Sebastes Fasciatus Research Articles

Geographic variation and juvenile migration in Atlantic redfish inferred from otolith microchemistry

Golden redfish (Sebastes marinus) and deep-sea redfish (S. mentella) are heavily exploited fish resources in the North Atlantic, but their stock delineation remains unresolved. The present study examined the use of otolith microchemistry as a stock separation tool for redfish. By determining minor and trace elements in redfish otoliths from various areas in the North Atlantic, geographic and temporal variations in otolith microchemistry were investigated. Relatively high temporal stability in otolith elemental composition was found for juvenile redfish from nursery areas off East Greenland. Elemental concentrations in the nucleus, juvenile and marginal otolith zones differed significantly between areas and showed consistent longitudinal trends for some elements. Multivariate analysis of element constituents by area, however, revealed poor geographic separation (< 50% cross-validated classification) for both species. Otoliths of juvenile S. mentella from demersal nursery grounds and adjacent pelagic habitats showed no significant differences between areas. The results are in accordance with the recently observed low morphometric and genetic heterogeneity of redfish across the North Atlantic. It is, however, unclear if the lack of clear spatial separation by natal signatures is due to a common origin of the investigated fish or due to limited variability of the chemical composition of their ambient environment.

Age determination and growth of Atlantic redfish (Sebastes marinus and S. mentella): bias and precision of age readers and otolith preparation methods

Abstract Age determination of Atlantic redfish (Sebastes spp.) has proven difficult and has led to inconsistent age and growth estimates in the past. Using otoliths of the two major commercial species, golden redfish (Sebastes marinus) and deep-sea redfish (S. mentella), a series of exchange schemes was carried out to assess bias and precision of age readings between four readers and between two preparation methods. Considerable bias between readers and moderate precision were observed for the S. marinus readings, especially for ages >20 years, with coefficients of variation (CV) of 7.7–12.0% and average percent error (APE) of 5.4–8.5%. Agreement between readers increased from 17–28% to 45–61% when allowing deviations of ±1 year, and to 80–92% with ±3 years tolerance. The age of S. marinus determined from broken and burnt otoliths was estimated to be slightly lower than when the age of the same individuals was determined from thin-sectioned otoliths. The bias and precision estimates obtained from the S. mentella material were generally poorer than for S. marinus (CV 8.2–19.1%, APE 5.8–13.5%), but similar to reported values for other long-lived fish species. Better than 50% agreement was only achieved with ±3 years tolerance. Growth rates differed significantly between species, confirming slower growth for S. mentella. For S. marinus, only one reader comparison revealed significantly different growth functions, whereas almost all S. mentella reader pairs showed significant differences in growth curves. Section and break-and-burn readings of S. marinus did not differ significantly. Average ages of around 9–10 years were determined for juvenile S. mentella 24–30 cm long, which were likely to have migrated from East Greenland into the Irminger Sea, based on earlier observations. As some of the error in the age determinations presented could be attributed to interpretation differences between readers, further intercalibration of redfish ageing is urgently needed in order to provide consistent input data for stock assessment.

Variation in Habitat use by Juvenile Acadian Redfish, Sebastes fasciatus

A basic paradigm in behavioral ecology is that organisms expand their distribution as preferred sites become saturated with individuals that reduce the availability of resources (e.g., shelter, prey) on a per capita basis. Previous fish community studies at Stellwagen Bank National Marine Sanctuary have shown that juvenile Acadian redfish Sebastes fasciatus ( 20 cm TL) also occurred in dense cerianthid habitats. Two explanations for these distributions can be advanced. The simplest is that redfish use both boulder and cerianthid habitats on an encounter basis, regardless of habitat saturation or predation pressure. Alternatively, boulder reefs serve as recruitment habitats and cerianthid habitats serve as a conduit for redfish moving away from saturated boulder reef sites, essentially serving as elements of a 'redfish pump'.

In situ target strength studies on Atlantic redfish (Sebastes spp.)

In situ acoustic target strength (TS) experiments were conducted on Atlantic redfish ( Sebastes spp.) in Newfoundland waters (1996–1998) using deep-tow dual beam and hull-mounted split beam echosounders (38 kHz). The dual and split beam mean TSs did not differ. The deep-tow system was deployed at various depths over several aggregations. Calibration corrections were made for depths from 5–70 m (<1 dB). The TS declined at ranges <50 m from the top of the fish shoal suggesting avoidance behaviour. It was biased upward at ranges >200 m and a number of fish per sampled volume >0.04. After being controlled for variations related to range, reverberation volume and fish density the TS did not differ with respect to depth, distance from bottom, fish sex ratio, condition factor or weight. The mean length was the dominant influence on the mean TS. Pooled ex situ experimental data and controlled in situ data – which did not differ – indicated a length-based regression (weighted by s.e. −1 ) in standard format: TS=20 log [length (cm)] −68.7 (r 2 =0.49).

Geometric morphometrics reveals body shape differences between sympatric redfish Sebastes mentella, Sebastes fasciatus and their hybrids in the Gulf of St Lawrence

Geometric morphometrics reveals body shape differences between sympatric redfish Sebastes mentella, Sebastes fasciatus and their hybrids in the Gulf of St Lawrence

An hypothesis on endogenous hydrostasis in Atlantic redfish ( Sebastes spp.)

We propose the hypothesis that Atlantic redfish have an endogenous cycle in the resorption and secretion of swimbladder gas. We measured the in situ acoustic target strength (TS) of redfish during diel vertical migration and found no effect of depth, which is inconsistent with Boyle’s law. We performed an ex situ experiment on an immobilized redfish and observed systematic changes in TS of approximately 2 dB at night when vertical migration occurs. The observed change in TS is consistent with a swimbladder volume change that would maintain redfish near neutral buoyancy throughout the range of their vertical migration.

Target Strength of encaged Atlantic redfish (Sebastes spp.)

Redfish ( Sebastes spp.) were caught at sea with feather hooks, kept alive in sea cages for >12 hours at 30 m depth, then transferred to cages at 10 m depth for another 12 h. Most fish survived this procedure in excellent condition. A total of 16 fish of length 24.5–30 cm were placed one at a time in an acoustically inert monofilament cage where target strength (TS) was measured for two hours using a 38 kHz split-beam echo-sounder. An underwater video camera enabled continuous monitoring of fish and cage. The best fit length based regression obtained from these data was TS=19 log [length (cm)]−66.6, in the standard format: TS=20 log [length (cm)]−68.1 (r 2 =0.18). TS varied by less than 4 dB over a range of tilt angles from −50° to 70° off dorsal aspect.

Evidence for broadscale introgressive hybridization between two redfish (genus Sebastes) in the North-west Atlantic: a rare marine example.

The evolutionary importance of introgressive hybridization has long been recognized by plant evolutionists, and there is now a growing recognition for its potential role in animals as well. Detailed empirical investigations of this evolutionary process, however, are still lacking in many animal groups, particularly in the marine environment. Using integrated microsatellite DNA data (eight loci analysed over 803 individuals representing 17 sampling locations) and multivariate statistical procedures (principal component, factorial correspondence and admixture proportion analyses), we: (i) provide a detailed dissection of the dynamics of introgressive hybridization between Sebastes fasciatus and S. mentella, two economically important redfishes from the North-west Atlantic; and (ii) infer the factors potentially involved in the maintenance of the hybrid zone observed in the gulf of St. Lawrence and south of Newfoundland. This study provided one of the rare examples of extensive introgressive hybridization in the ocean, and highlighted the predominant role of this process in shaping the extent of genetic diversity, interspecific differences and population structuring among redfishes from the North-west Atlantic. The extensive (average rate of introgression = 15%) but geographically circumscribed and asymmetrical pattern of introgressive hybridization, the sympatric persistence of two reproductively isolated introgressed groups, the differential patterns of linkage disequilibrium among samples, and the maintenance of genetic integrity of both species outside the defined zone of introgression despite high potential for gene flow, all implicated selection in promoting and maintaining the observed pattern of introgression.

Some problems and solutions for the measurement of fish target strength: A study case with Atlantic redfish (Sebastes spp.)

Potential biases in the measurement of redfish target strength (TS) were examined by comparing ex situ and in situ approaches. Ex situ experiments were conducted on individuals after developing a method to maintain live fish in good condition. The main problem with the manipulation of these species was the inflation and distortion of the swimbladder. To minimize this bias, fish were kept in sea cages after acclimation at depth and TS was measured in a camera-monitored apparatus set in proximity to the capture site. A series of in situ acoustic-trawl experiments was conducted on several aggregations of redfish in Newfoundland waters. TS were collected using a hull-mounted EK500 split-beam transducer and a deep-tow dual-beam system. The dual-beam transducer was calibrated at different depths to test if change in pressure and/or temperature affected its sensitivity. This system was used to measure aggregations of fish under different transducer depth. The data indicated that biases in in situ TS estimates increased with the range of observation, the density of fish, and the presence of multiple targets formed by the clustering of smaller organisms. Depending on the nature of the bias, TS can be over- or underestimated by as much as 6 dB.

Potential of microsatellites for individual assignment: the North Atlantic redfish (genus Sebastes) species complex as a case study.

We used the four redfish taxa (genus Sebastes) from the North Atlantic to evaluate the potential of multilocus genotype information obtained from microsatellites in assigning individuals at two different levels of group divergence. We first tested the hypothesis that microsatellites can diagnostically discriminate individual redfish from different groups. Second, we compared two different methods to quantify the effect of number of loci and likelihood stringency levels on the power of microsatellites for redfish group membership. The potential of microsatellites to discriminate individuals from different taxa was illustrated by a shared allele distance tree in which four major clusters corresponding to each taxa were defined. Concomitant with this strong discrimination, microsatellites also proved to be powerful in reclassifying specimens to the taxon of origin, using either an empirical or simulated method of estimating assignment success. By testing for the effect of both the number of loci and the level of stringency on the assignment success, we found that 95% of all specimens were still correctly reclassified with only four loci at the most commonly used criterion of log0. In contrast, the results obtained at the population level within taxa highlighted several problems of assignment that may occur at low levels of divergence. Namely, a drastic decrease of success with increasing stringency illustrated the lack of power of our set of loci. Strong discrepancy was observed between results obtained from the empirical and simulated methods. Finally, the highest assignment success was obtained when reducing the number of loci used, an observation previously reported in studies of human populations.

Isolation and characterization of polymorphic microsatellite markers in the North Atlantic redfish (Teleostei: Scorpaenidae, genus Sebastes).

Redfish {genus Sebastes) are marine, viviparous and commercially important fish of the North Atlantic. For the last 30 years, a considerable amount of effort has been invested to study the evolutionnary relationships and the population genetic structure of tliis species complex. The complex is composed of four currently recognized taxa: Sebastes fasciatus, S. mentella, S. mariniis and S. vivipams. However, genetic studies relying on proteins and/or mitochondrial DNA markers have generally revealed low levels of genetic variation within and between redfish taxa (McGlade et al. 1983; Nedreaas & Naevdal 1991a), and hampered the analysis of young stages (Nedreaas & Naevdai 1991b). Consequently, there was a need for genetic markers with a higher resolution that could detect differences at any level of genetic differentiation (species, stocks), and any developmental stages. We report here the isolation and characterization of eight microsatelHtes from the Atlantic redfish complex that may be useful for a wide range of applications throughout the Atlantic Ocean.

Low levels of interspecific dna sequence variation of the mitochondrial 16S rRNA in north atlantic redfish sebastes (Pisces, scorp aenidae)

Abstract During an attempt to develop a molecular method for identification of species and morphs of Atlantic Sebastes, extremely low levels of interspecific sequence variation in a mitochondrial large subunit (16S) ribosomal RNA were found. Nucleotide sequencing of a 480 base pair portion of the gene from representatives of six phenotypes of four species of Sebastes was executed. No variation was found among the individuals of ‘Regular’ S. marinus, ‘giant’S. marinus, ‘oceanic’S. mentella, and ‘deepsea’ S. mentella analyzed. Sequences from S. fasciatis and S. viviparus differed with only one base each from the marinuslmentella haplotype. The low level of genetic variation at this gene makes it unsuitable as a target for methods to identify North Atlantic Sebastes. Level of variation may indicate recent evolutionary divergence between the species.

An in situ target strength model for Atlantic redfish

An in situ target strength (TS) model for Atlantic redfish is proposed based on a series of acoustic-trawl experiments conducted at the outer edge of the Green and Grand Banks in Newfoundland waters (NAFO div. 3Ps) in July 1996 and January 1997. Acoustic data were collected using a SIMRAD EK500 echosounder with a hull-mounted 38-kHz split beam transducer and a deep-tow system with a 38-kHz dual beam transducer that can be towed down to 400-m depth. Bottom and midwater trawling sets were performed to account for fish species composition and length distributions. Study sites were selected on the basis of low variance in individual fish size and the absence of other fish species. The model tests the dependence of TS on diel migratory behavior, TS methodology (split and dual beam), distance from transducer, fish density and size, and the presence and relative abundance of zooplanktonic organisms (krill).

Parasites of sharp-beaked redfishes (Sebastes fasciatus and Sebates mentella) collected from the Gulf of St. Lawrence, Canada

Parasites of sharp-beaked redfishes (<i>Sebastes fasciatus</i> and <i>Sebates mentella</i>) collected from the Gulf of St. Lawrence, Canada

Evaluation of Methods for Separation of Gulf of St. Lawrence Beaked Redfishes,Sebastes fasciatusandS.mentella: Malate Dehydrogenase Mobility Patterns Compared with Extrinsic Gasbladder Muscle Passages and Anal Fin Ray Counts

Malate dehydrogenase (MDH) electrophoretic mobility patterns were used as a standard against which field methods involving anal fin ray counts (AFCs) and extrinsic gasbladder muscle (EGM) rib passage patterns were compared to separate the beaked redfish species, Sebastes fasciatus and S. mentella. The frequencies of MDH-A phenotypes were determined for 1125 beaked redfish examined from a winter survey in 1983 and 376 from a summer survey in 1984. Allele frequencies were calculated from the MDH-A phenotypic data for the winter survey. The low mobility of the A2phenotype was characteristic of 90% of S. fasciatus sampled at depths &lt; 320 m in winter and at depths &lt; 250 m in summer. The high-mobility A1and heterozygotic A1/A2phenotypes were prevalent in 95% of S. mentella sampled below these depths. The mobility patterns agreed with predominant AFCs ([Formula: see text] for S. fasciatu[Formula: see text] for S. mentella) for all stations in the deep and shallow zones. The MDH mobility patterns showed 93% agreement with EGM patterns for S. fasciatus but only 53% agreement for S. mentella. An overlap of AFCs, of main EGM patterns, and of tendon to vertebrae attachments and the variation from set to set in A1/A2heterozygotic phenotypes suggest that these species hybridize in the Gulf of St. Lawrence.

210Pb/226Ra Determination of Longevity in Redfish

Examination of annular growth rings apparent in charred otolith cross sections is the basis for reports of extreme longevity in the rockfish genus Sebastes, but the interpretation of the annuli has long been disputed. We used a radiochemical assay of the otolith core to confirm our interpretation of annuli in Atlantic redfish, Sebastes mentella, to at least an age of 65 yr. Through measurement of the radioactive disequilibrium between 226Ra and 210Pb, it appears that redfish live to an age of at least 75 yr in the waters off of Nova Scotia.

Growth-maturation interactions of Acadian redfish (Sebastes fasciatus Storer) in the Gulf of Maine-Georges Bank region of the Northwest Atlantic

Growth-maturation interactions of Acadian redfish (Sebastes fasciatus Storer) in the Gulf of Maine-Georges Bank region of the Northwest Atlantic

Biochemical separation of Atlantic Canadian redfish: Sebastes mentella and Sebastes norvegicus

One of the problems for management of the redfish fishery in the Gulf of St. Lawrence is the difficulty in distinguishing between the different species: deepwater redfish (Sebastes mentella), golden redfish (Sebastes norvegicus), and Acadian redfish (Sebastes fasciatus). Controversy exists concerning whether S. mentella and S. norvegicus are separate species because of similarity of meristic characters and other attributes. We describe a procedure that distinguishes these two forms by isoelectric focusing using polyacrylamide gels of water-soluble muscle proteins. In our samples, the lower part of the gel of S. mentella consistently shows three major protein bands, while that of S. norvegicus shows only one major band. The isoelectric focusing banding patterns from our study agree with those found by other workers for redfish from Greenland and Norway. The unequivocal isoelectric focusing separation and its concordance with morphometric characters indicate that S. mentella and S. norvegicus are genetically distinct, reproductively isolated species.

Helminth parasites of redfish (Sebastes fasciatus) from the Scotian Shelf, Bay of Fundy, and eastern Gulf of Maine

Examination of alimentary tracts of 319 redfish (Sebastes fasciatus) from the Scotian Shelf, Bay of Fundy, and eastern Gulf of Maine yielded 13 helminth species: 7 Digenea, 3 Cestoda, 2 Nematoda, and 1 Acanthocephala. Total species composition was virtually identical with that found in the redfish of the Labrador–Newfoundland area. Prevalence and intensity of infection were low and showed little variation with area or fish length except in the case of the nematodes Anisakidae for which low prevalence and intensity (3.9 and 1.0, respectively) in the eastern Gulf of Maine contrasted with higher values (39.1–71.4 and 1.7–7.7, respectively) in the remainder of the survey area. The general pattern of species numbers was low numbers (2–4) in the fish of the Gulf of Maine and southwest Nova Scotia, and higher numbers (8–13) in those of the central and northeast Scotian Shelf. Small- to intermediate-sized fish contained more species (7–12) than the largest fish (4). The combination of exceptionally low prevalence of Anisakidae and low parasite species numbers in redfish of the eastern Gulf of Maine area suggests that the stock there is distinct from those of the Scotian Shelf and Bay of Fundy.

Development of deep-water redfish (Sebastes mentella) larvae, with comparative notes on newly extruded Acadian redfish (Sebastes fasciatus) from the Flemish Cap

Planktonic redfish larvae of the genus Sebastes were collected from Flemish Cap, an offshore Northwest Atlantic fishing bank east of the island of Newfoundland, Canada. A protocol based on discriminant function analysis and previously published age–length relationships was used to identify specimens of S. mentella and newly extruded (&lt; 9 mm) S. fasciatus. On Flemish Cap, newly extruded larvae of S. mentella and S. fasciatus do not differ significantly in body proportions, fin morphology, or numbers of body myomeres but do differ significantly in pigmentation patterns on the head, nape, dorsal body midline, and numbers of subcaudal melanophores. A developmental series of S. mentella is described in terms of morphometry, meristics, occurrence of head spines, and pigmentation patterns and compared to previously published data on Sebastes spp. from other areas. The utility of various characters in relation to their use as identification criteria is discussed. The results of this morphological analysis support the contention that S. mentella and S. marinus larvae are more similar to each other than either of them is to S. fasciatus.