Effects of temperature on egg and larval survival of
cod (Gadus morhua) and sprat (Sprattus sprattus) in the
Baltic Sea – implications for stock
development
A.
Nissling-2004
Hydrobiologia,
514 (1-3): 115-123
Abstract:
Stock
development of cod and sprat, two major fish species in the Baltic Sea, is
linked by trophic interactions. Depending on recruitment success the Baltic
may be pushed towards either a cod- or a clupeid dominated system. Both cod
and sprat spawn in the Baltic deep basins at strongly varying hydrographical
conditions with survival during the egg and early larval stages regarded as
a major bottleneck. Due to differences in egg specific gravity, cod and
sprat eggs occur at different depths and are thus subject to different
hydrographical conditions. For sprat, weak year-classes have been associated
with low water temperatures during peak spawning. For cod the shift in peak
spawning from spring to summer during the 1990s has been discussed as a
reason for the poor recruitment at present as delayed spawning may involve
egg development at too high temperatures. In the present study cod and sprat
eggs and yolk sac larvae were incubated at different temperatures, 1–11
°C for cod and 1–13
°C for sprat. No difference in viable hatch occurred in the range 3–9
°C for cod and in the range 5–13
°C for sprat. Larval viability decreased at 11
°C for cod and at le5 °C
for sprat. Comparing the results with vertical egg distribution and
temperature profiles from field studies suggested no major influence of
temperature on cod reproduction, but a considerable effect on sprat. The
results imply that different environmental conditions; frequency of major
saline water inflows into the Baltic Sea for cod, and water temperature in
the upper layers, e.g. following severe/mild winters, for sprat, involve
different opportunities for egg and larval survival and may thus cause a
displacement in the balance between cod and sprat.
(Ar
Research Station, Gotland University College, SE-62035 Fårösund,
Sweden, E-mail: anders.nissling@hgo.se)