ANNALES • Ser. hist. nat. 11- 2001 • I (23) original scientific paper UDC 574.5:597(497.4) received: 3.4.2001 MARBLE TROUT (SALMO MARMORATUS) AND BULLHEAD (COTTUS GOBIO) IN TWO SLOVENE RIVERS (ADRIATIC SEA BASIN) Suzana ŠUMER FBRA d.o.o. Ljubljana, SI-1370 Logatec, Cesta 5. maja 3E E-mailr suzana.5umer@ebra.si Srečko LE1NER Croatian Natural History Museum, HR-100GQ Zagreb, Oemelrova 1 Mela POVŽ Fisheries Research Institute Ljubljana, 51-1000 Ljubljana, Župančičeva "5 ABSTRACT Population density, growth and condition of marble trout Sal mo marmorafus Cuvier, 1829 in the river TrebuScica and bullhead Cottus gobio Linnaeus, 1758 in the river Bela were estimated. Ageing of bullhead could not be established due to its lack of scales. In the TrebuSdca, marble troul is a dominant species, with high density of 955 specimens/ha and low biomass of 26 kg/ha. The youngest marble trout specimens (age groups 0 and 1) constitute 81% of the entire estimated population. The mean condition factor was low (0.8J) with the highest growth rate of 615 cm long trout (1.56 and 0.86, respectively). For the conservation of this species, no further introduction of brown and rainbow trout is recommended and angling restrictions of marble trout applies. In the river Beta, about 86% (specimens/ha) and 35% (kg/ha) of the total fish population are represented by bullheads. Bullheads' density of 11,708 specimens/ha is the first record of such high density in Slovenia. The mean condition factor of bullhead was rather high (1.01). Key words: marble trout, bullhead, population density, age, growth, condition, Slovenia TROTA MARMORATA (SALMO MARMORATUS) E SCAZZONE (COTTUS GOBIO) IN DUE FIUMI IN SLOVENIA (BACIMO ADRIATICO) SINTESI L'articolo riporta i dati inerenti la densità di popolazione, la crescita e la condicione delta trota marmorata (Salrno marmorat.us Cuvier, 1829) nel fiume Trebut cica e dello scazzone (Cottus gobio Linnaeus, 1758) net fiume Bela. Per la trota marmorata sono state stud i ate anche le classi d'età. La trota marmorata è la specie dominante net TrebuScica, con una densità moho alta pari a 955 individui per ha ed un basso valore di biomassa, 26 kg per ha. Gli individui più giovani di questa specie (classi d'età 0 e I) rappresentano f'81% dell'intera popolazione stimata. L'indice di condizione medio è risultato basso, pari alio 0.83, con il più alto tasso a'i crescita delle trote di 6-15 cm (rispeltivamente 1.56 e 0.86). Per fa tutela di quests specie, gli aulori raccomandano di evitare ulteriori introduzioni di esemplari di trota fario e trota irtdea, nonché di applicare r&strizioni alia pesca della trota marmorata. Nel fiume Bela lo scazzone rappresenta l'86% (esemplari per ha) ed il 35% (kg per ha) dell'intera popolazione ittica. La densità dello scazzone, pari a 11708 individui per ha, corrisponde alla densità più alta mai segnalata in Slovenia. Parole chiave: trota marmorata, scazzone, densità di popolazione, età, crescita, condizione, Slovenia 29 ANNALES • Ser. hist. nat. 11- 2001 1 (23) Su.'jfia SUMEK ef af: MARBLE TROUT tSALMOMARMORATUS} AND BULLHEAD (COITUS GOSIOI IN TWO SLOVENE RIVERS {ADRIATIC SEA BASIN), 29-34 introduction The marble trout (Salmo marmocatus Cuvier, 1829) is the second largest European, exclusively freshwater salmonid species, it inhabits fast running streams with gravel bottom, low summer water temperature and high dissolved oxygen content. Marble trout is endemic to the Adriatic Sea basin, listed in Annex tl at "Council on the Conservation of Natural Habitats and of Wild Fauna and Flora" (Council Directive 92/43/EEC). in the Red Data List of the freshwater fish and lampreys of Slovenia (Pov2, 1996), the species is listed as endangered and it is protected by the National and Regional laws. The marble trout has restricted geographical distribution in the basin of the Po in northern Italy and in the Adriatic basins of the former Yugoslavia and Albania (Crivelli et a I., 2000). The bullhead (Coitus gobio Linnaeus, 1758,) is a small benthic. fish living in clear and well-oxygenated waters, inside the saimonid zone. Bullhead, too, is threatened by water pollution and stream regulation, and the species is listed in the Slovenian Red Data List (Povz, 1996) as vulnerable. It has been protected by the "Decree of Protection of Endangered Animal Species" (Official Journal R Slovenia No. 57/1993). Data presented in this paper are part of a complex ichthyological investigation, commissioned and financed by the manager of the freshwater fish populations in these rivers - the Fishery Society of Tolmin. The aim of this investigation was to asses, on the basis of certain physical, chemical and biological features, the ecological condition of the streams and to implement the proposals for further fishery management. The field-work was conducted in September 1998 and March 1999, but due to the prolonged rainy period and devastating floods in November 1998, only the 1998 data are presented herewith. This work was read at the "International Symposium on Freshwater Fish Conservation: Options for the Future" held in Albufeira in Portugal (Sumer etai, 2000). Data presented in this paper are the very first on the marble trout and bullhead populations concerning the Bela and Trebuscica rivers. The condition factors of both species and instantaneous growth rates for marble trout have never been calculated before in this country. MATERIAL AND METHODS Study area The river Bela is a north-western tributary of the river NadiZa. Only part of the Nadila, with its source in Italy, flows along the Slovenian border area and joins the river Ter in Italy. The Bela, with its source at 1,140 m a.s.L, is only 6.29 km long and flows into the Nadi2a at an altitude of about 300 m a.s.l. (Fig. 1). Unfortunately, there are no data available on the drainage area, river hydrology, or water quality. The Bela was regulated in 1930. Its upper course has few 1-2 m high artificial weirs. This part is the trout's nursery stream. In its lower 4 km long course angling is practised- The investigation was carried out on the site located about 1 km upstream of the Bela's mouth. The 70 m long net-blocked segment (471 m2) was selected to cover potential habitat types available to the dealt with fish species. The river Trebuscica is a 16.4 km long south-western tributary of the Idrijca. Its source is at 1,125 m a.s.l. and joins the Idrijca at about 183 m a.s.l. (Fig. 1). Its catchment area covers 74 km*. According to the Hydromete-orological Institute of Slovenia (1999 and 2000), the annual water level fluctuated from 0.45 - 0.63 m to the highest .3.27 m. Annual water discharge varied from 0.5 m3/s to 2.7 m3/s with the maximum of 58.7 m:i/s. The upper 6 km of the Trebuscica is a sanctuary area, inhabited by geneticaily pure marble trout, followed by 1 km of nursery stream. The lower 9.4 km long course is used for angling. The investigation was carried out on the site some 3.5 km upstream of the mouth. The 150 m long net-blocked segment (2,136 m2) was selected to cover potential habitat types available to the dealt with fish species. Sampling and methods Fish sampling was carried out on September 19, 1998. Fish were progressively captured and removed during three to four passes with DC electrofishing equipment until the last catch reached about 15% of the first catch- Sampled sections were blocked at the upper and lower ends with 6-mm seins. Captured fish were anaesthetised, identified, measured to the nearest mm (TL) and weighed to the nearest g. Ten to twenty scales were removed below the adipose fin arid above the lateral line from each marble trout. Scales' annuli were examined at x 20-40 magnification, and annuii were identified following the criteria presented by Ricker (1968). The age of fish was presented as the age groups where age group 0 refers to the first year of life. Ageing of bullhead could not be estimated, as its body is not covered with scales. The Zippin method (Higgins, 1985), where the numbers of fish in successive catches decrease (n1>n2>n3 etc.), and the Carle-Strub method, where n1>n2256 mm, cobbles: 64-256 mm, grave!: 2-64 mm, sartd: 0.06-2 mm. Legenda: W: povprečna širina (m), D: povprečna globina (cm), Min-Max: najnižje - najvišje vrednosti, veliki kamni >256 mm, večji prodniki: 64-256 mm, prod: 2-64 mm, pesek: 0,06-2 mm. Tab. 2: Fish density (specimens/ha) and biomass (kg/ha) with ± 95% CI (± 95% Confidence interval) in the Bela and Trebuščka rivers. Tab. 2: Gostota (število rib/ha) in biomasa (kg/ha) rib ± 95% CI (± 95% interval zaupanja) v Beli in Trebuščki. RIVER BELA RIVER TREBUŠČICA Species specimen s/ha kg/ha speci mens/ha kg/ha S. marmoratus 319 (±8) 7.7 (±1.8) 955 (±77) 25.6 (±1.9) S. t. m. h rio. 43 (±0) 12 (±0) 75 (±0) 4.2 (±0) S. t. m. (ario x S. marmoratus 1,940 (±29) 127.8 (±2.9) 585 (±11.5) 18.9 (±0.4) O my kiss 1,241 (±33) 74.6 (±5) 252(±24) 11.7 (±0.8) Thymallus thymallus 24 (±5) 2.7 (±0.9) Phoxinus phoxinus 30 (±8) 0.6 (±0) Barbus caninus 20 (±8) 1.1 (±0) C. gobio 11,708 (±1,811) 75.2 (±0) TOTAL 13,619 (±745) 212 (±26) 1,926 (±58) 64.4 (±2.6) Tab. 3: Mean body length, weight, condition factor, and growth rate of Salmo marmoratus from the river Trebuščka and of Cottus gobio from the river Bela. Tab. 3: Povprečna telesna dolžina, teža, indeks kondicije in stopnja rasti soške postrvi Salmo marmoratus v reki Trebuščici in kaplja Cottus gobio v reki Beli. River Trebuščica - S. marmoratus River Beia -C. gobio Parameters Age group (years) 0 1 2 3 4 7 n 59 91 24 2 7 1 400 L 8(±1.24) 13.3(±1.06) 17.4 (±1.48) 21.8 (±1.06) 28 (±0.58) 41 9.1 (±2.17) L-range 6-11.5 11.5-15 15.5-19.8 21-22.5 27-28.5 4.5-13.5 W 4.3 (±2.43) 20.3 (±4.93) 47.8 (±13.12) 85 (±18.38) 189.4 (±15.95) 700 8.9 (±5.38) W-range 1.8-14 10-32 30-70 72-98 160-206 0.8-24 K 0.78 (±0.1 5) 0.85 (±0.07) 0.89 (±0.07) 0.82 (±0.06) 0.86 (±0.04) 1.02 1.01 (±0.13) K-range 0.78-1.1 0.66-1.04 0.76-0.99 0.78-0.86 0.81-0.92 0.58-1.27 G - 1.56 0.86 - - Legend: n = number of fish caught, L = mean total length (cm) ±SD (standard deviation), W = mean weight (g) ±SD, K - mean condition factor ±SD, G = instantaneous growth rate of weight. Legenda: n = število ujetih rib, L = povprečna totalna dolžina (cm) ±SD (standardna deviacija), VV = povprečna te?a (g) ±SD, K = povprečni indeks kondicije ±SD, G = trenutna stopnja rasti v teži. 32 ANNALES Ser. hist nat. I I 2001 1 (23) Suzana SUMER el a/.: MARBLE TROUT (SALMO MARMORA/USl AND PULL HEAD I CO 11 US COB'Oi !N TWO SLOVENE RIVERS (ADRIATIC SEA BASIN), 29-34 According to Gaudin & Caillere (1990), C. gobto prefers shallow waters and slow to moderate current velocities, shaded areas and scarce emergent vegetation. They cite the results of other authors according to whom, quite on the contrary, the species can be found also in the zones where velocity is high. Its presence is dependent on substrate, the granulometry characterized by enough coarse elements. The low banks of the Bela offer no overhanging vegetation and therefore no shaded areas. The river bed microhabitats had patches of algae, and occasionally Fontinalis sp. appeared. The number of caught bullheads was nearly the same along the entire sampling location, regardless of riffles and pools. According to Caudin & Caillere (1990), C. gobio is indifferent to water depth (up to 6-9 m) but prefers coarse bottom material that gives it shelter. The Bela bottom materia! consists of rubbles and boulders as the main fish cover areas. The length of the specimens (Tab. 3) was inside the length intervals cited by Oiiva et at. (1968), Ladiges & Vogt (1979) and Terofal (1996). The mean condition bullheads' factor was rather high 1.01. According to the high population density and the estimated condition factor it appears that the Bela holds favourable environmental conditions for this species. The river Trebuscica In general, the lower course of the TrebuScica is wider than the Bela, characterized by more fluctuating water depth and stream width and less diverse bottom substrate (Tab. 1). Twenty different macroinvertebrates taxa were identified. Their low biomass (6 kg/ha) is among the lowest benthic biomasses recorded in the streams of the Adriatic Sea basin (with regard to the September sampling). Its water quality is 2ncl class (betamesosaprobic). Surrounding areas are free of industry, but with more inhabitants, villages and arable land. In the Trebusdica, too, all determined chemical concentrations were bellow regulated concentrations for unpolluted waters (Zupan et al.r 1996). Six fish species and a hybrid (S. marmoratus x S. trutta m. fario) of the families Salmonidae, Cyprinidae and Thymallidae inhabit the Trebuscica. 5. marmoratus makes 49% of the Trebuicica's total estimated population density and 40% of its total biomass. Its population density is among the highest in the Slovenian Adriatic Sea basin streams (Tab. 2). The estimated biomass was low due to high abundance (81%) of young fish (age groups 0 and 1). There were only few sexually mature specimens of age groups 3 and 4. in comparison with other salmonids,'the condition factor of the marble trout was the lowest, while the growth rate of 6-15 cm long specimens was the highest (Tab. 3). The reason for the lowest condition factor may be associated with !i mited environmental conditions and introduced indigenous fish species occupying available ecological niches in the stream. The relatively high abundance of young fish is clue to the fishery management. From 1996 on, marble trout of size 9-15 cm have been intensively stocked. At the same time there is also a possibility of migrations from the upper course of the river, inhabited only with marble trout (sanctuary and nursery stream segments). There are numerous young fish, with very few catc.hable size adults. in Slovenia, strong decline of this species has been recorded during the last 80 years, it is threatened by a permanent introduction of brown trout (Salmo trutta), water pollution, river regulation and reservoir constructions (Pov2 et at., 1996). The marble trout is heavily affected by stocked alien Atlantic 5. trutta and Danubian and/or Mediterranean Salmo species, and presently there are only few populations of marble troul that are believed to be unaffected by introgression (Delling et al„ 2000). By the end of the last century, brown trout of different origins have been introduced into geographical area where the marble trout occurs, quickly resulting in hybrid populations (Crivelli et a!., 2000). In the Adriatic basin of Slovenia, the first introductions took place in 1906 (Pov2 el al., 1996). During the marble trout rehabilitation project, which began in 1993, eight genetically pure populations were discovered in headwater streams in the upper reaches of the Soca river in Slovenia, the Trebuifiica being one of them. As a result of the first phase of this project, the prohibition on the release of Salmo trutta in the Soca watershed became effective in 1996 with the "Curricular for the ban of brown trout stocking in the Adriatic Sea basin, Slovenia" (Ministry of Agriculture, Forestry and Food, March 25th, 1996). Both rivers are rather narrow with low water level (especially the Bela). According to the September data, the amount of food source is quite limited. The latter and the genetic conservation of marble trout were the most important reasons for the recommendation of a suitable management based on no introduction of other fish species and angling restrictions of marble trout. 33 ANNALES • Ser. hist. nat. 11 • 2001 1 (23) Suzana ŠUMER eč jL MARBLi TROUT (SALMO MAfiMORATUSl AND BlJLtHtAD (CCTTUS COBIO) IN TVVO SIOVENE RIVCRS (ADR1ATIC SEA BASEN). 29-34 SOŠKA POSTRV (SALMO MARMORATUS) IN KAPELJ (COTTUS COBIO) V DVEH SLOVENSKIH REKAH SEVERNOjADRANSKEGA POVODjA Suzana ŠUMER EBRA d.o.o. Ljubljana, SM370 Logatec,. Cesta 5. maja 3E. E-mail: suzanasurner@ebra.si Srečko LEiNER Hrvatski prirodoslovni muzej, HR-10000 Zagreb, Demetrova 1 Mela POVŽ Zavod za ribištvo, $1-1000 Ljubljana, Zupančičeva 9 POVZETEK Avtorji pričujočega raziskovalnega dela so merili populacijsko gostoto, stopnjo rasti in kondicijsko stanje soške postrvi Salmo marmoratus Cuvier, 1929 v reki Trebuščici ter kaplja Cottus gobio Linnaeus, 1758 v reki Beli. Starostno strukturo so ugotavljali !e pri soški posrtvi. Soška posta je v Trebuščici dominantna vrsta z visoko gostoto 955 osebkov/ha in nizko biomaso 26 kg/ha. Najmlajši osebki soške postrvi (starostna skupina med 0 in 1) sestavljajo 81% celotne ocenjene populacije. Povprečni indeks kondicije je bil nizek (0,83) z visoko stopnjo rasti 6-15 cm dolgih postrvi (1,56 oz. 0,86). Za zaščito avtohtone soške postrvi avtorji odsvetujejo nadaljnje vlaganje amerikank in potočnih postr\'i in hkrati vztrajajo pri omejitvah športnega ulova soške postni. Kaplji v reki Beli sestavljajo kakih 86% (osebkov/ha) in 35% (kg/ha) celotne ribje populacije. Njihova gostota 11.708 osebkov/ha je najvišja, kar jih je biio doslej zabeleženih v Sloveniji. Povprečni indeks kondicije kapijevje bi! razmeroma visok (1,01). Ključne besede: soška postrv, kapelj, populacijska gostota, starost, stopnja rasti, kondicijsko stanje, Slovenija REFERENCES Allan, J. D. (1995): Stream Ecology. Chapman and Hail, London-Madras, 60 pp. Compagnat, P., F. Vancayseele & A. Rumeau (1994): Indice Bioiogique Global Normalise I.B.G.N., NF t 90350, Giude Technique. Grenoble: Cabinet GAY Environnement, p. 68. CriveHi, A. J, G. Poizat, P. Berrebi, D. Jesenšek & }.-?. Rubin (2000): Conservation Biology applied to Fish; The example of a project for rehabilitating the marble trout (Salmo marmoratus) in Sfovenia. Cybium, 24(3), 21 1-230. Dell ing, B., A. Crivelli, J.-F. Rubin & P. Berrebi (2000); Morphological variation in hybrids between Salmo marmoratus and alien Salmo species in the Volarja stream, Soča River basin, Slovenia. J. Fish Bio!., 57, 1199-1212. Gaudin, P. & L. Caillere (1990); Microdistribution of Cottus gobio L. and fry of Salmo trutta L. in a first order stream. Polskie Archiwum Hydrobiologii, 37(1-2), 81-93, Hydrometeorological institute of Slovenia (1999, 2000): Hidrološki letopis Slovenije 1997, 1998 (The 1997 Hydrological annals of Slovenia, The 1998 Hydro-logical annals of Slovenia). Hydrometeofologica! institute of 5lovenia, Ljubljana, 143 pp., 145 pp. Higgins, P. J. (1985): An interactive computer program for population estimation using Zippin Method. Agriculture and Fisheries Management, 1, 287-295. Ladiges, W. & D. Vogt (1979): Die Su&wasser-fische Curopas. Hamburg and Berlin: Paul Parey, 175 pp. Lobon-Cervia, J, (1984): Electrofishing techniques and the removal methods for estimating fish abundance in rivers. PhD Thesis, National Museum of Natural Sciences, Madrid, 51 pp. Oiiva, O., S. Hrabe & j. Lac (1968): Stavovce Slovenska I, Ryby, oboj2ivelniky a plazy. Vydyvytelstvo Siovenskej Akademie Ved, Bratislava, 204 pp. Platts, W. S., W. F. Megahan & G. W. Minshal (1983): Methods for Evaluating Stream, Riparian and Biotic Conditions. General Technical Report INT-138, Ogden, Utah, 50 pp. Povz, M. (1996): The Red Data List of the freshwater lampreys (Cyclostomata) and fish (Pisces) of Slovenia. In: Kirchofer, A. & D. Hefti (eds): Conservation of Endangered Freshwater Fish in Europe. Birkhauser Verlag, Basel, 63-72. Povi, M., D. Jesensek, P. Berebi & A. |. Crivelli (1996): The Marble trout Salmo trutta marmoratus, Cuvier 1817 in the Soca River Basin, Slovenia. Le Sambuc, Tour du Valat Publication, p. 65. Ricker, W. E. (1968): Methods for Assessment of Fish Production in Fresh Waters. Blackwell Scientific Publications, Oxford and Edinburgh, 102 pp. Sumer, S,, M. Povz & S. Leiner (2000): Status of Salmo marmoratus Cuv. and Cottus gobio L. in two rivers in Slovenia (Adriatic Sea basin). Symp. on the Freshwater Fish Conservation - options for the future. Abstract book, Portugal, Algatve, p. 43 Terofal, F. (1996): SuSwasser-fische. Mosaik Verlag GmgH, Munchen, 204 pp. Veiasco, J. C., P. A. Rincon & J. lobon-Cervia (1990): Age, growth and reproduction of the cyprinid Rutilus iemmingii in the River Huebra, Central Spain. J. Fish Biol., 36, 469-480. Zupan, M,, S. Brumen, T. Cegnar, M. Dobnikar, }. Gr-bovic, M. Kolbezen, G, Kosi, C. Krusnik, S. Lapajnc & P. Mihorko (1996): Kakovost vode v Sloveniji v letu 1994 (The water quality in Slovenia in the year 1994). Hydrometeorological Institute of Slovenia. Ljubljana, 62 pp. 34