We examined how the climate regime shift around 2000 affected Antarctic krill recruitment variability at the North Antarctic Peninsula (NAP) and South Georgia (SG) during the period of 1990s through to 2000s. We used sea surface temperature (SST) as a proxy of the monthly sea ice extent and related it to the recruitment index (proportion of 1-year-old krill) of each succeeding year for NAP and SG by examining the correlation of the time series before and after 2000. For NAP, recruitment index was negatively correlated with winter SST at NAP in the 1990s but with autumn SST in the 2000s, suggesting that good recruitment was supported by extensive winter sea-ice in the 1990s but by extensive autumn sea-ice in the 2000s. This was attributed to the regime shift featured by winter warming and autumn cooling after 2000. For SG, recruitment was negatively correlated with winter SST at NAP in the 1990s but positively correlated with autumn SST in the southern Scotia Sea (SSS) in the 2000s. According to particle tracking experiment from NAP to SG in relation to the sea-ice extent and position of SACCF (Southern Antarctic Circumpolar Current Front), less sea-ice extent in 2000s meant less larvae distributing as north as SACCF, resulting in much fewer larval being transported to SG. Hence, we hypothesized that the regime shift weakened the connection between NAP and SG, but instead SSS became the main driver of recruitment at SG. We presume the krill population demonstrated adaptability to the regime shift by offsetting the unfavorable winter condition with the favorable autumn condition at NAP and for SG, replacing the source of recruits with those closer to it.

The need for the management of commercially targeted species and surrounding ecosystems has become more apparent in conjunction with the thriving commercial exploration of open seas. Despite the growing global interest in how fishing activity impacts seamount ecosystems, data regarding to the fishing impacts of gillnets on seamount ecosystems are scarce, and quantitative comparisons between trawls and gillnets are surprisingly limited. Our quantitative comparative studies using observer data collected at the southern Emperor Seamounts area revealed that the quantity and quality of bycatches of four key demersal benthos, denoted as Vulnerable marine ecosystem (VME) indicator taxa designated in the convention text of The North Pacific Fisheries Commission (three orders of dominant corals, Antipatharia, Scleractinia, and “Gorgonian” (Alcyonacea with solid axis), and Porifera), were not inherently different between the gear types, and operational tactics, such as depth or positions, might be prior factors largely affecting bycatches of benthic assemblages in the fishing activities carried out at Emperor Seamounts. Additionally, assessments of multiyear operational data revealed temporal shifts in the species composition of cold-water coral bycatches. Overall, the synthesis of bycatch occasions provided by scientific observers enabled us to reveal (1) the variations in bathymetric distributions and the contribution of local topographies toward demersal benthic organisms and (2) fishing operational features, such as operation positions and depth, which may strongly affect bycatches.

The Antarctic toothfish (Dissostichus mawsoni) is an important fishery species widely distributed in the Southern Ocean, especially in areas covered by sea ice. Understanding fish distributions and life cycles, including the transport and survival of eggs and larvae, is essential for the assessment and sustainable management of the fishery. However, owing to difficulties with in situ winter observations, information on the early life stages of D. mawsoni is lacking. Here, we investigated the transport pathways of fish eggs and larvae through a particle tracking study, using satellite-derived ocean surface velocities in the East Antarctic region, which includes important D. mawsoni habitats and exploratory fisheries. Our results indicate that particles released from continental slopes are more likely to be successfully transported to suitable settlement grounds than those released from the BANZARE Bank (the southern region of the Kerguelen Plateau), which is situated further north and has been hypothesized to be a potential spawning ground for D. mawsoni. This study demonstrates successful source-settlement connections in relation to ocean recirculation and suggests important settlement regions for D. mawsoni larvae in the East Antarctic region.

Long-term patterns in trajectories of natural communities provide insights into ecological resilience, but their assessment requires long-term census data. We analyzed 16-year census data for intertidal communities from 30 rocky shores along Japan’s Pacific coast to assign community change to four possible trajectories (stable, reversible, abrupt, or linear) representing different aspects of ecological resilience, and to estimate multiple metrics of temporal invariability (species richness, species composition, and community abundance). We examined (1) how the prevalence of the four trajectories differs among regions, (2) how the features (model coefficients) of each trajectory vary among regions, and (3) how the temporal invariabilities differ among trajectories and regions. We found that the stable trajectory was the most common. Its features differed among regions, with a faster recovery to steady-state equilibrium in low-latitude regions. Furthermore, trajectories and temporal invariabilities both varied among regions, seemingly in association with the strength of ocean current fluctuations. Thus, the relationship between community temporal invariability and trajectory may be weak or absent, at least at the regional scale.

We provide a preliminary estimate of the growth equation for splendid alfonsino Beryx splendens in the south-western Indian Ocean. However, the result was considerably different from the previous estimates from the same area and from different areas, and the difference is not likely to be an artifact of the age estimation procedure. Further research is required to determine the cause of those differences and to obtain a reliable growth equation. Recommendations (working papers only) 1. The growth equation estimated in this study should be interpreted with caution, as it differs considerably from previous studies and the cause of the difference is unclear. A preliminary estimation of the splendid alfonsino growth equation in the south-western Indian Ocean Kota Sawada and Takehiro Okuda Oceanic Ecosystem Group, National Research Institute of Far Seas Fisheries, Japan Fisheries Research and Education Agency, Japan Abstract We provide a preliminary estimate of the growth equation for splendid alfonsino Beryx splendens in the south-western Indian Ocean. However, the result was considerably different from the previous estimates from the same area and from different areas, and the difference is not likely to be an artifact of the age estimation procedure. Further research is required to determine the cause of those differences and to obtain a reliable growth equation.We provide a preliminary estimate of the growth equation for splendid alfonsino Beryx splendens in the south-western Indian Ocean. However, the result was considerably different from the previous estimates from the same area and from different areas, and the difference is not likely to be an artifact of the age estimation procedure. Further research is required to determine the cause of those differences and to obtain a reliable growth equation.

Risks to deepwater chondrichthyans (sharks, rays, and chimaeras) from fishing are poorly understood, particularly in areas beyond national jurisdiction. We adapted productivity-susceptibility analysis (PSA) and sustainability assessment for fishing effects (SAFE) to assess the vulnerability of 173 deepwater chondrichthyans to various demersal fishing gears in the Southern Indian and South Pacific Oceans. Several species were categorized as being at high or extreme vulnerability, including some deepwater shark species in the Southern Indian Ocean that are reported to be commercially targeted. There was good concurrence between PSA and SAFE results for species categorized as being at high or extreme vulnerability by the SAFE, but as expected there was an overall greater number assessed to be as higher vulnerability using PSA due to its precautionary nature. Our results indicate probable misclassifications in the PSA relative vulnerability rankings, highlighting the value of applying more quantitative tools, such as SAFE, when adequate data are available. Our findings indicate that better catch, effort, and biological information are needed to inform the assessment and management of deepwater chondrichthyans. If targeted fishing of deepwater shark species continues in the Southern Indian Ocean, improved assessments and estimates of sustainable yields are urgently required to mitigate the risk of overexploitation.

We analyzed diel vertical migration (DVM) of overwintering Antarctic krill at South Georgia, a region that remains ice-free during the austral winter. We considered DVM in relation to krill body length, based on Japanese krill fishery data (1990-2012), and examined DVM in relation to food availability and predator (Antarctic fur seal) avoidance. We report that diel changes in median trawling depth (a proxy for krill vertical distribution) showed significant interannual variation; the overall trend was such that during both daytime and nighttime, the larger the average size of krill, the deeper their median depth. Consistent with the literature, this size-dependent DVM relates to food availability and size-dependent diet; that is, with increasing body length, krill tend to rely less on phytoplankton (which are available in surface layers) as a winter food source. Concerning predator avoidance, and based on analyses using an optimal foraging dive model for fur seals, DVM showed close agreement with size-dependent predation risk; that is, larger krill remained deeper, thereby reducing mortality from fur seals. Therefore, DVM of overwintering krill appears to reflect a compromise between adequate feeding conditions and minimizing predation risk. There was, however, an exception that krill occurred at a shallow depth in winter 2006 when phytoplankton abundance was particularly low and krill density was very high. This supports the hypothesis that physiological demands (i.e. hunger) may become a more important factor affecting DVM than predator avoidance under conditions of insufficient food availability.

Streams depleted of their native salmonid populations are often stocked with domesticated fish for supplementation. However, these domesticated salmonids have a lower adaptability to environmental conditions and thus have a lower survival rate than "native" salmonids. Recent studies suggest the stocking of "semi-native" strains of fish (hybrids between native males and domesticated females) as an alternative to domesticated fish. We evaluated the difference in the apparent survival rates of semi-native and domesticated juvenile char after their stocking in mountain streams. The analysis used multi-site variable time-series data with a Bayesian multivariate state-space model reflecting the characteristics of the data, including time-series variation, site-specific effects, and observation error. The resulting odds ratio, which represents the general and potential strain effect of the semi-native char stocking, was 2.49(95% CI = 2.12-2.94), implying that the apparent survival - rate of the semi-native char was approximately 2.5 times higher than that of the domesticated char in the mountain streams studied. The results suggest that hybridization might be a viable approach for stocking and harvest augmentation of the commercial and recreational fisheries in fragmented populations.

Summary Estimation of transition probabilities of sessile communities seems easy in principle but may still be difficult in practice because resampling error (i.e. a failure to resample exactly the same location at fixed points) may cause significant estimation bias. Previous studies have developed novel analytical methods to correct for this estimation bias. However, they did not consider the local structure of community composition induced by the aggregated distribution of organisms that is typically observed in sessile assemblages and is very likely to affect observations. We developed a multistate dynamic site occupancy model to estimate transition probabilities that accounts for resampling errors associated with local community structure. The model applies a nonparametric multivariate kernel smoothing methodology to the latent occupancy component to estimate the local state composition near each observation point, which is assumed to determine the probability distribution of data conditional on the occurrence of resampling error. By using computer simulations, we confirmed that an observation process that depends on local community structure may bias inferences about transition probabilities. By applying the proposed model to a real data set of intertidal sessile communities, we also showed that estimates of transition probabilities and of the properties of community dynamics may differ considerably when spatial dependence is taken into account. Results suggest the importance of accounting for resampling error and local community structure for developing management plans that are based on Markovian models. Our approach provides a solution to this problem that is applicable to broad sessile communities. It can even accommodate an anisotropic spatial correlation of species composition, and may also serve as a basis for inferring complex nonlinear ecological dynamics.

Understanding the community structure of oceanic higher trophic level (HTL) organisms (e.g., sharks, tunas, salmons, and squids) is fundamental to management of marine resources in a way that ensures their sustainable use and maintains marine ecosystem functionality and biodiversity. We analyzed the spatial structure of HTL assemblages in the western North Pacific Ocean using driftnet survey data collected at latitudes of 35–46 °N along transect lines at 144 °E, 155 °E, and 175.5 °E longitude in July and August 2011. We proposed a new dissimilarity metric segmentation procedure (Dissimilarity Segmentation) based on the differences of mean Bray-Curtis dissimilarity indices between two individual driftnet hauls within the same subarea or among different subareas. Dissimilarity Segmentation allowed us to divide the western North Pacific Ocean into three subareas: a northern subarea (>41°N including 41°N on the 175.5°E transect), a transition subarea (37–41°N), and a southern subarea (<37°N). The HTL biomass in the northern subarea was high, and the species diversity was low; dominant and common species accounted for most of the biomass. The HTL assemblage in the southern subarea was composed of many species that were uncommon or rare; the biomass was lower, and the species diversity was higher than in the northern subarea. In the transition subarea, neon flying squid accounted for most of the biomass, and although the biomass was intermediate, species diversity was highest among the three subareas. Canonical correspondence analysis with oceanic environmental variables, principally chlorophyll a, sea surface salinity, and sea surface height, as the explanatory variables accounted for 43.6% of the variance of the HTL pelagic species composition. This result suggests that the HTL pelagic community in the western North Pacific is influenced largely by productivity and oceanic physical structure. These results suggest that an analytical approach based on Dissimilarity Segmentation combined with medium- to long-term survey datasets could facilitate the investigation of spatial-temporal variations in the spatial structure of HTL pelagic communities and the environmental causes thereof.

North Pacific armorhead Pentaceros wheeleri specimens collected through pelagic surveys in the North Pacific were analyzed to estimate the distribution, hatching season, growth, and the duration of the epipelagic life stage. Most pelagic specimens were collected in the central and eastern North Pacific (36–50°N, 178°E–137°W). This area was considered to be the nursery ground where larvae and juveniles inhabit until subsequent settlement to seamounts. The pelagic specimens were aged 0, 1, and 2 years, and their hatching periods were estimated to be from December to February based on the analysis of daily growth increments of otoliths. Standard length-at-age data were fitted to the mixed model of the von Bertalanffy growth curves, and growth coefficients L ∞, k, and t 0 were estimated to be 308 and 290 mm, 0.909 and 1.055, and 0.183 and 0.256 years for males and females, respectively. The standard length of fish at age 2.5 years was estimated at 263–271 mm, which is close to the size of demersal fish commonly harvested from the southern Emperor-northern Hawaiian Ridge seamounts. Since only a few age 3 fish were collected in pelagic samples, presumably most individuals shift to demersal life on seamounts before age 3.

We analyzed the stomach contents and nitrogen and carbon stable isotope ratios of three deep-sea fishes Pentaceros wheeleri (North Pacific armorhead), Beryx splendens (splendid alfonsino), and Allocyttus folletti (oxeye oreo)—to elucidate interspecific and intraspecific differences in prey use among demersal fishes in the Emperor Seamount waters (North Pacific Ocean). Principal component analysis using an index of relative importance revealed interspecific differences in prey use: P. wheeleri preyed on plankton and benthos; B. splendens on micronekton and plankton, and A. folletti on micronekton. The relationship between the index of relative importance in B. splendens and body length also indicated ontogenetic shifts in prey use. High percentage of empty stomachs and low stomach fullness index in P. wheeleri indicated this species’ limited feeding ability during its demersal life on seamount. Nitrogen isotope ratio analysis suggested that the trophic level of A. folletti was the highest, followed by large B. splendens, small B. splendens, and P.wheeleri. Variation in carbon isotope ratio values were small, indicating that primary producers were similar. Differences in nitrogen isotope ratio (trophic level) coincided with differences in prey use by the three fishes. Thus, these species are likely able to coexist in seamount waters by partitioning their use of benthos, plankton, and micronekton food resources. They might be supported by food supplied from the surrounding water columns by horizontal flux of plankton or vertical migration of micronekton in the deep scattering layer because except for the benthic prey of P. wheeleri they consumed plankton and micronekton.

There are increasing demands for evaluation of the current status of marine ecosystems and impacts of environmental change and anthropogenic activities, but for the open ocean available data are quite limited. The Japanese driftnet survey dataset of Hokkaido University was used to analyze the spatio-temporal variations in the higher trophic level (HTL) community structure in the western North Pacific. The analyses were conducted by using subset of the data that was collected along four regularly surveyed transect lines at 155°E, 170°E, 175°E and 180°E spanning from 36 to 48°N and from 1982 to 1996. Non-size-selective multiple mesh driftnets were used in the survey. Total number of individuals, species richness and Simpson index of species diversity indicated a longitudinal gradient with a lower abundance and diversity in the eastern area. Latitudinal gradient was clear for numerical abundance and species richness, but no trend for Simpson diversity index. Temporal patterns in the HTL community structure were not consistent among the three metrics: numerical abundance showed a significantly decrease and increasing fluctuations in later years, species richness was increased along years, and Simpson index did not show any clear temporal trends. The inconsistency in the temporal patterns of community metrics was considered to arise from the effects of the sampling scheme on community measurements and/or complex structural changes such as the emergence of dominant species related to regime shifts. These results suggest the importance of proper consideration of temporal changes in the sampling scheme when analyzing long-term data.

Many marine benthic invertebrates pass through a planktonic larval stage whereas others spend their entire lifetimes in benthic habitats. Recent studies indicate that non‐planktonic species show relatively greater fine‐scale patchiness than do planktonic species, but the underlying mechanisms remain unknown. One hypothesis for such a difference is that larval dispersal enhances the connectivity of populations and buffers population fluctuations and reduces local extinction risk, consequently increasing patch occupancy rate and decreasing spatial patchiness. If this mechanism does indeed play a significant role, then the distribution of non‐planktonic species should be more aggregated – both temporally and spatially – than the distribution of species with a planktonic larval stage. To test this prediction, we compared 1) both the spatial and the temporal abundance–occupancy relationships and 2) both the spatial and the temporal mean–variance relationships of population size across species of rocky intertidal gastropods with differing dispersive traits from the Pacific coast of Japan. We found that, compared to planktonic species, non‐planktonic species exhibited 1) a smaller occupancy rate for any given level of mean population size and 2) greater variations in population size, both spatially and temporally. This suggests that the macroecological patterns observed in this study (i.e. the abundance–occupancy relationships and mean–variance relationships of population size across species) were shaped by the effect of larval dispersal dampening population fluctuation, which works over both space and time. While it has been widely assumed that larval dispersal enhances population fluctuations, larval dispersal may in fact enhance the connectively of populations and buffer population fluctuations and reduce local extinction risks.

Explanations for why population dynamics vary across the range of a species reflect two contrasting hypotheses: (i) temporal variability of populations is larger in the centre of the range compared to the margins because overcompensatory density dependence destabilizes population dynamics and (ii) population variability is larger near the margins, where populations are more susceptible to environmental fluctuations. In both of these hypotheses, positions within the range are assumed to affect population variability. In contrast, the fact that population variability is often related to mean population size implies that the spatial structure of the population size within the range of a species may also be a useful predictor of the spatial variation in temporal variability of population size over the range of the species. To explore how population temporal variability varies spatially and the underlying processes responsible for the spatial variation, we focused on the intertidal barnacle Chthamalus dalli and examined differences in its population dynamics along the tidal levels it inhabits. Changes in coverage of barnacle populations were monitored for 10.5 years at 25 plots spanning the elevational range of this species. Data were analysed by fitting a population dynamics model to estimate the effects of density-dependent and density-independent processes on population growth. We also examined the temporal mean-variance relationship of population size with parameters estimated from the population dynamics model. We found that the relative variability of populations tended to increase from the centre of the elevational range towards the margins because of an increase in the magnitude of stochastic fluctuations of growth rates. Thus, our results supported hypothesis (2). We also found that spatial variations in temporal population variability were well characterized by Taylor's power law, the relative population variability being inversely related to the mean population size. Results suggest that understanding the population dynamics of a species over its range may be facilitated by taking the spatial structure of population size into account as well as by considering changes in population processes as a function of position within the range of the species.

To understand the patterns and processes associated with the population dynamics of Balanus glandula during the early phase of invasion along the Pacific coast of eastern Hokkaido, population surveys were conducted from 2002 to 2011 at five shores, each consisting of five paired plots (scraped recruitment plot and unscraped establishment plot), along 49 km of coastline located 144 km east of the eastern front of the invasion of this species in 2000. Larval recruitment was first detected in 2004, but the establishment of a population was not observed until 2 years later at the westernmost shore of the study area. Occurrence increased from non-native barnacle present in 4 % of plots in 2006 to 100 % in 2011, but mean coverage remained low (<5 %) in 2011. Most local population coverage fluctuated without indicating clear temporal trends, but coverage in one plot showed a consistent pattern of rapid increase. Local extinctions occurred, but rates of local extinction decreased with time as larval recruitment increased. Lag times between recruitment and establishment occurred for 64 % of the paired plots and ranged from 1 to 4 years. Lag times decreased after 5 years, when larval recruitment increased. These findings suggest that the intensity of larval recruitment determined invasion dynamics during this early phase of the invasion, and the monitoring of recruitment is therefore essential for early detection of invasions by sessile marine organisms and prediction of their range expansion.

Although researchers recognize that population dynamics can vary in space and time as a result of differences in biotic and abiotic conditions, spatial and temporal variability in the patterns and processes of population dynamics have not been well documented on a seasonal time frame. We quantified seasonal changes in the coverage of intertidal barnacles, Chthamalus spp., with data collected for as many as 9 years at 88 plots in five regions located along more than 1800 km of the Pacific coastline of Japan from 31 degrees N to 43 degrees N. To examine how seasonal changes and the spatial heterogeneity of environments can interact to influence patterns and processes of population dynamics, we analyzed the data with two models of population variability: a population dynamics model, which provides knowledge about processes that determine population growth rates; and Taylor's power law, which summarizes the relationship between the temporal mean and variance of the size of a population (temporal mean-variance relationship). We found that seasonal differences were prevalent in population growth rates, as well as in the strength and spatial scales of processes that determine population growth rates. In addition, the seasonality of these rates and processes varied between habitats at different spatial scales ranging from the scale of among-rocks within a shore to that of among-regions located in different latitudes, suggesting that the effects of seasonal environmental fluctuations on population growth can depend on the spatial heterogeneity of biotic and abiotic conditions that vary at multiple spatial scales. In contrast, the evidence for spatiotemporal differences in temporal mean-variance relationships was weak. Unlike theoretical expectations, spatiotemporal differences in the variability of population size were best explained by a unique power law, despite remarkable regional and seasonal differences in the processes that determine population growth rates. These results suggest that spatiotemporal environmental variability can affect population dynamics at multiple spatial scales but do not necessarily alter the scaling law of population size variability.