Inter-river, -annual and -seasonal variability in fecundity of Atlantic salmon, Salmo salar L., in rivers in Newfoundland and Labrador, Canada

Abstract  Fecundity is an integral component of the calculation of Atlantic salmon, Salmo salar L., egg depositions in rivers. Fecundity determinations can be time consuming and prohibitively expensive in terms of application on a broad scale. Consequently, where river specific and annual data are not available, default means are used in calculations in Newfoundland and Labrador. It is important therefore to know the extent of variability among rivers, years and seasons and the potential error involved in using default values. Annual fecundity data were available for one river in Labrador and nine rivers in Newfoundland. Fecundity was determined from ovaries collected in the recreational fishery in the summer for all 10 rivers. For three of these rivers, fecundity determined from summer sampling was compared with that obtained from sampling at time of spawning in autumn. There was significant variability in fecundity with length as a covariate among rivers, years and seasons. Mean number of eggs per female decreased between 8.3% and 29.0% from summer to autumn while mean number of eggs per cm decreased from 5.0% to 28.5%. Depending on the measure of relative fecundity used (no. of eggs kg⁻¹ or no. of eggs cm⁻¹), results of simulations showed that estimates of egg deposition incorporating defaults can deviate from those obtained by applying year-specific and river-specific values by 50–75%, without adjusting for the seasonal reduction in fecundity, and by 30–50% with an adjustment. A sensitivity analysis revealed that of three parameters used in the calculation of egg deposition (size, percent female and fecundity), fecundity was the most influential.     

Modelling the dispersal of Calanus finmarchicus on the Newfoundland Shelf: implications for the analysis of population dynamics from a high frequency monitoring site

We investigated the drift of passive particles on the Newfoundland Shelf and western Labrador Sea using numerical simulations to assess the possible sources of plankton collected at a high frequency sampling site (S27; 47.55°N, 52.59°W) located near the coast of Newfoundland, Canada. We also summarized data detailing the seasonal stage succession of Calanus finmarchicus at that site, as well as along three oceanographic sections sampled in the spring, summer and autumn across the adjacent continental shelf. Simulations indicated that the Labrador and Newfoundland Shelves represent the major sources of particles transiting through the S27 site, with relatively minor contributions from the western Labrador Sea which are significant during a few months each year. The latter point may be affected by uncertainty in the representation of cross‐shelf transport associated with seasonal or short‐term variations in atmospheric and oceanic forcing, which may also affect the strength and location of bifurcation of the inner branch of the Labrador Current around the Grand Banks. Nevertheless, our results indicated that drift along the inner shelf is likely to be the primary source of copepods collected at S27 throughout most of the year. This in turn suggested that there may be a higher degree of connectivity between conditions in coastal areas of Newfoundland and those in Baffin Bay and west Greenland than with the southern half of the Labrador Sea.     

Modelling advection of cod eggs and larvae on the Newfoundland Shelf

We investigate interannual variations in dispersion for the drift and retention of cod eggs and larvae on the Newfoundland Shelf using a two-dimensional Lagrangian tracking model. The velocity field for the drift model is obtained from a diagnostic calculation of objectively analysed density data. Time-dependent currents are generated using an inertial-current slab model driven by observed winds. Eggs and larvae are treated as passive drifters seeded in a dispersion model of the Newfoundland Shelf region. We identify favourable and unfavourable zones of retention on the Newfoundland Shelf. We show that northerly, shelf-break spawning locations are more favourable than southerly shelf-break spawning locations for northern cod, ( Gudus morhua , in NAFO divisions 2J3KL).     

Recent Advances in Lumpfish Cyclopterus lumpus and Ocean Pout Macrozoarces americanus Larviculture

The aquaculture of marine finfish in Newfoundland presents a challenge due to the cold-water (<0 C) conditions which occur over a four to five month period. As part of a continuing research program on the culturing of cold-water marine finfish species we report on preliminary results of two "new" aquaculture species. The lumpfish and the Ocean pout both occur along the coast of Newfoundland and are adapted to a cold-water environment. Lumpfish have been reared from egg masses collected from the wild or from eggs stripped in the hatchery. Eggs and larvae are relatively large and larvae are well developed at hatch. Larvae will feed on day-old Artemia nauplii after four to six days. Survival over the first eight weeks is high but declines over the first year. Lumpfish cultured in the laboratory become sexually mature and produce eggs (roe) at the end of their second year. Ocean pout have been cultured only from egg masses collected from the wild. Eggs and larvae are extremely large compared to other marine finfish currently being cultured. Larvae hatch during the cold-water period, absorb the yolk-sac within 24 hours and are ossified at hatch. Juveniles feed on Artemia nauplii within two days at very low temperatures. Survival is comparatively high (75–80%) over the first year. Initial results are encouraging but more research is required before commercial production of these species would be feasible.     

The ecological impact of the Great Salinity Anomaly in the northern North-west Atlantic

In a number of recent papers Cushing has advocated that the Great Salinity Anomaly (GSA), which entered the northern North Atlantic in the early 1970s, adversely affected the recruitment of a number of deep-water fish stocks of this ocean. Cushing envisages that a temperature anomaly accompanying the GSA slowed and/or delayed growth in the spring phytoplankton bloom which sequentially affected zooplankton growth and fish recruitment. We test a number of hypotheses relating to Cushing's picture, focusing on the waters of the West Greenland, Labrador and Newfoundland Shelves. We find that, south of Greenland waters, there were no significant temperature anomalies corresponding to the GSA. In addition we show that stability of the shelf waters increased during the GSA, casting doubt on the contention that the phytoplankton bloom was delayed by retardation of the spring stabilization of the water column due to the influence of cold water. Our analysis indicates that the food chain coupling of environment to recruitment (climate to phytoplankton to zooplankton to fish) is not strong in the study region.     

Assessing connectivity patterns among management units of the Newfoundland and Labrador shrimp population

The Eastern Canadian northern shrimp population, representing one of the most important fisheries in the region, decreased dramatically since the mid‐2000s to a historical low in 2017, but changes were not spatially uniform. Applying a biophysical model within Newfoundland and Labrador (NL) management areas, we investigated connectivity processes during the long pelagic larval phase (2–3 months) of Pandalus borealis and key drivers of larval dispersal in different environmental conditions. We selected 3 years representative of contrasting North Atlantic Oscillation (NAO) phases to assess potential larval dispersal patterns of the northern shrimp population in NL, and hierarchically assessed the impact of the timing of release (yearly and daily), release location, and vertical migration behaviour on shrimp larval dispersal. Overall, we found that populations located on the northern Newfoundland and Labrador shelf supplied potential settlers to southern populations because of the dominant Labrador Current. Ocean circulation and current velocities during the NAO positive year differed from other years, generating contrasting settlement spatial patterns. Larval release location and vertical migration behaviour were the two most important influences on the strength of larval supply and settlement patterns. Inclusion of diel and ontogenic swimming behaviour increased settlement success of larvae released from inshore areas, regardless of study years. Our study improves understanding of northern shrimp stock‐recruitment relationships, their sensitivity to changing environmental conditions, and spatially non‐homogeneous population decline for bentho‐pelagic species with a long larval phase, which could potentially help improve management strategies.     

Processes controlling retention of spring‐spawned Atlantic cod (Gadus morhua) in the western Gulf of Maine and their relationship to an index of recruitment success

Atlantic cod, Gadus morhua, harvested in US waters are currently managed as a Gulf of Maine stock and as a stock comprising Georges Bank and southern New England populations. Over the past two and a half decades, success of age‐1 recruitment to the Gulf of Maine stock has varied by more than an order of magnitude. To investigate the hypothesis that this variation is related to variation in the transport of larval cod to nursery areas, we carried out model simulations of the movement of planktonic eggs and larvae spawned within the western Gulf of Maine during spring spawning events of 1995–2005. Results indicate that the retention of spring‐spawned cod, and their transport to areas suitable for early stage juvenile development, is strongly dependent on local wind conditions. Larval cod retention is favored during times of downwelling‐favorable winds and is least likely during times of upwelling‐favorable winds, during which buoyant eggs and early stage larvae tend to be advected offshore to the Western Maine Coastal Current and subsequently carried out of the Gulf of Maine. Model results also indicate that diel vertical migration of later stage larvae enhances the likelihood of retention within the western Gulf of Maine. Consistent with model results is a strong correlation between age‐1 recruitment success to the Gulf of Maine cod stock and the mean northward wind velocity measured in Massachusetts Bay during May. Based on these findings, we propose a wind index for strong recruitment success of age‐1 cod to the Gulf of Maine stock.     

Bio-physical modelling of the early life stages of haddock, Melanogrammus aeglefinus, in the North Sea

An individual-based modelling approach was developed to investigate the spatial and temporal patterns in the recruitment processes of North Sea haddock, Melanogrammus aeglefinus . The approach was based on the realization that the survivors to recruitment of an annual cohort are most probably not drawn at random from the initial population of eggs, but represent the fastest-growing individuals. Individual growth rates reflect the unique exposure of each larva to the environment along its drift trajectory. In this context, the environment refers to a wide range of factors affecting growth such as food, turbulence and temperature. A combination of a model of egg production by the adult stock, a particle-tracking scheme, and a model of larval growth and mortality rate was used to simulate the dispersal trajectories, and the survival of haddock larvae spawned at different times and locations on the continental shelf. The particle tracking was driven by flowfields from a climatological implementation of the Hamburg Shelf–Ocean Model (HAMSOM) for the North Sea and NE Atlantic. The system was able to resolve spatial and temporal patterns in the recruitment process and indicated that the surviving population of larvae was drawn from a restricted part of the spawning distribution. The results have the potential to guide the development of future conservation measures in fisheries management.     

三峡库区丰都江段鱼类早期资源现状研究

探究三峡库区丰都江段鱼类早期资源现状,评估长江上游梯级水库群联合调度对鱼类早期资源的影响,可为三峡库区渔业资源管理和保护措施制定提供科学依据。2018年5-7月,在三峡库区丰都江段利用圆锥网在左岸、江心和右岸进行鱼卵、鱼苗逐日取样调查。结果显示,调查期间共采集鱼卵7426粒、鱼苗15461尾,隶属于5目、10科、40种(鱼卵16种,仔鱼36种),其中产漂流性卵鱼类19种。估算通过丰都断面的卵苗径流量为290.55×10⁸粒(尾),其中鱼卵89.84×10⁸粒,鱼苗200.71×10⁸尾;四大家的卵苗总径流量为2.24×10⁸粒(尾),其中鱼卵0.95×10⁸粒,鱼苗1.29×10⁸尾。调查期间出现3次产卵高峰,集中在5月下旬和6月下旬。各类仔鱼数量呈现出不同的时间动态,太湖新银鱼(Neosalanx taihuensis)、吻鰕虎鱼属(Rhinogobius sp.)、鲤(Cyprinus carpio)主要出现在5月,四大家鱼以及宜昌鳅鮀(Gobiobotia filifer)主要出现在6月。研究表明,三峡库区靠近库尾段的鱼类早期资源丰富,库尾江段仍存在四大家鱼产卵场。     

Walleye pollock recruitment in Shelikof Strait: applied fisheries oceanography

Fisheries-Oceanography Coordinated Investigations (FOCI) is a National Oceanic and Atmospheric Administration (NOAA) research programme seeking to understand recruitment processes of commercially exploited Alaskan fishes. The FOCI is mainly comprised of scientists at the Pacific Marine Environmental Laboratory and the Alaska Fisheries Science Center who study both the biotic and abiotic environment, including processes within larval patches through integrated field, laboratory, and modelling studies. The initial focus of studies was walleye pollock ( Theragra chakogramma ) spawning in Shelikof Strait, Gulf of Alaska. The choice of this population for our research was based on development of a large fishery and the substantial variation in recruitment that was observed in the late 1970s and early 1980s. Also, the early life history of this population is quite predictable and restricted both temporally and spatially. Walleye pollock spawn consistently in a small part of Shelikof Strait in early spring from which a large patch of eggs and later larvae is produced. In most years this concentration of larvae drifts to the south-west through the strait during April and May. Large numbers of larvae are often found in eddies which frequent the area and we have observed improved feeding conditions for larvae, in as opposed to out of eddies. We have found that first-feeding larvae have higher survival rates during calm periods, rather than in storms, and that in many years recruitment is largely set by the end of the larval period, although in some years age-0 juvenile mortality is also important. FOCI now generates information that is being used for management of this resource.     

Relationships between temperature and landing patterns in the southern Labrador and eastern Newfoundland inshore cod fishery

The temporal pattern of cod landings in the inshore trap fishery off the east coast of Newfoundland and Labrador is examined in this study. Unlike previous studies which have been broad scale or of a localized nature, this analysis looks at variations within fishing seasons and among fishing areas in trap landings. A significant relationship between water temperature and the weekly pattern is demonstrated. Significant spatial patterns in weekly landings are described and related to longshore differences in the seasonal variation in temperature.     

Analysis of fish eggs and larvae flowing into the Three Gorges Reservoir on the Yangtze River,China

Studies on fish eggs and larvae are important for understanding the recruitment dynamics of fish assemblages and their relationships with environmental conditions. Located in the upper reaches of the Yangtze River, China, the Three Gorges Reservoir (TGR) is one of the largest reservoirs in the world, where the fish resource ecology has drawn great attention. With the purpose of evaluating fish recruitment in the TGR, in the present study, samples of fish eggs and larvae were collected at Luoqi County, the upper end of the TGR, from April 15th to July 29th 2011. From the samples collected, we identified 46 fish species belonging to nine families and five orders. The most abundant species were in the Cultrinae, Gobiidae, and Gobioninae. An estimated 12.4 billion fish eggs and larvae drifted into the TGR. There were approximately 2.6 billion Pseudolaubuca sinensis, 1.9 billion Hemiculter leucisculus, and 1.8 billion Gobiidae. The spawning grounds of fishes that release pelagic eggs are in the reaches 13–162 km upstream from our sampling site. More attention should be paid to protecting the habitat in large free stretches upstream of the reservoir, since these areas are important spawning grounds for many fishes. Also, an ample natural flooding regime should be retained in this region.     

The influence of environment and spawning distribution on the survival of anchovy (Engraulis encrasicolus) larvae in the Bay of Biscay (NE Atlantic) investigated by biophysical simulations

A growth and survival model of the early life stages was run along virtual drift trajectories tracked in a hydrodynamic model to simulate the annual recruitment process of anchovy (Engraulis encrasicolus) in the Bay of Biscay (NE Atlantic). These biophysical simulations concerning three different years were analysed in order to investigate the influence of environment and spawning dynamics on the survival of larvae and juveniles. The location of space–time survival windows suggested major environmental mechanisms involved in simulated recruitment variability at the different scales – retention of larvae and juveniles in favourable habitats over the shelf margins and turbulence effects. These small‐scale and meso‐scale mechanisms were related to the variations in wind direction and intensity during spring and summer. Survival was also variable according to the origin of the drift trajectories, that is spawning distribution in space and time. The observed spawning distribution (according to field surveys) was compared with the spawning distribution that would maximize survival (according to the biophysical model) on a seasonal scale, which revealed factors not considered in the biophysical model (e.g. spawning behaviour of the different age classes). The variation of simulated survival according to spawning distribution was examined on a multi‐annual scale and showed a coherent pattern with past and present stock structures. The interaction processes between the population (influence on spawning) and its environment (influence on survival) and its implications on recruitment and stock dynamics are discussed.     

Influence of climate and abundance on migration timing of adult Atlantic salmon (Salmo salar) among rivers in Newfoundland and Labrador

Evidence mounts for the influence of climate variability on temporal trends in the phenology of many organisms including various species of fish. Accordingly, we examined variation in adult Atlantic salmon Salmo salar run timing in thirteen Newfoundland and Labrador rivers where returns were monitored at fishways or fish‐counting fences. Run timing varied significantly among rivers with the median date of return differing by up to 5 weeks. Duration of runs was generally short with most adults returning over a period of three to 5 weeks. A mixed model analysis incorporating a first‐order autoregressive error structure was used to generalise changes in run timing among all monitored rivers. Results indicated that the median date of return has advanced by almost 12 days over a 35‐year interval from 1978 to 2012, while several individual rivers have advanced by almost 21 days. The influence of climate on median timing was evident when the simultaneous effects of both climate and salmon abundance were controlled. We found earlier runs associated with overall warmer climate conditions on the Newfoundland and Labrador Shelf. Results contrast with those from the north‐east Atlantic where Atlantic salmon are returning later in some rivers coincident with warming climate conditions.     

Evidence for the presence of a viral non-lymphocystis type disease in winter flounder, Pseudopleuronectes americanus (Walbaum), from the north-west Atlantic

Abstract. A non-lymphocystis type disease associated with virus particles has been documented in winter flounder, Pseudopleuronectes americanus (Walbaum), taken from a small estuary in Conception Bay, Newfoundland. The papillomatosis-type lesions found on the dorsal surface of the fish contained numerous electron-dense particles, approximately 30 nm in diameter. A number of lines of evidence, including cytochemical studies, indicated that the particles were not glycogen but virions. Sensitivity to deoxyribonuclease enzyme treatment and the presence of crystalline viral'factories' in the nuclei of infected cells further suggested that the particles were small DNA virions. Characteristics including nucleic acid composition, particle size, site of multiplication and the lack of an envelope indicate that this fish virus is similar to the Papovaviridae and Parvoviridae families of mammalian viruses. Lymphocystis is common in flatfish populations along the Newfoundland and Labrador coasts of the N.W. Atlantic, but this is the first record of flatfish infection with a small DNA virus.     

Life cycle of Crangon crangon in the North Sea: a simulation of the timing of recruitment as a function of the seasonal temperature signal

The brown shrimp C. crangon supports a large commercial fishery in British, Belgian, Dutch, German and Danish waters. It produces eggs throughout the year with two seasonal peaks in summer and winter, respectively. Uncertainty exists with regard to the relative importance of the two egg production seasons for the mass invasion of juvenile recruits of 10–20 mm length in May/June, which is the dominant seasonal signal in the German and Dutch Wadden Sea, and which is presumed to grow into the exploitable stock by the autumn, causing the typical rise of commercial catches at that time of the year. A simulation model was developed that predicts the daily abundance of juvenile recruits attaining a given length, typically in the range of 10–20 mm. The model uses: (i) experimental data on the development times of eggs and larvae and the growth rates of juveniles; (ii) field data on the seasonal temperature cycle in different years (1986, 1992 and 1993 or mean conditions) and areas (German and Dutch Wadden Sea) of the North Sea; and (iii) a calculated index of the relative seasonal egg production intensity of adult C. crangon . Predictions of the simulations are compared with field observations on the seasonal occurrence of juvenile recruits in the German and Dutch Wadden Sea. Using temperature data from German waters, in the simulations peak recruitment was predicted to occur 1–2 months later than that observed in the field. However, if seasonal temperature data from Dutch waters were used, the predicted time of the first mass occurrence of recruits matched the field observations more closely. Simulations revealed that the first mass invasion of juveniles originates almost entirely from the winter egg production. It was also found that the simulated recruitment is condensed into a peak, which is narrower after a cold winter.     

Modelling potential spawning habitat of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) in the Bay of Biscay

Large amplitude variations in recruitment of small pelagic fish result from interactions between a fluctuating environment and population dynamics processes such as spawning. The spatial extent and location of spawning, which is critical to the fate of eggs and larvae, can vary strongly from year to year, as a result of changing population structure and environmental conditions. Spawning habitat can be divided into ‘potential spawning habitat’, defined as habitat where the hydrographic conditions are suitable for spawning, ‘realized spawning habitat’, defined as habitat where spawning actually occurs, and ‘successful spawning habitat’, defined as habitat from where successful recruitment has resulted. Using biological data collected during the period 2000–2004, as well as hydrographic data, we investigate the role of environmental parameters in controlling the potential spawning habitat of anchovy and sardine in the Bay of Biscay. Anchovy potential spawning habitat appears to be primarily related to bottom temperature followed by surface temperature and mixed‐layer depth, whilst surface and bottom salinity appear to play a lesser role. The possible influence of hydrographic factors on the spawning habitat of sardine seems less clear than for anchovy. Modelled relationships between anchovy and sardine spawning are used to predict potential spawning habitat from hydrodynamical simulations. The results show that the seasonal patterns in spawning are well reproduced by the model, indicating that hydrographic changes may explain a large fraction of spawning spatial dynamics. Such models may prove useful in the context of forecasting potential impacts of future environmental changes on sardine and anchovy reproductive strategy in the north‐east Atlantic.     

Modelling the effect of buoyancy on the transport of anchovy (Engraulis capensis) eggs from spawning to nursery grounds in the southern Benguela: an IBM approach

An individual‐based model (IBM) was used to investigate the effects of physical and biological variables on the transport via a jet current of anchovy (Engraulis capensis) eggs from spawning to the nursery grounds in the southern Benguela ecosystem. As transport of eggs and early larvae is considered to be one of the major factors impacting on anchovy recruitment success, this approach may be useful to understand further the recruitment variability in this economically and ecologically important species. By coupling the IBM to a 3D hydrodynamic model of the region called Plume, and by varying parameters such as the spatial and temporal location of spawning, particle buoyancy, and the depth range over which particles were released, we could assess the influences of these parameters on transport success. A sensitivity analysis using a General Linear Model identified the primary determinants of transport success in the various experimental simulations, and model outputs were examined and compared with patterns observed in field studies. Model outputs compared well with observed patterns of vertical and horizontal egg distribution. Particle buoyancy and area of particle release were the major single determinants of transport success, with an egg density of 1.025 g cm^?3 maximizing average particle transport success and the western Agulhas Bank being the most successful spawning area. This IBM may be useful as a generic prototype for other upwelling ecosystems.     

Target spawning requirements for Atlantic salmon, Salmo salar L., in Newfoundland rivers

Abstract In recent years, there has been increasing pressure from user groups in Newfoundland and Labrador, Canada, to manage Atlantic salmon, Salmo salar L., on a river-specific basis. The requirement to maximize benefits to users while ensuring that conservation goals are met has resulted in an initiative to develop river-specific target spawning requirements. In Newfoundland, anadromous juvenile Atlantic salmon make widespread use of lacustrine habitat for rearing. Depending on the river, lacustrine habitat can account for a substantial proportion of total production. Therefore, target spawning requirements for a number of rivers in several management areas were derived in terms of the contribution of both riverine and lacustrine habitats. The approach adopted, and derivations of associated parameter values, are reviewed, and limitations and research needs are discussed.     

Influence of larval transport and temperature on recruitment dynamics of North Sea cod (Gadus morhua) across spatial scales of observation

The survival of fish eggs and larvae, and therefore recruitment success, can be critically affected by transport in ocean currents. Combining a model of early‐life stage dispersal with statistical stock–recruitment models, we investigated the role of larval transport for recruitment variability across spatial scales for the population complex of North Sea cod (Gadus morhua). By using a coupled physical–biological model, we estimated the egg and larval transport over a 44‐year period. The oceanographic component of the model, capable of capturing the interannual variability of temperature and ocean current patterns, was coupled to the biological component, an individual‐based model (IBM) that simulated the cod eggs and larvae development and mortality. This study proposes a novel method to account for larval transport and success in stock–recruitment models: weighting the spawning stock biomass by retention rate and, in the case of multiple populations, their connectivity. Our method provides an estimate of the stock biomass contributing to recruitment and the effect of larval transport on recruitment variability. Our results indicate an effect, albeit small, in some populations at the local level. Including transport anomaly as an environmental covariate in traditional stock–recruitment models in turn captures recruitment variability at larger scales. Our study aims to quantify the role of larval transport for recruitment across spatial scales, and disentangle the roles of temperature and larval transport on effective connectivity between populations, thus informing about the potential impacts of climate change on the cod population structure in the North Sea.