Fish Recovery Research Articles

Conflicts between Native Fish and Nonnative Sport Fish Management in the Southwestern United States

The ubiquitous presence of nonnative fishes, both sport and nongame, within waters of the southwestern United States is the foremost factor preventing immediate conservation and recovery of imperiled native fishes. We present evidence that the two fishery types cannot be co-managed in sympatry if natives are to persist. A dual responsibility of federal and state fish and wildlife agencies to manage both fishery types creates internal conflicts that typically are resolved in favor of nonnative sport fisheries, despite existence of the Endangered Species Act. We advocate designation of watersheds to be managed exclusively for one fishery type or the other, and implementation of an aggressive program to eliminate nonnatives in native-designated waters and protect against their reinvasion. To mitigate institutional conflicts, agency infrastructures should be segregated to promote independent management of native fisheries and introduced sport fisheries. This approach can fulfill mandates of both the Endangered Species Act and the 1996 Fish and Wildlife Service policy on recreational fishing.

Predatory Fish Removal and Native Fish Recovery in the Colorado River Mainstem

Mechanical predator removal programs have gained popularity in the United States and have benefited the recovery of several native trout and spring fish. These successes have been limited to headwater streams and small, isolated ponds or springs. Nevertheless, these same approaches are being applied to large river systems on the belief that any degree of predator removal will somehow benefit natives. This attitude is prevalent in the Colorado River mainstem where recovery and conservation programs are struggling to reverse the decline of four endangered fish species. Predator removal and prevention are major thrusts of that work but unfortunately, after 10 years and the removal of >1.5 million predators, we have yet to see a positive response from the native fish community. This leads to the obvious question: is mechanical removal or control in large (>100 cfs base flow) western streams technically or politically feasible? If not, recovery for some mainstem fishes may not be practical in the conventional sense, but require innovative management strategies to prevent their extirpation or possible extinction. This article examines (1) what has been attempted, (2) what has worked, and (3) what has not worked in the Colorado River mainstem and provides recommendations for future efforts in this critical management area.

U.S. Ocean Fish Recovery: Staying the Course

This Policy Forum is a defense of existing, embattled U.S. legislative policy toward ending overfishing and rebuilding depleted populations within a specified time frame. The United States now uniquely has numerous marine species whose recovering populations are linkable to federal rebuilding mandates. Yet lawsuits and congressional bills introduced at the behest of the fishing industry would relax or eliminate the law9s recovery mandates. We show quantitatively that the existing timetable is responsible, reasonable, and biologically feasible.

Threatened fishes of the world: Menidia extensa (Hubbs & Raney 1946) (Atherinopsidae)

Common names: Waccamaw silverside. Conservation status: Listed as threatened by U.S. Fish & Wildlife Service (1987). Identification: Freshwater, lacustrine derivative of the allopatric Menidia beryllina. Long, slender-bodied atherinid (body depth 7–8 times in SL) reaching maximum length of 84 mm. D1 III–VI; D2 7–11; A 19 (17–21); vertebrae 42–45; lateral scales 44–50. Overall silvery to translucent, with melanophores lining the posterior edge of dorsal, lateral scales. Scales poorly developed and deciduous. This species is not sexually dimorphic, with the exception of pre-spawning females being slightly more robust than males. Drawing by E.F. Menhinick. Distribution: One of three endemic fishes in Lake Waccamaw, Columbus County, North Carolina (Hubbs & Raney 1946, Frey 1951). Specimens have been collected occasionally in the headwaters of the Waccamaw River, just below the Lake Waccamaw dam during periods of high water (Shute et al. 1981). These specimens were likely washed over the dam during high flows and do not represent an isolated, reproducing population. Abundance: Very common – one of most abundant species in Lake Waccamaw. Habitat and ecology: Found in large schools near the surface in open water areas, typically above sandy bottoms and areas with little vegetation. Diet consists mainly of zooplankton, especially cladocerans. Minor food sources include ostracods and aquatic insects (Davis & Louder 1969). Menidia extensa is one of the most important forage species in the lake (Rohde et al. 1994). Reproduction: The following life history information is taken primarily from Davis & Louder (1969). Spawning occurs from March through July, which is marked by a large migration from open waters to vegetated near-shore spawning grounds. No parental care is exhibited. Best described as an annual species – most individuals die after spawning and do not live into their second year. Individuals become sexually mature at approximately 30 mm SL (Shute 1980). Threats: The shoreline of Lake Waccamaw is becoming densely developed. Homes and cottages cover nearly three-fourths of the shoreline while the remaining one-fourth lies within Lake Waccamaw State Park. Coincident to this development is the potential for increase in nutrient loading in the lake (Shute 1997). Nutrient loading increases the potential for wide-scale algal blooms and corresponding eutrophication. Because M. extensa has an annual life cycle, it is susceptible to rapid extinction given reproductive failure for even a single year. Additionally, the recent invasion of the lake by the brook silverside (Labidesthes sicculus), is of concern (Moser et al. 1998). The potential for negative interactions between these two atherinids is unknown; early indications are that there is some habitat segregation (Rohde unpubl.). Conservation actions: The U.S. Fish and Wildlife Service recovery plan (1993) calls for protection of critical habitat, research to determine the specific habitat requirements of all life stages, and bi-annual monitoring of the population as well as water and habitat quality monitoring. Research is also being conducted on captive propagation of this species.

Toxicity of cypermethrin on total lipids and free fatty acids in liver, muscle, kidney and ovary of Clarias batrachus (L) and recovery response

Alterations in the levels of lipid metabolites, total lipids and free fatty acids, were studied in physiologically important tissues viz; liver, muscle, kidney and ovary of a freshwater edible fish Clarias batrachus. The fish was exposed to sublethal concentration (1/3 of LC50 value for 96 h) of a synthetic pyrethroid insecticide, cypermethrin for 1, 5 and 10 days. After 10 days of exposure, fish were released into fresh water and total lipids and free fatty acids were determined at intervals of 1, 5 and 10 days to assess fish recovery response after cessation of cypermethrin exposure. Fish showed an increased rate of lipogenesis in liver, muscle, kidney and ovary during the exposure period followed by a decrease after transfer of fish into fresh water. There was also an elevation in liver and kidney free fatty acids contents, while the muscle and ovary free fatty acid contents were reduced during exposure period. The alterations in free fatty acids were restored to near normal values after 10 days of cessation of exposure.

Differential recovery of Pacific Island fish remains

The effects of differential recovery have been documented and discussed for almost a century. Screening experiments using comparative collections are one avenue for understanding recovery bias because they develop expectations about what is likely to be recovered. In this study, modern reference specimens of Pacific Island fish were screened through 1/4 inch (6.4 mm) and 1/8 inch (3.2 mm) mesh. Recovery rates are examined across taxa, body size, and element type. The experimental recovery rates are then compared to those from an archaeological fish assemblage from the Moturakau rockshelter, Aitutaki, Cook Islands, to examine how well the data derived from screening experiments are able to predict archaeological recovery patterns. The experimental data is able to accurately predict the taxa recovered in the Moturakau sample. The impact of differential recovery on a variety of interpretations utilizing archaeological fish remains is then discussed.

Measuring marine fish biodiversity: temporal changes in abundance, life history and demography

Patterns in marine fishes biodiversity can be assessed by quantifying temporal variation in rate of population change, abundance, life history and demography concomitant with long-term reductions in abundance. Based on data for 178 populations (62 species) from four north-temperate oceanic regions (Northeast Atlantic and Pacific, Northwest Atlantic, North mid-Atlantic), 81% of the populations in decline prior to 1992 experienced reductions in their rate of loss thereafter; species whose rate of population decline accelerated after 1992 were predominantly top predators such as Atlantic cod (Gadus morhua), sole (Solea solea) and pelagic sharks. Combining population data across regions and species, marine fishes have declined 35% since 1978 and are currently less than 70% of recorded maxima; demersal species are generally at historic lows, pelagic species are generally stable or increasing in abundance. Declines by demersal species have been associated with substantive increases in pelagic species, a pattern consistent with the hypothesis that increases in the latter may be largely attributable to reduced predation mortality. There is a need to determine the consequences to population growth effected by the reductions in age and size at maturity, and in mean age and size of spawners, concomitant with population decline. We conclude that reductions in the rate of population decline, in the absence of targets for population increase, will be insufficient to effect a recovery of marine fishes biodiversity, and that great care must be exercised when interpreting multi-species patterns in abundance. Of fundamental importance is the need to explain the geographical, species-specific and habitat biases that pervade patterns of marine fishes recovery and biodiversity.

Power of monitoring programmes to detect decline and recovery of rare and vulnerable fish

Summary Abundance trends provide key guidance when setting conservation priorities, whether indicating population decline, stability or recovery. Knowledge of the power of surveys to detect trends is essential, as the consequences of not detecting a real trend can be profound. Unfortunately, some surveys have been established with no assessment of power, and others are used to study species that were not their original focus. The latter is common in the marine environment, where rare fish are monitored using catch data from surveys that target more abundant commercially fished species. We calculated the power of a large‐scale annual monitoring survey (the English North Sea bottom trawl survey) to detect decline and recovery of species that are vulnerable to fishing. As fisheries exploitation invariably precedes scientific investigation, the survey began after many vulnerable species had already been depleted. The power of the survey to detect declines in the abundance of vulnerable species on time scales of < 10 years was low and the survey often failed to detect declines that would lead to listings under the IUCN A1 Red List criteria. Thus conservation prioritization based solely on survey data may fail to identify species at risk of regional extinction. If conservation measures were effective, and vulnerable populations recovered at the maximum potential rate, 5–10 years of monitoring would often be required to detect recovery. Power to detect trends in abundance was increased by developing a composite indicator that reflected trends in abundance of several vulnerable species. This indicator provided an overview of their conservation status. Synthesis and applications. Consistent with the precautionary principle, conservation prioritization and management action should not depend on the statistical significance of recent abundance trends when low power is a consequence of historical depletion. If the conservation prioritization and management of rare and/or vulnerable species have to be predicated on evidence of significant declines, then higher type 1 error rates (falsely detecting a decline) should be acceptable. This is because the costs of type 1 errors are lower than those of type 2 (failure to detect a real decline).

Extinction, survival or recovery of large predatory fishes

Large predatory fishes have long played an important role in marine ecosystems and fisheries. Overexploitation, however, is gradually diminishing this role. Recent estimates indicate that exploitation has depleted large predatory fish communities worldwide by at least 90% over the past 50-100 years. We demonstrate that these declines are general, independent of methodology, and even higher for sensitive species such as sharks. We also attempt to predict the future prospects of large predatory fishes. (i) An analysis of maximum reproductive rates predicts the collapse and extinction of sensitive species under current levels of fishing mortality. Sensitive species occur in marine habitats worldwide and have to be considered in most management situations. (ii) We show that to ensure the survival of sensitive species in the northwest Atlantic fishing mortality has to be reduced by 40-80%. (iii) We show that rapid recovery of community biomass and diversity usually occurs when fishing mortality is reduced. However, recovery is more variable for single species, often because of the influence of species interactions. We conclude that management of multi-species fisheries needs to be tailored to the most sensitive, rather than the more robust species. This requires reductions in fishing effort, reduction in bycatch mortality and protection of key areas to initiate recovery of severely depleted communities.

Severe, chronic proliferative kidney disease (PKD) induced in rainbow trout Oncorhynchus mykiss held at a constant 18°C

Proliferative kidney disease (PKD), caused by the myxozoan parasite Tetracapsuloides bryosalmonae, is well documented as a seasonal disease of rainbow trout Oncorhynchus mykiss. Water temperatures influence the course of the infection both within the fish and the invertebrate host, the recovery of fish from the disease being accelerated with decreasing water temperatures. During this study, groups of rainbow trout were held at a constant temperature (18 degrees C) for a sustained period of time following initial exposure to T. bryosalmonae. While the majority of these fish had recovered from the clinical disease after 9 mo, 10% remained infected, showing clinical signs of disease. A histological study revealed that the majority exhibited very high parasite loads and unusually severe symptoms of PKD. This demonstrates that while most rainbow trout can recover from PKD independent of water temperature, there exists a sub-population that cannot.

Control of saprolegniosis in the eel Anguilla australis Richardson, by Aeromonas media strain A199

The probiotic activity of Aeromonas media strain A199 for the control of saprolegniosis at low water temperatures was trialled in a laboratory-based challenge using the eel, Anguilla australis Richardson. Eels were challenged in the presence of a physiological and physical stress akin to that preceding the winter outbreaks of saprolegniosis in farms. The concentration of Saprolegnia parasitica cysts was 9±1.2 cysts/ml for the initial challenge. Morbidity due to saprolegniosis was low, at 27% in A199-treated tanks, in comparison to the 44% recorded for the non-treated control tanks. The subsequent addition of live A199 cultures to the treatment tanks resulted in the recovery of fish suffering from saprolegniosis ( p=0.038), with temperature appearing to be a factor regulating the effect of A199. It was concluded that A199 is a potential agent for the management of winter outbreaks of saprolegniosis in eels.

Visibility of Visual Implant Elastomer Tags in Atlantic Salmon Reared for Two Years in Marine Net-Pens

Abstract We evaluated detectability of visual implant elastomer (VIE) tags in individual Atlantic salmon Salmo salar reared from smolts to adults in commercial marine net-pens. A total of 9,000 individual smolts were marked (adipose eye, lower jaw, or both) with colored VIE tags. During the period from March 1998 to December 2000 (2–28 months after tagging) a total of 3,220 fish were visually inspected for VIE tags. Tag detection rates remained high (>90%) for the first 17 months after tagging but then declined sharply, particularly for VIEs in the jaw. Use of a UV light significantly increased detection of both eye and jaw VIE tags. We conclude that VIE tags are optimal for use in Atlantic salmon when recovery of fish occurs within 17 months of tagging.

The ability of clove oil and MS-222 to minimize handling stress in rainbow trout (Oncorhynchus mykiss Walbaum)

The effects of 60-mg L-1 clove oil and 60-mg L-1 tricaine methanesulphonate (MS-222) on the blood chemistry of rainbow trout were compared after exposure to handling stress via caudal puncture blood sampling. Fish sampled by caudal puncture and subsequently exposed to anaesthetics showed a typical handling stress response over a 48-h period. There were no significant differences between the responses of fish exposed to equal concentrations of clove oil and MS-222, with the following exceptions: the blood glucose at full anaesthesia, and lactate at full recovery increased significantly in the clove oil-exposed fish. In a subsequent experiment, the stress response observed in fish sampled by caudal puncture and exposed to clove oil and MS-222 was compared with a non-anaesthetized control group. The increases in plasma cortisol levels were significantly lower at recovery in fish treated with either anaesthetic compared with the control fish. Fish exposed to MS-222 had significantly higher cortisol levels at 1 h. These findings show that few differences exist between the anaesthetic effects of clove oil and MS-222 on the physiological response of fish to stress. However, clove oil is more effective at reducing the short-term stress response induced by handling and blood sampling, and is recommended as an alternative fish anaesthetic.

Increased recovery of brain acetylcholinesterase activity in dichlorvos-intoxicated European eels Anguilla anguilla by bath treatment with N-acetylcysteine.

Organophosphate (OP) pesticides are widely used as antiparasitic chemicals in finfish aquaculture. However, current antidotes cannot be applied to treat intoxicated fish. We showed in previous studies the importance of glutathione (GSH) metabolism in pesticide resistance of the European eel Anguilla anguilla L. The present work studied the effects of the antioxidant and glutathione pro-drug N-acetyl-L-cysteine (NAC) on the recovery of European eels exposed for 96 h to a sublethal concentration (0.17 mg l(-1); 20% of its 96 h LC50) of the OP pesticide dichlorvos (2,2-dichlorovinyl dimethyl phosphate; DDVP). This insecticide and acaricide decreased muscular GSH content and increased oxidised glutathione (GSSG), lowering the GSH:GSSG ratio, which is indicative of a condition of oxidative stress. Acetylcholinesterase (AChE) and glutathione reductase (GR) activities in the brain, which were biomarkers of neurotoxicity and oxidative stress, respectively, were also highly inhibited. Recovery in a 0.5 mM (81.6 mg l(-1)) NAC concentration ameliorated muscular GSH depletion, GSH:GSSG ratio, and the inhibition of brain AChE and GR activities. Hence, this is the first evidence of improved recovery of organophosphate-poisoned fish by bath treatments.

Evaluation of fish sampling using rotenone in a navigation lock

Annual sampling in locks with rotenone has been a principal means of assessing fish populations in the commercially navigable portions of the Ohio River. Despite extensive use, sampling in locks with rotenone and interpretation of the data obtained have not been adequately evaluated. The purpose of our study was to determine the degree of inter- and intra-seasonal variation in lock samples, estimate correction factors (CFs) for fish recovery rates, and compare lock samples to other fish collections from the navigational pools above and below the lock. Lock samples from all seasons had a greater proportion of pelagic and demersal fish than samples from the navigational pools, which contained greater proportions of littoral species. CF for non-recovery of fish were determined. Spring and summer lock collections yielded several more species and estimates of overall fish biomass were an order of magnitude higher than fall collections. Within season variation between lock samples was relatively low; however, variation in lock samples among seasons was high, equivalent to that seen among the annual samples from the 1980s. Thus, single-season sampling may not be adequate, and fall may be the least preferred season.

A Critique of the Recovery of Greenback Cutthroat Trout

Abstract: There are no examples of recovery of fish listed under the U.S. Endangered Species Act, but the number of federally threatened greenback cutthroat trout ( Oncorhynchus clarki stomias) populations is approaching the delisting goal. We evaluated recovery of this subspecies in light of developing theory in conservation biology and with regard to recovery of other salmonids in the inland western United States. Four of the five criteria used to define populations that would count toward delisting appeared to underestimate the risk of extinction of those populations. Typically, recovery goals for numbers of greenback cutthroat trout populations were less stringent than those for other inland salmonids petitioned for listing or listed as threatened under the Endangered Species Act and were comparable to those for a federally endangered species. Before delisting is considered, we propose that historical populations be replicated in additional waters to protect genetic diversity and that existing populations be enlarged to reduce their vulnerability to demographic variation, to increase their access to refugia, and to permit reestablishment of mobile life histories. Existing stocks should also be evaluated to determine whether they represent distinct population segments.

Physiological stress responses, egg survival and sperm motility for rainbow trout broodstock anesthetized with clove oil, tricaine methanesulfonate or carbon dioxide

Egg survival, sperm motility and physiological stress responses (plasma cortisol, glucose and chloride) of rainbow trout ( Oncorhynchus mykiss) broodstock were compared among three anesthetics: tricaine methanesulfonate (MS-222), clove oil in the form of AQUI-S® (a proprietary mix of 50% isoeugenol and other ingredients) and carbon dioxide gas. Concentrations of 60 mg/l tricaine, 20 mg/l isoeugenol (40 mg/l AQUI-S) and 220–275 mg/l carbon dioxide were based on preliminary tests and chosen to standardize induction time among anesthetics. Plasma glucose, chloride and cortisol concentrations indicated that none of the anesthetics used after crowding and netting completely eliminated the stress response. The return to prestress cortisol levels differed among the three anesthetics. Fish anesthetized with AQUI-S had significantly lower cortisol concentrations at 1 or 7 h postimmersion than the other anesthetics and controls, but were elevated at 24 h. Plasma cortisol in tricaine- and CO 2-treated fish returned to prestress levels within 7 and 24 h, respectively, whereas cortisol levels in control fish remained elevated at 24 h. Sperm motility and duration of motility were assessed for a practical range of concentrations: tricaine, 15–100 mg/l; AQUI-S, 10–100 mg/l; CO 2, 50–173 mg/l. The percentage of motile sperm was unaffected by anesthetic treatment, averages ranging from 68% to 87%. However, duration of motility decreased as anesthetic concentration increased, averages ranging from 55 to 36 s for tricaine and from 56 to 37 s for AQUI-S. Duration of sperm motility was low (31–43 s) for all levels of CO 2 tested. Fish recovery time was significantly longer for fish anesthetized by AQUI-S (370 s) than the either CO 2 or tricaine (192 and 199 s, respectively). Gender had no effect on recovery time. Egg survival to the eyed stage and to hatch was not significantly different among anesthetic treatments and controls. No delayed mortality was observed for any of the fish handled and bled for the test. Results indicated that tricaine, AQUI-S and CO 2 were all suitable for broodfish anesthesia, but the longer recovery time and lower cost for AQUI-S may make it more useful than the alternatives. None of the anesthetics wholly suppressed the stress responses during a typical spawning process, but did help reduce the duration of the stress responses and eased handling without compromising egg viability.

Influence of population decline, fishing, and spawner variability on the recovery of marine fishes

Based on an analysis of 90 marine fish populations, collapses (the greatest proportional reduction in spawner biomass over 15 years) are predicated typically by dramatic increases in fishing mortality and recoveries are more likely to occur when exploitation is reduced. However, among populations for which fishing mortality declined after collapse, recovery was independent of exploitation rate, even when fishing mortality (F) post‐collapse was expressed as a function of each population's maximum growth rate (r). After a period of 15 years, many populations that experienced 15 year declines >60% exhibited little or no recovery, despite considerable reductions in fishing mortality. This suggests that factors other than fishing may be considerably more important to recovery, and fishing less important, than previously thought. Furthermore, among populations for which fishing mortality decreased post‐collapse, rate of population decline was a reliable predictor of recovery. With the possible exception of clupeids, variation in marine fish breeding population size was found to differ little from that of other vertebrates, and such variability appears to have no effect on rate of recovery. In addition to providing an empirical framework for the study of population collapse and recovery, the analyses presented here provide a means of assessing the precautionary nature of various population‐decline thresholds used to assign extinction risks to marine fish.

Influence of population decline, fishing, and spawner variability on the recovery of marine fishes

Influence of population decline, fishing, and spawner variability on the recovery of marine fishes

Nonnative Fish Control and Endangered Fish Recovery: Lessons from the Colorado River

Native freshwater fish populations are declining in North America and more than 100 fishes are federally listed as threatened or endangered. The Colorado River system in the southwestern United States has been especially affected. Most of its native fish populations are in decline, including four “big river” fishes, Colorado pikeminnow (Ptychocheilus lucius), humpback chub (Gila cypha), bonytail (G. elegans), and razorback sucker (Xyrauchen texanus), whose populations have declined so precipitously that they are endangered. Physical habitat alteration caused native fish declines, but nonnative fishes pose a more serious threat to native fishes than previously thought. Nonnative fish control measures needed in the upper Colorado River system, identified in part by a workshop of experts, include: (1) preventing movements of game fishes out of impoundments and curtailing future stockings, (2) reducing numbers of small, nonnative cyprinids in shoreline habitat used as rearing areas by young native fishes, and (3) increasing the harvest of channel catfish (Ictalurus punctatus) and common carp (Cyprinus carpio) in the mainstream. Large-scale implementation of these nonnative fish control measures has proven difficult. Recovery efforts have identified the need for developing nonnative fish control strategies and testing methodologies, but no solutions have emerged. A holistic approach, including ecosystem recovery plans, should be used in systems where more than one species share common problems, such as interactions with nonnative fishes. Nonnative fish interactions should be suspected as a potential cause of declining native fish populations.