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Environmental conditions, population density, and prey type influence the lipid reserves of Baltic herring in the northern Baltic Sea

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Change of climate is expected to influence the energy content of fish by affecting the environmental conditions where lipids are produced, transferred, accumulated and consumed. We examined the lipid content of the Baltic herring (Clupea harengus membras) spawning in the Archipelago Sea during a period of declining salinity, high variability in temperature, and increasing population size in the Bothnian Sea. Contemporary samplings of zooplankton in the feeding area (Mäkinen et al. 2017) enabled comparisons of fatty acid (FA) composition between herring and its prey Limnocalanus macrurus, which forms a major source of energy in the Bothnian Sea in May-June (Rajasilta et al. 2015).
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Rajasilta, M¹, Hänninen, J¹, Laaksonen, L², Laine, P¹, Suomela, JP ³, Vuorinen, I¹, Mäkinen, K¹
¹ Archipelago Research Institute, Biodiversity Unit, University of Turku
² Business, ICT and Chemical Engineering, Turku University of Applied Sciences
³ Food Chemistry and Food Development, Department of Biochemistry, University of Turku
The long-term study is part of Herring Project, conducted in the Archipelago Research Institute since 1984
LIMNOCALANUS - A MEDIATOR OF PUFA FROM
SPRING BLOOM TO HERRING?
POTENTIAL IMPLICATIONS TO HERRING STOCK AND FOOD
WEBS
Environmental conditions, population density, and prey type influence
the lipid reserves of Baltic herring in the northern Baltic Sea
References: Linko, R. R., Kaitaranta, J. K,. and Vuorela, R. 1985. Comparison of the fatty acids in Baltic herring and available plankton feed. Comp. Biochem. Physiol. 82B: 699705.; Mäkinen, K., Elfving, M., Hänninen, J., Laaksonen, L., Rajasilta, M., Vuorinen, I. and Suomela, J.-P. 2017. Fatty acid composition and lipid content in the copepod Limnocalanus macrurus during summer
in the southern Bothnian Sea. Helgol. Mar. Res. 71(11):1-12. doi: 10.1186/s10152-017-0491-1.; Rajasilta, M., Hänninen, J., and Vuorinen, I. 2015. Decreasing salinity improves the feeding conditions of the Baltic herring (Clupea harengus membras) during spring in the Bothnian Sea northern Baltic. ICES J. Mar. Sci. 71(5): 1148-1152. doi:10.1093/icesjms/fsu047.
Contact information: Katja Mäkinen, kamaki@utu.fi, Archipelago Research Institute, University of Turku
Fig. 1 A) Lipid content (% wt.w) of spawning female herring during 1987-2013 &
2013-2014 (black solid line) together with linear trend line (black arrow) and min
and max values (black dashed line). B) Lipid content and mesentric fat (% w.wt.)
of overwintering herring in outer archipelago in 1988 and 2017. ND= No Data.
Project website:
45% REDUCTION IN SPAWNING HERRING LIPID RESERVES
The average lipid content of spawning female decreased from 5-6 % (w.wt.) to
1.5 % (w.wt.) during 1987-2006, and remained also low in 2013-2014
High interannual variation, indicating an increasing trend in the variability of the
lipid content during 19872006
Explained by decreasing surface water salinity (20 m), increasing stock size
and decreasing Jan-Apr surface temperature (20 m)
Decrease also visible in lipid content and mesentric fat of herring overwintering
in the outer archipelago in 1988 vs. 2017
Methods: Lipid extraction with Soxhlet method, data analysed with Generalised
Linear Mixed models (Procedure Glimmix in SAS 9.3),Pearson product-moment
correlation and Student’s t-test
Change of climate is expected to influence the energy content of fish by affecting the environmental conditions
where lipids are produced, transferred, accumulated and consumed. We examined the lipid content of the Baltic
herring (Clupea harengus membras) spawning in the Archipelago Sea during a period of declining salinity, high
variability in temperature, and increasing population size in the Bothnian Sea. Contemporary samplings of
zooplankton in the feeding area (Mäkinen et al. 2017) enabled comparisons of fatty acid (FA) composition between
herring and its prey Limnocalanus macrurus, which forms a major source of energy in the Bothnian Sea in May-
June (Rajasilta et al. 2015).
Acknowledgements: salinity data from ICES Helcom dataset, herring population data from ICES stock assesment report (2015)
Herring contained a high proportion of polyunsaturated fatty
acids (PUFA), EPA and DHA. The proportion of these essential
FA (EFA) has increased since 1976 (Linko et al. 1976)
Lipids of herring contained 70% the same FA as those of
Limnocalanus, but their relative proportions were not equal
~30% dissimilarity between herring and Limnocalanus FA,
explained by the FA 16:0, "Others", 18:1(n-9), EPA, DHA,
16:1(n-7), 18:2(n-6) (in decreasing order of importance)
As an abundant and high-quality prey, Limnocalanus has most
likely improved the survival of adult herring, resulting in the
population growth
Methods: FA analysed with modified Folch method and Gas
chromatography with flame ionization detection (GC-FID), data
analysed with Pearson correlation, One-way analysis of
similarity (ANOSIM) and Similarity Percentage analysis
(SIMPER)
Results indicate to increased energy consumption and prolonged starvation
in the spawning population and possibly also in the population, overwintering
in the Archipelago Sea
Possible explanations are changes in osmoregulation, higher wintertime basic
metabolic needs, increased wintertime swimming activity, and increased
interspecific feeding competition.
The initial size of the lipid depositions is determined by the quantity and
quality of food in the feeding area, therefore, the increase of Limnocalanus is
likely to play an important role
Climate models predict a further decline of salinity and increase of
temperature Negative effects on lipid reserves likely to continue
Low lipid content of herring can reduce female offspring production, modify
migratory patterns, affect predator populations and reduce the concentration
of lipophilic toxic compounds in food webs
Increased abundance of high-quality prey may have caused also positive
effects for herring at the spawning time when the requirement of EFA is
particularly high in females

Supplementary resource (1)

Data
March 2018
Marjut Rajasilta · Jari Hänninen · Lea Laaksonen · Päivi Laine · Katja Mäkinen
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