Estimation of Maternal effects On the sustainability of large pelagic populaTIONs – EMOTION

There is now a general recognition of the fishing overcapacity in all world oceans and of the necessity to reducing exploitation rates to rebuild marine resources. While fisheries science has focused in the last decades on developing more realistic population dynamics models, the collection of data on biological processes has been widely neglected. Such information is however crucial for understanding the productivity of fish populations and their resistance to environmental changes and fisheries. Fishing is a size-selective process that induces truncation of the age-structure of fish populations through the selective removal of larger, older individuals from the pristine stock. The increasing allocation of reproductive resources for postnatal use with age has however been recently shown in many long-living fish and shark species and commonly called 'maternal effect'. The negative impacts of maternal effect induced by fishing include: (i) the shortening in the time and change in location of spawning and (ii) the decrease in the production and quality of eggs. Current assessment models based on spawning stock biomass as an index of reproductive potential can therefore substantially underestimate the effects of fishing and yield to overoptimistic diagnostics about the stock status. Despite the recognition of the importance of accounting for maternal effects into fisheries management, no study has been conducted until now to identify and quantify maternal effects for large pelagic species.
The overall objective of the EMOTION project is to test and quantify the maternal effect on large pelagic species through the case study of tunas and billfishes of the Western Indian Ocean, i.e. skipjack Katsuwonus pelamis, yellowfin Thunnus albacares, and swordfish Xiphias gladius. Testing this hypothesis requires addressing several interrelated questions about growth, condition, and reproduction that are all major components of maternal effect.
First, we will take advantage of the extensive tuna tagging dataset recently acquired in the Indian Ocean to estimate the complex growth of large pelagics by using novel integrated modelling approaches. A simulation model will be developed to assess the impact of fishing selectivity on the functional form of growth. Growth will be subsequently used to estimate the age of fish sampled within the project and appreciate their spawning experience.
Then, we will test several methods for assessing LPS condition and investigating the individual condition variability. The study of lipid and fatty acid distribution in tissues will provide information on lipid dynamic and energy allocated to offspring during the reproductive cycle. Data and information acquired will thus be crucial to discriminate the maternal and condition-related effects on energy allocation.
Finally, the reproductive biology of skipjack, yellowfin, and swordfish will be analysed to study and update our knowledge on their reproductive strategy and estimate their reproductive potential.
The evidence of a maternal effect for large pelagic species will be tested through the statistical modelling of data collected, and the negative impact of maternal effects induced by fishing on reference points for fisheries management will be assessed through the development of a simulation modelling approach.