Scientific publications

The outcome of a non-hatchery method for chum salmon (Oncorhynchus keta) reproduction is presented. The method was tested in small tributaries to Malka River (Sea of Okhotsk catchment, Tatar Strait). Specially designed incubation nests were deployed on the bottom of river stretches with rapids. Each device is a streamlined flattened vessel with two layers of incubation plates with wells for individual egg. There is a water inlet in the bottom of the device to secure continuous supply of fresh water; water with embryos’ waste products is washed out of the device through an outlet tube on the top. The nest allows incubating fertilized chum salmon eggs during the winter and get viable larvae in spring, who would then either disperse across the rapid by themselves or be taken out of the devices to be post-reared in pools. The trial revealed both strengths(higher capacity for the incubated eggs –up to 404 chum salmon eggs per device, slots in the bottom of the wells preventing eggs from falling through to the underlying collection chamber during incubation but at the same time allowing the movement of larvae to the collection chamber after hatching) and structural flaws (poor water flow in the cassette installation mode, as well as flow blockage by sand clogging the water intake pipe). Overall, the hatching rate was 97.8 %. Not more than 48.7 % exited the next as larvae. Mortalities were partially due to the blockage of flow through the devices as a result of a critical drop in the water level during the winter low water period, and to the high sediment load, up to 25 cm. Losses were higher, in some devices up to 100 %, in the nests with cassette-type installation. After a minor upgrade, the device can be used to restore the numbers of chum salmon and other Pacific salmon species in small rivers.