Grabowski TB and EC Franklin. 2017. What can volunteer angler tagging data tell us about the status of the Giant Trevally (ulua akuea) Caranx ignobilis fishery in Hawaii: revisiting data collected during Hawaiʻi’s Ulua and Papio Tagging Project 2000-2016. Report provided by the Cooperative Fish and Wildlife Research Unit Program under agreement with the U.S. Fish and Wildlife Service. U.S. Department of Interior, Fish and Wildlife Service, Cooperator Science Series FWS/CSS-126-2017, National Conservation Training Center.
Giant Trevally (ulua aukea) Caranx ignobilis is one of the most highly prized and frequently targeted nearshore species. However, there is very little information on its current status in Hawaiian waters. This study uses mark-recapture data collected as part of recreational angler tagging program conducted by the Hawaii Department of Land and Natural Resources-Division of Aquatic Resources during 2000-2012. Mark-recapture data were used to estimate von Bertalanffy growth curve parameters and survivorship. Growth curves generated from the mark-recapture data suggested that Giant Trevally from the main Hawaiian Islands may be growing faster and reach a smaller maximum size than individuals in the Northwest Hawaiian Islands, but there are a number of issues rendering this conclusion uncertain. The survivorship of Giant Trevally was positively associated with age, in part due to ontogenetic habitat shifts that result in older fish moving to offshore habitats where they are less vulnerable to anglers. When compared to stock assessments performed using commercial landings data and fisheries-independent visual surveys, the mark-recapture data produced similar estimates for the average length of exploited fish, a metric highly negatively correlated to fishing mortality. These results emphasize the need for additional information on the biology of Giant Trevally in Hawaiian waters and suggest that the data collected from this recreational angler tagging program may be useful to generate reliable estimates of mortality for stock assessment purposes.