A review of the Reproductive biology of the Swordfish (Xiphias gladius) in the Indian Ocean

This paper review the reproductive biology of swordfish (Xiphias gladius) in the Pacific, Atlantic and Indian Oceans as well as the Mediterranean Sea, with particular focus in the Indian Ocean to inform the next swordfish stock assessment scheduled for 2023, as part of the ‘GERUNDIO’ project. The review focuses on the reproductive strategy, seasonal and geographical spawning activity, maturity patterns and fecundity of swordfish. In general, available literature on swordfish reproductive biology is scarce, with most of the studies located in the Atlantic and Pacific Oceans. Swordfish is characterised as a multiple spawner species showing an asynchronous oocyte development and indeterminate fecundity. Swordfish size at maturity and fecundity studies have revealed significant variation both between and within oceans depending on sex, geographical area and environmental conditions. However, the differences could also stem from the different techniques used to determine the maturity status of individual fish among studies and estimate fecundity and/or the limited samples used.

Swordfish stock assessment is sex-disaggregated to account for a number of sex-specific population characteristic such as, among others, growth and maturation. Although the swordfish maturity ogives for the Indian Ocean (Poisson and Fauvel, 2009a) and South-West Pacific Ocean (Farley et al., 2016) had a similar 50% length, following recommendations from WPB15, the assessment used the age-based logistic ogive from Farley et al. (2016) (applying the new otolith-based growth from SW pacific). However, considering that (i) there are clear differences in growth and maturation by sexes, (ii) Farley et al. (2016) did not estimate maturity ogives for males but Poisson and Fauvel (2009a) did, (iii) length based maturity ogive for females estimated by Farley et al. (2016) and Poisson and Fauvel (2009a) are similar, (iv) Poisson and Fauvel (2009a) maturity ogive was estimated using samples from the South-West Indian Ocean; it is recommemded to explore the possibility of using the Poisson et al. (2009a) length-based maturity ogives by sex, converted to age-based maturity ogives using Farley et al. (2016) growth curves by sex.