Journal of Sea Research 58 (2007) 163–165www.elsevier.com/locate/seares

Short communication

Sea growth of anadromous brown trout (Salmo trutta)

J.J. de Leeuw ⁎, R. ter Hofstede, H.V. Winter

Wageningen IMARES, Institute for Marine Resources and Ecosystem Studies, P.O. Box 68, 1970 AB IJmuiden, The Netherlands

Received 19 July 2006; accepted 5 December 2006Available online 20 December 2006

Abstract

Sea growth rates were studied in anadromous brown trout caught in Lake IJsselmeer, The Netherlands. Growth in the first yearat sea was estimated at 26 cm from length-frequency distributions, and at 21 cm from back-calculated growth rates from scalereadings. These estimates are considerably higher than sea growth rates observed in populations at higher latitudes (Norway,Sweden), but compare well with the limited information on sea growth rates estimated for anadromous trout in the River Rhine andrivers in Normandy (France).© 2007 Elsevier B.V. All rights reserved.

Keywords: Sea trout; Length; Cohort; Latitude; Rhine; Lake IJsselmeer

Brown trout Salmo trutta exhibit variable lifehistories: either a life cycle fully completed in freshwa-ter, or a life cycle including a growing phase at sea(anadromous or sea trout), also called morph fario andmorph trutta, respectively (Elliott, 1994; Baglinière andMaisse, 1999). The two life history strategies arerecognised by phenotypic characteristics. In contrast totheir resident congeners, population dynamics andgrowth performance of the marine life stages of browntrout are poorly known (Olsen et al., 2006). Spawninggrounds and nursery of the young are in shallow rivers(Elliott, 1994; Baglinière and Maisse, 1999). After 1–3(up to 8) y, juveniles (so-called ‘smolts’) migrate to thesea in spring and may return to freshwater in autumn.Immature sea trout may undertake annually repeatedseasonal migrations between sea and estuaries or makeupstream excursions (so-called ‘dummy-runs’) or stay

⁎ Corresponding author. Tel.: +31 255 564646; fax: +31 255564644.

E-mail address: joep.deleeuw@wur.nl (J.J. de Leeuw).

1385-1101/$ - see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.seares.2006.12.001

away from freshwater for several years (Alm, 1950;Jonsson and Jonsson, 2002). The sea-run phase isgenerally assumed to be a phase of rapid growth inpreparation of reproduction and attaining larger body sizeto increase reproductive output (McDowell, 1988;L'Abée-Lund et al., 1989; Thorpe, 1994). However,information on actual growth rates of sea trout is generallyconfined to the juvenile life stages in freshwater (e.g.Elliott, 1994), while published data on growth rates at seaare limited to Scandinavian populations (e.g. Alm, 1950;Jonsson, 1985; Berg and Jonsson, 1990; Jonsson et al.,1991; L'Abée-Lund, 1994; Olsen et al., 2006).

We report growth data of sea trout from the closed-off estuary of Lake IJsselmeer, The Netherlands.Growth rates at sea were estimated from both length-frequency distributions and from scale readings of seatrout bycatches in commercial fisheries with fyke netsand gill nets in 1994–2000. Lake IJsselmeer (1840 km2)is a shallow, freshwater lake (mean depth 4.5 m)between the River IJssel, a lower branch of the Rhine,and the Wadden Sea/North Sea. Water temperature

Fig. 1. (a) Total body length of sea-run trout in relation to time of the year (day numbers) in Lake IJsselmeer (1994–2000). (b) Total body length fordifferent sea-run cohorts based on scale readings of sea trout caught in June and October 1998 and 1999. Dotted lines represent the split of first andlater cohorts (cf. Hartgers and Buijse, 2002).

Table 1Mean length per cohort of sea trout caught in fyke nets and gill nets inspring (May-June) and autumn (October-November) in Lake IJsselmeer(sample sizes between brackets)

year cohort 1, May-June

cohort 1, Oct-Nov cohort 2, May-June

mean length (cm)±SD (n)

mean length (cm)±SD (n)

mean length (cm)±SD (n)

1994 40±3 (28)1995 26±5 (96) 41±7 (70) 50±4 (54)1996 24±6 (54) 49±8 (23) 52±6 (34)1997 23±5 (157) 38±6 (27) 54±6 (24)1998 24±5 (894) 41±5 (34) 47±4 (93)1999 24±5 (973) 41±5 (230) 50±4 (159)2000 23±5 (350) 47±7 (69) 51±5 (158)average 24±5 (2524) 41±5 (481) 50±4 (522)

Cohorts were separated based on length (dotted line Fig. 1a; Hartgersand Buijse, 2002).

164 J.J. de Leeuw et al. / Journal of Sea Research 58 (2007) 163–165

ranges from ∼3 °C in midwinter to ∼20 °C inmidsummer. Sea trout can migrate between LakeIJsselmeer and the Wadden Sea through the dischargesluices in the 32 km long barrier dam Afsluitdijk.

Total body length of 3527 sea trout increased over theyear and at least two distinct cohorts could be discerned.(Fig. 1a; data in Hartgers and Buijse, 2002; line sepa-rating cohorts over the year: length(cm)=0.685⁎ (daynumber)+30). The number of sea trout in the first cohortof year x was closely correlated to the number in thatcohort in the following spring (r2 =0.87). In addition,the average length of a cohort in autumn of year x waswell correlated to the average length of that cohort in thefollowing spring (year x+1)(r2 =0.75). Both observa-tions support our method of splitting cohorts fromlength-frequency distributions.

Most of the fish were sampled in May-June andOctober-November (Fig. 1a). The average length of thefirst cohort (sea age 0) in May-June was 24 cm with littlevariation among years (Table 1). Average length of thefirst cohort in October-November was 41 cm, while anaverage length of 50 cm was reached after the winter(sea age 1). Average sea growth rate was thus estimatedat 3.4 cm mo−1 in the first summer (April-September)and 1.3 cm mo−1 in the subsequent winter (October-March), in total 26 cm in their first year at sea.

Back-calculated growth rates (DeVries and Frie,1996) based on scale readings of 50 individuals (caughtin 1998 and 1999, body lengths 16–86 cm) confirmedthat the first cohort observed in splitting the length-frequency distribution (Fig. 1a) consisted of sea trout intheir first year at sea (Fig. 1b). Most larger individualshad spent 2 y at sea and the maximum was 4–5 y at sea.Sea growth was estimated at 21 cm (SD 6.5, n=21) inthe first full year at sea (cohort 1 in Fig. 1b) and 20 cm

(SD 5.5, n=6) in the second year. Thus, scale readingsyielded somewhat lower growth rates than length-frequency distributions. Scale readings suggested flex-ibility in frequency and duration of the time spent at sea(not necessarily full years, and winter may be spent atsea or not), as found elsewhere (Berg and Jonsson,1990; Jonsson and Jonsson, 2002; Knutsen et al., 2004).This variation in sea-going behaviour causes some biasin estimates of growth rates, both from length-frequencydistributions (cohorts not well discernible especiallyafter more than one year at sea) and from scale readings(year rings unclear). The scale readings indicated thatsea trout in the IJsselmeer had lived 1 (75%), 2 (20%) or3 (5%) y in freshwater before migrating downstream.

Sea growth rates for Lake IJsselmeer compare wellwith other estimates for sea trout populations in theRhine at Iffezheim, Germany (Roche, 1992) and in the

Fig. 2. Growth of sea trout in populations at different latitudes. 53° N:Lake IJsselmeer (SR = scale readings, LF = length frequency data) andthe River Rhine at Iffezheim (Roche, 1992); 49° N: Rivers Orne andTouques (Richard and Baglinière, 1990); 59° N: Åva (Alm, 1950), 60°N: Lake Vangsvatnet (Jonsson, 1985).

165J.J. de Leeuw et al. / Journal of Sea Research 58 (2007) 163–165

rivers Orne and Touques in Normandy, France (recon-structed from photographs of scales in Richard andBaglinière, 1990; Fig. 2). In Vangsvatnet, Norway(60° N), scale readings of 603 sea trout that had spent1–5 y at sea (Jonsson, 1985) showed a lower growth ratethan those of the Rhine (53° N) and Norman (46° N)populations, while intermediate growth rates were foundin Åva, Sweden (59° N; Alm, 1950; Fig. 2). A decreasingtrend in sea growth rate with latitude was also found in25 Norwegian rivers (Jonsson et al., 1991; L'Abée-Lund, 1994). Length increments in the first year at seawere 9.4 cm at 64° N to 20.4 cm at 58° N, which links upwith the 26 cm at 53° N in the Rhine population. Apartfrom a latitudinal gradient as explained from watertemperature differences (Jonsson et al., 1991), growthrates vary among river systems, probably due to differentfeeding conditions at sea, and also vary with time spent atsea, owing to the flexible behaviour in coastal waters,estuaries and rivers (Elliott, 1994). The Norman andNorwegian data suggest strong retardation of growthafter 3 or 4 y spent at sea, probably as a consequence ofonset of reproduction (Jonsson et al., 1991).

Acknowledgements

We thank the fishermen of Lake IJsselmeer forcollecting trout specimens, Leo Schaap for scale read-ings, and two anonymous referees for comments on themanuscript. This study resulted from research programsfunded by the Ministry of Transport and Public Works

(Rijkswaterstaat RIZA and RDIJ) and the Ministry ofAgriculture, Nature Management and Fisheries, TheNetherlands.

References

Alm, G., 1950. The sea trout population in de Åva stream. Rep. - Inst.Freshw. Res. 31, 26–56.

Baglinière, J.L., Maisse, G., 1999. Biology and Ecology of the Brownand Sea Trout. Springer-Praxis series in Aquaculture and Fisheries,Cornwall, UK.

Berg, O.K., Jonsson, B., 1990. Growth and survival rates of theanadromous trout, Salmo trutta, from the Vardnes River, northernNorway. Environ. Biol. Fisches 29, 145–154.

DeVries, D.R., Frie, R.V., 1996. Determination of age and growth, In:Murphy, B.R., Willis, D.W. (Eds.), Fisheries Techniques, second ed.American Fisheries Society, Bethesda, Md., pp. 483–513.

Elliott, J.M., 1994. Quantitative Ecology and the Brown Trout. OxfordSeries in Ecology and Evolution, New York.

Hartgers, E.M., Buijse, A.D., 2002. The role of Lake IJsselmeer, a closed-off estuary of the River Rhine, in rehabilitation of salmonidpopulations. Fisheries Manag. Ecol. 9, 127–138.

Jonsson, B., 1985. Life history patterns of freshwater resident and sea-run migrant brown trout in Norway. Trans. Am. Fish. Soc. 114,182–194.

Jonsson, N., Jonsson, B., 2002. Migration of anadromous brown troutSalmo trutta in a Norwegian river. Freshw. Biol. 47, 1391–1401.

Jonsson, B., L'Abee-Lund, J.H., Heggberget, T.G., Jensen, A.J., Johnson,B.O., Naesje, T.F., Saettem, L.M., 1991. Longevity, body size, andgrowth in anadromous brown trout (Salmo trutta). Can. J. Fish.Aquat. Sci. 48, 1838–1845.

Knutsen, J.A., Knutsen, H., Olsen, E.M., Jonsson, B., 2004. Marinefeeding of anadromous Salmo trutta during winter. J. Fish Biol. 64,89–99.

L'Abée-Lund, J.H., 1994. Effect of smolt age, sex and environmentalconditions on sea at first maturity of anadromous brown trout(Salmo trutta) in Norway. Aquaculture 121, 65–71.

L'Abée-Lund, J.H., Jonsson, B., Jensen, A.J., Saettem, L.M.,Heggberget, T.G., Johnson, B.O., Naesje, T.F., 1989. Latitudinalvariation in life-history characteristics of sea-run migrant browntrout (Salmo trutta). J. Anim. Ecol. 58, 525–542.

McDowell, R.M., 1988. Diadromy in fishes. Migrations BetweenFreshwater and Marine Environments. Croom Helm, London.

Olsen, E.H., Knutsen, H., Simonsen, J.H., Jonsson, B., Knutsen, J.A.,2006. Seasonal variation in marine growth of sea trout, Salmotrutta, in coastal Skagerrak. Ecol. Freshw. Fish 15, 446–452.

Richard, A., Baglinière, J.L., 1990. Description et interprétation desécailles de truites de mer (Salmo trutta) de deux rivières de basse-Normandie: l'Orne et la Touques. Bull. Fr. Pêche Piscic. 396,239–257.

Roche, P., 1992. Mise en évidence de l'écotype truite de mer dans lescaptures de grandes truites (Salmo trutta L.) du Rhin supérieur.Bull. Fr. Pêche Piscic. 324, 36–44.

Thorpe, J.E., 1994. Salmonid flexibility: responses to environmentalextremes. Trans. Am. Fish. Soc. 123, 606–612.