Search

Aim: Previous analyses of marine fish species richness based on presence-absence data have shown changes with latitude and average species size, but little is known about the underlying processes. To elucidate these processes we use metabolic, neutral and descriptive statistical models to analyse how richness responds to maximum species length, fish abundance, temperature, primary production, depth, latitude and longitude, while accounting for differences in species catchability, sampling effort and mesh size. Data: Results from 53,382 bottom trawl hauls representing 50 fish assemblages. Location: The northern Atlantic from Nova Scotia to Guinea. Time period: 1977–2013. Methods: A descriptive generalized additive model was used to identify functional relationships between species richness and potential drivers, after which nonlinear estimation techniques were used to parameterize: (a) a ‘best’ fitting model of species richness built on the functional relationships, (b) an environmental model based on latitude, longitude and depth, and mechanistic models based on (c) metabolic and (d) neutral theory. Results: In the ‘best’ model the number of species observed is a lognormal function of maximum species length. It increases significantly with temperature, primary production, sampling effort, and abundance, and declines with depth and, for small species, with the mesh size in the trawl. The ‘best’ model explains close to 90% of the deviance and the neutral, metabolic and environmental models 89%. In all four models, maximum species length and either temperature or latitude account for more than half of the deviance explained. Main conclusions: The two mechanistic models explain the patterns in demersal fish species richness in the northern Atlantic almost equally well. A better understanding of the underlying drivers is likely to require development of dynamic mechanistic models of richness and size evolution, fit not only to extant distributions, but also to historical environmental conditions and to past speciation and extinction rates, Sí

Vertical divergence in marine organisms is being increasingly documented, yet much remains\ud to be done to understand the role of depth in the context of phylogeographic reconstruction\ud and the identification of management units. An ideal study system to address this issue is the\ud beaked redfish, Sebastes mentella – one of four species of “redfish” occurring in the North\ud Atlantic – which is known for a widely-distributed “shallow-pelagic” oceanic type inhabiting\ud waters between 250 and 550m, and a more localised “deep-pelagic” population dwelling\ud between 550 and 800m, in the oceanic habitat of the Irminger Sea. Here, we investigate the\ud extent of population structure in relation to both, depth and geographic spread of oceanic\ud beaked redfish throughout most of its distribution range. By sequencing the mitochondrial\ud control region of 261 redfish collected over a decadal interval, and combining 160 rhodopsin\ud coding nuclear sequences and previously genotyped microsatellite data, we map the existence\ud of two strongly divergent evolutionary lineages with significantly different distribution\ud patterns and historical demography, and whose genetic variance is mostly explained by depth.\ud Combined genetic data, analysed via independent approaches, are consistent with a late\ud Pleistocene lineage split, where segregation by depth likely resulted from the interplay of\ud climatic and oceanographic processes with life-history and behavioural traits. The on-going\ud process of diversification in North Atlantic S. mentella may serve as an “hourglass” to\ud understand speciation and adaptive radiation in Sebastes and in other marine taxa distributed\ud across a depth gradient.

Beaked redfish inhabits North Atlantic waters in the depth range 100–950 m, over the continental shelf, slope and the open ocean. Individuals can live demersal or pelagic, at various stages of their life cycle. The geographical distribution of the species extends to most of the Atlantic waters from Newfoundland and the Labrador basin in the west to the Barents Sea in the east. Monitoring beaked redfish is challenging because of the species wide geographical distribution and large scale migrations; deep distribution, which complicates trawling and hydroacoustic surveys; difficulties with tagging; and persistent difficulties in taxonomic identification. These challenges make it a particularly problematic species to observe with conventional research methods. We review these key challenges and provide recommendations for the coordinated observation of Sebastes mentella in the North Atlantic that would best contribute to the assessment and ecological research on this species.

Elevated ocean temperatures have been predicted to lead to a poleward shift in the latitudinal distribution ranges of fish species. Different responses of fish species to increased temperatures might lead to changes in assemblage structure and local species richness. In this study, the assemblage structure and diversity of groundfish in Icelandic waters were examined using data from a standardized groundfish survey conducted annually in 1996–2007. We used hierarchical cluster analysis to define assemblages in two time periods and canonical correspondence analysis to explore the relationships between the assemblages and temperature, depth, latitude, longitude and year. We further used two estimates of diversity, species richness and the Shannon index. Four major species assemblages were identified. Assemblages in the hydrographically stable deep waters north of the country were consistent during the study, while assemblage structure in the more variable shallow waters underwent some changes. For this period of generally increasing sea temperature, the canonical correspondence analysis also revealed a shift towards species representative of warmer temperatures. Diversity was shown to be highly variable both temporally and spatially, and also to vary with depth and temperature. Species richness increased with temperature and time southwest of the country, but decreased northeast of the country. The different trends detected between the northern and southern areas illustrate the importance of performing analyses at the most appropriate scale.

Stefánsson, M. Ö., Reinert, J., Sigurðsson, Þ., Kristinsson, K., Nedreaas, K., and Pampoulie, C. 2009. Depth as a potential driver of genetic structure of Sebastes mentella across the North Atlantic Ocean. – ICES Journal of Marine Science, 66: 680–690. A primary question that remains to be answered about the fishery for Sebastes mentella is whether it exploits several stocks within the North Atlantic Ocean. To address this issue, 1240 redfish were collected from several fishing grounds in late 2006 and early 2007 and genotyped at 12 microsatellite loci. Contemporary allele frequencies were compared with archived data to examine the temporal stability of the genetic structure. The analyses all revealed the presence of three genetically distinguishable clusters, which persisted throughout the study period, suggesting that the genetic structure detected is genuine. Cluster D included fish from the deep Irminger Sea and west Faroe Islands, and Cluster I included fish only from the Icelandic shelf. All other fish grouped in a third cluster (S). Further analyses revealed that the genetic pattern observed was not primarily attributable to isolation by distance, but rather to depth distribution.

The deepwater redfish Sebastes mentella has a wide distribution in the North Atlantic Ocean. In the Irminger Sea, there is evidence for two phenotypes (deep-sea and oceanic) of deepwater redfish. The two phenotypes have overlapping geographic distributions but differ in depth preferences. There are two hypotheses on deepwater redfish stock structure in the Irminger Sea. One suggests that mature individuals of a single stock segregate according to size and age and therefore that the phenotypes represent different life stages of the same stock. The other hypothesis suggests that there are two different stocks and that these stocks segregate mainly according to depth. Additionally, it is not clear whether the fish of the deep-sea phenotype in the Irminger Sea and those on the Icelandic continental shelf represent one stock. Analysis of genetic variability at eight allozyme markers in 1,763 deepwater redfish from 26 samples collected at different depths in the Irminger Sea and the Icelandic continent...

This paper describes the pelagic fishery for deep-sea redfish, Sebastes mentella, in the Irminger Sea and adjacent waters, from the start of commercial exploitation of the resource in 1982. The information prior to 1990 is mostly based on ICES reports and unpublished data, but from 1990, logbook data from a joint database on a haul-by-haul basis from the Faroe Islands, Germany, Greenland, Iceland, Norway, and Russia are used to describe the fishery. The nations listed are the main ones operating on the resource, catching about 80% of the total reported catches in recent years. The logbook data include inter alia information on positions, catch, and trawling time. Additionally, some nations also include information on gear type and size of gear used, and in some cases also trawling depth. Length distributions of commercial catches from various fleets for the whole period have also been collected, and are shown along with information on the mean lengths in the catches for the whole period. The paper therefore provides a detailed overview of the fishery in terms of area, season, depth, and size composition of the catches from the start of the pelagic fishery to the present, allowing better understanding of the behaviour of the fishery and, in turn, providing improved background for assessment of the resource in the future.

Sequence variation of a 250–bp (base pair) fragment of the mitochondrial cytochrome b gene has been studied using polymerase chain reaction and direct sequencing of 519 Atlantic cod Gadus morhua from Iceland and 78 cod from Greenland. Twenty-four variable nucleotide sites, mostly silent, define 34 haplotypes. The amount of variation is high (?C=0·73, π=0·52 per 100 bp) with five haplotypes at polymorphic frequencies in Iceland and a number of widely dispersed rather rare haplotypes. A tree of genetic relationships among haplotypes has considerable homoplasy yet it is relatively shallow implying a high turnover of variants of the polymorphism. Net nucleotide genetic divergences among localities are nil. Geographic locality overall area, and inshore/offshore comparison explain none of the variation in an AMOVA, all the variation is among individuals and a null hypothesis of non-differentiation of haplotype frequencies among localities or overall areas cannot be rejected. A temporal year-class effect is found. The evolutionary difference between Greenland and Iceland cod is not significant and the percentage of variation accounted for by the Greenland/Iceland difference is half of what a temporal effect within Iceland explains. There is no evidence for considering the cod at Greenland and Iceland to consist of separate evolutionary units and the question of separate management units must address the lack of diagnostic genotypes and evidence for gene flow from clinal variation.

This study provides evidence of the influence of hydrography and large scale ocean circulation on the geographical distribution of beaked redfish (Sebastes mentella) in the Irminger Sea on the interannual time scale, from 1992 to 2011. The results reveal the average relationship of adult pelagic redfish to their physical habitat from 100 to 800 m depth: the most preferred latitude, longitude, depth, temperature and salinity for redfish are approximately 58°N, 41°W, 557 m, 4.5 °C and 34.87, respectively. The redfish habitat corresponds in a temperature–salinity (TS) diagram to a mixing triangle between East Greenland Current Water (EGCW), Labrador Sea Water (LSW) and Irminger Current Water (ICW). The geographical centre of mass of the redfish distribution (as revealed by acoustic fish density) indicates displacements from year to year. Changes in hydrographic conditions were investigated in detail for possible reasons for these displacements. Empirical Orthogonal Analysis reveals that maximum variations of water mass volume on an interannual time-scale in the study region correspond to ICW and LSW changes, while EGCW remains comparatively stable. Indices of redfish geographical centroid, LSW volume, ICW temperature and Subpolar Gyre (SPG) intensity suggest that the geographical redfish displacements are closely related to interannual changes of ICW modulated by the SPG intensity with a lag of 1 or 2 years. In comparison, LSW seems to have no impact on the redfish distribution at the studied depth range. The time lag between ICW and redfish displacements indicates an indirect influence of temperature on redfish. Hence, changes of chlorophyll-a (from satellite imagery), as a proxy for primary production, were used in a first approach to study the role of food availability. The analysis is based on acoustic and trawl data from nine expeditions coordinated by the International Council for the Exploration of the Sea (ICES), around 71,000 hydrographic stations from the Integrated Climate Data Center, World Ocean Database 2009 and Coriolis (among others), 60 years of circulation data from the Max-Planck Institute Ocean Model and 14 years of satellite chlorophyll-a from SeaWiFS, MODIS-Aqua and MERIS.

14 páginas, 4 figuras.--Steve Cadrin ... et al.-- Acceso avanzado online., Throughout their range, Sebastes spp. are adapted to a diversity of ecological niches, with overlapping spatial distributions of different species that have little or no morphological differences. Divergence of behavioural groups into depth-defined adult habitats has led to reproductive isolation, adaptive radiation, and speciation in the genus Sebastes. Recent genetic research, supported by life-history information, indicates four biological stocks of Sebastes mentella in the Irminger Sea and adjacent waters: a western stock, a deep-pelagic stock, a shallow-pelagic stock, and an Iceland slope stock. Congruent differences in fatty acids and parasites suggest that these genetically distinct populations are adapted to disparate trophic habitats in pelagic waters (shallower and deeper than the deep-scattering layer) and in demersal habitats on the continental slope. Morphology of pelagic forms is also more streamlined than demersal forms. Although genetic differences and evidence for reproductive isolation are clear, these populations appear to share common nursery habitats on the Greenland shelf. We propose a redefinition of practical management units near the Irminger Sea based on geographic proxies for biological stocks and minimizing mixed-stock catches according to the spatial patterns of the recent fishery.

Previous work has identified maximum body size as an important functional life-history trait for marine fish species influencing their growth, natural mortality, recruitment, and resilience to exploitation. We use data from a large number of scientific bottom trawl surveys from West Greenland to the Adriatic Sea to compare the distribution of species richness and average number of individuals caught per hour of trawling across different fish communities. Although highly variable the data reveal several overall patterns. Going from north to south the total species richness and the total number of individuals caught per hour of trawling increase, while the average log maximum length of the individuals shows a consistent decrease. In contrast the average log maximum length of the species recorded remains stable throughout the area. The mesh size in the codend and the total number of hauls are significant covariates. We briefly discuss to what extent these patterns reflect differences in fish community structure with latitude or are generated by differences in levels of exploitation.