Recovery Of Fish Populations Research Articles

Recovery potential of fish and coral populations following ecological disturbance

AbstractThe health of coral reef benthic and fish communities is implicitly connected, yet typically studied and managed separately. By developing a coupled reef population model that connects coral populations and reef fish biomass through the habitat complexity that corals build and fish live among, we aim to address this gap by holistically quantifying ecological feedbacks and responses to ecological stressors. We explored the impacts of fishing effort in conjunction with three types of ecological disturbances as they propagated through a coral reef ecosystem: (1) a disturbance that disproportionately affected small, bio‐energetically vulnerable colonies, (2) a disturbance that predominantly affected large, mechanically vulnerable colonies, and (3) a disturbance that affected colonies of all sizes randomly. We found that joint coral and fish population recovery was fastest and most complete under events affecting small colonies, followed by recovery from disturbances affecting random sizes, and lastly large‐colony disturbances. These results suggest that the retention versus loss of large coral colonies with high reproductive potential critically influenced population recovery. Low fishing levels maintained fish and coral populations and allowed for recovery after disturbances, whereas high fishing levels prevented recovery due to greater fish‐dependent coral mortality. Finally, we tested various formulations of the relationship between coral size and habitat complexity (i.e., exponential, linear, logarithmic) that constrain fish carrying capacity. All formulations led to similar population projections in most disturbance scenarios, but there were exceptions where the timing and trajectory of recovery differed, such as faster and greater recovery potential when complexity is logarithmic with respect to coral size. These findings suggest that fishing and habitat complexity mediate the recovery of coral reef populations, emphasizing the importance of describing linkages between coral size distribution and reef habitat structure. Furthermore, our results highlight the utility of the coupled‐model framework for understanding and managing the impact of disturbances at ecosystem scales.

Impact of Pollution and Toxic Stress on Fish Health: Mechanisms, Consequences, and Mitigation Strategies

Pollution poses a dire threat to fish health and aquatic ecosystems, permeating through various pathways and wreaking havoc on biological processes crucial for fish survival. Pollutants infiltrate fish through multiple routes, inducing direct toxicity and disrupting fundamental functions such as metabolism, hormonal regulation, and immune responses. These detrimental effects manifest in a plethora of consequences, including stunted growth, diminished energy reserves, heightened vulnerability to environmental stressors, reproductive impairments, increased susceptibility to diseases, and behavioral alterations that imperil their survival. To address this pressing crisis, proactive measures are indispensable, necessitating stringent regulations, the adoption of sustainable practices, and the enhancement of water treatment facilities to curtail the release of pollutants into aquatic environments. Simultaneously, reactive strategies must be deployed, focusing on remediation efforts to cleanse contaminated areas, facilitating the recovery of fish populations, and undertaking broader ecosystem restoration initiatives. Continuous research and vigilant monitoring play pivotal roles in discerning the nuanced impacts of pollution on fish health and gauging the efficacy of mitigation endeavors. Safeguarding fish populations is imperative for their well-being and preserving the health and equilibrium of the entire aquatic ecosystem, underscoring the urgency of concerted action to combat pollution's detrimental effects.

MPA-FishMApp – A Citizen Science App That Simplifies Monitoring of Coral Reef Fish Density and Biomass in Marine Protected Areas

Monitoring changes in fish density and biomass inside marine protected areas (MPAs) through fish visual census (FVC) can determine if MPAs are achieving their goal of promoting fish population recovery. Simplified FVC methods have been developed for citizen scientists to enable them to monitor fish populations in MPAs. However, MPA monitoring programs led by local stakeholders remain rare and difficult to sustain due to technical barriers related to FVC data management. Here, we describe and evaluate a novel online app called MPA-FishMApp, which we developed to help stakeholders of MPAs that protect coral reefs in the Philippines efficiently store, analyze, and visualize FVC data. MPA-FishMApp is coupled to a simplified FVC method wherein the observer records only 21 reef fish species groups during surveys. The app provides a simple data entry interface, cloud storage, and algorithms to estimate fish density and biomass. Spatial and temporal trends in fish density and biomass can be instantaneously visualized in the app based on relative importance to fisheries. Field testing suggested that the MPA-FishMApp methodology (simplified FVC and app) is sensitive enough to detect qualitative patterns showing differences in density and biomass that may develop between MPAs and fished sites, especially in fishes that are highly important to fisheries. However, users must have sufficient training and experience in simplified FVC to produce reliable data. MPA-FishMApp may help reverse the lack of monitoring in MPAs across the Philippines and offers an accessible, transparent, and auditable venue for collaboration between citizen scientists and professional scientists.

Impacts of Recreational Angling on Fish Population Recovery after a Commercial Fishing Ban

It is often assumed that recreational fishing has negligible influences on fish stocks compared to commercial fishing. However, for inland water bodies in densely populated areas, this assumption may not be supported. In this study, we demonstrate variable stock recovery rates among different fish species with similar life histories in a large productive inland freshwater ecosystem (Kaunas Reservoir, Lithuania), where previously intensive commercial fishing has been banned since 2013. We conducted over 900 surveys of recreational anglers from 2016 to 2021 to document recreational fishing catches and combined these catch estimates with drone and fishfinder device-based assessments of recreational fishing effort. Fish population recovery rates were assessed using a standardized catch-per-unit-effort time series in independent scientific surveys. We show that recreational fishing is slowing the recovery of predatory species, such as pikeperch Sander lucioperca (Linnaeus, 1758) and Eurasian perch Perca fluviatilis Linnaeus, 1758. The estimated annual recreational catches for these species were 19 tons (min-max of 7–55 tons) and 9 tons (4–28), respectively, which was considerably higher than the average commercial catch before the fishery closure (10 and 1 tons, respectively). In contrast, the recovery of roach Rutilus rutilus (Linnaeus, 1758), rarely caught by anglers (annual recreational catch of ca 3 tons compared to ca 100 tons of commercial catch), has been rapid, and the species is now dominating the ecosystem. Our study demonstrates that recreational fishing can have strong and selective impacts on fish species, reduce predator abundance, alter relative species composition and potentially change ecosystem state and dynamics.

Mutually promoting or constraining? Disentangling the superimposed effect of velocity and illuminance on fish motion in low‐velocity flows with a novel metric

Abstract Global climate change, species invasion, and human activities such as the construction of hydraulic facilities are contributing to the worldwide degradation of fish stocks. As a pivotal environmental factor that affects fish migration and population distribution, the low‐velocity flow has not drawn enough attention despite its extensive presence in various ecoregions. To understand the behavioural profiles of fish in low‐velocity flow, we examined the motility and swimming performance of two representative cyprinids, grass carp (GC, Ctenopharyngodon idella) and silver carp (SC, Hypophthalmichthys molitrix), under the combined effect of different flow velocities and illuminance ranges. The two species were exposed to two flow velocities (0.15 and 0.25 m/s) and three illuminance ranges (100.0–0.9 lx, 300.0–2.5 lx, and 700.0–4.9 lx). A novel behavioural metric, composed of light preference, swimming speed, rheotaxis index (RI), swimming stability (SS), and the probability of moving forwards/backwards over a certain distance (PMf‐0.1 and PMb‐0.1), was developed to fully characterise the motion strategy of fish. By analysing the individual distribution in light gradient, we confirmed the scototaxis of GC and found the oscillating light preference in SC that changed from 84.41–10.18 to 6.00–2.08 lx and disappeared with increasing illuminance. The RI and SS increased at the fast flow velocity (0.25 m/s) for both species, and SC was more forward‐prone and more stable than GC. Despite the fluctuating light preference, the higher illuminances heightened the RI and SS in SC, while in GC, higher illuminances inhibited the SS and had no impact on the RI. The results of PMf‐0.1 and PMb‐0.1 indicated that a higher flow velocity could facilitate the temporary upstream swimming in both species, while illuminance could only promote the same effect in SC. Finally, our study proposed possible manoeuvres in fine‐scale spatio‐temporal scenarios such as attraction flow and non‐traditional passages and provided valuable insights into fish community dynamics, laying the groundwork for alleviating the threat from invasive species and for future fish population recovery.

Effects of marine protected areas on fish communities in a hotspot of climate change and invasion

The positive ecological effect of fully protected Marine Protected Areas (MPAs) on fish populations has been widely explored. Key indicators of fully protected MPAs effectiveness include an increase in biomass, density, and body size of commercially exploited large fishes. Fully protected MPAs are also hypothesized to be more resilient to both marine invasions and ocean warming, but this has seldom been tested. The eastern Mediterranean (Levantine) basin is the warmest region in the Mediterranean. Moreover, this region is the front-line of biological invasion from the Red Sea via the Suez Canal. Thus, MPAs in this region are faced with both high numbers of exotic species and warm temperatures. Assessing the performance of MPAs in this region is important for understanding their effectiveness under adverse future conditions worldwide. The ecological effectiveness of four MPAs along the Levantine Israeli coast was followed along over five years and compared with adjacent fished control area. Sampling was conducted in both old (>20 years of enforcement) and young MPAs, which only recently became fully protected. Using SCUBA diving surveys, 978 visual transects were performed to assess fish abundance, size, and diversity. We found clear indications for the benefits of the MPAs as evident by higher numbers of large fishes and groupers within protected areas. In the largest and oldest MPA we also found higher total and commercial fish biomass. In addition, we show a clear increase in the number of groupers over time, both within and outside MPAs, that may be associated with increased fishing regulation and enforcement. We found no clear evidence for a lower number of exotic species within MPAs. Our findings suggest that restrictions on recreational and commercial fishing within MPAs benefit the recovery of fish populations even in warm waters and when faced with marine invasions, and that the effectiveness of MPAs may be evident after only a few years of protection.

Slow Recovery of Headwater-Stream Fishes Following a Catastrophic Poisoning Event

Abstract Accidental spills of chemicals and other pollutants can decimate populations of stream-dwelling species. Recovery from such accidents can be relatively fast and complete when the affected stream reaches can be recolonized from upstream and downstream sources. However, faunal recoveries from accidental spills that extirpate populations from entire headwater streams have not been extensively documented, and understanding resilience of headwater-stream biota is relevant for assessing threats to at-risk species. We assessed recovery of fish populations in a 5.7-km-long headwater stream in the southeastern United States following a complete, or nearly complete, fish-kill caused by a chemical spill near the source of the stream. We sampled for fishes at five stream locations, two downstream and three upstream from a perched, culverted road-crossing located 2.4 km upstream from the stream mouth, over a period of 18.5 mo following the poisoning event. We observed 11 fish species, representing ≤65% of the fish species expected based on occurrences in nearby tributary streams. In postpoisoning sampling, only three of these taxa were observed upstream of the culvert; all 11 species, including the federally threatened Cherokee Darter Etheostoma scotti, were found downstream of the culvert but were mostly represented by a few, large individuals. In contrast, dead individuals of at least eight taxa including the Cherokee Darter were observed upstream of the culvert at the time of the fish-kill. These observations provide evidence of slow recovery of a headwater fish fauna, and especially upstream of a barrier to fish movement, where the recolonization sources are primarily downstream. Additional case studies may reveal whether this result applies generally to headwater streams. Slow recovery could make species that primarily inhabit or maintain greatest abundances in headwaters, including multiple at-risk fishes, particularly vulnerable to the threat of accidental spills that result in local population extirpation.

Rapid recovery of normal gill morphology and blood physiology in brown trout (<em>Salmo trutta</em>) after short-term exposure to toxic concentrations of aqueous aluminium under non-steady state chemical conditions

Freshwater acidification is characterised by elevated concentrations of aqueous aluminium. Global emissions of acidifying agents are reduced due to international agreements, and freshwater acidification has shifted from chronic to a more episodic character. The recovery of fish populations in acidified areas is likely to depend on the individual’s ability to recover from short-time aluminium exposures. We exposed brown trout (Salmo trutta) to an Al-rich medium, nominal concentration 600 µg L–1, for 0.5, 2, 6, 8 and 11 hours, before transfer to circumneutral Al-poor water for recovery. As controls, fish were either exposed for 11 hours to an acidified Al-poor medium or to untreated water. Some mortality during the first 24 hours of the recovery period occurred in fish exposed for 11, 8 and 6 hours to aluminium. No mortality during recovery was observed in the remaining groups. Aluminium exposure led to increased haematocrit and plasma lactate concentration, decreased plasma chloride concentration, deposition of aluminium on gill surfaces, and morphological alteration of the gill structures. The responses depended on exposure time. Aluminium deposited on the gill disappeared and plasma lactate levels were at control levels after 1 day in the recovery water, while haematocrit and plasma chloride levels were at control levels after 14 days of recovery. Gills in fish exposed to aluminium for 11 hours were almost fully recovered after 14 days. We conclude that the toxic response in brown trout exposed to an acutely toxic aluminium challenge is reversible. Moreover, the first 24 hours after aluminium exposures is the most critical period for the fish recovery. Further, it takes no more than 14 days for brown trout to fully recover from an acute toxic aluminium exposure, and only 1 day if the aluminium challenge is moderate.

The importance of biophysical context in understanding marine protected area outcomes for coral reef fish populations

Multiuse marine protected areas (MPAs) that utilize a mosaic of no-take and sustainable use zones are an increasingly common tool for promoting fish population recovery while minimizing socioeconomic conflict. However, significant gaps remain in our understanding of the effects of multiuse MPAs on reef-fish populations, and how protection from fishing may interact with biophysical gradients to drive ecological outcomes. Here, we examine changes in fish assemblages inside and outside of two multiuse MPAs in Raja Ampat, Indonesia, over the first four to five years after their implementation. We use linear models to assess the impact of protection status, anthropogenic pressure, and biophysical gradients on changes in four biological metrics: abundance, biomass, mean size, and size-spectra. In addition, we use multivariate analyses to assess whether fish assemblages in protected and unprotected reefs diverged after MPA establishment. We find that both fish abundance and biomass were driven equally or more by benthic characteristics than protection status and that these environmental impacts were decoupled from the effects of MPAs. Contrary to expectations, increases in abundance were more pronounced in unprotected reefs, where fish assemblages diverged from protected reefs through an increase of herbivorous parrotfishes (Subfamily Scarinae) likely driven by increased algal production on hard-bottom reef areas. However, mean size and size-spectra improved in sustainable use zones compared to unprotected reefs, demonstrating that non-exclusionary management can provide ecological benefits, especially when combined with nearby no-take areas. Increased mean size was also associated with lower human population sizes, suggesting a strong influence of fishing pressure, which is mediated by MPAs. Our findings suggest that multiuse MPAs can quickly achieve some fisheries management objectives and that these effects are likely to increase over longer timescales. However, biophysical context can have significant impacts on reef-fish assemblages that are distinct from the effects of overlying fisheries management.

Automatic detection and classification of fish calls in the Northern Gulf of Mexico using energy detectors and a convolutional neural network

Long-term passive acoustic monitoring datasets can require substantial effort for manual analysis; therefore, automatic methods are a more effective way to conduct these analyses and extract calls of interest. In this study, acoustic recordings from the northern Gulf of Mexico, about 60 km north of the 2010 Deepwater Horizon oil spill location, collected between July 2010 and May 2017 were analyzed to determine if fish call abundance has changed after the oil spill. An energy detector was created to extract six likely fish calls found in these data and a neural network was subsequently applied to classify the detections into different call categories. Data augmentation and iterative training were used to optimize classification and compensate for the low number of training images for a couple call types. Daily, monthly, and yearly patterns in calls were investigated and a hypothesis was tested that there was an increase in call abundance over time, indicating recovery of fish populations since the oil spill. Such long-term studies demonstrate that PAM can be used as a population assessment tool for fisheries management.

Protecting nursery areas without fisheries management is not enough to conserve the most endangered parrotfish of the Atlantic Ocean

Marine protected areas (MPAs) are a primary strategy for marine conservation worldwide, having as a common goal the protection of essential habitats to enhance fish population recovery. However, MPAs alone may not be effective because species are not isolated from critical impacts occurring outside their boundaries. We evaluated how protecting critical nursery habitats affect the population of an important fishing target, using a 6-year database to predict juvenile hotspots and estimate population trends of the endemic and endangered parrotfish Scarus trispinosus within a mosaic of MPAs at the Abrolhos Bank, NE Brazil. We found that important nursery habitats are within no-take areas, but both juvenile and adult populations still show a declining trend over time. MPAs failed to ensure population maintenance and recovery likely due to overfishing in adjacent areas and the lack of compliance to management rules within multiple-use and within no-take MPAs. MPAs alone are not enough to protect ecologically important endangered species, but is still one of the only conservation strategies, particularly in developing countries. Our results shed light on the need for a wider adoption of more effective conservation policies in addition to MPAs, both in Brazil and in countries with similar governance contexts.

Population Dynamics of Sex‐Changing Fish Species in Marine Protected Areas

Easter et al. used population models to analyze the expected pattern of recovery of sex-changing fish populations inside marine protected areas (MPAs). Many fishes begin life female and then change to male when older. In these female-first (protogynous) species, harvest tends to selectively remove males, shifting sex ratios and impairing reproduction. Setting expectations for population recovery inside MPAs requires understanding how quickly sex ratios (and reproduction) rebound. Easter et al. show that whether sex-changing populations recover faster or slower than non-sex-changing species depends on how many males a population needs for successful reproduction. This quantity can be estimated using field experiments. These photographs illustrate the article “Influence of protogynous sex change on recovery of fish populations within marine protected areas” by E. E. Easter, M. S. Adreani, S. L. Hamilton, M. S. Steele, S. Pang, and J. W. White published in Ecological Applications. https://doi.org/10.1002/eap.2070

Influence of protogynous sex change on recovery of fish populations within marine protected areas.

Marine protected areas (MPAs) are increasingly implemented as a conservation tool worldwide. In many cases, they are managed adaptively: the abundance of target species is monitored, and observations are compared to some model-based expectation for the trajectory of population recovery to ensure that the MPA is achieving its goals. Most previous analyses of the transient (short-term) response of populations to the cessation of fishing inside MPAs have dealt only with gonochore (fixed-sex) species. However, many important fishery species are protogynous hermaphrodites (female-to-male sex-changing). Because size-selective harvest will predominantly target males in these species, harvesting not only reduces abundance but also skews the sex ratio toward females. Thus the response to MPA implementation will involve changes in both survival and sex ratio, and ultimately reproductive output. We used an age-structured model of a generic sex-changing fish population to compare transient population dynamics after MPA implementation to those of an otherwise similar gonochore population and examine how different features of sex-changing life history affect those dynamics. We examined both demographically open (most larval recruitment comes from outside the MPA) and demographically closed (most larval recruitment is locally produced) dynamics. Under both scenarios, population recovery of protogynous species takes longer when fishing was more intense pre-MPA (as in gonochores), but also depends heavily on the mating function, the degree to which the sex ratio affects reproduction. If few males are needed and reproduction is not affected by a highly female-biased sex ratio, then population recovery is much faster; if males are a limiting resource, then increases in abundance after MPA implementation are much slower than for gonochores. Unfortunately, the mating function is largely unknown for fishes. In general, we expect that most protogynous species with haremic mating systems will be in the first category (few males needed), though there is at least one example of a fish species (though not a sex-changing species) for which males are limiting. Thus a better understanding of the importance of male fish to population dynamics is needed for the adaptive management of MPAs.

Where Predators and Prey Meet: Anthropogenic Contact Points Between Fishes in a Freshwater Estuary

The Sacramento–San Joaquin Delta has been invaded by several species of non-native predatory fish that are presumed to be impeding native fish population recovery efforts. Since eradication of predators is unlikely, there is substantial interest in removing or altering manmade structures in the Delta that may exacerbate predation on native fish (contact points). It is presumed that these physical structures influence predator-prey dynamics, but how habitat features influence species interactions is poorly understood, and physical structures in the Delta that could be remediated to benefit native fish have not been inventoried completely. To inform future research efforts, we reviewed literature that focused on determining the effects of predator-prey interactions between fish, based on contact points that are commonly found in the Delta. We also performed a geospatial analysis to determine the extent of potential contact points in the Delta. We found that the effects of submerged aquatic vegetation (SAV) and artificial illumination are well studied and documented to influence predation in other freshwater systems worldwide. Conversely, other common structures in the Delta—such as docks, pilings, woody debris, revetment, and water diversions—did not have the same breadth of research. In the Delta, the spatial extent of the different types of contact points differed considerably. For example, 22% of the Delta water surface area is occupied by SAV, whereas docks only cover 0.44%. Our conclusion, based on both the literature review and spatial analysis, is that the effects of SAV and artificial illumination on predation warrant the most immediate future investigation in the Delta.

Linking fisheries to land use: How anthropogenic inputs from the watershed shape fish habitat quality

Aquatic ecosystems are increasingly threatened by anthropogenic stressors, both at local and larger scales. For instance, runoff from intensively cultivated areas leads to higher nutrient and sediment concentrations deteriorating water quality, which potentially trigger trophic state changes. Unfortunately, we have a poor understanding of the complex relationships linking water quality degradation and different ecosystem components. Here we analyze the long-term cascading effects of several anthropogenic stressors on both submerged aquatic vegetation (SAV) and the key traits of an exploited yellow perch (Perca flavescens, YP) population from the watershed of Lake Saint-Pierre — the largest fluvial lake of the St. Lawrence River (Québec, Canada). Lake Saint-Pierre drains one of the most impacted watersheds in Eastern Canada and had sustained a YP fishery (worth up to 10 M$ CAN/year) until the population collapsed in the mid-1990s. SAV abundance has declined since the 1980s, partially overlapping with the YP collapse. Within a structural equation modeling framework, we tested the links between changes in both SAV abundance and the YP fishery with abiotic stressors acting at both local and larger scales. Our results show that both SAV and YP declines are causally associated with anthropogenic nutrient and sediment loadings from the watershed. The decline of YP landings is also explained by a reduction in SAV abundance and YP juvenile growth, mainly caused by a sharp decrease in water transparency over the last decades. These results suggest a causal association between environmental degradation due to nutrients and sediments and different components of the trophic aquatic network. Such an integrative approach is crucial for the development of management strategies that consider cultivated lands and aquatic systems as a continuum rather than separate compartments. SAV restoration is thus a critical feature contributing to water depuration and promoting the recovery of fish populations threatened by habitat degradation.

Automatic detection and classification of fish calls in the Northern Gulf of Mexico using energy detectors and a convolutional neural network

Passive acoustic monitoring (PAM) is a relatively low-cost way to collect long-term datasets of animal occurrence, which is particularly effective when the animals are not constantly present. However, these long datasets can require substantial effort for manual analysis; therefore, automatic methods are a more effective way to conduct these analyses and extract calls of interest. In this study, acoustic recordings from the northern Gulf of Mexico, about 60 km north of the 2010 Deepwater Horizon oil spill location, collected between July 2010 and May 2017 were analyzed to determine if fish call abundance and diversity has changed after the oil spill. An energy detector was created to extract seven likely fish calls found in these data and a neural network was subsequently applied to classify the detections into different call categories. Daily, monthly, and yearly patterns in calls were investigated and a hypothesis was tested that there was an increase in call abundance and diversity over time, indicating recovery of fish populations since the oil spill. Such long-term studies demonstrate that PAM can be used as a population assessment tool for fisheries management.

Managing dams for energy and fish tradeoffs: What does a win-win solution take?

Management activities to restore endangered fish species, such as dam removals, fishway installations, and periodic turbine shutdowns, usually decrease hydropower generation capacities at dams. Quantitative analysis of the tradeoffs between energy production and fish population recovery related to dam decision-making is still lacking. In this study, an integrated hydropower generation and age-structured fish population model was developed using a system dynamics modeling method to assess basin-scale energy-fish tradeoffs under eight dam management scenarios. This model ran across 150 years on a daily time step, applied to five hydroelectric dams located in the main stem of the Penobscot River, Maine. We used alewife (Alosa pseudoharengus) to be representative of the local diadromous fish populations to link projected hydropower production with theoretical influences on migratory fish populations on the model river system. Our results show that while the five dams can produce around 427 GWh/year of energy, without fishway installations they would contribute to a 90% reduction in the alewife spawner abundance. The effectiveness of fishway installations is largely influenced by the size of reopened habitat areas and the actual passage rate of the fishways. Homing to natal habitat has an insignificant effect on the growth of the simulated spawner abundance. Operating turbine shutdowns during alewives' peak downstream migration periods, in addition to other dam management strategies, can effectively increase the spawner abundance by 480–550% while also preserving 65% of the hydropower generation capacity. These data demonstrate that in a river system where active hydropower dams operate, a combination of dam management strategies at the basin scale can best balance the tradeoff between energy production and the potential for migratory fish population recovery.

Integrating Results of Field Biomonitoring and Mesocosm Experiments To Validate Postspill Impacts of Petroleum Hydrocarbons on Stream Benthic Communities.

We integrated the results of field surveys with a mesocosm experiment to quantify the ecological impacts of a gasoline and diesel spill on a third-order stream in western Colorado (United States). The spill caused a massive fish-kill of brown trout ( Salmo trutta) and mottled sculpin ( Cottus bairdii), which extended several kilometers downstream. Despite significant decreases in petroleum hydrocarbon concentrations, subsequent surveys indicated little recovery of fish populations 4 years after the spill. Benthic macroinvertebrate communities were also affected, yet some metrics commonly used to assess stream ecological integrity (e.g., total abundance and species richness) showed no difference between impacted and reference sites. The failure of some groups to recover 2.5 years after the spill was likely a result of their comparatively slow reproduction and recolonization rates. To support our hypothesis that effects observed in the field resulted from petroleum exposure, we conducted a mesocosm experiment in which benthic macroinvertebrate communities were exposed to a simulated diesel spill. We observed significant decreases in the abundance of most macroinvertebrate groups at the lowest exposure concentration (75 mg/L diesel) and a strong concentration-dependent drift response across all groups. Our study suggests that relatively small petroleum spills can significantly affect stream communities, and these effects may persist several years after sediment concentrations return to background levels.

Fine-scale genetic structure of rabbitfish, Siganus fuscescens, in Penghu Archipelago following a mass mortality event caused by extreme cold winter weather

In the winter of 2007–2008, a large number of fish were killed by chilling damage that occurred in the Pescadores (Penghu Archipelago). Such extreme weather events can cause rapid population changes, which provide an opportunity to understand the possible restoration mechanism of coral reef fishes in the Pescadores. The fine-scale genetic structure of the rabbitfish, Siganus fuscescens (Siganidae), was assessed using amplified fragment length polymorphism analysis. Significant genetic differences (lower gene flow) were observed between rabbitfish from the northern and southern parts of the Pescadores (Chenkong-Soukang, Φ ST 0.075, P < 0.001) but not between those from the northern Pescadores and northeastern Taiwan (Chenkong-Keelung, Φ ST 0.03, P > 0.02). The northern Pescadores and northeastern Taiwan have been shown to be relatively connected. The population structure of rabbitfish has complemented and helped support fish population recovery after several chilling events in the Pescadores.

The intrinsic vulnerability to fishing of coral reef fishes and their differential recovery in fishery closures

Coral reef fishes differ in their intrinsic vulnerability to fishing and rates of population recovery after cessation of fishing. We reviewed life history-based predictions about the vulnerability of different groups of coral reef fish and examined the empirical evidence for different rates of population recovery inside no-take marine reserves to (1) determine if the empirical data agree with predictions about vulnerability and (2) show plausible scenarios of recovery within fully protected reserves and periodically-harvested fishery closures. In general, larger-bodied carnivorous reef fishes are predicted to be more vulnerable to fishing while smaller-bodied species lower in the food web (e.g., some herbivores) are predicted to be less vulnerable. However, this prediction does not always hold true because of the considerable diversity of life history strategies in reef fishes. Long-term trends in reef fish population recovery inside no-take reserves are consistent with broad predictions about vulnerability, suggesting that moderately to highly vulnerable species will require a significantly longer time (decades) to attain local carrying capacity than less vulnerable species. We recommend: (1) expanding age-based demographic studies of economically and ecologically important reef fishes to improve estimates of vulnerability; (2) long term (20–40 years), if not permanent, protection of no-take reserves to allow full population recovery and maximum biomass export; (3) strict compliance to no-take reserves to avoid considerable delays in recovery; (4) carefully controlling the timing and intensity of harvesting periodic closures to ensure long-term fishery benefits; (5) the use of periodically-harvested closures together with, rather than instead of, permanent no-take reserves.