Ovulatory Rhythm and a Method to Determine the Stage of Spawning in Atlantic Cod (Gadus morhua)

1990 ◽  
Vol 47 (6) ◽  
pp. 1185-1193 ◽  
Author(s):  
O. S. Kjesbu ◽  
P. R. Witthames ◽  
P. Solemdal ◽  
M. Greer WalKer
Keyword(s):  
Standard Deviation ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Stock Assessment ◽  
Growth Period ◽  
Fish Stock ◽  
Oocyte Growth ◽  
Size Frequency Distribution ◽  
Fish Stock Assessment ◽  
Linear Regressions

The size frequency distribution of the vitellogenic oocytes in Atlantic cod (Gadus morhua) changes in a predictable manner as spawning progresses. This change was studied by sampling successive batches of eggs from reared cod kept in the laboratory. The shape of the vitellogenic oocyte mode was described by measuring the diameter, standard deviation, and skewness and kurtosis. Linear regressions were derived which related the portion of the total number of eggs spawned per season (PES) to the number of vitellogenic oocytes per gram of the ovary and in relation to the standard deviation of the distribution. This method which allows the PES in a spawning fish to be estimated has the following applications. For fish stock assessment purposes fecundity estimates can be made on spawning rather than prespawning fish and residence times on spawning grounds can be calculated. In addition successive batches of eggs can be identified and studied. This is important in hormonal and larval studies. A detailed description is given of the oocyte growth during the ovulatory rhythm. The rhythm consists of four periods: arrest, final growth, hydration, and ovulation. It is suggested that the egg size is determined during the final growth period.

scholarly journals Non-linearity in stock–recruitment relationships of Atlantic cod: insights from a multi-model approach

2019 ◽  
Vol 77 (4) ◽  
pp. 1492-1502 ◽  
Author(s):  
Camilla Sguotti ◽  
Saskia A Otto ◽  
Xochitl Cormon ◽  
Karl M Werner ◽  
Ethan Deyle ◽  
...  
Keyword(s):  
Environmental Variables ◽  
Gadus Morhua ◽  
Fishery Management ◽  
Atlantic Cod ◽  
Stock Assessment ◽  
Fish Stock ◽  
Recovery Potential ◽  
Stock Recruitment ◽  
Model Approach ◽  
Non Parametric

Abstract The stock–recruitment relationship is the basis of any stock prediction and thus fundamental for fishery management. Traditional parametric stock–recruitment models often poorly fit empirical data, nevertheless they are still the rule in fish stock assessment procedures. We here apply a multi-model approach to predict recruitment of 20 Atlantic cod (Gadus morhua) stocks as a function of adult biomass and environmental variables. We compare the traditional Ricker model with two non-parametric approaches: (i) the stochastic cusp model from catastrophe theory and (ii) multivariate simplex projections, based on attractor state-space reconstruction. We show that the performance of each model is contingent on the historical dynamics of individual stocks, and that stocks which experienced abrupt and state-dependent dynamics are best modelled using non-parametric approaches. These dynamics are pervasive in Western stocks highlighting a geographical distinction between cod stocks, which have implications for their recovery potential. Furthermore, the addition of environmental variables always improved the models’ predictive power indicating that they should be considered in stock assessment and management routines. Using our multi-model approach, we demonstrate that we should be more flexible when modelling recruitment and tailor our approaches to the dynamical properties of each individual stock.

scholarly journals Detecting regime shifts in fish stock dynamics

2015 ◽  
Vol 72 (11) ◽  
pp. 1619-1628 ◽  
Author(s):  
Tommi Perälä ◽  
Anna Kuparinen
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Stock Assessment ◽  
Detection Algorithm ◽  
Regime Shifts ◽  
Change Point Detection ◽  
Fish Stock ◽  
Fish Stocks ◽  
Data Generating Process ◽  
Change In Mean

Environmental factors such as water temperature, salinity, and the abundance of zooplankton can have major effects on certain fish stocks’ ability to produce juveniles and, thus, stock renewal ability. This variability in stock productivity manifests itself as different productivity regimes. Here, we detect productivity regime shifts by analyzing recruit-per-spawner time series with Bayesian online change point detection algorithm. The algorithm infers the time since the last regime shift (change in mean or variance or both) as well as the parameters of the data-generating process for the current regime sequentially. We demonstrate the algorithm’s performance using simulated recruitment data from an individual-based model and further apply the algorithm to stock assessment estimates for four Atlantic cod (Gadus morhua) stocks obtained from RAM legacy database. Our analysis shows that the algorithm performs well when the variability between the regimes is high enough compared with the variability within the regimes. The algorithm found several productivity regimes for all four cod stocks, and the findings suggest that the stocks are currently in low productivity regimes, which have started during the 1990s and 2000s.

Detecting and correcting underreported catches in fish stock assessment: trial of a new method

2010 ◽  
Vol 67 (8) ◽  
pp. 1247-1261 ◽  
Author(s):  
Nicolas Bousquet ◽  
Noel Cadigan ◽  
Thierry Duchesne ◽  
Louis-Paul Rivest
Keyword(s):  
Gadus Morhua ◽  
Stock Assessment ◽  
Population Analysis ◽  
Assessment Model ◽  
Fish Stock ◽  
Stock Biomass ◽  
Stock Assessments ◽  
Spawning Stock ◽  
Age Structured ◽  
Fish Stock Assessment

Landings from fisheries are often underreported, that is, the true landings are greater than those reported. Despite this bias, reported landings are widely used in fish stock assessments, and this might lead to overoptimistic exploitation strategies. We construct a statistical stock assessment model that accounts for underreported landings using the theory of censoring with sequential population analysis (SPA). The new model is developed and implemented specifically for the cod stock ( Gadus morhua ) from the southern Gulf of St. Lawrence (Canada). This stock is known to have unreported overfishing during 1985–1992. We show in simulations that for this stock, the new censored model can correctly detect the problematic landings. These corrections are nearly insensitive to subjective boundaries placed on real catches and robust to modifications imposed in the simulation of landings. However, when surveys are too noisy, the new SPA for censored catches can result in increased uncertainty in parameters used for management such as spawning stock biomass and age-structured stock size.

Fish stock assessment a manual of basic methods

Marine Policy ◽  
1984 ◽  
Vol 8 (1) ◽  
pp. 68-69
Author(s):  
Stephen J. Lockwood
Keyword(s):  
Stock Assessment ◽  
Fish Stock ◽  
Fish Stock Assessment

scholarly journals Accuracy of Acoustic Methods in Fish Stock Assessment Surveys

Sonar Systems ◽  
10.5772/18631 ◽  
2011 ◽  
Author(s):  
S. Georgakarakos ◽  
V. Trygonis ◽  
J. Haralabous
Keyword(s):  
Stock Assessment ◽  
Fish Stock ◽  
Acoustic Methods ◽  
Fish Stock Assessment

Analysis of Threshold-Induced Bias Inherent in Acoustic Scattering Cross-Section Estimates of Individual Fish

1975 ◽  
Vol 32 (12) ◽  
pp. 2547-2551 ◽  
Author(s):  
R. T. Weimer ◽  
J. E. Ehrenberg
Keyword(s):  
Cross Section ◽  
Stock Assessment ◽  
Acoustic Scattering ◽  
Operating Conditions ◽  
Scattering Cross Section ◽  
Fish Stock ◽  
Small Fish ◽  
Scattering Cross ◽  
Electronic Circuitry ◽  
Fish Stock Assessment

During acoustic fish stock assessment surveys, it is often desirable to measure the distribution of the acoustic scattering cross-section of single fish. One of the problems in such measurements is that a threshold in the electronic circuitry discriminates against small fish. This effect is analyzed in detail, and an expression is derived for the threshold-induced bias in the mean scattering cross-section estimate. Results are plotted for a typical set of operating conditions.

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