Investigating growth and reproduction of the Mediterranean swordfish Xiphias gladius through a full life cycle bioenergetics model

Abstract

A Wisconsin type bioenergetics model was developed to investigate the growth and reproduction of the Mediterranean swordfish Xiphias gladius L., 1758. Reproduction was simulated using an energy allocation algorithm with a fixed part of assimilated energy stored for egg production. Stomach contents were used to estimate the daily ration of swordfish (3% of body weight for adults) in order to calibrate the consumption compartment. The model outputs of growth were in agreement with fisheries observation data, with estimates of annual egg production (~17.5 million eggs) per individual similar to those stemming from stock assessment datasets. Our study highlights the importance of bioenergetics in the reproduction of swordfish, suggesting that each individual is reproductively active for ~15 d, while the commonly reported spawning season of the whole population lasts ~90 d. Sensitivity analysis showed that swordfish growth and reproduction is largely controlled by consumption and respiration parameters. We provide a detailed description of a full life cycle swordfish bioenergetics model that could be embedded as a module in an end-to-end modelling framework, ultimately describing the population dynamics of the Mediterranean swordfish stock in relation to environmental variability.