Application of a Multispecies Approach for Assessing the Population Abundance and the Age–Structure of Fish Stocks

1981 ◽  
Vol 38 (4) ◽  
pp. 424-431 ◽  
Author(s):  
Jacek Majkowski
Keyword(s):  
Fish Species ◽  
Age Structure ◽  
Cohort Analysis ◽  
Laboratory Data ◽  
Single Species ◽  
Fish Predation ◽  
Fish Population ◽  
Natural Mortality ◽  
Population Abundance ◽  
Fish Stocks

Application of a multispecies approach for assessing the population abundance and the age-structure of fish stocks is proposed. The main objective of this approach is to eliminate a bias in the results of cohort analysis (the most frequently used single-species procedure for assessing the fish population age-structure) caused by uncertainties in the external estimates of natural mortality rates. The approach is applicable if fish predation is a major cause for fish natural mortality and all fish species which significantly interact among themselves through predation are taken into account. It is additionally assumed that these fish species do not leave the area under consideration. Compliance with these conditions allows the prediction, on the basis of ecological theory and required field and laboratory data, of a major component of natural mortality, predation mortality, within extended cohort analysis. The paper describes the proposed procedure (extended cohort analysis) and outlines possible ways of collecting the required input data.Key words: assessment, fish population abundance, age-structure, multispecies approach, natural and fishing mortality

Multispecies versus Single-Species Assessment of North Sea Fish Stocks

1987 ◽  
Vol 44 (S2) ◽  
pp. s360-s370 ◽  
Author(s):  
Niels Daan
Keyword(s):  
Population Analysis ◽  
Stomach Contents ◽  
Single Species ◽  
Fish Stock ◽  
Natural Mortality ◽  
Stock Management ◽  
Fish Stocks ◽  
Virtual Population Analysis ◽  
Virtual Population ◽  
Class Strength

Development of multispecies virtual population analysis (MSVPA), which assesses interspecific and intraspecific predation through an analysis of stomach contents, has verified the hypothesis that predation among exploited fish species contributes significantly to their natural mortality and that predation, and thus natural mortality, is inherently variable from year to year. In single-species virtual population analysis (SSVPA), natural mortality is assumed to be constant. MSVPA also suggests that natural mortality among young fish after recruitment is much higher than previously thought. Although catch quotas based on predictions of short-term catches from multispecies assessments would appear to differ little from those derived from single-species assessments, and certain problems remain to be resolved before multispecies assessments can be accepted for fish stock management, the method has considerable implications for management. For instance, it suggests that effects of mesh sizes and bycatch on fisheries need reevaluation and that year class strength may not be as fixed as previously assumed.

scholarly journals Tracking red deer population size using deterministic cohort analysis

2021 ◽  
Author(s):  
Valerio Donini ◽  
Luca Corlatti ◽  
Luca Pedrotti
Keyword(s):  
Population Size ◽  
Cervus Elaphus ◽  
Red Deer ◽  
Cohort Analysis ◽  
Cost Effective ◽  
Natural Mortality ◽  
Relative Index ◽  
Deer Population ◽  
Monitoring Tools ◽  
Over Time

AbstractReliable and cost-effective monitoring tools to track population size over time are of key importance for wildlife management and conservation. Deterministic cohort analysis may be used to this aim, especially in hunted populations, but it requires that all mortality events are recorded and that individual age at death is known exactly. In this study, we investigated the reliability of cohort analysis as a relative index to track over-time variation in red deer (Cervus elaphus) abundance, in the absence of exact information about natural mortality and age. Visual tooth inspection was used to age 18,390 individuals found dead or hunted between 1982 and 2020 within the Trentino sector of the Stelvio National Park and the Val di Sole hunting district (Central Italian Alps). Temporal trend of reconstructed population size was checked using spring spotlight counts as a benchmark, through the Buishand range test and a linear model. Our results showed a significant and positive relationship between reconstructed population size and spring spotlight counts between 1982 and 2013, suggesting that cohort analysis could reliably track red deer population trend up to 7 years in the past. With a relative error of  +  1.1 (SD  =  1.5) years in the estimation of age, and fairly stable hunting pressure, our results support the use of deterministic cohort analysis as a relative index of abundance for monitoring red deer over time, even in the absence of exact information about natural mortality. Under violation of assumptions, however, the performance of deterministic reconstruction should be carefully inspected at the management scale.

Virtual Population Analysis (VPA) Equations for Nonhomogeneous Populations, and a Family of Approximations Including Improvements on Pope's Cohort Analysis

1986 ◽  
Vol 43 (12) ◽  
pp. 2406-2409 ◽  
Author(s):  
Alec D. MacCall
Keyword(s):  
Mortality Rate ◽  
Population Analysis ◽  
Seasonal Pattern ◽  
Cohort Analysis ◽  
Natural Mortality ◽  
Close Approximation ◽  
Virtual Population Analysis ◽  
Virtual Population ◽  
Special Case

A set of "backward" virtual population analysis (VPA) equations relates catch (Ct) from continuous fishing between times t and t + 1 to population n size (Nt, Nt+1) when a portion of the stock is unavailable to fishing. The usual VPA equations become a special case where the entire stock is available (i.e. the stock is homogeneous). A close approximation to the VPA equations is Nt = Nt+1 exp(M) + CtM/(1 − exp(−M)), which has properties similar to Pope's "cohort analysis" and is somewhat more accurate in the case of a continuous fishery, especially if the natural mortality rate (M) is large. Much closer simple approximations are possible if the seasonal pattern of catches is known.

THE EFFECT OF SEASONAL HARVESTING ON A STAGE-STRUCTURED DISCRETE MODEL WITH BIRTH PULSES

2006 ◽  
Vol 16 (09) ◽  
pp. 2575-2586 ◽  
Author(s):  
SHUJING GAO ◽  
LANSUN CHEN
Keyword(s):  
Single Pulse ◽  
Stage Structure ◽  
Single Species ◽  
Fish Population ◽  
Basins Of Attraction ◽  
Fish Stock ◽  
Strong Impact ◽  
Natural Period ◽  
Discrete Population ◽  
Mature Fish

In this paper, we propose an exploited single-species discrete population model with stage structure for the dynamics in a fish population for which births occur in a single pulse once per time period. Using the stroboscopic map, we obtain an exact cycle of the system, and obtain the threshold conditions for its stability. Bifurcation diagrams are constructed with the birth rate (or harvesting effort) as the bifurcation parameter, and these are observed to display complex dynamic behaviors, including chaotic bands with period windows, pitchfork and tangent bifurcation, nonunique dynamics (meaning that several attractors or attractor and chaos coexist), basins of attraction and attractor crisis. This suggests that birth pulse provides a natural period or cyclicity that makes the dynamical behaviors more complex. Moreover, we show that the timing of harvesting has a strong impact on the persistence of the fish population, on the volume of mature fish stock and on the maximum annual-sustainable yield. An interesting result is obtained that, after the birth pulses, the population can sustain much higher harvesting effort if the mature fish is removed as early in the season as possible.

New Scientific Information Can Help to Inform the Evaluation of EU Deep-sea Fisheries Regulations

2021 ◽  
pp. 1-20
Author(s):  
Phillip J Turner ◽  
Matthew Gianni ◽  
Ellen Kenchington ◽  
Sebastian Valanko ◽  
David E Johnson
Keyword(s):  
Deep Sea ◽  
Scientific Information ◽  
Fish Population ◽  
Molecular Techniques ◽  
Fish Stocks ◽  
Horizon 2020 ◽  
Management Measures ◽  
Sea Fish ◽  
The Eu ◽  
Fish Population Structure

Abstract The European Union’s deep-sea fisheries regulations (Regulation (EU) No. 2016/2336) established obligations to manage deep-sea fisheries and to protect vulnerable marine ecosystems (VMEs). The European Commission is scheduled to complete a review of the regulations in 2021, providing an opportunity for new scientific information to be incorporated into the implementation of the regulations. Here, we summarise research outputs from the EU-funded Horizon 2020 ATLAS Project and explain their relevance to the regulation of deep-sea fisheries in EU waters. ATLAS research has increased our understanding of the distribution of VMEs and their importance in terms of ecosystem functioning. ATLAS research has also highlighted the utility of molecular techniques to understand fish population structure and the potential for habitat suitability models to help incorporate climate change into decision-making. Building on these scientific advances, we provide recommendations to help increase the effectiveness of management measures to conserve deep-sea fish stocks and protect VMEs.

Influence of errors in natural mortality estimates in cohort analysis

1997 ◽  
Vol 54 (7) ◽  
pp. 1608-1612 ◽  
Author(s):  
G Mertz ◽  
R A Myers
Keyword(s):  
Mortality Rate ◽  
Similar Pattern ◽  
Cohort Analysis ◽  
Transient Behavior ◽  
Natural Mortality ◽  
Exact Formulation ◽  
Fishing Mortality ◽  
Bias Factor ◽  
Special Case ◽  
Mortality Estimates

The accuracy of the estimation of cohort strength from catch data may be greatly degraded if a poor estimate of the natural mortality rate is entered into the calculation. A straightforward, exact formulation for the error in cohort reconstruction due to a misspecified natural mortality rate is presented. The special case of constant fishing mortality is particularly transparent, allowing the error to be segmented into easily interpreted terms. A change in the fishing mortality may result in a distinct hump in the transient behavior of the bias factor, rather than a simple monotonic adjustment. This implies a similar pattern in estimated cohort strength.

scholarly journals STUDY OF SINGLE-SPECIES POPULATION MODELS

2020 ◽  
pp. 161-166
Author(s):  
Marthak Rutu
Keyword(s):  
Spatial Heterogeneity ◽  
Environmental Effects ◽  
Age Structure ◽  
Single Species ◽  
Research Paper ◽  
Population Models ◽  
Deterministic Models ◽  
One Dimensional ◽  
Species Population ◽  
Single Species Population

In this research paper one dimensional population models developed centuries ago shows that growth and/decay of single homogeneous populations But environmental effects spatial heterogeneity or age-structure deterministic models prevailing single species population models.

The community structure of larval fish populations in an area of the Celtic Sea in 1998

2002 ◽  
Vol 82 (4) ◽  
pp. 641-648 ◽  
Author(s):  
S. Acevedo ◽  
O. Dwane ◽  
J.M. Fives
Keyword(s):  
Community Structure ◽  
Fish Species ◽  
Larval Fish ◽  
Single Species ◽  
Coastal Fish ◽  
Larval Stages ◽  
Celtic Sea ◽  
Sea Area ◽  
Insight Into ◽  
Fish Distributions

Ichthyoplankton from an area in the Celtic Sea was studied to provide an insight into the fish larval community structure in March, May and June 1998. Three station groups were defined each month, Neritic, Transition and Oceanic. The Neritic assemblages included larval stages of coastal fish species and the Oceanic assemblages included mesopelagic and high-oceanic fish species which were not recorded from any of the Neritic stations. The Transition stations usually contained species characteristic of both the Neritic and Oceanic assemblages. It is suggested that these broad patterns of larval fish distributions are constant features of the Celtic Sea area, probably related to the spawning location of the adults. The area is, in general, species poor, with the Oceanic stations usually dominated by a single species, indicating the presence of a large spawning school of fish.

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