Population dynamics of harvested species with complex age structure (for Pacific salmons fish stocks as an example)

2006 ◽  
Vol 198 (3-4) ◽  
pp. 463-472 ◽  
Author(s):  
E.Ya. Frisman ◽  
E.V. Last ◽  
E.I. Skaletskaya
Keyword(s):  
Population Dynamics ◽  
Age Structure ◽  
Fish Stocks

Population Dynamics of Exploited Fish Stocks at Low Population Levels

Science ◽  
1995 ◽  
Vol 269 (5227) ◽  
pp. 1106-1108 ◽  
Author(s):  
R. A. Myers ◽  
N. J. Barrowman ◽  
J. A. Hutchings ◽  
A. A. Rosenberg
Keyword(s):  
Population Dynamics ◽  
Fish Stocks

scholarly journals Evidence of a variable “unsampled” pelagic fish biomass in shallow water (<20 m): the case of the Gulf of Lion

2006 ◽  
Vol 63 (3) ◽  
pp. 444-451 ◽  
Author(s):  
P. Brehmer ◽  
J. Guillard ◽  
Y. Guennégan ◽  
J.L. Bigot ◽  
B. Liorzou
Keyword(s):  
Time Series ◽  
Population Dynamics ◽  
Shallow Water ◽  
Pelagic Fish ◽  
Fish Density ◽  
Fish Biomass ◽  
Small Pelagic Fish ◽  
Fish Stocks ◽  
Gulf Of Lion ◽  
Bottom Depth

Abstract Studies of small pelagic fish biomass are limited by the fact that research vessels and fishing boats are usually restricted to working areas with a bottom depth >20 m. Consequently, “unsampled” areas can represent a large proportion of the continental shelf, and the biomass in those areas can be important and must be taken into account in assessment methods in order to avoid misleading interpretations in population dynamics. A time-series ten years long has been compiled from acoustic-assessment surveys of small pelagic fish stocks, and the results show an overall increase in the acoustic fish density towards the coast, where values were the highest. Additional experiments on transects covering shallow-water areas (5–20 m) were conducted from 2001 to 2003 with small boats and a research vessel to evaluate the acoustic fish density in those areas. The results confirmed that the fish biomass in shallow water is significant, sometimes very large, and should be evaluated to avoid underestimation. Therefore, surveys should be conducted in shallow water, if at all possible, as well as at greater depths when carrying out surveys destined to support assessment exercises.

scholarly journals Age-structure-dependent recruitment: a meta-analysis applied to Northeast Atlantic fish stocks

2010 ◽  
Vol 67 (9) ◽  
pp. 1921-1930 ◽  
Author(s):  
Thomas Brunel
Keyword(s):  
Opposite Direction ◽  
Age Structure ◽  
Environmental Variability ◽  
Meta Analysis ◽  
Stock Level ◽  
Fish Stocks ◽  
Biological Basis ◽  
Northeast Atlantic ◽  
Age Diversity ◽  
Meta Analyses

Abstract Brunel, T. 2010. Age-structure-dependent recruitment: a meta-analysis applied to Northeast Atlantic fish stocks. – ICES Journal of Marine Science, 67: 1921–1930. Exploitation alters the age structure of fish stocks. Several stock-specific studies have suggested that changes in the age structure might have consequences for subsequent recruitment, but the evidence is not universal. To investigate how common such effects are among 39 Northeast Atlantic fish stocks, relationships were tested between age structure (spawner mean age, age diversity, and proportion of recruit spawners) and recruitment (number of recruits, sensitivity to environment, and recruitment variability). Significant correlations in the expected direction were observed for a few stocks, but not for the majority; significant correlations in the opposite direction were also found. Meta-analyses combining the stock-level tests revealed that none of the effects were significant overall. However, effects were significant for some species (cod, haddock, and plaice) and indices. The low variability in the age structure might explain the absence of significant effects for individual stocks. Other reasons could be the absence of a biological basis (reproductive characteristics not dependent on age) or the stronger influence of environmental variability than of age structure on recruitment.

scholarly journals A fish for all seasons: Spatial and temporal variation in patterns of demographic heterogeneity for Retropinna retropinna

2021 ◽  
Author(s):  
◽  
Christopher McDowall
Keyword(s):  
Population Dynamics ◽  
Seasonal Variation ◽  
New Zealand ◽  
Age Structure ◽  
Growth Rates ◽  
Environmental Conditions ◽  
Environmental Variation ◽  
Life Cycles ◽  
Demographic Heterogeneity ◽  
Demographic Attributes

<p>Demographic heterogeneity can have big effects on population dynamics, but for most species we have limited understanding of how and why individuals vary. Variation among individuals is of particular importance for stage-structured populations, and/or where species have ‘complex life-cycles’. This is especially relevant in the case of amphidromous fishes that typically spawn in river mouths and estuaries, develop at sea and return to freshwater to finish development. These fish face strong selection pressures as they negotiate challenges around dispersal and development in order to reproduce successfully. Quantifying variation amongst individual fish can improve understanding of their population dynamics and suggest possible drivers of variation.  I evaluate patterns and sources of variation in demographic attributes of the New Zealand smelt (Retropinna retropinna). R. retropinna is an amphidromous fish that is endemic to New Zealand. While most populations have a sea-going larval stage, a number of landlocked freshwater populations occur, with the largest landlocked population residing in Lake Taupo. Here R. retropinna are presented with a variety of littoral feeding/spawning habitats and environmental conditions that may vary across distinct regions of the lake. In addition, the protracted spawning period for this species in Lake Taupo (occurring over eight months of the year) provides additional scope for seasonal variation to influence demographic attributes of individuals.  I sampled R. retropinna from discrete coastal habitats (beach or river) that were located in the eastern, southern and western regions of the lake. I evaluated patterns of variation in the size-structure, age-structure and morphology of R. retropinna among habitats and/or regions across Lake Taupo. I used otoliths to reconstruct demographic histories (ages, growth rates, hatch dates) of individuals, and used a set of statistical models to infer spatial variation in demographic histories. I found differences in size and age structure between regions, and a temporal effect of hatch date on larval/juvenile growth rates.  In addition, I obtained samples of R. retropinna from a sea-going population at the Hutt river mouth (sampled fish were presumed to be migrating upstream after their development period in Wellington Harbour and/or adjacent coastal environments). While Lake Taupo is large, deep, fresh, oligotrophic and strongly stratified for 8-9 months outside of winter, Wellington Harbour is less than a sixth of the area, shallow, saline, eutrophic and never stratified. These greatly differing environmental conditions led me to expect that these systems’ R. retropinna populations would carry significantly different demographic attributes. I compared the hatching phenology, recruitment age, body morphology, and individual growth histories (reconstructed from otoliths) of R. retropinna sampled from Lake Taupo and Wellington Harbour. I explored the relationships between demographic variation and environmental variation (water temperature, chlorophyll a) for the two systems and found that this additional environmental information could account for much of the seasonal variation in daily otolith increment widths of R. retropinna. My results also suggest that while the two sampled populations likely share similar hatching and spawning phenologies, individuals from Lake Taupo tend to grow more slowly, particularly during winter, and end up smaller than sea-going fish sampled near Wellington. I speculate that these differences reflect variation in food supply (zooplankton may be limited in Lake Taupo over winter).  Overall, my results demonstrate a high degree of variation in morphological and life-history traits within a single species, potentially driven by an interaction between environmental variation and timing of development. My work contributes to a growing body of literature on demographic heterogeneity, and may help to inform the management of landlocked populations of R. retropinna in Lake Taupo.</p>

Dynamic modes of exploited limited population: results of modeling and numerical study

2016 ◽  
Vol 11 (1) ◽  
pp. 1-13 ◽  
Author(s):  
Г.П. Неверова ◽  
G.P. Neverova
Keyword(s):  
Population Dynamics ◽  
Density Dependence ◽  
Population Size ◽  
Age Structure ◽  
Birth Rate ◽  
Numerical Study ◽  
Dynamic Regime ◽  
Demographic Parameters ◽  
Current Population

The paper investigates the model of population dynamics with age structure and density dependence of birth rate. We consider two situations: 1) the population develops freely and 2) the population is exploited. It was shown that harvesting leads to the stabilization of the dynamics. There is multiregimism, i.e. different dynamic regimes are possible with the same values of demographic parameters. It is shown that even a single harvesting in the current population size could lead to a change of the observed dynamic regime.

scholarly journals Decomposing variation in population growth into contributions from environment and phenotypes in an age-structured population

2011 ◽  
Vol 279 (1727) ◽  
pp. 394-401 ◽  
Author(s):  
Fanie Pelletier ◽  
Kelly Moyes ◽  
Tim H. Clutton-Brock ◽  
Tim Coulson
Keyword(s):  
Population Dynamics ◽  
Population Growth ◽  
Age Structure ◽  
Life History Traits ◽  
Population Fluctuations ◽  
Relative Importance ◽  
Ecological Interactions ◽  
Structured Population ◽  
Individual Covariates ◽  
Age Structured

Evaluating the relative importance of ecological drivers responsible for natural population fluctuations in size is challenging. Longitudinal studies where most individuals are monitored from birth to death and where environmental conditions are known provide a valuable resource to characterize complex ecological interactions. We used a recently developed approach to decompose the observed fluctuation in population growth of the red deer population on the Isle of Rum into contributions from climate, density and their interaction and to quantify their relative importance. We also quantified the contribution of individual covariates, including phenotypic and life-history traits, to population growth. Fluctuations in composition in age and sex classes ((st)age structure) of the population contributed substantially to the population dynamics. Density, climate, birth weight and reproductive status contributed less and approximately equally to the population growth. Our results support the contention that fluctuations in the population's (st)age structure have important consequences for population dynamics and underline the importance of including information on population composition to understand the effect of human-driven changes on population performance of long-lived species.

Optimizing Survey Design for Determining Age Structure of Fish Stocks: an Example from British Columbia Pacific Herring (Clupea harengus pallasi)

1983 ◽  
Vol 40 (5) ◽  
pp. 588-597 ◽  
Author(s):  
J. F. Schweigert ◽  
J. R. Sibert
Keyword(s):  
Age Structure ◽  
Survey Design ◽  
Clupea Harengus ◽  
Pacific Herring ◽  
Stage Design ◽  
Fish Stocks ◽  
Cost Structures ◽  
Survey Statistics ◽  
Clupea Harengus Pallasi ◽  
Survey Designs

Sampling commercial catches of fishes is considered for the first time from the viewpoint of survey statistics. The determination of the age-structure of Pacific herring (Clupea harengus pallasi) is approached as a multistage subsampling problem. Optimum allocation of sampling resources is obtained by minimizing the product of total cost and total variance. Optimal survey designs are analyzed for a variety of reasonable cost structures for all age-classes. The most reasonable design that applies to all areas of the coast is to use a two-stage design, including a single sample of about 60 aged fish per vessel. The number of vessels to sample is a function of the required precision and available resources.

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