Genetic diversity and population structure of sea trout in Gulf of Finland:

implications for conservation and management

Riho Gross, Marja-Liisa Koljonen, Oksana Burimski, Jarmo Koskiniemi

• There are approximately 1000 sea trout populations in the Baltic Sea of which about 500 reproduce naturally in Baltic rivers, including about 100 populations in Gulf of Finland (HELCOM 2011).

• Based on electrofishing surveys of parr densities, the sea trout populations in the Gulf of Finland are in an adverse state due to excessive fishing pressure, obstacles to migration, habitat degradation and variation in water flow.

• Stocking of sea trout is widely practiced with the aim of increasing their production. Potential threats:

– irreversible changes of the genetic composition of native populations due to direct (stocking for enhancing purposes) or indirect (immigration of hatchery fish from neighboring rivers) impact;

– non-natural selective pressures under captive conditions (domestication effect) or loss of genetic variation through genetic drift and inbreeding (that always occur in populations of restricted size such as hatchery stocks) may compromise local adaptations of the native populations and pose threat to the evolutionary potential of the species.

• In contrast to the Atlantic salmon, the current knowledge of genetic diversity and structure of sea trout populations in the Baltic Sea is very limited. Only local populations in different countries (e.g. Denmark, Sweden, Poland, Lithuania) have been studied by using various genetic markers but information about the populations in the whole Baltic Sea or even within different major subdivisions of it (including the Gulf of Finland) is still missing.

Background

Average densities of 0+ trout in Estonian (EE) Finnish (FI) and Russian (RU) rivers in Gulf of Finland (ICES 2012)

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

Estonia

NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN 14 6 8 9 12 10 21 6 15

Finland

0 196 260 271 330 318 288 348 176 332 330 398 379 428 373 310 281 190 279 258 316 291 213 239

Russia

NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN 5 3 0 13 95 25 10 3 7

25

125

225

325

425

Sea trout smolt releases (*1000) to the Gulf of Finland by country in 1988-2011

Aims of the study

• to reveal the genetic structure of sea trout populations within the Gulf of Finland

• to estimate the level of genetic variation of sea trout populations within the Gulf of Finland

• to give general recommendations for management

MaterialSampled sea trout rivers in the Gulf of Finland

(22 populations)

(16 populations)

(12 populations)

Sampled sea trout rivers in the Gulf of Riga and from Estonian islands

7 populations

5 populations

Methods:

• Genomic DNA was isolated from fin clips or muscle tissue• 15 microsatellite loci: Ssosl417, Str60INRA, SSa407,

SSosl1311, BS131, SSosl438, Strutta58, SSsp2201, Str15INRA, OneU9, Str73INRA, Ssa85, Str85INRA, SSsp1605, Ssa197

• PCR amplification products were separated by capillary electrophoresis on AB3500 (Tartu) and AB3130 (Helsinki) Genetic Analyzers and the sizes of the microsatellite alleles were determined using Genemapper software

• Allele sizes of microsatellite loci were calibrated and standardized by exchange of reference samples

Data analysis• The genotype data were analysed by standard population genetic

analysis tools (GENEPOP, ARLEQUIN, FSTAT, POPULATIONS, MEGA)• Genetic diversity was estimated as an allelic richness and an

average observed/expected heterozygosity of populations• The level of population differentiation was esimated by pair-wise FST

values• Hierarchical distribution of genetic diversity was estimated by

AMOVA method• Genetic similarities/dissimilarities between populations were

estimated based on pair-wise DA genetic distances and depicted graphically as an unrooted neighbour-joining dendrogram

Results and Discussion

Genetic similarity of sea trout populations:NJ dendrogram (Nei’s Da distance)

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Sip

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87

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80

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onjo

ki

Vanta

anjok

i

Kymijo

ki

Summanjoki

99

AurajokiFiskarsinjoki

99Kiskonjoki

53

PaimionjokiUskelanjoki

78

KarjaankjokiSiuntionjoki

Urpalanjoki

Vilajoki

VirojokiMustajoki

SantajokiVammeljoki

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ista

52

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70

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95

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Population structure

Average genetic diversity of sea trout populations in different geographic regions

Estonia + Luga, Sista Finland Fin/Rus Russian Karelia

Genetic diversity of sea trout populations in the Gulf of Finland

Differentiation of sea trout populations

Fst = 0.031

Fst = 0.106 Fst = 0.060

Fst = 0.137

• global FST = 0.108• 4.8 % - between geographic

regions • 6.0 % - among populations

within the geographic regions• 89.2 % - within populations

Gulf of Finland:

EST_G. Fin FIN_G. Fin FIN/RUS_G. Fin RUS_G. Fin EST_G. Riga EST_IslandsEST_G. Finland 0.040 0.115 0.123 0.075 0.068 0.063FIN_G. Finland 0.115 0.132 0.172 0.138 0.148 0.116FIN/RUS_G. Finland 0.123 0.172 0.132 0.115 0.139 0.105RUS_G. Finland 0.075 0.138 0.115 0.062 0.094 0.080EST_G. Riga 0.068 0.148 0.139 0.094 0.059 0.075EST_Islands 0.063 0.116 0.105 0.080 0.075 0.028 Average from other 0.089 0.138 0.131 0.100 0.105 0.088

Average FST within (along diagonal) and between regions:

Conclusions• The average level of genetic variation of sea trout populations in Gulf of Finland

was comparable to that in Gulf of Riga but a little bit lower than in Estonian islands.

• Within countries, the level of genetic variation among populations was relatively similar in Estonia and Russia but more variable in Finland and Finnish/Russian border area. Populations with the highest genetic variation should be considered as a basis for forming hatchery stocks within each region.

• The overall level of genetic differentiation between studied populations in Gulf of Finland was moderate (FST = 0.108). The populations were most differentiated in Finland and Finnish/Russian border area and least differentiated in Estonia and Russia.

• Based on genetic distances, the populations clustered well according to the geographic regions. These 4 geographic groupings should be managed separately.

• The results of our study allow to propose genetic management and conservation units for sea trout in the whole Gulf of Finland and enable genetic data based planning for hatchery rearing and enhancement releases.

Thank you for your attention!