Ecosystem-based management outperforms species-focused stocking for enhancing fish populations.

Ecosystem-based management is costly. Therefore, without rigorously showing that it can outperform traditional species-focused alternatives, its broad-scale adoption in conservation is unlikely. We present a large-scale replicated and controlled set of whole-lake experiments in fish conservation (20 lakes monitored over 6 years with more than 150,000 fish sampled) to examine the outcomes of ecosystem-based habitat enhancement (coarse woody habitat addition and shallow littoral zone creation) versus a widespread, species-focused alternative that has long dominated fisheries management practice (i.e., fish stocking). Adding coarse woody habitats alone did not, on average, enhance fish abundance, but creating shallow water habitat consistently did, especially for juvenile fish. Species-focused fish stocking completely failed. We provide strong evidence questioning the performance of species-focused conservation actions in aquatic ecosystems and instead recommend ecosystem-based management of key habitats.

Big-data approaches lead to an increased understanding of the ecology of animal movement.

Understanding animal movement is essential to elucidate how animals interact, survive, and thrive in a changing world. Recent technological advances in data collection and management have transformed our understanding of animal "movement ecology" (the integrated study of organismal movement), creating a big-data discipline that benefits from rapid, cost-effective generation of large amounts of data on movements of animals in the wild. These high-throughput wildlife tracking systems now allow more thorough investigation of variation among individuals and species across space and time, the nature of biological interactions, and behavioral responses to the environment. Movement ecology is rapidly expanding scientific frontiers through large interdisciplinary and collaborative frameworks, providing improved opportunities for conservation and insights into the movements of wild animals, and their causes and consequences.

The battle between harvest and natural selection creates small and shy fish.

Harvest of fish and wildlife, both commercial and recreational, is a selective force that can induce evolutionary changes to life history and behavior. Naturally selective forces may create countering selection pressures. Assessing natural fitness represents a considerable challenge in broadcast spawners. Thus, our understanding about the relative strength of natural and fisheries selection is slim. In the field, we compared the strength and shape of harvest selection to natural selection on body size over four years and behavior over one year in a natural population of a freshwater top predator, the northern pike (Esox lucius). Natural selection was approximated by relative reproductive success via parent-offspring genetic assignments over four years. Harvest selection was measured by comparing individuals susceptible to recreational angling with individuals never captured by this gear type. Individual behavior was measured by high-resolution acoustic telemetry. Harvest and natural size selection operated with equal strength but opposing directions, and harvest size selection was consistently negative in all study years. Harvest selection also had a substantial behavioral component independent of body length, while natural behavioral selection was not documented, suggesting the potential for directional harvest selection favoring inactive, timid fish. Simulations of the outcomes of different fishing regulations showed that traditional minimum size-based harvest limits are unlikely to counteract harvest selection without being completely restrictive. Our study suggests harvest selection may be inevitable and recreational fisheries may thus favor small, inactive, shy, and difficult-to-capture fish. Increasing fractions of shy fish in angling-exploited stocks would have consequences for stock assessment and all fisheries operating with hook and line.

Behavioural and fitness effects of translocation to a novel environment: Whole-lake experiments in two aquatic top predators.

Translocation into a novel environment through common fisheries management practices, such as fish stocking, provides opportunities to study behavioural and fitness impacts of translocations at realistic ecological scales. The process of stocking, as well as the unfamiliarity with novel ecological conditions and the interactions with resident fish may affect translocated individuals, leading to alterations of behaviours and causing fitness impacts. Our objectives were to investigate how aquatic top predators behaviourally establish themselves and compete with resident individuals following introduction in a novel lake environment and to investigate the resulting fitness consequences. Using high-resolution acoustic telemetry, we conducted whole-lake experiments and compared the activity, activity-space size and fate of translocated and resident individuals in two model top predators, the northern pike Esox lucius (n = 160) and European catfish Silurus glanis (n = 33). Additionally, we compared the reproductive success of translocated and resident northern pike. The experiment was conducted with large (adult) individuals of different origins, resilient to predation, but subject to agonistic interactions and competition with resident fish. Over a period of several months, the translocated catfish exhibited consistently larger activity-space sizes than resident catfish, but did not differ from residents in activity and survival. The pike from one of the two translocated origins we tested also showed elevated space-use, and both translocated origins revealed higher mortality rates than their resident conspecifics, indicating maladjustment to their novel environment. When non-resident pike reproduced, they overwhelmingly produced hybrid offspring with resident fish, indicating that introductions fostered gene flow of non-native genes. Our study indicates that fish introductions result in behavioural and fitness impacts even in large-bodied top predators that experience low levels of natural predation risk.

The value artificial lake ecosystems provide to recreational anglers: Implications for management of biodiversity and outdoor recreation.

Small lakes largely outnumber large lakes among the world's lentic ecosystems. Despite being common landscape elements, however, little is known about the value small lakes provide to recreationists. This paper presents results of an economic valuation study concerned with small gravel pits in Lower Saxony, Germany. Gravel pits are artificially created lake ecosystems that, particularly in Europe, are regularly used and managed by privately organized recreational anglers in an angling club context. A stated choice experiment provided insights into anglers' preferences for the abundance of target fish species, biodiversity of taxa other than fishes in the lakes as well as in the lake surroundings, and about the use of gravel pits by other recreationists for walking, swimming or boating. Latent class analysis identified five segments that varied in preferences. For the majority of anglers, the value of angling at gravel pit lakes was improved by an increase in the abundance of predatory fishes. Additionally, the presence of aquatic and terrestrial endangered species at the lakes increased the value of the ecosystems as perceived by the majority of anglers. By contrast, the presence of other recreational uses reduced the value of angling, with swimming being considered the most disturbing, while the degree of shoreline development had the least impact on the recorded choices. The results suggest that managing the gravel pit lakes for high biodiversity and the presence of desired game fish species maximizes the value for anglers. However, also two smaller segments with anglers revealing lexicographic preferences were identified. These anglers expressed either strong preferences against swimming in the lakes or strongly preferred the opportunity to use boats. Lake management may address the preference heterogeneity and the aversion against other recreational uses, such as swimming, by spatial zoning.

Effect of recreational-fisheries management on fish biodiversity in gravel pit lakes, with contrasts to unmanaged lakes.

Gravel pit lakes are novel ecosystems that can be colonized by fish through natural or anthropogenic pathways. In central Europe, many of them are managed by recreational anglers and thus experience regular fish stocking. However, also unmanaged gravel pits may be affected by stocking, either through illegal fish introductions or, occasionally, by immigration from connected water bodies. We sampled 23 small (< 20 ha) gravel pit lakes (16 managed and 7 unmanaged) in north-western Germany using littoral electrofishing and multimesh gillnets. Our objective was to compare the fish biodiversity in gravel pit lakes in the presence or absence of recreational fisheries. Given the size of the sampled lakes, we expected species poor communities and elevated fish diversity in the managed systems due to regular stocking of game fish species. Our study lakes were primarily mesotrophic and did not differ in key abiotic and biotic environmental characteristics. Lakes of both management types hosted similar fish abundances and biomasses, but were substantially different in terms of fish community structure and species richness. Fish were present in all lakes, with a minimum of three species. Higher α-diversity and lower ß-diversity was discovered in managed gravel pit lakes compared to unmanaged lakes. Consequently, recreational-fisheries management fostered homogenization of fish communities, by stocking a similar set of fish species desired by anglers such as piscivorous fish and large bodied cyprinids. However, unmanaged gravel pit lakes were also affected by human-mediated colonization, presumably by illegal fish releases. Hardly any non-native species were detected, suggesting that recreational-fisheries management did not foster the spread of exotic species in our study region.

Toward a mechanistic understanding of vulnerability to hook-and-line fishing: Boldness as the basic target of angling-induced selection.

In passively operated fishing gear, boldness-related behaviors should fundamentally affect the vulnerability of individual fish and thus be under fisheries selection. To test this hypothesis, we used juvenile common-garden reared carp (Cyprinus carpio) within a narrow size range to investigate the mechanistic basis of behavioral selection caused by angling. We focused on one key personality trait (i.e., boldness), measured in groups within ponds, two morphological traits (body shape and head shape), and one life-history trait (juvenile growth capacity) and studied mean standardized selection gradients caused by angling. Carp behavior was highly repeatable within ponds. In the short term, over seven days of fishing, total length, not boldness, was the main predictor of angling vulnerability. However, after 20 days of fishing, boldness turned out to be the main trait under selection, followed by juvenile growth rate, while morphological traits were only weakly related to angling vulnerability. In addition, we found juvenile growth rate to be moderately correlated with boldness. Hence, direct selection on boldness will also induce indirect selection on juvenile growth and vice versa, but given that the two traits are not perfectly correlated, independent evolution of both traits is also possible. Our study is among the first to mechanistically reveal that energy-acquisition-related behaviors, and not growth rate per se, are key factors determining the probability of capture, and hence, behavioral traits appear to be the prime targets of angling selection. We predict an evolutionary response toward increased shyness in intensively angling-exploited fish stocks, possibly causing the emergence of a timidity syndrome.

Performance assessment of two whole-lake acoustic positional telemetry systems--is reality mining of free-ranging aquatic animals technologically possible?

Acoustic positional telemetry systems (APTs) represent a novel approach to study the behaviour of free ranging aquatic animals in the wild at unprecedented detail. System manufactures promise remarkably high temporal and spatial resolution. However, the performance of APTs has rarely been rigorously tested at the level of entire ecosystems. Moreover, the effect of habitat structure on system performance has only been poorly documented. Two APTs were deployed to cover two small lakes and a series of standardized stationary tests were conducted to assess system performance. Furthermore, a number of tow tests were conducted to simulate moving fish. Based on these data, we quantified system performance in terms of data yield, accuracy and precision as a function of structural complexity in relation to vegetation. Mean data yield of the two systems was 40% (Lake1) and 60% (Lake2). Average system accuracy (acc) and precision (prec) were Lake1: acc = 3.1 m, prec = 1.1 m; Lake2: acc = 1.0 m, prec = 0.2 m. System performance was negatively affected by structural complexity, i.e., open water habitats yielded far better performance than structurally complex vegetated habitats. Post-processing greatly improved data quality, and sub-meter accuracy and precision were, on average, regularly achieved in Lake2 but remained the exception in the larger and structurally more complex Lake1. Moving transmitters were tracked well by both systems. Whereas overestimation of moved distance is inevitable for stationary transmitters due to accumulation of small tracking errors, moving transmitters can result in both over- and underestimation of distances depending on circumstances. Both deployed APTs were capable of providing high resolution positional data at the scale of entire lakes and are suitable systems to mine the reality of free ranging fish in their natural environment. This opens important opportunities to advance several fields of study such as movement ecology and animal social networks in the wild. It is recommended that thorough performance tests are conducted in any study utilizing APTs. The APTs tested here appear best suited for studies in structurally simple ecosystems or for studying pelagic species. In such situations, the data quality provided by the APTs is exceptionally high.

Recreational fishing selectively captures individuals with the highest fitness potential.

Fisheries-induced evolution and its impact on the productivity of exploited fish stocks remains a highly contested research topic in applied fish evolution and fisheries science. Although many quantitative models assume that larger, more fecund fish are preferentially removed by fishing, there is no empirical evidence describing the relationship between vulnerability to capture and individual reproductive fitness in the wild. Using males from two lines of largemouth bass (Micropterus salmoides) selectively bred over three generations for either high (HV) or low (LV) vulnerability to angling as a model system, we show that the trait "vulnerability to angling" positively correlates with aggression, intensity of parental care, and reproductive fitness. The difference in reproductive fitness between HV and LV fish was particularly evident among larger males, which are also the preferred mating partners of females. Our study constitutes experimental evidence that recreational angling selectively captures individuals with the highest potential for reproductive fitness. Our study further suggests that selective removal of the fittest individuals likely occurs in many fisheries that target species engaged in parental care. As a result, depending on the ecological context, angling-induced selection may have negative consequences for recruitment within wild populations of largemouth bass and possibly other exploited species in which behavioral patterns that determine fitness, such as aggression or parental care, also affect their vulnerability to fishing gear.

Coexistence of behavioural types in an aquatic top predator: a response to resource limitation?

Intra-population variation in behaviour unrelated to sex, size or age exists in a variety of species. The mechanisms behind behavioural diversification have only been partly understood, but density-dependent resource availability may play a crucial role. To explore the potential coexistence of different behavioural types within a natural fish population, we conducted a radio telemetry study, measuring habitat use and swimming activity patterns of pike (Esox lucius), a sit-and-wait predatory fish. Three behavioural types co-occurred in the study lake. While two types of fish only selected vegetated littoral habitats, the third type opportunistically used all habitats and increased its pelagic occurrence in response to decreasing resource biomasses. There were no differences in size, age or lifetime growth between the three behavioural types. However, habitat-opportunistic pike were substantially more active than the other two behavioural types, which is energetically costly. The identical growth rates exhibited by all behavioural types indicate that these higher activity costs of opportunistic behaviour were compensated for by increased prey consumption in the less favourable pelagic habitat resulting in approximately equal fitness of all pike groups. We conclude that behavioural diversification in habitat use and activity reduces intraspecific competition in preferred littoral habitats. This may facilitate the emergence of an ideal free distribution of pike along resource gradients.

A behavioral perspective on fishing-induced evolution.

The potential for excessive and/or selective fishing to act as an evolutionary force has been emphasized recently. However, most studies have focused on evolution of life-history traits in response to size-selective harvesting. Here we draw attention to fishing-induced evolution of behavioral and underlying physiological traits. We contend that fishing-induced selection directly acting on behavioral rather than on life-history traits per se can be expected in all fisheries that operate with passive gears such as trapping, angling and gill-netting. Recent artificial selection experiments in the nest-guarding largemouth bass Micropterus salmoides suggest that fishing-induced evolution of behavioral traits that reduce exposure to fishing gear might be maladaptive, potentially reducing natural recruitment. To improve understanding and management of fisheries-induced evolution, we encourage greater application of methods from behavioral ecology, physiological ecology and behavioral genetics.