Age, growth, maturity, and mortality of the Alaska skate, Bathyraja parmifera, in the eastern Bering Sea

The Alaska skate, Bathyraja parmifera, is the most abundant species of skate on the eastern Bering Sea shelf, accounting for over 90% of total skate biomass. However, little is known regarding the life history of this species despite its common occurrence as bycatch in several Bering Sea fisheries. This is the first study to focus on the age and growth of B. parmifera. From 2003 to 2005, more than one thousand specimens were collected by fisheries observers and on scientific groundfish surveys. Annual banding patterns in more than 500 thin sections of vertebral centra were examined for age determination. Caudal thorns were tested as a potentially non-lethal ageing structure. Annual band pair deposition was verified through edge and marginal increment analyses. A three-parameter von Bertalanffy growth function and a Gompertz growth function were fit to observed length-at-age data. Both models provided significant fits, although the Gompertz function best described the overall pattern of growth in both males and females, based upon statistical criteria and parameter estimates. Age and size at 50% maturity were 9 years and 92 cm TL for males and 10 years and 93 cm TL for females. The maximum observed ages for males and females were 15 years and 17 years, respectively. Estimates of natural mortality (M) ranged from 0.14 to 0.28, and were based on published relationships between M and longevity, age at maturity, and the von Bertalanffy growth coefficient. Due to these life history characteristics and a lack of long-term species-specific stock data, a conservative management approach would be appropriate for B. parmifera.     

Reproduction of the sandpaper skate,Bathyraja kincaidii (Garman 1908) in the eastern North Pacific

The sandpaper skate, Bathyraja kincaidii, is commonly taken as bycatch in trawl fisheries off central California. The impact of fisheries exploitation on this population is unknown, however little is known about its biology, including its reproductive life history. To determine reproductive aspects of B. kincaidii, 506 individuals were collected from commercial trawls, museum collections, and monthly trawl and longline surveys conducted by the National Marine Fisheries Service. Males ranged from 112 to 635 mm TL, whereas females ranged from 113 to 610 mm TL. Males reach first maturity at 440 mm TL and at ~3 years, whereas females reach first maturity at 450 mm TL, approximately 1 year later. Size and estimated age at 50 % maturity were similar between sexes: 492 mm TL and 7.5 years for males and 467 mm TL and 7.1 years for females. Gonadosomatic index (GSI) and hepatosomatic index (HSI) values indicate a continuous reproductive cycle, with a seasonal peak in the summer and fall, and a resting period following egg case deposition.     

Diet and scavenging habits of the smooth skate Dipturus innominatus

The diet of smooth skate Dipturus innominatus was determined from examination of stomach contents of 321 specimens of 29·3-152·0 cm pelvic length, sampled from research and commercial trawlers at depths of 231-789 m on Chatham Rise, New Zealand. The diet was dominated by the benthic decapods Metanephrops challengeri and Munida gracilis, the natant decapod Campylonotus rathbunae and fishes from 17 families, of which hoki Macruronus novaezelandiae, sea perch Helicolenus barathri, various Macrouridae and a variety of discarded fishes were the most important. Multivariate analyses indicated the best predictors of diet variability were D. innominatus length and a spatial model. The diet of small D. innominatus was predominantly small crustaceans, with larger crustaceans, fishes and then scavenged discarded fishes increasing in importance as D. innominatus got larger. Scavenged discards were obvious as fish heads or tails only, or skeletal remains after filleting, often from pelagic species. Demersal fish prey were most frequent on the south and west Chatham Rise, in areas where commercial fishing was most active. Dipturus innominatus are highly vulnerable to overfishing, but discarding practices by commercial fishing vessels may provide a positive feedback to populations through improved scavenging opportunities.     

Greater silver smelt, Argentina silus in Icelandic waters

This paper presents results obtained from data on the greater silver smelt Argentina silus in Icelandic waters collected by the Marine Research Institute, Iceland, mainly since 1981. The greater silver smelt is most abundant in the waters off the south-east coast of Iceland clockwise to those off the west coast, but the species has also been observed off the north coast. Differences in the size composition in relation to area and depth are described. The preferred depth range of the greater silver smelt was found to be 300-600 m and the preferred temperature was about 6°C. Ageing is described showing a relatively fast growth up to the age of 8-9 years. The age/length and length/weight relations are given. Females grow faster than males. The 50% maturity point is reached by males at a length of 36-37 cm and at an age of approximately 8 years, and by females at a length of 37-38 cm and approximately 9 years. Spawning takes place to some extent year round but with one or two periods of greater intensity. Results from experimental fishing are described and problems in connection with a Commercial fishery are discussed.     

Age and growth of the roughtail skate Bathyraja trachura (Gilbert 1892) from the eastern North Pacific

This study provides the first published age estimates for the roughtail skate, Bathyraja trachura. Age and growth characteristics of B. trachura, a poorly-known deepwater species, were determined from samples collected along the continental slope of the contiguous western United States. A new maximum size was established at 91.0 cm TL. Age was determined using a traditional structure (vertebral thin sections) with widespread application on multiple skate species and a non-lethal structure (caudal thorns) recently used for age analysis on skate species. Caudal thorns were determined not to be a useful ageing structure for this species based on poor precision and significantly lower age estimates when compared to age estimates from vertebral thin sections. The best model for describing growth of B. trachura was the two parameter VBGF, assuming annual vertebral band deposition and using length-at-age data. Although females grew slower and reached a larger maximum size than males, their growth was not statistically different (ARSS; P = 0.90); therefore, data were pooled (L_∞ = 99.38, k = 0.09). Annual band deposition was found to be a reasonable assumption for this species, but has yet to be validated. The maximum age estimated for B. trachura was 20 years for males and 17 years for females using vertebral thin sections.     

Distribution and some biological features of bottom skate <Emphasis Type="Italic">Bathyraja bergi</Emphasis> in the Russian waters of the Sea of Japan

The spatial and depth-related distribution, the size spectra, and the feeding peculiarities have been studied for the bottom skate Bathyraja bergi in the Russian waters of the Sea of Japan for the trawl catches performed in 1986?2015. The species is found at the depths of 38?577 m at the water temperature of 0.3?3.8°C; during the warm season, the fish keep mainly at the shelf, while they keep at the continental slope in the cold period of the year. This species is found nearly everywhere at the preferred depth range, except a part of the Strait of Tartary. The highest population density has been registered in the southwestern Peter the Great Gulf, along the border with the Korean waters. The schools of the bottom skate of the continental slope and the island shallows do not interact with each other. The specimens reach a body length of 129 cm and a body weight of 13.84 kg. The feeding habits indicate that this species is a predator; decapods (59.9%), cephalopods (23.0%), and fish (15.3%) dominate in the food. In spring, average daily ration constitutes 0.9% of the body weight. In the Russian waters of the Sea of Japan, the bottom skate is a common species, however, it is not abundant; the biomass of the population in this area is approximately 1500 tons.     

Food habits of the sandpaper skate, Bathyraja kincaidii (Garman, 1908) off central California: seasonal variation in diet linked to oceanographic conditions

The stomachs of 130 sandpaper skates, Bathyraja kincaidii (Garman, 1908), were sampled from off central California to determine their diet composition. The overall diet was dominated by euphausiids, but shrimps, polychaetes and squids were also important secondary prey. A three-factor MANOVA demonstrated significant differences in the diet by sex, maturity status and oceanographic season using numeric and gravimetric measures of importance for the major prey categories. These three main factors explained more variation in diet than interactions between the factors, and season explained the most variance overall. A detailed analysis of the seasonal variation among the prey categories indicated that abundance changes in the most important prey, euphausiids, were coupled with seasonal changes in the importance of other prey. When upwelling occurred and productivity was great (Upwelling and Oceanic seasons), euphausiids were likely highly abundant in the study area and were the most important prey for B. kincaidii. As productivity declined (Davidson Current season), euphausiids appeared to decrease in abundance and B. kincaidii switched to secondary prey. At that time, gammarid amphipods and shrimps became the most important prey items and polychaetes, mysids and euphausiids were secondary.     

Organisation of the Hb 1 genes of the Antarctic skate Bathyraja eatonii: new insights into the evolution of globin genes

An extensive investigation of the organisation of globin genes has greatly contributed to the understanding of universal mechanisms of gene evolution and expression. Cartilaginous fish are the first organisms that have evolved the tetrameric form of hemoglobin (Hb). So far, there has been absolute lack of data about globin genes in chondrichthyans. Bathyraja is the dominant rajid south of 60 degrees S. In the framework of the investigations on globin genes of Antarctic red-blooded and Hb-less fish we obtained the cloning of the alpha- and beta-globin cDNAs of the main Hb (Hb 1) of the skate Bathyraja eatonii. Then, a genomic fragment of 6.2 kb was isolated where the Hb 1 alpha and beta genes are linked in a tail-to-head (3' to 5') orientation. The beta-globin gene promoter region and the chromosomal organisation of the Hb 1 genes of B. eatonii have been compared to their homologues in other vertebrates. The finding of a tail-to-head linkage of the Hb 1 alpha- and beta-globin genes in B. eatonii is the first characterisation of the organisation of globin genes in chondrichthyes; such finding offers a novel contribution to the understanding of the evolution of this class of genes. Moreover, the characterisation of chondrichthyan genes is very important for gaining insight into the ancestral state of vertebrate genomes.     

The occurrence of Calanidae species in waters off Argentina

As food of planktivorous fish and likely good predictors of natural perturbations, members of the family Calanidae are recognised to be key species in ecosystems worldwide. The distribution and seasonal relative abundance of the Calanidae species occurring in the Argentine Sea were reviewed from published and unpublished data collected over the last three decades. Species are also figured in order to elucidate any possible taxonomic uncertainty. Calanoides cf. carinatus, Calanus australis and Calanus simillimus are the most abundant calanids in the region. The former two species typically inhabit inner and middle shelf waters decreasing offshore, while Calanus simillimus is distributed in the middle and outer shelf, its abundance increasing towards the shelf-break. The southern limit of the distribution of Calanoides cf. carinatus appears to be 46° S. Calanus australis is the most common large copepod in coastal and inner shelf waters off southern Patagonia. Neocalanus tonsus and Calanoides patagoniensis are a much rarer species. The latter is recorded in the southwestern Atlantic, for the first time, immediately east of Magallanes Strait and the Beagle Channel. The taxonomic status and worldwide biogeographic distribution of the region's calanids are briefly described and the patterns identified off Argentina are discussed in relation to the major hydrographic characteristics.     

Dietary comparisons of six skate species (Rajidae) in south-eastern Australian waters

The diet of six skate species caught as bycatch in south-eastern Australian waters was examined over a 2-year period. The skates were segregated into two regions (continental shelf and continental slope) based on prey species and depth of capture. The shelf group consisted of four species, Dipturus sp. A, D. cerva, D. lemprieri and D. whitleyi, while the slope group comprised two species, Dipturus sp. B and D. gudgeri. The two groups varied in feeding strategies with the shelf species generally occupying a broader feeding niche and preying on a larger diversity of prey including a variety of crustaceans (brachyurans, anomurans, achelates, carideans and dendobranchiates), cephalopods, elasmobranchs and teleosts. Within the slope group, Dipturus sp. B and D. gudgeri were more specialised. Dipturus sp. B preyed primarily on anomurans (galatheids) and bachyurans (homolids), whereas D. gudgeri preyed primarily on teleosts. A size related change in diet was evident for all species with the exception of D. gudgeri in which all sizes preyed predominantly on teleosts. Smaller representatives of the four shelf species all preyed on numerous amounts of caridean shrimps, in particular Leptochela sydniensis. In contrast, the continental slope species, Dipturus sp. B consumed anomurans when small, shifting to brachyurans with increasing size. Of the six skate species examined in this study, three were secondary consumers (trophic level <3) and the remaining three tertiary consumers (trophic level >4). Although ANOSIM found significant differences in dietary composition between species within groups, there was some overlap in prey species amongst co-existing skates, which suggests that there is some degree of resource partitioning amongst them.     

Spatial distribution,size composition,and dynamics of catches of the Okhotsk skate <Emphasis Type="Italic">Bathyraja violacea</Emphasis> in the North Pacific Ocean

The results of the long-term (1963–2015) studies of spatial and vertical distributions, dynamics of abundance and size composition of the Okhotsk skate Bathyraja violacea in the North Pacific Ocean are presented. This species is the most abundant at depths of 100–400 m; in the cold season, it migrates to the larger depths for wintering, while it migrates to shallower depths in the warm season. Specimens of the length 12 to 132 cm with prevalence of skates of 50 to 80 cm long were recorded in catches. The difference between males and females in body weight and length was not considerable. Condition factor of specimens decreases from January to August and begins to increase in September. Males dominate among the skates up to 30 cm long, females dominate in the size groups of 30–60 cm and >70 cm, while an almost equal sex ratio is observed in the size group of 60–70 cm. The dynamics of the catches of the Okhotsk skate vary in different regions: in the western Bering Sea and in the Sea of Okhotsk, the catches consistently increased during the study period, the catches increased to the mid-1980s–early 1990s in the Kuril and Kamchatka waters of the Pacific Ocean, and then a decrease has been observed; in the eastern Bering Sea, the peak of catches occurred in the mid-1970s, and then they decreased subsequently.     

Fishery and Ontogenetic Driven Changes in the Diet of the Spiny Dogfish, Squalus acanthias, in Patagonian Waters, Argentina

The diet of the spiny dogfish in northern and central Patagonian waters was studied from the by-catch of the bottom trawling fisheries directed to Argentine hake Merluccius hubbsi and Argentine red shrimp Pleoticus muelleri between 1996 and 1998. Food habits were analyzed in relation to sex and maturity of sharks. Also, the relationship between diet and abundance of the main prey was explored. Intraspecific diet comparisons were performed. Differences in diet were found between immature individuals, mature males, and mature females. The Argentine shortfin squid Illex argentinus, the Argentine hake and ctenophores Pleurobrachia pileus were the most important prey for the spiny dogfish. Immature and small individuals were pelagic predators. After sexual maturity, the spiny dogfish shifted its diet. Mature and large individuals tended to reduce the consumption of ctenophores, and increase the consumption of demersal and benthic species. Previous diet studies on the spiny dogfish in 1984–1985 and 1994 indicated that the Argentine hake was the most important prey. In the present study, carried out in 1998, squid was the most important prey, followed by the hake. This diet change was related to the major decrease of hake due to overfishing and the increase of squid abundance between 1994 and 1999.     

Breaking with tradition: redefining measures for diet description with a case study of the Aleutian skate Bathyraja aleutica (Gilbert 1896)

Characterization of fish diets from stomach content analysis commonly involves the calculation of multiple relative measures of prey quantity (%N,%W,%FO), and their combination in the standardized Index of Relative Importance (%IRI). Examining the underlying structure of dietary data matrices reveals interdependencies among diet measures, and obviates the advantageous use of underused prey-specific measures to diet characterization. With these interdependencies clearly realized as formal mathematical expressions, we proceed to isolate algebraically, the inherent bias in %IRI, and provide a correction for it by substituting traditional measures with prey-specific measures. The resultant new index, the Prey-Specific Index of Relative Importance (%PSIRI), is introduced and recommended to replace %IRI for its demonstrated more balanced treatment of the relative measures of prey quantity, and less erroneous behavior across taxonomic levels of identified prey. As a case study, %PSIRI was used to examine the diet of the Aleutian skate Bathyraja aleutica from specimens collected from three ecoregions of the northern Gulf of Alaska (GOA) continental shelf during June-September 2005?C2007. Aleutian skate were found to primarily consume the commonly abundant benthic crustaceans, northern pink shrimp Pandalus eous and Tanner crab Chionoecetes bairdi, and secondarily consume various teleost fishes. Multivariate variance partitioning by Redundancy Analysis revealed spatially driven differences in the diet to be as influential as skate size, sex, and depth of capture. Euphausiids and other mid-water prey in the diet were strongly associated with the Shelikof Strait region during 2007 that may be explained by atypical marine climate conditions during that year.     

Reproductive biology of the skate, Rioraja agassizii (Müller and Henle, 1841), off Puerto Quequén, Argentina

A total of 230 specimens of the skate, Rioraja agassizii, was collected from the commercial bottom trawl fishery of Puerto Quequén, Argentina. During the warmer seasons greater proportions of females were sampled. The largest male and female sampled were 629 and 698 mm total length (TL), respectively. Sexual dimorphism was detected in the relationship between weight ( W )−TL and disc width (DW)−TL, in that females were heavier and wider than males. The smallest mature male and female were 485 and 530 mm TL, respectively. TL at 50% maturity (TL_50%) was estimated at 504 and 570 mm for males and females, respectively. Females exhibited heavier livers than males throughout their lifetimes. Seasonal variations in the gonadosomatic (GSI) and hepatosomatic (HSI) indices, and in the width of the left oviducal gland (OG), along with the greater number of pregnant females sampled during spring, suggested that the peak of the egg laying season could be during this season. The egg cases presented a mean length of 69.01 ± 5.53 mm, mean width of 43.40 ± 1.86 mm and mean weight of 17.00 ± 4.59 g. According to these results specimens from Puerto Quequén and southern Brazil appeared to differ in size, the peak of the egg-laying season and in egg dimensions.     

Diet of the Antarctic starry skate Amblyraja georgiana (Rajidae, Chondrichthyes) at South Georgia (Southern Ocean)

Stomach contents were identified from 206 Antarctic starry skate (Amblyraja georgiana) that were collected during three groundfish surveys (September 2007, April 2008 and January 2009) at South Georgia, Southern Ocean. The diet of A. georgiana varied with skate size and between years. Preferred prey included fish (particularly for larger individuals) and Antarctic krill, Euphausia superba, as well as amphipods, polychaetes and other benthic fauna. The skate A. georgiana appears to be an opportunistic predator, and the clear presence of Antarctic krill in this demersal predator’s diet may indicate a benthic habit of this euphausiid species, which has hitherto mainly been considered as occupying a purely pelagic niche.     

<Emphasis Type=Italic>Bathyraja leucomelanos</Emphasis>, a new species of softnose skate (Chondrichthyes: Arhynchobatidae) from New Caledonia

A new species of softnose skate (Arhynchobatidae) is described, based on a single adult male measuring 895 mm TL that was collected at a depth of 953–1,022 m on the Coriolis Bank off western New Caledonia in the southwestern Pacific Ocean. The specimen conforms to the genus Bathyraja in having the rostral cartilage continuous with the neurocranium and very slender and uncalcified over its length. Bathyraja leucomelanos sp. nov. differs from its congeners through a combination of the following characters: distinctive coloration of the disc with white dorsal and black ventral surfaces, dorsal surface of the disc entirely covered with dermal denticles, ventral surface naked, anterior portion of the anterior margin of the disc straight, snout long and very broad with orbit about 6.0 times in preorbital length, orbit 0.73 times interorbital width, mouth 6.8% TL, tail 0.88 times precloacal length, accessory terminal 2 cartilage of the clasper having an expanded disc-shaped tip, and alar thorn tip undulating. Molecular barcoding from the COI sequence reveals that this new species is genetically close to B. spinicauda from the North Atlantic Ocean.     

Feeding habits of ocellate spot skate,Okamejei kenojei (Müller & Henle, 1841), in coastal waters of Taean,Korea

The feeding habits of Okamejei kenojei were studied using 592 specimens collected in the coastal waters of Taean, Korea from April 2008 to March 2009. O. kenojei is a bottom‐feeding carnivore that consumes mainly shrimp, fishes, and crabs. Its diet also includes small quantities of amphipods, mysids, cephalopods, euphausiids, copepods, isopods, and polychaetes. The total length (TL) of individuals in this study ranged from 8.2 to 49.0 cm. Cluster analysis based on %IRI (index of relative importance) identified three size classes. Group A (< 20 cm TL) ate primarily caridean shrimp and amphipods; group B (20–30 cm TL) ate exclusively shrimp; and group C (> 30 cm TL) ate penaeoidean shrimp, fishes, and crabs. O. kenojei showed ontogenetic changes in feeding habits. Although shrimps were the primary food consumed by all size groups, the proportion of shrimp in the total diet decreased and the consumption of fishes and crabs gradually increased with the body size of O. kenojei. Size of the prey organisms also increased. Smaller individuals fed mainly on small prey, such as amphipods, mysids, and small shrimp, whereas larger individuals preferred larger prey, such as larger shrimp, fishes, and crabs. The size‐related diet breadth and the percentage of empty stomachs were significant; the diet breadth gradually increased with body size, whereas the percentage of empty stomachs decreased. Seasonal changes in the O. kenojei diet were not significant, but shrimp constituted 97.3% of the summer diet by %IRI. Seasonal changes in diet breadth and the percentage of empty stomachs were not significant.     

Distribution and some biological features of skate <Emphasis Type="Italic">Bathyraja parmifera</Emphasis> (Rajidae,Rajiformes) in the northwestern part of the Sea of Japan

In the northwestern part of the Sea of Japan, skate Bathyraja parmifera in catches of the bottom trawl occurs at depths of 40 to 830 m at the near-bottom temperature of 0.4–4.9°C. Throughout the year, the skate performs migrations within the continental slope and, in the feeding period, inhabits mainly the depth range of 300 to 500 m. Maximal average density of aggregations of B. parmifera is observed in waters of northern Primorye; minimal average density is observed in Peter the Great Bay and on the Yamato Bank. In catches, skates with a length of 17–130 cm and a weight of 0.5–18.8 kg are recorded; however, fish with a length of 80–115 cm dominate. Individuals with a length of up to 40 cm feed mainly on amphipods, and larger immature and adult individuals feed on decapods, cephalopods, and fish. The value of the daily ration of B. parmifera with its growth decreases from 2.4 to 0.9% of the body weight. Specific ecological features of B. parmifera are a cause of its considerable underfishing by the bottom trawl; therefore, the total resource of this species in the considered region may be at the level of maximal estimates obtained during surveys and comprise no less than 20000 t.