Send O de s o Rep in s o ep in s@ben hamscience.ae
46 The Open Fish Science Jou nal, 2014, 7, 46-58
1874-401X/14 2014 Ben ham Open
Open Access
Spawning-Age Di e ences and hei Tempo al T ends in Wild and
Sea-Ranched A lan ic Salmon S ocks, om S ock Mix u e Da a
I ma Kallio-Nybe g1,*,#, Ma ja-Liisa Koljonen2 and I ma Saloniemi3
1Finnish Game and Fishe ies Resea ch Ins i u e, Ko sholmanpuis ikko 16, FI-65100 Vaasa, Finland; 2Finnish Game
and Fishe ies Resea ch Ins i u e, P.O. Box 2, FI-00791 Helsinki, Finland; 3Uni e si y o Tu ku, Depa men o Biology,
Labo a o y o Gene ics, FI-20014 Tu ku, Finland
Abs ac : O igin and age was de e mined o indi idual ish caugh in o sho e ca ches o A lan ic salmon s ocks (Salmo
sala L.) in he Bal ic Sea o e he yea s 2000–2009. DNA mic osa elli e loci and smol age we e used o p obabilis ically
assign e u ning spawne s o hei s ock o o igin. Da a o his s udy we e based on app oxima ely 2600 ca ch samples o
he i e mos common wild and ou sea- anched, ha che y- ea ed s ocks. Spawning age, and sex a io di e ed bo h
wi hin and be ween hese wild, and sea- anched g oups. The emales we e mainly (78.7%) wo sea-win e s old and he
males usually (68.7%) only one sea-win e old. In bo h sexes, he mean age a ma u i y was lowe in he ha che y- ea ed,
sea- anched s ocks han in na u ally ep oducing s ocks. In he 2000s, he e was a weak dec easing end in he male
spawning age, bu no in ha o emales. The sex- a io o he spawne s was emale dominan in he na u ally ep oducing
s ocks, bu male dominan in ha che y- ea ed s ocks. Published his o ical da a om wo o he same i e s sugges ha he
majo i y o males we e mul i-sea-win e spawne s in he 1930s, and a ia ion in he age dis ibu ion o he spawne s has
become na owe and skewed owa ds a younge age in he p esen da a (2000–2009) compa ed o he ea lie si ua ion.
Keywo ds: Bal ic sea, gene ic mixed s ock analysis, indi idual assignmen , Salmo sala , sea age a ma u i y, sex.
INTRODUCTION
The spawning age, o age a ma u i y, o he anad omous
A lan ic salmon (Salmo sala ) is a he i able ai , and i s
a ia ion has been shown o ha e adap i e componen s [1].
The homing o salmonids o hei na al i e has led o adap-
a ion o local en i onmen al condi ions [2, 3]. Spawne s o a
la ge i e a e known o be olde and la ge han hose o a
small i e , as ish size is a esponse o he discha ge o he
i e , and o he dis ance o he eeding a eas in he sea [4-7].
Because he g ow h a e and spawning age o salmonids
a e nega i ely co ela ed [8], selec ion a o ing g ow h ends
o lowe he spawning age. In addi ion o he gene ic back-
g ound, en i onmen al ac o s in he sea a ec he numbe o
yea s spen on he eeding mig a ion be o e ma u a ion [9,
10]. The spawning age o A lan ic salmon a ies om one o
i e yea s, calcula ed as he numbe o win e s spen in he
ma ine eeding a eas a e hei wo o i e eshwa e yea s
in he i e [11, 12]. Occasionally, salmon a e able o eco e
om hei i s spawning and e u n o he sea, and e en
spawn o a second ime [5, 13, 14], bu in he Bal ic Sea he
p opo ion o such ish is cu en ly only a ew pe cen [15].
*Add ess co espondence o his au ho a he Finnish Game and Fishe ies
Resea ch Ins i u e, Ko sholmanpuis ikko 16, FI-65100 Vaasa, Finland; Tel:
+358 295 327 678; E-mail: i ma.kallio-nybe g@luke. i
#The Finnish Game and Fishe ies Resea ch Ins i u e will me ge wi h MTT
Ag i ood Resea ch Finland, he Finnish Fo es Resea ch Ins i u e and he
s a is ical se ices o he In o ma ion Cen e o he Minis y o Ag icul u e
and Fo es y Tike on 1 Janua y 2015, o o m Na u al Resou ces Ins i u e
Finland.
As a nea ly semelpa ous ish, he inal body size o he
A lan ic salmon depends on i s age a ma u i y. In he Bal ic
Sea, he size o one-sea-win e (1 SW) ish in he ca ch is
abou 60–65 cm, while ha o h ee-sea-win e (3 SW) ish
is abou 95–100 cm [16]. Body size is impo an om he
pe spec i e o bo h ishe ies managemen and he conse a-
ion o iabili y. La ge ish inc ease he comme cial alue o
he ca ch, bu besides his, he spawning size is also an im-
po an e olu iona y ai ela ed o ecundi y and he i ness
o indi iduals and he popula ion as a whole [17]. Small e-
males, in pa icula , p oduce ewe , smalle , and weake eggs
han la ge emales, and hus a change in he emale spawning
size may educe he i ness o he whole popula ion. The
collapse o he A lan ic cod (Gadus mo hua) s ock is a a-
mous example o ishe ies selec ion leading o a dec eased
spawning age and hus also body size [18, 19].
Ha che y ea ing is likely o a ec he spawning age, e-
duce i ness in he wild, and ha e ad e se e ec s on se e al
adap i e ai s in salmon [20]. Hyb idiza ion o ea ed and
wild ish may also change he spawning age and o he li e-
his o y ai s o he s ocks [21-24]. Domes ica ion selec ion
in ha che ies ends o a o a high g ow h a e and ea ly sex-
ual ma u i y [21, 25, 26], and ishe ies usually selec agains
a la ge size and la e spawning age [27-29]. A end owa ds
younge spawne s was obse ed in he 20 h cen u y o many
salmon s ocks, as a ma ked decline in ei he he p opo ion
o olde , mul i-sea-win e (MSW), o o epea edly spawning
salmon [30-32]. These ends ha e also been epo ed in Bal-
ic Sea salmon [15, 33].
The es ima ed na u al p oduc ion o salmon smol s is be-
low he po en ial le el in many Bal ic Sea i e s [34], and
Spawning Age Di e ences in A lan ic Salmon S ocks The Open Fish Science Jou nal, 2014, Volume 7 47
many salmon s ocks ha e been los because o he d edging
and damming o i e s o hyd opowe p oduc ion since he
1940s. Salmon s ocks o igina ing om he cu en ly closed
i e s ha e been main ained by ea ing o sp ing om bo h
ha che y b oods ocks and sea- anched pa en s [16]. Since he
1980s, ishing p essu e has been hea y, and i has h ea ened
he na u ally ep oducing s ocks [12, 15, 35, 36]. In addi ion,
since he 1990s, high pos -smol mo ali y o unknown ea-
sons has impai ed he s a e o he na u al s ocks [26, 37-39].
Changes in adap i e ai s such as a dec ease in he spawning
age and size may cons i u e u he isks o he iabili y o
he emaining wild s ocks.
He e, we analyzed s ock-speci ic spawning ages om
sea-caugh ish by i s iden i ying he s ock o o igin o in-
di idual ishes wi h a gene ic indi idual assignmen me hod,
and hen using his s ock iden i y o de ine he s ock-speci ic
spawning age dis ibu ions o he nine A lan ic salmon
s ocks mos commonly con ibu ing o he ca ches. Ou s udy
app oach allowed us o e eal p e iously unknown di e -
ences in spawning age, which is an e olu iona ily impo an ,
adap i e quan i a i e ai and usually a ies among i e
s ocks o A lan ic salmon. In addi ion, we we e able o ana-
lyze wo ime in e als, ends du ing a en-yea pe iod in
con empo a y s ocks, and also his o ical changes since he
1930s o wo s ocks o which his o ical in o ma ion was
a ailable. Al hough gene ic di e en ia ion in adap i e quali-
a i e ai s is in heo y known o occu , epo s on hese di -
e ences a e a e, and ye hey ha e e olu iona y signi i-
cance. A lan ic salmon s ocks a e a a ge o many ypes o
human in e e ence, and a e hus likely o change gene ically
because o his, in addi ion o changes caused by a ying
na u al selec ion p essu es.
The goal o his s udy was o desc ibe s ock-speci ic
spawning age dis ibu ions, hei po en ial di e ences, and
also he changes o e ime, om 2000 o 2009, in i e wild
(To nionjoki Wild, Simojoki, Kalixäl en, Byskeäl en, Vin-
deläl en) and ou ha che y- ea ed (To nionjoki Ha che y,
Iijoki, Oulujoki, Luleäl en) A lan ic salmon s ocks (Fig. 1).
The To nionjoki salmon s ock had bo h a wild and sea-
anched componen . In addi ion, we compa ed da a om he
1930s, a ailable om one o he cu en wild s ocks (Ka-
lixäl en) and one o he cu en ha che y- ea ed s ocks
(Luleäl en) when hey we e bo h s ill wild [40], wi h in o -
ma ion on hese same s ocks in hei con empo a y s a e.
These his o ical samples we e aken be o e he o sho e ish-
e y o ha che y ea ing had s a ed. The po en ial causes o
he obse ed di e ences and changes we e examined in ela-
ion o hei ep oduc ion (ha che y) his o ies.
MATERIAL AND METHODS
Annual Sampling o he Spawne s
In o al, 7 414 e u ning salmon we e sampled by ishe men
du ing May o July in 2000 and in 2002–2009 om he salmon
ca ches in he no he n Bal ic Sea. The sampling a eas co e-
sponded o ICES subdi isions 29, 30, and 31
(Fig. 1) along he spawning mig a ion ou e o he ish om he
Bal ic Main basin o he no he n he Gul o Bo hnia (GB):
1) he Åland Sea (ÅS), subdi ision 29; samples mainly
aken in week 22;
2) he Bo hnian Sea (BS), subdi ision 30; mainly sampled
in week 25; and
3) he Bo hnian Bay (BB), subdi ision 31; mainly sampled
in week 26 (Fig. 1).
Fig. (1). Map o he Bal ic Sea showing he Bo hnian Bay i e s
and he sampling si es (*) in Finnish and Swedish coas al wa e s in
he Åland Sea (ÅS), he Bo hnian Sea, and in he Bo hnian Bay.
The ca ch leng h (indi idual o al leng h) and he sex o
he ish, as well as he ca ch da e and si e, we e eco ded on
cap u e, and scale samples we e aken om each ish o
DNA analysis and age de e mina ion. Bo h he eshwa e
yea s and sea win e yea s we e sepa a ely de e mined om
scales. The eshwa e age in o ma ion was used as one a i-
able in indi idual assignmen .
As all cap u ed indi iduals we e mig a ing owa ds i e
mou hs in o de o spawn in he au umn o he same yea , he
sea age and he age a ma u i y o spawning age we e in his
case he same. In o ma ion on he sex was no a ailable o
all indi iduals, bu hose wi hou his in o ma ion we e ex-
cluded om he analysis. In p ac ice, all o he s udied ish
(99.99%) we e i s - ime spawne s.
Ca ch samples we e collec ed om he coas al ap ne
and d i ne ishe y, along he spawning mig a ion ou e
om he Bal ic Main Basin owa ds he no he n spawning
i e s. The da a we e pooled o e en yea s o each s ock o
analyze he mean spawning age dis ibu ion. Thus, annual
a ia ion in he spawning mig a ion is no assumed o a ec
29
27
31
30
32
26
28
25
2424
0 200 km
To nionjoki
Kalixäl en
Simojoki
Iijoki
Oulujoki
25°
60°
Bo hnian
Sea
Bo hnian
Bay
GULF OF BOTHNIA
ÅS
FINLAND
SWEDEN
GULF OF FINLAND
BALTIC
MAIN BASIN
Umeäl en
Luleäl en
*
*
*
*
*
*
*
*
**
*
Vindeläl en
Byskeäl en
48 The Open Fish Science Jou nal, 2014, Volume 7 Kallio-Nybe g e al.
he esul s. The spawning mig a ion las s only a limi ed ime
and peaks in June. Fo each si e, he peak week could e en
be de ined (see abo e). The sampling co e ed he whole
ishing season. The es ima ed s ock g oup p opo ions om
he i s i e yea s (2000–2005) om he same ca ches ha e
p e iously been published [34]. A compa ison o he p esen
si ua ion wi h he si ua ion 70–80 yea s ago was possible by
making use o da a on Luleäl en and Kalixäl en salmon
s ocks published by Alm [40].
The legal minimum landing size o A lan ic salmon in he
Bal ic Sea is gene ally 60 cm. Howe e , in he Bo hnian
Bay, whe e he majo i y o ish om all s udied s ocks we e
caugh (65%–91%) (Table 2), he legal minimum landing
leng h is 50 cm (since 1993) [37], hus also allowing he
smalles ma u e males o be caugh .
Salmon S ocks
Fi e wild and ou ea ed and sea- anched salmon s ocks,
which we e he mos abundan s ocks in he ca ches, we e
chosen o he cu en s udy (Table 1). The home i e s o all
hese s ocks d ain in o he Bo hnian Bay, he no he nmos
pa o he Bal ic Sea, and he s ocks ha e e y simila mi-
g a ion pa e ns. The ish om all hese s ocks unde ake
hei eeding mig a ion o he Bal ic Main Basin, and e u n
as spawne s o hei home i e s ea ly in he summe , mainly
du ing a ew weeks in June [6, 25].
The spawning en i onmen and i s selec i e ac o s di e
be ween he wild and he sea- anched ha che y s ocks, bu
he condi ions and eeding a eas in he sea a e common o all
ish, so he obse ed di e ences be ween wild and sea-
anched g oups a e assumed o be a esul o ei he di ec
di e ences in he ep oduc ion en i onmen o he gene ic
selec ion i causes [6].
The To nionjoki Ri e is he bo de i e be ween Fin-
land and Sweden. I suppo s a wild, na u ally ep oducing
salmon s ock ( e e ed o he e as To nionjoki W salmon).
Smol p oduc ion collapsed in he 1980s [12], bu he s ock
has now eco e ed (Table 1). The no he nmos spawning
si es a e loca ed abou 500 km om he i e mou h [41].
Rea ed To nionjoki (To nionjoki R) salmon smol s
ha e been eleased bo h in o hei home i e [12] and in o
he nea by Kemijoki es ua y [16] (Table 1). The b oods ocks
a e es ablished om ish caugh in he wild [42].
The Simojoki salmon is he o he wild Finnish salmon
s ock on he Bal ic Sea coas . I was nea ex inc ion in he
1980s [36]. Following suppo i e s ockings, es o a ion o
he i e , and ishing egula ion, he s a us o he s ock has
imp o ed [12, 15, 36].
The Iijoki salmon has been main ained as a b oods ock
since he 1960s, when he i e was dammed o hyd oelec-
ic powe p oduc ion. The ea ed smol s ha e mainly been
p oduced by using b oods ocks ha we e o iginally ounded
om ish o he i e be o e i was dammed [43]. The num-
be o successi e ha che y gene a ions was 4.5 in 1995 [44].
Mo e ecen ly, ascending spawne s ha e been used as pa -
en s o b oods ocks [42]. The loss o he na u al smol p o-
duc ion o he Iijoki salmon has been compensa ed o by
annual smol eleases in o he es ua y o he i e (Table 1).
The Oulujoki salmon is a ea ed mixed s ock including
gene ic ma e ial om a leas he Finnish Iijoki, To nionjoki,
and Oulujoki, and he Swedish Skelle eäl en s ocks [45].
The na u al salmon un o he Oulujoki salmon ended in he
1960s, when he i e was dammed. The numbe o succes-
si e ha che y gene a ions was se en in 1995 [44]. To com-
pensa e o he los smol p oduc ion, 100 000 ea ed smol s
a e annually eleased in o he es ua y [43].
The Kalixäl en Ri e suppo s a na u al salmon s ock
(Table 1). Toge he wi h he To nionjoki Ri e , his i e
main ains he wo la ges wild salmon s ocks wi hin he Bal-
ic Sea ange.
The Luleäl en salmon is cu en ly a ea ed ha che y
s ock. The loss o na u al smol p oduc ion has been com-
pensa ed o by he annual elease o 540 000 smol s [46]
(Table 1). The p oduc ion o smol s is based on he annual
cap u e o spawne s om he i e mou h.
The Byskeäl en salmon is a Swedish wild salmon s ock
(Table 1).
The Vindeläl en Ri e suppo s a na u al salmon s ock.
I is a ibu a y o he Ri e Umeäl en. The Umeäl en
salmon is a ha che y s ock, and egula annual eleases (94
000 smol s) a e ca ied ou wi h his s ock [46] (Table 1).
Iden i ica ion o he Ri e S ock o O igin
F eshwa e age dis ibu ions and mul ilocus geno ype
equencies a 17 DNA mic osa elli e loci in baseline s ocks
and ca ch samples we e used o es ima e he s ock composi-
ion o he ca ches and he s ock o o igin o indi idual ish.
Fo he eshwa e age, o smol age, wo age classes we e
used: ei he 1- and 2-yea -olds (Type 1) o olde smol s
(Type 2). This classi ica ion was used as one a iable in he
analysis, simila ly o a p e ious in es iga ion [47].
In addi ion o he eigh mic osa elli e loci used in Kol-
jonen (2006) [34], a u he nine loci we e analyzed o in-
c ease he o al numbe o 17, so ha a ia ion was de e -
mined a he ollowing 17 mic osa elli e loci: (1) SSa14 [48],
(2) SSa171 [49], (3) Ssa197 [49], (4) SSa202 [49], (5)
SSa289 [48], (6) SSa407 [50], (7) SSa85 [48], (8) 8SSaD157
[51], (9) SSosl417 [52], (10) SSosl438 [52], (11) SSosl85
[52], (12) SSsp1605 [53], (13) SSsp2201 [53], (14)
SSsp2210 [53], (15) SSsp2216 [53], (16) SSsp3016 [53] and
(17) SSspG7 [53]. In addi ion o ca ch da a, he same esh-
wa e age dis ibu ion and DNA mic osa elli e da a o 17
loci we e a ailable o all po en ially con ibu ing s ocks, o
baseline s ocks [47].
The polyme ase chain eac ion (PCR) and DNA labeling
we e pe o med as desc ibed in Säisä e al. [54]. Mic osa el-
li e geno ypes we e de ec ed wi h an Applied Biosys ems
ABI 3130 au oma ed DNA sequence and analyzed wi h
GENEMAPPER Analysis So wa e e sion 4.0, wi h he size
s anda d o Applied Biosys ems GeneScan 500LIZ. Au o-
ma ic ou pu s we e checked manually. The same se o 17
DNA mic osa elli e loci was also used in he ca ch analysis
o Vuo i e al. [55].
The Bayesian es ima ion me hod o mixed s ock analysis
was used in he calcula ions pe o med wi h he BAYES
p og am [56]. Gene ic in o ma ion on 33 A lan ic salmon
Spawning Age Di e ences in A lan ic Salmon S ocks The Open Fish Science Jou nal, 2014, Volume 7 49
Table 1. Cu en (2010) na u al smol p oduc ion le els o he i e wild A lan ic salmon s ocks and he numbe o annually
eleased smol s o he ou ha che y s ocks included in he analysis [37, 46].
No Ri e s ock Coun y P opaga ion Na u al smol
p oduc ion Released smol s
1 To nionjoki, W Finland, Sweden Wild 1 000 000 -
2 To nionjoki, H Finland Ha che y - 615 000
3 Simojoki Finland Wild 36 000 -
4 Iijoki Finland Ha che y - 310 000
5 Oulujoki Finland Ha che y - 100 000
6 Kalixäl en Sweden Wild 700 000 -
7 Luleäl en Sweden Ha che y - 540 000
8 Byskeäl en Sweden Wild 100 000 -
9 Vindeläl en Sweden Wild 100 000 -
Table 2. The mean p opo ion (as a pe cen age) o e nine yea s (2000–2009) o nine A lan ic salmon s ocks in he ca ches om
h ee Bal ic Sea a eas: ICES sub-di isions 29 (Åland Sea), 30 (Bo hnian Sea), and 31 (Bo hnian Bay) (Fig. 1), when he
h eshold alue o co ec indi idual assignmen (P > 0.59) was applied. The sample size (n) is p esen ed o each s ock.
Ri e s ock Åland Sea % Bo hnian Sea % Bo hnian Bay % Sample n
To nionjoki W 8 25 67 738
Kalixäl en 12 23 65 325
Byskeäl en 4 5 91 201
Vindeläl en 6 27 67 105
Simojoki 1 22 77 99
To nionjoki H 5 6 79 416
Iijoki 2 12 86 276
Oulujoki 1 10 89 281
Luleäl en 15 17 68 142
s ocks a ound he Bal ic Sea was a ailable as baseline s ock
da a o he ca ch analysis [34]. O hese, 20 we e s ocks o
i e s d aining in o he Bo hnian Bay and ha ing s ocks ha
could occu in he analyzed ca ches. In all, 20 chains we e
un o he pos e io p obabili y dis ibu ions o each ca ch
sample o all he Gul o Bo hnia samples o e he yea s.
The p io o each po en ial baseline s ock had a maximum
p opo ion o 82.5% in u n, and he o he s e enly 0.05%.
The con e gence o he chains o he pos e io p obabili y
dis ibu ion was es ed and app o ed o each ca ch sample
wi h con e gence s a is ics [57], included in he BAYES
so wa e package. The las 1000 MCMC i e a ions o each
5000-i e a ion chain we e combined and used o desc ibe he
pos e io p obabili y dis ibu ions o he p opo ions o each
baseline s ock, and co espondingly o es ima e he p obabil-
i y o each indi idual ish belonging o any o he baseline
s ocks. Addi ional de ails o he baseline s ocks and es ima-
ion me hod a e p o ided in Koljonen [34], Koljonen e al.
[58], and [37].
Only ish assigned o he nine no he nmos s ocks we e
included in o his s udy (Table 3), as hei numbe s we e
la ge enough o allow pa i ioning in o se e al age classes. In
o de o educe he le el o unce ain y ela ed o indi idual
assignmen s, only indi iduals wi h a p obabili y o co ec
sou ce assignmen abo e 0.59 we e included in he cu en
analyses. Wi h his h eshold alue, he p obabili y o he
nex likely s ock was on a e age only 0.12 ± 0.11 (n = 2583,
Table 3), meaning ha he second bes s ock candida e was
no longe e y likely o be co ec , and cases wi h e y simi-
la p obabili ies o wo s ocks we e excluded. The p obabil-
i y o he hi d bes s ock candida e was in his case only
0.02. Al oge he , 2583 ish wi h comple e sex and sea age
in o ma ion we e assigned o hese nine s ocks when using
he h eshold p obabili y alue o 0.59. A e his, he
mean p obabili y o co ec indi idual assignmen o
all nine s ocks was 0.85 (± 1.13; see Table 3), and a ied
om 0.8 o 0.9.
50 The Open Fish Science Jou nal, 2014, Volume 7 Kallio-Nybe g e al.
Table 3. Salmon s ocks, and hei sample sizes (n) wi h he h eshold le el o co ec indi idual assignmen P > 0.59. The mean
p obabili y o co ec indi idual assignmen o he i s (P1), second (P2), and hi d (P3) sou ce s ock o o igin is shown,
and he sex a io ( he p opo ion o males) o he same da a.
S ock, wild (W) o
ha che y (H)
n
P > 0.59 Mean P1 Mean P2 Mean P3 Sex a io
To nionjoki, W 738 0.83±0.12 0.14±0.11 0.02±0.03 0.43
Kalixäl en, W 325 0.79±0.12 0.18±0.11 0.02±0.03 0.41
Byskeäl en, W 201 0.85±0.13 0.11±0.10 0.03±0.04 0.42
Vindeläl en, W 105 0.90±0.11 0.07±0.08 0.02±0.03 0.46
Simojoki, W 99 0.83±0.13 0.11±0.10 0.04±0.04 0.58
To nionjoki, H 416 0.83±0.13 0.11±0.09 0.03±0.03 0.60
Iijoki, H 276 0.88±0.12 0.08±0.08 0.02±0.03 0.69
Oulujoki, H 281 0.91±0.12 0.06±0.08 0.02±0.03 0.62
Luleäl en, H 142 0.86±0.12 0.09±0.08 0.03±0.04 0.54
To al 2583 0.85±0.13 0.12±0.11 0.02±0.03
Al hough some unce ain y emained in he indi idual as-
signmen , he me hod iden i ied he s ocks consis en ly and
cohe en ly o e he yea s [37]. The emaining unce ain y
only ends o mix he popula ions and hus educe he po en-
ially obse able di e ences. This same indi idual assign-
men me hod has been used by Palm e al. [58] and Vuo i
e al. [55] wi h he whole ange o indi idual assignmen
p obabili ies. Mo an e al. 2014 [59] es ed he use o p ob-
abili y h eshold alues in a simila app oach, when analyz-
ing ai di e ences om da a o mixed agg ega es.
STATISTICS
The s ock- and sex-speci ic sea-age dis ibu ions (1–5
SW) o all nine salmon s ocks we e compa ed by using he
 es (SAS FREQ p ocedu e) [60], bu in some analyses
only h ee sea-age ca ego ies (1SW; 2SW; 3–5SW) we e
used, because o small numbe s o indi iduals in he olde
age classes. The mean sea age in he s ocks was calcula ed
sepa a ely o males and emales. The di e ences in sea age
be ween s ocks we e compa ed using he K uskall-Wallis
es (SAS NPAR1WAY p ocedu e)[60].
The long- e m changes in sex a ios and sea-age dis ibu-
ions be ween con empo a y and his o ical da a we e ana-
lyzed by using he  es and - es .
Linea eg ession (SAS REG p ocedu e) was used in ana-
lyzing he associa ion be ween he mean male age (p opo -
ion o males) and emale age, and be ween he mean male
age and he sex a io o each o he s udied s ocks.
Changes in he p opo ions o he olde age classes as a
unc ion o ime (yea s 2000–2009, a con inuous a iable)
we e analyzed o all he ish caugh in Gul o Bo hnia
(Fig. 1, subdi isions 30 and 31). As he numbe o olde
spawne s was so low, he spawning age was analyzed as a
binomial a iable wi h he SAS GENMOD p ocedu e [60],
and di e ences be ween s ocks we e examined by using
odds a ios (OR). Fo males, he sea age ( esponse a iable)
was ca ego ized in o ei he 1 SW (one sea-win e ) o MSW
(mul i-sea-win e ) ( e e ed o he e as model 1; SAS GEN-
MOD), and o emales ei he young (1–2 SW) o old (3–5
SW) ( e e ed o he e as model 2; SAS GENMOD) in linea
eg ession models [60].
RESULTS
Spawning Age Di e ences Among Salmon S ocks
The spawning-age dis ibu ions o he nine A lan ic
salmon s ocks di e ed signi ican ly om each o he bo h
wi hin and be ween he wild and ea ed g oups, and espe-
cially be ween sexes (Fig. 2, Tables 4 and 5). In p ac ice,
males we e egula ly one yea younge han emales. Males
we e ei he one o wo sea-yea s old and emales wo o
h ee sea-yea s old. On a e age, abou 70% (68.7%, 51.1–
87.9%) o he spawning males in all ou con empo a y
salmon s ocks we e g ilse, i.e. 1 SW salmon, and only 5%
o hem ma u ed in hei hi d yea o la e in he sea
(Table 4). Fo emales, only less han 10% (7.2%, 2–17%)
ma u ed a an age o 1 sea-yea , and he la ge majo i y,
abou 80% (78.7%, 59–90%), ma u ed as 2 SW ish. On
a e age, 14% o emales spen mo e han wo win e s in he
sea (Table 4).
Signi ican di e ences in spawning age dis ibu ions
could be obse ed among bo h wild and sea- anched s ocks.
Among he wild salmon s ocks, he spawning-age dis ibu-
ion o males o he Swedish Byskeäl en salmon di e ed
s a is ically signi ican ly ( es ) om ha o males o he
o he i e s (Tables 4 and 5). This s ock had a clea ly highe
p opo ion (15.5%) o old, 3 SW, male spawne s han he
o he wild s ocks, o which he a e age was only 6.7%.
Among he wild emales, he Vindeläl en salmon had he
oldes spawne s, as o e one- hi d o hem we e a leas h ee
sea-win e s old (33% we e 3 SW o olde ), and he emale
age dis ibu ion o his s ock di e ed signi ican ly ( es )

Spawning Age Di e ences in A lan ic Salmon S ocks The Open Fish Science Jou nal, 2014, Volume 7 51
Fig. (2). A e age spawning-age dis ibu ion in males and emales o nine A lan ic salmon s ocks in he Bal ic Sea o e he yea s 2000–2009
(wild s ocks i s ) and also in he 1930s [40] in males (Ma30’s) and emales (Fe30’s).
om ha o he all o he wild s ocks, excep he Simojoki
salmon (Tables 4 and 5). The age dis ibu ion o Kalixäl en
emale spawne s di e ed in he opposi e di ec ion, as a clea
majo i y (89.6%) o Kalixäl en emale spawne s we e only 2
SW old.
Among he sea- anched popula ions, male spawning ages
di e ed in se e al cases, bu he emales we e mo e simila
in age. Al hough in all ou sea- anched ha che y s ocks he
p opo ion o male g ilse was nea ly 80% (79.8%), he
ha che y s ocks ne e heless di e ed signi ican ly om each
o he in pai wise compa isons, excep o Oulujoki and
To nionjoki (Table 5). The emale spawning-age dis ibu-
ions o he sea- anched ha che y s ocks we e qui e simila ,
and only he Iijoki s ock wi h i s younges emale spawne s
de ia ed s a is ically signi ican ly om he o he s ocks
(Tables 4 and 5). Among he Iijoki salmon, as many as
17.4% we e emale g ilse, which a e e y a e in he wild.
The wo o he sea- anched salmon s ocks mainly main ained
as b oods ocks, he Iijoki and Oulujoki s ocks, also di e ed
om each o he , as olde spawne s we e mo e common
among he Oulujoki han he Iijoki salmon in bo h sexes
(Tables 4 and 5).
The spawning-age di e ences be ween he wild and
ha che y g oups we e la ge, especially o males. The mean
spawning age o wild males was 1.5 sea-yea s and o sea-
anched ea ed males 1.32 sea-yea s, while he co espond-
ing ages o emales we e 2.12 sea-yea s and 2.00 sea-yea s
(Table 4). In p ac ice, all sea- anched s ocks di e ed highly
signi ican ly in ela ion o spawning-age dis ibu ion om all
he o he wild s ocks, excep om he Simojoki s ock (Table
5). The Simojoki salmon s ock, howe e , also pa ially has a
ha che y his o y.
The oldes spawne s we e 5-SW-old emales, and hese
we e ound in bo h he Byskeäl en and wild To nionjoki
salmon s ocks. The p opo ion o hese old, 4–5 SW emales
was only 1% in all con empo a y salmon s ocks. The oldes
male spawne s (4 SW) o igina ed om he wild To nionjoki
salmon s ock.
The Ri e To nionjoki salmon s ock cu en ly has bo h a
wild and a sea- anched componen . Fo bo h sexes, he mean
spawning age was highe o he wild han he sea- anched
componen (Table 4). The p opo ion o old, MSW males
was wice as high in he wild To nionjoki s ock componen
(42.1%, n = 316) as in he sea- anched componen (21.5%, n
= 251), al hough hey sha ed he same gene ic backg ound
and had been exposed o he same sea en i onmen and o -
sho e ishe y. The mean male spawning age had changed
om 1.48 o 1.23 sea-yea s. In emales, he mean spawning
age had changed om 2.13 sea-yea s o 2.01 sea-yea s (Ta-
ble 4). The la ges change in emales was in he p opo ion
o one-yea -old spawne s, as hey composed abou 4.7% in
he wild componen bu 10.9% in he sea- anched compo-
nen . Old emale spawne s (4 SW and 5 SW) we e only
ound in he wild componen o he To nionjoki salmon (Ta-
ble 4; Fig. 2).
Tempo al T ends in Spawning Age and Sex Ra io
When all males we e di ided in o only wo age classes
acco ding o hei spawning age, ei he g ilse, i.e. 1 SW
males (n = 786), o olde , MSW males (n = 336), he mean
spawning age di e ed highly signi ican ly be ween he
s ocks (GENMOD; Type 3 es : P < 0.001) [61]. The e was
also a sligh indica ion o a dec easing end in male spawn-
ing age o e he en-yea pe iod om 2000 o 2009 (P =
0.096) (Fig. 3a, model 1). In addi ion, he p opo ion o old
(MSW) males was a leas wo imes highe in he na u ally
ep oducing To nionjoki and Kalixäl en s ocks han in he
sea- anched s ocks (2.3 < OR < 7.0). In he Iijoki sea-
anched s ock, he p opo ion o MSW males was less han
hal (0.14 < OR < 0.53) o ha in all he o he s ocks
(Table 6). The p opo ion o MSW ish was highe in all
wild salmon s ocks han in he ea ed s ocks (OR > 1,
Table 6; Fig. 3a).
When he emales we e di ided in o wo spawning age
classes, ei he younge 1–2 SW (n = 881) o olde 3–5 SW (n
=132) spawne s, he spawning age o emales di e ed be-
ween salmon s ocks (P < 0.01) bu no be ween yea s (Fig.
3b; model 2), and no end o e ime could hus be obse ed
in he emale spawning age o he con empo a y s ocks. The
di e ences be ween sea- anched and wild s ocks we e also
smalle among emales han males (Table 6), and he
0 %
10 %
20 %
30 %
40 %
50 %
60 %
70 %
80 %
90 %
100 %
To nio W
Kalixäl en
Byskeäl en
Vindeläl en
Simojoki
To nio H
Iijoki
Oulujoki
Luleäl en
To nio W
Kalixäl en
Byskeäl en
Vindel
Simojoki
To nio H
Iijoki
Oulujoki
Luleäl en
Kalixäl en
Luleäl en
Kalixäl en
Luleäl en
Males 2000-2009
Females 2000-2009
Ma30's
Fe30's
5 Sea-win e
4 Sea-win e
3 Sea-win e
2 Sea-win e
1 Sea-win e
52 The Open Fish Science Jou nal, 2014, Volume 7 Kallio-Nybe g e al.
Table 4. S udied A lan ic salmon s ocks, sample sizes, mean spawning age (x) i s s anda d e o (S.E.) and spawning-age dis ibu-
ion o nine s ocks in o e 2000–2009 and also in wo s ocks (Kalixäl en, Luleäl en) in he 1930s [40], sepa a ely o e-
males (F) and males (M). SW = sea win e = sea age.
Salmon s ock Sample Mean Spawning age (%)
n x S.E. 1 SW 2 SW 3 SW 4 SW 5 SW
Females 2000s
To nionjoki W 422 2.13 0.02 4.7 79.6 14.2 0.9 0.6
Kalixäl en 192 2.08 0.03 2.1 89.6 6.8 1.5
Byskeäl en 117 2.10 0.04 5.1 82.0 11.1 0.9 0.9
Vindeläl en 57 2.28 0.08 7.0 59.6 31.6 1.8
Simojoki 42 2.14 0.08 7.1 71.5 21.4
All wild emales 830 2.12 0.02 4.4 80.5 13.6 1.1 0.4
To nionjoki H 165 2.01 0.04 10.9 77.0 12.1
Iijoki 86 1.87 0.05 17.4 77.9 4.7
Oulujoki 106 2.06 0.05 10.4 73.6 16.0
Luleäl en 65 2.03 0.07 13.9 69.2 16.9
All ea ed emales 422 2.00 0.02 12.6 75.1 12.3
All emales 1252 2.08 0.01 78.7 13.2 0.7 0.2
Males 2000s
To nionjoki W 316 1.48 0.03 57.9 36.1 5.7 0.3
Kalixäl en 133 1.54 0.05 51.1 43.6 5.3
Byskeäl en 84 1.63 0.08 52.4 32.1 15.5
Vindeläl en 48 1.52 0.09 54.2 39.6 6.2
Simojoki 57 1.33 0.07 70.2 26.3 3.5
All wild males 638 1.50 0.02 56.6 36.5 6.7 0.2
To nionjoki H 251 1.23 0.03 78.5 19.1 2.4
Iijoki 190 1.13 0.03 87.9 11.0 1.0
Oulujoki 175 1.28 0.04 74.9 22.2 2.9
Luleäl en 77 1.36 0.08 75.3 13.0 11.7
All ea ed males 693 1.32 0.02 79.8 17.0 3.2
All males 1331 1.36 0.02 68.7 26.3 4.9 0.1
Females 1930s
Kalixäl en 95 2.21 0.09 26.0 30.0 41.0 3.0
Luleäl en 107 2.50 0.07 6.0 41.0 48.0 5.0
Males 1930s
Kalixäl en 66 2.17 0.05 41.0 15.0 30.0 14
Luleäl en 82 2.46 0.12 23.0 27.0 30.0 20
All F 1930s 202 2.27 0.06 15.8 35.6 44.6 4.0
All M 1930s 148 2.33 0.09 31.1 21.6 30.4 16.9
Spawning Age Di e ences in A lan ic Salmon S ocks The Open Fish Science Jou nal, 2014, Volume 7 53
Table 5. Tes esul s o he di e ences in spawning-age dis ibu ions (

 es ) o he nine A lan ic salmon s ocks analyzed in his
s udy. See spawning age dis ibu ions and sample sizes in Table 4. Tes esul s o males a e shown in he uppe iangle
and o emales in he lowe iangle.
Wild s ocks Ha che y s ocks
Male
Female
To nionjoki W
Kalixäl en
Byskeäl en
Vindel äl en
Simojoki
To nionjoki H
Iijoki
Oulujoki
Luleäl en
To nionjoki W ns * ns ns *** *** *** ***
Kalixäl en ** * ns ns *** *** *** ***
Byskeäl en ns ns ns * *** *** *** **
Vindeläl en ** *** ** ns ** *** * **
Simojoki ns ** ns ns ns ** ns ns
To nionjoki H * *** ns ** ns * ns **
Iijoki *** *** ** *** ** ns ** ***
Oulujoki ns *** ns * ns ns * **
***P < 0.001, **P < 0.01, *P < 0.05.
Fig. (3). The p opo ion o olde spawne s in he six A lan ic salmon spawning s ocks o e he yea s 2000–2009 in he Bal ic Sea. The esul s
o he p opo ion o spawning mul i-sea-win e (MSW; 2–4 sea win e s) males (a; model 1) and old emales (3–4 sea win e s) (b, model 2)
a e acco ding o GENMOD models wi h he s ock and yea as p edic o s.
p opo ions o olde emales in wild s ocks did no always
su pass hose in he ha che y s ocks. The Kalixäl en males
we e he oldes (49% MSW; Tables 4 and 6), bu emales o
he Kalixäl en s ock we e qui e young, and clea ly younge
han he emales o he ea ed Oulujoki salmon and he Si-
mojoki salmon (OR < 1).
The his o ical spawning-age dis ibu ions o Kalixäl en
and Luleäl en salmon s ocks epo ed by Alm [40] clea ly
di e ed om he p esen da a (2000–2009) o bo h sexes
( es : P < 0.001) (Fig. 2; Table 4). Cu en ly, spawne s a e
younge .
The mean spawning age in he his o ical Luleäl en wild
s ock was 2.5 sea-yea s o bo h emales and males, and i is
cu en ly 2.03 sea-yea s o emales and 1.36 sea-yea s o
males in he sea- anched Luleäl en s ock (Table 4). In he
wild Kalixäl en s ock, he spawning age has also dec eased
since he 1930s, al hough he s ock is s ill wild, so no
changes could ha e esul ed om ha che y ea ing in his
case. In he his o ical sample, he spawning age o bo h sexes
was o e wo yea s, wi h he emale spawning age being
2.21 sea-yea s and ha o males 2.17 sea-yea s. In he con-
empo a y da a, he mean o emales was 2.08 and o males
1.54 sea-yea s (Table 4). The spawning age o emales had
hus clea ly dec eased less han ha o he males.
In he 1930s, nea ly hal (44%) o Kalixäl en male
spawne s we e olde , 3 SW o 4 SW old, bu in he p esen
da a only 5% we e 3 SW old male spawne s, as hyphena ion
has no been used elsewhe e. Fo emales, he 3 SW spawn-
e s p e iously o med he la ges g oup, in bo h his o ical
Kalixäl en (41%) and in he Luleäl en (48%) s ocks, bu
a p esen hei p opo ion is only 6.8% in Kalixäl en
and 16.9% in Luleäl en. These di e ences be ween
54 The Open Fish Science Jou nal, 2014, Volume 7 Kallio-Nybe g e al.
Table 6. Odds a ios (OR) (95% CL in pa en heses) o an olde spawning age in di e en A lan ic salmon s ock pai s. In all com-
pa ed s ocks, he male spawne s o he i s s ocks we e olde han hose o he second s ock o he pai , and usually also in
emales bu in wo cases he o de o he age dis ibu ions o he s ocks we e in emales he opposi e (º) (OR < 1). The al-
ues a e based on models 1 and 2 in Fig. (3).
S ock pai s Male, OR(CL) Female, OR (CL)
To nio W & To nio H 2.9 (1.9-4.2)*** ns
To nio W & Ii 5.4 (3.3-8.8)*** 3.7 (1.3-10.6)*
To nio W & Oulu 2.4 (1.5-3.6)*** ns
To nio W & Kalix ns 2.0 (1.1-3.6)*
To nio H & Ii 1.9 (1.1-3.2)* ns
To nio H & Kalix 3.8 (2.4-6.0)*** ns
Simo & Ii 3.1 (1.5-6.3)** 5.5 (1.6-19.1)**
Kalix & Simoº 2.3 (1.2-4.4)* 0.33 (0.14-0.81)*
Oulu & Ii 2.3 (1.3-3.9)** 4.0 (1.3-12.3)*
Kalix & Ii 7.0 (4.1-12.2)*** ns
Kalix & Ouluº 3.1 (1.9-5.1)*** 0.46 (0.22 – 0.97)*
***P < 0.001, **P < 0.01, *P < 0.05, ns = nonsigni ican .
his o ical and con empo a y spawning age dis ibu ions in
Kalixäl en and Luleäl en s ocks we e highly signi ican o
bo h males (Kalix:  es , = 49.9, d = 3: P < 0.001; Lule:
 = 47.7, d = 3: P < 0.001) and emales (Kalix:  = 111.8,
d = 3: P < 0.0015; Lule:  = 23.0, d = 3: P < 0.001).
Fo bo h sexes, he change owa ds younge spawne s
was la ge in he sea- anched Luleäl en s ock han in he
wild Kalixäl en s ock in he compa ison wi h he his o ical
da a. In he 1930s, he mean male spawning age o he wild
Kalixäl en (mean age 2.17) and Luleäl en (2.46) salmon did
no di e (K uskall-Wallis es :  = 2.7, d = 1: P = ns), bu
males o he Luleäl en ha che y s ock a e now younge
(1.36) han Kalixäl en wild males (1.54) (K-W:  = 7.6, d
= 1: P < 0.01) (Fig. 2; Table 4). In he 1930s, wild Luleäl en
emales we e olde (mean 2.50) han wild Kalixäl en e-
males (2.21) (K-W: P < 0.05 and dis ibu ion:  =15.1, d =
3: P < 0.01), bu he mean spawning age is now app oxi-
ma ely he same in bo h s ocks (Luleäl en 2.03; Kalixäl en
2.08) (K-W: P = ns) and he dis ibu ions di e ( = 22.0, d
= 3; P <0.001). Ha che y ea ing has educed he spawning
age o bo h sexes in he Luleäl en s ock (K-W: P < 0.001).
The di e ence in spawning age be ween sexes also in-
c eased om he 1930s o he 2000s. In 1930s, he spawning
age o emales (mean: 2.21) and males (2.17) in he wild
Kalixäl en s ock did no di e (K uskall-Wallis es : P = ns),
bu in he 2000s, males we e younge (1.54) han emales
(2.08) (K-W: P < 0.001). Simila ly, in he 1930s, he spawn-
ing age o emales (mean: 2.50) and males (2.46) in he
Luleäl en s ock was simila (K uskall-Wallis es : P = ns),
bu in he 2000s, spawning males we e younge (1.36) han
emales (2.03) (K-W: P < 0.001). In he 1930s, old males
and emales we e equally common (app oxima ely hal o
males 3–4 SW), bu old emales (8–17% 3–4 SW) a e cu -
en ly mo e common han old males (5–12% 3–4 SW) in
hese s ocks (1930s Kalixäl en, male & emale,  es :  =
12.9, d = 3: P < 0.01; p esen Kalixäl en, male & emale: 
= 111.1, d = 3: P < 0.001).
The sex a io (males/ emales) o he wild Kalixäl en
salmon spawne s in he 2000s and 1930s was he same (0.41;
= 0.0, d = 1: P = ns), bu o he Luleäl en salmon s ock
he sex a io has changed om emale dominance o a sligh
male dominance, when changing om wild o ha che y p o-
duc ion, as he p opo ion o males has inc eased om 0.43
o 0.54 o e ime ( = 3.8, d = 1: P = 0.051) (Fig. 4a).
The sex a ios o salmon s ocks a ied ma kedly om
0.41 ( emale dominance) in he wild Kalixäl en s ock o
0.69 (male dominance) in he Iijoki ha che y s ock (Fig. 4a).
The mean sex a io o he i e wild s ocks was 0.46, and o
he ou ea ed s ocks as high as 0.61 (Table 3). The male
spawning age was also lowes in hose popula ions ha had a
male-biased sex a io (male spawning age = 2.20-
1.54*p opo ion o males, F = 106.9(1,7), P < 0.001; yea s
2000–2009) (Fig. 4a). Thus, i males we e abundan , hey
we e also young. The male and emale spawning ages o he
same s ocks also usually co ela ed (male sea-age = 1.02-
0.74* emale sea-age, F = 6.5(1,7), P < 0.05) (Fig. 4b).
DISCUSSION
The numbe o gene ically di e en ia ed salmon s ocks
has changed d ama ically in he Bal ic Sea [12, 15, 61] since
he 1930s. Besides he loss o s ocks, ascending salmon a e
now younge , he e is less a ia ion in he spawning age, and
he ha che y- ea ed spawning s ocks ha e become male-
domina ed when compa ed o his o ical na i e s ocks o he
same i e . An ongoing sligh dec ease in he male spawning
age was e en obse ed a e 2000. The spawning age s uc-
u e o wild and sea- anched s ocks as g oups di e ed and
also he ha che y and wild componen s o he same i e