-14.t Procladius concinnus Coq. Common, 1920, shallow zones. Chironomus ferrugineovittatus Zett. Present, 1920, 4-7-foot zone. C. tentans F. Common, 1920, chiefly in shallow zones. 4- Tolerant or inclijferent spec.i,es that has dropped out since 1913-14. Chironomus decorus Joh . Present, 1913-14. • Occurrence in 1913--H principally below Beardstown; in 1920, 2.5 mil s below Ha\'ana to 1.5 miles below head of Grand Island. • t All these species were present or common both in the river and the lakes above Havana, 1913-14, but were not found in either of those ranges last year, if the occurrence of C. ferrugvneovittatus in Quiver· Lake in 1920 be excepted. 57 While sludge-worms showed some increase in this section since 1915, their gain was slight and of very small moment compared with the in­ creases sho:wn in five years either in the Peoria section or in the reach just north of Havana. All of the small oligochaetes taken, however, be­ longed to genera of the family Tubificidae, about half of them being species of the genus Tubifex. Though, as already mentioned, a marked increase in variety a well as an actual average increase in poundage since 1915, is plainly shown by the group of "other insects, etc.", there were a good many eliminations from the lists even in this group in the five years preceding 1920. Non­ insect groups or insects other than Chironomidae that were readily taken in this part of the river in 1913-1915 but that did not ap­ pear in collections in 1920, include the little crustaceans Asellus and Hyalella; two or three species of Ephemeridae ; two species of Corixidae; adult bottom-beetles of the genus Stenelmis; several fresh-water sponges; and at least one genus and species of Bryozoa, namely, Paludicella sp., which was formerly common on almost all the dead shells of Unionidae. Total average-valuations of all small bottom-animals for this sec­ tion in 1920-30 pounds per acre in the channel, 89 pounds in the 4-7- foot zone, and 526 pounds in the 1-3-foot zone-exceed 1915 figures in the first and last instances; while in the 4-7-foot zone they were well • under the· older valuations, as shown in the table following. Both in the channel and in the 1-3-foot zone the decreases in snails were more than made up for by increases in midge larvae and "other insects" and mis­ cellaneous species. In the 4-7-foot zone the increase in snails was great­ er and the increase in Chironomidae and minor insects, etc., less, either r-elatively or absolutely or both, . tha!l in the 1-3-foot zone. To what extent these zonal differences in distribution both of the total bottom fauna and its subdivisions may be connected with differences in whole­ someness of conditions on different sections of the river floor, or to what extent they may reflect mere casual migration of surviving species fol­ lowing a general mortality, our present data give us no certain ba is for an opinion. 5 ALL SMALL BOTTOM-ANIMALS, HAVANA TO GRAND ISLAND*, 1915 AND 1920 1. Average numbers per square yard Viviparidae and Pleuroceridae Sphaeriidae Amnicolidae, Val- validae, etc. Cbironomidae Oligocbaeta Ot her insects, worms, Crus tacea, etc. Grand total I Channel I 4-7-ft. zone I 1-3-ft. zone 1915 1920 1915 1920 1915 1920 6 6 0 trace 0.5 3 15 10 2 0 36 2 78 73 84 4 2 9 20 128 I 192 9 12 0 170 33 27 99 89 2 6 0 12 251 I 208 ------- 104 12 0 244 24 429 813 --- -- * T o 1 mil e be low h ead o f G ra n d I s la nd in 1 920; to h ead of G rand Island in 1915 . 2. Averag e pounds per acre Viviparidae and P leuroceridae Sphaeriidae Amnicolidae, Val­ va tidae, etc. Total sn a ils Chironomidae Oligocbaeta Oth er insects, worms, rust acea, etc. Gra nd total Per cent . sna.ils I Channel I 4- 7-ft. zone . I 1- 3-ft. zone 1915 1920 1915 1920 1915 1920 16 3 0 19 trace 0.1 3 22 86.3 9 1 0 10 6 I trace I 14 30 33.3 1 235 42 0.1 277 0.3 0.3 5 283 97 .8 11 386 6 44 0 0.1 17 430 45 1 1 0 26 4 89 435 19.1 1 98.8 312 6 0 318 122 1 85 526 60.4 59 Three all-Bottom-land Lakes and one Sand-beach Lake between Liverpool and Havana (Mile 199.0-207.0 below Lake Michigan) The season's collections in Liverpool, Dogfish, and Thompson lakes in 1920 were taken in early September in almost uniformly muddy bot­ tom between near shore and the six-foot line. All of the stations visited in these lakes at that time were in open water, though a large part of tlie same area in all of the lakes and most of it in some of them was well supplied with coarse vegetation bet.ween 1913 and 1915. Mud, spongy with gas, was taken at two of the tations in Liverpool Lake and there was more or less foulness of odor and abundant bubbling at all stations in all three lakes. While odor were particularly bad in the Liverpool Lake samples, they were not nearly so bad either in Thompson or Dogfish. In the last-named lake there was a light covering of lighter colored silt over older gassy black mud, the topmost layer having its origin less than six months before in the dredging operations for an agricultural drainage district immediately north. In Quiver Lake the samples from muddy bottom in open water ( mostly in the old vegetation zone, as in the other three lakes) all had bad odor and gave off abundant bubbles. Samples from the mud and mud and shell bottom in the deeper "channel" through this lake, and from the mud and sand near the east beach were decidedly less gassy and more wholesome in odor. While not less than six families of snails, represented by about a dozen species, were common or abundant in 1913-1915 in each of these four lakes, no snails at all were taken in Liverpool or Dogfish lakes in September, 1920, and in Thompson Lake only a small number of a single species. In Quiver Lake, as in Dogfish and Liverpool lakes , no snails at all were found in the shallower, more stagnant open portion less than six feet in depth; but in the "channel" fed by Quiver Creek, and toward shore on the east side, good numbers of Pleurocera, and small numbers of l.1usculium transversum and Vivipara subpu,rpitrea were taken. The table following shows the detailed changes in the composition of the snail fauna in Thompson Lake only. It represents very well, also, with only slight alterations, the changes that have taken place in Dogfish and Liverpool lakes, and in the muddy portion of Quiver, the principal requirement being to transfer the little surviving sphaeriid at the head of the table to the list of species underneath that have dropped out since 1913-1915. SNAIL F AUNA 0 ~' BOTTOM: Mu os OF THOMPSON L A K E:, 1913-1915 TO 1920 I. Species s1wviving in 1920. 1. Sphaeriidae Musculium transversum Present, 1920, in very small numbers in Thompson Lake only out of four lakes examined. Was common to abun­ dant in all lakes of this district, 1913-15. IL Species t hat have dropp,ed 01a since 1913-15, and dis tributi on in that per i od. 1. Viviparidae 1. Campeloma subsolidum Common, all zones. " 2. Lioplax subcarinata Common, deeper water. " 3. Vivipara contectoides Abundant locally ; present nearly everywhere . .. 4. V. subpurpurea Infrequent. 2. Amnicolidae 5. Amnicola emarginata Common locally. " 6. Somatogyrus sp. Infrequent. 3. Valvatidae 7. Valvata bicarinata Common to abundant. " 8. V. tricarinata " " • 4. Planorbinae 9. Planorbis trivolvis Common, shallower zones. 5. Physidae 10. Physa sp. " " " 6. Sphaeriidae 11. Musculium jayanum Scattered occurrences. ' 12. Pisidium sp. Abundant locally. O') 0 61 The drop in average weight-valuation of the snail fauna in these four lakes, except in the less injured portions of Quiver Lake mentioned, amounts to little short of total disappearance-namely, from 122-363 pounds per acre to nothing at all in Liverpool, Dogfish, and the muddier, more stagnant portion of Quiver; and from 409 pounds to 4 pounds per acre in Thompson. The decrease in snail poundage since 1915 in Thompson Lake, where it is in the least ratio, was 99.1 per cent., which is greater even than the percentage decline in the river channel between Liverpool and Havana. In the Quiver Lake channel the drop in valuation figures since 1915 is only about 70 per cent., leaving an average of 248 pounds per acre in the limited range in September, 1920. Shoreward on the muddy side of Quiver Lake an average valuation of 109 pounds per acre in 1920 stands without a separate l 914 or 1915 figure for comparison. Liverpool Lake* I Thompson Lake* Dogfish Laket Quiver Laket Quiver Lake "channel" Quiver Lake, sandy shore, east side S N AIL FAU NA oF BOTTOM Muns, FOUR LAKll:S NORTH OF HAVANA , 1914- 1915 TO 1920 AVERAGE NU1\1BER PER SQU ARE YARD I. Mud Bottom, 2 to 6 Feet 1914- 1915 1920 and Sphaeriidae Amnicolidae, 0 .f and Sphaeriidae Amnicolidae, 0 .f Viviparidae I I Valvatidae, I T t 1 I Viviparidae I I Valvatidae, I T t 1 Pleuroceridae etc. snai s Pleuroceridae etc. snai s 23 113 68 85 160 common 17 153 138 50 0 0 10 98 164 74 50 864 370 209 ------ 0 0 0 0 11. Sandy or Sand and Mud Bottom 0 160 169 0 common 91 0 8 0 0 0 3 0 0 0 0 0 0 0 8 0 0 169 94 • Figures in 1914- 15 columns are for y ear 1915. t Figures in 1914- 15 columns a re for year 1914. ~ ~ • 8, \II J•'Al f 'IA ot' Bo•1vru)1 Muus, FOUlt LAKl•:s NOltTll Ok' l--1 1\1 ,\'\A , 1914 - 1915 TO 1920 AVERAGE VALUATION S , l'OUNUS !'rnlt ,\l ' ltF I. Mud Botto:n, 2 to 6 Feet 1914-1915 1920 I '7iviparidae I \ Valvatidae, I I Viviparidae I I Valv-atidae;-1 Tota Pleur~~iridae Sphaeriidael Amn~~~~idae, 8~~\f~ Pleur~~iridae Sphaeriidae Amn~~~~idae, snail~ Liverpool Lake"' Thompson Lake• Dogfish Laket Quiver Laket 117 438 336 329 4 16 10 17 1 5 9 17 · 122 459 355 363 0 0 0 0 ll. Sandy or Sand and Mud Bottom ---- Quiver L ake "channel'' I 800 I 0 I Quiver Lake, sandy shore, east side I common I 0 I • Fig ur t:s in I !l 14-1915 columns are for year 1915. t F igures in 1914- 19) 5 columns a re for y ear 191-1 . 0 I 800 I 248 I 0 I common I 109 I I 0 4 0 0 0 2 I I 0 0 0 0 0 0 I I 0 4 0 0 248 111 O} v;) 6-± In Thompson, Dogfish, and Liverpool lakes in September. 19 0, not only was it true that not a sing! definitely recognized clean-water chiro­ nomid of the previous period ( 1913-1915) was found surviving in the larval or pupal stage in the mud , but, as well, the list both of new en­ trant and survivals, of whatever habit of preference, showed up very meagerly both in variety and abundance as compared with the li t and tigures for the Peoria Lake di trict and the river just above Havana. Both in Thompson and Liverpool lakes, however, there did appear la t year mall number of one new form of po ibly tolerant habit, thi opinion being based only on its taxonomic nearne to Chiro11011111s d cc oms Joh. In neither of the e two lakes nor in Dogfi h Lake wa th re any evidence of the recent intrusion of species of distinctly pollutional habit, while in the muddier portions of Quiver Lake two of the older clean-water Chironomidae (C. f errugineovdtat11s Zett., and Palpomyia lungipennis Lw.) that were formerly pre ent in all the lake of this group were the principal components of the 1920 chironomid population in eptember. The changes i'n total chironomid poundages since 1914--1915 in all of these four lakes except Quiver, quite contrary to those in the Illinoi River opposite, are in the direction of decrease rather than increase. the average yield in 1920 ( 9 pounds per acre in Dogfish, 4 pounds in Thomp­ son, 2 pounds in Liverpool) being in no ca e over 50 per cent. of the 1914-1915 yields. and at the lowe~t only 5 per cent.; while they are only 5 to 7 per cent. of the 1920 yield of Chironornidae from the river muds between Liverpool and Havana. The di crepancies between lake and river figures for immature midae in thi portion of the river sy tern. contrasting with essentially imilar changes both in river and lake in the nail group, may be concerned with the fact of _the greater ease of spread of the eggs and larvae of the midges down stream with the advance of pollution than b)' wing across the timbered ridges that separate the river from the lakes. At any rate, two of the principal pollutional or tolerant specie contributing to last year's large river poundages of Chironomidae ju t above Havana (C. pl11111os11s Linn., and C. dccorns Joh.) did not up to that time appear to have been uccessful in making the trip. 65 Mro ,E LAR\'AE ( CJITROXO:\lI0AE) OF BOTTO;\f Mro, OF LIVERPOOL, DOGFISH, QUIVER, ANO THOMPSON LARES, 1913-1914 TO 1920-JULY-O TOilF.R 1. Tolerant spec'ies or speci s of clonbtful l)refr•r ence that hav come in si ncr 1913-14. Chironomus sp. near decorus Joh., No. 2. Common, 1920, Thompson Lake only. C. sp. near decorns Joh., No. 1. 'ommon, 1920, Liverpool Lake only. 2. Formerly commion cleaner-water species still surviving in 1920. Chironomus ferrugineovittatus Zett. Present, 1920, Quiver Lake only. Palpomyia longipennis Lw. Present, 1920, Quiver Lake only. S. Gleaner-water species that have clroJ)]}ecl out since 1918-1911,. Tanypus monilis L. Common, all lakes. 1913-1914. Procladius concinnus Coq. Common, all lakes, 1913-1914. P. sp. near concinnus Coq. Common, most lakes, 1913-1914. Chironomus tentans F. Abundant, all lakes, 1913-1914. C. modestus Say. Common, all lakes, 1913-1914. 4. Tolerant species that have drovped 011,t since 1.91.3-1914. Chironomus lobiferus Say. Present, 1913- 1914, Thompson Lake only. C. decorus Joh. Present, 1913- 1914; lake not stated. MIDGE LARVAE (CHlROXOMJDAE) OF BOTIO:\I M D, , LAKE NORTH OF HAVANA, 1914-15 AND 1920-JULY-O TOllER I. Mud bottom, 2 to 6 feet Number per f?quare yard Pound's per acre 1914-1915 I 1920 I Liverpool Lake* 38 14 Thompson Lake* 12 24 . Dogfish Laket 60 24 Quiver Laket 33 54 Ill. River. Liverpool to Ha- Channel, 0 950 vana, 1915, for comparison 4-7 ft., 0 225 II. Sandy or sand and mud bottom Quiver ''channel" • 0 Quiver Lake, sandy shore east side Not separately counted • Figur sin 1914-15 columns ar fo1 ) ea r J!ll ;;. t Figures in 1914-15 <'olumns a r fo r yf'a l ' J!ll4 0 6 1914-1915 26 8 30 6 0 0 0 Not separately valued I 1920 --- 2 4 9 12 164 45 I 0 1 66 The increase in sludge-worms in Liverpool, Dogfish, and Thompson lakes since 1915, though comparing with decreases in midge larvae, as already mentioned, was greater even than the increase in these worms in the Illinois River channel opposite, apparently proving that this group has been able to accompany the pollution inward from the river, even if the midges have not. The sludge-worms in the first-named lake amounted in figures per square yard to 389 in September, 1920, as compared with none at all in the collections of July-October, 1915 ; and in pounds per acre to 14 in 1920 as against none in the former period. In Quiver Lake in 1920 , both in the muddy portion and in the sandier areas, while the in­ crease in small oligochaetes since 1915 is evident enough, it is very much le than in the other three lakes. The small oligochaetes taken in Liver­ pool, Dogfish, and Thompson in 1920 were nearly all Tubificidae and a great majority of them belonged to the genus Tubifex. In the Quiver Lake samples, on the other hand, small non-tubificid Oligochaeta were vi ibly more common than Tubificidae. SLU DOE· WORMS , (PRINCIPALLY T UBIFI IDAE), LAKES NORTH OF H AVANA, 1914-15 AND 1920 I. Mud bottom, 2 to 6 feet Number per square yard Pound's per acre 1914-1915 I 1920 .. Liver pool Lake* 0 389 Thompson Lake* 0 128 Dogfish Laket I 0 128 I Quiver Laket 12 48 Ill. Ri ver, Liverpool to Ha-lChannel, 0 89 vana, 1915, for comparison 4- 7 ft., 0 4 II. Sandy or sand and mud bottom Quiver Lake "channel"* 0 Quiver Lake, sandy shore eas t s ide Not separately. counted! • F ig ures in 1914-1916 columns are for y ear 1916. t F igures in 1914-1916 columns are for year 1914. 0 30 . I 1914-1916 \ 1920 0 0 0 0.4 0 0 0 Not separately valued 14 4 4 2 3 0.1 0 1 67 Not only in Thompson, Dogfish and Liverpool lakes in 1920, but in Quiver Lake also in its muddy part, we found nothing at all surviving out of a list of some ten or twelve families of minor insects and miscel­ b.neous small bottom-animals other than the groups already passed in re­ view that were common in all of these lakes in 1914--1915. Though this item of loss in the lakes near Havana has been greater since 1915 than in the river just above Havana, the decrease in poundage therein in com­ parison to totals of all small bottom-animals has not been very large, the fi gures that follow showing that at the best the total weight of "other in­ ~ects, etc.," in the bottom muds of these lakes in 1914--1915 did not run to twenty pounds per acre. In the Quiver Lake "channel" and in the and and mud toward the beach side our collections showed leeches, Bryozoa, larvae of caddis-flies and nymphs of Odonata in good variety and number, the "channel" average in 1920 ( 32 pounds per acre ) being larger than in 1915. "OTHER INSE TS,'' WOR?,I. . CRr. TACF.A , ~:Tc· . . OF TH E BOTTO:ill :.\lr n~. LAKES NORTH OF H AVAN A, 1914-15 AND 1920 I. Mud bottom, 2 to 6 feet Number per square yard Pound's per acre 1914---1915 I 1920 Liverpool Lake* Thompson Lake* Dogfish Laket Quiver Laket I 16 0 32 0 22 0 83 0 II. Sandy or sand and mud bottom Quiver Lake "channel" * 26 Quiver Lake, sandy shore, east side JNot separately c~mnted • Figures in 1914-1915 columns are for year 1915. t Figures in 1914-1915 columns are for year 1914. 36 15 1914-1915 3 5 13 19 3 Not separately valued I 1920 0 0 (} 0 32 8 The decrease in average valuation of all small bottom-animals in the four lakes since 1915, with the sandy portions of Quiver Lake omitted, has been in ratios quite similar to those of average decline in the period in .. he n\·er oppo-ite, -viz .. :::9: to 9, A per cent. ~uch a decrea~e, on a ba e oi only 150 to -!00 pound- per acre a oi 1915. e-vidently lea-ve- a much ..:n alier re idue in he lakes than remain in the ri,·er of the enormou-Iy greater poundage: hat were there in and before l~Jl5. A -ver ae total­ . undaue- in rhese four lake . with the e.xception_ mentioned, in fact noun ed o only 1· to 16 pound per acre in l!J'> a compared \Yith ..J pound and .., , pound- in the channel and -!-, -ioot zone oi the riYer Oi)pO i e and ·i h 5.1-0 pound and '> ,1'22 pound- in the corre pondinu ri ·er zone: in the former period. Compared ·ith thi enom1ou fallinu off in yield- in he three all-bot 01 - and lake: and the -ta!!Ilant ponion oi ui ·er, the decrea_e in poundage oi ail bottom-animal in the mud-:and­ and--he 1 bottom oi Lhe Qui-ver Lake channel amounted to only 65 per cent. :ince 1915, leaYing an average oi '> 0 pound- per acre in eptember, 1 ! :.> • • in he :-i ·e:- ju abo,·e HaYcina. the PTeat part oi he decline in ake :ield oi all bottom-animal ince 191-1-1915 ha- re-ulted irom .. he de· ruction oi the nail·. he percentaae oi total-, ·eiaht Yaluation· contri uted b_· the small .. Iollu_ca dropping during the fi.-e or ix-year eriod · rorn 9 .. 2 to 33.3 per cent. in Thomp~on Lake. and in the other three lake . excepting the andy portion , irom "1- ., 3 per cent. to none at all. A.LL lLU.L BOT'TO.!·A..·r LU.!. L .\KE :\'ORTH OF fu,A.~.\. 1914-15 .\50 1920 1. Average otal -i:alua ion. JJ01aids per acre. and percentagP by WPight of ar;erage total hauls contr·buted by snails I. ?\lud bo om. 2 o 6 feet Pounds per acre Per cent. nails, Per cent. Li ·er ool L.* Thompson L.* Dogfi.-h L.t Quiver L.f 1914-15 149 .r;2 397 ') . ., r-o, decrease. 1914-15 1920 o 1920 16 9.2 12 9,.4 14 96., 1-1 96.3 inu"d on ""x r,noe) by weight 1914-15 ' 1920 1. 0 9-: .2 33.3 9.4 0 93.6 0 G9 II. Sandy or sand and mud bottom Quiver Lake "channel" • 803 280 65.1 99.6 88.5 Quiver Lake, 1rot 121 sandy shore, separately east side valued • Figures in 1!1U-l!ll:i columns aie for year 1r,1;; . t Figures in BH-1~15 columns are for year HtU. .?. Composition, by weight, of the uranrl total. pollut lo nnl RJH~rlcR 1 1,f'H po.lJ11f IOfl • u l 1JL lo lnn m Rl'N'llill 192 130 I 1 ~ I 31 60 I 8·1 1;19 :n -t • I I NS I 60 + :l7 I I 20 I I 20 I I I .... ~ ~ .Cl .Cl C :) .d .cl ~. :;,; I d. ':: o ~ ~ = I ~ : :~ ~~ : ~ b::, ~._ ::r: 1 .;;!: "'= S t S j ~t ii1~i1i~ ~1 ::::: i:: :::- .- .:: ... .... di - G) -t:it::. ...._ ~.::a:2t:= + + ~ 100 {i!)II I 174 111 16 1 -11 9G 120 ~, .. ,, , n ll lv• HJJ N'J4 •fl. "'· = ~ ; ~ ~ E : !1 I; ::~ ~..:: (i;j I I T r, t.al . l111·tud 1111( fl /•jr of, 11, ·, r l alll I · I u , n••t JD Jiff t,NiJO l!:" r1J)UIUIJ l ,216 201 r--;44 332 10 950 JO -I 225 I 15 I !]4 24 :1 6 l '' ~7 170 ~ 1 D6 !l44 I I-,- -1 I 12 I 2-l , · I 54 - ,-',---,-'-1 ',---I i-- 20 16 ~ 74 • Plu ~ s ig n m~ans romrn011, on lJa SiS o f a clu lt !A ;ind pu p ti 1•,1H iai-•. ALL SMALL BOTI'OM-ANIMALS, STEWART LAKE, 1915 AND 1920 111UD BOTTOM,, 2 TO 5 FEET Number per square yard Pounds per acre Viviparidae and Pleuroceridae Sphaeriidae Amnicolidae, Valvatidae, etc. Total snails . .. ............ . Chironomidae Oligochaeta Other insects, worms, Crustacea, etc. Grand total ................ Percentage of snails 1915 21 32 37 1920 0 4 0 ••• ·1 • • • • • • • • • • • • • • • • • • • • • • • • 8 74 3 12 43 0 . . . . . . . . . . . . . . . . . . . . . . ... . . . . I· .. ...... ... .... ........... · I 1915 41 13 12 66 2 0.1 6 74 89.1 1920 0 2 0 2 28 0.4 0 30 6.5 Estimated Reduction of Midsummer Surplus Stocks in the Com­ bined Acreage between Chillicothe and Lagrange Dam (103 Miles) since 1914-1915 \i\Thile the necessarily re tricted range of our bottom-and weed-fauna survey of 1920, compared with that of July-October, 19]± and 1915, leaves more gaps to be supplied by estimate in any general comparison than is perhaps best, it has seemed worth while, as a conclu ion to the present paper, t_o make some computations of the approximate total las. since 1914-1915 in surplus bottom- and weed-fauna stock. a of the midsummer period for the entire acreage of river and lakes in the former­ ly enormously rich middle Illinois Valley di trict between the head of Peoria Lake and the Lagrange dam. These calculations have involved a partial reapportionment, by estimate largely, both of acreages and of ' acre-yields, as of 1908-1915, as published in a preceding paper,* these • The Small Bottom and Shore Fauna of the Illinois River and its Connectln~ Lakes, Chillicothe to Grafton: its Valuation; its Sources of Food Supply; and it~ · Relation to th Fi h ry. By R. E. I ic-hanh;on. Hui. Ill. Nat. Hist. Surv., V I. 13 , Art. X\'. 1921. 74 being here estimated as actual, outside of levees, and not as in the virgin valley-for the purpose of comparison with the 1920 data rather than with the fish-yield figures of 1908 ; and involving as well, the application in some cases of both river and lake acre-yield-figures for limited areas studied in 1920 to much larger acreages not collected in that year. For these reasons, only general results are given here, and tabulation is avoided as giving too much of an air of certainty to figures that are at the best only approximations. In the 60.5 miles between Chillicothe and Havana in July-October, J 914-15 it appears, then, that there were surplus stocks of both bottom and weed animals, after deduction of shell weight, amounting to around i7,500 000 pounds in a combined open river and lake acreage, including Peoria Lake of about 29,000 acres at an approximate gage of ten feet, Peoria, or eight feet, Havana. Of this total I have estimated that about 2,700,000 pounds were in the bottom muds of the river and the wide waters of Peoria Lake between Chillicothe and the dam at Copperas Creek; about 3,800,000 pounds in the river muds between Copperas Creek dam and Havana; and about 3,000,000 pounds on the lake and other backwater floors between opperas Cre k and Havana. Considerably more than half of the total, that is, over 18,000,000 pounds ( 65 per cent.) of it, seems to have been made up of the small weed-living specie , of which Peoria Lake apparently furnished more than 4,000,000 pounds a few years ago, and the rich lakes between Copperas Creek dam and Havana, around 14,000,ff00 pounds. Applying to these same acreages uch average weights per acre as are suggested by the findino-s of Augu t-September, 1920, we note first an estimated reduction since 1915 in the bottom fauna of Peoria Lake and adjacent river between hillicothe and Copperas Creek that amounts roughly to 50 per cent., and that affects about 10,000 acres at the lower gages of the ten years preceding 19 0. Next are calculated reductions of 92 to 93 per cent. in the bottom fauna of some 1,400 acres of river and ome 1 ,000 acres of lakes between opperas Creek dam and Havana; and la t, reduction to practical nullity in the case of the acre-yield figures of small weed-animals both of the weedy acreage of Peoria Lake, estimated at 2,000 acres in ln0-1914, and of the one-time approximate 10,000 acres of shallow weed-area in the lakes between Copperas Creek dam and Havana. The total loss in poundage of surplus stocks between Chillicothe and Havana in five years appears indeed to have surpassed 25,500,000 pounds, or to have amounted on the average for both river and lakes, including both bottom and weed populations, to over 93 per cent. The extent of the los is better appreciated when it is known that it is usual to figure that the weight of fish living on animal food can be increased about one pound for each five pounds of such food eaten. From this view-point the loss in potential fish-yield apparently stands at some­ thing like 5,000,000 pounds yearly for the section, if also it be true, as is 75 generally assumed, that stocks of the kind in q11estion in the run of years at least reproduce themselves in weight once annually. Below Havana we lack data for carrying out computations in the detail or with anywhere near the exactness attempted for the 60-mile section to the north, particularly in the case of the bottom and weed fauna of the lakes, having collected in only one of these in 1920. Vv e note, first, of the 4,500 odd acres of river between Havana and the dam a t Lagrange, an apparent slight gain over 1915 in the bottom yields, which is, however, probably no greater than the normal error to be expected with the apparatus and methods used . Offsetting this gain fu rther to the point in fact of rendering it negligible, are suggested losses of enormous size since 1914-1915 both in the bottom and weed fauna of the lakes and other backwaters in the 42.5 miles which, combined, seem to have amounted to fully half the total stocks in the entire river and lake acreage open a little more than five years ago, or to more than twenty times the total bottom-fauna stocks of the section. This result, or a loss in the lake weed- and bottom-fauna of around 9,000 ,000 pounds, is simply arrived at if we estimate the loss in both the bottom- and weed-fauna stocks since 1915 at only 50 per cent. If we base conclusions for the entire acreage between H avana and the dam, on the recorded kind and extent of change in Stewart Lake since 1915 we must e timate the combined loss in both bottom and weed animals as even greater than 50 per cent., since it appears that on the weed-fauna side both the acreage and its average yield have probably been reduced that much. nd a most of the lake acreage between H avana and the dam at Laorange has since 1915 been north rather than south of the lower end of Stewart Lake, and therefore probably equally with it exposed to invasion by fou l water and sediments, the estimate of a nine-million-pound loss in this district since 1915 may be allowed to stand as a minim um probable fi gure. Combining a minimum loss in the first 42.5 mil es south of Havana of 9,000,000 pounds with one of 25 500,000 pounds between Chill icothe and that point, we have, then, it seems, to reckon on not less than 34,500,000 pounds total reduction in the midsummer stocks of small bottom- and weed-animals in five years in about 103 miles ; or, putting it another way, on about 7,000,000 pounds potential fi sh-yield missing from any new cal­ culation we wish to make about the more recent value of a 103-mile ec­ tion of the Illinois River fi shery that was, only a few years ago, among the richest of its kind in the fre h-water stream systems of the world, being then uninjured, so far as could be seen, by the increasing pollution from the population and industries to the north that has recently so nearly overwhelmed it. It will be noted that 7,000,000 pounds is little less than a third of the largest total fi sh-catch ev r taken from the entire Illinois River ( catch of 1908), more than half of estimated total ields in 1912 and 1913, and not improbably more than the total yield fo r the whole year 1920.