Some statistical aspects of the long-term gill net monitoring programme for pike Esox lucius in Windermere (English Lake District)

For more than 55 years, data have been collected on the population of pike Esox lucius in Windermere, first by the Freshwater Biological Association (FBA) and, since 1989, by the Institute of Freshwater Ecology (IFE) of the NERC Centre for Ecology and Hydrology. The aim of this article is to explore some methodological and statistical issues associated with the precision of pike gill net catches and catch-per-unit-effort (CPUE) data, further to those examined by Bagenal (1972) and especially in the light of the current deployment within the Windermere long-term sampling programme. Specifically, consideration is given to the precision of catch estimates from gill netting, including the effects of sampling different locations, the effectiveness of sampling for distinguishing between years, and the effects of changing fishing effort

Recreational fisheries in the UK: natural capital, ecosystem services, threats, and management

The island nature of the UK has led to its long history of commercial marine fisheries, with associated recreational fisheries along and near to its extensive shoreline. In addition, an abundance of fresh waters provides extensive recreational fisheries, but few commercial fisheries, on rivers and lakes where catch-and-release is prevalent. Here, an overview is presented of these fisheries by describing their main features using the concepts of natural capital and ecosystem services and then considering the threats that they face and the management that has been developed in response. In the marine environment, a wide range of fish species is targeted, but the Orders Gadiformes, Perciformes, and Pleuronectiformes are particularly important. Far fewer species are available for exploitation in fresh waters, but the Orders Cypriniformes, Perciformes, and Salmoniformes are fished extensively. In total, the UK has in excess of three million recreational anglers in a population of approximately 65 million people. Threats to UK recreational fisheries include overfishing, physical habitat modification, acidification, chemical pollution, eutrophication, endocrine disrupters, nanoparticles, species introductions, and climate change. Great scientific and management advances have been made such that most of the required aquatic biological management activities are now based on mature science and are in many cases now largely operational matters. In addition, the work of the UK statutory bodies for fisheries is increasingly supplemented by the efforts of more independent groups, including through citizen science. Ecosystem-based management is now commonplace and activities have expanded above and away from the water to include the management of anglers and other members of society. The UK’s recreational fisheries continue to face substantial challenges, but there are also substantial grounds for great optimism for their future

Digestive rates of old and new leaves of Sarracenia purpurea without the assistance of Diptera inquilines.

Natural History & EvolutionPrevious research of the purple pitcher plant (Sarracenia purpurea) characterizes the effects of aging on its pitcher leaves, though to date there are no studies that characterize changes in plant-produced digestive enzymes in relation to age. This study looked at the digestive rates in 20 old and new pitchers with and without their Dipteran inquilines, in Mud Lake Bog, MI. Digestion of flies did not differ significantly between pitchers with and without the Diptera in both old and new leaves (P>0.5). During the course of the study the Diptera reoccurred in all but three pitchers, though digestion between old and new pitchers still did not differ significantly (P>0.5). These data suggest that there is no relative difference in digestive rate due to age, though this study could not fully account for purely plant-based digestion.http://deepblue.lib.umich.edu/bitstream/2027.42/89054/1/Bouyoucos_Winfield_2011.pd

Long-term changes in the diet of pike (Esox lucius), the top aquatic predator in a changing Windermere

1. Pike (Esox lucius) is a key and flexible piscivore in many fresh waters of the northern temperate zone, but no previous studies have provided a continuous long-term perspective on its diet in response to changing environmental conditions. Here, we describe its winter diet from 1976 to 2009 in the North and South Basins of the lake of Windermere, U.K., where climate change, eutrophication and species introductions have combined to induce fundamental changes in the fish community. 2. A total of 6637 adult pike (fork length 390 to 1090 mm) was examined and found to have consumed a total of 4436 fish prey of which 98% of individuals identifiable to species comprised native Arctic charr (Salvelinus alpinus), brown trout (Salmo trutta), perch (Perca fluviatilis) and pike and non-native roach (Rutilus rutilus). Over the 34-year study period, the dietary importance of the salmonids Arctic charr and brown trout decreased, while that of the percid perch, the esocid pike and particularly the cyprinid roach increased. These changes were particularly marked in the more eutrophicated South Basin of the lake. 3. The above chronological trends in species-specific contributions to the diet composition of pike had considerable overall impacts. In the 1970s, pike diet composition was dominated by Arctic charr and brown trout which together comprised 94% of the diet. In contrast, in the 2000s, these two species accounted for just 55% of the diet, with perch and roach now comprising 41%. 4. Recent changes observed in the Windermere fish community of a decrease in native salmonids and an increase in cyprinids are consistent with the generally expected effects of climate change in the northern temperature zone. Here, we have shown that they have led to corresponding changes in the diet composition of pike. In turn, this may have implications for lake’s food web structure through shortening food chain length from the primary producers to the top aquatic predator

Quantifying biased agonism of adenosine and calcitonin-like receptors

G protein-coupled receptors (GPCRs) elicit an ability to activate multiple downstream signalling pathways. It is becoming evident that for many GPCRs, agonists are able to activate several of these pathways, each to differing extents; a phenomenon termed pathway bias, or biased agonism. Here, work is presented quantifying biased agonism for the: adenosine A1 and A2A receptors, as well as the calcitonin-like receptor (CLR). For the adenosine receptors, novel selective, and non-selective, agonists are identified and characterised. Further, the extent of biased agonism is determined for A1R agonists with respect to their abilities to positively and negatively regulate cAMP production, mobilise intracellular Ca2+ and activate ERK1/2. The activity of triazoloquinazoline compounds against the A2AR is validated, identifying 3 to be selective. Further investigations into the ability of triazoloquinazolines to mediate cAMP production and ERK1/2 activation uncovers each tested agonist to be biased towards activating ERK1/2, at the A2AR. A characterisation of the effects of receptor activity modifying proteins (RAMPs) upon signalling from the CLR is presented: quantifying the extent of biased agonism, with respect to the ability of RAMP-CLR heterodimers to: mediate cAMP production and inhibition, as well as mobilise intracellular Ca2+, uncovering this to be a Gαq/11-mediated process. Further, through applying a saturation mutagenesis approach to the CLR, a potential interaction is identified between intracellular loop 1 (ICL1) and helix 8, which is broken upon receptor activation, further identifying ICL1 to be a region of the CLR responsible for influencing G protein specificity. Ultimately, these findings relating to both adenosine and CLR-based receptors uncovers further evidence of biased agonism at GPCRs, which may have potential implications upon improving the efficacy and safety profiles of novel pharmaceutics targeting these clinically relevant GPCRs

Fitness consequences of early life conditions and maternal size effects in a freshwater top predator

1. Conditions experienced in early life stages can be an important determinant of individual life histories. In fish, environmental conditions are known to affect early survival and growth, but recent studies have also emphasized maternal effects mediated by size or age. However, the relative sensitivity of the mean fitness (population growth rate λ) to different early life impacts remain largely unexplored. 2. Using a female-based integral projection model (IPM) parameterised from unique long-term demographic data for pike (Esox lucius), we evaluated the relative fitness consequences of different early life impacts, including i) maternal effects of length on egg weight, potentially affecting offspring (first year) survival, and ii) effects of temperature on offspring growth and survival. Of the seven vital rates defining the model, offspring survival could not be directly estimated and four scenarios were defined for this rate. 3. Elasticity analyses of the IPM were performed to calculate i) the total contribution from different lengths to the elasticity of λ to the projection kernel, and ii) the elasticity of λ to underlying variables of female current length, female offspring length at age 1, and temperature. These elasticities were decomposed into contributions from different vital rates across length. 4. Egg weight increased with female length, as expected, but the effect leveled off for the largest females. However, λ was largely insensitive to this effect, even when egg weight was assumed to have a strong effect on offspring survival. In contrast, λ was sensitive to early temperature conditions through growth and survival. Among mature females, the total elasticity of λ to the projection kernel generally increased with length. The results were robust to a wide range of assumptions. 5. These results suggest that environmental conditions experienced in early life represent a more important driver of mean population growth and fitness of pike than maternal effects of size on offspring survival.We discuss two general mechanisms underlying the weak influence of this maternal effect, suggesting that these may be general for long-lived and highly fecund fishes. This model and results are relevant for management of long-lived top-predators, including many commercially important fish species

Harvest-induced disruptive selection increases variance in fitness-related traits

The form of Darwinian selection has important ecological and management implications. Negative effects of harvesting are often ascribed to size truncation (i.e. strictly directional selection against large individuals) and resultant decrease in trait variability, which depresses capacity to buffer environmental change, hinders evolutionary rebound and ultimately impairs population recovery. However, the exact form of harvest-induced selection is generally unknown and the effects of harvest on trait variability remain unexplored. Here we use unique data from the Windermere (UK) long-term ecological experiment to show in a top predator (pike, Esox lucius) that the fishery does not induce size truncation but disruptive (diversifying) selection, and does not decrease but rather increases variability in pike somatic growth rate and size at age. This result is supported by complementary modelling approaches removing the effects of catch selectivity, selection prior to the catch and environmental variation. Therefore, fishing most likely increased genetic variability for somatic growth in pike and presumably favoured an observed rapid evolutionary rebound after fishery relaxation. Inference about the mechanisms through which harvesting negatively affects population numbers and recovery should systematically be based on a measure of the exact form of selection. From a management perspective, disruptive harvesting necessitates combining a preservation of large individuals with moderate exploitation rates, and thus provides a comprehensive tool for sustainable exploitation of natural resources