Stephen David Gregory

Centre for Environment, Fisheries and Aquaculture Science | CEFAS · Weymouth Laboratory

Anadromous salmonids migrate seaward to exploit feeding and growth opportunities in marine habitats, yet how smolt biological characteristics influence their marine migratory behavior remains poorly understood. This study used 9 years of trout (Salmo trutta) population monitoring data from 15,595 tagged age‐0+ parr, 1033 smolts detected migrating d...

Native to Central and Eastern Europe, the euryhaline pikeperch Sander lucioperca can acclimatize to elevated salinity levels (e.g., up to 30‰), but it remains unknown whether their invasive populations use this ability to inhabit and/or disperse through brackish waters, such as estuaries and inshore areas. To test whether invasive pikeperch show a...

WKBSalmon reviewed the implementation of a Life Cycle Model (LCM) for wild anadromous Atlantic salmon (Salmo salar L.) covering their natal north Atlantic range. The LCM is a time iterative, Bayesian hierarchical model incorporating salmon records of fifteen countries at 25 stock-units. It tracks salmon of two explicit sea-age streams, namely, one-...

For effective fishery management, estimated stock sizes, along with their uncertainties, should be accurate, precise, and unbiased. Atlantic salmon Salmo salar stock assessment in England and Wales (and elsewhere across the Atlantic) estimate returning salmon stocks by applying a measure of rod exploitation rate (RER), derived from less abundant fi...

This study provides a regional picture of long‐term changes in Atlantic salmon growth at the southern edge of their distribution, using a multi‐population approach spanning 49 years and five populations. We provide empirical evidence of salmon life history being influenced by a combination of common signals in the marine environment and population‐...

WGNAS met to consider the status of and threats to Atlantic salmon in the North Atlantic Salmon Conservation Organisation (NASCO) commission areas: West Greenland (WGC), North American (NAC), and Northeast Atlantic (NEAC). Many updates are provided for 2021 and 2022 as WGNAS was not able to address all terms of reference (ToRs) in 2022. Information...

Monitoring the first seaward migration of juvenile salmonids, known as smolts, is challenging because there is limited tracking technology suited to their small size. Nevertheless, for their management and conservation purpose, it is critical to understand this phase of their life cycle when they adapt to increased salinity, novel predators and new...

ICES, in consultation with the North Atlantic Salmon Conservation Organisation (NASCO), convened a series of workshops to explore how to use biological and environmental data in models to advance the conservation of wild Atlantic salmon (Salmo salar L.) at sea. This workshop set out to consider multiple candidate hypotheses contributing to changes...

The ongoing declines in Atlantic salmon populations across its range underscore the need for co-ordinated scientific-based knowledge to support management and decisions for their conservation. Current salmon management actions remain largely focused on addressing bottlenecks to production in the freshwater phase of the life-cycle, whereas the conti...

Fish somatic growth is indeterminate and can be influenced by a range of abiotic and biotic variables. With climate change forecast to increase the frequency of warming and unusual discharge events, it is thus important to understand how these variables currently influence somatic growth and how that might differ for specific age-classes and/ or li...

Aquatic habitats are severely threatened by human activities. For anadromous species, managing freshwater habitats to maximize production of more, larger juveniles could improve resilience to threats in marine habitats and enhance population viability. In some juvenile salmonid habitats, complexity created by large substrates provides resources and...

Populations of Atlantic salmon Salmo salar have experienced precipitous declines in abundance since the 1970s. This decline has been associated with reduced numbers of adult salmon returning to fresh water from their marine migration, i.e., their marine return rates (MRR). Thus, understanding the factors that affect MRR is of crucial conservation i...

• Migration enables animals to access important resources throughout their lifetime but exists in a trade-off with elevated mortality risk. In spring, juvenile Atlantic salmon (smolts) migrate from their natal rivers for marine feeding grounds, with the timing of their marine entry a potentially important determinant of their long-term survival. Ho...

1. Human-induced environmental change is a major stressor on freshwater habitats that has resulted in the population declines of many freshwater species. Ontogenetic shifts in habitat use and associated (st)age-specific requirements mean that impacts of environmental stressors can influence (st)ages in a population differently, and yet relatively f...

Previous work suggests that juvenile salmon recruitment in rain‐fed rivers is negatively influenced by warm and wet winters and cool springs. We tested whether this is generally applicable to a southern England chalk stream characterized by comparatively stable discharges and temperatures. We found that warm spawning and cool emergence temperatures...

ICES (International Council for the Exploration of the Sea) Scientific Reports / Rapports Scientifiques du CIEM (Conseil International pour l'Exploration de la Mer), Volume 3, Issue 24 Recommended format for purpose of citation: ICES. 2021. Workshop for Salmon Life Cycle Modelling (WKSalModel). ICES Scientific Reports. 3: 24. 20 pp. A workshop of...

Recent decline in abundance of Atlantic salmon (Salmo salar) and concomitant changes in life history may result from a decline in the growth conditions during marine migration. Available literature suggests the existence of a sex-specific reaction norm linking maturation with environmental growth conditions at sea. However, the extent to which this...

Understanding salmonid discharge requirements can help inform management to conserve wild populations in a changing climate. This study developed Bayesian hierarchical mixed‐effects models relating 0+ Atlantic salmon (Salmo salar L.) and trout (Salmo trutta L.) densities to different aspects of river discharge. Associations between these densities...

• Understanding the effects of density‐dependent and density‐independent factors on recruitment is often inhibited by difficulties quantifying their relative contributions in highly variable recruitment data. Use of data‐driven statistical methods with data that include one or more extreme recruitment events could help overcome these difficulties....

Smolt lengths are increasingly recognised as an important determinant of salmonid marine survival rates. Overwintering growth rates could thus strongly influence adult return rates. In Atlantic salmon Salmo salar, most overwintering studies focus on rivers in harsh climates with minimal growth, yet in more southerly rivers, overwintering growth rat...

Understanding juvenile salmonid habitat requirements is critical for their effective management, but little is known about these requirements in lowland rivers, which include important but unique salmonid habitats. We compared the relative influence of in‐stream Ranunculus cover, water depth, prey abundance, distance upstream and two previously une...

Recent declines in Atlantic salmon Salmo salar populations are generally attributed to factors in their marine life-phase. However, it is postulated that factors affecting their freshwater life-phase might impact their marine survival, such as the influence of body size. While larger smolts are widely hypothesized to have higher marine survival rat...

Recent declines in Atlantic salmon Salmo salar populations are generally attributed to factors in their marine life-phase. However, it is postulated that factors affecting their freshwater life-phase might impact their marine survival, such as the influence of body size. While larger smolts are widely hypothesized to have higher marine survival rat...

Recruitment of salmonids is a result of density‐dependent factors, specifically egg production in the previous year, and density‐independent environmental processes driven by discharge and temperature. With the plethora of knowledge on major drivers of Atlantic salmon Salmo salar and brown trout Salmo trutta recruitment, there is a requirement to e...

Adult return rates for wild Atlantic salmon Salmo salar smolts captured in a rotary screw trap and tagged with coded wire (CW) tags were compared with a control group, using detections from passive integrated transponder (PIT) antennae systems over 7 years in a small chalk stream in southern England, U.K. Compared with control smolts, capture and C...

Recruitment of salmonids is a result of density‐dependent factors, specifically egg production in the previous year, and density‐independent environmental processes driven by discharge and temperature. With the plethora of knowledge on major drivers of Atlantic salmon Salmo salar and brown trout Salmo trutta recruitment, there is a requirement to e...

A general framework is presented that should enhance our understanding of how intrinsic factors, such as body size, and extrinsic factors, such as climate, affect the dynamics and demographics of fish populations. Effects of intrinsic factors, notably studies relating juvenile Atlantic salmon Salmo salar body size to their probability to return as...

Migration between freshwater nursery grounds and saltwater feeding areas is a critical event in sea trout life history. During their seaward migration, smolts encounter both natural and man-made obstructions as well as increased exposure to predators. This is particularly true in the transition zone between freshwater and saltwater where smolts ent...

Allee effects have important implications for many aspects of basic and applied ecology. The benefits of aggregation of conspecific individuals are central to Allee effects, which have led to the widely held assumption that social species are more prone to Allee effects. Robust evidence for this assumption, however, remains rare. Furthermore, previ...

Understanding the geographical scales at which environmental variables affect an individual's body size, and thus their mortality risk, can inform management strategies to help conserve wild populations under climate change. Yet, our current understanding of these relationships is based on studies done at different scales that report inconsistent f...

Atlantic salmon are an ecologically and economically important migratory fish in the UK, whose stocks have been declining over the past 30 years. Future climate and water use changes have the potential to alter the reproductive behaviour and distribution of salmon within a river, by restricting times and ability to access suitable spawning areas. A...

Aim Deforestation and climate change are two of the most serious threats to tropical birds. Here, we combine fine‐scale climatic and dynamic land cover models to forecast species vulnerability in rain forest habitats. Location Sulawesi, Indonesia. Methods We sampled bird communities on four mountains across three seasons in Lore Lindu National Pa...

Species distribution models have come under criticism for being too simplistic for making robust future forecasts, partly because they assume that climate is the main determinant of geographical range at large spatial extents and coarse resolutions, with non-climate predictors being important only at finer scales. We suggest that this paradigm migh...

Aim Habitat fragmentation threatens species’ persistence by increasing subpopulation isolation and vulnerability to stochastic events, and its impacts are expected to worsen under climate change. By reconnecting isolated fragments, habitat corridors should dampen the synergistic impacts of habitat and climate change on population viability. Choosin...

To investigate potential range shifts in a changing climate it is becoming increasingly common to develop models that account for demographic processes. Metapopulation models incorporate the spatial configuration of occupied habitat (i.e. arrangement, size and quality), population demographics, and inter-patch dispersal making them suitable for inv...

Southeast Asian deforestation rates are among the world's highest and threaten to drive many forest-dependent species to extinction. Climate change is expected to interact with deforestation to amplify this risk. Here we examine whether regional incentives for sustainable forest management will be effective in improving threatened mammal conservati...

Land-cover change projections. Maps showing land cover change projections at 2011, 2041, 2071 and 2100 under (a) current-day SFM and (b) complete SFM implementations. (TIFF)

Per cent wet season precipitation delta maps under each CO2 mitigation scenario. Per cent wet season precipitation delta maps at 2041, 2071 and 2100 relative to 2010 for Ref and Pol scenarios. (TIFF)

Land cover change predictors. Table of variables considered important predictors of land cover change. (DOC)

Predicted nest count residuals. Map of Sabah showing the residuals from the hurdle boosted regression tree Species Distribution Model. Note that the residuals are highest were the model predicted a nest count and lowest were the model predicted a nest presence. Shaded areas are commercials forest reserves and protected areas. (TIFF)

Relationship between nest count predictions and an independent orangutan nest count dataset. Plot showing the ordinary least squares (OLS) and robust iterative re-weighted least squares (IWLS) fits when predicting our SDM model predictions with data published in [25]. (TIFF)

Land-cover class gains and losses and projected changes between 2010–2100. Plots showing (a) the observed gains and losses of cells in each land cover class, and (b) the projected changes in each land class between 2010–2100 in forest reserves and unprotected forests for the current-day SFM scenario. Absolute gains and losses in least-widespread cl...

Per cent dry season precipitation delta maps under each CO2 mitigation scenario. Per cent dry season precipitation delta maps at 2041, 2071 and 2100 relative to 2010 for Ref and Pol scenarios. (TIFF)

Degree Centigrade temperature delta maps under each CO2 mitigation scenario. Degrees Centigrade temperature delta maps at 2041, 2071 and 2100 relative to 2010 for Ref and Pol scenarios. (TIFF)

Spatial predictors. Spatial predictors used to build the Species Distribution Models and notes on their processing. (DOC)

Predictor importance for predicting 2010 observed land-cover. Plots showing the relative importance of spatial predictors in predicting observed 2010 land cover in (a) forest reserves and (b) unprotected forests. (TIFF)

Accuracy statistics for the random forest models of 2010 land-cover predictions. Prediction error rates were low for the most-widespread land-cover classes but high for the least-widespread classes (e.g., mangrove and cleared land) because they constituted less than 5% of the land cover. (DOC)

Cited By (since 1996):1, Export Date: 26 November 2013, Source: Scopus, Art. No.: e43846

Invasive rodents occur on over 80% of the world's island groups, invasions are continuing, and rodent impacts on insular wildlife have been well demonstrated. The extent of this problem calls for tools to aid large-scale prioritisation among the many candidate eradication operations. As conservation funds are limited, biologists have responded with...

Extensive theoretical work on demographic Allee effects has led to the latent assumption that they are ubiquitous in natural populations, yet current empirical support for this phenomenon is sparse. We extended previous single-taxon analyses to evaluate the empirical support for demographic Allee effects in the per capita population growth rate of...

A.M. Kramer & J.M. Drake (2010) Experimental demonstration of population extinction due to a predator-driven Allee effect. Journal of Animal Ecology, 79, 633–639. Experimental evidence of extinction via an Allee effect (AE) is a priority as more species become threatened by human activity. Kramer & Drake (2010) begin the International Year of Biodi...

Cited By (since 1996):22, Export Date: 26 November 2013, Source: Scopus

In this paper, we review mate-finding Allee effects from ecological and evolutionary points of view. We define ‘mate-finding’ as mate searching in mobile animals, and also as the meeting of gametes for sessile animals and plants (pollination). We consider related issues such as mate quality and choice, sperm limitation and physiological stimulation...

Endemic Nesoryzomys swarthi and invasive Rattus rattus exist in unlikely sympatry in Galápagos as female N. swarthi suffer from competition with R. rattus. This study evaluates the role of feeding habits in facilitating their co-occurrence. Spool-and-line tracking of 85 N. swarthi and 33 R. rattus was used to quantify their selected diets, foods of...

The introduction and spread of the black rat Rattus rattus is believed to have caused the worst decline of any vertebrate taxon in Galápagos. However, the "extinct" Santiago rice rat Nesoryzomys swarthi has recently been rediscovered in sympatry with R. rattus providing the first exception to this general pattern of displacement. We carried out an...