Stage duration estimation for Calanus populations, a modelling study

Abstract

Population dynamics of Calanus finmarchicus have been modelled using very finely divided representation of the stock accord~ng to age-within-stage, in the manner of models developed by C. S. Davis, A. Sciandra, F. Carlotti and others. A key assumption of the model is that development rate is relatively insensitive to food-limitation, so that stage duration can be represented by a temperature function alone. We used the Belehradek function for this purpose, noting that better data are needed for fitting its parameters. The model closely simulates the timing of stage progression and relative stage abundances of C. finmarchicus in the Malangen fjord system (northern Norway) during the winter-spring generation. The model 1s sensitive to the resolution of the age-within-stage division, but it is fully stable at 0.5 h increments. Modifications of the model simulated several methods for field estimation of stage duration in Calanus (or other highly seasonal copepod populations). A method based on changes in stage proportions (the 'Heinle graph' method) is biased by confounding of the effects of developmental progress and mortality on stage proportions. However, the model shows that the bias is mild and the method gives useful estimates of stage duration. Simulation of a method based on molting rate deterrninations ('Kirnmerer experiments') showed its unsuitability for highly seasonal stocks In which stage composition is changing rapidly. Differences in C. finmarchicus survivorship schedules between constant and continuously increasing temperatures were simulated, showing that such differences in pattern are critical to annual survival and stock production. Simple methods for fitting mortality rates to data using the model were extremely sensitive to sampling noise. More complex methods may succeed but remain to be developed.

Effects of temperature and circulation on the population dynamics of Calanus finmarchicus in the Gulf of St. Lawrence and Scotian Shelf: Study with a coupled, three‐dimensional hydrodynamic, stage‐based life history model

“…We did not focus on individual growth as we were concerned here with first-order biophysical influences on numbers of C. finmarchicus rather than biomass. Although our mathematical model differs from more detailed life-history models, such as age-within-stage models, the model we present here yielded a realistic ontogeny and annual abundance pattern, i.e., a cascading of the population through eggs to adults with consistently lower abundance, by an order of magnitude or more, from eggs and naupliar to copepodids as in previous modeling studies [e.g., Tande and Slagstad, 1992;Miller and Tande, 1993;Carlotti and Radach, 1996]. The resemblance of the simulated and observed life stage abundance and a final CVd population similar in abundance to the initial population and with a realistic distribution, show the ability of this simplified model to simulate a mean climatological state of the populations of C. finmarchicus in the eastern Canadian waters.…”

Coupling of an individual‐based population dynamic model of Calanus finmarchicus to a circulation model for the Georges Bank region

“…There are several models representing the development of C. ®nmarchicus for various purposes. Miller and Tande (1993) modelled developmental timing for a single cohort with prolonged reproduction (as occurs in northern Norwegian fjords) by a very ®nely divided age-within-stage representation. Their goal was to test the methodological validity of several ®eld techniques for estimating stage duration.…”

“…At each hourly time step, each individual is subjected to a random chance of dying at a mortality rate set for each stage. For G 1 we have used the ad hoc, stagewise survivorship rates from Miller and Tande (1993), while lower survivorship was applied to G 2 (Table 1). The G 2 rates were chosen to produce 50 000±60 000 G 2 resting C5 from 500 G 0 females (after application of the G 2 /G 1 generational multiplier, see below).…”

Mortality estimation for planktonic copepods: Pseudocalanus newmani in a temperate fjord

“…those developing at high latitudes). Early methods for deriving stage durations and mortality rates from cohorlt analysis have been criticized because of the interdepend.ence of these two quantities (Braner and Hairston 1989;Miller and Tande 1993), and remedies have been proposed (Aksnes and Hoisaeter 1987). However, for multivoltine populations, clear recognition of a sequence of unambiguous discrete cohorts remains less the rule than the exception, highlighting the need for alternative mortality estimation procedures.…”