Expanding fisheries research on the Ob River: Implementing the Comprehensive Whitefish Restoration Program

 

For the first time in 25 years, a large-scale expedition was conducted to census juveniles of this valuable fish species in the Ob River delta before its mouth enters the Gulf of Ob. This area, known for its extensive shallow sandbars interspersed with depressions (pits and channels) called salmas, is a key feeding ground for immature whitefish and occupies approximately 4,000 square kilometers of the Ob River delta. According to available archival data, it is here that juvenile muksun and a significant portion of juvenile nelma, broad whitefish, whitefish, and peled grow, develop, and gain weight annually, from spring to winter. Furthermore, the breeding stock of these species "rests" here after spawning, as whitefish spawning in the harsh northern conditions is not annual and requires the accumulation of resources for recovery and continued reproduction.

 

The research lasted over three weeks. Scientists conducted comprehensive ichthyological, hydrobiological, and hydrochemical reconnaissance studies over an area of ​​approximately 450 square kilometers, primarily along the coast of Yarango Island.

 

Test catches and hydroacoustic surveys were conducted using equipment capable of determining the size composition and abundance of fish even at minimal depths—down to a meter. Scientists assessed the size and weight characteristics of the caught specimens and their physiological condition. Further office processing will determine the age composition of the fish and calculate their numbers by species in the surveyed area, taking into account the salma habitats with varying depths, currents, and bottom structure.

 

Preliminary results have shown that the salma fish population has changed in recent decades. Whitefish—muksun, broad whitefish, nelma, peled—continue to inhabit the area, but while they were once prevalent, now the dominant group is fish from the "particular" group: ruff, roach, pike, dace, and burbot. The collected scientific data will allow, for the first time in many years, a quantitative assessment of the abundance of juvenile muksun, nelma, and broad whitefish during one of the key periods of their life cycle.

 

"Conducting a census of juvenile whitefish in their feeding grounds is a crucial step in the upcoming assessment of the effectiveness of the comprehensive restoration of Ob whitefish, which will be jointly carried out by the scientific community, subjects of the Tyumen (including the northern autonomous okrugs) and Tomsk regions, and aquaculture enterprises," noted Yana Kapustina, Deputy Head of the Tyumen Branch of VNIRO. "The data obtained will help us understand how many juveniles successfully survive, develop, and replenish commercial stocks. This is the cornerstone for forecasting and making sound management decisions when restoring muksun, nelma, and broad whitefish populations. The results of the studies conducted on the salmas will be processed and analyzed in the laboratories of the Tyumen Branch of VNIRO and will form the basis for the state forecast of total allowable catches (TACs) for these valuable ichthyofauna species in the coming years, as well as adjusting the program for their artificial reproduction."

 

The experience gained will be used to implement improved methods for studying the ichthyofauna of salmas, taking into account the specific conditions of these fish. This will allow us to evaluate the reproduction efficiency of muksun, nelma, and broad whitefish during artificial rearing at fish hatcheries and from natural spawning, determine the survival rate of juveniles in a changing environment, and develop scientifically based recommendations for adjusting fisheries regulations and expanding restoration efforts for valuable fish species.

 

VNIRO Press Service