After a century of research into the drivers of early life (EL) growth and mortality, fisheries science has acquired limited capacity to predict future recruitment. A meta-analysis of stock ...assessment time series revealed that it may be difficult to identify stock– or environmental–recruitment drivers given limited variability in spawner biomass, recruitment, and survivorship in most populations. In nearly 50% of the stocks, there was limited information at low spawner biomass, limiting the reliability of fits to stock–recruitment models. Furthermore, variations in survivorship in 50% of year-classes resulted in less than a 2.5-fold change in recruitment. Simulations of three scenarios of change in EL growth and mortality rates demonstrated that they must covary positively to reproduce variations in survivorship consistent with observations. The potentially limited reliability of stock–recruitment relationships to predict year-class strength in many stocks and the low variability in survivorship in a large proportion of year-classes has important implications for the development of projections of stock productivity used in scientific advice. Furthermore, if a positive growth–mortality relationship underlies variations in survivorship, new research approaches are required to understand the trophic relationships that govern the dynamics of early life stages of fish and patterns of recruitment variability.
This study evaluated the distribution of major calanoid copepods in the western Labrador Sea in relation to that of the myctophid Benthosema glaciale, and investigated patterns of prey composition ...and feeding periodicity by the latter to assess the potential impact of mesopelagic fish on copepod populations that reside in the deep ocean. Hydroacoustic surveys indicated that B. glaciale and the deep-scattering layer are widely distributed throughout the region with limited evidence of patchiness, with an average abundance of 6 fish m−2 and biomass of 9.3gm−2. There was clear evidence of diurnal variations in feeding activity that was achieved through vertical migration from several hundred meters depths to the surface layer. B. glaciale fed principally on calanoid copepods, with prey size dependent on the length of the fish but the relative variability in prey size was independent of predator length. Average rations were generally less than 1% of body weight per day, and the patterns of diurnal vertical migration by myctophids suggest that individuals fed once every two days rather than daily. The estimated mortality caused by B. glaciale on the calanoid populations, which considers most sources of uncertainty, ranged from 0.002 to 1.8% d−1, with the mid-point of these estimates being ∼0.15% d−1, which is well below the estimated mortality rates of 10–20% d−1 based on vertical life tables. From observations from this and other ecosystems, understanding and contrasting the drivers of population dynamics and productivity of calanoid copepods in different deep basins of the North Atlantic will likely require a more comprehensive characterization of the plankton and pelagic and oceanic fish faunas of the epipelagic and mesopelagic zones and their trophic relationships and interactions.
► The deep-scattering layer was ubiquitous across the Labrador Sea and showed limited patchiness. ► Calanoid copepods were the principle prey of Benthosema glaciale. ► The overall impact of B. glaciale on the copepods populations appeared to be modest (<1%/d). ► Prey size was significantly related to predator length but niche breadth was not. ► Evacuation rates and patterns of vertical migration indicate low metabolic demands by B. glaciale.
Survival through the larval phase is predicated on the probabilities of successful feeding, which dictates growth rates, and the probabilities of encountering predators. Here I perform a synthesis of ...feeding, growth, and mortality rates estimated during several studies from coastal Newfoundland, Canada, to provide a description of the probability distribution that can serve as a foundation of the expected distribution of vital rates. The standardized observations clearly follow that of skewed distributions, appropriately fit to a probability gamma distribution, with feeding demonstrating a stronger degree of skewness than either mortality or growth, possibly because each vital rate integrates prey–predator interactions over different time scales. Commonality in the underlying form of the distribution of vital rates in larval fish, along with clear functional relationships between gamma parameters, represents a probabilistic basis of expectations against which observations from prior or new studies can be contrasted. An example of the use of such expectations demonstrates that they can provide useful contextual information about the contrast among observations and our ability to identify their relationship with environmental drivers.
Abstract This study contrasts diet composition patterns of larval fish categorized as strong and weak foragers, identified from quadratic relationships between larval length and the number of prey ...eaten, for 11 fish species. Two sets of alternative hypotheses test whether strong foragers (1) exhibit precocious behaviour by eating later developmental stages of copepods, and (2) take advantage of random encounters with zooplankton, based on the contrast between the two categories in each 1 mm length-class. Results indicate that strong foragers shift their feeding toward earlier copepod developmental stages, which was most apparent in four flatfish species, and demonstrate stronger overall prey selectivity than weak foragers. Inverse modeling revealed the latter is achieved through increases in apparent prey perception and/or responsiveness to dominant prey types (i.e. nauplii and copepodites) and declines for less frequent prey (e.g. veliger and Cladocera). Foraging strength increased modestly with larger eye diameter and mouth gape. Two possible explanations for prey selection patterns are that strong foragers have inherently different capacity to perceive and attack prey, or that after initially eating sufficient large prey to meet metabolic requirements fuller stomachs depend on the ability of larval fish to take advantage of random encounters.
Abstract
Data on individual stomach contents were used to describe length-dependent differences in feeding success of larvae of 11 species of fish found in coastal Newfoundland, Canada. Copepods ...dominated the diet with a gradual shift from nauplii to copepodites in all species. Differences in feeding success in both prey number and gut fullness among individual larvae was linked to increasing individual diet diversity in all taxa, although there was a weak decline in mean prey size. Maxilla and body length, within and among taxa, have a dominant positive influence on the potential feeding success of larval fish. In addition to differences in average stomach weight, the variability in number of prey per stomach among individuals indicates that each species perceives their prey environment in different ways. Taxonomic proximity had limited effect on differences in feeding success among taxa. The results suggest that behavioural differences among individuals and taxa, that likely reflect swimming capacity and/or prey perception/capture ability, are likely to be important elements contributing to feeding success. Body and mouth size may represent key characteristics that should be considered in evaluating differences in feeding success among species as well as among individuals within and among cohorts.
Syntheses of carbonate chemistry spatial patterns are important for predicting ocean acidification impacts, but are lacking in coastal oceans. Here, we show that along the North American Atlantic and ...Gulf coasts the meridional distributions of dissolved inorganic carbon (DIC) and carbonate mineral saturation state (Ω) are controlled by partial equilibrium with the atmosphere resulting in relatively low DIC and high Ω in warm southern waters and the opposite in cold northern waters. However, pH and the partial pressure of CO
(pCO
) do not exhibit a simple spatial pattern and are controlled by local physical and net biological processes which impede equilibrium with the atmosphere. Along the Pacific coast, upwelling brings subsurface waters with low Ω and pH to the surface where net biological production works to raise their values. Different temperature sensitivities of carbonate properties and different timescales of influencing processes lead to contrasting property distributions within and among margins.
The Northwest Atlantic marine ecosystem off Newfoundland and Labrador, Canada, has been commercially exploited for centuries. Although periodic declines in various important commercial fish stocks ...have been observed in this ecosystem, the most drastic changes took place in the early 1990s when the ecosystem structure changed abruptly and has not returned to its previous configuration. In the Northwest Atlantic, food web dynamics are determined largely by capelin (Mallotus villosus), the focal forage species which links primary and secondary producers with the higher trophic levels. Notwithstanding the importance of capelin, the factors that influence its population dynamics have remained elusive. We found that a regime shift and ocean climate, acting via food availability, have discernible impacts on the regulation of this population. Capelin biomass and timing of spawning were well explained by a regime shift and seasonal sea ice dynamics, a key determinant of the pelagic spring bloom. Our findings are important for the development of ecosystem approaches to fisheries management and raise questions on the potential impacts of climate change on the structure and productivity of this marine ecosystem.
The photosynthetic performance of marine phytoplankton varies in response to a variety of factors, environmental and taxonomic. One of the aims of the MArine primary Production: model Parameters from ...Space (MAPPS) project of the European Space Agency is to assemble a global database of photosynthesis–irradiance (P-E) parameters from a range of oceanographic regimes as an aid to examining the basin-scale variability in the photophysiological response of marine phytoplankton and to use this information to improve the assignment of P-E parameters in the estimation of global marine primary production using satellite data. The MAPPS P-E database, which consists of over 5000 P-E experiments, provides information on the spatio-temporal variability in the two P-E parameters (the assimilation number, PmB, and the initial slope, αB, where the superscripts B indicate normalisation to concentration of chlorophyll) that are fundamental inputs for models (satellite-based and otherwise) of marine primary production that use chlorophyll as the state variable. Quality-control measures consisted of removing samples with abnormally high parameter values and flags were added to denote whether the spectral quality of the incubator lamp was used to calculate a broad-band value of αB. The MAPPS database provides a photophysiological data set that is unprecedented in number of observations and in spatial coverage. The database will be useful to a variety of research communities, including marine ecologists, biogeochemical modellers, remote-sensing scientists and algal physiologists. The compiled data are available at https://doi.org/10.1594/PANGAEA.874087 (Bouman et al., 2017).
We report on the patterns in zooplankton community structure on the Newfoundland and Labrador Shelf from seasonal collections along oceanographic sections during 2000–2007. We use a combination of ...constrained and unconstrained multivariate methods to assess latitudinal and cross shelf patterns in community structure. Both physical and biological features of the region are dominated by the cross-shelf gradient in water mass characteristics although there is evidence of a latitudinal gradient that may be a reflection of the influence of freshwater outflow from the Arctic. All analyses reveal a strong and consistent pattern in species composition among water masses that extends across spring, summer and autumn, although there are some variations that occur among seasons that reflect differences in development state of certain taxa. The strong association between community structure and water mass characteristics in the region may be the result of the Newfoundland and Labrador Shelf being at the intersection of several major oceanographic domains, bounded by strong Labrador and Gulf Stream currents, that allows the formation and persistence of well defined zooplankton communities. Our findings have implications for the region’s potential as a monitoring location for long term changes in ocean state.
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