Variation In Recruitment Research Articles

A Comparison of Grass Carp Population Characteristics Upstream and Downstream of Lock and Dam 19 of the Upper Mississippi River

Abstract Grass Carp Ctenopharyngodon idella have been intentionally stocked for aquatic vegetation control across the Midwestern United States for several decades. During the 1970s, escapement of Grass Carp into the Missouri River facilitated their naturalization into much of the Mississippi River basin, including the Upper Mississippi River. Lock and Dam 19 (LD19) in Keokuk, Iowa, is a high-head dam that represents a focal point for naturalized Grass Carp management where populations may differ between upstream and downstream pools as result of limited upstream migration, but potential differences between populations have yet to be evaluated to the best of our knowledge. The objective of this study was to compare the relative abundance, size structure, condition, growth, and recruitment variability of Grass Carp collected upstream and downstream of LD19. We sampled Grass Carp monthly (April–October) during 2014 and 2015 from four locations in the Des Moines River (downstream of LD19) and five locations throughout the Skunk, Iowa, and Cedar rivers (upstream of LD19) using boat electrofishing and trammel net sets. We captured 29 Grass Carp upstream of LD19 compared with 179 individuals captured downstream. Trammel nets only captured Grass Carp downstream of LD19; trammel net catch per unit effort upstream of LD19 was low and ranged from 0.0 to 8.0 fish/net lift (mean ± SE = 0.39 ± 0.13). Electrofishing catch per unit effort ranged from 0.0 to 22.7 fish/h (1.49 ± 0.30) and was higher downstream (2.42 ± 0.30) of LD19 than upstream (0.57 ± 0.07). Grass Carp downstream of LD19 tended to be smaller, younger, of lower body condition, had higher mortality rates, and were slower growing compared with those collected upstream and to populations documented in other systems. Understanding and monitoring adult Grass Carp population characteristics upstream and downstream of LD19 is necessary to determine how they may change in response to ongoing harvest efforts for invasive carps in these river reaches.

Multiscale relationships between stream temperature and juvenile recruitment in an imperilled freshwater fish

The distribution and population structure of organisms is governed by a broad suite of biotic and abiotic variables, interacting across multiple scales. Recruitment is a key demographic process critical to the maintenance of successful populations. Isolating and quantifying the multiscale environmental drivers of recruitment is vital for species conservation, especially for those species with traits that increase their susceptibility to local extirpation. We developed a Bayesian hierarchical model to quantify the relationship between the rate of recruitment in a locally threatened river blackfish (Gadopsis marmoratus) and environmental predictors across two spatial scales. There was a 0.99 probability that increased broad-scale stream temperature negatively affected juvenile recruitment rate. We also found that there was a 0.97 probability that the fine-scale relationship between recruitment rate and riparian foliage cover was dependent on temperature. This suggests that broad-scale thermal conditions provide the template upon which at least one local environmental variable influences recruitment rate. Understanding drivers influencing key population processes and the spatial scales at which they operate is critical to gaining an insight into likely changes in population persistence for potentially imperilled species, along with the potential future effects of habitat degradation and climate warming on freshwater fishes in general.

Disentangling the influence of fishing, demography, and environment on population dynamics of Iberian Peninsula waters fish stocks

AbstractOverexploitation and climate change are increasingly causing unanticipated changes in marine ecosystems such as higher variability in fish recruitment or shifts in species dominance and distribution that alter the productivity of fish stocks. This study analyses how external and internal drivers influence population dynamics of hake (Merluccius merluccius), white anglerfish (Lophius piscatorius), four-spot megrim (Lepidorhombus boscii), and horse mackerel (Trachurus trachurus) of Iberian Peninsula waters of the Northeast Atlantic across different spatiotemporal scales. Available spawning stock biomass and recruitment have been used as biological data, whereas fishing mortality, demographic data as well as climatic and oceanographic data have been used as drivers. The obtained results indicate that population dynamics of these species are mainly driven by oceanographic variability at regional scale along with fishing pressure and demographic factors, while the impact of large-scale climate indices was minimal. The identified variables represent relevant oceanographic regional processes candidate to be potentially integrated into the stock assessment models and management procedures of these important fishery resources.

Duality of trophic supply and hydrodynamic connectivity drives spatial patterns of Pacific oyster recruitment

The recent discovery of Pacific oyster Crassostrea gigas (also known as Magallana gigas) spatfields in a Mediterranean lagoon intensely exploited for shellfish farming (Thau lagoon) revealed significant contrasts in spatial patterns of recruitment. We evaluated the processes that drive spatial patterns in oyster recruitment by comparing observed recruitment, simulated hydrodynamic connectivity and ecological variables. We hypothesized that spatial variability of recruitment depends on (1) hydrodynamic connectivity and (2) the ecology of the larval supply, settlement, metamorphosis, survival and biotic environmental parameters. We assessed recruitment at 6-8 experimental sites by larval sampling and spat collection inside and outside oyster farming areas and on an east-west gradient, from 2012-2014. Hydrodynamic connectivity was simulated using a numerical 3D transport model assessed with a Eulerian indicator. The supply of large umbo larvae did not differ significantly inside and outside oyster farming areas, whereas the supply of pediveligers to sites outside shellfish farms was structured by hydrodynamic connectivity. Inside shellfish farming zones, unfavorable conditions due to trophic competition with filter-feeders jeopardized their settlement. In this case, our results suggest loss of settlement competence by oyster larvae. This confirms our hypothesis of top-down trophic control by the oysters inside farming zones of Thau lagoon in summer that fails to meet the ecological requirements of these areas as oyster nurseries. Knowledge of oyster dispersal, connectivity and recruitment in coastal lagoons will help local development of sustainable natural spat collection. On a global scale, our method could be transposed to other basins or used for other species such as mussels, clams or scallops, to better understand the spatial patterns of bivalve recruitment. Management of the oyster industry based on natural spat collection will help develop a sustainable activity, based on locally adapted oyster strains but also by reducing the risks of transferring pathogens between basins and the global carbon footprint of this industry.

Long‐term variability and density dependence in Hudson River Dreissena populations

Abstract We used a 27‐year record of Dreissena populations in the freshwater tidal Hudson River to describe interannual variation in population density, body size, and body condition; estimate long‐term variation in recruitment, survivorship, and shell growth; and assess possible controls on the populations. Dreissena populations in the Hudson have been highly variable, with interannual ranges of c. 100‐fold in abundance and biomass, and 7‐fold in mean body mass. This large interannual variation arises from both long‐term trends and 2–5‐year cycles. Long‐term trends include the 2008 appearance of the quagga mussel (Dreissena rostriformis), which still forms a small part (<10%) of the dreissenid community, and a decline in zebra mussel body size. The decline in body size was caused by a long‐term decline in adult survivorship rather than a decline in rates of shell growth. We could detect no long‐term trends in adult abundance or spread of Dreissena onto soft sediments in the Hudson. We observed persistent, strong cycles in adult abundance and body size. These were driven by the appearance and decay of eight dominant year classes over the 27 years of our study, and were a result of temporal variation in recruitment rather than temporal variation in survivorship. The observed strongly irregular recruitment appears to arise from strong adult–larval interactions, and is consistent with previous simulation model results showing that interactions between adults and larvae can drive persistent cycling. We found evidence that negative density dependence affects recruitment, somatic growth, and body condition of Dreissena in the Hudson. Warm summers may also cause high adult mortality. We put our results into the context of a conceptual model of Dreissena population dynamics, and argue that neither the dynamics nor the controls of populations of these important invaders is known satisfactorily.

A long-term study of whiting, Merlangius merlangus (L) recruitment and population regulation in the Severn Estuary, UK.

Data collected by power station impingement sampling, plus plankton and trawl netting over the last 50 years is used to analyse the dynamics of the whiting, Merlangius merlangus (L.) subpopulation within the Bristol Channel, UK, ecosystem. In Northern Europe, whiting is a dominant member of the inshore community and is commercially exploited. Contemporaneous long-term data for fish and crustacean species gives an exceptional opportunity to explore regulatory interactions for a gadoid fish with high between-year recruitment variability. There is considerable between year variation in whiting recruitment and growth which relates to both biotic and physical variables. However, analysis of a 40-year annual abundance time series detected density-dependent regulation with no long-term trend. Over an extended spawning season, a series of recruitment cohorts travel up estuary to their nursery grounds. The average size at the end of their first year relates to the timing of the dominant cohort within the extended spawning season. Whiting are locked into a web of predator-prey, host-parasite and commensal relationships which act to damp deviations from carrying capacity caused by habitat variability. River flow and seawater temperature change whiting distribution and abundance both directly and via their effects upon prey and predator species. The abundance of two prey, the shrimp, Crangon crangon, and sprat, Sprattus sprattus, positively influence growth and local abundance, conversely, Conger eel, Conger conger, the top predator, has a negative relationship with whiting abundance. During autumn and winter O-group whiting are particularly dependent on C. crangon for food. Whiting appears an ideal candidate for an ecosystem-based fisheries management approach. They are generalist predators eating locally abundant animals smaller than themselves. Carrying capacity likely reflects the total resource base of crustaceans and small fish available.

Water temperature during winter may control striped bass recruitment during spring by affecting the development time of copepod nauplii

AbstractStriped bass (Morone saxatilis) are anadromous fish that support an important fishery along the east coast of North America. In Chesapeake Bay, strong juvenile recruitment of striped bass can occur when larvae overlap with high concentrations of their zooplankton prey, but the mechanisms fostering the temporal overlap are unknown. Here, the influence of winter temperature on the peak abundances of a key prey, Eurytemora carolleeae, was estimated with a temperature-dependent developmental model. The role of these peaks in regulating striped bass recruitment was explored in three nursery areas: upper Chesapeake Bay, Choptank River, and Patuxent River. Model results indicated that cold winters delay the timing and increase the size of peak E. carolleeae spring abundance. When the model output was used in regression relationships with striped bass juvenile recruitment and freshwater discharge, the regression models explained up to 78% of annual recruitment variability. Results suggests that cold, wet winters could increase the chance of a match between striped bass larvae and high concentrations of their prey. This mechanistic link between winter temperatures and striped bass production, acting through prey dynamics, could further understanding of fish recruitment variability and indicates that warmer winters could negatively affect some striped bass populations.

Environmentally driven forecasts of northern rock sole (Lepidopsetta polyxystra) recruitment in the eastern Bering Sea

AbstractNorthern rock sole recruitment in the eastern Bering Sea has been hypothesized to (a) depend on wind‐driven surface currents linking spawning and nursery areas, (b) be density‐dependent, and (c) be negatively impacted by cold bottom temperatures over a large nursery area during the first summer of life. A suite of models was developed to test these hypotheses. Data included 32 years of recruitment and spawning biomass estimates derived from a stock assessment model and wind and temperature indices customized to the environmental exposure of age‐0 northern rock sole in the eastern Bering Sea. The predictive ability of the models was evaluated, and the models were used to forecast recruitment to age‐4 for recent year classes which are poorly retained by the standard multi‐species bottom trawl survey gear. Models which included wind and temperature indices performed better than a naïve forecast based on the running mean. The best‐performing model was a categorical model with wind and temperature thresholds, which explained 49% of the variation in recruitment. Ricker models performed more poorly than models without a spawning biomass term, providing no evidence that recruitment is related to stock size. The models forecast higher recruitment for the most recent year classes (2015–2018) than for prior year classes with observed poor recruitment (2006–2013). These environment‐based recruitment forecasts may improve recruitment estimates for the most recent year classes and facilitate study of the effects of future climate change on northern rock sole population dynamics.

Oceanographic drivers of petrale sole recruitment in the California Current Ecosystem

AbstractThis paper investigates environmental drivers of U.S. West Coast petrale sole (Eopsetta jordani) recruitment as an initial step toward developing an environmental recruitment index that can inform the stock assessment in the absence of survey observations of age‐0 and age‐1 fish. First, a conceptual life history approach is used to generate life‐stage‐specific and spatio‐temporally specific mechanistic hypotheses regarding oceanographic variables that likely influence survival at each life stage. Seven life history stages are considered, from female spawner condition through benthic recruitment as observed in the Northwest Fisheries Science Center West Coast Groundfish Bottom Trawl Survey (age‐2 fish). The study area encompasses the region from 40 to 48°N in the California Current Ecosystem. Hypotheses are tested using output from a regional ocean reanalysis model outputs and model selection techniques. Four oceanographic variables explained 73% of the variation in recruitment not accounted for by estimates based exclusively on the spawning stock size. Recruitment deviations were (a) positively correlated with degree days during the female precondition period, (b) positively correlated with mixed‐layer depth during the egg stage, (c) negatively correlated with cross‐shelf transport during the larval stage, and (d) negatively correlated with cross‐shelf transport during the benthic juvenile stage. While multiple mechanisms likely affect petrale sole recruitment at different points during their life history, the strength of the relationship is promising for stock assessment and integrated ecosystem assessment applications.

Management strategies for spasmodic stocks: a Canadian Atlantic redfish fishery case study

There exist few recommendations for managing stocks with spasmodic recruitment, despite such stocks being not uncommon. Management procedures (MPs), developed for two species of redfish (Sebastes mentella and Sebastes fasciatus) in eastern Canada, are recommended for setting catch limits during periods of high and low abundance. A well-designed fishery-independent trawl survey is essential to provide advance warning of strong recruitment events and project future recruitment. Under an “inventory management” strategy, a more appropriate aim in spasmodic stocks may be to maximize the number of years with “good catches,” instead of maximizing total catches, as is traditionally considered in management strategy evaluation (MSE). Following a spasmodic recruitment event, an empirical harvest control rule based on larger fish delays the harvest of large cohorts by a few years, targets more commercially valuable fish sizes, and reduces the risk of growth overfishing. Capped MPs produced longer periods of large catches than uncapped MPs. MPs allowed for low harvests during periods of low abundance, thus avoiding unnecessary hardship in the industry. MPs evaluated here could be good candidates for other stocks with similar or less extreme recruitment variability.

How current reporting practices may mask differences: a call for examining cancer-specific demographic enrollment patterns in cancer treatment clinical trials

BackgroundA lack of diversity among clinical trial (CT) participants remains a critical problem. Few studies have examined recruitment variability in cancer treatment CTs by cancer type. Given the increasing organ-specific specialization of oncologic care, an understanding of this variability may affect institutional recruitment practices. MethodsThis study examines three data sources from 2010 through 2014. The analyzed sample includes 3,580 CT participants identified in the institutional Clinical Trials Management System (C TMS) database and 20,305 incident cases of invasive cancer within a Comprehensive Cancer Center (CCC) institutional catchment area. A total of 341,114 incident cases of primary invasive cancer were identified through the California Cancer Registry (CCR). The primary study measurements were sociodemographic characteristics of the three populations (age, sex, race/ethnicity, and health insurance). ResultsRacial/ethnic disparities were observed, with more incident cases of Whites seen in cancer center (68%) and enrolled in CTs (72%) compared to incident cases in catchment area (67%) (p<0.001) overall. More older adults (65) were enrolled in prostate cancer CTs (58%) than seen in cancer center (45%) (p<0.001). Alternatively, fewer older adults were enrolled in breast and colorectal CTs than seen in cancer center (p<0.001). Among colon (p<0.001), breast (p<0.001), and prostate (p=<0.001) cancer types, insurance type significantly varied between incident cases in catchment area, cancer center, and among CT participants. For colorectal cancer, no difference in sex distribution was observed overall. A significant difference in insurance type within each cancer type was observed (p<0.001). ConclusionsThese findings suggest that reporting overall recruitment frequencies may mask differences by cancer type.

Understanding temperature effects on recruitment in the context of trophic mismatch

Understanding how temperature affects the relative phenology of predators and prey is necessary to predict climate change impacts and recruitment variation. This study examines the role of temperature in the phenology of a key forage fish, the lesser sandeel (Ammodytes marinus, Raitt) and its copepod prey. Using time-series of temperature, fish larval and copepod abundance from a Scottish coastal monitoring site, the study quantifies how thermal relationships affect the match between hatching in sandeel and egg production of its copepod prey. While sandeel hatch time was found to be related to the rate of seasonal temperature decline during the autumn and winter through effects on gonad and egg development, variation in copepod timing mostly responded to February temperature. These two temperature relationships defined the degree of trophic mismatch which in turn explained variation in local sandeel recruitment. Projected warming scenarios indicated an increasing probability of phenological decoupling and concomitant decline in sandeel recruitment. This study sheds light on the mechanisms by which future warming could increase the trophic mismatch between predator and prey, and demonstrates the need to identify the temperature-sensitive stages in predator-prey phenology for predicting future responses to climate change.

Multi‐scale integration of tree recruitment and range dynamics in a changing climate

AbstractAimThe rate and magnitude of climate‐induced tree range shifts may be influenced by range‐wide variation in recruitment, which acts as a bottleneck in tree range dynamics. Here, we compare range predictions made using standard species distribution models (SDMs) and an integrated metamodelling approach that assimilates data on adult occurrence, seedling recruitment dynamics, and seedling survival under both current and future climate, and evaluate the degree to which information provided by seedling data can improve predictions of range dynamics.LocationThe interior west region of the United States.Time period1990–2015.Major taxa studiedFive widespread conifer tree species.MethodsWe used a previously published metamodelling framework to combine information from SDMs of adult tree occurrence and sub‐models describing seedling recruitment dynamics and seedling survival into a single set of predictions for the probability of occurrence for each species. The integrated framework links sub‐models to a SDM to generate cohesive predictions that consider information and uncertainty contained in all datasets. We then compared predictions from the integrated model to SDM predictions.ResultsIntegration of seedling information served primarily to improve characterization of model uncertainty, particularly in regions where recruitment may be limited by temperatures that exceed seedling tolerance. Integration constrained response curves very slightly across most climate gradients, particularly across temperature gradients. These differences were primarily attributable to the isolated effects of temperature on seedling survival and not to recruitment dynamics.Main conclusionsOur results indicate that range‐wide variation in recruitment both now and in the future is most uncertain along the edges of occupied regions, which increases uncertainty in projections of future species occurrence along range margins. Overall, the broad‐scale climatic dependence of the regeneration niche appears weaker than that of the adult climatic niche, and this enhances uncertainty in predicting range‐wide responses of these species to climate change.

Adaptation of North Atlantic Albacore Fishery to Climate Change: Yet Another Potential Benefit of Harvest Control Rules

Fisheries are constrained by ecosystem productivity and management effectiveness. Climate change is already producing impacts on marine ecosystems through overall changes in habitats, productivity and increased variability of environmental conditions. The way how these will affect fisheries is under debate and, also is the best course of actions to face this global challenge. harvest control rules are sets of pre-agreed rules that can be used to determine catch limits periodically and describe how harvest is automatically controlled by management in relation to the state of some indicator of stock status. In 2017, the International Commission for the Conservation of Atlantic Tunas adopted a harvest control rule for North Atlantic albacore. This harvest control rule was evaluated using Management Strategy Evaluation against the main sources of uncertainty inherent to this fishery. Here, we use the same framework to evaluate the robustness of the adopted rule against two types of potential climate change impacts on North Atlantic albacore dynamics. First, we evaluate how the control rule would perform in the event of overall changes in productivity in the North Atlantic and second, against increases in climate driven recruitment variability. Overall, our results suggest that the adopted harvest control rule is robust to these climate driven impacts and also suggests bounds at which the current management framework would be vulnerable to climate change. Throughout the manuscript we also discuss the potential of harvest control rules and harvest strategies to adapt fisheries management to a changing environment. Our main conclusion is that despite the many uncertainties on climate impacts on fisheries, efficient fisheries management will be critical to ensure the sustainability of fisheries in the future.

Patterns of juvenile reef-fish recruitment in Kenya’s shallow fringing- lagoon reefs

Studies to understand local-scale patterns in the recruitment of juvenile coral-reef fishes within the western Indian Ocean (WIO) region are few, yet such knowledge is important in fisheries management. Underwater visual census surveys were conducted at five shallow fringing-lagoon reef sites along the Kenyan coast, between June 2012 and March 2016, to quantify patterns in the abundance of new recruits and juveniles. Recruitment was observed year-round, with a consistent pronounced seasonal peak in recruit densities and species richness during December to April of each year, which was strongly correlated with high sea temperatures. Annual variations in recruitment were also observed, with a higher recruitment peak in 2013 as compared with in other years. A total of 112 species belonging to 19 families were identified, dominated by species belonging to the Pomacentridae, Labridae and Apogonidae, which altogether represented 91% of the total number of recruits recorded. The species with the largest number of recruits (Chromis viridis, Thalassoma hebraicum and Gomphosus caeruleus) showed evidence of year-round recruitment, although the timing of recruitment peaks was not consistent. Multivariate analysis of the species composition separated mainland from offshore fringing-reef sites, and also revealed strong habitat associations, pointing towards increasing recruit abundance with increasing live hard-coral cover and rugosity. Live hard-coral cover, which constituted an average of 21%, was associated with 63% of the total number of recruits recorded. This study contributes new insight into local-scale patterns of juvenile reef-fish recruitment in Kenya and the WIO region, and demonstrates the important nursery function of shallow fringing-lagoon reefs.

Pengaruh Proses Rekrutmen dan Seleksi terhadap Kinerja Karyawan : Studi pada PT. Dian Bahari Sejati

Based on the data processing hasi it is known that the selection in which the company has an influence on employee performance partially . The most dominant variable affecting the performance of employees, especially in PT. Dian Bahari Sejati is the selection , the reason for the selection of variables having the largest value of the regression coefficient when compared with variable recruitment , so that the second hypothesis can be said to be proven . Simultaneously, it is known that the process of recruitment and selection simultaneously have an influence on the performance of employees at PT. Dian Bahari Sejati.The influence of variables X1 ( recruitment ) to variable Y ( company performance ) indicated by the value of the correlation coefficient ( r xy ) of 0.727 . While the R -square is 0.528 or 52.80 % , showing approximately 52.80 % variable Y ( the performance of the company's employees ) can be explained by the recruitment process variable ( X1 ) , or in practice it can be said that the contribution of the recruitment process ( X1 ) to variable Y ( performance of employees ) is 52.80 % . The rest is influenced by other variables not examined . The influence of X2 ( selection) to variable Y ( the performance of employees ) indicated by the value of the correlation coefficient ( r xy ) of 0.655 . While the R -square is 0.429 or 42.90 % , showing approximately 42.90 % variable Y ( the performance of the employee ) can be explained by the selection of variables ( X2 ) , or in practice it can be said that the contribution of selection (X2 ) to variable Y ( employee performance ) is 42.90 % . The rest is influenced by other variables not examined .The influence of variables X1 ( recruitment ) and X2 ( selection) to variable Y ( the performance of employees ) indicated by the multiple correlation coefficient of 0.565 , while the R -square value is 0.319 or 31.90 % , showing approximately 31.90 % variable Y can be explained by the recruitment process variable ( X1 ) and selection (X2 ) to variable Y ( the performance of the employee ) is 31.90 % . The rest is influenced by other variables not examined . Or proposed hypothesis can be accepted or recruitment process and se ; of selection has a positive and significant effect on the performance of employees at PT. Dian Bahari Sejati.

Seedling recruitment correlates with seed input across seed sizes: implications for coexistence.

Understanding controls on recruitment is critical to predicting community assembly, diversity, and coexistence. Theory posits that at mean fecundity, recruitment of highly fecund small-seeded plants should be primarily microsite limited, which is indicated by a saturating recruitment function. In contrast, species that produce fewer large seeds are more likely to be seed-limited, which is characterized by a linear recruitment function. If these patterns hold in nature, seed predation that disproportionately affects larger-seeded species can limit their establishment. We tested these predictions by comparing recruitment functions among 16 co-occurring perennial forb species that vary by over two orders of magnitude in seed size. We also assessed how postdispersal seed predation by mice influenced recruitment. We added seeds at densities from zero to three times natural fecundity of each species to undisturbed plots and examined spatial variation in recruitment by conducting experiments across 10 grassland sites that varied in productivity and resource availability. Consistent across two replicated years, most species had linear recruitment functions across the range of added seed densities, indicative of seed-limited recruitment. Depending on year, the recruitment functions of only 19-37% of target species saturated near their average fecundity, and this was not associated with seed size. Recruitment was strongly inhibited by rodent seed predation for large-seeded species but not for smaller-seeded species. Proportional recruitment was more sensitive to spatial variation in recruitment conditions across sites for some small-seeded species than for large-seeded species. These results contradict the common belief that highly fecund small-seeded species suffer from microsite-limited recruitment. Rather, they imply that, at least episodically, recruitment can be strongly correlated to plant fecundity. However, proportional recruitment of small-seeded species was inhibited at productive sites to a greater extent than large-seeded species. Results also show that in a system where the dominant granivore prefers larger seeds, low-fecundity large-seeded species can suffer from even greater seed-limited recruitment than would occur in the absence of predators.

The Decline and Recovery of a Crab Population From an Extreme Marine Heatwave and a Changing Climate

Driven by a very strong La Nina event and a record strength Leeuwin Current, the 2011 Western Australian marine heatwave (MHW) raised sea surface temperatures (SSTs) along the Western Australian coastline up to 5oC between November 2010 and March 2011. This single thermal perturbation led to several mortality events and recruitment impairment of commercially important species including Australia’s single highest producing blue swimmer crab (Portunus armatus) fishery in Shark Bay. Monthly catch landings dramatically declined from 166 t in April 2011 to <10 t by December 2011 promoting its closure in 2012 to allow for stock recovery. Examination of stock-environment relationships critical to the recruitment of blue swimmer crabs living towards their thermal maxima, showed juvenile P. armatus to be most susceptible to heat stress when mean water temperatures between December and January were greater than 24°C, and detrimental when they exceed 26°C as was the case during the 2011 MHW when SSTs reached 29°C. Partial recovery of the crab stock 18 months after the MHW was strongly associated with mean summer temperatures returning below 24°C. Together with a change in management to a quota system, the fishery returned to full recovery status in 2018 with sustainable catch levels of up to 550 t. Long term fishery productivity is now at high risk from climate change impacts with shifts in winter water temperatures being cooler by 2°C and occurring earlier by few months inside the Bay. This cooling trend appears to be impacting the spawning period with the timing of peak recruitment also occurring earlier, shifting from February to November. The impacts of the 2011 MHW highlighted the risk to stock sustainability through external drivers such as climate change that was previously poorly understood. Therefore, responding to climate change is now about managing risks to achieve a balance between fisheries sustainability and economic viability. Increased stock monitoring now provides biomass measures 12 months prior to the fishing season, a form of stock forecasting that stakeholders can utilise to better manage their fishing business and minimise economic loss, while a flexible harvest strategy now responds to recruitment variation and climate extremes.

Potential changes in the distribution of suitable habitat for Pacific sardine (Sardinops sagax) under climate change scenarios

The Pacific sardine, Sardinops sagax, is the most important fishery by volume in Mexico; however, this small pelagic species shows fluctuations in catch due to its susceptibility to environmental changes. In turn, this susceptibility leads to variations in distribution, abundance, and recruitment, making the Pacific sardine highly vulnerable to the effects of global climate change. In this study, we analyze the effects of environmental variability on the Pacific sardine distribution through the development of the habitat suitability for the Mexican Pacific. We used bathymetry, sea surface temperature (SST), sea surface salinity (SSS) and net primary productivity (NPP) to develop an ecological niche model to forecast the suitable habitat of the Pacific sardine and reproduce the historical patterns for the 2003–2017 period. We then used this model to make future projections to the year 2100 using the emission scenarios RCP 2.6, 4.5, and 8.5 proposed by the Intergovernmental Panel on Climate Change. Under the RCP models, on average, the greatest impact of climate change was observed inside the Gulf of California, with an increase in SST (+1.68 °C) and a decrease in 25% of NPP (−256 mg C m−2 d−1) reducing habitat availability for this species by 95. Stocks on the Pacific coast are projected to fluctuate substantially, similar to past events driven by environmental variability. At the regional level, a loss of suitable habitat of up to 50% is expected by the end of this century for the Pacific sardine.

Biomass and population structure of a geoxyle, Lannea edulis (Sond.) Engl., at a savanna woodland site in Zambia

Geoxyles are plants with massive underground and diminutive aboveground parts and in sub-Saharan Africa this life form is most diverse in south-central Africa. However, little is known about the population ecology of these plants, especially in south-central Africa. The purpose of this research was to investigate the demography and biomass structure of Lannea edulis, a widespread geoxyle in south-central Africa, using census, phenology and biomass data obtained over a 20-year period at a site in central Zambia, southern Africa. Mast fruiting in L. edulis is rare and seed germination rate and seedling mortality vary from year to year, resulting in episodic recruitment of juveniles into the population. Juvenile plants have a tuberous fleshy root that is transformed into a thick-barked woody taproot in adults. Frequent dieback of aerial shoots due to fire and herbivory induces the formation and growth of subsurface stems. The average oven-dry biomass of a L. edulis plant was 370 g of which shoots and roots represented 10% and 90%, respectively, thereby confirming that this geoxyle has indeed massive belowground parts. The demography of L. edulis is greatly influenced by variable annual recruitment of juveniles into the population and large individuals were estimated to live for more than 60 years.