S U M M A R YIn 1997, a seismic experiment using an airgun array and ocean bottom seismographs (OBSs) was performed in the forearc region of the northeastern Japan (NEJ) arc. The objectives of this experiment were to clarify seismic structures of the forearc region off Sanriku, Japan using airgun-OBS data and to understand the nature of the Japan trench seismogenic zone. Fundamental features of the structure are as follows:(i) The subduction angle becomes steeper from east to west, from 3 to 8 to 11 • , with the top of the plate located at depths of 11 km (40 km west from the trench), 21 km (120 km west from the trench) and 28 km (140 km west from the trench), respectively. (ii) The NEJ Moho beneath the forearc is defined at a depth of approximately 20 km. (iii) P-wave velocity of the island arc upper mantle is approximately 8 km s −1 . (iv) The P-wave velocity of the Cretaceous sedimentary layer exhibits significant lateral variability (4.0-5.5 km s −1 ) in the E-W direction.(v) The upper crust of NEJ forearc also has the significant lateral heterogeneity (5.0-6.3 km s −1 ) in the E-W direction, but not in the N-S direction. (vi) The middle crust defined on land extends in some locations 40 km east of the coastline. (vii) Lateral variability in the P-wave velocity of the lower crust (6.7-7.0 km s −1 ) is small compared with that of the upper crust.According to these results, it is suggested that the rupture areas of large earthquakes (>M7) in this region are limited within the contact zone between the NEJ arc crust and the subducting oceanic crust. Although a thin layer with low velocity is probably present within this contact zone, the serpentinization of uppermost mantle wedge of the NEJ arc by reaction between the mantle materials and the water from the thin layer beneath forearc region is limited. This might indicate that a significant volume of water and sediments subduct with the slab to depths of over 20 km.

For maintaining social and financial support for eradication programs of invasive species, quantitative assessment of recovery of native species or ecosystems is important because it provides a measurable parameter of success. However, setting a concrete goal for recovery is often difficult owing to lack of information prior to the introduction of invaders. Here, we present a novel approach to evaluate the achievement level of invasive predator management based on the carrying capacity of endangered species estimated using long-term monitoring data. In Amami-Oshima Island, Japan, where the eradication project of introduced small Indian mongoose is ongoing since 2000, we surveyed the population densities of four endangered species threatened by the mongoose (Amami rabbit, the Otton frog, Amami tip-nosed frog, and Amami Ishikawa's frog) at four time points ranging from 2003 to 2011. We estimated the carrying capacities of these species using the logistic growth model combined with the effects of mongoose predation and environmental heterogeneity. All species showed clear tendencies toward increasing their density in line with decreased mongoose density, and they exhibited density-dependent population growth. The estimated carrying capacities of three endangered species had small confidence intervals enough to measure recovery levels by the mongoose management. The population density of each endangered species has recovered to the level of the carrying capacity at about 20–40% of all sites, whereas no individuals were observed at more than 25% of all sites. We propose that the present approach involving appropriate monitoring data of native organism populations will be widely applicable to various eradication projects and provide unambiguous goals for management of invasive species.

Summary1. An understanding of the underlying processes and comprehensive history of invasive species is necessary to assess the long-term effectiveness of invasive species management. However, continuous, long-term labour-intensive population surveys on invasive species are often not feasible. Thus, it is important to learn about their dynamics through management action and its consequences. 2. Amami Island, Japan, has an ongoing large-scale and long-term eradication programme of invasive small Indian mongooses. To estimate the long-term pattern of population size and the parameters determining the dynamics, including anthropogenic removal, we applied a surplus-production model within a Bayesian state-space formulation incorporating the initial population size, number of captures and capture effort. Using the estimated process model directly, we conducted stochastic simulations to evaluate the feasibility of eradication. 3. Estimated 32-year annual capture probability of mongooses has increased since their introduction. The population size started to decline in 2001; mean population size in 2000 was 6141 (95% CI: 5415-6817), and declined to 169 (95% CI: 42-408) by 2011. Parameter estimates of a Weibull catchability model indicated that there was large individual heterogeneity in the probability of being captured, and per-effort capture probability declined with an increase in annual capture effort. 4. The simulation study indicated that the eradication feasibility in 2023 would be over 90% if the same annual capture effort is upheld as in 2010 (2 075 760 corrected trap-days). However, increasing annual capture effort would have little effect on shortening the time to eradication. 5. Synthesis and applications. A hierarchical model that incorporates multiple types of data to reveal long-term population dynamics has the potential to be updated with the outcomes of control efforts, and will enhance adaptive management of invasive species. This approach will offer valuable information about trade-offs between time to eradication success and effort per unit time in a long-term eradication project, and the length of time needed to continue management actions to achieve eradication success.

Invasive species and anthropogenic habitat alteration are major drivers of biodiversity loss. When multiple invasive species occupy different trophic levels, removing an invasive predator might cause unexpected outcomes owing to complex interactions among native and non-native prey. Moreover, external factors such as habitat alteration and resource availability can affect such dynamics. We hypothesized that native and non-native prey respond differently to an invasive predator, habitat alteration and bottom-up effects. To test the hypothesis, we used Bayesian state-space modelling to analyse 8-year data on the spatio-temporal patterns of two endemic rat species and the non-native black rat in response to the continual removal of the invasive small Indian mongoose on Amami Island, Japan. Despite low reproductive potentials, the endemic rats recovered better after mongoose removal than did the black rat. The endemic species appeared to be vulnerable to predation by mongooses, whose eradication increased the abundances of the endemic rats, but not of the black rat. Habitat alteration increased the black rat's carrying capacity, but decreased those of the endemic species. We propose that spatio-temporal monitoring data from eradication programmes will clarify the underlying ecological impacts of land-use change and invasive species, and will be useful for future habitat management.

Abstract. In 1997, a seismic experiment using an airgun array and ocean bottom seismographs (OBSs) was performed in the forearc region of the northeast Japan (NEJ) arc. The objectives of this experiment were to clarify whole of the velocity structure around the forearc region of NEJ arc including a detailed plate boundary structure and the heterogeneous structure. In this paper, we estimated the heterogeneous velocity structure around the forearc region of northeast Japan by applying 2-D ray tracing and travel time inversion to the airgun-OBS data. The depth where the island arc Moho comes into contact with the subducting oceanic crust is about 20 km. We suggest the existence of an oceanic layerl overlying the oceanic crust subducting down to at least near 18 km by comparing observed waveforms with these calculated using the reflectivity method.