Annie Larson | Geology Reports

USGS2024

Age, growth, and reproductive biology of Achilles tang (Acanthurus achilles) around Hawai'i Island, USA

A culturally important food fish in Hawai'i, Achilles tang ( Acanthurus achilles Shaw), recently experienced sharp declines in biomass, density, and average length in west Hawai'i Island. In December 2022, State resource managers placed a 2-year moratorium on the Achilles tang fishery in west Hawai'i Island so that the cause of the collapse could be explored. The lack of life-history information for Achilles tang from Hawai'i, or elsewhere in its range, has been noted as an impediment to decision-making. Therefore, our objectives were to characterize this population’s age, growth, and reproductive biology. In working with community fishers, we collected 363 individuals ranging 69 – 264 mm in fork length (FL) and 0 – 39 years in age based on estimates from otoliths. Achilles tang in Hawai'i exhibit a high growth rate, reaching 138 ± 11 mm FL (mean ± SE) in their first year, and exhibit relatively little growth after their second year (< 5 mm yr −1 ). The majority of males (92.0% of n = 101) and females (73.6% of n = 159) were classified as spawning capable or actively spawning, without annual or lunar periodicity. Our study highlights that the basic biology of Achilles tang poses unique challenges to fisheries managers looking to ensure its sustainable harvest. Future research will aim to characterize the susceptibility of recruits’ habitat to local environmental stressors and the relative connectivity of juvenile and adult habitats.

Hawaii↗

USGS2024

Assessing habitat use and population dynamics of fisheries resources at Kaloko Fishpond

Throughout Hawai'i, fishponds are considered by their local communities as important cultural touchstones, a source of local, sustainably produced food, and an important component to the development of community-based management for nearshore fisheries. Within Kaloko-Honokōhau National Historical Park, the restoration of Kaloko Fishpond for traditional aquaculture management is a goal of both the National Park Service (NPS) and Hui Kaloko-Honokōhau, a community-based group of kia'i, i.e., caretakers and native Hawaiian cultural practitioners. However, existing data on the demographics and condition of the fish populations within the pond, and the fish-habitat quality are poor to non-existent. Therefore, the objectives of this study were to: catalog fish species composition and distribution in the pond; estimate the abundance of focal species/taxonomic groups; and evaluate the occupancy patterns of the invasive algae Acanthophora spicifera and Upside-down Jellyfish Cassiopea andromeda. As part of these objectives, a survey protocol and analysis framework were designed and evaluated to ensure that the NPS and community group would be able to refine and implement them to continue their monitoring efforts. We conducted dual-observer shore-based visual surveys multiple times per week during September-October 2020 and April-September 2022. A total of 41 species/taxonomic groups were recorded over the course of the surveys. The largest number of species/taxonomic groups were observed at survey stations located on or near the kuapā, or wall separating the fishpond from the ocean. N-mixture models fitted to the data estimated a total population of 353 – 392 mullets, 134 – 192 flagtails (āholehole), and 189 – 277 Milkfish (Awa) Chanos chanos occurring within the 1.2-ha portion of Kaloko Fishpond that could be surveyed visually from the shoreline. Multi-season occupancy models fitted to the surveyed presence of A. spicifera and Upside-down Jellyfish indicted sites throughout most of the pond exhibited moderate and consistent occupancy (ψ = 0.30 – 0.40) throughout much of the pond, except for the northeast corner of the pond (Kaloko Iki) where colonization rates were lower and extinction rates higher than other areas within Kaloko. The visual survey method developed for this study provides a low-cost and effective starting point for the development of methodology that can be used both by NPS personnel and volunteers from the community group. However, we were only able to estimate fish populations for approximately 24% of the area of Kaloko Fishpond with this method. Given that the deeper areas of Kaloko Fishpond are completely inaccessible to the visual survey method used, generating population estimates for the entire pond based on the parameters estimated in the current study is not recommended without further investigation into fish movement and habitat use. Various means to refine this protocol to better meet the needs and abilities of the NPS and community group are proposed.

Hawaii↗