Bulletin of the Sea Fisheries Institute 1 (155) 2002 - CEEMaR

20
NATALIA KRASOVSKAJA
Table 6. Some characteristics of the herring spawning in the Vistula Lagoon in 1951-2000 by periods
Period
Mean water
temperature during
mass spawning [ o C]
Interval between the
first entrance and
onset of mass
spawning [days]
Duration of
herring presence
in the lagoon
[days]
Share of mass
spawning in
total presence
period [%]
Share of herring
in pre-spawning
stages [%]
1951-1954 12.4 20 81 32.3 51.9
1955-1959 12.2 19 65 43.8 41.5
1960-1969 12.1 14 64 48.3 30.6
1970-1979 8.4 11 69 55.8 19.0
1980-1989 7.8 8 67 49.2 21.7
1990-2000 6.6 9 75 59.1 15.7
ing “wave” and the onset of mass spawning was a maximum one. The share of herring in prespawning
stages of maturity in the total catches reached more than 50%, on average, i.e. it was
maximum as compared to other periods (Table 6), as if the large schools migrated into the
lagoon and stayed there in pre-spawning condition for more than 30 days at water temperature
corresponding to mass spawning during subsequent years. The mass spawning period constituted
only 32.3% of the entire period that herring were in the lagoon, while in other periods
under consideration it exceeded 44%. This scenario hardly seems probable, and it is very likely
that much of the fish were subjected to heavy exploitation in the Russian part of the lagoon
immediately after their arrival and prior to breeding. These speculations are supported by the
previously cited differences between catch dynamics in the Russian and Polish parts of the
Vistula Lagoon.
DISCUSSION
The presence of Baltic herring in the Vistula Lagoon has been documented since the earliest
times (Filuk 1968), but according to Seletskaya (1956), catches of it were either insignificant
or, in some cases, not recorded at all in the total catches. Only since the end of the 1920s has the
mass influx of herring occurred. Evidently, the increase in water salinity from the 1920s, which
occurred after a drain from one of the branches of the Vistula from the lagoon into the Gulf of
Gdañsk was removed and the Baltiysk Strait was artificially deepened, created new ecological
conditions which enhanced the intensity of the herring spawning migration into the lagoon.
Thus, shallow water, rapid warming in spring, good aeration, high production and an acceptable
salinity level became favorable to herring reproduction.
The present review indicates that there is high amplitude in the inter-annual variability of
spawning timing of Baltic herring in the Vistula Lagoon within a wide range of environmental
conditions and stock characteristics.
Berenbeim and Shapiro (1977) investigated the influence of environmental conditions on
herring catches in the Vistula Lagoon during the 1950s and 1960s. They reported a positive
correlation between the timing and duration of spawning and catch per pound net values. If the
period until 2000 is considered, the results are different with regard to the influence of spawning
stock levels. Environmental factors appear to have a prevalent effect on spawning timing.