Alosa tanaica
Black Sea shad was the species most frequently caught during the monitoring
research surveys, its distribution covering all 10 perimeters of the site ROSCI
0066. The highest number of individuals was caught in the Zatoane and Sachalin
perimeters (almost 26% each), Sulina (around 18%), Sf. Gheorghe (around 16%)
and Perisor (around 8%).
Even though in small numbers, Pontic shad was also caught in the other
perimeters of the MPA, namely Periboina (around 1%), Chituc (around 1%),
Periteasca, Gura Portitei and Vadu (less than 1%) (Figs. 26.19 and 26.20).
According to Table 26.3 and after applying the methodology for reporting under
Article 17 of the Habitats Directive, it resulted that the overall conservation status
for the species A. tanaica (Black Sea shad) in the marine zone of the Danube Delta
(ROSCI 0066) is favourable (FV), status which applies for the entire Romanian
coastal area.
The conservation status for the other shad species reported in ROSCI 0066,
namely Azov shad (Alosa maeotica, Grimm, 1901) is unknown due to lack of data.
The species has not been reported in the lagoons and coastal lakes for about
50 years, its last record being in Lake Razelm in 1968. Under such circumstances,
records in Romanian fishery statistics for the past 5 years should be reconsidered
(Mihailescu 2015).
Moreover, during the Biogeographical Seminar for the Black Sea marine region
(Brindisi, Italy, 15–17 June 2010), it was proposed to remove this species from the
reference list, due to the following accounts: A. maeotica is a non-anadromous
species, rather stenohalyne, living in the brackish Black Sea coastal waters. It does
not enter the Danube or the Delta like the other shad species, but it remains in the
estuarine waters off the Danube mouths and rarely penetrates the Razelm-Sinoie
Lagoon System.
The morphological differentiation from A. immaculata is made by the number of
gill spines, the scales of the ventral area (quite larger and sharper in A. maeotica)
and the eyes (larger) (Banarascu 1964). These criteria are very week, mainly for
species with high morphological variability. In addition, a recent study
(Mezhzherin et al. 2009) on the allozyme variability in A. immaculata,
A. maeotica and A. caspia, based on the analysis of 19 enzyme loci and a series
of loci coding structural proteins in the muscle, showed a high degree of monomorphism and the absence of any differentiation between the alleles of the three
taxa, thus confirming that they belong to the same species. Thus, the three forms are
just eco-phenotypes of the same species (A. immaculata), phenomenon which often
occurs in anadromous fish, and must not be considered different species
(Mezhzherin et al. 2009).
Huso huso
During the monitoring period of marine fish species, the occurrence in catches of
the beluga was very scarce throughout 1 year (in 2012 only 5 individuals were
caught by scientific fishing, of which 4 were tagged and released into the sea).
26 Conservation Status of the Fish Fauna in the Danube Delta Marine Zone
459
Black Sea shad was the species most frequently caught during the monitoring
research surveys, its distribution covering all 10 perimeters of the site ROSCI
0066. The highest number of individuals was caught in the Zatoane and Sachalin
perimeters (almost 26% each), Sulina (around 18%), Sf. Gheorghe (around 16%)
and Perisor (around 8%).
Even though in small numbers, Pontic shad was also caught in the other
perimeters of the MPA, namely Periboina (around 1%), Chituc (around 1%),
Periteasca, Gura Portitei and Vadu (less than 1%) (Figs. 26.19 and 26.20).
According to Table 26.3 and after applying the methodology for reporting under
Article 17 of the Habitats Directive, it resulted that the overall conservation status
for the species A. tanaica (Black Sea shad) in the marine zone of the Danube Delta
(ROSCI 0066) is favourable (FV), status which applies for the entire Romanian
coastal area.
The conservation status for the other shad species reported in ROSCI 0066,
namely Azov shad (Alosa maeotica, Grimm, 1901) is unknown due to lack of data.
The species has not been reported in the lagoons and coastal lakes for about
50 years, its last record being in Lake Razelm in 1968. Under such circumstances,
records in Romanian fishery statistics for the past 5 years should be reconsidered
(Mihailescu 2015).
Moreover, during the Biogeographical Seminar for the Black Sea marine region
(Brindisi, Italy, 15–17 June 2010), it was proposed to remove this species from the
reference list, due to the following accounts: A. maeotica is a non-anadromous
species, rather stenohalyne, living in the brackish Black Sea coastal waters. It does
not enter the Danube or the Delta like the other shad species, but it remains in the
estuarine waters off the Danube mouths and rarely penetrates the Razelm-Sinoie
Lagoon System.
The morphological differentiation from A. immaculata is made by the number of
gill spines, the scales of the ventral area (quite larger and sharper in A. maeotica)
and the eyes (larger) (Banarascu 1964). These criteria are very week, mainly for
species with high morphological variability. In addition, a recent study
(Mezhzherin et al. 2009) on the allozyme variability in A. immaculata,
A. maeotica and A. caspia, based on the analysis of 19 enzyme loci and a series
of loci coding structural proteins in the muscle, showed a high degree of monomorphism and the absence of any differentiation between the alleles of the three
taxa, thus confirming that they belong to the same species. Thus, the three forms are
just eco-phenotypes of the same species (A. immaculata), phenomenon which often
occurs in anadromous fish, and must not be considered different species
(Mezhzherin et al. 2009).
Huso huso
During the monitoring period of marine fish species, the occurrence in catches of
the beluga was very scarce throughout 1 year (in 2012 only 5 individuals were
caught by scientific fishing, of which 4 were tagged and released into the sea).
26 Conservation Status of the Fish Fauna in the Danube Delta Marine Zone
459