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Understanding the role different habitats play in the life histories of fishes is important for the development of holistic aquatic ecosystem management plans. We used otolith trace element analysis to reconstruct the life history of estuarine triplefin Forsterygion nigripenne and infer its habitat use. Analysis of otoliths using laser ablation inductively coupled plasma mass spectrometry showed an elemental profile without prominent changes in elemental concentration. The otolith elemental profiles were not indicative of movement between waters with substantial Sr:Ca and Ba:Ca differences. The Sr:Ca and Ba:Ca profiles were indicative of within—and near—estuary movements encompassing short time periods. Overall, the otolith microchemical profile was likely indicative of a life history closely associated with estuaries. However, it is difficult to rule out brief excursions to the marine environment given that may not have been of sufficient duration to be recorded in the elemental composition of the otolith. This suggests that F. nigripenne is the only species in southern New Zealand known to be closely associated with estuarine habitat for its entire life cycle.

Despite aquatic invasive species (AIS) being a widely recognized threat to native biodiversity in streams on subtropical and tropical oceanic islands across the Pacific, AIS management has been constrained by concerns that methods of removal could result in more harm than good. In this study, we assessed the effectiveness and outcomes of combining hand-netting and streamside sequestration of native species with AIS removal via three-pass electrofishing tailored for Hawaiian Island watersheds. Removals were conducted in 13 watersheds on the island of O‘ahu following a before-after, control-impact design to assess how AIS removal and post-removal community reassembly varied by surface flow and target species of interest. We found that removals resulted in a sharp reduction in AIS densities without altering native species densities. Removal efficacy was greatest in streams with intermediate mean discharge irrespective of target group or pre-removal AIS densities. Long-term monitoring demonstrated that removals led to persistent shifts in community composition reflecting sustained reductions in AIS densities. These findings indicate that electrofishing can be a valuable tool for AIS management in Hawaiian and other subtropical Pacific island streams, so long as steps are taken to minimize potential harm to at-risk and culturally important native species.

Increasing jellyfish abundance has been documented worldwide, though few studies have used standardized long-term data to examine jellyfish abundance across environmental gradients. Such datasets can provide an opportunity to analyze historical trends, document rates of change, and identify potential mechanisms of change. This study used standardized fishery monitoring data from Texas Parks and Wildlife Department from 1983 to 2013 to identify the abundance trends of three common scyphozoan jellyfish species in eight Texas bays that span environmental gradients. We hypothesized that jellyfish abundance would vary across the environmental gradient and jellyfish abundance would increase with increasing salinity and temperature. Although no strong abundance trends were observed, abundance peaks occurred in some bay systems. Salinity and temperature were found to be the most influential factors for jellyfish occurrence while dissolved oxygen ranked the lowest. Bell-curve functions generalized the relationship between salinity and scyphozoan abundance and identified abundance peaks at high estuarine salinities for A. aurita, and differing tolerance ranges for each species. Temperature relationships were generalized with a sigmoid function and highlighted tolerance at the highest water temperatures observed. These findings suggest that some jellyfish species may respond positively in Texas bays if climate change increases salinity and temperature regimes of estuaries.

We assessed the prevalence of life history variation across four of the five native amphidromous Hawai'ian gobioids to determine whether some or all exhibit evidence of partial migration. Analysis of otolith Sr.: Ca concentrations affirmed that all are amphidromous and revealed evidence of partial migration in three of the four species. We found that 25% of Lentipes concolor (n = 8), 40% of Eleotris sandwicensis (n = 20) and 29% of Stenogobius hawaiiensis (n = 24) did not exhibit a migratory life-history. In contrast, all individuals of Sicyopterus stimpsoni (n = 55) included in the study went to sea as larvae. Lentipes concolor exhibited the shortest mean larval duration (LD) at 87 days, successively followed by E. sandwicensis (mean LD = 102 days), S. hawaiiensis (mean LD = 114 days) and S. stimpsoni (mean LD = 120 days). These findings offer a fresh perspective on migratory life histories that can help improve efforts to conserve and protect all of these and other at-risk amphidromous species that are subject to escalating anthropogenic pressures in both freshwater and marine environments.