New publication: A statistical regression approach to estimate zooplankton mortality from spatiotemporal survey data
Mortality is notoriously difficult to estimate for zooplankton populations in the open ocean due to the confounding effect of advection. The vertical life table (VLT) approach is commonly used, but has been shown to be sensitive to both spatial and temporal trends in recruitment. Here, we estimate mortality rates of Calanus finmarchicus copepodites from spatiotemporally resolved data from the highly advective Norwegian Sea–Barents Sea in spring and summer. We apply both the VLT and a statistical regression approach (SRA), specifically taking into account the effects of advection and spatiotemporal trends in recruitment. Testing the two methods on a simulated dataset shows that the SRA performs better than the most commonly used version of the VLT when trends in recruitment are present. Overall, the SRA appears to be a robust method for spatiotemporally resolved survey data influenced by advection and spatiotemporal trends in recruitment. The estimated mortality rates are relatively low (0.03–0.07 d−1) and indicate increased mortality for the oldest stage pair (copepodites CIV–CV) compared to earlier stages. The results are discussed in the light of previous mortality rate estimates for C. finmarchicus.
First published online: 29 April 2016