Southern Grand 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.

Acoustic occurrence of beaked whales off eastern Canada, 2015-2017

Several beaked whale species occur off eastern Canada. However, except for the northern bottlenose whale (NBW; Hyperoodon ampullatus), their distribution and annual occurrence remain largely unknown, which complicates management efforts to assess the status of poorly known species and effectively protect those species considered at risk. The main objective of this paper is to provide a year-round and pluriannual description of the minimum acoustic occurrence of the NBW, Sowerby’s (SBW; Mesoplodon bidens), Cuvier’s (CBW; Ziphius cavirostris), True’s (TBW; M. mirus) and Gervais’ (GBW; M. europaeus) beaked whales. Twenty-five acoustic recorders were deployed off eastern Canada between May 2015 and November 2017. Beaked whale echolocation clicks were detected using a combination of automated detectors and manual validation at 12 of these stations. Detections were generally restricted to deep continental slope waters. All detected species occurred in the southern part of the study area (off the Scotian Shelf and southern Grand Banks), while only NBWs were detected at the northern edge, off southern Labrador. Clicks identified as TBW or GBW were restricted to, but occurred annually in, the southern areas. All other species were present, at least seasonally, east and north of the Grand Banks. NBWs occurred every day in the Gully Canyon, where SBWs also occurred regularly. While these results should be interpreted as minimum species presence and considered with regards to detector performance, they provide important information regarding beaked whales’ use of areas off eastern Canada where these species have generally received no or very limited monitoring effort.

Electronic tags reveal high migratory diversity within the largest Atlantic halibut (Hippoglossus hippoglossus) stock

Growing evidence suggests that complex spatial structure occurs within the Scotian Shelf and southern Grand Banks (SSGB) Atlantic halibut stock, yet large knowledge gaps remain about diversity of migratory and spawning behaviors. Here, 71 pop-up satellite archival tags were deployed on large Atlantic halibut (FL: 87–166 cm) between 2012 and 2020. Migration tracks were successfully reconstructed for 43 fish using a hidden Markov geolocation model, and temperature and depth time series were available for an additional nine fish (total n = 52). Five migratory behavior categories were identified: shelf residency, slope residency, shelf-channel migration, shelf-slope migration, and dispersal. High-resolution data for four of 20 physically recovered tags provided evidence of putative spawning behavior in deep channels on the continental shelf and along the continental slope between January and February. Additionally, four halibut displayed previously undocumented periods of sustained, oscillatory vertical movements along the continental slope between November and February. The high migratory diversity observed in this study provides support for the existence of multiple resident and migratory contingents in the SSGB stock in the apparent absence of significant genetic structure.

Re-evaluation of the Mesozoic–Cenozoic biostratigraphy of the Laurentian Subbasin of the Scotian Basin, offshore eastern Canada

We use new and existing nannofossil, palynological, and microfossil biostratigraphic data in conjunction with lithologic and geophysical logs from four wells to establish a series of sequence-stratigraphic events in the Mesozoic–Cenozoic of the Laurentian Subbasin of offshore Newfoundland, eastern Canada. Well biostratigraphic events are integrated with reflection seismic in the area to correlate regional seismic stratigraphic surfaces. The four wells are: Bandol-1, Emerillon C-56, East Wolverine G-37, and Heron H-73. We extend the event stratigraphic scheme previously developed for the Scotian Margin, offshore Nova Scotia, into new areas to the east along the southern Grand Banks, where we recognize four new well-log sequence stratigraphic events, and we modify the definition of a previously recognized regional surface. The new and modified regional surfaces are the Early Albian Unconformity, the Late Bathonian Maximum Flooding Surface (MFS), the Late Bajocian MFS (renamed from Bathonian/Bajocian MFS), the ?Bajocian/Toarcian Unconformity, and the Late Pliensbachian MFS. We recognize the "Avalon Unconformity" and "Base-Tertiary Unconformity" of previous studies as amalgamations of multiple smaller-scale unconformities and refine their age in the studied wells. A major improvement over our earlier Scotian Margin event schemes is the extension of the event stratigraphy into the Early Jurassic using a suite of marine biostratigraphic markers. We compare the Early Jurassic event scheme to Deep Sea Drilling Project Site 547B on the conjugate Moroccan Margin to better constrain potential source rock intervals and the early history of the central Atlantic Ocean.

Identification of recruitment regime shifts with a hidden Markov stock-recruitment model

Abstract Stock-recruitment relationships (SRRs) may differ substantially among environmental regimes. We developed a methodology including a Hidden Markov Stock-recruitment Model (HMSM), the maximum likelihood approach and a model selection procedure to identify abrupt changes of stock-recruitment (SR) dynamics. This method allows us to objectively identify the unobserved regimes, estimate regime-specific parameters, and predict the transition probabilities among regimes. First, we used simulation to verify that our method could identify the correct number of regimes and estimate the model parameters well. Then, we applied the models to an Atlantic cod stock on the southern Grand Bank off Newfoundland, Canada. Results indicated that the HMSM assuming 2 regimes performed the best, and the cod stock shifted to a regime characterized with lower productivity and higher density dependence in late 1980s. Additionally, the estimated probability to return to the previous high-productivity regime was very low, suggesting the cod stock may remain at the low-productivity regime for a prolonged period. Overall, we consider the methodology proposed in this paper as a useful tool to model regime shifts of SRRs in fisheries stock assessment.

Seafloor biodiversity of Canada's three oceans: Patterns, hotspots and potential drivers

AbstractAimWe examined the relationships between bathymetry, latitude and energy and the diversity of marine benthic invertebrates across wide environmental ranges of Canada's three oceans.LocationCanadian Pacific, Arctic and Atlantic Oceans from the intertidal zone to upper bathyal depths, encompassing 13 marine ecoregions.MethodsWe compiled 35 benthic datasets that encompass 3,337 taxa (70% identified to species and 21% to genus) from 13,172 samples spanning 6,117 sites. Partitioning the analyses by different gear types, ecoregions or sites, we used Hill numbers to examine spatial patterns in α‐diversity. We used resampling and extrapolation to standardized sampling effort and examined the effects of depth, latitude, chemical energy (export particulate organic carbon [POC] flux), thermal energy (bottom temperature) and seasonality of primary production on the benthic biodiversity.ResultsThe Canadian Arctic harboured the highest benthic diversity (e.g. epifauna and common and dominant infauna species), whereas the lowest diversity was found in the Atlantic. The Puget Trough (Pacific), Beaufort Sea, Arctic Archipelago, Hudson Bay, Northern Labrador and Southern Grand Bank (Atlantic) were the “hotspots" of diversity among the ecoregions. The infauna and epifauna both exhibited hump‐shaped diversity–depth relationships, with peak diversity near shelf breaks; latitude (positively) predicted infaunal diversity, albeit weakly. Food supply, as inferred from primary production and depth, was more important than thermal energy in controlling diversity patterns. Limitations with respect to calculating POC flux in coastal (e.g. terrestrial runoff) and ice‐covered regions or biological interactions may explain the negative POC flux–infaunal diversity relationship.Main ConclusionsWe show previously unreported diversity hotspots in the Canadian Arctic and in other ecoregions. Our analyses reveal potential controlling mechanisms of large‐scale benthic biodiversity patterns in Canada's three oceans, which are inconsistent with the prevailing view of seafloor energy–diversity relationships. These results provide insightful information for conservation that can help to implement further MPA networks.

Modeling the distribution of thorny skate (Amblyraja radiata) in the southern Grand Banks (Newfoundland, Canada)

Globally, commercial fisheries have had a strong impact on elasmobranch populations directly through high catch rates and indirectly through bycatch. Consequently, the abundance of many species is declining to the extent that some are considered under threat of extinction. Regionally, this negative trend is also evident in the international waters of the southern Grand Banks (off the coast of Newfoundland, Canada), where the occurrence of the thorny skate (Amblyraja radiata) has declined by nearly 70% in recent decades. This study used Bayesian species distribution models to investigate the habitat preference and biomass trends of the thorny skate during a 14-year period (2003–2017), linking five environmental predictors (i.e., bathymetry, sea bottom temperature, seabed aspect, slope, and rugosity) and prey distribution with fishery-independent data. Our findings identify some of the sensitive habitats for this species and the ecological factors that may be driving its population dynamics in the area. We argue that knowledge about the factors influencing the distribution of this species and spatiotemporal effects could be exploited as potential mitigation measures for future fishery management strategies.

Spatiotemporal bycatch analysis of the Atlantic halibut (Hippoglossus hippoglossus) longline fishery survey indicates hotspots for species of conservation concern

The Atlantic halibut (Hippoglossus hippoglossus) longline fishery is the second most valuable groundfish fishery in Atlantic Canada and received Marine Stewardship Council certification in 2013. The bottom longline fishery accounts for most halibut landings but incidentally catches nontargeted species (bycatch). Since 1998, Fisheries and Oceans Canada and the halibut fishing industry performed annual longline surveys across the Scotian Shelf and Southern Grand Banks stock management area to monitor halibut abundance, and at‐sea observers also recorded bycatch information. We examined the species composition and proportion of the survey bycatch and analyzed temporal and spatial trends in standardized weight of (a) halibut catch, (b) total bycatch, and (c) bycatch of species of conservation concern. From 1998 to 2016, 70% of the total catch by weight and 85% by number of individuals were bycatch. Over 100 identified species of finfish, sharks, skates, benthic invertebrates, marine mammals, and seabirds were caught as bycatch in the survey. This included four species listed under the Species at Risk Act (Northern wolffish, Anarhichas denticulatus; spotted wolffish, A. minor; Atlantic wolffish, A. lupus; Atlantic cod, Gadus morhua), and another 14 species awaiting a listing decision based on assessments by the Committee on the Status of Endangered Wildlife in Canada. Generally, the standardized weight of halibut and barndoor skate (Dipturus laevis) increased over time, while Atlantic cod, spiny dogfish (Squalus acanthias), white hake (Urophycis tenuis), and thorny skate (Amblyraja radiata) decreased. Spatial patterns indicated high bycatch levels on the southern Scotian Shelf and southern edge of the Southern Grand Banks, with hotspots for certain species of conservation concern. Our results identify temporal trends in threatened species and areas where they are susceptible to the Atlantic halibut longline fishery which can inform recovery strategies, bycatch levels and spatial zoning in fisheries management and marine conservation.

Migration patterns and putative spawning habitats of Atlantic halibut (Hippoglossus hippoglossus) in the Gulf of St. Lawrence revealed by geolocation of pop-up satellite archival tags

AbstractCharacterizing migratory behaviours contributes to the sustainable management of marine fishes by resolving stock structure and identifying the timing and locations of events within fish life cycles. The migratory behaviour of Atlantic halibut (Hippoglossus hippoglossus) in the Gulf of St. Lawrence (GSL), Canada was characterized over an annual cycle using pop-up satellite archival tags (n = 15). Daily probability density functions of individual halibut positions were estimated using a geolocation model specifically developed to track demersal fish species in the GSL. Reconstructed migration routes (n = 8) revealed that Atlantic halibut displayed seasonal migrations, moving from deeper offshore waters in the winter to shallower nearshore waters in the summer. Variability in migratory behaviours was observed among individuals tagged at the same location and time. One individual resided year round in the vicinity of the tagging site, three individuals displayed homing behaviour, and four individuals did not return to the tagging site. The identification of presumed spawning rises for two individuals suggested that spawning of Atlantic halibut occurred in the GSL. Although based on a limited number of individuals, these results suggest that Atlantic halibut in the GSL forms a philopatric population, supporting the current separate management of this stock from the adjacent Scotian Shelf and southern Grand Banks stock.

Perspectives provided by bottom trawl transect surveys conducted in the 1950s and 1960s on the dynamics of commercially exploited groundfish species on southern Grand Bank and St. Pierre Bank

Perspectives provided by bottom trawl transect surveys conducted in the 1950s and 1960s on the dynamics of commercially exploited groundfish species on southern Grand Bank and St. Pierre Bank

The recovery of Atlantic halibut: a large, long-lived, and exploited marine predator

AbstractAtlantic halibut (Hippoglossus hippoglossus) have a long history of exploitation in the Northwest Atlantic and have gone through several periods of high biomass followed by a population crash. An assessment model using data collected on the Scotian Shelf and southern Grand Banks shows that the population peaked in 1984, then decreased sharply to a low in 1993. Several management measures were taken during the decline, including reductions in total allowable catch and a minimum size limit. Concurrently, removals by the otter trawl fishery were drastically reduced following the collapse of the cod (Gadus morhua) fishery. In 2003, recruitment increased and continued to be high for 6 years. Fishing mortality rates were moderate in the late 1990s and 2000s and the population increased. By 2009, the Atlantic halibut population was highly productive with both high biomass and high levels of recruitment. The coincidence in the timing of population recovery and management actions indicates that effective management contributed to the recovery of Atlantic halibut.

Changes in the exploited demersal fish assemblages in the Southern Grand Banks (NAFO Divisions 3NO): 2002–2013

Abstract The Newfoundland Shelf supported one of the world’s greatest fisheries until the main commercial species collapsed more than two decades ago. We calculated three ecological indices for individual populations and five for community from the data obtained in the research surveys conducted by Spain in NAFO Regulatory Area Divisions 3NO between 2002 and 2013. We use data for 24 species to study the dynamics of major demersal fish assemblages (38–300, 301–600, and 601–1460 m depth) and evaluated how they have responded to different levels of exploitation. Trends and changes for individual populations (abundance and biomass, intrinsic population rate of growth, and mean length) and for all the community (ABC curves, indices of faunal diversity, proportion of non-commercial species, mean length in community and size spectra) were used to test ecological trends. Indices showed no homogeneous status and responded to different exploitation patterns, management, and environmental regimes in each assemblage. Our results show an improvement in the shallower and deeper assemblages and that fishing effort does not explain differences among each assemblage.

Persistence and Variation on the Groundfish Assemblages on the Southern Grand Banks (NAFO Divisions 3NO): 2002-2011

Data from EU-Spain (Instituto Espanol de Oceanografia) bottom trawl surveys in the NAFO Regulatory Area (2002–2011) were analyzed to examine patterns on the South of Grand Banks (NAFO Div. 3NO) of groundfish assemblage structure and diversity in relation to depth. The 1160 hauls from the slope surveys spanned between 38 and 1460 m in depth. We focused on the 28 most abundant species, which made up 92.6% of the catch in terms of biomass. Assemblage structure was strongly correlated with depth. For the most part, changes in assemblages seem to be fairly continuous, although there were more abrupt changes at 300 m. Five assemblages were identified. Two shallow assemblages were found in the shelf. Assemblage I (Shallow) comprises the strata with depths lesser than 150 and include yellowtail flounder (Limanda ferruginea), American plaice (Hippoglossoides platessoides), Northern sand lance (Ammodytes dubius), moustache sculpin (Triglops murrayi), capelin (Mallotus villosus) and web sculpin (Hemitripterus americanus). Assemblage II (Shallow) includes the strata with depths between 151 and 300 m and comprises Atlantic cod (Gadus morhua), American angler (Lophius americanus), wolfish (Anarichas lupus) and thorny skate (Amblyraja radiata). Assemblage III (Intermediate) contains the depth strata between 301 and 600 m. Redfish (Sebastes spp.), spotted wolfish (Anarichas minor), Arctic eelpout (Lycodes reticulatus), Northern wolfish (Anarichas denticulatus), white hake (Urophycis tenuis), witch flounder (Glyptocephalus cynoglossus) and longfin hake (Phycis chesteri) were included in the intermediate assemblage. Finally, we found two deep clusters: Assemblage IV (Deep) contains the depths between 601 and 1000 m, and Assemblage V (Deep) the depth strata greater than 1001 m. Greenland halibut (Reinhardtius hippoglossoides), marlin-spike (Nezumia bairdii), roughhead grenadier (Macrourus berglax) and spinytail skate (Bathyraja spinicauda) formed Assemblage IV. Snubnosed spiny eel (Notacanthus chemnitzii), blue antimora (Antimora rostrata), Northern cutthroat eel (Syphanobranchus kaupii), roundnose grenadier (Coryphaenoides rupestris), black dogfish (Centroscyllium fabricii), Arctic skate (Amblyraja hyperborea) and longnose chimera (Harriotta raleighana) made up the deepest assemblage. Despite dramatic changes in biomass and abundance of the species in the area, the boundaries and composition of the assemblages seem to be similar to the period before the collapse. Although some changes were evident, the main ones were replacements of the dominant species in several assemblages and bathymetric range extension of distribution of some species. Yellowtail flounder appears to be the dominant species in the shallowest assemblage instead of Atlantic cod and American plaice that were dominant in the period before the collapse in the area; redfish is the dominant species in the second shallow and intermediate assemblages. Diversity appears inversely related to biomass in the different assemblages. Despite the fishing effort in the deep waters of the Grand Banks, the overall pattern of demersal fish assemblages remains similar over time. This pattern is similar in other Atlantic areas; it indicates that changes in the fish populations in Northwest Atlantic have been produced on a large scale and are not limited to specific areas.

Fishing and Natural Mortality Rates of Atlantic Halibut Estimated from Multiyear Tagging and Life History

AbstractFishing mortality and natural mortality rates for Atlantic HalibutHippoglossus hippoglossuson the Scotian Shelf and southern Grand Banks were estimated from a multiyear tagging study. Models that were used to estimate mortality rates incorporated tag loss. Between 2006 and 2008, 1,913 Atlantic Halibut were double‐tagged with t‐bar anchor tags; as of 26 August 2010, 368 of these fish had been recaptured. We estimated instantaneous fishing mortality (F) separately for each cohort in the first year (on average, 6 months) after release to allow newly tagged animals to mix with the population. A two‐parameter model was used to describe tag loss. Tag loss was estimated at 13% per year in the first year and 10% per year in the second and subsequent years. Using the multiyear model with incomplete mixing and assuming 90% tag reporting and 80% survival from tagging, average instantaneous natural mortality (M) of Atlantic Halibut was estimated to be 0.22 andFwas estimated to be 0.15 in 2007, 0.24 in 2008, and 0.18 in 2009. These estimates ofFwere comparable to those from the stock assessment population model. However, the estimates ofMwere higher than inferred estimates ofMbased on life history and growth. Estimates ofFandMwere sensitive to the minimum size of Atlantic Halibut at the time of release. An increase inFwith size is consistent with fishery size selectivity resulting from either gear selectivity or the distribution of fishing effort where there is spatial heterogeneity in the size composition. We suggest thatMmay have been overestimated because of emigration from the study area.

Does increased information about reproductive potential result in better prediction of recruitment?

The relationship between stock size and recruitment is an essential element in the understanding of the productivity of a population. However, predicting the number of recruits produced by a population has proven to be a difficult challenge. This may in part be a result of poor estimation of reproductive potential (RP). We determined if including increased information on reproductive biology in indices of RP results in better predictions of recruitment. We investigated some of the conditions that lead to better (or worse) recruitment prediction when more biologically complex indices of RP are used. Data from four populations in the Northwest Atlantic were examined: southern Grand Bank (NAFO Division 3NO) cod ( Gadus morhua ), Flemish Cap (NAFO Division 3M) cod, Newfoundland (NAFO Division 3LNO) American plaice ( Hippoglossoides platessoides ), and Greenland halibut ( Reinhardtius hippoglossoides ) (NAFO Subarea 2 + Division 3KLMNO). Stock–recruit models paired with complex indices of RP gave a better estimate of recruitment in slightly more than half of the tests conducted. When there were larger trends in the reproductive biology (maturity at age, sex ratio and egg production), more complex indices of RP were more likely to provide a better estimate of recruitment.

Elastic thickness estimates at northeast passive margin of North America and its implications

Global estimates of the elastic thickness (Te) of the structure of passive continental margins show wide and varying results owing to the use of different methodologies. Earlier estimates of the elastic thickness of the North Atlantic passive continental margins that used flexural modelling yielded a Te value of ∼20–100 km. Here, we compare these estimates with the Te value obtained using orthonormalized Hermite multitaper recovered isostatic coherence functions. We discuss how Te is correlated with heat flow distribution and depth of necking. The E–W segment in the southern study region comprising Nova Scotia and the Southern Grand Banks show low Te values, while the zones comprising the NE–SW zones, viz., Western Greenland, Labrador, Orphan Basin and the Northern Grand Bank show comparatively high Te values. As expected, Te broadly reflects the depth of the 200–400 ◦ C isotherm below the weak surface sediment layer at the time of loading, and at the margins most of the loading occurred during rifting. We infer that these low Te measurements indicate Te frozen into the lithosphere. This could be due to the passive nature of the margin when the loads were emplaced during the continental break-up process at high temperature gradients.

Using bycatch data to understand habitat use of small cetaceans: lessons from an experimental driftnet fishery

AbstractStenson, G. B., Benjamins, S., and Reddin, D. G. 2011. Using bycatch data to understand habitat use of small cetaceans: lessons from an experimental driftnet fishery. – ICES Journal of Marine Science, 68: 937–946. Many marine mammals inhabit offshore areas where it is difficult to determine distribution and abundance. Historical bycatch data of marine mammals in the Northwest Atlantic obtained from the Canadian experimental Atlantic salmon (Salmo salar) driftnet fishery were examined to obtain information on seasonal distribution and relative abundance. From 1965 to 2001, 47 cruises were undertaken totalling 12 566.5 km-h of fishing effort; four species of small cetacean and two species of pinniped were caught. Harbour porpoises (Phocoena phocoena) were the most frequently caught species in all areas except the Labrador Sea, where Atlantic white-sided dolphins (Lagenorhynchus acutus) were more common. Long-finned pilot whales (Globicephala melas), common dolphins (Delphinus delphis), harp seals (Pagophilus groenlandicus), and harbour seals (Phoca vitulina) were also taken occasionally. Although typically considered an inshore species, harbour porpoises were regularly reported in deep water (>2000 m), in the Newfoundland Basin and Labrador Sea. Atlantic white-sided dolphins were often caught along the edge of the continental shelf and appeared to prefer relatively warm water. Finally, catch records indicate that waters of the Newfoundland Basin and Southern Grand Banks may contain important winter habitat for several small species of cetacean.

Age determination, bomb-radiocarbon validation and growth of Atlantic halibut (Hippoglossus hippoglossus) from the Northwest Atlantic

Atlantic halibut (Hippoglossus hippoglossus) is the largest and one of the most widely-ranging and commercially-valuable groundfish in the Atlantic Ocean. Although presumed to be long-lived, their age and growth has not been validated. Ages were estimated by counting growth increments from approximately 2400 thin-sectioned sagittal otoliths collected from the Scotian Shelf and southern Grand Banks off eastern Canada. The accuracy of age estimates made from otolith thin sections was validated using bomb-radiocarbon assays of 13 otolith cores whose year of formation ranged from 1949 to 1975, encompassing the timeframe of the global radiocarbon pulse. Known-age juvenile halibut from a culture facility were used to identify the approximate location of the first annulus. Growth rate for males and females was similar up to about 70 cm (~5 years), after which point male growth slowed, while female growth continued to an age of up to 38 years and a maximum observed size of 232 cm. Males grew to an observed maximum length of about 175 cm and a maximum age of 50 years. A comparison of age estimates for otoliths collected in a ‘historic’ time frame (1963 to 1974) with those from recent years (1997 to 2007) shows that growth rate has not changed appreciably between the two time periods. Small but significant growth differences were observed between the Scotian Shelf and southern Grand Banks for both sexes, while large differences in length at age were observed between halibut caught with longline compared to otter trawl due to differences in length-based gear selectivity. Age interpretations based on sectioned otoliths tended to be 10–15% different than those based on break and burn, although the age comparison was confounded by other variables and must be considered provisional. Atlantic halibut is a long-lived fish, living up to at least 50 years, an important consideration for the management of the fishery.

Impact of environmental temperature on Atlantic cod Gadus morhua energy allocation to growth, condition and reproduction

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 404:185-195 (2010) - DOI: https://doi.org/10.3354/meps08502 Impact of environmental temperature on Atlantic cod Gadus morhua energy allocation to growth, condition and reproduction M. J. Morgan*, R. M. Rideout, E. B. Colbourne Fisheries and Oceans Canada, St. John’s, Newfoundland A1C 5X1, Canada *Email: joanne.morgan@dfo-mpo.gc.ca ABSTRACT: The effect of temperature on the allocation of energy to growth, condition and reproduction was examined in juvenile and adult Atlantic cod Gadus morhua inhabiting the southern Grand Bank off Newfoundland, Canada. The study period included both the warmest and coldest environmental conditions in the area over the past 60 yr. Temperature did not influence growth in length or weight, perhaps because growth at higher temperatures was limited by prey availability. Temperature significantly influenced both gutted body condition and liver condition (observed weight divided by predicted weight at length), but the effect was not consistent between the 2 measures of condition. Gutted body condition was highest at warm temperatures, whereas liver condition was highest at low temperatures. Measures of reproductive investment showed clear temperature effects. Fish matured earlier at both low and high temperatures than at intermediate temperatures. Fecundity of southern Grand Bank cod was highest at low temperatures, while the gonadosomatic index (GSI) was highest at warm temperatures. The lack of correlation with fecundity indicates that GSI may not be a good metric of reproductive investment but may be an indicator of how close fish are to spawning. The lower maturity and fecundity at intermediate temperatures could indicate a decrease in reproductive potential under these environmental conditions. Temperature throughout the entire year influenced fish condition, but only temperature during October to May affected reproductive investment. Most of the metrics were highly correlated between males and females, suggesting that both sexes make similar decisions about energy allocation over the observed temperature range. KEY WORDS: Cod · Growth · Reproduction · Temperature Full text in pdf format PreviousNextCite this article as: Morgan MJ, Rideout RM, Colbourne EB (2010) Impact of environmental temperature on Atlantic cod Gadus morhua energy allocation to growth, condition and reproduction. Mar Ecol Prog Ser 404:185-195. https://doi.org/10.3354/meps08502 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 404. Online publication date: April 08, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Dispersion of Eggs, Larvae and Pelagic Juveniles of White Hake (Urophycis tenuis) in Relation to Ocean Currents of the Grand Bank: A Modelling Approach

White hake (Urophycis tenuis) is a temperate demersal fish species distributed in the northwest Atlantic. On the Grand Bank, it is concentrated mainly to the southwest where water temperatures are warmest. Survey data indicate that mature adult females aggregate on the southwest (SW) Grand Bank slope in spring and first-year juveniles settle on the southern, shallow Grand Bank in autumn. Dispersion patterns and survival potential of eggs, larvae and juveniles were investigated with respect to the effects of location (horizontal and vertical) and timing (monthly) of spawning under monthly-mean circulation fields, M2 tidal currents and associated turbulent mixing computed from a three-dimensional regional ocean circulation model. The results indicate that releases below the surface Ekman layer and in late spring have the highest chances for juveniles to settle in the southern Grand Bank nursery area in autumn. On an interannual scale, the strong recruitment of the 1999 yearclass has been used as an example to examine the potential linkage between recruitment and the strength of the Labrador Current. A weak along-slope current and strong on-bank flow contributed to the strong recruitment of the 1999 year-class.