Marine reserves promote cycles in fish populations on ecological and evolutionary time scales

Marine reserves are considered essential for sustainable fisheries, although their effectiveness compared to traditional fisheries management is debated. The effect of marine reserves is mostly studied on short ecological time scales, whereas fisheries-induced evolution is a well-established consequence of harvesting. Using a size-structured population model for an exploited fish population of which individuals spend their early life stages in a nursery habitat, we show that marine reserves will shift the mode of population regulation from low size-selective survival late in life to low, early-life survival due to strong resource competition. This shift promotes the occurrence of rapid ecological cycles driven by density-dependent recruitment as well as much slower evolutionary cycles driven by selection for the optimal body to leave the nursery grounds, especially with larger marine reserves. The evolutionary changes increase harvesting yields in terms of total biomass but cause disproportionately large decreases in yields of larger, adult fish. Our findings highlight the importance of carefully considering the size of marine reserves and the individual life history of fish when managing eco-evolutionary marine systems to ensure both population persistence as well as stable fisheries yields.

Transient demographic dynamics of recovering fish populations shaped by past climate variability, 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. Persistent 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. Many historically depleted marine fish stocks have begun showing signs of recovery in recent decades following the implementation of stricter management measures. But these interventions coincide 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 northeast Atlantic ecoregions, 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 discontinuously 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.

Sperm and northern bottlenose whale interactions with deep-water trawlers in the western North Atlantic

Commercial fisheries have increased in all the world's oceans with diverse unintended impacts on marine ecosystems. As a result of resource overlap, interactions between cetaceans and fisheries are a common occurrence and, in many cases, can give rise to significant conservation issues. Research on the distribution and types of such interactions is important for efficient management. In this study, we describe the behaviors of two whale species: sperm whales (Physeter macrocephalus) and northern bottlenose whales (Hyperoodon ampullatus), interacting with benthic trawlers fishing off the eastern Grand Banks of the western North Atlantic in 2007. Whale interactions were only observed when vessels were targeting Greenland halibut (Reinhardtius hippoglossoides) in deep-water fishing areas and were most common during net hauling. Sperm whales and northern bottlenose whales appeared to engage in feeding behavior close to the surface during hauling, especially during the latter stages, suggesting they targeted fish escapees rather than discards. Using photo-identification methods, seven individual sperm whales were identified with multiple resights of six individuals being recorded over an almost two month period. The maximum distance between two resights was 234 km, suggesting individual sperm whales were repeatedly targeting and even following fishing vessels over multiple days and between fishing areas. By contrast, there were no photographic resights of individual northern bottlenose whales within this study, or with substantial photo-identification catalogues from other adjacent high density areas, suggesting that individuals of this species may be less likely to follow vessels or move between areas. This study documents the earliest confirmed records of northern bottlenose whales in this remote region. These interactions and high encounter rates may indicate that adjacent populations are recovering from the previous century of commercial whaling. Our study provides new insights and details on whale-fisheries interactions, which can inform future research and help managers understand the real and perceived impacts of depredation behaviour on fisheries and whales.

Using ecosystem health and welfare assessments to determine impacts of wild collection for public aquariums

Aquatic ecosystems are currently facing a multitude of stressors from anthropogenic impacts, including climate change, pollution, and overfishing. Public aquariums positively contribute to ecosystems through conservation, education, and scientific advancement; but may also negatively detract from these systems through collection of animals from the wild and sourcing from commercial suppliers. Changes within the industry have occurred, although evidence-based assessments of 1) how aquariums collect and maintain their populations to determine sustainability of the environment they have harvested; and 2) the welfare of these harvested animals once within the aquariums are still needed. The objectives of this study were to assess the ecosystem health of locations aquariums frequently visit to collect fish from the wild, and then evaluate the wellbeing of fishes at aquariums after extended periods in captivity. Assessments included use of chemical, physical, and biological indicators at field sites, and use of a quantitative welfare assessment at aquariums for comparison to species reared through aquaculture. Anthropogenic pressures at field sites were observed, but no evidence of high degradation or compromised health of animals were found. Welfare assessments of aquarium exhibit tanks produced high-positive scores overall (> 70/84), demonstrating that both wild collected (avg. score 78.8) and aquaculture fishes (avg. score 74.5) were coping appropriately within their environments. Although findings indicated that fish can be taken from the wild at low-moderate rates without any deleterious impact on the environment and cope equally well in aquarium settings, alternatives such as aquaculture should be considered as a strategy to reduce pressure on known stressed aquatic environments or where significant numbers of fishes are being taken.

Spatial variation in food web structure in a recovering marine ecosystem

Spatial heterogeneity in food web structure and interactions may reconcile spatial variation in population and community dynamics in large marine ecosystems. In order to assess food web contributions to the different community recovery dynamics along the Newfoundland and Labrador shelf ecosystem, we quantified species interactions using stable isotope mixing models and food web metrics within three sub-regions. Representative samples of each species caught in trawls and plankton tows were analyzed for stomach contents and stable isotope ratios (δ15N and δ13C) to parameterize isotope mixing models. Regional variation, highlighted by the diets of three economically important species, was observed such that the southern region demonstrated a variety of trophic pathways of nutrient flow into the higher food web while the diets of fish in the northern regions were typically dominated by one or two pathways via dominant prey species, specifically shrimp (Pandalus sp.) and hyperiids. Food web metrics indicated that the low-diversity northern regions had higher connectance and shorter food chain lengths. This observed regional variation contributes to our understanding of the role of specific forage species to the ecosystem which is an essential contribution towards ecosystem-based management decisions.

The dynamics of the fishing fleet in China Seas: A glimpse through AIS monitoring

Monitoring fishing activities is crucial for marine conservation but challenging in practice, because the ability in tracking fisheries has been limited on varying spatial and temporal scales. The challenge is for both developed and developing countries, and is outstanding in China which is characterized by the world's largest fishing fleet. The advance of Automatic Identification System (AIS) provides the opportunity to enforce monitoring and to promote the compliance of responsible fisheries. Here, the dynamics of fishing fleets in China Seas were integrally investigated for the first time. We demonstrated heavy fishing efforts widely distributed across China Seas, whereas most vessels were concentrated along the coastal line. The temporal pattern of fishing efforts was dominated by summer moratorium, and intensive fishing occurred immediately before and after the moratorium. We highlight that most fishing activities occurred in a remarkably limited spatial and temporal scope, particularly trawling vessels which spent a few months on fishing every year and covered a small geographical area. Additionally, considerable fishing efforts have transferred from Eastern China Sea to the coastal areas of south China in response to an extension of summer moratorium, which requires the fishing moratorium beginning one month earlier since 2017. We argue that summer moratorium cannot effectively control overall fishing efforts, but rearrange the same level of efforts in space and time. We highlight caveats in the interpretation of AIS data in terms of reception issues, meanwhile the novel information provided by AIS can refine the understanding of fleet dynamics and contribute to adaptive fisheries management over broad spatial and temporal scales.

Rapid evolution in salmon life history induced by direct and indirect effects of fishing

Understanding the drivers of evolution is a fundamental aim in biology. However, identifying the evolutionary impacts of human activities is challenging because of a lack of temporal data and limited knowledge of the genetic basis of most traits. Here, we identify the drivers of evolution toward maturity at an earlier age in Atlantic salmon through two types of fisheries-induced evolution acting in opposing directions: an indirect effect linked with harvest of a salmon prey species (capelin) at sea (selection against late maturation) and a direct effect due to net fishing in rivers (selection against early maturation). Because capelin are harvested as an aquaculture feed protein source, we hereby determine an indirect path by which salmon aquaculture may influence wild salmon populations.

Temporal and regional variation in catch across an extensive coastal recreational fishery: Exploring the utility of survey methods to guide and assess spatio-temporal management initiatives

As global research into recreational fishing gains momentum due to the pursuit's biological, social and economic impacts, information on regional and temporal patterns of recreational exploitation will continue to enable objective assessment and development of management initiatives for exploited species. This paper demonstrates the utility of offsite survey methods in assessing spatial and temporal differences in recorded catches from a large, diffuse and heterogenous coastal recreational fishery. Using the estuarine recreational fishery that operates along the coast of New South Wales, Australia as a case study, survey data was employed to quantify annual (June 2013-May 2014) state-wide estuarine catch. Generalized linear mixed effects models were then applied to expanded catch estimates from surveyed households to examine the influence of zone and season on the kept and released numbers of snapper (Pagrus auratus), dusky flathead (Platycephalus fuscus) and bream (Acanthopagrus spp. complex comprised of A. butcheri, A. australis and their hybrids). For kept bream, significant differential seasonal effects were observed in all regions except the Mid-South Coast. For released bream, numbers were greatest in Sydney and during Summer and Winter. For kept snapper, the greatest harvest was recorded in the Mid-South Coast but season had no effect. Differential seasonal effects were found in each zone for released snapper. For kept dusky flathead, the greatest numbers were recorded in Sydney and the Mid-South Coast but season had no effect. We conclude by assessing some current spatial and temporal management initiatives in light of the uncovered patterns of recreational catch and consider the implications of these patterns in terms of future ecosystem-based management recommendations aimed at achieving ecological, social and economic sustainability in fisheries.

Impacts of fishing on the Caribbean white sea urchin, Lytechinus variegatus, in Margarita Island, Venezuela

The Caribbean white sea urchin, L. variegatus, is locally harvested in Margarita Island and other locations of southeastern Venezuela. The recent reduction of densities raises concerns about potential impacts for overfishing. Densities of L. variegatus were estimated at Impact and Control locations between late-2012 and mid-2015 to 1) test temporal changes, comparing with 1997-1998 estimations, 2) the effect of seasonal closure on resource recovery and 3) the effect of local expansion. The results suggest that, after a period of fourteen years, an important decrease in L. variegatus densities occurred, as well as a lack of population recovery in fishing areas during seasonal closures. Furthermore, during the monitoring program, it was observed fishing activities in one Control location that subsequently showed clear patterns of population depletion, like other Impact locations. Fishing impact on L. variegatus populations is severe, persistent and expands over time without evidence of recovery, therefore it is expected that local populations of L. variegatus would collapse under current exploitation levels. However, due to the L. variegatus life history and its distribution range, recovery of impacted populations could be possible via recruitment of planktonic larvae if effective management actions are imposed. It is recommended to exercise more regulations on fishing activities and to execute management measures that allow recovering the stocks to maintain local populations of sea urchin.

Indigenous Environmental Justice within Marine Ecosystems: A Systematic Review of the Literature on Indigenous Peoples’ Involvement in Marine Governance and Management

We develop and apply a systematic review methodology to identify and understand how the peer-reviewed literature characterises Indigenous peoples’ involvement in marine governance and management approaches in terms of equity and justice worldwide. We reviewed the peer-reviewed English-language research articles between January 2015 and September 2020 for examples of Indigenous peoples’ involvement in marine governance and management using the analytical lens of environmental justice. The majority of research studies highlighted that Indigenous peoples experienced some form of environmental injustice linked to existing marine governance and management, most notably in the context of inequitable decision-making procedures surrounding the establishment and operation of marine protected areas. However, there are significant gaps in the current literature, including a notable absence of studies exploring Indigenous women and other gender minorities’ involvement in marine planning and management and the limited number of studies about Indigenous peoples living throughout Asia, the Arctic, Russia, and Africa. More studies are needed to explore collaborative and intersectional approaches, including co-governance and co-management and ecosystem-based management, and critically evaluate what constitutes inclusive, equitable, and just marine governance and management processes, practices, and outcomes for different Indigenous peoples occupying diverse social–ecological systems.

Variation of δ18O in otoliths of Stellifer lanceolatus and Eucinostomus gula environmental change indicator in Terminos Lagoon, Mexico

Environmental changes have been associated with natural climatic variability or human activity. Water resources management is, perhaps, the most drastic change observed in the coastal environment. However, external forcings such as the El Niño event have important implications in the global and regional hydrological balance. These environmental changes have an impact on the density and biomass of the ichthyofauna in the Terminos Lagoon (TL) for the past 30 years, presumably, associated with variations in the temperature and surface salinity of the sea. Therefore, in the present study, δ¹⁸O was quantified in otoliths of two important species due to their dominance: Stellifer lanceolatus and Eucinostomus gula, and to understand the environmental changes reflected in both species. The δ¹⁸O was analyzed in otoliths of these two species captured in 1998/1997, 2006/2007 and 2016/2017 and were compared with in situ temperature and salinity data. Sea surface temperature and salinity increased by 2 °C and 9, respectively, between 1997 and 2017. Stellifer lanceolatus δ¹⁸O values was in isotopic equilibrium with seawater calcite; while, E. gula is not in isotopic equilibrium. The δ¹⁸O of S. lanceolatus and E. gula varied significantly with the increase in salinity (R² = 0.8987 and R² = -0.2964) and not with the sea surface temperature. S. lanceolatus is an excellent bioindicator of changes in sea surface salinity in this region of the Gulf of Mexico.

Offshore multi-purpose platforms for a Blue Growth: A technological, environmental and socio-economic review

"Blue Growth" and "Blue Economy" is defined by the World Bank as: "the sustainable use of ocean resources for economic growth, improved livelihoods and jobs, while preserving the health of ocean ecosystem". Multi-purpose platforms (MPPs) can be defined as offshore platforms serving the needs of multiple offshore industries (energy and aquaculture), aim at exploiting the synergies and managing the tensions arising when closely co-locating systems from these industries. Despite a number of previous projects aimed at assessing, from a multidisciplinary point of view, the feasibility of multipurpose platforms, it is here shown that the state-of-the-art has focused mainly on single-purpose devices, and adopting a single discipline (either economic, or social, or technological, or environmental) approach. Therefore, the aim of the present study is to provide a multidisciplinary state of the art review on, whenever possible, multi-purpose platforms, complementing it with single-purpose and/or single discipline literature reviews when not possible. Synoptic tables are provided, giving an overview of the multi-purpose platform concepts investigated, the numerical approaches adopted, and a comprehensive snapshot classifying the references discussed by industry (offshore renewables, aquaculture, both) and by aspect (technological, environmental, socio-economic). The majority of the multi-purpose platform concepts proposed are integrating only multiple offshore renewable energy devices (e.g. hybrid wind-wave), with only few integrating also aquaculture systems. MPPs have significant potential in economizing CAPEX and operational costs for the offshore energy and aquaculture industry by means of concerted spatial planning and sharing of infrastructure.

Assessing spatio-temporal changes in marine communities along the Portuguese continental shelf and upper slope based on 25 years of bottom trawl surveys

The Portuguese continental coast is influenced by several oceanographic processes and is located near the confluence of three biogeographic realms (from the North Atlantic, South Atlantic and Mediterranean). Given these features, the topography of the Portuguese coast, possible variations in fishing effort and reported increasing sea surface temperature in the last decades, we hypothesized that changes in marine communities in space and time occurred since 1990. In this study, research survey data collected yearly along the Portuguese continental slope (20-500 m deep) from 1990 to 2016 were analysed with the objective of identifying spatio-temporal changes. Latitude and depth were found to play a major role in communities' spatial differentiation, probably associated to temperature, and three ecological areas were defined (north, southwest and south). In the studied period, Macroramphosus spp. abundance showed a marked decrease in all areas whereas Sparids increased in abundance in the south. Despite these major changes and fluctuations in species abundance over time no major trends in communities were observed. Fishing activity, environmental conditions (including climate change) and biotic factors are all drivers possibly responsible for those changes.

Effects of widespread human disturbances in the marine environment suggest a new agenda for meiofauna research is needed

The response of an ecological community to a disturbance event, and its capacity to recover, are of major interest to ecologists, especially at a time of increasing frequencies and intensities of environmental change brought about by humans. Meiofauna, a group of small-sized organisms, are an abundant and ubiquitous component of seafloor communities that respond rapidly to environmental change. We summarise the available research on the response of metazoan meiofauna to the most widespread anthropogenic disturbances in the marine environment, including bottom fishing, the introduction of invasive species and anthropogenic climate change. We show that disturbance effects on habitats interact critically with effects on resident meiofauna species. Their responses are consistent with competitive replacement, where disparate disturbance effects on competing species drive shifts in dominance and intra- and interspecific interactions. The widespread replacement of habitat-specific ecological specialists by broadly-adapted ecological generalists and opportunists results in biotic and functional homogenisation of once disparate biotas. Anthropogenic disturbances may facilitate novel interactions among meiofauna species, and between meiofauna and other benthic organisms, but the number and breadth of these interactions is likely to be limited. Knowledge about the dependence of meiofauna species on their environment and on other benthic species has been growing. Future studies will be most meaningful if this knowledge is expanded alongside understanding the potential of locally adapted species to respond to shifts in environmental conditions.

Network of small no-take marine reserves reveals greater abundance and body size of fisheries target species

No-take marine reserves (NTRs), i.e. areas with total fishing restrictions, have been established worldwide aiming to promote biodiversity and ecosystem conservation. Brazil has 3.3% of its exclusive economic zone protected by 73 different NTRs, however, most of them currently lack scientific knowledge and understanding of their ecological role, particularly regarding rocky reefs in subtropical regions. In this context, this study aimed to contrast a network of NTRs with comparable fished sites across a coastal biogeographic gradient to investigate the effect of fishing and habitat variability on the abundance and body size of rocky reef fish. We used Baited Remote Underwater stereo-Video (stereo-BRUVs) and Diver Operated stereo-Video (stereo-DOVs) systems to simultaneously sample reef fish and habitat. Model selection and results identified habitat and biogeographic variables, such as distance from shore, as important predictor variables, explaining several aspects of the fish assemblage. The effect of protection was important in determining the abundance and body size of targeted species, in particular for epinephelids and carangids. Conversely, species richness was correlated with habitat complexity but not with protection status. This is the first study using these survey methods in the Southwestern Atlantic, demonstrating how a network of NTRs can provide benchmarks for biodiversity conservation and fisheries management.

Varying demographic impacts of different fisheries on three Mediterranean seabird species

Fisheries have an enormous economic importance, but reconciling their socio-economic features with the conservation and sustainability of marine ecosystems presents major challenges. Bycatch mortality from fisheries is clearly among the most serious global threats for marine ecosystems, affecting a wide range of top predators. Recent estimates report ca. 200,000 seabirds killed annually by bycatch in European waters. However, there is an urgent need to rigorously estimate actual mortality rates and quantify effects of bycatch on populations. The Mediterranean Sea is one of the most impacted regions. Here, we estimate for the first time both bycatch mortality rates and their population-level effects on three endemic and vulnerable Mediterranean taxa: Scopoli's shearwater, Mediterranean shag, and Audouin's gull, that die in different types of fishing gears: longlines, gillnets and sport trolling, respectively. We use multi-event capture-recapture modelling to estimate crucial demographic parameters, including the probabilities of dying in different fishing gears. We then build stochastic demography models to forecast the viability of the populations under different management scenarios. Longline bycatch was particularly severe for adults of Scopoli's shearwaters and Audouin's gulls (ca. 28% and 23% of total mortality, respectively) and also for immature gulls (ca. 90% of mortality). Gillnets had a lower impact, but were still responsible for ca. 9% of juvenile mortality on shags, whereas sport trolling only slightly influenced total mortality in gulls. Bycatch mortality has high population-level impacts in all three species, with shearwaters having the highest extinction risk under current mortality rates. Different life-history traits and compensatory demographic mechanisms between the three species are probably influencing the different bycatch impact: for shearwaters, urgent conservation actions are required to ensure the viability of their populations. Results will be very useful for guiding future seabird conservation policies and moving towards an ecosystem-based approach to sustainable fisheries management.

Operationalizing the social-ecological systems framework to assess sustainability

Meeting human needs while sustaining ecosystems and the benefits they provide is a global challenge. Coastal marine systems present a particularly important case, given that >50% of the world’s population lives within 100 km of the coast and fisheries are the primary source of protein for >1 billion people worldwide. Our integrative analysis here yields an understanding of the sustainability of coupled social-ecological systems that is quite distinct from that provided by either the biophysical or the social sciences alone and that illustrates the feasibility and value of operationalizing the social-ecological systems framework for comparative analyses of coupled systems, particularly in data-poor and developing nation settings.

Environmental governance is more effective when the scales of ecological processes are well matched with the human institutions charged with managing human–environment interactions. The social-ecological systems (SESs) framework provides guidance on how to assess the social and ecological dimensions that contribute to sustainable resource use and management, but rarely if ever has been operationalized for multiple localities in a spatially explicit, quantitative manner. Here, we use the case of small-scale fisheries in Baja California Sur, Mexico, to identify distinct SES regions and test key aspects of coupled SESs theory. Regions that exhibit greater potential for social-ecological sustainability in one dimension do not necessarily exhibit it in others, highlighting the importance of integrative, coupled system analyses when implementing spatial planning and other ecosystem-based strategies.

Rising catch variability preceded historical fisheries collapses in Alaska

Statistical indicators such as rising variance and rising skewness in key system parameters may provide early warning of "regime shifts" in communities and populations. However, the utility of these indicators has rarely been tested in the large, complex ecosystems that are of most interest to managers. Crustacean fisheries in the Gulf of Alaska and Bering Sea experienced a series of collapses beginning in the 1970s, and we used spatially resolved catch data from these fisheries to test the predictions that increasing variability and skewness would precede stock collapse. Our data set consisted of catch data from 14 fisheries (12 collapsing and two non-collapsing), spanning 278 cumulative years. Our sampling unit for analysis was the Alaska Department of Fish and Game statistical reporting area (mean n for individual fisheries = 42 areas, range 7-81). We found that spatial variability in catches increased prior to stock collapse: a random-effects model estimating trend in variability across all 12 collapsing fisheries showed strong evidence of increasing variability prior to collapse. Individual trends in variability were statistically significant for only four of the 12 collapsing fisheries, suggesting that rising variability might be most effective as an indicator when information from multiple populations is available. Analyzing data across multiple fisheries allowed us to detect increasing variability 1-4 years prior to collapse, and trends in variability were significantly different for collapsing and non-collapsing fisheries. In spite of theoretical expectations, we found no evidence of pre-collapse increases in catch skewness. Further, while models generally predict that rising variability should be a transient phenomenon around collapse points, increased variability was a persistent feature of collapsed fisheries in our study. We conclude that this result is more consistent with fishing effects as the cause of increased catch variability, rather than the critical slowing down that is the driver of increased variability in regime shift models. While our results support the use of rising spatial variability as a leading indicator of regime shifts, the failure of our data to support other model-derived predictions underscores the need for empirical validation before these indicators can be used with confidence by ecosystem managers.

Quantifying the balance between bycatch and predator or competitor release for nontarget species

If a species is bycatch in a fishery targeted at its competitor or predator, it experiences both direct anthropogenic mortality and indirect positive effects through species interactions. If the species involved interact strongly, the release from competition or predation can counteract or exceed the negative effects of bycatch. We used a set of two- and three-species community modules to analyze the relative importance of species interactions when modeling the overall effect of harvest with bycatch on a nontarget species. To measure the trade-off between direct mortality and indirect positive effects, we developed a "bycatch transition point" metric to determine, for different scenarios, what levels of bycatch shift overall harvest impact from positive to negative. Under strong direct competition with a targeted competitor, release from competition due to harvest leads to a net increase in abundance even under moderate levels of bycatch. For a three-species model with a shared obligate predator, the release from apparent competition exceeds direct competitive release and outweighs the decrease from bycatch mortality under a wide range of parameters. Therefore, in communities where a shared predator forms a strong link between the target and nontarget species, the effects of indirect interactions on populations can be larger than those of direct interactions. The bycatch transition point metric can be used for tightly linked species to evaluate the relative strengths of positive indirect effects and negative anthropogenic impacts such as bycatch, habitat degradation, and introduction of invasive species.

River food web response to large-scale riparian zone manipulations

Conservation programs often focus on select species, leading to management plans based on the autecology of the focal species, but multiple ecosystem components can be affected both by the environmental factors impacting, and the management targeting, focal species. These broader effects can have indirect impacts on target species through the web of interactions within ecosystems. For example, human activity can strongly alter riparian vegetation, potentially impacting both economically-important salmonids and their associated river food web. In an Olympic Peninsula river, Washington state, USA, replicated large-scale riparian vegetation manipulations implemented with the long-term (>40 yr) goal of improving salmon habitat did not affect water temperature, nutrient limitation or habitat characteristics, but reduced canopy cover, causing reduced energy input via leaf litter, increased incident solar radiation (UV and PAR) and increased algal production compared to controls. In response, benthic algae, most insect taxa, and juvenile salmonids increased in manipulated areas. Stable isotope analysis revealed a predominant contribution of algal-derived energy to salmonid diets in manipulated reaches. The experiment demonstrates that riparian management targeting salmonids strongly affects river food webs via changes in the energy base, illustrates how species-based management strategies can have unanticipated indirect effects on the target species via the associated food web, and supports ecosystem-based management approaches for restoring depleted salmonid stocks.

A trophic cascade triggers collapse of a salt-marsh ecosystem with intensive recreational fishing

Overexploitation of predators has been linked to the collapse of a growing number of shallow-water marine ecosystems. However, salt-marsh ecosystems are often viewed and managed as systems controlled by physical processes, despite recent evidence for herbivore-driven die-off of marsh vegetation. Here we use field observations, experiments, and historical records at 14 sites to examine whether the recently reported die-off of northwestern Atlantic salt marshes is associated with the cascading effects of predator dynamics and intensive recreational fishing activity. We found that the localized depletion of top predators at sites accessible to recreational anglers has triggered the proliferation of herbivorous crabs, which in turn results in runaway consumption of marsh vegetation. This suggests that overfishing may be a general mechanism underlying the consumer-driven die-off of salt marshes spreading throughout the western Atlantic. Our findings support the emerging realization that consumers play a dominant role in regulating marine plant communities and can lead to ecosystem collapse when their impacts are amplified by human activities, including recreational fishing.

Global distribution and conservation of marine mammals

We identified 20 global key conservation sites for all marine (123) and freshwater (6) mammal species based on their geographic ranges. We created geographic range maps for all 129 species and a Geographic Information System database for a 46,184 1° x 1° grid-cells, ∼10,000-km(2). Patterns of species richness, endemism, and risk were variable among all species and species groups. Interestingly, marine mammal species richness was correlated strongly with areas of human impact across the oceans. Key conservation sites in the global geographic grid were determined either by their species richness or by their irreplaceability or uniqueness, because of the presence of endemic species. Nine key conservation sites, comprising the 2.5% of the grid cells with the highest species richness, were found, mostly in temperate latitudes, and hold 84% of marine mammal species. In addition, we identified 11 irreplaceable key conservation sites, six of which were found in freshwater bodies and five in marine regions. These key conservation sites represent critical areas of conservation value at a global level and can serve as a first step for adopting global strategies with explicit geographic conservation targets for Marine Protected Areas.

Eco-evolutionary trophic dynamics: loss of top predators drives trophic evolution and ecology of prey

Ecosystems are being altered on a global scale by the extirpation of top predators. The ecological effects of predator removal have been investigated widely; however, predator removal can also change natural selection acting on prey, resulting in contemporary evolution. Here we tested the role of predator removal on the contemporary evolution of trophic traits in prey. We utilized a historical introduction experiment where Trinidadian guppies (Poecilia reticulata) were relocated from a site with predatory fishes to a site lacking predators. To assess the trophic consequences of predator release, we linked individual morphology (cranial, jaw, and body) to foraging performance. Our results show that predator release caused an increase in guppy density and a “sharpening” of guppy trophic traits, which enhanced food consumption rates. Predator release appears to have shifted natural selection away from predator escape ability and towards resource acquisition ability. Related diet and mesocosm studies suggest that this shift enhances the impact of guppies on lower trophic levels in a fashion nuanced by the omnivorous feeding ecology of the species. We conclude that extirpation of top predators may commonly select for enhanced feeding performance in prey, with important cascading consequences for communities and ecosystems.

Consumer-resource dynamics: quantity, quality, and allocation

BACKGROUND

The dominant paradigm for modeling the complexities of interacting populations and food webs is a system of coupled ordinary differential equations in which the state of each species, population, or functional trophic group is represented by an aggregated numbers-density or biomass-density variable. Here, using the metaphysiological approach to model consumer-resource interactions, we formulate a two-state paradigm that represents each population or group in a food web in terms of both its quantity and quality.

METHODOLOGY AND PRINCIPAL FINDINGS

The formulation includes an allocation function controlling the relative proportion of extracted resources to increasing quantity versus elevating quality. Since lower quality individuals senescence more rapidly than higher quality individuals, an optimal allocation proportion exists and we derive an expression for how this proportion depends on population parameters that determine the senescence rate, the per-capita mortality rate, and the effects of these rates on the dynamics of the quality variable. We demonstrate that oscillations do not arise in our model from quantity-quality interactions alone, but require consumer-resource interactions across trophic levels that can be stabilized through judicious resource allocation strategies. Analysis and simulations provide compelling arguments for the necessity of populations to evolve quality-related dynamics in the form of maternal effects, storage or other appropriate structures. They also indicate that resource allocation switching between investments in abundance versus quality provide a powerful mechanism for promoting the stability of consumer-resource interactions in seasonally forcing environments.

CONCLUSIONS/SIGNIFICANCE

Our simulations show that physiological inefficiencies associated with this switching can be favored by selection due to the diminished exposure of inefficient consumers to strong oscillations associated with the well-known paradox of enrichment. Also our results demonstrate how allocation switching can explain observed growth patterns in experimental microbial cultures and discuss how our formulation can address questions that cannot be answered using the quantity-only paradigms that currently predominate.

Ecosystem-based fisheries management requires a change to the selective fishing philosophy

Globally, many fish species are overexploited, and many stocks have collapsed. This crisis, along with increasing concerns over flow-on effects on ecosystems, has caused a reevaluation of traditional fisheries management practices, and a new ecosystem-based fisheries management (EBFM) paradigm has emerged. As part of this approach, selective fishing is widely encouraged in the belief that nonselective fishing has many adverse impacts. In particular, incidental bycatch is seen as wasteful and a negative feature of fishing, and methods to reduce bycatch are implemented in many fisheries. However, recent advances in fishery science and ecology suggest that a selective approach may also result in undesirable impacts both to fisheries and marine ecosystems. Selective fishing applies one or more of the "6-S" selections: species, stock, size, sex, season, and space. However, selective fishing alters biodiversity, which in turn changes ecosystem functioning and may affect fisheries production, hindering rather than helping achieve the goals of EBFM. We argue here that a "balanced exploitation" approach might alleviate many of the ecological effects of fishing by avoiding intensive removal of particular components of the ecosystem, while still supporting sustainable fisheries. This concept may require reducing exploitation rates on certain target species or groups to protect vulnerable components of the ecosystem. Benefits to society could be maintained or even increased because a greater proportion of the entire suite of harvested species is used.

Incorporating biogeography into evaluations of the Channel Islands marine reserve network

Networks of marine reserves are increasingly a major component of many ecosystem-based management plans designed to conserve biodiversity, protect the structure and function of ecosystems, and rebuild and sustain fisheries. There is a growing need for scientific guidance in the design of network-wide monitoring programs to evaluate the efficacy of reserves at meeting their conservation and management goals. Here, we present an evaluation of the Channel Islands reserve network, which was established in 2003 off the coast of southern California. This reserve network spans a major environmental and biogeographic gradient, making it a challenge to assess network-wide responses of many species. Using fish community structure data from a long-term, large-scale monitoring program, we first identified persistent geographic patterns of community structure and the scale at which sites should be grouped for analysis. Fish communities differed most among islands with densities of individual species varying from 3- to 250-fold. Habitat structure differed among islands but not based on reserve status. Across the network, we found that, after 5 years, species targeted by fishing had higher densities (1.5×) and biomass (1.8×) inside reserves, whereas nontargeted species showed no significant differences. Examining trophic groups, piscivore and carnivore biomass was significantly greater inside reserves (1.8× and 1.3× more, respectively), whereas the biomass of planktivores and herbivores was similar inside and out. A framework for incorporating biogeographic variation into reserve network assessments is critical as we move from the evaluation of single reserves to networks of reserves.

Fishery-independent data reveal negative effect of human population density on Caribbean predatory fish communities

BACKGROUND

Understanding the current status of predatory fish communities, and the effects fishing has on them, is vitally important information for management. However, data are often insufficient at region-wide scales to assess the effects of extraction in coral reef ecosystems of developing nations.

METHODOLOGY/PRINCIPAL FINDINGS

Here, I overcome this difficulty by using a publicly accessible, fisheries-independent database to provide a broad scale, comprehensive analysis of human impacts on predatory reef fish communities across the greater Caribbean region. Specifically, this study analyzed presence and diversity of predatory reef fishes over a gradient of human population density. Across the region, as human population density increases, presence of large-bodied fishes declines, and fish communities become dominated by a few smaller-bodied species.

CONCLUSIONS/SIGNIFICANCE

Complete disappearance of several large-bodied fishes indicates ecological and local extinctions have occurred in some densely populated areas. These findings fill a fundamentally important gap in our knowledge of the ecosystem effects of artisanal fisheries in developing nations, and provide support for multiple approaches to data collection where they are commonly unavailable.