Estimating trends in fishing mortality at age and length directly from research survey and commercial catch data

1998 ◽  
Vol 55 (5) ◽  
pp. 1248-1263 ◽  
Author(s):  
Alan F Sinclair
Keyword(s):  
Population Analysis ◽  
New Method ◽  
Natural Mortality ◽  
Population Abundance ◽  
Similar Magnitude ◽  
Fishing Mortality ◽  
Commercial Catch ◽  
Relative Population ◽  
Research Survey

Relative fishing mortality (R) is estimated directly as the ratio of commercial catch divided by a research vessel survey index of relative population abundance. If the survey is conducted near the middle of the fishing year, its catchability is constant, and the rate of catch reporting remains constant, R will be proportional to the actual fishing mortality (F). Trends in R will reflect trends in F. A case study is presented where R at age and length are compared with estimates obtained with sequential population analysis (SPA). They were found to be of similar magnitude and trend. This new method would be useful for stocks where SPA is not possible. It would also be a useful addition to analytical assessments where SPA is used; it provides estimates of relative F at length, it is insensitive to changes in natural mortality provided the research survey occurs close to the middle of the fishing year, and it provides useful diagnostics for interpreting SPA results.

Statistical analysis of catch-at-age data with correlated errors

1995 ◽  
Vol 52 (6) ◽  
pp. 1265-1273 ◽  
Author(s):  
Ransom A. Myers ◽  
Noel G. Cadigan
Keyword(s):  
Statistical Model ◽  
Estimation Error ◽  
Fish Abundance ◽  
Fishing Mortality ◽  
Correlated Errors ◽  
Commercial Catch ◽  
Commercial Fish ◽  
Research Survey ◽  
The World ◽  
Survey Estimates

We extend the statistical model used to estimate abundance from commercial catch-at-age data for many of the major commercial fish species in the world. The model we consider combines commercial catch-at-age data and research survey estimates of fish abundance; we extend the model to allow correlated errors among ages within a year for the survey estimates of fish abundance. We also formulate a method for modeling the fishing mortality on the oldest ages of the fish caught. Estimates are obtained using maximum likelihood. We conclude that the level of correlation among ages is sufficiently large to produce large biases in the standard methods for some stocks. The statistical model that includes correlated errors greatly reduces bias and increases efficiency if the correlation in the estimation error is large.

A comparison of gamma and lognormal maximum likelihood estimators in a sequential population analysis

2001 ◽  
Vol 58 (3) ◽  
pp. 560-567 ◽  
Author(s):  
Noel G Cadigan ◽  
Ransom A Myers
Keyword(s):  
Maximum Likelihood ◽  
Population Analysis ◽  
Maximum Likelihood Estimators ◽  
Fish Populations ◽  
Population Abundance ◽  
Catch Per Unit Effort ◽  
Gamma Model ◽  
Commercial Catch ◽  
Stock Size ◽  
Gamma Distributions

We analyze the model used to assess most major commercial marine fish populations, namely, sequential population analysis (SPA). This model estimates population abundance by combining catch-at-age data with research surveys or commercial catch per unit effort indices of abundance. We examine two maximum likelihood estimators of SPA parameters. These estimators are based on assuming that the stock-size indices are from lognormal or gamma distributions. Using simulations, we find that both types of estimators can have significant biases; however, our results indicate that it is preferable to use the gamma model, because it tends to have lower bias and variability, even when the true distribution of the stock-size indices is lognormal.

Incorporating Uncertainty into Fishery Models

2002 ◽  
Keyword(s):  
Striped Bass ◽  
Population Model ◽  
Input Data ◽  
Stock Assessment ◽  
Population Analysis ◽  
Natural Mortality ◽  
Fishing Mortality ◽  
Sources Of Uncertainty ◽  
Incorrect Model ◽  
Age Structured

<em>Abstract.—</em> A stock assessment of Atlantic striped bass <em>Morone saxatilis </em> was presented to illustrate potential sources of uncertainty in application of an age-based population model. Erroneous conclusions in stock assessment can result from incorrect model selection, input data that are not representative of the target population, and improper configuration of the selected model. Influence of incorrect input data and model configuration was investigated using striped bass catch-at-age data analyzed with a tuned virtual population analysis model (ADAPT VPA). Variations in model configurations were explored in addition to sensitivity to input parameters such as natural mortality. Violation of the assumption of constant natural mortality-at-age had a significant influence on the resulting estimates of <EM>F </EM> and stock size. Discard losses, particularly from the commercial fishery, were the largest source of uncertainty in the catch-at-age. Uncertainty due to process error in the VPA model was characterized by bootstrap realizations of the nonlinear least-squares estimates of fishing mortality. The implications associated with fishing at various <EM>F</EM> s were also examined using a stochastic projection model. A comparison of fishing mortality estimates derived from two independent models, an age-structured population model and a tag-recovery model, indicated that both methods produced equivalent results. Evaluation of the striped bass stock assessment demonstrates that uncertainty could result from a variety of sources but this variability was only partially captured within the model framework. Understanding the possible sources of uncertainty and implications in interpreting model results should benefit the analyst in providing assessment advice to managers.

Trends in Fishing Mortality Rate along with Errors in Natural Mortality Rate can cause Spurious Time Trends in Fish Stock Abundances Estimated by Virtual Population Analysis (VPA)

1989 ◽  
Vol 46 (12) ◽  
pp. 2129-2139 ◽  
Author(s):  
Michael F. Lapointe ◽  
Randall M. Peterman ◽  
Alec D. MacCall
Keyword(s):  
Mortality Rate ◽  
Time Trends ◽  
Biological Effects ◽  
Population Analysis ◽  
Fish Stock ◽  
Natural Mortality ◽  
Fishing Mortality ◽  
Management Actions ◽  
Virtual Population Analysis ◽  
Virtual Population

Many researchers have reported biases in estimates offish abundance reconstructed by virtual population analysis (VPA). We document that VPA can produce changing levels of bias through time, thereby creating spurious time trends in recruitment and stock biomass estimates. We generated catch data from empirically based simulations of nine fish populations, estimated abundances using VPA with a deliberately mis-specified natural mortality rate, M, and compared the estimates to the models' "true" abundances. A period of increasing fishing mortality rate, F, combined with an overestimate of M produced spurious decreasing time trends in estimated abundance and recruitment, even when the true time series of F was known. Analogously, an underestimate of M led to a spurious increasing time trend. Bias was increased by a higher true M, and (for a given total change in F) by a slower increase in F. Because field estimates of M are uncertain and trends in F are common, some apparent trends (or lack of them) in abundances reconstructed by VPA may be artifacts. Therefore, inferences about the results of past management actions and about physical or biological effects on variability in recruitment must be made cautiously when VPA estimates are used.

STRATEGI KOMUNIKASI CROWDFUNDING PADA KOLASE.COM

2019 ◽  
Vol 2 (2) ◽  
pp. 177-187
Author(s):  
Venessa Agusta Gogali ◽  
Fajar Muharam ◽  
Syarif Fitri
Keyword(s):  
Social Media ◽  
Communication Strategies ◽  
Communication Strategy ◽  
New Method ◽  
Media Communication ◽  
Social Activists ◽  
Social Media Communication

Crowdfunding is a new method in fundraising activities based online. Moreover, the level of penetration of social media to the community is increasingly high. This makes social activists and academics realize that it is important to study social media communication strategies in crowdfunding activities. There is encouragement to provide an overview of crowdfunding activities. So the author conducted a research on "Crowdfunding Communication Strategy Through Kolase.com Through Case Study on the #BikinNyata Program Through the Kolase.com Website that successfully achieved the target. Keywords: Strategic of Communication, Crowdfunding, Social Media.

A new method to improve the NMR log interpretation in drilling mud-invaded zones: A case study from the Brazilian Pre-salt

2021 ◽  
pp. 108692
Author(s):  
Bruno Valle ◽  
Patrick Führ Dal’ Bó ◽  
Jeferson Santos ◽  
Lucas Aguiar ◽  
Pedro Coelho ◽  
...  
Keyword(s):  
New Method ◽  
Drilling Mud ◽  
Log Interpretation

scholarly journals A Weighted-Time-Lag Method to Detect Lag Vegetation Response to Climate Variation: A Case Study in Loess Plateau, China, 1982–2013

2021 ◽  
Vol 13 (5) ◽  
pp. 923
Author(s):  
Qianqian Sun ◽  
Chao Liu ◽  
Tianyang Chen ◽  
Anbing Zhang
Keyword(s):  
Climate Change ◽  
Loess Plateau ◽  
Time Lag ◽  
New Method ◽  
Climate Factors ◽  
The Loess Plateau ◽  
Climate Conditions ◽  
Vegetation Growth ◽  
Lag Effect

Vegetation fluctuation is sensitive to climate change, and this response exhibits a time lag. Traditionally, scholars estimated this lag effect by considering the immediate prior lag (e.g., where vegetation in the current month is impacted by the climate in a certain prior month) or the lag accumulation (e.g., where vegetation in the current month is impacted by the last several months). The essence of these two methods is that vegetation growth is impacted by climate conditions in the prior period or several consecutive previous periods, which fails to consider the different impacts coming from each of those prior periods. Therefore, this study proposed a new approach, the weighted time-lag method, in detecting the lag effect of climate conditions coming from different prior periods. Essentially, the new method is a generalized extension of the lag-accumulation method. However, the new method detects how many prior periods need to be considered and, most importantly, the differentiated climate impact on vegetation growth in each of the determined prior periods. We tested the performance of the new method in the Loess Plateau by comparing various lag detection methods by using the linear model between the climate factors and the normalized difference vegetation index (NDVI). The case study confirmed four main findings: (1) the response of vegetation growth exhibits time lag to both precipitation and temperature; (2) there are apparent differences in the time lag effect detected by various methods, but the weighted time-lag method produced the highest determination coefficient (R2) in the linear model and provided the most specific lag pattern over the determined prior periods; (3) the vegetation growth is most sensitive to climate factors in the current month and the last month in the Loess Plateau but reflects a varied of responses to other prior months; and (4) the impact of temperature on vegetation growth is higher than that of precipitation. The new method provides a much more precise detection of the lag effect of climate change on vegetation growth and makes a smart decision about soil conservation and ecological restoration after severe climate events, such as long-lasting drought or flooding.

A new method for determining platy particle aspect ratio: A kaolinite case study

2014 ◽  
Vol 97-98 ◽  
pp. 125-131 ◽  
Author(s):  
Hongfei Cheng ◽  
Zhiliang Zhang ◽  
Qinfu Liu ◽  
Joseph Leung
Keyword(s):  
Aspect Ratio ◽  
New Method ◽  
Particle Aspect Ratio
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