Biology subjects

Goto, D.

Publications and source records attributed to Goto, D..

5 recordsLinked to original sources

bioRxiv2024

Cascading consequences of shifting ice phenology in an exploited lake

Ice phenology (onset and breakup of ice cover) regulates the timings of seasonal life history events of many animal and plant species in high-latitude lakes in the Northern Hemisphere, promoting the coexistence of species that share resources like food and shelter. Increasingly warmer, more variable Earths climate is, however, shifting ice phenology, modifying habitat conditions, and in turn reshaping the population and interaction dynamics of many species, threatening their persistence. Applying multivariate autoregressive state-space time series modeling to extensive historical and contemporary monitoring records (spanning 36 to 113 years) of limnological and biological surveys and fishery catches, we explore how shifting ice phenology propagates through a food web over time by modulating thermal profiles and limnological properties in Lake Simcoe, a large, intensely exploited system in southern Ontario, Canada. Analysis shows that increasingly earlier ice breakups, later ice freeze-ups, earlier thermal stratification onset, and later turnover since the early 1980s, attenuated algal production. This in turn, combined with increasingly more abundant invasive species (dreissenids) that promoted greater water clarity over prolonged stratification periods, diminished zooplankton abundances. These limnological changes filtered through plankton communities further modified the population and community dynamics of higher trophic-level species like fish with differential thermal preferences, interactively with time-varying non-climate drivers. Although management interventions-reductions in nutrient loading and fishing effort in particular-in recent decades aided the recoveries of depleted cold-adapted fish populations (including lake trout, lake whitefish, and cisco), their interaction patterns and strengths with species adapted to warmer conditions were reshuffled by advanced timings of ice breakup and delayed timings of ice freeze-up. These findings reveal how complex food web dynamics can emerge from ecologically divergent responses that reshape species interactions within and among trophic levels under shifting ice phenology filtered through bottom-up processes, likely buffering destabilizing effects of a changing climate.

ecology↗

bioRxiv2023

Transient demographic dynamics of recovering fish stocks shaped by past climate, harvest, and management

Large-scale commercial harvesting and climate-induced fluctuations in ocean properties shape the dynamics of marine populations as interdependent drivers at varied timescales. Selective removals of larger, older members of a population can distort its demographic structure, eroding resilience to fluctuations in habitat conditions and thus amplifying volatility in transient dynamics. Through the implementation of stricter management measures, many historically depleted fish stocks began showing signs of recovery in recent decades. But these interventions coincided with accelerated changes in the oceans triggered by increasingly warmer, more variable climates. Applying multilevel models to annual estimates of demographic metrics of 38 stocks comprising 11 species across seven ecoregions in the northeast Atlantic Ocean, this study explores how time-varying local and regional climates contributed to the transient dynamics of recovering populations exposed to variable fishing pressures moderated by management actions. Analyses reveal that progressive reductions in fishing pressure and shifting climate conditions nonlinearly shaped rebuilding patterns of the stocks through restorations of maternal demographic structure (reversing age truncation) and reproductive capacity. As the survival rate and demographic structure of reproductive fish improved, transient growth became less sensitive to variability in recruitment and juvenile survival and more to that in adult survival. As the biomass of reproductive fish rose, recruitment success also became increasingly regulated by density-dependent processes involving higher numbers of older fish. When reductions in fishing pressure were insufficient or delayed, however, stocks became further depleted, with more eroded demographic structures. Although warmer local climates in spawning seasons promoted recruitment success in some ecoregions, changing climates in recent decades began adversely affecting reproductive performances overall, amplifying sensitivities to recruitment variability. These shared patterns underscore the value of demographic transients in developing robust strategies for managing marine resources. Such strategies could form the foundation for effective applications of adaptive measures resilient to future environmental change.

ecology↗

bioRxiv2020

A precautionary solution to estimation bias in shaping safe harvest boundaries

Biased estimates of population status are a pervasive conservation problem. This problem has plagued assessments of commercial exploitation of marine species and can threaten the sustainability of both populations and fisheries. We develop a computer-intensive approach to minimize adverse effects of persistent estimation bias in assessments by optimizing operational harvest measures (harvest control rules) with closed-loop simulation of resource-management feedback systems: management strategy evaluation. Using saithe (Pollachius virens), a bottom-water, apex predator in the North Sea, as a real-world case study, we illustrate the approach by first diagnosing robustness of the existing harvest control rule and then optimizing it through propagation of biases (overestimated stock abundance and underestimated fishing pressure) along with select process and observation uncertainties. Analyses showed that severe biases lead to overly optimistic catch limits and then progressively magnify the amplitude of catch fluctuation, thereby posing unacceptably high overharvest risks. Consistent performance of management strategies to conserve the resource can be achieved by developing more robust control rules. These rules explicitly account for estimation bias through a computational grid search for a set of control parameters (threshold abundance that triggers management action, Btrigger, and target exploitation rate, Ftarget) that maximize yield while keeping stock abundance above a precautionary level. When the biases become too severe, optimized control parameters- for saithe, raising Btrigger and lowering Ftarget-would safeguard against overharvest risk (<3.5% probability of stock depletion) and provide short-term stability in catch limit (<20% year-to-year variation), thereby minimizing disruption to fishing communities. The precautionary approach to fine-tuning adaptive risk management through management strategy evaluation offers a powerful tool to better shape sustainable harvest boundaries for exploited resource populations when estimation bias persists. By explicitly accounting for emergent sources of uncertainty our proposed approach ensures effective conservation and sustainable exploitation of living marine resources even under profound uncertainty. Open Research StatementData sets and code utilized for this research are available on Figshare. DOI: https://doi.org/10.6084/m9.figshare.13281266

ecology↗

bioRxiv2020

Managing Arctic predator harvest instability amplified by variable prey productivity and ocean temperature

Sustainable human exploitation of marine living resources stems from a delicate balance between short-term yield stability and long-term population persistence to achieve socioeconomic and conservation goals. However, imperfect knowledge of how oscillations in ecosystem processes regulate fluctuations in exploited populations can obscure the risk of missing management targets. We illustrate how the harvest policy to suppress short-term yield fluctuation inadvertently disrupts population cycles and yield stability of exploited, long-lived predators under stochastically fluctuating environmental forces (food availability and regional climate) using Northeast Arctic (NEA) cod (Gadus morhua, an apex predatory fish) as a case study. We use a stochastic, empirically parameterized multispecies model to simulate NEA cod population dynamics through life-history processes; Barents Sea capelin (Mallotus villosus, a pelagic forage fish) modulates cod productivity through density-dependent cannibalism-predation dynamics, whereas sea temperature regulates cod consumption, growth, and recruitment. We first test how capelin and sea temperature fluctuations regulate patterns in cod yield fluctuation and then quantitatively assess how fishing pattern designed to limit yield between-year variance (within 50-5%) perturbs cod population-catch dynamics. Simulations suggest that capelin and temperature interactively contribute to shifting cyclic patterns in cod yield fluctuation primarily through cod cannibalism-predation dynamics. Wavelet analyses further show that muffling yield variance (30 % or less) reshapes the cyclicity (shorter period and greater amplitude) of cod population size and demography, thereby becoming progressively unsynchronized with fishing pressure. Our work reveals unintended consequences of managing transient dynamics of fished populations: the interworking of population cycle destabilized by inadvertently intensifying fishing pressure, amplifying yield fluctuation and, in turn, elevating overharvest risk when not accounting for compounded effects of stochasticity in ecologically connected processes. These policy implications underscore the need for an ecosystem approach to designing ecologically sound management measures to safely harvest shared living resources while achieving socioeconomic security in increasingly more dynamic oceans in the Arctic and elsewhere.

ecology↗

bioRxiv2019

Divergent population recovery trajectories following sex-biased perturbation in life history traits

Uncertainty in risks posed by emerging stressors such as synthetic hormones impedes conservation efforts for threatened vertebrate populations. Synthetic hormones often induce sex-biased perturbations in exposed animals by disrupting gonad development and early life-history stage transitions, potentially diminishing per capita reproductive output of depleted populations and, in turn, being manifest as Allee effects. We use a spatially-explicit biophysical model to evaluate how sex-biased perturbation in life history traits of individuals (maternal investment in egg production and male-skewed sex allocation in offspring) modulates density feedback control of year class strength and recovery trajectories of a long-lived, migratory fish-shovelnose sturgeon (Scaphirhynchus platorynchus)-under spatially and temporally dynamic synthetic androgen exposure and habitat conditions. Simulations show that reduced efficiency of maternal investment in gonad development prolonged maturation time, increased the probability of skipped spawning, and, in turn, gradually shrunk spawner abundance, weakening year class strength. However, positive density feedback quickly disappeared (no Allee effect) once the exposure ceased. By contrast, responses to the demographic perturbation manifested as strong positive density feedback; an abrupt shift in year class strength and spawner abundance followed after more than two decades owing to persistent negative population growth (a strong Allee effect), reaching an alternate state without any sign of recovery. When combined with the energetic perturbation, positive density feedback of the demographic perturbation was dampened as extended maturation time reduced the frequency of producing male-biased offspring, allowing the population to maintain positive growth rate (a weak Allee effect) and gradually recover. The emergent patterns in long-term population projections illustrate that sex-biased perturbation in life history traits of individuals can interactively regulate the strength of density feedback in depleted populations such as Scaphirhynchus sturgeon to further diminish reproductive capacity and abundance, posing increasingly greater conservation challenges in chemically altered riverscapes.

ecology↗