Gulf Of St. Lawrence Research Articles

A new high-resolution Coastal Ice-Ocean Prediction System for the East Coast of Canada

The Coastal Ice Ocean Prediction System for the East Coast of Canada (CIOPS-E) was developed and implemented operationally at Environment and Climate Change Canada (ECCC) to support a variety of critical marine applications. These include support for ice services, search and rescue, environmental emergency response and maritime safety. CIOPS-E uses a 1/36° horizontal grid (~ 2 km) to simulate sea ice and ocean conditions over the northwest Atlantic Ocean and the Gulf of St. Lawrence (GSL). Forcing at lateral open boundaries is taken from ECCC’s data assimilative Regional Ice-Ocean Prediction System (RIOPS). A spectral nudging method is applied offshore to keep mesoscale features consistent with RIOPS. Over the continental shelf and GSL, the CIOPS-E solution is free to evolve according to the model dynamics. Overall, CIOPS-E significantly improves the representation of tidal and sub-tidal water levels compared to ECCC’s lower resolution systems: RIOPS (~ 6 km) and the Regional Marine Prediction System – GSL (RMPS-GSL, 5 km). Improvements in the GSL are due to the higher resolution and a better representation of bathymetry, boundary forcing and dynamics in the upper St. Lawrence Estuary. Sea surface temperatures show persistent summertime cold bias, larger in CIOPS-E than in RIOPS, as the latter is constrained by observations. The seasonal cycle of sea ice extent and volume, unconstrained in CIOPS-E, compares well with observational estimates, RIOPS and RMPS-GSL. A greater number of fine-scale features are found in CIOPS-E with narrow leads and more intense ice convergence zones, compared to both RIOPS and RMPS-GSL.

Modelling the complete life cycle of an arctic copepod reveals complex trade-offs between concurrent life cycle strategies

Calanus hyperboreus is a large-bodied, biomass dominant species that performs a crucial ecosystem energy transfer by converting the spring phytoplankton bloom into lipid reserves that fuel the higher trophic levels of the Gulf of St. Lawrence (GSL) pelagic ecosystem, including the critically endangered North Atlantic right whale (Eubalena glacialis). Given that the GSL, the southernmost core habitat of C. hyperboreus, is undergoing rapid warming, developing a population model allows us to synthesize existing knowledge of the species, and to examine the species response to environmental conditions. To simulate the multi-year life cycle in the northwest GSL, model equations are implemented for ingestion, assimilation, respiration, egg production, stage development, mortality, and vertical migration behaviors including dormancy entry and exit. The 1-D particle-based model predicts the evolution of individual stage, structural mass, lipid, age, sex, abundance, and egg production, as well as the seasonal evolution of the population structure in the northwest GSL. Individual lipid-based thresholds inform the timing of ontogenetic vertical migration. Life cycle targets defined from a literature review are used to guide model parameterization and assess its performance. The simulated population structure, phenology, and size at stage are generally consistent with observations. Under 10 years of repeat year forcing, the model simulates a quasi-stable overwintering population composed of late stages CIV, CV and CVI. Observations suggest that stage CIV is the first overwintering stage in the GSL, and point to the occurrence of iteroparous females. Using the model, the relative success of diverse dormancy and reproductive phenotypes are explored. Second reproduction females reproduce earlier in winter than first reproduction females, with implications for the ability of the new generation to match the spring bloom and accumulate sufficient lipid to overwinter as stage CIV. Without iteroparity, the time window of reproduction contracts and the population is reduced, underscoring the role of a flexible multi-year life cycle in population success.

Drivers of growth in strong year classes of the deepwater redfish (Sebastes mentella) population from the Gulf of St. Lawrence derived from otolith increment-based growth chronologies.

The case of the deepwater redfish (Sebastes mentella) in the Gulf of St. Lawrence (GSL) is a compelling example of drastic fluctuations in annual recruitment strength, characteristic of spasmodic stocks. After three decades of low abundance, the emergence of three consecutive strong year classes in 2011-2013 resulted in an unprecedented increase in biomass. In spasmodic stocks such as GSL redfish, strong year classes sustain both the biomass and catch for decades. Therefore, understanding the growth dynamics of these cohorts is essential. In the present study, we reconstructed the annual growth rates of redfish using otolith increment-based annual chronology and investigated the drivers of growth variation in redfish strong year classes of the early 2010s and early 1980s. Stock biomass was identified as the main extrinsic driver of redfish growth, suggesting intense competition for food at high conspecific density. Warming of deep waters in the GSL, where adult redfish settle, positively correlated with individual growth. However, recent warming of the cold intermediate layer showed a negative correlation with redfish growth, likely related to the shrinking of the habitat this water mass provides for various redfish cold-water prey rather than to a direct effect of temperature. Reconstruction of redfish annual growth trajectories from birth to capture emphasized the importance of carryover effects in the growth potential of strong year classes. This work provided an important first outlook of the factors driving growth variation in GSL redfish spasmodic stock and explored midterm consequences of density-dependent pressures on biological parameters of the population.

Mixing behaviour and sources of Ag, Pd, and other trace elements in the Estuary and Gulf of St. Lawrence under winter conditions

The marine chemistry of platinum group elements is poorly documented despite robust evidence of their widespread emissions and deposition around the globe. Here, we report the concentrations and discuss the geochemical behaviours of Ag, Pd and other trace and ultra-trace elements in the Estuary and Gulf of St. Lawrence (EGSL). We highlight the contrasting mixing behaviours of these elements, i.e., conservative (Cd, Re) vs. non-conservative (Ag, Pd), in samples collected during the winter and under ice-covered conditions. We ascribe the contrasting geochemical behaviour of these elements to their differential affinity for reactive surfaces carried into the estuary from the frozen watersheds. We also report an increase of the concentrations of Ag (up to 40 pmol L−1), Pd (up to 10 pmol L−1) and Pt (up to 0.4 pmol L−1) in the bottom and oxygen-depleted waters of the Gulf of St. Lawrence (GSL). A strong correlation between dissolved Pt concentrations and the stable carbon isotopic composition of the dissolved inorganic carbon (δ13C-DIC) suggests that the increased mobility of Pt may result from the aerobic mineralization of organic carbon or the oxidation of Pt-bearing organic complexes. Molar Pt/Pd ratios in the three water masses that compose the water column in the EGSL highlight a potential influence of anthropogenic sources near urban centers. The signature of continental end-members will be required to confirm the impacts of road traffic on the estuarine geochemistry of these elements.

Otoliths as chemical archives through ontogeny reveal distinct migratory strategies of Atlantic halibut within the Gulf of St. Lawrence

Abstract In marine fishes of commercial interest, defining habitat use and migration strategies through ontogeny can help better understand the structure and dynamics of harvested populations and guide their management. The present study relied on otolith chemistry to identify three contingents within the Atlantic halibut (Hippoglossus hippoglossus) stock in the Gulf of St. Lawrence (GSL). We differentiated two chemical signatures from otolith edges, one for shallow (<100 m) and another one for deep (>100 m) waters. By identifying transitions between the deep and shallow habitats, we found that most halibut display migrations from the deep waters to shallow waters during the first 3 years of life. After reaching maturity, most halibut distributing in northern regions of the GSL became full-time residents in deep areas of the GSL. In contrast, halibut found in summer on the shallow plateau of the southern GSL displayed migrating behaviour between shallow (summer) and deep (winter) waters throughout their lives, either on an annual or irregular basis. Overall, our results demonstrate that otolith chemical signatures serve as natural markers of geographically distinct marine environments, facilitating the identification and reconstruction of environmental histories of long-lived marine fishes.

Migratory movements of fin whales from the Gulf of St. Lawrence challenge our understanding of the Northwest Atlantic stock structure

Fin whales, Balenoptera physalus, are capital breeders, having the potential to separate breeding and feeding both spatially and temporally. Fin whales occur throughout the Northwest Atlantic, but stock structure and seasonal movements remain unclear. By deploying satellite transmitters on 28 individuals, we examine movement patterns within and beyond the Gulf of St. Lawrence (GSL), Canada, and challenge the current understanding of stock structure. Eight individuals left the GSL in autumn, with five tags persisting into January. Migration patterns of these whales showed considerable variation in timing and trajectory, with movements extending south to 24°N, and thus beyond the assumed distribution limit of the species in the Northwest Atlantic. A rapid return to the Scotian Shelf or Gulf of Maine was observed from several whales after incursions in southern waters, suggesting that fin whales in the Northwest Atlantic may not have a common winter destination that fits the definition of a breeding ground. Area-restricted search (ARS) behavior dominated fin whale activities during summer (92%) and fall (72%), with persistence into the winter (56%); ARS occurred at multiple locations in the GSL, Scotian Shelf and Shelf edge, and near seamounts of the North Atlantic, having characteristics consistent with foraging areas.

Spatial variability in size and lipid content of the marine copepod Calanus finmarchicus across the Northwest Atlantic continental shelves: implications for North Atlantic right whale prey quality.

Copepod size and energy content are influenced by regional and seasonal variation in temperature and food conditions, with implications for planktivorous consumers such as the endangered North Atlantic right whale (Eubalaena glacialis). Historical data (1990-2020) on Calanus finmarchicus stage CV copepodite prosome length and oil sac metrics were analyzed to determine the extent of variation in individual body size and estimated lipid and energy content in five regions of the Northwest Atlantic continental shelves [Gulf of Maine (GoM), Scotian Shelf (SS), Gulf of St. Lawrence (GSL), St. Lawrence Estuary (SLE) and Newfoundland Shelf]. Large-scale spatial patterns in size and lipid content were related to latitude, indicating that C. finmarchicus CV in the GSL and SLE were historically larger in body size, and had significantly higher lipid content compared with those in the GoM and the SS. The observed patterns of C. finmarchicus CV size and lipid storage capacity suggest that regional variation in whale prey energy content can play a role in the suitability of current and future whale foraging habitats in the Northwest Atlantic, with the larger lipid-rich individuals in the GSL providing a high-quality diet compared with those in southern areas.

A biophysical model of Calanus hyperboreus in the Gulf of St. Lawrence: Interannual variability in phenology and circulation drive the timing and location of right whale foraging habitat in spring and early summer

Since 2015, North Atlantic right whale (NARW) occurrences have considerably increased in the Gulf of St. Lawrence (GSL), likely driven by a decrease in the availability of their historically preferred prey, the lipid-rich Calanus spp. (Copepoda), in their traditional foraging habitats. In the southern GSL (sGSL) where most NARW sightings occurred in recent years, the large bodied and lipid-rich Calanus hyperboreus dominates the Calanus spp. biomass in the spring and early summer, with important interannual variability hypothesized to be driven by variations in phenology and transport. This study examined the seasonal and interannual variability of phenology and relative distribution of C. hyperboreus biomass in the sGSL during the spring and early summer from 2016 to 2019, using a 3-D coupled biophysical model. We simulated the development and advection of the new cohort of C. hyperboreus from first copepodite (CI) stages in early spring to mid-July, a period during which they enter diapause as lipid-rich fourth copepodite (CIV) stages. Our study confirmed that C. hyperboreus distribution in the sGSL is mainly influenced by transport from adjacent deeper areas through interactions between ocean circulation and early copepodite stages during the spring. Model results indicated variable numbers of simulated individuals from the Laurentian Channel were transported annually to the sGSL during their active stages, entered diapause, and were retained near the seafloor in the summer. Biophysical simulation outputs could therefore contribute to seasonal-scale advice on locations of NARW potential foraging habitat formation and improve understanding NARW seasonal dynamics in the sGSL.

Characterizing the Variability of a Physical Driver of North Atlantic Right Whale Foraging Habitat Using Altimetric Indices

Physical ocean circulation features, especially the Gaspé Current (GC) intrusion, influence the transport and aggregation of whale prey, thereby influencing the whale foraging habitat in the Gulf of St. Lawrence (GSL), Canada. We employ satellite altimetry-derived sea level anomaly (SLA) indices to monitor interannual variations in the intensity of the GC in the North Atlantic Right Whale (Eubalaena glacialis; NARW) habitat in the GSL. Measurements of surface slope and volume transport are taken from the SLA profiles along a repeating ground track of the Jason-2/3 satellites. These are employed as complementary proxies in characterizations of physical processes in the GSL. The relationship between altimetric indices and indices of zooplankton abundance are explored in the southern GSL. Results demonstrate that an altimetric index estimated from surface slope (Indexslope−half) is correlated with river discharge of the St. Lawrence River and can be utilized to infer variations in GC intensities. Time series of the altimetric indices during 2009–2021 are found to exhibit interannual and seasonal environmental variability, which influence transport into the southern GSL. As captured by the altimetric indices, these features of the surface ocean circulation can be linked to zooplankton variations in the Shediac Valley, where NARWs are frequently observed. Therefore, in linking physical drivers of ocean dynamics to the NARW foraging habitat, variations in these indices can also potentially help describe some features of the distribution patterns of NARW sightings in this area.

Spatiotemporal modelling of Greenland halibut maturation across the Northwest Atlantic

AbstractModelling life history trait variation at appropriate spatial and temporal scales is crucial for understanding population dynamics and developing effective fisheries management strategies. However, most efforts to model life history traits ignore spatial correlations and make a priori assumptions about the spatial structuring of populations, potentially clouding the ability to recognize true spatial structure. Here we develop spatiotemporal maturation models for Greenland halibut (Reinhardtius hippoglossoides) in the Northwest Atlantic, a species with large-scale movement patterns that can lead to uncertainty regarding effective stock boundaries. Our analysis using data from three Fisheries and Oceans Canada survey regions, Baffin Bay and Davis Strait in the eastern Canadian Arctic, Newfoundland and Labrador (NL), and the northern Gulf of St. Lawrence (GSL), is the first at such a large spatial scale. We also extend the traditional binary maturity status to a multinomial one that accounts for seasonal changes in maturation. Results show a decreasing temporal trend in size at maturity across the entire area. Spatial results regarding size at maturity provide new insight linking Greenland halibut south of Newfoundland (Northwest Atlantic Fisheries Organization Subdivision 3Ps) to the GSL stock rather than the NL stock. Results also highlight parts of the Davis Strait area, where size at maturity is smaller than in waters both north and south. Multinomial model results identify areas in GSL and Davis Strait that may be important for reproductive development in the summer and fall. Our analyses also reveal constraints on size at maturity that correspond with the well-known positive association between fish length and bottom depth. Broad-scale analyses of high resolution spatial patterns in life history traits, such as those performed here for Greenland halibut maturation, may identify recurrent patterns of association with environmental or habitat characteristics that might not otherwise be evident on a stock- or survey-specific basis.

Spatiotemporal variability in otolith elemental fingerprint and the potential to determine deepwater redfish (Sebastes mentella) origins and migrations in the Estuary and Gulf of St. Lawrence, Canada

Connectivity processes have major implications in defining the resiliency of fish populations to overexploitation. A preliminary estimate of population exchange rates can be done by identifying the natal origin of adult fish. In this study, otolith elemental fingerprints were used as natural marker of origins and movements of Deepwater redfish (Sebastes mentella) in the Gulf of St. Lawrence (GSL). We specifically targeted the strong 2011–2013 cohorts that supported the rapid recovery of the GSL stock after its collapse in the 1990s. Elemental fingerprints were extracted from the core (proxy for larval origin) and edge (proxy for capture location) of otoliths using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We observed an East to West gradient in the multi-elemental fingerprint of the otolith edge in the GSL, as well as evidence of temporal variation between 2016 and 2018. Cluster analysis of the core fingerprint revealed the existence of two chemically distinct natal sources of variable contribution between the Saguenay Fjord, the western GSL and the eastern GSL. This new insight on the population structure of redfish in the GSL at an ecologically relevant scale constitutes important knowledge for the assessment and sustainable management of a key recovering resource.

Nature-based coastal restoration: Development of an early-rearing production protocol of sugar kelp (Saccharina latissima Linnaeus) for bottom planting activities in the Gulf of St-Lawrence (Québec, Canada)

Successful bottom planting of indigenous macroalgae Saccharina latissima aimed at coastal restoration purposes require the mass production in controlled conditions of strongly fixed, healthy sporophytes followed by optimal transfer techniques in order to ensure viability and vigor of the young seedlings about to be directly introduced in the coastal environment. Early development of S. latissima submitted to different combinations of substrate type (natural vs artificial brick-shaped substrate), gametophyte spraying method (water-based vs binder-based) and water velocity (0.1 vs 0.2 m s-1) was evaluated during a growth trial that lasted 42 days. Overall, all experimental groups (8 in triplicate) reached the targeted length of 15 mm between 35-42 days post-seeding. No strong indications that the proposed 2×2×2 factorial design generated long lasting effects on growth and development indicators were observed (thallus length, SGR and % coverage). The observation of no persistent difference in the growth response of S. latissima under all experimental conditions, demonstrates that it is well suited for mass production of seedlings. Our results and evidenced-based practices led us to conclude that the use of an artificial substrate in combination with a binder-based gametophyte pulverization and the application of a velocity 0.2 m s-1 during early-growth could be adopted in a standardized protocol. We argue that 1) artificial substrates (uniform shape, stackable and rough surface) will most likely allow better use of a vessel’s open deck space and adherence of the developing holdfast; 2) the use of a binder may slow down the dehydration of the propagules and promote adhesiveness to the substrate during rearing, handling and transfer operations and under varying flow rates or wave actions respectively and 3) highest velocity should promote the selection of propagules with strongest attachment and thus possibly limit post-transfer dislodgement. We suggest further studies should 1) focus on identifying optimal gametophyte concentration at the spraying step, in order to reduce production costs and maximise productivity of seedling operations and 2) include biomass determination (g of tissue per cm2) in combination to the semi-quantitative density evaluation (% coverage) based on image-analysis, in order to improve our global assessment of growth.

Validation of the water content of the digestive gland as an indicator of nutritional condition in the American lobsterHomarus americanus(H. Milne Edwards, 1837) (Decapoda: Nephropidae)

AbstractSimple nutritional condition indicators are needed to provide information on the influence of ecosystem changes on the populations of the American lobster Homarus americanus (H. Milne Edwards, 1837) on various timescales. This study validates the use of the water content (% wet mass) of the digestive gland as an indicator of nutritional condition in the lobster (carapace length 65–127 mm) by assessing its capacity to estimate digestive-gland lipid reserves under variable environmental and physiological conditions. The validation was completed using samples from wild lobsters dissected shortly after being captured during different seasons and in various locations in the St. Lawrence Estuary and Gulf of St. Lawrence (GSL), and data from an environmentally realistic laboratory study on post-ovigerous females from the southern and the northern GSL sampled at different stages of their molt cycle. In both wild and experimental lobsters, water content was the best predictor of lipid reserves compared to other condition indicators (i.e., condition factor, various digestive-gland indices, and hemolymph Brix index). A strong linear relationship was found between lipid and water contents. Lipid content and interrelated molting status were identified as two important factors leading to the variations in water-fat regression equations among groups of wild or experimental lobsters. As lipid content could vary spatiotemporally in unexpected ways in a changing environment, it is recommended to use a sampling event-specific regression line to estimate digestive-gland lipid content from measured water content in field monitoring programs. Combining water content with molt status indicators such as Brix index is recommended to support interpretation of the observed variations in condition.

Climatology of Transport in the Strait of Belle Isle

AbstractThe Strait of Belle Isle (SBI) is an important pathway for water mass exchanges between the Labrador Shelf and the Gulf of St. Lawrence (GSL), particularly for transport toward the GSL. Seasonal and inter‐annual variability of transport in the SBI are examined using 15 years of moored acoustic Doppler current profiler data. Tidal currents are largely along strait and homogeneous with depth. Transports are toward the GSL on average, lowest (−1.0 ± 0.8 dSv) from April to July, and highest (−4.0 ± 1.1 dSv) from September to January. Averaged seasonal transports are usually within one standard deviation of previously published modeled values. The volume of winter Labrador Shelf water (LShW) entering the GSL is computed by transport integration and compares well with integrated volumes that meet LShW temperature‐salinity criteria during an annual March survey of the GSL. Integrating over the whole year showed that on average 649 ± 397 km3 enters the GSL after the March surveys are conducted, independently of the volume that has entered up to March; this addition represents on average about a third of the total volume. Annual volumes of LShW calculated from transport suggest that flow through the SBI accounts for 12%–18% of the GSL winter surface mixed layer. Cross‐strait current shear may affect transport integration values, but sea surface temperature data suggests this bias is limited to the summer. Corrections are empirically derived to account for cross‐strait shear in our transport calculation. The corrected time series suggests that the average transport may be flowing toward the Labrador Shelf in July (0.6 ± 1.0 CI [0.1 1.1] dSv).

Benthic Foraminiferal Assemblages from the Laurentian Channel in the Lower Estuary and Gulf of ST. Lawrence, Eastern Canada: Tracers of Bottom-Water Hypoxia

ABSTRACT Over the past century, an increase in temperatures and a decrease in dissolved oxygen concentrations have been observed in the bottom waters of the Laurentian Channel (LC), throughout the Lower St. Lawrence Estuary (LSLE) and the Gulf of St. Lawrence (GSL), eastern Canada. To document the impact of these changes, we analyzed the benthic foraminiferal assemblages and geochemical signatures of four sediment cores taken in the LC. Radiometric measurements (210Pb, 226Ra, 137Cs) indicate that the studied cores encompass the last 50 years of sedimentation in the LSLE and the last ∼160 years in the GSL. The sedimentary record shows a 60 to 65% decrease in benthic foraminiferal taxonomic diversity in the LC since the 1960s. An accelerated change in the foraminiferal assemblages is observed at approximately the same time at all studied sites, around the late 1990s and the early 2000s, towards populations dominated by the hypoxia-tolerant indicator taxa Brizalina subaenariensis, Eubuliminella exilis, and Globobulimina auriculata. This evolution of assemblages reflects incursions of the hypoxic zone into the western GSL over the last decades. The results of our multivariate analyses highlight the potential of benthic foraminiferal assemblages as a proxy of bottom-water hypoxia.

Comparison of SMOS, SMAP and In Situ Sea Surface Salinity in the Gulf of St. Lawrence

ABSTRACT The Gulf of St. Lawrence (GSL) is an Eastern Canada semi-enclosed sea under the influence of the freshwater discharge from the Great Lakes – St. Lawrence River drainage basin. Studying the variability of oceanographic conditions in the GSL under a changing climate is important for ecosystem and fisheries management. To supplement the available in situ sea surface salinity (SSS) measurements with satellite SSS data, this study compares all available years of Soil Moisture Ocean Salinity (SMOS) and Soil Moisture Active and Passive (SMAP) satellite SSS to in situ SSS observations. Despite the relatively cold water and proximity to land and sea ice, the satellite SSS is able to capture the interannual variability and annual cycle of SSS in the GSL, with correlations ranging from 0.80 to 0.85 in the Southern GSL, and 0.22 to 0.77 in the Northern GSL. All satellite SSS data products were able to detect the very low salinity year of 2017 in the Southern GSL.

The distribution of North Atlantic right whales in Canadian waters from 2015-2017 revealed by passive acoustic monitoring

Northward range shifts are increasingly being identified in mobile animals that are responding to climate change. Range shifts are consequential to animal ecology, ecosystem function, and conservation goals, yet for many species these cannot be characterised without means of synoptically measuring their distribution. The distribution of critically endangered North Atlantic right whale (Eubalaena glacialis; NARW) north of 45°N has been largely unknown due to a lack of systematic monitoring. The objectives of this study were to characterize the spatial and temporal variation in NARW acoustic occurrence in the northern portion of their foraging range. In addition, we sought to identify relevant NARW migratory corridors and explore potential previously unidentified high-use habitats beyond the highly surveyed Gulf of St. Lawrence (GSL). To achieve this, passive acoustic monitoring data were collected and analyzed from 67 moorings and 13 gliders deployed (across 38 recording stations) throughout the Atlantic Canadian continental shelf, between 42°N and 58°N during 2015 through 2017. The results support that while a portion of the population has moved northward into the GSL, this shift was constrained to temperate latitudinal ranges < 52°N during the study period. NARWs were not detected in the Labrador Sea and Newfoundland Shelf, despite their preferred prey occurring in those areas. NARWs were present on the Scotian Shelf (45°N) nearly year-round, but only from May through December in the Cabot Strait (50°N). These results indicate that the northern range of the population is probably influenced by energetic requirements to minimize the distance between suitable foraging habitat and low latitude calving grounds, rather than an absence of suitable foraging conditions in high latitude waters, or other environmental or physiological factors. This work provides critical information to conserve the species and mitigate human-induced risks.

Diet composition of redfish (Sebastes sp.) during periods of population collapse and massive resurgence in the Gulf of St. Lawrence

Redfish (Sebastes mentella and S. fasciatus) are back at spectacular record high levels in the Gulf of St. Lawrence (GSL) and the effects of this massive resurgence on other components of the food web remain largely unknown. To better understand the trophic implications of the surging redfish biomass within the GSL ecosystem, 3,690 stomachs containing food were collected during two periods: one characterised by low redfish abundance (1993–1999) and the other during a period of record abundance (2015–2019). Taxonomical analysis of stomach contents from individuals of different sizes from three subareas of the GSL was carried out to determine diet composition during both periods. Zooplankton represented the main prey category for small redfish (< 20 cm), which was driven by a predation on amphipods, mostly Themisto sp. in North-East Gulf, in the 1990s and on copepods of the genus Calanus in the deep channels and euphausiids in North-West Gulf in the 2010s. Themisto sp. still dominated the diet of medium (20–30 cm) redfish in the 1990s while the copepods were predominant during the 2010s. Shrimp consumption increased with redfish size and two species were particularly important in large redfish diet (≥ 30 cm) during both periods: pink glass shrimp (Pasiphaea multidentata), mostly in the Laurentian Channel and northern shrimp (Pandalus borealis), especially in North-East Gulf. Redfish predation on shrimp represents a major concern for the dynamics of the northern shrimp which supports a valuable fishery in the GSL but has been declining in abundance since several years. Piscivory was observed in large redfish diet, with capelin (Mallotus villosus) being the major fish prey in the 1990s and redfish (cannibalism) in the 2010s, suggesting density-dependent control at high density of small redfish. By presenting a detailed overview into the redfish diet composition and its temporal variability, the present study offers a first look into the possible future trophic impacts of a resurging groundfish in the GSL ecosystem.

Age-specific trace element bioaccumulation in grey seals from the Gulf of St. Lawrence

We measured concentrations of 19 trace elements and mercury speciation in grey seals (Halichoerus grypus) from the Gulf of St. Lawrence (GSL), Canada. With interest growing in commercializing grey seal products for human consumption in this region, our goal was to measure essential and non-essential trace elements in grey seals to evaluate health concerns and nutritional benefits. From 2015 to 2019, 120 grey seals were sampled by hunters and researchers at 4 sites in the GSL. Muscle, liver, heart and kidney samples were analyzed for 10 non-essential elements (Sb, As, Be, B, Cd, Pb, Hg, Ni, Tl, Sn) and 9 essential elements (Co, Cr, Cu, Fe, Mg, Mn, Mo, Se, Zn). Both total mercury (THg) and methylmercury (MeHg) were analyzed for a subset of samples. Results showed a two-step bioaccumulation pattern with lower element concentrations in the muscle (Fe, Mg, Se) and livers (Cd, Cr, Hg, Mn, Mo, Se) of young-of-the-year harvested in the winter (<6 wks old) compared to older animals feeding at sea. We did not observe progressive age-dependent bioaccumulation for older seals (∼5 mos–29 yrs). Sex-specific differences were not very pronounced, but a few elements were 30–70% higher in the muscle (THg, MeHg) and liver (Mn, Zn) of male seals. Comparison to Canadian dietary reference intakes shows that a weekly portion of liver from young-of-the-year (<6 wks old) is a good source of essential elements (Cu, Fe) and that muscle and liver from this age category do not exceed reference values for toxic elements (As, Cd, Pb, MeHg). Discussions with regional public health professionals are on-going to develop dietary recommendations for the consumption of older grey seals.

Revealing the relationship between feeding and growth of larval redfish (Sebastes sp.) in the Gulf of St. Lawrence

Abstract Year-class strength of fish stocks is often set during the larval stage, with fast growth being a favourable factor leading to strong recruitment. Following 30 years of poor recruitment, redfish (Sebastes sp.) in the Gulf of St. Lawrence (GSL) produced unprecedentedly strong year classes in 2011–2013. The relationship between larval diet and growth that potentially drove these successful recruitment events is unknown. Gut content and otolith microstructure of redfish larvae collected from the GSL in 1999 and 2000 were analysed in order to understand the relationship between recent feeding success and growth in larval redfish, and identify feeding behaviours that are associated with fast growth. Growth was positively correlated with larval body depth (BD), which was used as a morphological proxy for growth. Prey type and size were the best explanatory variables of larval BD after obligatory first-feeding. Larvae that consumed large naupliar stages of frequently consumed copepod taxa were deeper-bodied and grew more quickly than larvae that consumed redfish's preferred prey, Calanus finmarchicus eggs. Warming GSL waters have shifted the phenology of commonly consumed prey taxa earlier in the season, which may increase the overlap between redfish and naupliar prey that drive fast growth, survival, and potentially recruitment success.