Evaluation of Non-Lethal Sampling Methods for Age and Reproductive Status Determination of Tripletail Lobotes surinamensis

Tripletail (Lobotes surinamensis, Lobotidae) are a medium-sized, deep-bodied fish that occur in tropical and subtropical waters worldwide, including the coast of Georgia, USA. Typically these fish are found associated with submerged, emergent, or floating structure; but in the murky Atlantic Ocean off the Jekyll Island, Georgia coast, they float along the surface in large numbers from May through July. This aggregation is the target of an expanding recreational fishery and popularity of this sportfish is increasing across the southeast USA. Increasing popularity with anglers and the lack of basic life history data suggest the need for basic biological information for fisheries managers. Our primary goal was to increase the life history information of tripletail, specifically reproductive, age, and growth data, while evaluating non-lethal sampling techniques. A total of 226 tripletail were sampled primarily by hook-and-line methods from the Jekyll Island aggregation during March through August in 2009 and 2010. An experimental fish trawl was also used to capture tripletail (N = 11) during 2009. Fish were weighed and measured and a blood sample was collected from the caudal sinus for analysis of vitellogenin. Additionally, gonads were weighed and preserved for histological evaluation. Histological examination of tripletail testes (N = 119) revealed males in juvenile (2%), undeveloped (7%), early spermatogenic (21%), mid-spermatogenic (36%), and late spermatogenic (34%) reproductive stages. Histological examination of female ovaries (N = 99) revealed immature (67%), developing (23%), late developing (8%), and regressed (2%) reproductive stages; females with hydrated oocytes were not observed during the course of this study. Aging techniques for otoliths (N = 223) and first dorsal spines (N = 223) were used to estimate ages for each individual. Preliminary results show good agreement between the two aging structures within individual fish, indicating spines could be used and would allow researchers to sacrifice fewer fish. Tripletail appear to grow very rapidly and are capable of reaching 500 mm in one year. Otolith- and spine-based ages ranged from 1 to 5 years.  Managers charged with protecting this species will benefit from new information about the biology and ecology of the Jekyll Island aggregation.  Ongoing research into gonad histology and vitellogenin will be used to evaluate use of vitellogenin level as a non-lethal approach to determine sex and a reproductive status.