Diet, resource partitioning and gear vulnerability of Hawaiian jacks captured in fishing tournaments

Stomach content, capture method and capture location data were collected fo r 401 carangids captured during three annual 1-day fishing tournaments held at a coastal bay in Hawaii. Blue jack (Caranx melampygus), white jack (Car anx ignobilis) and island jack (Carangoides orthogrammus) were the most com mon species, accounting for 83.5, 8.5 and 5.2% of tournament catches, respe ctively. Geographical area fished consisted of a sheltered bay and the adja cent seaward coastal reef beyond. Area of capture and fishing method influe nced species and size of fish captured. Small (<350 mm fork length) C. mela mpygus and C ignobilis predominated in catches within the sheltered embayme nt indicating this may serve as a nursery area for these species. Conversel y most C. orthogrammus and all large (>500 mm) C. melampygus were captured outside Kaneohe Bay. Trolling (towing a surface lure) accounted for 80% of C. melampygus, 76% of C. orthogrammus and 55% of C. ignobilis captured. Dif ferential vulnerability to trolling may be related to interspecific differe nces in diet; captured C melampygus had fed primarily on fish whereas C. or thogrammus had consumed both fish and benthic crustaceans, and C ignobilis had eaten mainly benthic crustaceans. Differences in diet may indicate reso urce partitioning between these sympatric and closely related species. For C melampygus there was a consistent relationship between prey size and pred ator size. When conducted under scientific scrutiny, fishing tournaments ca n provide synoptic data on diet and gear vulnerability that would otherwise be very difficult to obtain. (C) 2001 Elsevier Science B.V. All rights res erved.