Comparing Inter-Island Condition, Determining Spawning Patterns, and Testing Environmental Effects on Catch Using Fish Market Survey Data from Oahu and Maui (Hawaii, USA)
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Kim, Kristian N.K.I.
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Marine Science
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Abstract
Hawaii's coral reef fishery is important as fishing provides both sustenance and a sense of community. Yet, Hawaii's reefs have been depleted, especially in densely human-populated areas. Fish market surveys are important as they can be used to determine fish size and species harvested, and how catch composition differs spatially and temporally. The data used in the current study were from Poseidon Fisheries Research's Hawaii Biosampling Project in which markets on Oahu and Maui were surveyed from July 2018 to July 2019.
Length-weight relationships for six fish species show two consistent patterns: i) Maui fishes are generally longer than Oahu fishes and ii) the larger size classes of Oahu fishes outweigh Maui fishes. A potential explanation for this finding is the release of interspecific and intraspecific competition on Oahu due to higher fishing pressure, allowing more food resources per individual fish.
Generalized additive models using moving averages with 95% confidence intervals show relative condition factor can capture spawning patterns on lunar and annual scales. Based on relative condition factor variation, all periods of inferred heightened spawning are associated with the new and full moons, with exact timing varying by species. Most species also have periods of inferred heightened spawning during Months 5-8 and some species with a second period during Months 1-3. These findings are supported by similarities in relative condition factors with gonadosomatic index patterns and in correspondence to hatch dates. The non-overlapping 95% confidence intervals of the moving averages show that relative condition factor changes significantly throughout the lunar cycle.
Principal component analyses and correlation tests show there are weak environmental relationships with fish count and median length. The number of species and the number of individual fish per species present in the markets are negatively correlated with high wind speed and positively correlated with lunar day. Other principal components for fish count and length indicate an out-of-phase relationship between herbivores and carnivores, with their number and size being negatively correlated. However, fish count and median length are not correlated to each other and differ in their sign of correlation with the environmental variables.
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Hawaii Pacific University