Upstream migration and marine early life history of amphidromous gobies inferred from otolith increments and microchemistry

Amphidromous gobies are circumtropically distributed in mountainous coasts typical of volcanic islands. More than nine goby species recruit seasonally from the Pacific coasts to the Hsuikuluan River estuary eastern Taiwan from the spring to the summer. Using two seasons of field observations and sample collections, we explore the recruitment of amphidromous gobies from the Pacific Ocean into the Hsuikuluan River and their upstream migratory behaviors from the estuary to the lower reaches of the river. A metamorphosis check in the otolith which corresponds to the drop of Sr/Ca ratios from higher > 4 × 10−3 to lower levels < 4 × 10−3 is found in most species after recruitment to fresh waters. The marine and freshwater stages for these goby species can therefore be confirmed from otolith microstructure and Sr/Ca ratio analysis, and age in days of these gobies is estimated from otolith daily increments. Rhinogobius gigas recruits to the estuary at 30–40 days after hatching, while the marine planktonic stage ranged from approximately 2–7 months for Awaous melanocephalus, Eleotris fusca, Glossogobius aureus, Sicyopterus japonicus (Tanaka, 1909), Stenogobius genivittatus, and Stiphodon elegans (Steindachner, 1879). The catch data from an artisanal fish trap show lunar and semi-lunar periodicity for the upstream migration of R. gigas and S. japonicus after a brief stay in the estuary. These two species accounted for more than 99 % of the upstream migratory gobies collected in the fish trap. The short marine larval stage and presumed retention at the inshore area help to explain the endemism of R. giga. In contrast, S. japonicus has a lengthy marine stage of 6–7 months, which obviously could allow dispersal over a wide geographic range.