SEAWARD DRIFT OF THE PONTIC SHAD LARVAE (ALOSA PONTICA) AND THE INFLUENCE OF DANUBE RIVER HYDROLOGY ON THEIR TRAVEL PATH THROUGH THE DANUBE DELTA SYSTEM.

The Pontic shad lives in the northwestern part of the Black Sea. It migrates in the Danube River for spawning. The larvae drift passively towards the sea when they reach the life stage ranging from pre-larvae to post-larvae. During the larval stage the Pontic shad is floating, mainly in the 0-50 cm upper layer of river. Upstream of the Danube Delta, in the straight sector of the river, alosids are distributed mostly towards the middle of the river, where the water velocity is higher. In the curved section of the river, upstream of the location of the Danube River splitting in the delta’s branches, the water current is outwardly pushing the shad larvae to the right shore, the Romanian, respectively. Therefore, Tulcea branch (Romanian) takes over 60-80 % from the total of Danubian larvae, even its water flow is smaller (40 %) than Chilia branch (the border of Romania and Ukraine). The distribution of larvae at the splitting point influences the repartition of adult migratory catch, at return for spawning, between Saint George branch (Romania) and Chilia branch. Consequently, the topography and hydrology of the river at the splitting point of the branceh which form the delta decide on the distribution of larvae, and later, when the shads are homing on the same way for spawning the sharing catch between Romania and Ukraine

Reproducibility of age determination by scale and vertebra in pontic shad (Alosa pontica Eichwald, 1838), from the Danube

Specimens of Pontic shad (Alosa pontica Eichwald, 1838) were collected during April and May of 2006 in the Danube River (rkm 863) just downstream of the Iron Gate (Djerdap) II dam. Twenty-eight scales and 30 vertebrae were prepared and given to five interpreters with fish aging experience of from 3 to 30 years and with shad aging experience of from 0 to 12 years. Interpreters with experience in shad age determination showed lower values for the index of average percent error (IAPE) and an index of coefficient of variation (ICV). In regard to within-interpreter reproducibility, no significant differences were found between scale and vertebrae as structure for age determination. The most experienced reader showed the lowest value for IAPE, while the least experienced reader showed the highest value for IAPE. The results of this work indicate that experience in age determination by particular structure had more impact on age determination precision than specificity of structure, scale or vertebra. More work is needed on adopting standard protocols that must include some sort of common interaction between responsible age readers.U ovoj studiji analizirana je primenljivost starosne determinacije pomoću krljušti i pršljenova kod Alosa pontica Eichwald, 1838 iz Dunava. Neophodno je više studija o sačinjavanju standardnih protokola koji bi bili evaluirani od strane kompetentnih stručnjaka.Projekat ministarstva br. 14304

Reproducibility of age determination by scale and vertebra in pontic shad (Alosa pontica Eichwald, 1838), from the Danube

Specimens of Pontic shad (Alosa pontica Eichwald, 1838) were collected during April and May of 2006 in the Danube River (rkm 863) just downstream of the Iron Gate (Djerdap) II dam. Twenty-eight scales and 30 vertebrae were prepared and given to five interpreters with fish aging experience of from 3 to 30 years and with shad aging experience of from 0 to 12 years. Interpreters with experience in shad age determination showed lower values for the index of average percent error (IAPE) and an index of coefficient of variation (ICV). In regard to within-interpreter reproducibility, no significant differences were found between scale and vertebrae as structure for age determination. The most experienced reader showed the lowest value for IAPE, while the least experienced reader showed the highest value for IAPE. The results of this work indicate that experience in age determination by particular structure had more impact on age determination precision than specificity of structure, scale or vertebra. More work is needed on adopting standard protocols that must include some sort of common interaction between responsible age readers.U ovoj studiji analizirana je primenljivost starosne determinacije pomoću krljušti i pršljenova kod Alosa pontica Eichwald, 1838 iz Dunava. Neophodno je više studija o sačinjavanju standardnih protokola koji bi bili evaluirani od strane kompetentnih stručnjaka.Projekat ministarstva br. 14304

SEAWARD DRIFT OF THE PONTIC SHAD LARVAE (ALOSA PONTICA) AND THE INFLUENCE OF DANUBE RIVER HYDROLOGY ON THEIR TRAVEL PATH THROUGH THE DANUBE DELTA SYSTEM.

The Pontic shad lives in the northwestern part of the Black Sea. It migrates in the Danube River for spawning. The larvae drift passively towards the sea when they reach the life stage ranging from pre-larvae to post-larvae. During the larval stage the Pontic shad is floating, mainly in the 0-50 cm upper layer of river. Upstream of the Danube Delta, in the straight sector of the river, alosids are distributed mostly towards the middle of the river, where the water velocity is higher. In the curved section of the river, upstream of the location of the Danube River splitting in the delta’s branches, the water current is outwardly pushing the shad larvae to the right shore, the Romanian, respectively. Therefore, Tulcea branch (Romanian) takes over 60-80 % from the total of Danubian larvae, even its water flow is smaller (40 %) than Chilia branch (the border of Romania and Ukraine). The distribution of larvae at the splitting point influences the repartition of adult migratory catch, at return for spawning, between Saint George branch (Romania) and Chilia branch. Consequently, the topography and hydrology of the river at the splitting point of the branceh which form the delta decide on the distribution of larvae, and later, when the shads are homing on the same way for spawning the sharing catch between Romania and Ukraine