Blog Archives

Adding Zero Catches

April 18, 2018
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Introduction Much of my work is with undergraduates who are first learning to analyze fisheries data. A common “learning opportunity” occurs when students are asked to compute the mean catch (or CPE), along with a standard deviation (SD), across multiple gear sets for each species. The learning opportunity occurs because some species will invariably not be caught in some gear...

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Collapsing Categories or Values

March 29, 2018
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Introduction I have received a few queries recently that can be categorized as “How do I collapse a list of categories or values into a shorter list of category or values?” For example, one user wanted to collapse species of fish into ...

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Stock-Recruitment Graphing Questions

December 12, 2017
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Stock-Recruitment Graphing Questions

A fishR user recently asked me In the book that you published, I frequently use the stock-recruit curve code. The interface that shows both the Ricker/Beverton-Holt figure with the recruit per spawner to spawner figure (i.e., the dynamic ...

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Plots of Back-Calculated Lengths-At-Age I

November 7, 2017
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Plots of Back-Calculated Lengths-At-Age I

Last spring, I posted about my version of a modified age-bias plot. One reader commented on that post via Twitter – “Now that you solved the age-bias plot, how about the ‘best’ display of back-calculated length-at-age data, with Von...

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Joy Plot of Length Frequencies

July 27, 2017
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Joy Plot of Length Frequencies

There has been a bit of a buzz recently about so-called “joyplots.” Wilke described joyplots as “partially overlapping line plots that create the impression of a mountain range.” I would describe them as partially overlapping densit...

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Age Bias Plot Changes in FSA

April 25, 2017
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Age Bias Plot Changes in FSA

In the last two weeks, I have posted twice about modifying age bias plots and Bland-Altman-like plots for comparing age estimates. From those posts, I have decided that I prefer to plot differences between the ages on the y-axis (as com...

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Bland-Altman Plot for Age Comparisons?

April 19, 2017
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Bland-Altman Plot for Age Comparisons?

Last week I posted about a modified age bias plot. In this post I began looking more deeply at an alternative plot called the Bland-Altman plot. Below, I describe this plot, demonstrate how to construct it in R, give a mild critique of its ...

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Modified Age Bias Plot

April 13, 2017
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Modified Age Bias Plot

Original Age Bias Plot Campana et al. (1995) introduced the “age bias plot” to visually assess potential differences in paired age estimates (e.g., between two structures such as scales and otoliths, between two readers, or between one ...

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Computing SE for PSD indices

December 9, 2016
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A user of my Introductory Fisheries Analyses with R book recently asked me how to compute standard errors (SE) for the various PSD indices by using the usual equation for the SE of a proportion (square root of p times (1-p) divided by n). B...

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Pauly et al. (1992) Seasonal Cessation in Growth Model

October 10, 2016
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I recently published a technical note in Fisheries Research that described an algorithm for implementing the “seasonal cessation in growth model” of @Paulyetal1992. Describing an algorithm for a growth model does not seem like a useful...

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