DOI: 10.7291/d1z40p
title: Morphological measurements of arm loss for eight octopus species

description: Sublethal predation is prevalent in multi-limbed marine invertebrates and
 holistically quantifying their injuries has potential to provide important
 ecological and physiological insights including the rate of trophic energy
 transfer. We demonstrate the utility of an Injury Severity Index (ISI) to
 holistically describe the magnitude of appendage injury in invertebrates,
 using data collected from octopuses in museums and the field. ISI, when
 applied to octopus, quantifies the numbers of arms lost and the proportion
 of tissue lost on a scale of 1.01-16.00. ISI revealed that museum
 specimens commonly lost part of one arm, with a mode ISI value of less
 than 2.00, while wild Octopus bimaculatus had a mean ISI value of 3.13,
 representing two to three arm injuries. We then calculated tissue volume
 lost using two methods for estimating arm length: 1) using scaling
 relationships between intact arms and body size, referred to here as
 scaling-based volume, and 2) calculating a mean length using intact arms
 of an individual, which we call in situ volume. We show that while both
 methods are comparably effective at estimating biomass transferred to
 sublethal predation in octopus populations, in situ volume has strong
 potential for calculations in the field to enhance long-term survey data.
description: The museum measurement data were calculated from observations of
 arm lengths, body sizes, and arm truncation injuries in museum specimens
 of <em>Octopus bimaculatus</em>, <em>O.
 bimaculoides</em>, <em>O. californicus</em>,
 <em>Paroctopus digueti</em>, <em>Enteroctopus
 dofleini</em>,<em> O. fitchi</em>, <em>O.
 hubbsorum</em>, and <em>O. rubescens.</em>
 The injury data (number missing, proportion of length missing,
 Injury Severity Index, two measures of volume estimates) were calculated
 based on the measurement data. The field data were
 collected from live <em>Octopus bimaculatus</em> surveyed
 around the Two Harbors small boat area on Santa Catalina Island,
 California, USA.
description: <strong>ln_IO</strong> is the natural log transformed
 interocular distance (distance between eyes) in mm. <strong>Total
 length missing </strong><strong>(%) </strong>is the
 summation of all of the proportions of arm length missing (used to
 calculate <strong>ISI</strong>).
 <strong>ISI</strong>, or Injury Severity Index, describes the
 overall injury of the octopus, and is calculated with the sum of the
 number of injured arms and the <strong>total length missing
 (%)</strong>. <strong>Sum(Vol_scaling_mm3)</strong> is
 the summation of the volumes missing from all injured arms of an
 individual octopus, using a length calculation based on arm scaling
 relationships from pristine arms. <strong>Sum(Vol_in
 situ_mm3)</strong> is the summation of the volumes missing from all
 injured arms of an individual octopus, using a length calculation based on
 the mean length of the pristine arms of an individual. 
 Accession numbers can be cross-referenced with Supplementary
 Table 2 in our manuscript. Generally, numbers without a letter prefix are
 from the California Academy of Sciences, ones with the prefix
 "SB" are from the Santa Barbara Museum of Natural History, and
 ones with an "M" prefix are from the Scripps Institute of
 Oceanography Benthic Invertebrate Collection.