Newfoundland Banks Research Articles

Time varying M with starvation mortality in a state-space stock assessment model: Part 2: Atlantic cod (Gadus morhua) on the southern Grand Bank of Newfoundland

State-space models are now a common tool for modeling time-varying ecological phenomena. This extends to state-space stock assessment models (SSAMs), recognized as pivotal components within the evolving landscape of next-generation stock assessment methodologies. Though methods are rapidly evolving, the estimation of time-varying rates of natural mortality (M) remains a challenge, and the sensitivity of stock assessments and management advice to assumed M values underscores the pressing need for improved estimation methods. Using southern Grand Bank (SGB) Atlantic cod as a case study, we introduce a novel approach to estimate time-varying M. We first convert a length-based starvation M index into an age-based index, which we then include in an age-based SSAM to estimate two components of M: starvation M and a remainder component. This produces a new SGB cod SSAM with time-varying total stock M. This model produces a large decrease (68 %) in the size of the model process errors (i.e., their standard deviation) and better fit compared to a model that did not account for time-varying M, indicating that the starvation M index improves our model of stock productivity. By leveraging readily available information on fish body condition and the proportion of fish in really poor condition, the proposed methods offer a valuable solution to the challenges associated with estimating time-varying M. The proposed methods offer a tractable solution to the common struggles associated with quantifying changes in fish productivity, which is crucial for the management of dynamic systems.

At the grand Newfoundland bank and Flemish cap bank

In this paper an overview of multi-year catch dynamics for 2001–2022 and main fishery objects exploitation rates is presented, for two banks located in the northwest part of Atlantic Ocean outside of the Exclusive Economic Zones and included in an international regulatory area. An analysis of Russian quotes realization rate in the mentioned area is performed, catch dynamics for Russian and international fishery is shown, both for exploited and less-exploited stocks.

Limited temporal variability in natural mortality for juvenile American plaice on the Grand Bank of Newfoundland

Increases in natural mortality have been suggested as a potential driver for both the collapse and lack of recovery for the American plaice (Hippoglossoides platessoides) population on the Grand Bank of Newfoundland in NAFO Divisions 3LNO. However, natural mortality is among the most difficult parameters to estimate since it can be confounded with other parameters and model misspecifications. One method used to avoid this confounding involves modeling unfished components of a population where total mortality and natural mortality are equal. Here, we use a state-space metapopulation dynamics model to investigate whether there is evidence that natural mortality rates for unfished juvenile American plaice have varied since the population collapse. In addition, our model examined the degree of synchrony in age-1 recruitment signals between each management Division. The best fitting model included temporal variability in natural mortality rates, but estimates did not frequently differ from zero. This indicates that change in natural mortality rates is not an important driver of current juvenile 3LNO American plaice stock dynamics. Instead, this model identified that juvenile stock dynamics were mainly affected by variations in age-1 recruitment. Furthermore, a correlation analysis of the temporal variations in recruitment showed that trends were somewhat dissimilar between NAFO Divisions 3L and 3NO. Overall, although increases in M have been suggested by recent studies, we did not find strong evidence for this in juvenile fish.

Natural mortality diagnostics for state-space stock assessment models

Stock assessment models often require an external estimate of the natural mortality rate (M) that is usually assumed to be the same for all ages and years in the model. Although the fixed M assumption can be a major oversimplification, model diagnostics (e.g. profile likelihoods) that can help provide an understanding of how the choice of M affects model fit are often not used in practice. In the state-space setting, model diagnostics are especially complicated because of the complex dependencies in the data caused by process errors. To get a better understanding of the effect of broad changes in M across all ages and years on the state-space model fit, we develop new methods that provide profile likelihoods for individual data sources (surveys, landings, age compositions) by decomposing the state-space integrated likelihood. We also use local influence diagnostics to assess the influence of age and year specific changes in M on model fit. We jointly call these methods M diagnostics and apply them to a case study for American plaice (Hippoglossoides platessoides) on the Grand Bank of Newfoundland. The M diagnostics indicate that most input data sources are fit better with a higher M in recent years. We suggest that M diagnostics should be routinely examined when formulating an assessment model.

A state-space stock assessment model for American plaice on the Grand Bank of Newfoundland

A state-space stock assessment model for American plaice on the Grand Bank of Newfoundland

Geology and prospects of oil and gas bearing of east — Canadian continental margins

At the limit of the East-Canadian continental margin there are three oil and gas regions from north to south: Labrador Sea shelves, margins of the Great Newfoundland Bank and the continental margin of Nova Scotia. In each of these distinguishing regions are a number of sedimentary basins completely plunging under the water. At the shelf of Labrador Sea distinguishing the following large sedimentary basins: Saglek, Hopdale and Havke, at the margin of Newfoundland Bank it is known the basins: Jeanne d’Arc, Flemish Pass and Orphan. At the Nova Scotia shelf there are Nova Scotian and Sable basins. It is remarkable at the lofty latitude like of Labrador Sea region the age of the productive sediments beginning from more ancient rocks (Paleozoic), than in basins situated in law latitude (Mesozoic). In consequence of this the stratigraphy diapason of oil and gas bearing of the north latitude is considerably wide. The prospect of oil and gas bearing in all region is related principally with continental slopes and turbidites sediments in its. Late Jurassic and early Cretaceous reservoirs would be the aim for deep drilling sediments. Wide distribution of late Cretaceous and early Tertiary prospects reservoirs of oil and gas is quite really so far as they are bedded in the shallow horizons. Also the prospect of oil and gas bearing at the margin of the basin is related to late Cretaceous and Tertiary sediments, to deposits of fan and diapirs salt.

Epibenthic assemblages of the Tail of the Grand Bank and Flemish Cap (northwest Atlantic) in relation to environmental parameters and trawling intensity

The structure, composition and distribution of epibenthic invertebrate assemblages on the Tail of the Grand Bank of Newfoundland and Flemish Cap (northwest Atlantic) were sampled using depth-stratified trawls. Faunal analysis of 152 uniquely identified taxa produced hierarchical synoptic tables of species associations with diagnostic indicators based on species fidelity. Twelve spatially coherent epibenthic megafaunal assemblages were identified, each with relatively sharp faunal boundaries and unique species attributes. These assemblages were shown a posteriori through ANOSIM to have statistically different species compositions, and were nested within three major regional-scale faunal groups: (I) the continental shelf of the Tail of the Grand Bank, typified by the sea cucumber Cucumaria frondosa and the sand dollar Echinarachnius parma; (II) the upper slope of the Grand Bank and top of Flemish Cap, typified by the sponges Radiella hemisphaerica and Iophon piceum and the sea star Ceramaster granularis; and (III) the lower slope of the Grand Bank and Flemish Cap, typified by the sea urchin Phormosoma placenta, and the sea pens Anthoptilum grandiflorum and Funiculina quadrangularis. Comparisons with literature on benthic species associations from a half century ago suggest that the assemblages identified herein have persisted in the area at least for decades. Detrended correspondence analysis (DCA) identified a well-defined biological gradient along the first axis with very high species turn-over. Ten environmental variables (including Trawling Intensity) were significantly correlated with the ordinated data. At one extreme the continental shelf faunal group (I) was associated with shallow depth (mostly, less than 200m), coarse sediments and cold and fresh water associated with the Labrador Current. At the other extreme the lower slope faunal group (III; stations below 500–600m throughout the study area) was strongly associated with deep water, muddy sediments, and warmer and saltier water. Conditional tests under a step-wise model identified the percentage of mud as having the greatest explanatory power (40%) of the tested environmental variables. Trawling Intensity explained 11% of the variation in the full data set in marginal tests. Species richness in the deep water assemblages (Cluster III) was significantly and negatively correlated with fishing intensity. The species most directly associated with high trawling intensity in the DCA were the hard-shelled scavenging and predatory gastropods and a thick-shelled bivalve, consistent with expectations based on the trawling impact literature. Our study fills a critical knowledge gap in this important fishing area, and our novel regional-scale maps of the epibenthic assemblages will facilitate the development of ecosystem-based models linking benthic and pelagic systems and inform biodiversity conservation.

Multilocus phylogeography and population structure of common eiders breeding in North America and Scandinavia

Aim Glacial refugia during the Pleistocene had major impacts on the levels and spatial apportionment of genetic diversity of species in northern latitude ecosystems. We characterized patterns of population subdivision, and tested hypotheses associated with locations of potential Pleistocene refugia and the relative contribution of these refugia to the post-glacial colonization of North America and Scandinavia by common eiders (Somateria mollissima). Specifically, we evaluated localities hypothesized as ice-free areas or glacial refugia for other Arctic vertebrates, including Beringia, the High Arctic Canadian Archipelago, Newfoundland Bank, Spitsbergen Bank and north-west Norway. Location Alaska, Canada, Norway and Sweden. Methods Molecular data from 12 microsatellite loci, the mitochondrial DNA (mtDNA) control region, and two nuclear introns were collected and analysed for 15 populations of common eiders (n = 716) breeding throughout North America and Scandinavia. Population genetic structure, historical population fluctuations and gene flow were inferred using F-statistics, analyses of molecular variance, and multilocus coalescent analyses. Results Significant inter-population variation in allelic and haplotypic frequencies were observed (nuclear DNA FST = 0.004‐0.290; mtDNA FST = 0.051‐0.927). Whereas spatial differentiation in nuclear genes was concordant with subspecific designations, geographic proximity was more predictive of inter-population variance in mitochondrial DNA haplotype frequency. Inferences of historical population demography were consistent with restriction of common eiders to four geographic areas during the Last Glacial Maximum: Belcher Islands, Newfoundland Bank, northern Alaska and Svalbard. Three of these areas coincide with previously identified glacial refugia: Newfoundland Bank, Beringia and Spitsbergen Bank. Gene-flow and clustering analyses indicated that the Beringian refugium contributed little to common eider post-glacial colonization of North America, whereas Canadian, Scandinavian and southern Alaskan post-glacial colonization is likely to have occurred in a stepwise fashion from the same glacial refugium. Main conclusions Concordance of proposed glacial refugia used by common eiders and other Arctic species indicates that Arctic and subarctic refugia were important reservoirs of genetic diversity during the Pleistocene. Furthermore, suture zones identified at MacKenzie River, western Alaska/Aleutians and Scandinavia coincide with those identified for other Arctic vertebrates, suggesting that these regions were strong geographic barriers limiting dispersal from Pleistocene refugia.

Estimating exploitation rates of migrating yellowtail flounder (Limanda ferruginea) using multistate mark–recapture methods incorporating tag loss and variable reporting rates

Multistate mark–recapture models can be used to model migration through stratification of the study area into states (location). However, the incorporation of both tag loss and reporting rates is new to the multistate paradigm. We develop a migration model for fish that incorporates tag loss and reporting rates but has as its primary purpose the modelling of exploitation and natural mortality rates. This model is applied to a 2000–2004 yellowtail flounder ( Limanda ferruginea ) tagging study on the Grand Bank of Newfoundland, Canada. We found that exploitation rates varied over both location and years, ranging from 0.000 to 0.047. Migration into the centre of the Grand Bank (state 2) was three times higher than migration out. The estimate of the instantaneous annual natural mortality rate was 0.256, which is equivalent to an annual survival rate of 0.880. We describe how these mortality estimates will be quite valuable in specifying an assessment model for this stock.

Too Big to Fail? The Newfoundland Bank Crash of 1894

Summary/Zusammenfassung Too Big to Fail? The Newfoundland Bank Crash of 1894 In the Newfoundland Bank Crash of 1894, the commercial banks in a duopolistic loan market both went under simultaneously. The banking system was “free”, as central bank, deposit insurance, and lender of last resort were all absent. The objective of this study is to shed light on our understanding of the working of a duopolistic bank loan market and to provide lessons for banking regulation and policies, the too-big-to-fail doctrine in particular. Our regression results suggest a price leader-follower relationship before 1887, and a drastic decline in exports that year triggered a regime change into simultaneous loan expansion that ultimately precipitated a systemic banking failure. The short-lived liquidity crisis, however, was alleviated by entries of Canadian banks. More important, results of intervention analysis suggest that the Crash did not have any significant adverse impact on the fishery sector, the pillar of the single-...

Le courant du Labrador et quelques-unes de ses conséquences géographiques

Le courant du Labrador et quelques-unes de ses conséquences géographiques

Is By-catch Mortality Preventing the Rebuilding of Cod (Gadus morhua) and American Plaice (Hippoglossoides platessoides) Stocks on the Grand Bank?

Cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) on the Grand Bank of Newfoundland supported substantial commercial fisheries for extensive periods in the past. Both stocks declined and have been under fisheries moratoria since 1994, but continue to be harvested as by-catch in other directed fisheries on the Grand Bank. For each stock, a precautionary spawning stock biomass limit reference point (Blim) has been established by the Scientific Council of the Northwest Atlantic Fisheries Organization. In this study, stochastic simulations were used to evaluate the probability distributions of the time horizons required to rebuild each of the two stocks to above Blim. A range of by-catch mortality levels, recruitment models, and body growth and maturation rates were applied in the simulations. Uncertainty in the estimates of the numbers at age in the last assessed year and uncertainty in future recruitment were also incorporated within the simulations. If by-catches are not substantially reduced, the modelling results indicate there is virtually zero probability of attaining Blim by 2020 for either the cod or American plaice stocks on the Grand Bank.

Decadal Changes in the Ocean Climate in Newfoundland and Labrador Waters from the 1950s to the 1990s

A review of decadal changes in the ocean climate in NAFO waters adjacent to Newfoundland and Labrador is presented based on standard station and section data and data from fishery resource assessment surveys. Both the annual trends and decadal means are examined for the decades of the 1950s to the 1990s. The analysis indicates that the 1950s and particularly the 1960s were the warmest decades during the latter half of the 20th century and the 1990s represent the third consecutive decade with below normal temperatures on the Newfoundland Shelf. The decadal mean salinity indicate that the magnitude of negative salinity anomaly on the inner Newfoundland Shelf during the 1990s was comparable to that experienced during the 'Great Salinity Anomaly' of the early 1970s. In addition, the decade of the 1990s has experienced some of the most extreme variations since measurements began during the mid-1940s. Ocean temperatures ranged from record low values during 1991 to record highs during 1999 in many areas, particularly on the Grand Bank of Newfoundland. The potential impact of the changes in ocean climate during the past several decades on marine production in Newfoundland waters is discussed.

Patterns of seasonal dynamics of remotely sensed chlorophyll and physical environment in the Newfoundland region

The patterns of seasonal variation of surface plant pigment concentration (Chl) in the Newfoundland region were studied using remotely sensed data from the coastal zone color scanner (CZCS) (1978–1986) and sea-viewing wide field-of-view sensor (SeaWiFS) radiometers (from September 1997 to October 1999). Sea surface temperature (SST) data obtained from AVHRR radiometers and sea surface height (SSH) data obtained from TOPEX/POSEIDON altimeter were then used to interpret the observed patterns in terms of physical factors which influence the growth of phytoplankton. Stable seasonal cycles of both SST and Chl were observed in all parts of the region under study (Labrador Current, Newfoundland Bank, Flemish Pass, frontal zone between Gulf Stream and Labrador Current). The SST values in the summer season during the 2 years under study (September 1997–October 1999) were up to 3°C higher as compared to climatologically averaged values. The seasonal pattern of Chl in the Labrador Current zone was typical of Arctic regions (one maximum in summer); in the Gulf Stream zone, it was typical of subtropical regions (smoothed maximum during winter); and in between these zones, the pattern was typical of mid-latitudes (two maxima, in spring and autumn). Over the Grand Newfoundland Bank, the seasonal pattern had one spring maximum, typical of shallow regions. The patterns of seasonal phytoplankton cycles resulted mainly from the meteorological factors influencing water stratification; the latter seems to be a crucial factor in either light or nutrient limitation of phytoplankton growth.

Seabird migration in the Canadian northwest Atlantic Ocean: moulting locations and movement patterns of immature birds

All seabirds in the northwest Atlantic Ocean migrate, but timing and routes are not well understood. We evaluate existing knowledge on seabird migration with data from the Programme intégré de recherches sur les oiseaux pélagiques (PIROP) data base, using observations of immature and moulting seabirds to track migration of the following species: Northern Fulmar (Fulmarus glacialis), Greater Shearwater (Puffinus gravis), Northern Gannet (Morus bassanus), Herring Gull (Larus argentatus), Iceland Gull (Larus glaucoides), Glaucous Gull (Larus hyperboreus), Great Black-backed Gull (Larus marinus), Black-legged Kittiwake (Rissa tridactyla), and Thick-billed Murre (Uria lomvia). The distributions of immature and moulting birds show strong seasonal patterns in the northwest Atlantic, and new transition zones and clear biological borderlines for seabird distribution were found. New data on timing and location of moulting Thick-billed Murres are presented. The southern Labrador Banks and Grand Banks (Thick-billed Murre, Northern Fulmar) and southeast Newfoundland and Georges Bank (Greater Shearwater) were identified as moulting grounds. In terms of marine conservation the following areas seem to be important for part of the life cycle of the species named: western Greenland, Cape Cod, Grand Banks, Labrador Banks, southwest Newfoundland, and the Grand Manan area.

The effect of stock abundance on range contraction of yellowtail flounder ( Pleuronectes ferruginea) on the Grand Bank of Newfoundland in the Northwest Atlantic from 1975 to 1995

Research vessel surveys showed that yellowtail flounder ( Pleuronectes ferruginea) on the Grand Bank, off New-foundland in the Northwest Atlantic, declined in abundance between the 1970s and the mid 1990s. The northern limit of distribution decreased substantially in the late 1980s and early 1990s, coincident with large declines in population abundance and a decrease in bottom water temperatures. This range contraction continued into the mid 1990s, despite a stabilization of the population size and a reversal of the cooling trend. In 1995, this species was rarely found on the northern Grand Bank. The area west of the Southeast Shoal on the southern Grand Bank had relatively high densities of yellowtail flounder throughout the period studied. The area occupied by the stock was positively correlated with stock abundance from surveys, but not with bottom temperatures from these same surveys. We conclude that the contraction in the area of distribution for this stock to the preferred habitat around the Southeast Shoal is primarily a function of low stock size, which resulted from increased fishing activity in the mid to late 1980s.

Was an increase in natural mortality responsible for the collapse off northern cod?

The collapse of the northern Atlantic cod (Gadus morhua) fishery off southern Labrador and to the northern Grand Bank of Newfoundland, once the largest cod fishery in the world, was a social and economic disaster for the region. An analysis of traditional catch-at-age data in conjunction with research surveys, which assumed that research survey estimation errors of abundance by age and year were independent, led assessment biologists to the conclusion that the collapse was caused by an increase in natural mortality in the first half of 1991. We constructed a statistical model to test this hypothesis. The results do not support the hypothesis. There is ambiguous evidence that natural mortality has increased since 1991; however, these results are found only in a model that has extraordinary patterns in the residuals. Our analysis suggests that even if natural mortality has been higher in recent years (as estimated using a model with correlated errors for research surveys), overfishing was sufficiently high to cause a collapse of this population. We also demonstrate that the usual assumption that estimation errors from research trawl surveys are independent is not valid, and can lead to invalid inference and unreasonable estimates of abundance.

Biogeography of Groundfish Assemblages on the Grand Bank

A 16-year time series (1971–82, 1984–87) of data from spring groundfish surveys was analyzed to identify, describe, and map six broad zoogeographic areas on the Grand Bank of Newfoundland, each characterized by a relatively homogeneous and persistent biological composition (a fish assemblage). The boundaries of these areas were strongly aligned with bottom depth and oceanographic features, confirming previous evidence from worldwide studies on the major determinants of the distribution of groundfish on continental shelves. Consideration of their overall biological coherence allowed a merging and reformulation of the original six assemblage areas into four coherent zoogeographic regions. Analysis of catch rates in the two major regions so defined suggested that species composition was relatively stable over time. Whether the Grand Bank assemblages correspond to groups of functionally-linked fishes remains an open question of considerable practical and theoretical interest. The definition of areas where species broadly recur and overlap provides a useful spatial scale for studies at the community level on the Grand Bank and has implications for multispecies management.

Factors influencing distribution of juvenile yellowtail flounder ( Limanda ferruginea) on the grand bank of Newfoundland

On the Grand Bank, off the coast of Newfoundland, yellowtail flounder is at its northern limit in abundance. The population is relatively sedentary and has formed the basis of a traditional trawler fishery since the middle 1960s. However, very little is known about this species' early life history stages and ecology. Beginning in 1985, bottom trawl surveys have been conducted annually to determine distribution and abundance of juvenile yellowtail flounder on the Grand Bank. It was found that both juveniles and adults maintained their shallow water depth distribution despite wide fluctuations in temperature. Based on the analyses of the distribution of age-1 group and older juveniles (up to 4 years) and incorporating historical information on egg and larval surveys, physical oceanography and substrate type in the region it was found that all early life history stages were retained in the same geographic area, on and adjacent to the Southeast Shoal on the southern Grand Bank. It is suggested that passive retention of eggs and larvae is related to a weak current regime on the southern Grand Bank. Age-1 group and older juveniles were consistently found on a sandy substrate in the same area, indicating that sediment size is an important factor influencing distribution. These observed patterns of distribution of eggs, larvae, and juveniles points to the Southeast Shoal area as being an oceanic nursery site for Grand Bank yellowtail flounder. But unlike the well-published North Sea coastal nurseries, this oceanic nursery also contains newly settled juveniles, older juveniles, and adults.

Feeding behaviour of the American plaice ( Hippoglossoides platessoides) on the southern Grand Bank of Newfoundland

This study shows that on the southern Grand Bank, the diet of American plaice between 40 and 55 cm long mainly consists of Ammodytes dubius and brittle stars; the third most important prey is Mallotus villosus. To analyse feeding intensity during a daily and annual cycle, we used three different indices: the mean weight fullness index, the percentage of empty stomachs and the daily ration. The daily feeding intensity shows maxima related to the kind of prey consumed. A. dubius is consumed in larger amounts late in the day, between 18.00 and 24.00 h; M. villosus and brittle stars are preyed upon more intensely between 12.00 and 18.00 h. The maximum feeding activity is in April, with a summer period of relatively high values, followed by autumn and winter when feeding intensity is low. The American plaice shows flexibility in its feeding behaviour which allows it to consume its prey in larger amounts when they are more accessible; this accessibility may be the cause of its daily and annual feeding cycle.