DOI: 10.5061/dryad.n560cd7
title: Data from: Validity of inferring size-selective mortality and a critical size limit in Pacific salmon from scale circulus spacing

description: Size-selective mortality owing to lack of energy reserves during the first
 marine winter has been suggested to be a result of juvenile salmon failing
 to reach a critical size or condition by the end of their first marine
 summer and not surviving the following winter due to this presumed energy
 deficit. This hypothesis implies a knife-edge mortality function based
 upon size, and is subject to empirical data support for acceptance. Scale
 circulus spacing has been interpreted as an index for body size, and we
 reviewed the effect of size-selective mortality with a knife-edge
 mortality function on descriptive statistics for a scale circulus spacing
 index (SCSI). In order to invoke size selection as an important driver of
 mortality during the first year of ocean rearing, it is necessary to
 demonstrate not only that size-selective mortality is directed towards the
 smaller members of the population, but that the selective nature of the
 mortality can account for a substantial portion of the observed mortality.
 If the assumption is made that a random sample of a single juvenile
 population has been obtained, then studies that employ a SCSI to infer
 size-selective mortality coupled with a critical size limit must
 demonstrate a shift toward larger values of the SCSI, but also a
 concomitant reduction in the variance and range of the SCSI and an
 increase in the skewness and kurtosis of the SCSI values. Through
 simulation we found that the percentage of adults that displayed a SCSI
 value greater than the maximum observed in the juvenile sample was highly
 dependent on the initial juvenile sample size and size-selective mortality
 rate. Geographical distributions of juvenile Pacific salmon can be
 stratified by size, with larger individuals migrating earlier from local
 ocean entry locations than smaller individuals, and thus differential
 timing migration of juveniles based upon body size prior to the collection
 of the marine juvenile sample may be a more plausible explanation of
 published trends in the SCSI, rather than invoking substantial
 size-selective mortality and a critical size limit.
description: Simulated
 Statistics-Knife Edge MortalityFile:
 SimulatedStatistics-KnifeEdgeMortality.csv This file contains the
 simulated data from a knife-edge size-selective mortality simulation.
 Description of the variables: Juveniles: Sample size for the juvenile
 population Adults: Sample size for the adult population Mortality:
 Mortality rate (in percent) Mean: Mean circuli spacing of the adult
 population Range: Difference between the maximum and minimum circuli
 spacing in the adult population Min: Minimum value of the circuli spacing
 in the adult population Max: Maximum value of the circuli spacing in the
 adult population SD: Standard deviation of the circuli spacing in the
 adult population Kurt: Kurtosis of the circuli spacing in the adult
 population Skew: Skewness of the circuli spacing in the adult population
 Percent: Proportion of the circuli spacing in the adult population that is
 outside (above) of the juvenile populationSimulatedStatistics-KnifeEdgeMortality.csvSimulatedStatistics-TwoSamplesFILE: SimulatedStatistics-TwoSamples.csv This file contains the simulated data from a sampling conducted on two populations. Description of the variables: Mean 1st: Mean circuli spacing in the first population Mean 2nd: Mean circuli spacing in the second population Sample size: Total number of circuli spacing in the sample Prop pop 1: Proportion of the samples coming from the first population Prop pop 2: Proportion of the samples coming from the first population Mean: Mean circuli spacing of the joint sample Range: Difference between the maximum and minimum circuli spacing in the joint sample Min: Minimum value of the circuli spacing in the joint sample Max: Maximum value of the circuli spacing in the joint sample SD: Standard deviation of the circuli spacing in the joint sample Kurt: Kurtosis of the circuli spacing in the joint sample Skew: Skewness of the circuli spacing in the joint sample Percent: Proportion of the circuli spacing in the adult population that is outside (above) of the joint sample