Population dynamics of marine fishes at low abundance

2012 ◽  
Vol 69 (7) ◽  
pp. 1150-1163 ◽  
Author(s):  
David M. Keith ◽  
Jeffrey A. Hutchings
Keyword(s):  
Population Dynamics ◽  
Population Growth ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Growth Models ◽  
Analytical Techniques ◽  
Allee Effects ◽  
Fisheries Science ◽  
Offspring Production ◽  
Per Capita

The recovery of depleted species depends on their population dynamics at low abundance. Classical population growth models, applied widely in fisheries science, assume that per capita offspring production increases as abundance declines (compensation). However, slow or absent recovery by many depleted fishes might reflect unexpectedly weak compensation or the presence of Allee effects (depensation). Using meta-analytical techniques to describe reproductive dynamics, we find considerable variability among 207 exploited marine fish stocks (104 species) in how standardized per capita population growth changes with abundance. Although many species exhibit strong compensatory dynamics (negative density dependence), others show much weaker compensation than expected, and some exhibit evidence of an Allee effect, such as Atlantic cod ( Gadus morhua ) and Alaskan walleye pollock ( Theragra chalcogramma ). As data at low levels of abundance become increasingly available, it appears that compensation, while strong in some species, is comparatively weak or nonexistent in others, thus providing an explanation for why the recovery of some depleted stocks, despite reductions in exploitation, has been considerably less than what classic models of population growth would otherwise suggest.

scholarly journals Increased natural mortality at low abundance can generate an Allee effect in a marine fish

2014 ◽  
Vol 1 (2) ◽  
pp. 140075 ◽  
Author(s):  
Anna Kuparinen ◽  
Jeffrey A. Hutchings
Keyword(s):  
Population Dynamics ◽  
Population Growth ◽  
Density Dependence ◽  
Gadus Morhua ◽  
Allee Effect ◽  
Population Regulation ◽  
Atlantic Cod ◽  
Adult Mortality ◽  
Natural Mortality ◽  
Density Dependent

Negative density-dependent regulation of population dynamics promotes population growth at low abundance and is therefore vital for recovery following depletion. Inversely, any process that reduces the compensatory density-dependence of population growth can negatively affect recovery. Here, we show that increased adult mortality at low abundance can reverse compensatory population dynamics into its opposite—a demographic Allee effect. Northwest Atlantic cod ( Gadus morhua ) stocks collapsed dramatically in the early 1990s and have since shown little sign of recovery. Many experienced dramatic increases in natural mortality, ostensibly attributable in some populations to increased predation by seals. Our findings show that increased natural mortality of a magnitude observed for overfished cod stocks has been more than sufficient to fundamentally alter the dynamics of density-dependent population regulation. The demographic Allee effect generated by these changes can slow down or even impede the recovery of depleted populations even in the absence of fishing.

Influence of growth and survival costs of reproduction on Atlantic cod, Gadus morhua, population growth rate

1999 ◽  
Vol 56 (9) ◽  
pp. 1612-1623 ◽  
Author(s):  
Jeffrey A Hutchings
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Environmental Stochasticity ◽  
Individual Growth ◽  
Growth And Survival ◽  
Individual Growth Rate ◽  
Age Structured ◽  
Reproductive Rates

A stochastic, age-structured life history model was used to examine how age at maturity (theta), pre- (Zimm) and postreproductive (Zmat) mortality, and postreproductive growth rate can affect maximum reproductive rates of fish at low population size. Simulations suggest that annual (r) and per-generation (R0) metrics of population growth for Newfoundland's northern Grand Bank Atlantic cod, Gadus morhua, are primarily influenced by changes to mortality prior to and following reproduction. At observed weights at age and Zmat = 0.2, r ranged between 0.135 and 0.164 for cod maturing at between 4 and 7 years. Incremental increases in either Zimm or Zmat of 0.1 were associated with 0.03-0.05 reductions in r. To effect similar reductions, individual growth rate would have to decline by approximately one half. At observed weights at age, increases in Zmat from 0.20 to 0.45 increased the probability of negative per-generation growth from 3 to 26% for cod maturing at 4 years and from 6 to 46% for cod maturing at 7 years. Thus, even in the absence of fishing mortality, little or no population growth by Atlantic cod may not be unexpected in the presence of environmental stochasticity, particularly when accompanied by increases in mortality and declining individual growth.

Is scientific inquiry incompatible with government information control?

1997 ◽  
Vol 54 (5) ◽  
pp. 1198-1210 ◽  
Author(s):  
J A Hutchings ◽  
C Walters ◽  
R L Haedrich
Keyword(s):  
Natural Resources ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Pacific Salmon ◽  
Scientific Information ◽  
Scientific Uncertainty ◽  
Information Control ◽  
Fisheries Science ◽  
Political Interference ◽  
Scientific Opinion

Government-administered science in Canada, and its potential for bureaucratic and political interference, merits examination in the wake of the biological and socioeconomic catastrophes associated with recent fishery collapses. We cite specific research on Atlantic cod (Gadus morhua) and Pacific salmon (Oncorhynchus spp.) habitat to illustrate how nonscience influences can interfere with the dissemination of scientific information and the conduct of science in the Canadian Department of Fisheries and Oceans. The present framework for linking fisheries science with fisheries management has permitted, intentionally or unintentionally, a suppression of scientific uncertainty and a failure to document comprehensively legitimate differences in scientific opinion. We suggest that the conservation of natural resources is not facilitated by science integrated within a political body. The formation of a politically independent organization of fisheries scientists, or some such reorganization of the link between scientific research and the management of natural resources, merits serious and open debate.

scholarly journals Unpacking the Allee effect: determining individual-level mechanisms that drive global population dynamics

2020 ◽  
Vol 476 (2241) ◽  
pp. 20200350
Author(s):  
Nabil T. Fadai ◽  
Stuart T. Johnston ◽  
Matthew J. Simpson
Keyword(s):  
Population Dynamics ◽  
Cell Biology ◽  
Allee Effect ◽  
Local Density ◽  
Growth Models ◽  
Logistic Growth ◽  
Allee Effects ◽  
Individual Level ◽  
Modelling Framework ◽  
Global Population

We present a solid theoretical foundation for interpreting the origin of Allee effects by providing the missing link in understanding how local individual-based mechanisms translate to global population dynamics. Allee effects were originally proposed to describe population dynamics that cannot be explained by exponential and logistic growth models. However, standard methods often calibrate Allee effect models to match observed global population dynamics without providing any mechanistic insight. By introducing a stochastic individual-based model, with proliferation, death and motility rates that depend on local density, we present a modelling framework that translates particular global Allee effects to specific individual-based mechanisms. Using data from ecology and cell biology, we unpack individual-level mechanisms implicit in an Allee effect model and provide simulation tools for others to repeat this analysis.

Comparison of size-at-age of larval Atlantic cod (Gadus morhua) from different populations based on size- and temperature-dependent growth models

2005 ◽  
Vol 62 (5) ◽  
pp. 1037-1052 ◽  
Author(s):  
A Folkvord
Keyword(s):  
Growth Rates ◽  
Laboratory Experiments ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Growth Models ◽  
Larval Growth ◽  
Growth Potential ◽  
Temperature History ◽  
Temperature Dependent ◽  
Dependent Growth

This study presents the first intraspecific evaluation of larval growth performance across several different experimental scales, environments, and regions of a marine fish species. Size- and temperature-dependent growth models for larval and early juvenile Atlantic cod (Gadus morhua) are developed based on selected laboratory experiments with cod fed in excess. Observed sizes-at-age of cod from several experiments and stocks are compared with predictions from the models using initial size and ambient temperature history as inputs. Comparisons with results from other laboratory experiments reveal that the model predictions represent relatively high growth rates. Results from enclosure experiments under controlled seminatural conditions generally provide growth rates similar to those predicted from the models. The models therefore produce suitable reference growth predictions against which field-based growth estimates can be compared. These comparisons suggest that surviving cod larvae in the sea typically grow at rates close to their size- and temperature-dependent capacity. This suggests that climatic influences will strongly affect the year-to-year variations in growth of cod during their early life history owing to their markedly temperature-dependent growth potential.

Life history consequences of overexploitation to population recovery in Northwest Atlantic cod (Gadus morhua)

2005 ◽  
Vol 62 (4) ◽  
pp. 824-832 ◽  
Author(s):  
Jeffrey A Hutchings
Keyword(s):  
Life History ◽  
Population Growth ◽  
Gadus Morhua ◽  
Life History Traits ◽  
Atlantic Cod ◽  
Hatching Rate ◽  
Northwest Atlantic ◽  
Annual Population ◽  
Age Structured ◽  
Negative Impacts

Changes to life history traits are often concomitant with prolonged periods of exploitation. In the Northwest Atlantic, 30- to 40-year declines of more than 90% of Atlantic cod (Gadus morhua) have been associated with significant reductions in age and length at maturity, changes most parsimoniously explained as genetic responses to fishing. Increased survival costs of reproduction associated with earlier maturity, resulting in higher natural mortality and shorter life span, negatively affect population growth rate and rate of recovery. Coupled with lower hatching rate among first-time spawners and smaller size at maturity, a modest reduction in age from 6 to 4 years can reduce annual population growth in Atlantic cod by 25%–30%, based on the output of a stochastic, age-structured life history model. Earlier maturity more than doubles the probability of negative population growth every generation. These results underscore the potential for fishing-induced changes to life history traits alone to generate slow or negligible recovery in marine fishes, exacerbating negative impacts on population growth resulting from ecosystem-level alterations to interspecific competition and predation.

Excitable and Nonexcitable Population Dynamics

2011 ◽  
Author(s):  
Kevin S. McCann
Keyword(s):  
Population Dynamics ◽  
Growth Rates ◽  
Growth Models ◽  
Population Models ◽  
Logistic Growth ◽  
Population Growth Rates ◽  
Discrete Equations ◽  
Sustained Oscillations ◽  
Continuous Models ◽  
Per Capita

This chapter examines the dynamics of basic population models, with a particular focus on the general biological conditions under which population dynamics are stabilized, or destabilized, by increased population growth rates. Three classes of population models are discussed in relation to excitable and nonexcitable interactions: continuous logistic growth models, discrete equations, and continuous models with stage-structured lags. The chapter shows how increasing per capita growth rates tend to stabilize population models as a result of excitable interactions; that is, when dynamic trajectories monotonically approach an equilibrium after a localized perturbation. However, lags in population models tend to give rise to dynamics with oscillatory decays to equilibrium or sustained oscillations around the carrying capacity. Such oscillatory decays or sustained oscillations are only further destabilized by increased growth or production rates. The chapter concludes with a review of empirical evidence for excitable dynamics.

Temporal and environmental variation in growth and maturity and effects on management reference points of Georges Bank Atlantic cod

2018 ◽  
Vol 75 (12) ◽  
pp. 2159-2171 ◽  
Author(s):  
Timothy J. Miller ◽  
Loretta O’Brien ◽  
Paula S. Fratantoni
Keyword(s):  
Temporal Variation ◽  
State Space ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Growth Models ◽  
Reference Points ◽  
Assessment Model ◽  
Georges Bank ◽  
Bottom Temperature ◽  
Demographic Rates

Temporal variation in demographic rates has been observed in various fish populations and environmental influences are likely to be a key factor. Here we show how it can be important to combine state-space models for environmental covariates and demographic rates when evaluating effects of the former on the latter. In an application to Georges Bank Atlantic cod (Gadus morhua), we show how estimates of the environmental covariate can be aliased with unknown temporal variation in growth rates and that stronger and opposite effects of the environment can incorrectly be found when the autocorrelation in the growth rate is not separately modeled. The perception of effects on maturity also depends on whether an appropriate distribution is considered for the maturity observations. Bottom temperature did not improve prediction of maturity parameters, but temporal variation driven by other sources did. Both bottom temperature and temporal variation improved performance of growth models. Finally, we found growth and maturity estimation to be important contributors to uncertainty of spawning biomass and biological reference points when incorporated into a state-space assessment model.

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