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  • 1
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    Trophic cascades in a formerly cod-dominated ecosystem (2005)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2005-06-11
    Description: Removal of top predators from ecosystems can result in cascading effects through the trophic levels below, completely restructuring the food web. Cascades have been observed in small-scale or simple food webs, but not in large, complex, open-ocean ecosystems. Using data spanning many decades from a once cod-dominated northwest Atlantic ecosystem, we demonstrate a trophic cascade in a large marine ecosystem. Several cod stocks in other geographic areas have also collapsed without recovery, suggesting the existence of trophic cascades in these systems.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Frank, Kenneth T -- Petrie, Brian -- Choi, Jae S -- Leggett, William C -- New York, N.Y. -- Science. 2005 Jun 10;308(5728):1621-3.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Fisheries and Oceans, Bedford Institute of Oceanography, Ocean Sciences Division, Post Office Box 1006, Dartmouth, Nova Scotia, B2Y 4A2, Canada. frankk@mar.dfo-mpo.gc.ca〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15947186" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Atlantic Ocean ; Biodiversity ; Biomass ; *Ecosystem ; Fisheries ; *Fishes ; *Food Chain ; Gadus morhua ; *Invertebrates ; *Phytoplankton ; Population Density ; Population Dynamics ; Predatory Behavior ; Principal Component Analysis ; Seals, Earless ; *Seawater ; Time Factors ; *Zooplankton
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Transient dynamics of an altered large marine ecosystem (2011)
    Nature Publishing Group (NPG)
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    Publication Date: 2011-07-29
    Description: Overfishing of large-bodied benthic fishes and their subsequent population collapses on the Scotian Shelf of Canada's east coast and elsewhere resulted in restructuring of entire food webs now dominated by planktivorous, forage fish species and macroinvertebrates. Despite the imposition of strict management measures in force since the early 1990s, the Scotian Shelf ecosystem has not reverted back to its former structure. Here we provide evidence of the transient nature of this ecosystem and its current return path towards benthic fish species domination. The prolonged duration of the altered food web, and its current recovery, was and is being governed by the oscillatory, runaway consumption dynamics of the forage fish complex. These erupting forage species, which reached biomass levels 900% greater than those prevalent during the pre-collapse years of large benthic predators, are now in decline, having outstripped their zooplankton food supply. This dampening, and the associated reduction in the intensity of predation, was accompanied by lagged increases in species abundances at both lower and higher trophic levels, first witnessed in zooplankton and then in large-bodied predators, all consistent with a return towards the earlier ecosystem structure. We conclude that the reversibility of perturbed ecosystems can occur and that this bodes well for other collapsed fisheries.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Frank, Kenneth T -- Petrie, Brian -- Fisher, Jonathan A D -- Leggett, William C -- England -- Nature. 2011 Jul 27;477(7362):86-9. doi: 10.1038/nature10285.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Ocean Sciences Division, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada. kenneth.frank@dfo-mpo.gc.ca〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21796120" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Aquatic Organisms/*physiology ; Atlantic Ocean ; Biomass ; *Ecosystem ; Fisheries ; Fishes/*physiology ; Population Density ; Time Factors ; Zooplankton/physiology
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 3
    Electronic Resource
    Electronic Resource
    Osmoregulation, nutritional effects and buoyancy of marine larval fish: a bioassay for assessing density changes during the earliest life-history stages (1997)
    Springer
    Marine biology 129 (1997), S. 1-9 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract It has been hypothesized that marine fish larvae in the advanced stages of starvation would show increased density (ρ = mass volume−1) from water loss due to osmoregulation failure. Changes in larval buoyancy are currently attributed to swim bladder regulation and protein synthesis or catabolism. Osmoregulation-related changes in density is an alternative mechanism, the importance of which remains untested in the laboratory and the influence of which on vertical distributions is unknown. We provide evidence that loss of osmotic control is a plausible mechanism for increased density of larval cod (Gadus morhua L.). Furthermore, our results show that this mechanism is not restricted to larvae in the advanced stages of starvation. “Relative” larval densities are estimated using a modified density gradient. We use a gravimetric method to separate the effects of nutrition from osmoregulation failure. We assessed the importance of sampling strata on estimates of larval density. Proportional sampling within three depth strata (stratified sample) produced the least biased method for determining the “average” density of a population of larvae in laboratory culture. Larvae sampled from the bottom third of the culture tank were significantly more dense then those sampled from the surface. This was true for larvae of all ages. The average change in density from hatching till death from starvation for larvae sampled in the surface stratum was nominal (Δρ = 5.0 × 10−4 g cm−3), while the change for those sampled from the bottom stratum was large (Δρ = 3.8 × 10−3 g cm−3). These large density differences suggest that larvae sampled from the bottom stratum were either osmotically stressed or were facultatively changing their density via regulatory pathways. Preliminary observations suggest that vitality is lower amongst those larvae which are sampled near the bottom. The small change in average density of larvae sampled from the surface stratum was due to starvation. The density differences we observed between “osmotically stressed” and “starving” larvae could readily have been misconstrued as differences in feeding and growth experienced by individual larvae. The potential bias of increased density from osmoregulation failure must be considered as a factor in experimental designs developed to assess the effect of fed and starved treatments on buoyancy for larvae of all ages. The simple bioassay we describe may prove useful both as a means of assessing larval condition and as a mechanism for evaluating factors affecting larval vertical distributions in the field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050139
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  • 4
    Electronic Resource
    Electronic Resource
    Importance of biotic and abiotic regulators of abundance of the intertidal amphipod Calliopius laeviusculus (Amphipoda: Gammaridae) and assessment of the accuracy and precision of sampling methods for detecting abundance changes (1993)
    Springer
    Marine biology 115 (1993), S. 75-83 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We examined seasonal patterns of abundance for the intertidal amphipod Calliopius laeviusculus (Amphipoda: Gammaridae). Amphipods were sampled with an epibenthic sled during the daytime high tide period from 18 May to 8 August 1988. Amphipod density increased from May to June and reached maxima in both late June and early August. Amphipod density was unrelated to any abiotic component measured in the intertidal community. These variables included sampling location, wave height, water column height, water temperature, salinity and cloud cover. Changes in abundance were related with sampling date and with the onset of capelin (Mallotus villosus) spawning activity in the intertidal. Capelin eggs are an important food item for amphipods. The accuracy of density estimates obtained with the epibenthic sled was assessed through comparison with densities obtained with a more efficient quadrat sampler. Sled samples consistently sampled ca. 1% of the amphipod population. We found that a large portion of the amphipod population burrowed into the sediment and was not effectively sampled by the sled. Sled sampler precision was roughly equivalent to that of quadrats with D (precision) ranging from 0.26 to 0.42 for sled samples and D=0.29 for quadrat samples. Although sample collection with the epibenthic sled was achieved more quickly and under a wider range of weather conditions than was possible with the quadrat sampler, the serious underestimate of amphipod density based on sled samples alone indicates that both sled and quadrat samples, obtained in concert, are required to obtain accurate measures of daily variation in C. laeviusculus abundance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349388
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  • 5
    Electronic Resource
    Electronic Resource
    Genetic relationships among the shads (Alosa) revealed by mitochondrial DNA analysis (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 43 (1993), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We surveyed restriction site differences in mitochondrial DNA. (mtDNA) among five species of shad (Alosa) from North America and Europe. Allis shad, Alosa alosa and twaite shad, Alosa fallax shared two divergent genotype groups, suggesting that the two forms are either a single species, or are distinct species that have hybridized. Phenetic and cladistic analyses of the relationships among the mitochondrial genotypes defined two groups of shad, corresponding to the subgenera, Alosa and Pomolobus. The mean estimated sequence divergence between the mtDNAs of these two groups of shad was 6.5%. Taken in conjunction with fossil data, this divergence estimate suggests that the rate of mtDNA divergence between the two subgenera has been almost 10-fold lower than the ‘conventional’ clock calibration for mtDNA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1993.tb01165.x
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  • 6
    Electronic Resource
    Electronic Resource
    Fisheries Ecology in the Context of Ecological and Evolutionary Theory (1994)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Ecology, Evolution, and Systematics 25 (1994), S. 401-422 
    Details
    ISSN: 0066-4162
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.es.25.110194.002153
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  • 7
    Electronic Resource
    Electronic Resource
    The Ecology of Fish Migrations (1977)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Ecology, Evolution, and Systematics 8 (1977), S. 285-308 
    Details
    ISSN: 0066-4162
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.es.08.110177.001441
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  • 8
    Electronic Resource
    Electronic Resource
    Predicting variability in catch-per-effort in Atlantic cod, Gadus morhua, trap and gillnet fisheries (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 35 (1989), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The relationships between catch rates and fish abundance, hydrographic conditions and fishing effort, for Atlantic cod caught by trapnets (fixed gear) and gillnets (non-fixed gear) in the northern Gulf of St Lawrence have been quantified. Daily changes in trap catch rates were accounted for by changes in salinity, currents and mean local cod densities in 1985 (R2= 0.78), and predicted 1986 trap catch rate changes (by 1985 model) were correlated significantly with those observed (r= 0.60, P 〈 0.05). In contrast, the daily changes in 1985 gillnet catch rates were determined by currents, maximum (not mean) local cod densities, and fishing effort (negative) (R2= 0.68), while predicted 1986 gillnet catch rates (by 1985 model) were significantly correlated with those observed (r= 0.35, P 〈 0.05). Seasonal catchability coefficients of the traps were similar in 1985 and 1986, but for gillnets this index was an order of magnitude higher in 1986 than in 1985.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1989.tb03057.x
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  • 9
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    Large scale synchrony is exploited populations [Ecology] (2016)
    National Academy of Sciences
    Details
    Publication Date: 2016-07-21
    Description: Synchronous variations in the abundance of geographically distinct marine fish populations are known to occur across spatial scales on the order of 1,000 km and greater. The prevailing assumption is that this large-scale coherent variability is a response to coupled atmosphere–ocean dynamics, commonly represented by climate indexes, such as the...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 10
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    Irruptive prey dynamics following the groundfish collapse in the Northwest Atlantic: an illusion? (2013)
    Oxford University Press
    Details
    Publication Date: 2013-10-15
    Description: Frank, K. T., Leggett, W. C., Petrie, B., Fisher, J. A. D., Shackell, N. L., and Taggart, C. T. 2013. Pelagic fish outbreak in the Northwest Atlantic - reality or illusion? – ICES Journal of Marine Science, 70: . The collapse of Northwest Atlantic groundfish in the early 1990s yielded a "natural experiment" within which to explore responses of ecosystems to a major perturbation. The "Pelagic Outburst" hypothesis was developed to explain an up to 900% increase in the abundance of small-bodied forage fishes and macroinvertebrates following this collapse and a subsequent trophic cascade extending across four trophic levels. Recently, this theory has been challenged and an alternative "Suprabenthic Habitat Occupation" (SHO) hypothesis has been advanced; it proposes the prey outburst associated with the forage fish component was an illusion created by changes in the vertical distribution of small pelagic fishes after the cod collapse in favour of a more bottom-oriented distribution that increased their vulnerability to bottom trawls. We evaluated the SHO hypothesis as it applied to the relationship between changes in the biomass of cod and the vertical distribution of herring and sand lance, the major small pelagic species of the Scotian Shelf ecosystem off eastern Nova Scotia. Contrary to predictions of the SHO hypothesis our initial conclusion that a pelagic outburst occurred in that ecosystem was confirmed and we found no evidence of a predator effect on vertical distributions of these species. We also explored the acoustic survey design and execution that generated the data that form the cornerstone of the SHO hypothesis, and the coherence between the behaviour depicted in these data and catch rates in the surface-oriented purse-seine fishery for herring operating at the time of these surveys. In combination, the results of our re-analysis of the population dynamics and behaviour of herring on the eastern Scotian Shelf, lead us to conclude that the SHO hypothesis, at least as it relates to the post-cod collapse dynamics of the affected Northwest Atlantic ecosystems, is not supported.
    Print ISSN: 1054-3139
    Electronic ISSN: 1095-9289
    Topics: Biology , Geosciences , Physics
    Published by Oxford University Press
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