sprat be fo re ic e c o ve r during ic e c o ve r a fte r
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Surfacing behavior and gas release of the physostome sprat
(Sprattus sprattus) in ice-free and ice-covered waters Ingrid Solberg1 and Stein Kaartvedt1,2 (2014)
1Red Sea Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia.
2Department of Biosciences, University of Oslo, PO Box 1066, Blindern 0316 Oslo, Norway
Most physostome fishes (including sprat) are without gas secretion
organs and likely refill their swimbladder by “gulping”
atmospheric air at the surface. Gas is released through their anal
duct. However, little is known about the frequency and diel time
scale for such events. The potential effect of ice cover is also
unknown.
Assess the surfacing and gas release behavior of sprat
throughout an entire winter by the use of stationary upward-
facing echosounders
Reveal how the physostome sprat respond to ice covering
Study site: Norwegian fjord (150 m) that became ice-covered in
mid-winter
Three echosounders were deployed from Nov 09 - Apr 10
200 kHz floating at 30 m (enhanced resolution in surface waters
enabled studies of individual behavior), 120 kHz (80 m) and 38
kHz (150 m)
Field campaigns supplemented the acoustic studies
Acoustic post-processing was performed using Sonar_5 Pro
(Balk & Lindem 2005) and LSSS (Korneliussen et al. 2006)
Manual target tracking (TT) was used to record surfacing fish
and to assess vertical swimming speed during surfacing events
Gas release events were manually registered
Abundance of sprat was determined by echo integration in
order to calculate frequency of surfacing- and gas release per
fish per day
Floating upward-facing echosounder-rig, cabled to shore. No
limitation of power or storage capacity provided long-term acoustic
measurements at a temporal resolution of seconds
The rate of surfacing was particularly high in ice-covered waters,
while the rate of gas release was very low
Estimated surfacing rate in
ice-free waters:
~ 3.5 times per fish day-1
Estimated surfacing rate in
ice-covered waters:
12.5 times per fish day-1
The vertical swimming speeds during surfacing were considerably
higher in ice-free conditions
Discussion / Conclusions
The correlation between surfacing and gas release in ice-free waters suggests
that the sprat gulped atmospheric air during excursions to the surface. The
frequent surfacing behavior indicates that gulping of atmospheric air is an
important element in the life of sprat. Hampered access to the surface by ice
cover affected both surfacing frequency and swimming behavior, and ice
covering may constrain physostome fish in yet unknown ways.
The sprat released gas
many times per day
( >35) during ice-free
conditions
Gas release was strongly
reduced during ice cover
The swimming speeds were significantly lower in ice covered waters
(two-way ANOVA, p < 0.0000)
The average downward swimming speed after surfacing in ice-free
waters was particularly high (~ 28 cm s-1)
Results
Sprat surfaced frequently at night during ice-free conditions,
- and released gas in the following hours during nighttime
In ice-covered waters, the sprat displayed a different behavior by
repeatedly ascending towards the ice
Acknowledgments
Anders Røstad and Thor A. Klevjer were instrumental in conducting the acoustic studies. We thank the crew of
RV Trygve Braarud for support during cruises and Rita Amundsen for technical assistance.
References Balk H, Lindem T (2005). Sonar4 and Sonar5-Pro post processing systems (operational manual). University of Oslo, Oslo.
Korneliussen RJ, et al. (2006). The Large Scale Survey System: LSSS. Proceedings of the 29th Scandinavian Symposium on
Physical Acoustics, Ustaoset.
De
pth
(m
)
18:05 18:07
0
3
6
20:45:30 20:49:00
Time (h) UTC
Sv (dB)
-74
-68
-62
-56
-50
-80
0
5
10
Searching for the
surface?
Rate
of gas r
ele
ase p
er
fish p
er
day
0
20
40
60
80
before ice cover during ice cover after ice cover
72
2
35
Rate
of surf
acin
g p
er
fish p
er
day
0
4
8
12
16
during ice coverbefore ice cover
3.8
12.5
2.6
after ice cover
Introduction
Objectives
Materials and methods
0
10
20
30
21:35 21:40 21:45D
ep
th (
m)
Time (h) UTC
Sprat
Surfacing sprat
0
10
20
05:55 06:00
De
pth
(m
)
Time (h) UTC
Sprat releasing air
Gas bubbles
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