Estimating copepod stage-specific mortality rates in open ocean waters: a case study from the northern Gulf of Mexico, USA

Knowledge of copepod stage-specific mortality rates is essential for understanding secondary production. A time-series of samples of the calanoid copepodClausocalanus furcatuswas collected from a petroleum platform in the northern Gulf of Mexico every 12 h for ~2 to 3 wk in March–April and May–June 2003. Egg and nauplii (stages I and II) abundances were estimated from 30 l Niskin water bottle samples, and abundances of later stages were estimated from vertical net tows. An inverse parameter estimation technique based on a stage-based matrix population model and a search procedure using the sequential quadratic programming algorithm was applied to estimate stage-specific mortality rates. Simulation experiments were conducted to test the robustness of this technique. When the technique was applied to simulated data with different levels of variability, introduced by lognormal error terms, the technique performed well at low to medium level of variability (coefficient of variation