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biomass comparison method for detecting human impacts on fish populations in the Pilica River, Poland
Fisheries Research 39 (1999) 229±240
Applicability of the abundance/biomass comparison method for detecting human impacts on ®sh populations in the Pilica River, Poland Tadeusz Penczak*, Andrzej Kruk Department of Ecology and Vertebrate Zoology, University of èoÂdzÂ, ul. Banacha 12/16 90-237, èoÂdzÂ, Poland Received 11 March 1998; accepted 11 August 1998
Abstract In the Pilica River, a tributary of the Vistula, the abundance/biomass comparison method was employed for assessing the impact of stresses on ®sh populations. Generally, the method proved a useful tool for estimating disturbances in ®sh communities caused by point source sewage inputs and all impacts of a dam. A high correlation was recorded between the ABC index and Simpson and Shannon indices, which also negatively respond to the investigated stresses. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Impounded river; Fish populations; Pollution; Engineering; Over®shing; ABC method; Simpson and Shannon indices
1. Introduction The abundance/biomass comparison method, also known as the ABC method, was proposed by Warwick (1986) as a technique for detecting the impact of pollution on communities of marine macrobenthos. As a means of comparing data sets from many sites, Meire and Dereu (1990) proposed the ABC index based on the k-dominance plots of Warwick (1986). In one published study the abundance/biomass comparison method was used for investigating ®sh communities in regulated and unregulated rivers in Belgium with different degrees of pollution (Coeck et al., 1993). It was therefore decided to employ the *Corresponding author. Tel.: +48-42-678-1364; fax: +48-42678-1364; e-mail: [email protected]
method for investigating ®sh communities in a large alluvial river in Poland, where besides pollution and engineering, over®shing by both anglers and poachers is an important factor dramatically diminishing ®sh populations. Another aim of this study is to verify the assumption that diversity indexes (Simpson and Shannon) can be correlated with the ABC index (Coeck et al., 1993). 2. Study area, material and methods 2.1. Study area The sampling sites and the general location are presented in Fig. 1. The 342 km long Pilica is fed by sources situated at an altitude of 348 m, and enters the Vistula at an altitude of 94 m a.s.l. The catchment
0165-7836/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S0165-7836(98)00201-X
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T. Penczak, A. Kruk / Fisheries Research 39 (1999) 229±240
Fig. 1. Localization of sampling sites in the Pilica River. Electrofishing sampling sites are labelled with rectangles containing numbers 1±48. Water sample sites for physico-chemical investigations are marked with triangles (") and numbers 1±18. Arrows (!) indicate main pointal sources of pollution and tributaries inputting the largest pollution loads.
T. Penczak, A. Kruk / Fisheries Research 39 (1999) 229±240
area of the Pilica River is 9245 km2 (Kleczkowski and Kowalski, 1978). The morphometry of the Pilica river bed, its structure, number and type of hiding places and hydroconstructions are given in Table 1. Although not all of them are marked in Fig. 1, the Pilica is fed with water by 19 tributaries, whose length ranges between 21±86 km, and a large number of tiny, several kilometer long streamlets (Penczak and Mann, 1990). In 1973 the construction of a dam reservoir supplying the million people agglomeration of èoÂdz City and its several neighbouring towns with drinking water was completed in the middle course of the Pilica. In the years preceding the closing of the sluices of the reservoir, the water of the Pilica was polluted at 20 points along its course. Also, most of its tributaries carried polluted waters. Before the closing of the sluices of the dam all main sources of pollution between the backwater of the reservoir and the town of Szczekociny (Fig. 1) had been cleared up, while strongly polluted waters of the large tributary, LuciaÎzÇa River, formerly ¯owing directly into the reservoir, had been diverted along a canal to the WolboÂrka River, entering to the Pilica several kilometers downstream of the dam. Point pollution inputs to the Pilica and water sample sites for physico-chemical investigations are shown in Fig. 1, while respective analysis results are presented in Tables 2 and 3. Data on the physico-chemical water variables were obtained from Voivodeship Inspectorates of Environmental Protection. The Pilica is mostly polluted by agricultural and the food processing industry (butcheries, dairies, distilleries, fruit processing plants) and domestic sewage from villages and small towns. Industrial sewage inputs are located mainly in the towns of Koniecpol, PrzedboÂrz and TomaszoÂw Mazowiecki (Fig. 1). 2.2. Material Fish samples are 16 746 lampreys and ®sh captured in 48 sites (Fig. 1) from 15 June to 19 September 1984. They belonged to 31 species and represented 11 guilds (Table 4) according to Balon (1990). 2.3. Methods Fish were caught from a boat (sites 4±48) or while wading (sites 1±3), using a full wave recti®ed, pulsed
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DC electro®sher (3 kW, 230 V, 3±10 A) operated through two anode dipnets (Mann and Penczak, 1984). Species composition and relative abundance were assessed from a single electro®shing operation at each site in accordance with the Beklemishev rule (Backiel and Penczak, 1989). This states that the length of a sampling site is suf®cient if the number of species recorded does not increase with farther increase in length sampled. Captured ®sh were transferred to a tank located on the boat or to a bucket on the bank, each of which were ®lled with water containing anaesthetic. After sampling, ®sh were identi®ed, counted, measured, weighed (to the nearest 0.1 g) and then returned to the river. Species composition, relative abundance and standing crop were assessed from a single electro®shing operation at each site. According to Warwick (1986), condition of an animal community can be illustrated with the use of combined k-dominance plots (Lambshead et al., 1983) of abundance and biomass, where species are ranked in order of importance on the x-axis (logarithmic scale) with percentage dominance on the y-scale (cumulative scale). To compare data sets from various sites the ABC index proposed by Meire and Dereu (1990) was used. It is calculated as a mean difference between cumulated biomass and number: ABC index
PN
i1
Bi ÿ Ai ; N
where Bi is the percentage domination of species i (ranked from the highest to the lowest biomass), Ai the percentage domination of species i (ranked from the most to the least abundant species), and N is the total number of species. The index is negative for situations characterised by a strong stress, close to zero for moderate stress, and positive for lack of stress (Meire and Dereu, 1990; Coeck et al., 1993). Also, indexes of species diversity: Simpson (D) and Shannon (H), calculated for 48 sites by Penczak and Mann (1990) to estimate their relationship with the ABC index, were employed: X D pi 2 ; Hÿ
X
pi ln pi ;
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T. Penczak, A. Kruk / Fisheries Research 39 (1999) 229±240
Table 1 Morphometry of the Pilica River Downstream (km)/stream order
Mean width/mean depth (m)
Bottom structure
Occurring factors
Hydrotechnical constructions, remarks
(0±11)/1
(2±2.5)/(0.3±0.5)
s, st, m
Fascine, canalised, numerous concrete weirs
(11±25)/(1±2)
5.6/(0.2±0.4)
s>st, m
(25±41.5)/2
(6±8)/0.5
s, m>st
(41.5±76.5)/3
(6±12)/(0.5±1.0)
s>g, m
(76.5±123)/4
(12±35)/(10.8±1.2)
s g
(123±169)/4(5)
(50±70)/(0.5±1.2)
s
b () e b e 0 () b c d a () b () c d e () a b () c () e () a b (0) c () e (0)
169±189 (189±202)/5
(40±60)/0.8(1.5)
s>g
(202±208)/5
50/1.0
s
(208±215)/5
40/1.5
s g, st
(215±255.5)/5
(60±80(100))/0.8(1.0)
s g>st
(255.5±281)/6
(50)70/1.0
s st, g
(281±342)/6
(70(55±80))/1.0(1.5)
s>g>st
(342±outlet)/6
40/1.5(2.0)
s>st
SulejoÂw reservoir a b c (0) e () a e a 0 () b c a (0) b () c e (, 0) a b (0) c (0) d 0 () e 0 () a (0) b () c () d 0 () b c d e 0 ()
As above Wild river, in some places a lot of fallen trees As above
As above
Wild natural river, beaches, sandy islands
Banks protected by fascine and revetment
Natural river, flowing through meadows Natural river, flowing through forest Banks protected by fascine and revetment on 255 km Natural river, islands, beaches
Banks protected by fascine and revetment (286 and 304 km) Banks protected by fascine and revetment
Explanations ± m: mud; s: sand; g: gravel; st: stones; a: meanders; b: hiding places (fascinewattle fence, roots, branches, fallen trees); c: canopy; d: overhanging willow branches; e: submerged plants; 0: none; : very little; : common; : abundant.
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Table 2 Concentration of dissolved oxygen, BOD, COD and suspension in the Pilica River in 1984 Number of water intake spot
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Down stream (km)
37 40 64 88 115 123 143 167 181 194 203 210 221 250 252 284 314 341
Dissolved oxygen (mg O2 dmÿ3)
BOD (mg O2 dmÿ3)
xann
Min.
Max.
xann
Min.
Max.
xann
Min.
Max.
xann
Min.
Max.
9.4 8.0 9.3 7.9 8.5 8.1 8.6 8.6 9.1 9.2 8.5 8.0 8.3 8.8 9.6 9.5 10.1 9.9
7.1 5.4 7.8 6.2 6.2 6.2 7.0 7.7 6.0 5.7 5.2 4.4 5.7 6.4 7.2 7.4 8.2 7.0
12.5 11.0 10.9 10.6 11.4 9.8 10.2 11.1 14.9 14.8 13.1 11.1 11.7 11.4 12.5 13.5 12.8 13.8
3.0 3.9 5.5 4.8 2.9 3.0 2.6 2.8 4.1 3.3 3.4 3.8 4.0 3.4 6.5 6.2 6.4 7.6
1.0 1.5 1.3 1.3 1.3 1.2 1.2 1.2 1.4 1.5 1.7 1.7 2.1 1.5 2.9 2.3 3.4 3.2
4.2 6.4 12.5 17.0 4.9 4.2 4.1 4.2 7.3 5.8 5.1 5.9 6.2 5.9 18.8 15.6 12.4 19.6
4.5 5.3 7.3 7.2 6.4 5.8 6.0 5.7 7.9 7.3 6.0 6.8 7.8 7.3 8.7 7.7 7.3 8.6
3.6 4.4 3.2 5.0 5.0 4.2 5.0 3.9 5.8 5.1 5.0 4.6 4.3 5.5 5.6 3.7 3.4 5.1
5.1 6.9 14.0 12.7 7.6 7.8 9.4 7.2 9.9 10.6 9.3 10.4 13.9 10.6 15.5 11.7 11.4 12.0
10 13 10 26 22 21 21 19 26 24 21 23 22 26 21 19 21 18
2 2 0 14 11 11 11 11 10 16 12 14 14 14 10 11 11 10
21 45 32 49 29 30 29 27 45 35 30 33 43 66 39 31 36 40
COD (mg O2 dmÿ3)
Organic suspension (mg dmÿ3)
Table 3 Concentration of ammonia nitrogen, nitrate nitrogen, phosphates and sulphates in the Pilica River in 1984 Number of water intake spot
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Downstream (km)
37 40 64 88 115 123 143 167 181 194 203 210 221 250 252 284 314 341
Ammonia nitrogen ÿ3 (mg NH 4 dm )
Nitrate nitrogen ÿ3 (mg NOÿ 3 dm )
xann
Min.
Max.
xann
Min.
Max.
xann
Min.
Max.
xann
Min.
Max.
0.36 0.33 0.76 0.09 0.07 0.10 0.07 0.01 0.12 0.13 0.11 0.29 0.17 0.09 0.66 0.40 0.44 0.38
0 0 0 0 0 0 0 0 0 0 0 0.05 0 0 0.13 0.16 0.20 0.19
1.00 1.20 2.10 0.48 0.37 0.47 0.42 0.07 0.39 0.42 0.41 0.83 0.38 0.32 4.29 0.67 0.67 0.72
1.14 0.96 0.98 0.45 0.47 0.52 0.44 0.46 0.14 0.16 0.29 0.59 0.55 0.40 0.35 0.36 0.43 0.45
0.70 0.70 0.70 0.27 0.28 0.39 0.21 0.34 0 0 0 0 0 0 0.08 0.09 0.09 0.08
1.70 1.50 1.30 0.62 0.66 0.64 0.59 0.65 0.42 0.33 0.51 1.03 0.96 0.86 0.87 0.75 0.93 2.10
0.22 0.29 0.20 0.39 0.22 0.32 0.26 0.24 0.30 0.10 0.14 0.39 0.30 0.28 0.45 0.25 0.72 0.29
0 0 0 0.12 0.16 0.14 0.03 0.13 0.05 0.05 0.07 0.23 0.20 0.18 0.22 0.17 0.13 0.14
0.56 0.66 0.58 0.85 0.32 0.87 0.48 0.76 1.45 0.23 0.20 0.96 0.35 0.57 2.20 0.33 4.37 0.53
24 23 21 32 37 30 32 29 36 42 42 136 118 121 42 39 44 39
21 20 16 21 18 16 21 19 28 26 30 112 88 106 23 18 29 30
28 25 25 73 70 37 53 36 43 55 87 155 139 131 64 51 69 52
where pi is the percentage of the specimens of a given species in the total number of specimens. Both indexes assume values from 0 (lowest diversity) to
Phosphates ÿ3 (mg POÿ3 4 dm )
Sulphates ÿ3 (mg SOÿ2 4 dm )
1 (highest diversity) (Odum, 1980) after scaling in this way: D by subtracting from 1 and H by dividing it by the natural logarithm of the number of species.
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Table 4 List of fish species in the Pilica River drainage basin listed according to the reproductive guilds (Balon, 1990); taxa revised after Kottelat (1997) Nonguarding and open substratum egg scattering (A.1) Pelagophil (A.1.1) Lithopelagophil (A.1.2) Lithophils (A.1.3)
Anguilla anguilla (L.) ± European eel Lota lota (L.) ± burbot Chondrostoma nasus (L.) ± nase Leuciscus cephalus (L.) ± chub Phoxinus phoxinus (L.) ± minnow Alburnoides bipunctatus (Bloch) ± spirlin Aspius aspius (L.) ± asp Barbus barbus (L.) ± barbel Barbus petenyi (Heckel) ± spotted barbel Leuciscus leuciscus (L.) ± dace Leuciscus idus (L.) ± ide Blicca bjoerkna (L.) ± silver bream Perca fluviatilis L. ± perch Gymnocephalus cernuus (L.) ± ruffe Rutilus rutilus (L.) ± roach Alburnus alburnus (L.) ± bleak Abramis brama (L.) ± bream Stizostedion lucioperca (L.) ± zander Esox lucius L. ± pike Scardinius erythrophthalmus (L.) ± rudd Tinca tinca (L.) ± tench Carassius carassius (L.) ± crucian carp Carassius gibelio (Bloch) ± giebel Cyprinus carpio L. ± common carp Misgurnus fossilis (L.) ± mud loach Cobitis taenia L. ± spined loach Cobitis aurata (Filipi) ± goldside loach Gobio gobio (L.) ± gudgeon Barbatula barbatula (L.) ± loach
Phytolithophils (A.1.4)
Phytophils (A.1.5)
Psammophils (A.1.6) Nonguarding and brood hiding (A.2) Lithophils (A.2.3)
Lampetra planeri (Bloch) ± brook lamprey Salmo trutta L. ± brown trout Rhodeus sericeus (Bloch) ± bitterling
Ostracophils (A.2.4) Guarding and clutch tending (B.1) Phytophils (B.1.4)
Leucaspius delineatus (Heckel) ± sunbleak Silurus glanis L. ± wels
Guarding and nesting (B.2) Ariadnophil (B.2.4)
Gasterosteus aculeatus L. ± stickleback Pungitius pungitius (L.) ± ten-spined stickleback Ameiurus nebulosus (Lesueur) ± brown bullhead Cottus gobio L. ± European bullhead
Speleophils (B.2.7)
These indices are indispensable because the Simpson index is weighed in favour of dominant species and the Shannon index in favour of rare ones (Odum, 1980).
3. Results The combined abundance/biomass curves for 43 of the 48 sites are given in Figs. 2 and 3. Sites 1±5 were
T. Penczak, A. Kruk / Fisheries Research 39 (1999) 229±240
235
Fig. 2. Combined k-dominance curves of biomass (-*-*-) and abundance (-&-&-) and the ABC index values for sites 6±27. Site 16, removed for graphical reasons, is almost identical with site 15.
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T. Penczak, A. Kruk / Fisheries Research 39 (1999) 229±240
Fig. 3. Combined k-dominance curves of biomass (-*-*-) and abundance (-&-&-) and the ABC index values for sites 29±48.
T. Penczak, A. Kruk / Fisheries Research 39 (1999) 229±240 Table 5 Values of ABC, Simpson (D) and Shannon (H) indices in given sites Site number
Downstream (km)
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
33 43 50 55 70 80 93 105 118 132 148 153 156 160 165 190 195 199 202 206 210 214 218 225 229 233 238 247 255 262 271 274 278 281 286 293 304 312 320 325 329 334 341
ABC ÿ2.48 3.99 1.15 3.42 1.02 ÿ1.07 3.52 ÿ6.38 ÿ6.74 ÿ7.99 ÿ7.77 ÿ6.94 ÿ9.33 ÿ6.86 0.67 ÿ7.85 ÿ7.73 0.07 ÿ2.76 ÿ4.03 ÿ3.96 ÿ9.71 3.42 ÿ13.23 ÿ11.90 ÿ3.25 ÿ7.70 2.50 ÿ4.15 ÿ0.74 ÿ7.36 4.78 0.94 ÿ6.22 4.09 ÿ2.12 ÿ2.39 ÿ4.56 2.66 2.14 ÿ0.89 2.36 ÿ1.10
D
H
0.73 0.78 0.79 0.78 0.65 0.79 0.85 0.79 0.75 0.78 0.80 0.76 0.75 0.55 0.76 0.50 0.58 0.82 0.68 0.63 0.77 0.72 0.75 0.64 0.69 0.60 0.65 0.76 0.78 0.82 0.57 0.81 0.71 0.71 0.80 0.75 0.60 0.72 0.84 0.86 0.81 0.81 0.81
0.73 0.78 0.80 0.74 0.61 0.71 0.80 0.69 0.68 0.69 0.72 0.68 0.69 0.49 0.69 0.44 0.46 0.75 0.61 0.53 0.72 0.63 0.70 0.49 0.58 0.51 0.56 0.68 0.71 0.81 0.55 0.78 0.66 0.61 0.73 0.66 0.53 0.66 0.79 0.84 0.77 0.72 0.70
excluded because of a low number of species, i.e. 2±5, for which the ABC index assumed alternately extraordinarily high and low values, largely distinct from our picture of the ®sh fauna. The ABC index values, excluding sites 1±5, are shown in Table 5.
237
Between the town of Szczekociny and the Czarna Wøoszczowska's mouth (sites 7±12) the values of the ABC index are positive, except one, site 11 (Figs. 2 and 3, Table 5). The Pilica River is less polluted there, as indicated by decreasing maximum values of most of its water variables (Tables 2 and 3), has sustained its natural bed structure, is ``dammed'' by fallen trees (hiding places) (Table 1), no poachers were encountered, and the number of anglers was low. In the river section between the out¯ows of the Czarna Wøoszczowska and Czarna Konecka Rivers (sites 7±12, Fig. 1) similar and strongly negative values of the ABC index were detected. The river is natural there, has well developed ecotones along banks, numerous large clumps of submerged vegetation, and slightly increased water quality (Tables 2 and 3). Numerous meetings with poachers and a high number of anglers encountered indicate that they may be responsible for a reduction of large ®sh there. At site 20, above the backwater of the reservoir, the ABC index has a positive value, close to zero (Table 5). In some tailwater sites the combined kdominance curves for abundance and biomass cross each other (sites 23, 24, 26, 31, Fig. 3), and with two exceptions as far as through site 32, the ABC index has negative values. The location of combined k-dominance curves for abundance and biomass, and values of the ABC index in the lower course of the Pilica (Drzewiczka River ± Vistula) assume alternately positive or negative values. The pressure of poachers is limited because the river is too deep to haul nets while wading there. Fish have many hiding places in the banks protected by fascine and revetment, the amount of dissolved oxygen in water is higher but BOD, COD, organic suspension, ammonia nitrogen and phosphates indicate a decrease in its quality (Table 2). The values of Simpson (preferring dominant species) and Shannon (preferring rare species) for the investigated sites are included in Table 5. The calculated correlation coef®cients for both these indexes with the ABC index are r0.53 and r0.63, respectively, at the signi®cance level of p0.001 from 40 d.f. (see Figs. 4 and 5). Because we cannot distinguish between the independent and dependent variables here, ellipses were used instead of linear regression for displaying the dependence tendency.
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T. Penczak, A. Kruk / Fisheries Research 39 (1999) 229±240
Fig. 4. Dependence between Simpson index and ABC index (r0.53).
Fig. 6 proves that in most cases the peaks of ABC, Simpson and Shannon indexes are in phase. Discrepancies concern only a section between the out¯ow of the Czarna Wøoszczowska and Czarna Konecka Rivers, where consequently negative values of the ABC index were recorded, at a quite high species number. A scarcity of big specimens was caused by numerous anglers and poachers. 4. Discussion Investigations of the main channel of the Pilica proved the value of the ABC method for estimating
the in¯uence of water pollution and other human impacts on abundance and biomass of ichthyofauna. As in the study by Coeck et al. (1993) the values estimated by the ABC method were declining below sewage inputs but not abruptly and consistently. When sewage inputs were sequenced along the river, the ABC index values remained negative but some exceptions occurred. When there were short gaps in sewage inputs then the value increased, which might be explained by the natural ability of a river to selfpuri®cation, and by ®sh migrations (Welcomme, 1985; Cowx, 1994). Similarly as in Coeck et al. (1993) no statistically signi®cant correlations between given water para-
Fig. 5. Dependence between Shannon index and ABC index (r0.63).
T. Penczak, A. Kruk / Fisheries Research 39 (1999) 229±240
Fig. 6. Changes in the ABC index (-*-*-) and Simpson and Shannon indices (- - -) along the Pilica River.
meters and the ABC index were detected. On Coeck's suggestion the degree of water pollution in the Pilica was expressed on the ®ve-degree scale of Chemical Index (CI) developed by the State Institute for Nature Management in Netherlands. Unfortunately, no statistically signi®cant correlations between CI and the ABC were recorded. In contrast to Coeck et al. (1993) no dependence between degree of river regulation and the ABC index was detected. This ensues from the fact that river regulation in Poland consists mainly in protecting eroded banks with fascine and revetments, and thus is of different character from that of the rivers investigated by Coeck et al. (1993) in Belgium. Decisively negative values of the ABC index recorded in the sites of the reservoir's tailwater are probably caused by the presence of the dam of this large reservoir. Stresses connected with impoundment are regarded as having catastrophic effects on ®sh populations (Petts, 1984; Orth and White, 1993). The negative values of the ABC index have also been caused by mass drifts of the young-of-the-year perch
239
and roach from the reservoir. These species had great reproductive successes in the reservoir. Such a phenomenon was also observed in another impounded lowland river of Central Poland (Warta River) and it was re¯ected in dramatic decreases in mean body weight (Penczak et al., 1998), which exert decisive impacts on the abundance/biomass comparison (Warwick, 1986). We believe that many ¯uctuating, low values of the ABC index in the Pilica may have been caused by over®shing. Poaching has been included among the most harmful stresses for ®sh populations in this river (Mann and Penczak, 1984; Penczak and Mann, 1993). In the quantitatively middle course of the Pilica River, between the mouths of the Czarna Wøoszczowska and Czarna Konecka Rivers, some commercial ®sh species were not represented by adults (Mann and Penczak, 1984). The highest number of poachers, and simultaneously plenty of anglers, were observed during the present study in this very section of the Pilica and it was just here where despite a rather good water quality, negative values of the ABC index were recorded in all sites (13±19) (Table 5). According to Warwick (personal communication) the ABC method may successfully indicate the presence of poachers, because they usually capture big ®sh, while Simpson and Shannon indices may fail to do so. Despite the ABC index displaying positive correlations with Simpson and Shannon indexes at the level p0.001 (Figs. 4 and 5), decisive and continuous discrepancies from this pattern occurred in the case of sites 13±18 (most of the poachers and the anglers) and also in the solitary ones in the lower course of the river (Fig. 6). Coeck et al. (1993) did not determine any signi®cant correlation between these variables, hence it is still a problem for discussion and further research. Acknowledgements Special thanks are directed to Johan Coeck (Belgium), Erik Mortensen (Denmark), Richard Warwick (UK) and two anonymous reviewers for critical comments on the manuscript. Authors also thank èukasz Gøowacki for help in preparing the English version of this manuscript. Field research was supported by the Main Board of the Polish Anglers Association, and the University of èoÂdzÂ.
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References Backiel, T., Penczak, T., 1989. The fish and fisheries in the Vistula River and its tributary, the Pilica River. In: Dodge, D.P. (Ed.), Proceedings of the International Large River Symposium, Honey Harbour, Ont., Canada, 14±21 September 1986. Can. Spec. Publ. Fish. Aquat. Sci. 106, pp. 488±503. Balon, E.K., 1990. Epigenesis of an epigeneticist: the development of some alternative concepts on the early ontogeny and evolution of fishes. Guelph Ichthyol. Rev. 1, 1±48. Coeck, J., Vandelannoote, A., Yseboodt, R., Verheyen, R.F., 1993. Use of the abundance/biomass method for comparison of fish communities in regulated and unregulated lowland rivers in Belgium. Regul. Riv. 8, 73±82. Cowx, I.G. (Ed.), 1994. Rehabilitation of Freshwater Fisheries. Fishing News Books, Blackwell, Oxford, 486 pp. Kleczkowski, A.S., Kowalski, J., 1978. Wody powierzchniowe dorzecza Pilicy (Surface waters of the Pilica catchment basin). In: Kleczkowski, A.S. (Ed.), Resources of the natural environment of the Pilica River basin and problems of its protection. Studies of Documentation Centre for Physiography, vol. 6, Polish Academy of Sciences, Cracow, pp. 51±70, (Engl. summ.). Kottelat, M., 1997. European freshwater fishes. Biologia Bratislava 52(Suppl.)5, 1±271. Lambshead, P.J.D., Platt, H.M., Shaw, K.M., 1983. The detection of differences among assemblages of marine benthic species based on an assessment of dominance and diversity. J. Nat. His. 17, 859±874.
Mann, R.H.K., Penczak, T., 1984. The efficiency of a new electrofishing technique in determining fish numbers in large rivers in Central Poland. J. Fish Biol. 24, 173±185. Meire, P.M., Dereu, J., 1990. Use of the abundance/biomass comparison method for detecting environmental stress: some considerations based on intertidal macrozoobenthos and bird communities. J. Appl. Ecol. 27, 210±223. Odum, E.P., 1980. Ecology. Holz-Saunders, London, 244 pp. Orth, D.J., White, R.J., 1993. Stream habitat management. In: Kohler, C.C., Hubert, W.A. (Eds.), Inland Fisheries Management in North America. American Fisheries Society, Blacksburg, pp. 205±230. Penczak, T., Gøowacki, è., Galicka, W., KoszalinÂski, H., 1998. A long-term study (1985±1995) of fish populations in the impounded Warta River, Poland. Hydrobiologia 368, 157± 173. Penczak, T., Mann, R.H.K., 1990. The impact of stream order on fish populations in the Pilica drainage basin, Poland. Pol. Arch. Hydrobiol. 37, 243±261. Penczak, T., Mann, R.H.K., 1993. A preliminary evaluation of the effect of human activity on the fish populations of the Pilica River, Central Poland. Pol. Arch. Hydrobiol. 40, 101± 115. Petts, G.E., 1984. Impounded rivers. Wiley, Chichester, 326 pp. Warwick, R.M., 1986. A new method for detecting pollution effects on marine macrobenthic communities. Mar. Biol. 92, 557± 562. Welcomme, R.L., 1985. River fisheries. FAO Fish. Tech. Pap. 262, 330 pp.
Applicability of the abundance/biomass comparison method for detecting human impacts on ®sh populations in the Pilica River, Poland Tadeusz Penczak*, Andrzej Kruk Department of Ecology and Vertebrate Zoology, University of èoÂdzÂ, ul. Banacha 12/16 90-237, èoÂdzÂ, Poland Received 11 March 1998; accepted 11 August 1998
Abstract In the Pilica River, a tributary of the Vistula, the abundance/biomass comparison method was employed for assessing the impact of stresses on ®sh populations. Generally, the method proved a useful tool for estimating disturbances in ®sh communities caused by point source sewage inputs and all impacts of a dam. A high correlation was recorded between the ABC index and Simpson and Shannon indices, which also negatively respond to the investigated stresses. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Impounded river; Fish populations; Pollution; Engineering; Over®shing; ABC method; Simpson and Shannon indices
1. Introduction The abundance/biomass comparison method, also known as the ABC method, was proposed by Warwick (1986) as a technique for detecting the impact of pollution on communities of marine macrobenthos. As a means of comparing data sets from many sites, Meire and Dereu (1990) proposed the ABC index based on the k-dominance plots of Warwick (1986). In one published study the abundance/biomass comparison method was used for investigating ®sh communities in regulated and unregulated rivers in Belgium with different degrees of pollution (Coeck et al., 1993). It was therefore decided to employ the *Corresponding author. Tel.: +48-42-678-1364; fax: +48-42678-1364; e-mail: [email protected]
method for investigating ®sh communities in a large alluvial river in Poland, where besides pollution and engineering, over®shing by both anglers and poachers is an important factor dramatically diminishing ®sh populations. Another aim of this study is to verify the assumption that diversity indexes (Simpson and Shannon) can be correlated with the ABC index (Coeck et al., 1993). 2. Study area, material and methods 2.1. Study area The sampling sites and the general location are presented in Fig. 1. The 342 km long Pilica is fed by sources situated at an altitude of 348 m, and enters the Vistula at an altitude of 94 m a.s.l. The catchment
0165-7836/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S0165-7836(98)00201-X
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T. Penczak, A. Kruk / Fisheries Research 39 (1999) 229±240
Fig. 1. Localization of sampling sites in the Pilica River. Electrofishing sampling sites are labelled with rectangles containing numbers 1±48. Water sample sites for physico-chemical investigations are marked with triangles (") and numbers 1±18. Arrows (!) indicate main pointal sources of pollution and tributaries inputting the largest pollution loads.
T. Penczak, A. Kruk / Fisheries Research 39 (1999) 229±240
area of the Pilica River is 9245 km2 (Kleczkowski and Kowalski, 1978). The morphometry of the Pilica river bed, its structure, number and type of hiding places and hydroconstructions are given in Table 1. Although not all of them are marked in Fig. 1, the Pilica is fed with water by 19 tributaries, whose length ranges between 21±86 km, and a large number of tiny, several kilometer long streamlets (Penczak and Mann, 1990). In 1973 the construction of a dam reservoir supplying the million people agglomeration of èoÂdz City and its several neighbouring towns with drinking water was completed in the middle course of the Pilica. In the years preceding the closing of the sluices of the reservoir, the water of the Pilica was polluted at 20 points along its course. Also, most of its tributaries carried polluted waters. Before the closing of the sluices of the dam all main sources of pollution between the backwater of the reservoir and the town of Szczekociny (Fig. 1) had been cleared up, while strongly polluted waters of the large tributary, LuciaÎzÇa River, formerly ¯owing directly into the reservoir, had been diverted along a canal to the WolboÂrka River, entering to the Pilica several kilometers downstream of the dam. Point pollution inputs to the Pilica and water sample sites for physico-chemical investigations are shown in Fig. 1, while respective analysis results are presented in Tables 2 and 3. Data on the physico-chemical water variables were obtained from Voivodeship Inspectorates of Environmental Protection. The Pilica is mostly polluted by agricultural and the food processing industry (butcheries, dairies, distilleries, fruit processing plants) and domestic sewage from villages and small towns. Industrial sewage inputs are located mainly in the towns of Koniecpol, PrzedboÂrz and TomaszoÂw Mazowiecki (Fig. 1). 2.2. Material Fish samples are 16 746 lampreys and ®sh captured in 48 sites (Fig. 1) from 15 June to 19 September 1984. They belonged to 31 species and represented 11 guilds (Table 4) according to Balon (1990). 2.3. Methods Fish were caught from a boat (sites 4±48) or while wading (sites 1±3), using a full wave recti®ed, pulsed
231
DC electro®sher (3 kW, 230 V, 3±10 A) operated through two anode dipnets (Mann and Penczak, 1984). Species composition and relative abundance were assessed from a single electro®shing operation at each site in accordance with the Beklemishev rule (Backiel and Penczak, 1989). This states that the length of a sampling site is suf®cient if the number of species recorded does not increase with farther increase in length sampled. Captured ®sh were transferred to a tank located on the boat or to a bucket on the bank, each of which were ®lled with water containing anaesthetic. After sampling, ®sh were identi®ed, counted, measured, weighed (to the nearest 0.1 g) and then returned to the river. Species composition, relative abundance and standing crop were assessed from a single electro®shing operation at each site. According to Warwick (1986), condition of an animal community can be illustrated with the use of combined k-dominance plots (Lambshead et al., 1983) of abundance and biomass, where species are ranked in order of importance on the x-axis (logarithmic scale) with percentage dominance on the y-scale (cumulative scale). To compare data sets from various sites the ABC index proposed by Meire and Dereu (1990) was used. It is calculated as a mean difference between cumulated biomass and number: ABC index
PN
i1
Bi ÿ Ai ; N
where Bi is the percentage domination of species i (ranked from the highest to the lowest biomass), Ai the percentage domination of species i (ranked from the most to the least abundant species), and N is the total number of species. The index is negative for situations characterised by a strong stress, close to zero for moderate stress, and positive for lack of stress (Meire and Dereu, 1990; Coeck et al., 1993). Also, indexes of species diversity: Simpson (D) and Shannon (H), calculated for 48 sites by Penczak and Mann (1990) to estimate their relationship with the ABC index, were employed: X D pi 2 ; Hÿ
X
pi ln pi ;
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T. Penczak, A. Kruk / Fisheries Research 39 (1999) 229±240
Table 1 Morphometry of the Pilica River Downstream (km)/stream order
Mean width/mean depth (m)
Bottom structure
Occurring factors
Hydrotechnical constructions, remarks
(0±11)/1
(2±2.5)/(0.3±0.5)
s, st, m
Fascine, canalised, numerous concrete weirs
(11±25)/(1±2)
5.6/(0.2±0.4)
s>st, m
(25±41.5)/2
(6±8)/0.5
s, m>st
(41.5±76.5)/3
(6±12)/(0.5±1.0)
s>g, m
(76.5±123)/4
(12±35)/(10.8±1.2)
s g
(123±169)/4(5)
(50±70)/(0.5±1.2)
s
b () e b e 0 () b c d a () b () c d e () a b () c () e () a b (0) c () e (0)
169±189 (189±202)/5
(40±60)/0.8(1.5)
s>g
(202±208)/5
50/1.0
s
(208±215)/5
40/1.5
s g, st
(215±255.5)/5
(60±80(100))/0.8(1.0)
s g>st
(255.5±281)/6
(50)70/1.0
s st, g
(281±342)/6
(70(55±80))/1.0(1.5)
s>g>st
(342±outlet)/6
40/1.5(2.0)
s>st
SulejoÂw reservoir a b c (0) e () a e a 0 () b c a (0) b () c e (, 0) a b (0) c (0) d 0 () e 0 () a (0) b () c () d 0 () b c d e 0 ()
As above Wild river, in some places a lot of fallen trees As above
As above
Wild natural river, beaches, sandy islands
Banks protected by fascine and revetment
Natural river, flowing through meadows Natural river, flowing through forest Banks protected by fascine and revetment on 255 km Natural river, islands, beaches
Banks protected by fascine and revetment (286 and 304 km) Banks protected by fascine and revetment
Explanations ± m: mud; s: sand; g: gravel; st: stones; a: meanders; b: hiding places (fascinewattle fence, roots, branches, fallen trees); c: canopy; d: overhanging willow branches; e: submerged plants; 0: none; : very little; : common; : abundant.
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Table 2 Concentration of dissolved oxygen, BOD, COD and suspension in the Pilica River in 1984 Number of water intake spot
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Down stream (km)
37 40 64 88 115 123 143 167 181 194 203 210 221 250 252 284 314 341
Dissolved oxygen (mg O2 dmÿ3)
BOD (mg O2 dmÿ3)
xann
Min.
Max.
xann
Min.
Max.
xann
Min.
Max.
xann
Min.
Max.
9.4 8.0 9.3 7.9 8.5 8.1 8.6 8.6 9.1 9.2 8.5 8.0 8.3 8.8 9.6 9.5 10.1 9.9
7.1 5.4 7.8 6.2 6.2 6.2 7.0 7.7 6.0 5.7 5.2 4.4 5.7 6.4 7.2 7.4 8.2 7.0
12.5 11.0 10.9 10.6 11.4 9.8 10.2 11.1 14.9 14.8 13.1 11.1 11.7 11.4 12.5 13.5 12.8 13.8
3.0 3.9 5.5 4.8 2.9 3.0 2.6 2.8 4.1 3.3 3.4 3.8 4.0 3.4 6.5 6.2 6.4 7.6
1.0 1.5 1.3 1.3 1.3 1.2 1.2 1.2 1.4 1.5 1.7 1.7 2.1 1.5 2.9 2.3 3.4 3.2
4.2 6.4 12.5 17.0 4.9 4.2 4.1 4.2 7.3 5.8 5.1 5.9 6.2 5.9 18.8 15.6 12.4 19.6
4.5 5.3 7.3 7.2 6.4 5.8 6.0 5.7 7.9 7.3 6.0 6.8 7.8 7.3 8.7 7.7 7.3 8.6
3.6 4.4 3.2 5.0 5.0 4.2 5.0 3.9 5.8 5.1 5.0 4.6 4.3 5.5 5.6 3.7 3.4 5.1
5.1 6.9 14.0 12.7 7.6 7.8 9.4 7.2 9.9 10.6 9.3 10.4 13.9 10.6 15.5 11.7 11.4 12.0
10 13 10 26 22 21 21 19 26 24 21 23 22 26 21 19 21 18
2 2 0 14 11 11 11 11 10 16 12 14 14 14 10 11 11 10
21 45 32 49 29 30 29 27 45 35 30 33 43 66 39 31 36 40
COD (mg O2 dmÿ3)
Organic suspension (mg dmÿ3)
Table 3 Concentration of ammonia nitrogen, nitrate nitrogen, phosphates and sulphates in the Pilica River in 1984 Number of water intake spot
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Downstream (km)
37 40 64 88 115 123 143 167 181 194 203 210 221 250 252 284 314 341
Ammonia nitrogen ÿ3 (mg NH 4 dm )
Nitrate nitrogen ÿ3 (mg NOÿ 3 dm )
xann
Min.
Max.
xann
Min.
Max.
xann
Min.
Max.
xann
Min.
Max.
0.36 0.33 0.76 0.09 0.07 0.10 0.07 0.01 0.12 0.13 0.11 0.29 0.17 0.09 0.66 0.40 0.44 0.38
0 0 0 0 0 0 0 0 0 0 0 0.05 0 0 0.13 0.16 0.20 0.19
1.00 1.20 2.10 0.48 0.37 0.47 0.42 0.07 0.39 0.42 0.41 0.83 0.38 0.32 4.29 0.67 0.67 0.72
1.14 0.96 0.98 0.45 0.47 0.52 0.44 0.46 0.14 0.16 0.29 0.59 0.55 0.40 0.35 0.36 0.43 0.45
0.70 0.70 0.70 0.27 0.28 0.39 0.21 0.34 0 0 0 0 0 0 0.08 0.09 0.09 0.08
1.70 1.50 1.30 0.62 0.66 0.64 0.59 0.65 0.42 0.33 0.51 1.03 0.96 0.86 0.87 0.75 0.93 2.10
0.22 0.29 0.20 0.39 0.22 0.32 0.26 0.24 0.30 0.10 0.14 0.39 0.30 0.28 0.45 0.25 0.72 0.29
0 0 0 0.12 0.16 0.14 0.03 0.13 0.05 0.05 0.07 0.23 0.20 0.18 0.22 0.17 0.13 0.14
0.56 0.66 0.58 0.85 0.32 0.87 0.48 0.76 1.45 0.23 0.20 0.96 0.35 0.57 2.20 0.33 4.37 0.53
24 23 21 32 37 30 32 29 36 42 42 136 118 121 42 39 44 39
21 20 16 21 18 16 21 19 28 26 30 112 88 106 23 18 29 30
28 25 25 73 70 37 53 36 43 55 87 155 139 131 64 51 69 52
where pi is the percentage of the specimens of a given species in the total number of specimens. Both indexes assume values from 0 (lowest diversity) to
Phosphates ÿ3 (mg POÿ3 4 dm )
Sulphates ÿ3 (mg SOÿ2 4 dm )
1 (highest diversity) (Odum, 1980) after scaling in this way: D by subtracting from 1 and H by dividing it by the natural logarithm of the number of species.
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Table 4 List of fish species in the Pilica River drainage basin listed according to the reproductive guilds (Balon, 1990); taxa revised after Kottelat (1997) Nonguarding and open substratum egg scattering (A.1) Pelagophil (A.1.1) Lithopelagophil (A.1.2) Lithophils (A.1.3)
Anguilla anguilla (L.) ± European eel Lota lota (L.) ± burbot Chondrostoma nasus (L.) ± nase Leuciscus cephalus (L.) ± chub Phoxinus phoxinus (L.) ± minnow Alburnoides bipunctatus (Bloch) ± spirlin Aspius aspius (L.) ± asp Barbus barbus (L.) ± barbel Barbus petenyi (Heckel) ± spotted barbel Leuciscus leuciscus (L.) ± dace Leuciscus idus (L.) ± ide Blicca bjoerkna (L.) ± silver bream Perca fluviatilis L. ± perch Gymnocephalus cernuus (L.) ± ruffe Rutilus rutilus (L.) ± roach Alburnus alburnus (L.) ± bleak Abramis brama (L.) ± bream Stizostedion lucioperca (L.) ± zander Esox lucius L. ± pike Scardinius erythrophthalmus (L.) ± rudd Tinca tinca (L.) ± tench Carassius carassius (L.) ± crucian carp Carassius gibelio (Bloch) ± giebel Cyprinus carpio L. ± common carp Misgurnus fossilis (L.) ± mud loach Cobitis taenia L. ± spined loach Cobitis aurata (Filipi) ± goldside loach Gobio gobio (L.) ± gudgeon Barbatula barbatula (L.) ± loach
Phytolithophils (A.1.4)
Phytophils (A.1.5)
Psammophils (A.1.6) Nonguarding and brood hiding (A.2) Lithophils (A.2.3)
Lampetra planeri (Bloch) ± brook lamprey Salmo trutta L. ± brown trout Rhodeus sericeus (Bloch) ± bitterling
Ostracophils (A.2.4) Guarding and clutch tending (B.1) Phytophils (B.1.4)
Leucaspius delineatus (Heckel) ± sunbleak Silurus glanis L. ± wels
Guarding and nesting (B.2) Ariadnophil (B.2.4)
Gasterosteus aculeatus L. ± stickleback Pungitius pungitius (L.) ± ten-spined stickleback Ameiurus nebulosus (Lesueur) ± brown bullhead Cottus gobio L. ± European bullhead
Speleophils (B.2.7)
These indices are indispensable because the Simpson index is weighed in favour of dominant species and the Shannon index in favour of rare ones (Odum, 1980).
3. Results The combined abundance/biomass curves for 43 of the 48 sites are given in Figs. 2 and 3. Sites 1±5 were
T. Penczak, A. Kruk / Fisheries Research 39 (1999) 229±240
235
Fig. 2. Combined k-dominance curves of biomass (-*-*-) and abundance (-&-&-) and the ABC index values for sites 6±27. Site 16, removed for graphical reasons, is almost identical with site 15.
236
T. Penczak, A. Kruk / Fisheries Research 39 (1999) 229±240
Fig. 3. Combined k-dominance curves of biomass (-*-*-) and abundance (-&-&-) and the ABC index values for sites 29±48.
T. Penczak, A. Kruk / Fisheries Research 39 (1999) 229±240 Table 5 Values of ABC, Simpson (D) and Shannon (H) indices in given sites Site number
Downstream (km)
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
33 43 50 55 70 80 93 105 118 132 148 153 156 160 165 190 195 199 202 206 210 214 218 225 229 233 238 247 255 262 271 274 278 281 286 293 304 312 320 325 329 334 341
ABC ÿ2.48 3.99 1.15 3.42 1.02 ÿ1.07 3.52 ÿ6.38 ÿ6.74 ÿ7.99 ÿ7.77 ÿ6.94 ÿ9.33 ÿ6.86 0.67 ÿ7.85 ÿ7.73 0.07 ÿ2.76 ÿ4.03 ÿ3.96 ÿ9.71 3.42 ÿ13.23 ÿ11.90 ÿ3.25 ÿ7.70 2.50 ÿ4.15 ÿ0.74 ÿ7.36 4.78 0.94 ÿ6.22 4.09 ÿ2.12 ÿ2.39 ÿ4.56 2.66 2.14 ÿ0.89 2.36 ÿ1.10
D
H
0.73 0.78 0.79 0.78 0.65 0.79 0.85 0.79 0.75 0.78 0.80 0.76 0.75 0.55 0.76 0.50 0.58 0.82 0.68 0.63 0.77 0.72 0.75 0.64 0.69 0.60 0.65 0.76 0.78 0.82 0.57 0.81 0.71 0.71 0.80 0.75 0.60 0.72 0.84 0.86 0.81 0.81 0.81
0.73 0.78 0.80 0.74 0.61 0.71 0.80 0.69 0.68 0.69 0.72 0.68 0.69 0.49 0.69 0.44 0.46 0.75 0.61 0.53 0.72 0.63 0.70 0.49 0.58 0.51 0.56 0.68 0.71 0.81 0.55 0.78 0.66 0.61 0.73 0.66 0.53 0.66 0.79 0.84 0.77 0.72 0.70
excluded because of a low number of species, i.e. 2±5, for which the ABC index assumed alternately extraordinarily high and low values, largely distinct from our picture of the ®sh fauna. The ABC index values, excluding sites 1±5, are shown in Table 5.
237
Between the town of Szczekociny and the Czarna Wøoszczowska's mouth (sites 7±12) the values of the ABC index are positive, except one, site 11 (Figs. 2 and 3, Table 5). The Pilica River is less polluted there, as indicated by decreasing maximum values of most of its water variables (Tables 2 and 3), has sustained its natural bed structure, is ``dammed'' by fallen trees (hiding places) (Table 1), no poachers were encountered, and the number of anglers was low. In the river section between the out¯ows of the Czarna Wøoszczowska and Czarna Konecka Rivers (sites 7±12, Fig. 1) similar and strongly negative values of the ABC index were detected. The river is natural there, has well developed ecotones along banks, numerous large clumps of submerged vegetation, and slightly increased water quality (Tables 2 and 3). Numerous meetings with poachers and a high number of anglers encountered indicate that they may be responsible for a reduction of large ®sh there. At site 20, above the backwater of the reservoir, the ABC index has a positive value, close to zero (Table 5). In some tailwater sites the combined kdominance curves for abundance and biomass cross each other (sites 23, 24, 26, 31, Fig. 3), and with two exceptions as far as through site 32, the ABC index has negative values. The location of combined k-dominance curves for abundance and biomass, and values of the ABC index in the lower course of the Pilica (Drzewiczka River ± Vistula) assume alternately positive or negative values. The pressure of poachers is limited because the river is too deep to haul nets while wading there. Fish have many hiding places in the banks protected by fascine and revetment, the amount of dissolved oxygen in water is higher but BOD, COD, organic suspension, ammonia nitrogen and phosphates indicate a decrease in its quality (Table 2). The values of Simpson (preferring dominant species) and Shannon (preferring rare species) for the investigated sites are included in Table 5. The calculated correlation coef®cients for both these indexes with the ABC index are r0.53 and r0.63, respectively, at the signi®cance level of p0.001 from 40 d.f. (see Figs. 4 and 5). Because we cannot distinguish between the independent and dependent variables here, ellipses were used instead of linear regression for displaying the dependence tendency.
238
T. Penczak, A. Kruk / Fisheries Research 39 (1999) 229±240
Fig. 4. Dependence between Simpson index and ABC index (r0.53).
Fig. 6 proves that in most cases the peaks of ABC, Simpson and Shannon indexes are in phase. Discrepancies concern only a section between the out¯ow of the Czarna Wøoszczowska and Czarna Konecka Rivers, where consequently negative values of the ABC index were recorded, at a quite high species number. A scarcity of big specimens was caused by numerous anglers and poachers. 4. Discussion Investigations of the main channel of the Pilica proved the value of the ABC method for estimating
the in¯uence of water pollution and other human impacts on abundance and biomass of ichthyofauna. As in the study by Coeck et al. (1993) the values estimated by the ABC method were declining below sewage inputs but not abruptly and consistently. When sewage inputs were sequenced along the river, the ABC index values remained negative but some exceptions occurred. When there were short gaps in sewage inputs then the value increased, which might be explained by the natural ability of a river to selfpuri®cation, and by ®sh migrations (Welcomme, 1985; Cowx, 1994). Similarly as in Coeck et al. (1993) no statistically signi®cant correlations between given water para-
Fig. 5. Dependence between Shannon index and ABC index (r0.63).
T. Penczak, A. Kruk / Fisheries Research 39 (1999) 229±240
Fig. 6. Changes in the ABC index (-*-*-) and Simpson and Shannon indices (- - -) along the Pilica River.
meters and the ABC index were detected. On Coeck's suggestion the degree of water pollution in the Pilica was expressed on the ®ve-degree scale of Chemical Index (CI) developed by the State Institute for Nature Management in Netherlands. Unfortunately, no statistically signi®cant correlations between CI and the ABC were recorded. In contrast to Coeck et al. (1993) no dependence between degree of river regulation and the ABC index was detected. This ensues from the fact that river regulation in Poland consists mainly in protecting eroded banks with fascine and revetments, and thus is of different character from that of the rivers investigated by Coeck et al. (1993) in Belgium. Decisively negative values of the ABC index recorded in the sites of the reservoir's tailwater are probably caused by the presence of the dam of this large reservoir. Stresses connected with impoundment are regarded as having catastrophic effects on ®sh populations (Petts, 1984; Orth and White, 1993). The negative values of the ABC index have also been caused by mass drifts of the young-of-the-year perch
239
and roach from the reservoir. These species had great reproductive successes in the reservoir. Such a phenomenon was also observed in another impounded lowland river of Central Poland (Warta River) and it was re¯ected in dramatic decreases in mean body weight (Penczak et al., 1998), which exert decisive impacts on the abundance/biomass comparison (Warwick, 1986). We believe that many ¯uctuating, low values of the ABC index in the Pilica may have been caused by over®shing. Poaching has been included among the most harmful stresses for ®sh populations in this river (Mann and Penczak, 1984; Penczak and Mann, 1993). In the quantitatively middle course of the Pilica River, between the mouths of the Czarna Wøoszczowska and Czarna Konecka Rivers, some commercial ®sh species were not represented by adults (Mann and Penczak, 1984). The highest number of poachers, and simultaneously plenty of anglers, were observed during the present study in this very section of the Pilica and it was just here where despite a rather good water quality, negative values of the ABC index were recorded in all sites (13±19) (Table 5). According to Warwick (personal communication) the ABC method may successfully indicate the presence of poachers, because they usually capture big ®sh, while Simpson and Shannon indices may fail to do so. Despite the ABC index displaying positive correlations with Simpson and Shannon indexes at the level p0.001 (Figs. 4 and 5), decisive and continuous discrepancies from this pattern occurred in the case of sites 13±18 (most of the poachers and the anglers) and also in the solitary ones in the lower course of the river (Fig. 6). Coeck et al. (1993) did not determine any signi®cant correlation between these variables, hence it is still a problem for discussion and further research. Acknowledgements Special thanks are directed to Johan Coeck (Belgium), Erik Mortensen (Denmark), Richard Warwick (UK) and two anonymous reviewers for critical comments on the manuscript. Authors also thank èukasz Gøowacki for help in preparing the English version of this manuscript. Field research was supported by the Main Board of the Polish Anglers Association, and the University of èoÂdzÂ.
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