Responses Of Fish Populations Research Articles

Ecological Restoration and Large‐Scale Ecological Disturbance: The Effects of Drought on the Response by Fish to a Habitat Restoration Experiment

Abstract Human‐induced erosion regularly delivers massive quantities of fine sediments into streams and rivers forming large static bodies of sediment known as sand slugs, which smother in‐stream habitat, alter community structure, and decrease biodiversity. Sand slugs are widespread in parts of southeastern Australia as well as in many other parts of the world, and there is now considerable interest in restoring such affected streams. The reintroduction of large timber is widely suggested as a strategy for restoring habitat complexity, but this has rarely been tested in sand slug–affected streams. We examined the response of fish populations to wood addition to two streams in southeastern Australia that have been impacted by sand slugs. Manipulated sites (three per treatment) had either one or four timber structures added, and these sites were compared with (three) unmanipulated (control) sites before and after the manipulation occurred. Despite a supraseasonal drought during the study, we observed short‐term increases in the abundance of Mountain galaxias (Galaxias olidus) at the four‐structure sites, while both the four‐structure and the one‐structure treatments appeared to buffer against drought‐induced declines in two other species, River blackfish (Gadopsis marmoratus) and Southern pygmy perch (Nannoperca australis), relative to controls. However, drought eventually caused the complete loss of surface water from these streams and the loss of fish from both manipulated and unmanipulated sites. Thus, although the study supports the use of timber structures as a means of increasing local fish abundances, these beneficial effects were, in these streams, contingent upon permanency of flow. Because sedimentation has depleted the number of permanent refuge pools in these creeks, recovery rates of the fauna (i.e., resilience) are likely to be slow. We therefore conclude that in streams subjected to frequent disturbance, restoring refugia may be as, if not more, important as restoring what we term residential habitat.

An approach to effectiveness monitoring of floodplain channel aquatic habitat: salmonid relationships

Rivers and streams that support anadromous salmonids are an important part of land management planning in southeastern Alaska and the Pacific Northwest of North America. Land managers and planners require a consistent set of protocols that include both the physical and biological aspects of the stream for effectiveness monitoring procedures to evaluate management activities in forested watersheds. We apply a quantitative method to estimate salmonid populations and link these estimates to a set of physical variables used in an assessment of channel condition at the reach scale. We are able to obtain precise estimates of juvenile salmonid populations at the habitat and reach scale; however, we find a lack of strong relationships between channel condition variables and salmonid densities. Nonetheless, a few trends appear, such as relationships between coho salmon and both pools and large wood. A significant and positive relationship exists between coho salmon fry density and two measures of pool frequency. Our results suggest that the response of fish populations to changes in the amount and quality of habitat can be measured by using the tested procedures. Complexity in habitat use, seasonal effects, and external factors tend to mask close relationships between fish populations and physical variables. We also discuss the implications for trophic status for fish populations and how this information may provide a more robust evaluation of land management activities on the aquatic biota in managed watersheds.

A fossil record of colonization and response of lacustrine fish populations to climate change

To study fish species colonization and the response of populations to climate change, we reexamined a well-preserved late Pleistocene to early Holocene fossil fish assemblage from lake deposits on the Missouri Coteau, North Dakota. The fossil fishes in the assemblage include complete specimens of yellow perch (Perca flavescens), brassy minnow (Hybognathus hankinsoni), blacknose shiner (Notropis heterolepis), banded killifish (Fundulus diaphanus), and brook stickleback (Culaea inconstans). The sequence of colonization is explained by individual thermal and relative water velocity tolerances for each species. There are six peaks in fish abundance during approximately 1000 years, indicating a response to environmental perturbations. Charcoal deposition from fires is inferred to represent episodic droughts during which nutrient levels were reduced and fish abundance declined. The fluctuations follow an overall trend of increased fish abundance during a time when lake-marginal vegetation changed from a spruce to a deciduous forest in response to climatic warming. This study provides insight into the complex effects of a changing climate on fish populations and demonstrates the potential of using fossils to examine the long-term abundance patterns of contemporary fish species.

Responses of wild fishes to alarm chemicals in pristine and metal-contaminated lakes

Responses of wild fish populations to alarm chemicals were examined in clean and metal-contaminated lakes in northern Ontario. Approximately 20 groups of three minnow traps were placed randomly in the littoral zone of each study lake. Within each minnow trap group, one trap was treated with a chemical alarm stimulus (Iowa darter (Etheostoma exile (Girard, 1859)) skin extract, prey-guild species, alarm cue present), one with swordtail (Xiphophorus helleri Heckel, 1848) skin extract (phylogenetically distant and allopatric from darters, alarm cue present but not recognized by darters), and one with distilled water (neutral control). Data included the identification and enumeration of fish captured in each trap after a 10-h set. Darters avoided areas labelled with the alarm stimulus relative to controls only in the clean lake; in contaminated lakes, darters did not avoid areas labelled with the alarm stimulus relative to controls. No effects of contamination on chemosensory function were observed for heterospecific non-darter prey-guild or predator-guild species. These findings suggest that chemical alarm systems do exist in nature, and that these systems appear to be affected by the presence of metals. Such pollution-related effects could lead to increased susceptibility of some fish species to predation and to population declines.

FLOW AND HABITAT EFFECTS ON JUVENILE FISH ABUNDANCE IN NATURAL AND ALTERED FLOW REGIMES

Conserving biological resources native to large river systems increasingly depends on how flow-regulated segments of these rivers are managed. Improving management will require a better understanding of linkages between river biota and temporal variability of flow and instream habitat. However, few studies have quantified responses of native fish populations to multiyear (>2 yr) patterns of hydrologic or habitat variability in flow-regulated systems. To provide these data, we quantified young-of-year (YOY) fish abundance during four years in relation to hydrologic and habitat variability in two segments of the Tallapoosa River in the southeastern United States. One segment had an unregulated flow regime, whereas the other was flow-regulated by a peak-load generating hydropower dam. We sampled fishes annually and explored how continuously recorded flow data and physical habitat simulation models (PHABSIM) for spring (April–June) and summer (July–August) preceding each sample explained fish abundances. Patterns of YOY abundance in relation to habitat availability (median area) and habitat persistence (longest period with habitat area continuously above the long-term median area) differed between unregulated and flow-regulated sites. At the unregulated site, YOY abundances were most frequently correlated with availability of shallow-slow habitat in summer (10 species) and persistence of shallow-slow and shallow-fast habitat in spring (nine species). Additionally, abundances were negatively correlated with 1-h maximum flow in summer (five species). At the flow-regulated site, YOY abundances were more frequently correlated with persistence of shallow-water habitats (four species in spring; six species in summer) than with habitat availability or magnitude of flow extremes. The associations of YOY with habitat persistence at the flow-regulated site corresponded to the effects of flow regulation on habitat patterns. Flow regulation reduced median flows during spring and summer, which resulted in median availability of shallow-water habitats comparable to the unregulated site. However, habitat persistence was severely reduced by flow fluctuations resulting from pulsed water releases for peak-load power generation. Habitat persistence, comparable to levels in the unregulated site, only occurred during summer when low rainfall or other factors occasionally curtailed power generation. As a consequence, summer-spawning species numerically dominated the fish assemblage at the flow-regulated site; five of six spring-spawning species occurring at both study sites were significantly less abundant at the flow-regulated site. Persistence of native fishes in flow-regulated systems depends, in part, on the seasonal occurrence of stable habitat conditions that facilitate reproduction and YOY survival.

Detecting Fish Population Responses to a Minimum Length Limit: Effects of Variable Recruitment and Duration of Evaluation

Abstract We used a simulation model to evaluate how recruitment variability and evaluation duration would affect fisheries managers' ability to detect fish population responses to a minimum length limit. Length limits modeled were 254 mm for white crappie Pomoxis annularis and 305, 356, and 457 mm for largemouth bass Micropterus salmoides. Simulations were conducted at recruitment variation (coefficient of variation, CV = 100 × SD/mean) of 20–100% for age-1 recruits. We evaluated how population density, population biomass, total catch (fish harvested and released), yield, and proportional stock density (PSD) would differ in response to a single 3-year or 5-year length limit evaluation. For white crappies, simulations suggested that a 254-mm length limit would not provide detectable differences (P > 0.10) in any population parameter if recruitment variability exceeded 90% for either evaluation period. Mean CV in recruits to age 0 or age 1 for empirical white crappie populations was 82% (range = 55–124, N =...

Simulation analysis of evolutionary response of fish populations to size-selective harvesting with the use of an individual-based model

Many studies have been devoted to analyze data and/or discuss theory addressing the potential evolutive impacts of anthropogenic exploitation in fish populations. However, not many conclusions about the nature of long term changes in fish populations have been derived from wild population observations. Simulation models can help to identify factors that play important roles in the evolution of fish through genetic change. The objective of this paper is to present an individual-based model with a genetic component using parameters common to fish population dynamics. Such a model could help us gain insight in the impact of selective fishing mortality on the characteristics of the progeny through genetic based changes. The model deviates from quantitative genetics on its handling of trait inheritance. It also establishes a link between large scale population dynamic processes such as recruitment and the contribution of individual fish to the spawning stock biomass (SSB) and the resulting distribution of trait inheritance. The model uses parameter values for cod ( Gadus morhua) from the literature to simulate four exploitation scenarios. The results indicate that smaller length-at-maturity, slower growth to smaller sizes and higher fecundity would be advantageous traits for adult survival under exploitation. However, the magnitude of such evolutive trend was very small with deterministic recruitment. Moreover, the effect of the selective forces determining the successful traits to be passed to the offspring was weakened even further under stochastic recruitment.

Individual-based model of sympatric populations of brown and rainbow trout for instream flow assessment: model description and calibration

This paper describes an individual-based model of sympatric populations of brown and rainbow trout in a stream habitat. The model provides a tool for projecting flow and temperature effects on trout populations by linking the hydraulic component of the instream flow incremental methodology/physical habitat simulation system (IFIM/PHABSIM) to an individual-based population model. PHABSIM simulates the spatial distribution of depth and velocity at different flows, and indirectly, the availability of spawning habitat, cover and feeding station. The individual-based model simulates reproduction, growth and mortality of individual trout as a function of flow and temperature. Population dynamics arise from the survival and reproduction of individual trout. The spatially explicit nature of the model permits evaluation of behavioral responses used by fish to changes in physical habitat. The model has been calibrated to a stream segment in the North Fork Middle Fork Tule River, California. Selected parameters were adjusted to calibrate the model for length and abundance (including production of a new year class) at the end of 1-year simulations for each of 9 years. Predicted and observed lengths were in good agreement, although neither varied appreciably among years. Predicted and observed abundances were not in as good agreement, and differed considerably for some years. These differences reflect a combination of uncertainties in the field data and uncertainties in the model structure and parameter values. Fifty-year simulations indicated that model projections of length and abundance were stationary, although abundance values fluctuated considerably. Seven advantages for using simulation models of this type are emphasized. How to most effectively interpret results from such simulation models as part of instream flow environmental assessments remains a challenge. Variability and uncertainty in both field data and replicate model simulations are realities that have implications for scientists, resource managers, and regulators in projecting growth and abundance responses of fish populations to alternative flow or temperature regimes.

Predator recognition and anti-predator responses in the rainbowfish Melanotaenia eachamensis

Predator evasion behaviour patterns of three populations of rainbowfish (Melanotaenia eachamensis) were compared. The populations differed in the level of complexity of their natural habitats and the type and extent of predation. The predator recognition abilities of fish were assessed by exposing them to models differing in their degree of predator realism. The availability of vegetated cover and the location of the models with respect to cover were manipulated. Fish from Lake Tinaroo, a relatively open habitat containing numerous predators, showed strong changes in elective group size (EGS) in response to the different models but did not rely on cover as a place of refuge. In contrast, Dirran Creek fish originate from a small, fast-flowing, structurally complex stream lacking predatory fish species, and they showed little ability to distinguish between the different models and responded to threat by spending longer in vegetated areas. Members of the Lake Eacham captive stock increased their EGS in response to models representing low threat and with more threatening models increased the amount of time spent in vegetated regions of the arena. The contrasting reactions to predatory threat displayed by these populations highlights the need to use a number of different response indices when comparing the anti-predator responses of different fish populations. These data suggest that the level of habitat complexity as well as prior predator experience influence anti-predator responses of different fish popu-lations.

Changes in the Habitat and Fish Community of the Milwaukee River, Wisconsin, Following Removal of the Woolen Mills Dam

We evaluated the response of fish habitat, biotic integrity, and populations of smallmouth bass Micropterus dolomieu and common carp Cyprinus carpio to the 1988 removal of the low-head Woolen Mills Dam from the Milwaukee River. After dam removal, instream habitat improvement work was done on a portion of river within the former impoundment, and a short reach just below the dam site was rerouted for bridge construction. Before dam removal in 1988, the two stations in the impounded reach of the river had fair habitat quality, few smallmouth bass, abundant common carp, and poor biotic integrity. Five years after dam removal, habitat quality was good to excellent, smallmouth bass abundance and biomass had increased substantially, common carp abundance and biomass had declined dramatically, and biotic integrity was good. A reference station on the nearby North Branch of the Milwaukee River had few major changes over the same time period, although common carp abundance and biomass did decline somewhat. Stations upstream and downstream of the impounded reach also experienced moderate declines in common carp populations, and the upstream station had a major increase in smallmouth bass abundance and biomass. Changes in size structure suggested that the smallmouth bass increases in the impounded and upstream stations were caused by increased recruitment rather than by permanent migration of fish from other areas. Habitat quality within the impounded reach increased more and faster in the station with instream improvement work, but the station without work also showed substantial gains in habitat quality through natural channel recovery processes. The station downstream from the dam experienced major declines in its smallmouth bass population and biotic integrity during channel rerouting in 1990. However, by 1993, both attributes had returned to 1988–1989 levels. We conclude that dam removal benefited habitat, fisheries potential, and biotic integrity in the Milwaukee River. Direct habitat improvement activities enhanced these benefits, but natural habitat recovery and removal of the dam as a barrier to fish movement accounted for many of the improvements we observed.

IMPORTANCE OF THE TEMPORAL ASPECTS OF HABITAT HYDRAULICS TO FISH POPULATION STUDIES

The direct and indirect influences of hydrology and hydraulics on the usability of stream habitats by stream fish are discussed. Most habitat–hydraulic models in use today emphasize the spatial aspects of habitat quality and quantity. It is our contention that the temporal dynamics of habitat quantity are a major influence, determining fish population responses in riverine environments. This may manifest through dramatic shifts in the velocity and temperature distributions over seasons and years as influenced by climatic conditions as well as reservoir operations. Time series simulations of usable habitat available to various life stages of brown and rainbow trout and smallmouth bass populations demonstrate that the usable space and its stability during the early life history is directly translated into year-class-strength for these fish populations. Riverine ecosystems are temporally dynamic due to the stochastic nature of precipitation events. Therefore an understanding of the temporal aspects of streamflow and habitat is essential to designing water management schemes intended to protect, enhance or restore riverine fish populations.

Fish population responses to stream habitat improvement in a concrete-lined channel.

Fish population responses to stream habitat improvement in a concrete-lined channel.

Effects of Fishing on the Ecosystem Structure of Coral Reefs.

Overfishing is considered one of the three most significant threats to coral reef ecosystems. Exponentially increasing human populations in the tropics have placed enormous demands upon reefs as a food source. At high intensities, termed ecosystem or Malthusian overfishing, fishing causes major direct and indirect effects on the community structure of fishes and other organisms. It reduces species diversity and leads to local extinctions not only of target species but also of other species not fished directly. Conceivably it could also lead to global extinctions. Loss of keystone species, such as predators of echinoderms, through fishing, can lead to major effects on reef processes, such as accretion of calcium carbonate. Ultimately, sustained heavy fishing may lead to loss of entire functional groups of species, resulting in impairment of the potentially important ecosystem functions provided by those groups. Overfishing has been shown to interact with other agents of disturbance to reduce the ability of reefs to recover from natural occurrences such as hurricanes. Effective management of fishing will require a deeper understanding of the effects of exploitation than we now possess. Research initiatives are underway to examine the responses of fish populations to fishing, generally responses to protection from fishing. There is, however, an urgent need to look beyond fish communities and to consider the entire reef ecosystem. Studies that integrate population and community biology with ecosystem processes will provide a much better understanding of the effects of biodiversity loss on reef function and will improve our ability to manage these complex systems. Efecto de la pesca sobre la estructura ecosistémica de los arrecifes de coral.

Rapid Build‐up of Fish Biomass in a Caribbean Marine Reserve

Marine reserves, where fishing is excluded, have been argued to be an effective means of managing complex reef fisheries and of protecting populations of species vulnerable to overfishing. The argument rests on predictions of increases in abundance and size of fishes after the elimination of fishing mortality, which in turn leads to greater egg production per unit of reef and greater export via pelagic dispersal to fishing grounds. This study reports responses of fish populations to area closure in a small Caribbean marine reserve surrounding the island of Saba in the Netherlands Antilles. Part of the reserve has been closed to fishing since 1987, and the remainder is subject only to light fishing. Fish populations were visually censused and sizes of individuals present estimated from counts in fished and unfished areas of the marine park in 1991 and 1993. For four of five commercially fished families, biomass was greater in the unfished area than in the fished. Predictions of greater abundance and size in the unfished area were upheld for many of the species observed. Between 1991 and 1993 overall biomass of commercially important families increased 60%, based largely on increases in abundance between years. The predatory snappers (Lutjanidae) increased 220%. Fishing pressure in Saba was reduced between censuses due to changing employment opportunities. It was notable that populations increased in both fished and unfish ed areas of the park, and the latter is probably an effect of this reduced fishing intensity. Reserves have been suggested as refuges for species vulnerable to overexploitation, especially groupers. Despite protection from fishing, the Saba Marine Park has low population densities of such species, perhaps due to a lack of supply of larvae from unprotected source areas. My study shows that target fish populations may respond swiftly to reductions in fishing pressure and that reserves could play an important role in fisheries management. But protection of vulnerable species is only likely to be successful if networks of reserves are established throughout species ranges to link larval supply and settlement areas.

Application of canonical variate analysis in the evaluation and presentation of multivariate biological response data

AbstractWe have applied canonical variate analysis procedures for evaluating multivariate responses of fish populations to various contaminant stressors. Using examples of fish populations experiencing high levels of PCBs in a reservoir and mixed contaminants in a stream, the significance of integrated stress responses among sample populations was compared statistically and graphically using two‐ and three‐dimensional data presentations. For fish from both systems, the most powerful axis of discrimination among sample populations was correlated with the activity of the detoxification enzyme, EROD (7‐ethoxyresorufin O‐deethylase). Indicators of organ dysfunction were the variables most correlated with the second axis of discrimination among sites in the PCB‐contaminated reservoir study. Indicators of lipid metabolism were the variables most correlated with the second and third axes of discrimination among stream fish. Canonical variate analysis procedures are useful for evaluating multivariate response data because they take into account the interrelations and associations among response variables and reveal the integrated nature of organism responses to stress. Using this procedure, the significance of integrated stress responses among different sample populations can be graphically compared and evaluated using two‐ or three‐dimensional data presentations. These types of graphical displays help provide an understanding of the relationships among sample populations that may not be evident from tabular or other types of data summaries. In addition, this approach can be useful in helping to identify factors such as toxicants or other environmental stressors which impair the health of aquatic ecosystems.

A sentinel monitoring framework for identifying fish population responses to industrial discharges

We previously proposed a classification scheme to describe the responses of fish populations to anthropogenic stress. The original framework separated impacted populations into five response patterns, but had several limitations and deficiencies, including the subsequent description of additional patterns and the absence a pattern reflecting no detectable response of the population. The response framework has been reorganized based on new information and response patterns described in published literature. The sentinel monitoring framework provides a tool for initial interpretation of adult fish surveys and description of priority areas for subsequent studies to allow identification of the mechanism of impact. Subsequent, focused, follow-up studies are required to identify the stressor(s) once the impact mechanism has been identified. Response pattern separation requires information from the sampled fish population including age structure, energy expenditure and energy storage. The patterns represent characteristic responses to changes in food availability, adult mortality, recruitment failure and metabolic disruption. The framework requires the identification and appropriate sampling of comparable reference sites, but the sentinel monitoring framework has proved to be a useful tool in preliminary trials, and should provide a focal point for cumulative effects studies using fish populations.

APPLICATION OF CANONICAL VARIATE ANALYSIS IN THE EVALUATION AND PRESENTATION OF MULTIVARIATE BIOLOGICAL RESPONSE DATA

We have applied canonical variate analysis procedures for evaluating multivariate responses of fish populations to various contaminant stressors. Using examples of fish populations experiencing high levels of PCBs in a reservoir and mixed contaminants in a stream, the significance of integrated stress responses among sample populations was compared statistically and graphically using two- and three-dimensional data presentations. For fish from both systems, the most powerful axis of discrimination among sample populations was correlated with the activity of the detoxification enzyme, EROD (7-ethoxyresorufin O-deethylase). Indicators of organ dysfunction were the variables most correlated with the second axis of discrimination among sites in the PCB-contaminated reservoir study. Indicators of lipid metabolism were the variables most correlated with the second and third axes of discrimination among stream fish. Canonical variate analysis procedures are useful for evaluating multivariate response data because they take into account the interrelations and associations among response variables and reveal the integrated nature of organism responses to stress. Using this procedure, the significance of integrated stress responses among different sample populations can be graphically compared and evaluated using two- or three-dimensional data presentations. These types of graphical displays help provide an understanding of the relationships among sample populations that may not be evident from tabular or other types of data summaries. In addition, this approach can be useful in helping to identify factors such as toxicants or other environmental stressors which impair the health of aquatic ecosystems.

Responses of fish populations and communities to pulp mill effluents: A holistic assessment

Fish populations residing in a river receiving bleached kraft mill effluents (BKME) and in an uncontaminated river were investigated to evaluate causal relationships between exposure to BKME and various indicators of fish health. The Index of Biotic Integrity demonstrated that species richness and composition were much lower in the contaminated river with an obvious imbalance in the trophic structure of the fish community. Biomolecular and biochemical responses such as DNA damage and elevated activity of detoxification enzymes indicated that fish in the contaminated river had been exposed to toxicants. The status of various condition indices such as the liver and visceral somatic indices suggested metabolic and nutritional imbalances in sunfish as a result of exposure to pulp mill effluents. Fish populations in the contaminated river also demonstrated an abnormal size distribution and age structure. Female redbreast sunfish from the BKME-impacted river contained a large number of atretic oocytes and had lower serum levels of estradiol than fish from the reference site. These observations plus data from previous developmental toxicity studies suggest that the primary mechanism by which BKME may affect fish populations in this river is through reproductive dysfunction and recruitment failure. Decreased recruitment may have caused a reduction in population size and resulted in decreased competition and increased resource availability. With increased food and habitat availability, more energy may have been available for growth and lipid storage of survivors in the contaminated river.

Relationships between physiological and fish population responses in a contaminated stream

AbstractRelationships between toxicant exposure, physiological effects, and population‐level responses were investigated in redbreast sunfish (Lepomis auritus) from a stream receiving chronic inputs of mixed contaminants. Elevated levels of detoxification enzymes, which provided evidence of direct toxicant exposure, were associated with low lipid levels, histopathological damage, and reduced growth for fish at the upper three sites in the contaminated stream. Decreased fecundity, exhibited by fish at the upper site, might have been due to the reduced capacity of the liver to manufacture yolk proteins. Reduction in lipid pools due to metabolic drains might have decreased the amount of physiological useful energy needed for growth resulting in smaller age‐specific sizes of fish at the upper three sites. This approach for investigating relationships between contaminant exposure, physiological effects, and population‐level responses such as growth and size distributions could serve as a model for designing biomonitoring studies and for stimulating further research to improve our ability to evaluate the ecological significance of chronic contaminant stressors on aquatic ecosystems.

Simulation of fish population responses to exploitation

A model that couples Larkin's predator-prey model, Ivlev's feeding model, Ursin's growth equation and the exponential mortality model was applied for simulation of the responses of fish populations to exploitation. Simulations were done without food-limited growth, with food-limited growth, with food limited growth and size-specific mortality, and with food-limited growth and age at maturity a function of size. Without food-limited growth there was no compensation for exploitation and the population became extinct with an increase in mortality. With food-limited growth the population compensated for fishing mortality; as abundance decreased, size increased, and production of eggs by the population increased. With either mortality or age at maturity a function of size, compensation was much higher than with food-limited growth alone. Recruitment decreased with increase in exploitation. There was an association between numbers of spawners and recruits, but both the number of spawners and the number of recruits were determined by food limited growth. If age at maturity is a function of size, there are fluctuations in population abundance when fishing mortality is low, but not when fishing mortality is high.