Predatory fish population dynamics and diet in a traditional Hawaiian fishpond

Overfishing and anthropogenic stressors have decimated Hawaiʻi’s coastal fisheries. Traditional Hawaiian fishponds, or loko iʻa, are a low-impact and culturally significant food source in the face of climate change and... [ view full abstract ]

Overfishing and anthropogenic stressors have decimated Hawaiʻi’s coastal fisheries. Traditional Hawaiian fishponds, or loko iʻa, are a low-impact and culturally significant food source in the face of climate change and increased concerns over food security.  Heʻeia Fishpond, on the windward side of Oʻahu, is currently trying to raise herbivorous fish as a local and sustainable food source.  It is therefore crucial to understand the population dynamics and diet of predatory fish to assess their potential impact on the food production species.  A mark-recapture experiment (the Lincoln-Petersen closed population estimator with Chapman correction) was conducted to estimate the population of predatory fish in the pond, and visual, genetic barcoding, and stable isotope analyses were used to assess their diet.  Catch-per-unit-effort data from community fishing days were also utilized to examine trends in the relative abundance of predator fishes.  Sphyraena barracuda had the largest population in Heʻeia fishpond at 189 individuals, follwed by Caranx ignobilis (89) and C. melampygus (19), which reflects trends in the CPUE from September 2016 – September 2017.  Diets of the three species consisted mainly of nearshore, estuarine fishes and crustaceans.  We did not find evidence that the predators consumed the herbivorous fishes typically raised as food, suggesting that they are either not specifically targeted by the dominant predators in the fisphond or are such low population sizes that they are not part of the predator’s diet.  Based on these findings, we recommend maintaining current strategies for management of Heʻeia Fishpond’s top predatory species.