Estimating mortality: Clarifying assumptions and sources of uncertainty in vertical methods
Authored by P Pepin, W C Gentleman, S Doucette
Date Published: 2012
DOI: 10.1016/j.jmarsys.2012.05.006
Sponsors:
National Science and Engineering Research Council of Canada (NSERC)
Platforms:
No platforms listed
Model Documentation:
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Abstract
Accurate estimates of stage-dependent mortality rates are critical for
understanding zooplankton dynamics. Existing methods for estimating
mortality from survey data include assumptions that are not always
evident, meaning practitioners may be unaware of errors or whether a
particular method is appropriate for their data. Here, a quantitative
analysis of three vertical (single time point) methods is conducted to
help improve confidence in mortality estimates. The underlying theory is
reviewed to clarify assumptions and sources of error. The Basic method
propagates errors. the Ratio method smoothes stage-to-stage variation, and the Alternative method is unrealistic when rates are constant.
Contrary to perception, all three methods neglect the influence of
advection. Application to field data for Calanus finmarchicus in the
Northwest Atlantic illustrates dependence of estimates on input
variables and choice of method. Variation among methods was generally
smaller than that caused by uncertainty in physiological rates, and
frequent violations of assumptions common to all methods seriously
limited their utility. Simulations with an individual-based model reveal
unacceptable sensitivity for the Basic method, whereas Ratio and
Alternative methods are relatively robust except for dynamic or
advective environments. Recommendations are given regarding ways to
detect whether these methods can be applied to survey data, as well as
to assess uncertainty. (C) 2012 Elsevier B.V. All rights reserved.
Tags
Population-dynamics
Georges bank
Growth-rates
Northwest atlantic
Egg-production
Planktonic copepods
Seasonal
dynamics
Copepod calanus-finmarchicus
Predation control
Oithona-similis