Assessing red drum spawning aggregations and abundance in the Eastern Gulf of Mexico: a multidisciplinary approach

Many marine fish form spawning aggregations (FSAs) and exhibit meta-population stock structure, affecting reproductive resilience and the optimal spatial scale of management. Red drum use a known FSA site off Tampa Bay (TB FSA site) and another presumed FSA site off Charlotte Harbor (CH FSA site). We studied these sites for 3 years (2012-2014) to assess space use and annual abundance at the TB FSA site using: (i) genetically profiled fish, non-lethally sampled by purse seine (n=9087); (ii) aerial surveys (n=37); and (iii) acoustic telemetry (n=122 fish). Thousands of fish concentrated at the TB FSA site to spawn each year, dispersing afterward to an area of at least approximate to 150km along the coast and 90km offshore. Fish acoustically tagged at the TB FSA site showed strong annual spawning site fidelity (91% in 2013 and 85% in 2014) and the straying rate to the CH FSA site to the south was low (6-13%). Annual abundance at the TB FSA site varied, with the estimated abundance in 2013 being four times greater than that estimated for 2014. Similarly, aerial surveys in 2013 sighted 2.5 times as many aggregations as in 2014. However, fine-scale space use, which typically goes unassessed in abundance estimates (short-term surface behaviour and temporary migration), also differed between these years and needs to be integrated into future capture-mark-recapture models.