Length-Weight Relationship in Adult Huchen Hucho Hucho (L., 1758) from Drina River, Serbia

Home , Alaska salmon fishery, Huchen, Oncorhynchus, Salmo, Una (Sava)

Biologia 66/1: 156—159, 2011 Section Zoology DOI: 10.2478/s11756-010-0135-2

Length-weight relationship in adult huchen Hucho hucho (L., 1758) from Drina River, Serbia

Predrag D. Simonovic´,VeraP.Nikolic´,AnaD.Tošic´ &SašaP.Maric´

University of Belgrade, Faculty of Biology, Institute of Zoology, Studentski trg 16, 11000 Belgrade, Serbia; e-mail: [email protected]; [email protected]; anatosic@ bio.bg.ac.rs; [email protected]

Abstract: Huchen Hucho hucho from the Drina River (Serbia) revealed recently the decrease in breakpoint values for both standard length (Sl)andweight(w) in relation to the values recorded in 1999 from 110 cm to 98.4 cm and from 16.5 kg to 10.5 kg, respectively. That might indicate to the change in certain population parameters that could have an inﬂuence to thegrowthintheadultperiodoflife. Key words: huchen; Drina River; length-weight relationship; split-linear regression; breakpoints

Introduction relationship. In addition to that, he favoured the or- dinary least-square regression, in contrast to the geo- Huchen (or Danubian salmon) Hucho hucho (L., 1758) metric mean regression Ricker (1975) and Anderson & is the largest World’s salmonid, as it attains the mass Gutreuter (1983) proposed, due to the difficulty of in- over 50 kg (Holčík et al. 1988; Mikavica & Savić 1999). terpretation of geometric mean regression. Its native dispersal area determines it an endemics An alternative approach to study the growth in fish of the Danube River drainage area, where it inhabits could be the detection of changes in growth mode and streams and rivers in highlands (200–600 m of altitude) the shifts from one developmental period to the next, with fast water current, moderate maximal water tem- as suggested by Balon (1990) in his saltatory theory of perature (usually up to 15 ◦C) and sufficient amount of development. Simonović&Nikolić (2007) revealed that dissolved oxygen (8–9 mg L−1), although it can sus- alterations in growth mode corresponded very well to tain more harsh conditions (e.g., water temperature up those shifts in stream-dwelling brown trout, which sup- to 22 ◦C and down to 5 mg L−1 of dissolved oxygen). ported the use of a non-invasive methodology consisting The strong human impact that huchen suffers lead to its of Piecewise Linear Regression (Nickerson et al. 1989) global threat to such extent it became a globally endan- of the length-weight relationship for detection of those gered species, whose conservation status was assigned shifts. VU (vulnerable) (A2bcde, B1 + 2bce; since 1994) by Despite of its importance in ecosystem and con- IUCN (2000). It also stands in the Appendix III of servational sense, data about population parameters the Bern Convention (Protected Fauna) and Annexes for free-living huchen in the natural habitats are II and IV of the EU Habitat Directive, as well as in the still scarce, probably due to difficulties in sampling list of protected species in Serbia (Anonymous 1993). and studying this fish that lives in large mountain Various length-weight models were used to predict rivers and reveals itself very rarely. Records about growth in terms of weight as some function of length the length-weight relationship b of 3.00 and 3.37 and to assess nutritional status as defined by condi- recently occur at the FishBase database for only tion. The study of condition assumes that heavier fish two huchen of 144 cm and 153 cm Tl in length, of the given length are in better condition. Such models respectively, from the unknown location in Europe were mainly used by fish culturists and much more sel- (http://www.fishbase.org/PopDyn/PopGrowthList.php dom by fisheries managers, and the oldest one by Fulton and http://www.fishbase.org/PopDyn/PopGrowthList. (1911) is still the most commonly used. Ricker (1975) php). Although length-weight relationship was exam- developed the relative condition factor as an extension ined for trout and salmon fish species for the manage- of Fulton’s condition factor by including the allomet- ment purpose and for the estimation of the status, i.e., ric relationship between length and weight. However, trophy value of trout caught by anglers (Barnham & several publications, e.g., Cone (1989) rised a ques- Baxter 1998), only one investigation of length-weight tion that the conversion of the two-dimensional length- relationship in huchen (Simonović et al. 2000) was ac- weight relationship into a single statistic result is a loss complished so far, revealing that mode of growth alters of information and an inaccurate representation of that from subadult to adult huchen, as well as that growth

c 2011 Institute of Zoology, Slovak Academy of Sciences Huchen length-weight relationship 157

Fig. 1. Relationship between logarithms of standard length (Sl)andweight(w) in adult huchen with the breakpoints for Sl and w (given as both logarithmic and real values) and diﬀerence in regression slopes occurring in smaller, i.e., younger adults (A1)andlarger, i.e., older ones (A2).

parameters do not differ in statistical sense between Results huchen from Drina, Una and Sana Rivers at the West- ern Balkans. Piecewise Linear Regression revealed that the growth of The aim of this paper is to reveal that length- huchen in the first part of their adult period of life (de- weight relationship in adult huchen from the same pop- noted A1) until the size Sl = 98.4 ± 1.32 cm and weight ulation is subject to change in time and to indicate to w = 10.471 ± 2.193 kg was different from that of huchen the need for further investigation of that relationship (denoted A2) of greater size (Fig. 1). That alteration in- in huchen, in order to understand its dependence of dicates the change in the mode of growth of two classes population characteristics and make an advancement of adult huchen, as revealed by slope coefficient b of lin- in management with the stocks of this endangers and ear regression parameters (length-weight relationship) endemic fish species for the series of huchen smaller than breakpoint values assigned A1 (Sl-w relationship bA1 = 2.187 ± 0.358; t = 6.100; df = 11; P < 0.001) and greater than those Material and methods assigned A2 (Sl-w relationship bA2 = 3.910 ± 0.474; t Data about the standard length (Sl)andweight(w)of = 8.251; df= 23; P < 0.001). Difference in Fulton’s Co- huchen were provided by fisheries managers and collected efficients FC for huchen in those two adult size cathe- in field by their guarding services in 2005–2007 period from gories (FcA1 = 1.074 ± 0.165; FcA2 = 1.190 ± 0.344) of the section of the Drina River between the dam of the hy- huchen mainly supported the detected change in their dropower plant “Perućac” and beginning of the reservoir of growth (t = 1.711; df = 36; P < 0.1). the hydropower plant “Zvornik”, about 110 km in length. The data set from 36 unsexed huchen for which both men- Discussion sural measures were taken were processed. All huchen were fished out by unknown anglers during the late autumn and winter periods, when the fishing season for them is legally Regarding that scales for age determination lacked in open in both Serbia and Bosnia & Herzegovina. Huchen were data obtained from fisheries managers, it was possible of the Sl range of 48–132 cm, whereas their range of w was only to extrapolate from the report of Mikavica & Savić 1.5–32.0 kg. The Piecewise Linear Regression (Nickerson et (1999) that age when huchen altered their growth was al. 1989) with the Sl as independent variable and w as de- the most likely greater than 8+, when huchen attain pendent variable, transformed into log10 values for linearity, mean Sl of 85.5 cm and mean w of 7.837 kg. The sex- was employed, in order to detect the breakpoint values of Sl ing of smaller huchen, less in size than 110 cm Sl was and w at which the length-weight relationship (Ricker 1958, not accomplished because they were to be released back 1975) alters. A brief explanation of the Piecewise Linear Re- into the water, since they were below the size allowed gression is given in Simonović&Nikolić (2007). That point of alteration served for the calculation of either b relation- for taking out, whereas larger ones were seen for der- ship between Sl and w, as well as for the calculation of the moplastics by anglers who caught them. Fultons Fc condition coefficient in two groups of huchen, Breakpoint values in both Sl and w recently smaller and larger ones. recorded for adult huchen were much lower than those 158 P.D. Simonovic´ et al.

Simonović et al. (2000) reported for eleven huchen of The smaller value for Sl-w relationship bA1 of small- the adult life period (88–124 cm in Sl and 6.1–25.5 kg in sized huchen and the greater value for Sl-w relationship w) as catches from the Drina River in the period 1998– bA2 of large-sized huchen obtained in the recent period 1999 (breakpoint values for Sl = 110.0 cm and for w = in comparison to the values from 1998–1999 indicate 16.541 kg). The recently obtained Sl–w relationship in an even stronger positive allometry for both growth- huchen of a size smaller than the breakpoint value was in-length and growth-in-weight, recently occurring in of lower value and that in huchen of a size greater than smaller and larger adult huchen, respectively. the breakpoint value was of higher value than in huchen Current scarcity of data about the population investigated in the period 1998–1999, when in huchen structure and natural production of huchen stock in smaller than 110 cm the Sl-w relationship was b =1.68 the section of the Drina River in concern is not suffi- ± 0.654 (t = 2.567; P ≈ 0.05), whereas in huchen larger cient for making inferences about factors affecting the than 110 cm Sl that relationship was b =3.23± 0.227 (t change in growth recorded in adult huchen. However, it = 14.247; P < 0.01). The Fulton Coefficients for those seems that this non-invasive method of investigation by two adult huchen cathegories in the 1998–1999 period Piecewise Linear Regression of length and weight that were Fc<110 cm Sl =1.01± 0.12, and Fc>110 cm Sl = provides detection of change in growth should be fur- 1.20 ± 0.17, respectively, which is very similar to the ther tested and complementedwiththeparametersof values obtained for that coefficient in two adult huchen population density and structure, as well as with those size classes recently investigated. Negative allometry in of huchen habitat, in order to assess the relationship smaller and positive allometry in larger adult huchen in- between them. Considering these relationships and us- dicating the faster gaining in weight in larger adults and ing this approach in the investigation of the stream- faster gaining in length in younger ones in samples from dwelling resident brown trout, Simonović&Nikolić both time periods, as well as the almost identical values (2007) revealed that the same approach could enrich for Fulton’s Coefficient FC obtained in the period before the knowledge about the amount of plasticity in the 2000 and recently corroborate the growth-related status life-history of huchen as endangered salmonid species of two adult categories of huchen and strongly validate and its dependence on various population and habitat the methodology applied here as consistent and reli- variables that might affect it. able. Barnham & Baxter (1998) considered the higher value of the Fulton Coefficient FC in larger adults in Acknowledgements comparison to the smaller ones a consequence of faster gain in weight in large fish, as revealed in a quantitative The research was supported by grant No. 173025 of the Min- evaluation of shape in salmonid fish. istry of Science and Technological Development and grant There are no reports about the dependence of “Research of Life History and Population Traits of Hunched length-weight relationship on sex in huchen of any size. in Serbia” of the Ministry of Environment Protection and Jasper & Evenson (2006) reported that in large (50–105 Spatial Planning of the Republic of Serbia. cm Sl) Chinook salmon Oncorhynchus tschawytscha (Walbaum, 1792) from the Yukon River in Alaska the References length-weight relationship did not differ between males and females at the same sampling sites. There are yet Anderson R.O. & Gutreuter S.J. 1983. 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They stated that those values entirely corre- fish. Fisheries Notes 5: 1–3. sponded to the size at which huchen shift from the ju- Cone R.S. 1989. The need to reconsider the use of condition in- venile to the adult period of ontogeny, as given by both dices in fisheries science. Trans. Am. Fish. Soc. 118 (5): 510– 514. Holčík et al. (1988) and Mikavica & Savić (1999). Mak- Fulton T.W. 1911. The sovereignty of the sea: A historical account ing such reliable statements for the change in growth of the claims of England to the dominion of the British seas in adult huchen is not possible. The recorded change in and of the evolution of the territorial waters, with special Sl-w relationship might also be related to the change reference to the rights of fishing and the naval salute. William Blackwood and Sons, Edinburgh, 799 pp. in their reproductive characteristics (e.g., decrease in Holčík J., Hensel K., Nieslanik L. & Skacel L. 1988. 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