EFFECTS OF FISH SIZE ON POST

Acta Sci. Pol., Piscaria 5(1) 2006, 17–28
EFFECTS OF FISH SIZE ON POST-STOCKING
MORTALITY AND GROWTH RATE OF BROWN
TROUT (Salmo trutta trutta m. fario L.) FRY
Leszek Augustyn1, Ryszard Bartel2, Piotr Epler3
1
Profesional and Vocational College, Nowy Sącz, Poland
Inland Fisheries Institute, GdaĔsk, Poland
3
Agricultural University, Kraków, Poland
2
Abstract. The study was aimed at comparing mortality and growth rate of the brown trout fry
released, in autumn 2001 and spring 2002, to three tributaries of River Kamienica
Nawojowska (the River Dunajec system in southern Poland). The released fish were tagged
by adipose fin clipping and Alcian Blue injection. The recapture operations were conducted
on 1 March and 2 September 2002. The fry released in autumn showed a higher daily
instantaneous mortality rate than that found in the brown trout released in spring. The daily
instantaneous growth rate was distinctly lower in the fish released in autumn than in those
stocked in spring. The daily instantaneous mortality and growth rates were significantly
dependent on the fry size.
Key words: brown trout, fry size, growth rate, mortality rate, stocking
INTRODUCTION
The brown trout is a species important for recreational fishery. The necessity of an
improved fishery-related management of rivers and brown trout is directly related to
problems of management efficiency [Augustyn 1999, 2004, Fisher and Burroughes 2003].
One of the major problems associated with stocking management is dramatic mortality of the
fish released to new habitats [Suboski and Templeton 1989, Berg and Jorgenson 1991,
Nåslund 1998, Brown and Laland 2001].
The study described in this paper was aimed at comparing mortality and growth
rates in brown trout fry of different size, released to mountain streams in autumn and
spring during their first winter and the second growth season.
Corresponding author – Adres do korespondencji: Dr Leszek Augustyn, OkrĊg PZW Nowy Sącz,
Inwalidów Wojennych 14, 33-300 Nowy Sącz, e-mail: [email protected]
L. Augustyn, R. Bartel, P. Epler
18
MATERIAL AND METHODS
The study involved the autumn (0+) and spring (1+) fry of the brown trout, grown out
from hatch to the stage of foraging larvae. The autumn fry were reared at the hatchery in
Nowy Sącz and released to each stream, at a density of 0.1 ind m-2, on 15 September,
15 October, and 15 November 2001. The fry were recaptured on 1 March 2002 (Table 1).
The spring fry were reared at the hatchery in àopuszna and released to each stream,
at a density of 0.1 ind m-2, on 15 March, 15 April, and 15 May 2002 to be recaptured on
2 October 2002. The fish were tagged by clipping their adipose fins and by injections of
Alcian Blue (65 mg·ml-1) applied to the skin at the base of the pectoral or ventral fins.
The recapture operations were carried out in two runs, using pulsating current (IUP 12).
The three streams stocked were tributaries of River Kamienica Nawojowska in the River
Dunajec system (southern Poland) (Fig. 1; Table 2):
–
–
–
àosiĔski Stream, 6.8 km long; 63.9 m·km-1 grade; the section to be stocked
began 5.1 km away from the sources and ended 0.7 km upstream of
the confluence with the Kamienica Nawojowska, at altitudes of 580–535 m
above sea level (asl).
Krysciów Stream, 7.3 km long; 61.8 m·km-1 grade; the section to be stocked
was situated at the altitudes of 580–540 m asl; it began 5.4 km away from
the sources and ended 1.2 km upstream of the confluence with the Kamienica
Nawojowska.
UhryĔski Stream, 9.8 km long; 47.4 m·km-1 grade; the section to be stocked
was situated at the altitudes 580–565 m asl; it began 6.2 km away from the
sources and ended 2.6 km upstream of the confluence with the Kamienica
Nawojowska.
Table 1. Basic characteristics of the brown trout fry used in experiments
Tabela 1. Podstawowe parametry uĪytego do eksperymentów narybku pstrąga potokowego
Type of fry
Rodzaj narybku
Autumn fry
Narybek jesienny
Spring fry
Narybek wiosenny
Dates
Daty
15 September 2001
15 wrzeĞnia 2001
15 October 2001
15 paĨdziernika 2001
15 November 2001
15 listopada 2001
15 March 2002
15 marca 2002
15 April 2002
15 kwietnia 2002
15 May 2002
15 maja 2002
Length – DáugoĞü
Weight – Masa
mean
Ğrednia
range
zakres
mean
Ğrednia
range
zakres
cm
cm
g
g
7.36
5.2–8.8
3.77
1.2–6.0
8.74
7.2–10.4
6.36
3.1–11.2
9.61
7.9–11.6
9.03
4.9–13.3
6.75
3.2–8.5
2.86
0.3–6.3
7.53
5.6–9.4
4.57
1.7–8.8
8.48
5.4–11.3
7.32
1.6–15.9
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Effects of fish size on post-stocking mortality...
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Fig. 1. Location of the study sections in the three tributaries of River Kamienica Nawojowska
(Kamienica N.)
Rys. 1. Lokalizacja badanych stanowisk w 3 potokach w dorzeczu Kamienicy Nawojowskiej
The daily instantaneous mortality rate (Z) and the daily instantaneous growth rate
(SGR) were compared between the two batches of fry using the formulae:
Z = 100 (-1·dt-1) · (ln N2 – ln N1) and SGR = 100 (ln W1 – ln W2) · dt-1
where:
Z, mortality rate;
dt, time, days;
N1, number of individuals relased;
N2, number of individuals recaptured;
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SGR, growth rate;
dt, time, days;
W1, mean individual weight of fry released;
W2, mean individual weight of recaptured fry.
L. Augustyn, R. Bartel, P. Epler
20
Table 2. Characteristics of stocking sites in the streams
Tabela 2. Charakterystyka stanowisk w poszczególnych potokach
Stream name – Stream name
Parameter
Parametry
àosiĔski
KryĞciów
UhryĔski
km
5.1–6.1
5.4–6.4
6.2–7.2
m·km-1
45
40
15
m asl
580–533
580–540
580–565
mean – Ğrednia
m
0.97
1.09
1.31
range – zakres
m
0.74–1.11
0.83–1.31
1.02–1.54
mean – Ğrednia
cm
14.8
14.5
16.3
range – zakres
cm
9.5–24.4
6.1–22.8
10.6–27.2
Distance from sources
OdlegáoĞü od Ĩrodeá
Grade
Spadki
Altitude
PoáoĪenie n.p.m
Channel width – SzerokoĞü koryt
Water depth – GáĊbokoĞü wody
In the downstream reaches of the Kamienica Nawojowska in Nowy Sącz there is
a hatchery that collects water from a stream bank location at 325 m asl. The water
temperature is measured twice daily. Comparing the temperatures measured at different
times at the hatchery and those measured in the stocked sections of the àosiĔski, KryĞciów,
and UhryĔski streams made it possible to develop an algorithm with which to calculate daily
water temperatures in each stream. During winter (November 2001–February 2002), water
temperature was calculated with the equation:
Tw = -0.162 + 0.843 t
(r = 0.9892; p < 0.0001); where:
Tw, temperature of stream water in winter;
t, water temperature at the hatchery.
In summer (March–August 2002), the water temperature was calculated with the
equation:
Ts = -0.293+0.947 t
(r = 0.9360, p < 0.0001); where:
Ts, temperature of stream water in summer;
t, water temperature at the hatchery.
Changes in water temperature in the streams are shown in Fig. 2. Cumulative temperatures
(degree days, Dº) were calculated for individual periods of time.
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Effects of fish size on post-stocking mortality...
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Fig. 2. Daily water temperatures and cumulative temperatures for streams (Dº) and periods
of study
Rys. 2. Przebieg dziennych temperatur wody oraz temperatury skumulowane (Dº) w potokach
w okresie badaĔ
RESULTS
The daily instantaneous mortality rates (Z) of the brown trout released in autumn
(0+ group) were found to range from 0.4192 to 0.8535%·d-1; the rates were higher than
those found in the brown trout stocked in spring (1+), which ranged from 0.3583 to
0.6008%·d-1 (Table 3). The differences were statistically significant (ANOVA; F5; 12 = 1.737;
P = 0.201) (Fig. 3). The mortality rates of the young-of-the-year brown trout (0+)
stocked on various dates in autumn (15 September, 15 October, and 15 November) were
not significantly different (ANOVA; F2; 6 = 0.5974; P = 0.580). Similarly, there were no
significant differences (ANOVA; F2; 6 = 0.3803; P = 0.699) between mortality rates of
Piscaria 5(1) 2006
L. Augustyn, R. Bartel, P. Epler
22
the 1+ brown trout released on different dates in spring (15 March, 15 April and 15 May).
The mortality rates of the brown trout released both in autumn and spring were found
to be dependent on the individual weight of the fry released (Fig. 4).
Table 3. Daily instantaneous mortality (Z) and growth (SGR) rates of brown trout fry released
in different periods
Tabela 3. Tempo dziennej chwilowej ĞmiertelnoĞci (Z) i wzrostu (SGR) narybku pstrągów potokowych
z zarybieĔ w róĪnych okresach
Date
Data
àosiĔski Stream
Potok àosiĔski
KryĞciów Stream
Potok KryĞciów
UhryĔski Stream
Potok UhryĔski
Z
SGR
Z
SGR
Z
SGR
%·day-1
%·day-1
%·day-1
%·day-1
%·day-1
%·day-1
15 September – 15 wrzeĞnia
0.8535
0.3602
0.7666
0.1033
0.5352
0.2152
15 October – 15 paĨdziernika
0.7598
0.4119
0.6939
0.0861
0.4767
0.2278
15 November – 15 listopada
0.6974
0.5342
0.6385
0.3558
0.4192
0.3526
15 March – 15 marca
0.6008
1.4620
0.5323
1.5768
0.4584
1.8265
15 April – 15 kwietnia
0.5482
1.4426
0.5233
1.6209
0.3915
1.8584
15 May – 15 maja
0.5466
1.5347
0.5157
1.6303
0.3583
1.8380
Fig. 3. Daily instantaneous mortality rates of brown trout fry stocked in different periods (means
and 95% confidence intervals)
Rys. 3. Tempo dziennej chwilowej ĞmiertelnoĞci pstrągów z zarybieĔ w róĪnych okresach
(przedziaá ufnoĞci 95%)
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Effects of fish size on post-stocking mortality...
23
Fig. 4. Changes in daily instantaneous mortality rates of brown trout stocked in autumn and
spring as a function of initial individual weight of fry
Rys. 4. Zmiany dziennego chwilowego tempa ĞmiertelnoĞci pstrągów z zarybieĔ jesiennych
i wiosennych w zaleĪnoĞci od wagi jednostkowej wpuszczanego narybku
Fig. 5. Daily instantaneous growth rates of brown trout fry stocked in different periods (means
and 95% confidence intervals)
Rys. 5. Dzienne chwilowe tempo wzrostu pstrągów z zarybieĔ w róĪnych okresach (przedziaá
ufnoĞci 95%)
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L. Augustyn, R. Bartel, P. Epler
The daily instantaneous growth rates (SGR) of the brown trout stocked in autumn
(0+ group) were found to range from 0.2152 to 0.5342%·d-1, i.e., lower than those shown
by the brown trout released in spring (1+) (1.4620 – 1.8584%·d-1) (Table 3).
The differences were statistically significant (ANOVA; F5; 12 = 63.97; P = 0.0000) (Fig. 5).
The growth rates of the 0+ brown trout released in autumn showed no significant
differences (ANOVA; F2; 6 = 1.776; P = 0.249), as did the growth rates determined in
the brown trout released in spring (ANOVA; F2; 6 = 4.953; P = 0.952).
The growth rates of the brown trout released both in autumn and spring were significantly
(P<0.001) dependent on the cumulative daily temperature (SGR = 0.211+0.000847 Dº;
r = 0.9261) and on the individual weight of the fry released (Fig. 6).
Fig. 6. Changes of daily instantaneous growth rates of brown trout stocked in autumn and spring
as a function of initial individual weight of fry
Rys. 6. Zmiany dziennego chwilowego tempa wzrostu pstrągów z zarybieĔ jesiennych i wiosennych
w zaleĪnoĞci od wagi jednostkowej wpuszczanego narybku
DISCUSSION
Since the mid-1930s, the ecologists have been differentiating between densitydependent (biotic) and density–independent (abiotic) factors that control the abundance
of natural animal populations. Ricker [1954] was the first to apply this dichotomy to
fisheries. Each of the factors affecting mortality integrates a network of relationships via
feedbacks; some of those are positive (enhancing) and others negative (attenuating).
Biotic feedbacks act as controls, i.e., the post-stocking mortality increases with density,
while physical environmental factors function as constraints, i.e., they underlie fluctuations
in sustainable fish densities [Cresswell et al. 1984, Zalewski et al. 1985, Marshall and
Crowder 1995, Barnard 2002, Milner et al. 2003].
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Effects of fish size on post-stocking mortality...
25
Another group of factors affecting the post-stocking mortality of the released fish
comprises variables related to the fish biological value [Brown and Laland 2001] and
stocking technique [Brown and Day 2002]. Specifically, the size of the released fish
was found to be one of the factors decisive for survival [Bartel 1993, DĊbowski and
Bartel 1996]. As shown by experiments, the mortality rate was lower in the fish that were
initially larger, which means that the fish were capable of a faster and better adaptation to
the living and feeding conditions in a new habitat. Domagaáa and Bartel [1999] achieved
a doubled survival rate of the fry by releasing larger fish who had developed faster on
account of rearing them in heated water.
The water temperature regime that reflects physiological processes is well
represented by the sum of degree-days. Crisp and Howson [1982] demonstrated that
mean weekly water temperatures and brown trout growth rate could be accurately
predicted from air temperatures with a 5–7 days-long time lag. Air temperatures are
strongly correlated with altitude [Hess 1965]. It may be assumed that the method of
calculating mean water temperatures used in this study was reliable. A close correlation
between water temperature and fish growth, emphasised by, i.a., Edwards et al. [1979],
Jensen [1985], and Andersen et al. [1992], results in an indirect effect of the temperature
on fish survival [Egglishaw and Shackley 1985].
Fig. 7. Relationship between daily instantaneous mortality (Z) and growth (SGR) rates of brown
9trout fry
Rys. 7. Związek pomiĊdzy tempem dziennej chwilowej ĞmiertelnoĞci (Z) i dziennym (SGR)
chwilowym tempem wzrostu narybku pstrągów potokowych
Our study suggests that the effectiveness of stocking does not depend only on the
timing of the release (spring or early autumn). The post-stocking mortality is a net result
of abiotic and biotic effects, intra- and interspecific competition and predation being
particularly important. The effects may be weakened by physiological and behavioural
adaptations of various individuals. When released, numerous fishes do not feed for
26
L. Augustyn, R. Bartel, P. Epler
some days [Paszkowski and Olla 1985], weeks [Cresswell et al. 1984], and even months
[Sosiak et al. 1979]. Therefore, compared to the date of release, more important for the
survival is that the brown trout released have enough fat reserves to sustain them when
they proceed to group-learn how to find the natural food [Brown et al. 2003]. Those fish
in good condition stand a better chance of surviving the period of learning how to find
and get natural food on their own. Therefore, despite the intensifying pressure of abiotic
factors, the 9 g mean individual weight brown trout fry released in November was in a much
better position with respect to survival than the fry released in October at the mean
individual weight as low as about 4 g.
Owing to an identical mechanism, the growth rate is significantly dependent on the
initial size of the fish released to the natural environment. The two variables were found
to be fairly closely related (p<0.01; Fig. 7). As demonstrated by this study, the brown
trout mortality may be greatly reduced under natural conditions by releasing larger
individuals, which – in the fishery practice – means the pond-reared fry. However,
a large-scale application of such methods may lead to physical and genetic degradation
of wild brown trout stocks [Barnard 2002]. Therefore, such activities should be
restricted to the water areas destined for recreational fishery. The autochthonous brown
trout populations should be diligently supported and protected [Augustyn 2004].
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WPàYW WIELKOĝCI NARYBKU PSTRĄGA POTOKOWEGO
(Salmo trutta trutta m. fario L.) NA TEMPO POZARYBIENIOWEJ
ĝMIERTELNOĝCI I WZROSTU
Streszczenie. Celem badaĔ byáo porównanie ĞmiertelnoĞci i wzrostu narybku pstrągów
potokowych wypuszczonych jesienią 2001 r. i wiosną 2002 r. do 3 dopáywów Kamienicy Nawojowskiej (system Dunajca – Polska S). Wypuszczane ryby byáy znakowane przez obciĊcie
páetwy táuszczowej i wstrzykniĊcie báĊkitu alcjanowego. Poáowy kontrolne wykonano 1 marca
i 2 wrzeĞnia 2002 roku. Narybek pstrągów potokowych wypuszczony jesienią miaá wyĪsze tempo
dziennej chwilowej ĞmiertelnoĞci niĪ pstrągi wypuszczone wiosną. Dzienne chwilowe tempo
wzrostu byáo zdecydowanie niĪsze u ryb wypuszczonych jesienią niĪ wiosną. Dzienne chwilowe
tempo ĞmiertelnoĞci i wzrostu istotnie zaleĪaáo od jednostkowej masy wpuszczanego narybku.
Sáowa kluczowe: pstrąg potokowy, tempo ĞmiertelnoĞci, wielkoĞü narybku, zarybienie
Accepted for print – Zaakceptowano do druku: 13.03.2006
Piscaria 5(1) 2006