Impact of Indian Ocean tuna fisheries on pelagic ecosystem based on LeMaRns model

Abstract:

In recent years fisheries management has gradually shifted from single-species management mode to ecosystem-based management mode. Due to the complexity, however, the ecosystem-based management has not been widely studied and implemented. Based on public databases in the Indian Ocean Tuna Commission (IOTC), Fishbase and other resources, a LeMaRns ecosystem model (Length-based Multi-species analysis by numerical simulation in R) was developed based on 19 major species in the Indian Ocean tuna fisheries, and changes of species and ecosystem structure at different fishing levels of four fishery types were predicted. The results showed that fishing would reduce the stock biomass, affect the interspecific relationship and further lead to the changes of stock biomass of other species. Large fish indicator (LFI) and mean maximum length (MML) are most sensitive to longline, and the decrease of the two indicators indicated that the proportion of large individual fish in the ecosystem decreases and the proportion of small individual fish increases, which may have a negative impact on the stability of the ecosystem and should be considered in fishery management. The study suggests that fishing has a negative impact on the ecosystem structure, however, fishery type imposed the impact differently with respect to various species. This should be taken into account when implementing ecosystem based management. Under the scenario of two times of recent fishing effort (2 × E_2010-2019), no stock was predicted to be in a state of collapse, and the relative stock biomass of skipjack tuna, albacore tuna, yellowfin tuna and bigeye tuna ranged 0.6-0.7, 0.6-0.7, 0.7-0.8 and 0.6-0.7, respectively, remained at a relatively high level, indicating that the stocks are in a healthy state. Finally, in order to better apply the LeMaRns model to the pelagic ecosystem system, several suggestions were made for further research: structural improvement of the LeMaRns model to better suit the actual situation, and conducting food web surveys and biological studies to ensure accurate data, and incorporating environmental factors, etc.