Mangrove Jack (Lutjanus argentimaculatus) are a long lived (>50 years), late maturing (~6 to 10 years) species that can grow to a large size (>1 metre). Their typical distribution in Australian waters extends from Perth, around the north of the continent to Sydney. Mangrove Jack spend several years as juveniles in freshwater and estuarine habitats before migrating to deeper, offshore waters as they near sexual maturity.
Mangrove Jack are popular amongst all fishing sectors; their aggressive feeding and tendency to aggregate (as both juveniles and adults) also makes them vulnerable to overfishing. Juvenile Mangrove Jack are primarily (but not exclusively) caught by Indigenous fishers, recreational fishers and charter boat clients around estuaries and inshore reefs, whereas adults are caught (occasionally in significant quantities) by offshore trawl operations to the west of Cape York.
The sustainability of Mangrove Jack is assessed under the national Status of Australian Fish Stocks (SAFS) reporting framework, which relies on an understanding of the stock structure of each focal species. Previous genetic analyses using mitochondrial and microsatellite markers suggest that Mangrove Jack form a single homogeneous stock in Australian waters. However, these analytical tools often lack the resolution necessary to detect fine-scale stock structure in larval dispersing fishes. This in turn compromises current stock assessment approaches for Mangrove Jack (undertaken at the jurisdictional or management unit level) as there may be a spatial mismatch between the area of the assessment unit/s and the true stock structure of this species; a situation confounded by a limited understanding of the dynamics of ontogenetic migration/connectivity in Mangrove Jack.
This being the case, there is a pressing need to examine the population structure and connectivity of Mangrove Jack across its Australian range. This will be achieved through a combination of cutting-edge genetic methods (i.e. single nucleotide polymorphisms), otolith micro-chemistry and parasite analyses, in order to address the national FRDC priority “Resolving stock uncertainty for priority species (including Mangrove Jack)”.
