Aleksei Stesko
Knipovich Polar Research Institute of Marine Fisheries and Oceanography, Murmansk, Russia Abstract
The paper presents new data of red king crab distribution in the Barents Sea and the White Sea as the results of trap surveys 2015-2017. King crab was observed at depths of 44-54 meters at the bottom salinity of 29.2 ‰ and the bottom temperature of 6.7°C in the White Sea and in eastern part of the Barents Sea at the temperature 0.06°C. According to the trap research, the red king crab is distributed in the “Gorlo” of the White Sea up to 66°37.40'N. The catches of the crab with a research drag (the Sigsby trawl) were registered at 66°37.30`N.
Keywords: Barents Sea, White Sea, red king crab, distribution, biology, salinity and temperature, traps, Sigsby trawl
Introduction
The red king crab was introduced into the Barents Sea for economic use by the fishing industry.
Today it is distributed in the Russian Economic Zone from the borders with the Kingdom of Norway in the west to the Vaigachsky district in Novaya Zemlya in the east and the “Gorlo” of the White Sea in the south. The crab is developing new water areas, the conditions in which may be even unfavorable. The given paper presents new data on the distribution of the red king crab in the Barents and White Seas.
In summer, in the “Gorlo” of the White Sea, salinity is the main limiting abiotic factor. Crabs were only caught only at a salinity of 28 ‰ and above. The “Gorlo” (throat) is characterized by strong tidal currents and a complex hydrological regime, which reduces the intensity of development of this area by the red king crab. Most likely, the crab makes regular migrations there from the north of the “Voronka” of the White Sea. Also in the “Gorlo” there are settlements of the Iceland scallop and, perhaps, this is one of the factors that leads to the migrations of the crab in search of food to the areas with unfavorable conditions.
Further research on the distribution of the red king crab in the “Gorlo” of the White Sea and towards the Kara Sea will help to determine the crab adaptive capabilities more accurately.
Material and methods
The paper uses materials obtained from the results of work during the integrated survey for the red king crab in the territorial waters of Russia in 2015-2017, the drag survey for Iceland scallop in 2017, as well as from the data on the joint Russian-Norwegian Ecosystem Survey in 2017.
In the caught crabs, sex, the intermolt category in males and the stage of maturity of the female roe were determined, the width of the carapace was measured, missing or regenerated legs and other injuries were recorded.
Also, the data on bottom temperature and salinity at the crab capture areas obtained during the surveys were used.
Results and discussion
In the Vaigachsky district (70°11 N 55°28 E), the red king crabs were caught as single specimens.
The depth of fishing was 154 m, the bottom salinity - 34.7 ‰, the temperature - 0.06 °C (Figure 1).
Figure 1. Current distribution of the red king crab in the Russian Economic Zone and areas of its capture in atypical habitats.
In 2015-2016, in the “Gorlo” of the White Sea, the crabs were caught by traps up to 66°37.40`N at a bottom temperature of 6.7 °C and a salinity of 29.2 ‰ and more. The depth of fishing was 44-54 m (Figure 2).
Figure 2. Bottom temperature (A) and salinity (B) in the “Gorlo” of the White Sea and adjacent areas in July 2015.
The specimens were predominantly represented by males and females with a carapace width of 90-120 mm. Catches of crab in the Gorlo of the White Sea were to 8.7 ind. / trap. Males of commercial size with a carapace width greater than 150 mm were observed as single individuals. All females were immature or non-breeding, individuals with external roe were not found (Figure 3).
The biological analysis did not reveal any pathologies in the caught crabs. In animals, encrusting of carapace was minimal.
Figure 3. The size composition of the red king crab in the trap catches in the “Gorlo” of the White Sea in 2015-2016.
In 2017, in the same area, the similar studies did not yield results. Fishing by Sigsby trawl conducted simultaneously with using traps also showed a zero crab capture. In the fishing area the bottom temperature was 5.18 ° C, and the salinity was 27.5 ‰. In the autumn of 2017, slightly southward of the area where fishing was carried out in the summer (66 ° 37.30`N), a non-breeding female of the red king crab with a carapace width of 106 mm was caught. At the site of the crab capture, the bottom salinity was 28.1 ‰, and the temperature - 7.7 °C.
The temperature optimum for the red king crab varies within 2-7 °C. Females with external roe are more warm-requiring. Unfavorable temperature and salinity are 0 °C and lower, and 30 ‰ and lower, respectively. Adult individuals can survive at a temperature of -1.7 °C and a salinity of 28-35 ‰. In the aquarium, for a short period (month), the crab lives at the salinity of 20 ‰. The red king crab larvae survive with a short-term salinity up to 25 ‰.
In the Vaigachsky region, bottom salinity does not go beyond the optimum for the red king crab, hence, its further distribution can be limited by temperature. In winter, this area is covered with ice, in addition, when moving to the “Gates” of the Kara Sea, the depth of the sea decreases and the freshening of the water area increases.
Conclusions
According to the trap research, the red king crab is distributed in the “Gorlo” of the White Sea up to 66°37.40'N.
The catches of the crab by a research drag (the Sigsby trawl) were registered at 66°37.30`N.
The red king crab in catches from the “Gorlo” of the White Sea is represented mainly by males and females with a 90-120 mm carapace width. The commercial crab males were occasionally recorded.
Females with external roe were not observed.
In the areas of the red king crab capture, the minimum salinity was 28.1 ‰.
Acknowledgement
The author is grateful to “Kovda” Ltd. for assistance in the collection of primary material in the autumn of 2017.