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This study analysed long-term trawl survey data to investigate changes in the spatial distribution, range boundaries, and catch rates of the five most common shark species in the Russian waters of the northwestern Pacific. Significant alterations in the spatial distributions of these shark species were observed during the study period. The 1980s witnessed the most widespread distribution and maximum catches of salmon and blue sharks. In the 2000s, the North Pacific spiny dogfish exhibited its broadest distribution, with maximum catches recorded in the 1980s and 2010s. The Pacific sleeper shark exhibited its widest distribution in the 1980s, with maximum catches occurring in the 2000s. Shortfin mako were recorded within the study area only in the 1980s and 2010s, with maximum catches occurring in the latter period. Shifts in the range of boundaries during the study period exhibited different patterns among the species. Statistically significant shifts in boundaries were found for Pacific spiny dogfish, salmon sharks, and Pacific sleeper sharks. During the review period, salmon shark catches significantly decreased in Pacific waters and in the study area as a whole, but the reasons for this difference have not yet been determined. For the other shark species, statistically significant changes in catch size were not revealed. The observed significant changes in the spatial distribution and position of the boundaries of the ranges are likely due to both subjective reasons and climatic changes. [ABSTRACT FROM AUTHOR]

Simple Summary: Deep-water skates play an important role as top predators in the North Pacific, yet they are also considered promising targets of bottom-trawl and longline fisheries. Moreover, skates are highly vulnerable to over-fishing due to their very long lifespans, late maturation, small litter size, long incubation period, etc. Despite their ecological and commercial importance, the distribution, basic biological traits, and dynamics of abundance of many deep-water skate species remain poorly understood, information that is critical for their conservation and management. The Aleutian skate Bathyraja aleutica is one of the more common deep-water species and is widely distributed across the North Pacific, but it remains largely understudied. In this paper, we compiled and analyzed long-term data records of the Aleutian skate in the North Pacific from various databases, which revealed new information on its spatial and vertical distribution, size composition, reproductive biology, and interannual catch dynamics. The results of long-term (1948–2021) studies on the spatial and vertical distribution, dynamics of abundance, and size composition of the Aleutian skate Bathyraja aleutica in the North Pacific Ocean are presented. Maximum densities of this species were characteristic of the eastern Bering Sea slope, off the central Aleutian Islands, consisting of the Pacific waters off southeastern Kamchatka and the northern Kurils, and northeastern Sakhalin. This species was most abundant at depths of 100–600 m; in the cold months, B. aleutica migrates to greater depths for over-wintering, and in warm months it feeds at shallower depths. Bathyraja aleutica was most common at the bottom, at temperatures around 3 °C. The total length of individuals ranged from 9.6–170 cm, with a predominance of skates with a length of 50–100 cm. Males did not differ significantly from females in body weight and length. The maximum values of the condition factor were typical for the autumn–winter period. Across years, there was an increase in Aleutian skate catch rates from the western Bering Sea and the Sea of Okhotsk, and a decrease in the Pacific waters off the Kuril Islands and Kamchatka, as well as in Alaskan waters. [ABSTRACT FROM AUTHOR]

Based on data sampled in 1992-2002, the occurrence, spatial distribution, bathymetry, bottom temperatures preferences, size composition, feeding, and some features of reproductive biology of mud skate Rhinoraja taranetzi in the Pacific waters off the northern Kuril Islands and southeastern Kamchatka are considered. Throughout the year, the mud skate was most abundant in the central part of the study area, from the coast of Onekotan Island to the southern tip of Kamchatka peninsula. The proportion of this species in bottom trawl catches in different seasons has changed slightly. However, maximum catch occurred in September-December. In April-May mud skates occupied shallower depths (mean 230-270 m), moving deeper in the summer period (mean 340-390 m). In December-March the skate occurred at lower bottom temperatures (mean 0.8-1.6°C) whereas the rest of the year it inhabited warmer waters with mean bottom temperatures of 2.5-3.1°C. Throughout the year decreasing body weight with depth was observed, indicating that adult and juvenile mud skates inhabit different depths. Total length of mud skates in catches ranged from 17 to 70 cm with a mean of 51.71 cm. Relation between total length (TL, cm) and body weight (W, g) was: W = 0.0029TL ( r = 0.978). Males were more abundant among small skates (<30 cm) only, whereas females predominated among larger skates (>30 cm) comprising about 70% in 60-70 cm length class. Female mud skates were longer and heavier than males (mean length 56.9 vs 51.2 cm and mean weight 1206 vs 807 g, respectively). This species is considered to be benthophagous, consuming mostly amphipods (34.9% by weight), polychaete worms (27.6%), decapod crustaceans (12.7%), and fishery discards (13.9%). Small skates (20-40 cm) fed mostly on amphipods (85.4%); medium-sized (40-60 cm) ate amphipods (40.2%), polychaetes (29.1%) and decapods (19.3%); the largest individuals (>60 cm) consumed fishery offal (27.9%) and less amphipods (26.6%) and polychaetes (27.7%). Preliminary data on the maturation of the species in the western Bering Sea showed that males and females become mature at lengths above 61 cm TL. [ABSTRACT FROM AUTHOR]

Based on the materials collected during the field expeditions in 1992-1996, the diets of 12 predatory and 2 predatory-like fish species from the Pacific waters of the northern Kuril Islands and southeastern Kamchatka have been considered. Some aspects of their trophic relations have been analyzed. Based on comparisons of dietary overlap indexes (DOI) and taking into account annual dynamics of feeding intensity and spatial distribution of the species considered, the level of interspecific feeding competition of 17 pairs of predatory fishes having most similar rations has been estimated. The highest competition has been recorded for the following fish pairs: Sebastes borealis and Sebastolobus macrochir, and Bathyraja aleutica and B. maculata. Other species demonstrated low competition due to different levels of their ration mismatching. dynamics of feeding activity, and patterns of spatial distribution. [ABSTRACT FROM AUTHOR]