630 BIOLOGY OF THE SEAS OF THE U.S.S.R. 



(except sterlet), Salmonidae and Cyprinidae of the Caspian Sea enter a river 

 for spawning and then return to the Sea. Among the herrings Caspialosa 

 volgensis and C. kessleri are migratory fish. The latter enters the Volga, with 

 its gonads still immature, from the beginning of April till the end of June, 

 moving upstream as far as Gorki, going up the Oka to Serpukhov and Kaluga, 

 and up the Kama to beyond Molotov. Caspialosa volgensis spawns mainly in 

 the lower Volga (up to Saratov) ; only a few of the fish go farther upstream. 

 Side by side with these there are semi-migratory herrings which spawn in the 

 pre-delta and delta of the Volga (C. caspia aestuarina, C. suvorovi) and herring 

 which enter fresher waters of the Sea for spawning but do not go upstream 

 (C. brashnikovi with its varieties and C. caspia with its sub-species). Thus an 

 examination of these herrings, so closely related to each other, reveals a series 

 of gradual transitions from the migratory to the marine fish. 



The migrations of Caspian herring within the limits of the Sea are regular 

 and fairly complex. In winter they all gather in the southern and central parts 

 of the Caspian (Fig. 295a), mostly within the area open to the influence of the 

 warm current running from the shores of Iran along the eastern coast of the 

 Southern Caspian. 



With the coming of warm spring weather, herrings approach the western 

 and part of the eastern shores of the Central and Southern Caspian, while 

 some breeds move into the Northern Caspian (Fig. 295b). The more cold- 

 loving herrings (C. brashnikovi, Alosa and the migrant herrings) are the first 

 to approach the shore. When the temperature of the coastal waters rises 

 above 12° С the herring move northward where the water is still much cooler. 

 They keep in the open sea away from the shore. Only some endemic Southern 

 Caspian herring can endure a comparatively high temperature, and they 

 spawn off the coast at a temperature of 12° and even higher. 



In summer the main mass of herrings is gathered in the Northern Caspian. 

 The fry of migratory herrings (C. brashnikovi, C. sphaerocephala and C. 

 saposhnikovi) come down to this area from the rivers Volga and Ural, attract- 

 ing the predatory herring which have remained in the Northern Caspian 

 after spawning, feeding on the fry of migratory herring and on the sprat. In 

 the summer large numbers of migratory herrings and of the Central Caspian 

 Alosa are found in this region. 



The entry of herrings into the warmer Central Caspian waters begins in the 

 autumn with the arrival of colder weather in the Northern Caspian. Herrings 

 and sprat young-of-the-year are the first to leave ; they are followed by adult 

 predatory herrings preying on them. With the drop in temperature herrings 

 move farther and farther south (Fig. 295c), lingering in shallow inlets and 

 bays, where they feed on plankton (C. caspia) and on the young fish (predatory 

 breeds). Moreover, they move much more slowly than in the spring, keeping 

 to the upper layer of water (15 to 25 m), since in the autumn only a shallow 

 layer is heated. 



Apart from the two herring species above, Caspiomyzon wagneri, two 

 species of Salmonidae (Stenodus leucichthys and Salmo trutta caspius) and the 

 Acipenseridae should be included in the group of migratory fish of marine 

 origin. Usually these fish make long spawning journeys; moreover, there are 



