Download Curonian Lagoon

Temporal development of the coastal fish community in the Curonian
Lagoon (Lithuania)
Authors: Justas Dainys and Linas Ložys
Key Message
Overall, in the fish community in the Curonian Lagoon there has rather stable between 1994-2011.
The fish community has rather been exhibiting annual fluctuations with respect to the majority of
the indicators assessed. The years of 1996, 1998 and 1999 do, however, to some extent differ
from the other years in the time-series. During these three years the abundance of perch and
piscivores was relatively high, as were the diversity, trophic level and proportion of piscivores.
Background and oceanographic information
Monitoring in the Curonian Lagoon is performed once a year in July at two sites (Atmata and
Dreverna). Average depth at Atmata is 4.5 m and about 2 m at the Dreverna site. The Atmata site
is characterized by silty bottoms and is located in the area of direct influence of the Nemunas
river; as a result the water is always fresh. The Dreverna site is characterized by sandy bottoms
and the water is fresh. The area is, however, occasionally affected by brackish water inflows from
the Baltic Sea. As a result the salinity in the area can temporarilly increase. Both areas are
affetcedby commercial and to some extent recreational fishing, as well as by predation from
cormorants.
Local pressure
Commercial fisheries exhibits one of the main pressures on Curonian Lagoon fish communityies.
The commercial fishery have got compensations to leave the sector, and the fishing efforts have
been reduced by more than a third (Figure 1). The landings are, however, still rather high
suggesting increased efficiency of the fishermen remaining in the sector. It is also known that
cormorants consume large numbers of fish (on average 653,3±59,4 tonnes during 2005-2010) in
12
2010
2008
10
2006
2004
2002
1996
1994
0,4
2000
Secchi depth
Temperature summer
Tot-P (mg/L)
0,05
Tot-N
Tot-P
1994
0,5
0,1
0
2010
14
2008
0,6
0,15
2006
16
2004
0,7
2002
18
0,2
2000
0,8
0,25
1998
20
2
1,8
1,6
1,4
1,2
1
0,8
0,6
0,4
0,2
0
1996
0,9
Tot-N (mg/L)
22
Temperature summer (°C)
1
1998
Secchi depth (m)
the Curonian Lagoon (Pūtys 2012a). About 6000 breading birds is found on the Curonian spit in
Juodkrante (in about 7 km from Dreverna monitoring site). First cormorants started breading at
the colony in 1989 and fast growth of the colony continued until 2003; after number of breading
birds fluctuated about 3000 pairs (Pūtys 2012b). Nutrient runoff (total phosphorous) to the
Curonian Lagoon from land, as a potiential pressure, has a tendency to decrease over the
assesement period 1994-2011, and the secchi depth increased during these years (Figure 1; data
provided by the Marine Research Department). Surface water temperature in the Curonian Lagoon
have increased by 0.6 °C during the period 1961–2005, however, no trend has been observed
during the assesment period (1994-2011; Figure 1). Water temperature appears to be the key
factor determining the seasonal and long-term variability of primary production and the abundance
of phytoplankton, and therefore also the level of biological production and trophic status in the
area. The rise in temperatures has also fostered the ongoing eutrophication and ‘hyperblooms’ of
cyanobacteria in the Curonian Lagoon, despite the reduction in external nutrient loading from land
in the form of fertilisers and industrial products. Increased incidence of more westerly winds in
combination with sea level rise and reduced river discharge has also resulted in a long-term
increase in annual mean salinity in the area (Dailidienė et al. 2012).
1600
Landings (tonnes)
1400
1200
1000
800
600
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
400
Figure 1. Temporal development in variables potentially affecting the state of fish communities in the Curonian lagoon.
A decreasing trend was seen in commercial landings of fish (R2 = 0.1, p < 0.05) and total phosphorous (R2 = 0.45, p <
0.05). Increasing trend was seen in Secchi depth (R2 = 0.34, p < 0.05). No trend was seen in the variables of total
nitrogen and summer temperature (p > 0.05).
Results and assessment
The indicators used below and their relevance for conveying developments in the environment are
derived from HELCOM (2012), and described in the main indicator fact sheet on Temporal
development of Baltic coastal fish communities and key species.
Overall state
Monitoring data cover the period 1994-2012. There is no overall temporal trend for the calculated
indicators (Figure 3-13). Total Abundance is correlated with Cyprinids as a result of that the fish
community in the area is dominated by freshwater species from the carp family. Total Abundance,
is also correlated to Piscivore Abundance and Abundance of Perch, mainly reflecting a dominance
of perch in all years of monitoring (Figure 2). Mean length perch and Mean Maximum Length
correlates negatively to Diversity Index and Abundance of Perch. Mean Trophic Level corelates to
Diversity Index and Abundance of Perch, and correlates negatively to Mean Length Perch. Some of
the indicators e.g. Mean Trophic Level and Piscivore Proportion are negatively correlated to Mean
Length Perch. Overall, the fish community in the Curonian Lagoon has not gone through any
significant change in its structure since the monitoring program started in 1994 (Figure 2).
Figure 2. Result of an analysis of all indicators together for the Curonian Lagoon area (PCA, years 1994-2011). In the
left hand plot, years located close to each other have similar values for the studied indicators. The black line connects
the years in a chronological order. The right hand plot shows the indicators mainly characterizing the different years, by
pointing in the direction of that year. Long vectors indicate a strong relationship between the indicator and the years
studied. Only the first two ordination axes of the PCA is presented, the first axis (PC-1) explained 46.6% of the total
variation observed in the data set, and the second axis (PC-2) explained 21.2%.
Species composition
Total Abundance
700
600
500
CPUE
400
300
200
100
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
0
Figure 3. Temporal development of the Total Abundance (CPUE, Catch Per Unit Effort) in the Curonian Lagoon. There is
no overall temporal trend for the indicator. Total Abundance is used as an index of the relative size and productivity of
the fish community. Increased abundance indicates increased nutritional conditions and production potential, whereas
decreased abundance indicates the opposite.
Perch Abundance
180
160
140
CPUE
120
100
80
60
40
20
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
0
Figure 4. Temporal development of the Perch Abundance (CPUE) in the Curonian Lagoon area. There is no overall
temporal trend for the indicator. Increased abundance indicates increased nutritional conditions and production
potential, whereas decreased abundance indicates the opposite.
Cyprinids
400
350
300
CPUE
250
200
150
100
50
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
0
Figure 5. Temporal development of Cyprinids (CPUE) in the Curonian Lagoon. There is no overall temporal trend for the
indicator. Cyprinids is an indicator of the abundance of species from the carp family, and is influenced by prevailing
nutrient and temperature conditions. Increased cyprinid abundance indicates increased nutritional conditions and
production potential, but also increased water temperatures.
Marine Species
1,4
1,2
1,0
CPUE
0,8
0,6
0,4
0,2
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
0,0
Figure 7. Temporal development of Marine Species (CPUE) in the Curonian Lagoon. There is high interannual variation
of this indicator over time. There is no overall temporal trend for the indicator. The indicator is sensitive to cold and
brackish water inflow into lagoon from Baltic sea. Increased abundance of marine species generally indicates increased
salinity and lower temperature.
Size structure
Large Individuals
7
6
5
CPUE
4
3
2
1
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
0
Figure 8. Temporal development of Large Individuals (CPUE) in the Curonian Lagoon. There is no overall temporal
trend for the indicator. Large Individuals is an indicator of the abundance of individuals in the fish community over 30
cm total length. As such it generally reflects the abundance of mainly large Roach and Pikeperch. The indicator is
dependent on the temperature conditions and fishing pressure, but to a lesser extent also by the nutrient status.
Generally, increased values of this indicator are associated with increased water temperature, lower fishing pressure and
increased nutrient conditions.
Mean Maximum Length
39
37
35
Cm
33
31
29
27
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
25
Figure 9. Temporal development of Mean Maximum Length (cm) in the Curonian Lagoon. There is no overall temporal
trend for the indicator. Mean Maximum Length is an indicator of the size structure in the fish community, and is a
measure of the relative abundances of large and small species in the community. As such it also to some extent
considers recruitment of different species. The indicator is dependent on the temperature conditions and fishing
pressure, but to a lesser extent also by the nutrient status. Generally, increased values of this indicator are associated
with increased water temperature, lower fishing pressure and increased nutrient conditions.
Mean Length Perch
22
21
20
Cm
19
18
17
16
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
15
Figure 10. Temporal development of Mean Length Perch (cm) in the Curonian Lagoon. There is no overall temporal
trend for the indicator. Mean Length Perch is an indicator of the demographic characters and size structure in the key
species Perch. The indicator is affected by variation in recruitment, extensive size selective fishing and changed
individual growth rate. As such it is dependent on the temperature conditions and fishing pressure. Generally, increased
values of this indicator are associated with increased water temperature and lower fishing pressure.
Trophic structure
Mean Trophic Level
3,6
3,5
3,4
3,3
INDEX
3,2
3,1
3
2,9
2,8
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
2,7
Figure 11. Temporal development of Mean Trophic Level in the Curonian Lagoon. There is no overall temporal trend for
the indicator. Mean Trophic Level reflect the trophic status of the fish community, where increasing values indicate that
a higher proportion of species at higher trophic levels, e.g., piscivorous fish and/or lower levels of the plankton- and
benthos-feeding species. Generally, the indicator is influenced by fishing pressure and nutrient levels. Since the indicator
is based on proportions of different species, it should preferably be interpreted in association with other indicators such
as Cyprinids and Piscivore Abundance.
Piscivore Abundance
180
160
140
120
CPUE
100
80
60
40
20
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
0
Figure 12. Temporal development of Piscivore abundance (CPUE) in the Curonian Lagoon. There is no overall temporal
trend for the indicator. High indicator values in 1999 is related with Piscivore abundance reflect the abundance of
piscivorous fish in the community but to some extent also the trophic status. Generally, the indicator has a positive
response to decreased fishing pressure.
Species diversity
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1,8
1,7
1,6
1,5
1,4
1,3
1,2
1,1
1
0,9
0,8
1994
Index
Diversity Index
Figure 13. Temporal development of Diversity Index (Shannon-Wiener Diversity Index) in the Curonian Lagoon. There
is no overall temporal trend for the indicator, but pronounced interannual variation is seen. The Shannon-Wiener index
reflects the species richness and equitability of the community. Increasing values indicate increasing numbers of species
with even proportion in the catch. Decreasing values indicate few dominating species and a community with a small
number of species. Calculations are based on the proportion of each species.
Methods used
Fishing with coastal survey nets (mesh sizes 17, 22, 25, 30 mm from knot to knot) was performed
annually from 1994 at two stations. The stations were repeatedly fished for three nights in the
middle July.
References
Dailidienė I., Davulienė L., Kelpšaitė L. and Razinkovas A. 2012. Analysis of the Climate Change in
Lithuanian Coastal Areas of the Baltic Sea. Journal of Coastal Research 28 (3): 557 – 569.
HELCOM. 2012. Indicator based assessment of coastal fish community status in the Baltic Sea
2005-2009. Balt. Sea Environ. Proc. No. 131B.
Pūtys Ž. 2012a. Great cormorant Phalacrocorax carbo sinensis diet and its effect on fish
populations and their community in the eutrophic Curonian Lagoon ecosystem. Summary of
doctoral dissertation, Vilnius, 48 pp.
Pūtys Ž. 2012b. Great cormorant Phalacrocorax carbo sinensis diet and its effect on fish
populations and their community in the eutrophic Curonian Lagoon ecosystem. Doctoral
dissertation, Vilnius, 151 pp. (In Lithuanian)
For reference purposes, please cite this Baltic Sea environment fact sheet as
follows:
[Author's name(s)], [Year]. [Baltic Sea environment fact sheet title]. HELCOM Baltic Sea
Environment
Fact
Sheets.
Online.
[Date
Viewed],
http://www.helcom.fi/baltic-seatrends/environment-fact-sheets/.
Last updated: 26 September 2013