Changes In Fish Populations Research Articles

Emerging negative Atlantic Multidecadal Oscillation index in spite of warm subtropics

Sea surface temperatures in the northern North Atlantic have shown a marked decrease over the past several years. The sea surface in the subpolar gyre is now as cold as it was during the last cold phase of the Atlantic Multidecadal Oscillation index in the 1990s. This climate index is associated with shifts in hurricane activity, rainfall patterns and intensity, and changes in fish populations. However, unlike the last cold period in the Atlantic, the spatial pattern of sea surface temperature anomalies in the Atlantic is not uniformly cool, but instead has anomalously cold temperatures in the subpolar gyre, warm temperatures in the subtropics and cool anomalies over the tropics. The tripole pattern of anomalies has increased the subpolar to subtropical meridional gradient in SSTs, which are not represented by the AMO index value, but which may lead to increased atmospheric baroclinicity and storminess. Here we show that the recent Atlantic cooling is likely to persist, as predicted by a statistical forecast of subsurface ocean temperatures and consistent with the irreversible nature of watermass changes involved in the recent cooling of the subpolar gyre.

How Fishes Can Help Us Answer Important Questions about the Ecological Consequences of Evolution

Much of the recent progress in the study of eco-evolutionary dynamics has occurred in fish models. In this review, I focus specifically on the mechanisms by which fish evolution affects ecological processes, highlighting outstanding questions and new frontiers. Fish evolution can alter the ecology of individuals by changing traits that underlie resource use or interactions with other species. Fish eco-evolutionary studies have focused on the ecological consequences of two kinds of effect traits (trophic traits and nutrient recycling traits), but questions remain about the relative influences of genetic and environmental factors. Other fish traits might also have large ecological effects, but we lack frameworks for identifying them, and it remains difficult to link the traits to their ecological consequences. The effect of fish evolution also depends on changes in fish populations, which might vary because of genetic or by environmental factors. Such changes can have dramatic impacts on the expression of e...

Who is to blame? Plausible pressures on small pelagic fish population changes in the northwestern Mediterranean Sea

Contribution to the Theme Section ‘Drivers of dynamics of small pelagic fish resources: biology, management and human factors’.-- 18 pages, 4 figures, 8 tables

Effectiveness of coral relocation as a mitigation strategy in Kāne'ohe Bay, Hawai'i.

Coral reef restoration and management techniques are in ever-increasing demand due to the global decline of coral reefs in the last several decades. Coral relocation has been established as an appropriate restoration technique in select cases, particularly where corals are scheduled for destruction. However, continued long-term monitoring of recovery of transplanted corals is seldom sustained. Removal of coral from a navigation channel and relocation to a similar nearby dredged site occurred in 2005. Coral recovery at the donor site and changes in fish populations at the receiving site were tracked periodically over the following decade. Coral regrowth at the donor site was rapid until a recent bleaching event reduced coral cover by more than half. The transplant of mature colonies increased spatial complexity at the receiving site, immediately increasing fish biomass, abundance, and species that was maintained throughout subsequent surveys. Our research indicates that unlike the majority of historical accounts of coral relocation in the Pacific, corals transplanted into wave-protected areas with similar conditions as the original site can have high survival rates. Data on long-term monitoring of coral transplants in diverse environments is central in developing management and mitigation strategies.

Global synthesis of the documented and projected effects of climate change on inland fishes

Although climate change is an important factor affecting inland fishes globally, a comprehensive review of how climate change has impacted and will continue to impact inland fishes worldwide does not currently exist. We conducted an extensive, systematic primary literature review to identify English-language, peer-reviewed journal publications with projected and documented examples of climate change impacts on inland fishes globally. Since the mid-1980s, scientists have projected the effects of climate change on inland fishes, and more recently, documentation of climate change impacts on inland fishes has increased. Of the thousands of title and abstracts reviewed, we selected 624 publications for a full text review: 63 of these publications documented an effect of climate change on inland fishes, while 116 publications projected inland fishes’ response to future climate change. Documented and projected impacts of climate change varied, but several trends emerged including differences between documented and projected impacts of climate change on salmonid abundance (P = 0.0002). Salmonid abundance decreased in 89.5% of documented effects compared to 35.7% of projected effects, where variable effects were more commonly reported (64.3%). Studies focused on responses of salmonids (61% of total) to climate change in North America and Europe, highlighting major gaps in the literature for taxonomic groups and geographic focus. Elucidating global patterns and identifying knowledge gaps of climate change effects on inland fishes will help managers better anticipate local changes in fish populations and assemblages, resulting in better development of management plans, particularly in systems with little information on climate change effects on fish.

Length Limits Fail to Restructure a Largemouth Bass Population: A 28‐Year Case History

AbstractLength limits have been implemented by fisheries management agencies to achieve population density, size structure, and angler satisfaction objectives. By redirecting harvest towards or away from particular length‐ or age‐groups, length limits rely on harvest by anglers to maintain a population at or near a desired state. The fish population changes that follow the implementation of harvest regulations may take several years to manifest, so long‐term monitoring may be needed to adequately evaluate length limits. We used an innovative application of cluster analysis to facilitate evaluation of the effects of three consecutive length limits on a population of Largemouth Bass Micropterus salmoides over a 28‐year period in Ross Barnett Reservoir, Mississippi. A 13–16‐in protected slot length limit (10 years), followed by a 15‐in minimum length limit (MLL; 11 years), followed by a 12‐in MLL (7 years) failed to restructure the Largemouth Bass population due to what we suggest was the expansion of a voluntary catch‐and‐release attitude that started in the first decade of the study period. Various population metrics shifted towards values expected in an unharvested population, and the observed shifts can be attributed to a harvest deficit created by the prevailing catch‐and‐release attitude. Largemouth Bass harvest regulations may no longer be relevant in many waters. The utility of regulations for restructuring Largemouth Bass populations is largely dependent on harvesting attitudes that vary geographically, depending on cultural characteristics and demographics.Received September 15, 2016; accepted March 15, 2017 Published online May 4, 2017

Fish communities in the Anthropocene: detecting drivers of changes in the deep peri-alpine Lake Geneva

Climate forcing, in combination with local anthropogenic pressures, has drastically modified the physical and chemical properties of lakes worldwide, affecting the abundance and diversity of fish populations. In the context of these combined changes, understanding the interactions between global and local forcing has become a major challenge for developing sustainable fisheries. We analyzed commercial landing statistics of Lake Geneva to describe the long-term changes in the abundance of exploited fish species and to identify mechanisms responsible for fish population changes. We showed a significant relationship between the decrease in phosphorus concentrations and structural changes in the composition of the fish community. Local management of reducing phosphorus loadings played a major role in the recovery of whitefish (Coregonus lavaretus) spawning areas and slowed the process toward more climate-induced percid and cyprinid communities. In addition, rising spring water temperatures have increased whitefish larval growth rates and improved whitefish recruitment. Unexpectedly, climate change and phosphorus reduction can have synergistic effects, and our results highlight the need to consider interactions between global and local anthropogenic forcing to fully understand and predict lake fish population variability in a warming world.

Economic and Conservation Impacts of Stocking Wild Florida Bass into Large Florida Lakes

AbstractSupplemental stocking of fingerling or advanced fingerling Largemouth Bass Micropterus salmoides is a common management strategy for augmenting natural production in low‐recruitment systems. Few studies, however, have evaluated the impact of stocking adult bass taken from donor lakes. Over a period of 6 years, University of Florida researchers stocked Florida Lakes Griffin and Dora with 24,781 wild Florida Bass M. s. floridanus collected by electrofishing from other Florida lakes. During stocking years, stocked fish made up to 10% of the population in Lake Griffin and 27% in Lake Dora from electrofishing samples. However, 1 year after all stocked fish had been released, the proportion of stocked bass had declined to less than 5%, and 3 years after it had declined to less than 1%. We did not detect an increase in recruitment (catch of age‐1 bass) following stocking, so any benefit from stocking was likely short‐lived. We also could not conclude that stocking was responsible for increasing fishing effort because total fishing effort did not increase after stocking. As a result, no additive economic benefits could be attributed to the stocking program. During randomized electrofishing sampling, we collected 51 wild bass that had been released during the stocking program, and genetic analysis determined that two (3.9%) were hybrids and had alleles from nonnative Largemouth Bass. The extrapolation of these results estimated that almost 1,000 hybrids had been introduced into Lakes Griffin and Dora, which were historically identified to contain pure Florida Bass populations. Future wild bass stocking programs should include an appropriate study design for evaluating changes in fish populations, changes in the fishery, and economic consequences of stocking. Furthermore, a risk–benefit assessment should be completed before any stocking program is initiated, including consideration of any potential impacts on biodiversity.Received February 26, 2015; accepted January 6, 2016 Published online May 9, 2016

Population crash in Lesotho's endemic Maloti minnow Pseudobarbus quathlambae following invasion by translocated smallmouth yellowfish Labeobarbus aeneus

Abstract A genetically distinct population of the Maloti minnow Pseudobarbus quathlambae (Lesotho's only endemic fish) is known only from the Mohale catchment, and was formerly abundant in the Senqunyane, Bokong and Jorodane rivers which flow into Mohale Reservoir. Situated ~4 km downstream of Mohale Reservoir, the Semongkoaneng waterfall has historically prevented larger fish species from moving upstream into areas inhabited by P. quathlambae. After the filling of the Mohale Reservoir in 2003, an inter‐basin transfer (IBT) linking it to Katse Reservoir was opened and in 2006 the smallmouth yellowfish Labeobarbus aeneus, a larger more aggressive species, was recorded in the reservoir, presumably introduced via the IBT. The objectives of the present study were to: (1) establish whether any additional non‐native fish species were present in the Mohale catchment; (2) ascertain whether L. aeneus has dispersed into the rivers flowing into Mohale Reservoir; and (3) gauge whether the Mohale population of P. quathlambae is in decline. Twenty‐eight sites situated on major rivers flowing into the reservoir, and four sites in the reservoir itself, were surveyed to evaluate changes in fish populations and habitat quality. Results indicate that P. quathlambae has all but disappeared from its natural range: only five individuals were recorded in the Jorodane and Bokong rivers, and none were recorded in the Senqunyane River – a former stronghold for the species. On the other hand, L. aeneus was recorded in all three rivers and is probably responsible for the decline of the P. quathlambae population, given that there does not appear to have been major deterioration in habitat conditions. Another non‐native fish, the Orange River mudfish Labeo capensis, was recorded in the Mohale catchment for the first time. Urgent conservation action is required to prevent the Mohale lineage of P. quathlambae from becoming extinct. Copyright © 2016 John Wiley & Sons, Ltd.

Fish Monitoring in Kornati National Park: Baited, Remote, Underwater Video (BRUV) Versus Trammel Net Sampling

We evaluated (1) the suitability of two alternative methods for fish monitoring: trammel net sampling and BRUV (Baited Remote Underwater Video), and (2) the potential to cross-calibrate the methods based on a set of shared species with high catch probabilities. A statistical power analysis concluded that BRUV can be conducted with sufficient sample size to perceive small changes in fish populations with high power, and therefore can be used as a sentinel monitoring method. We found that fish species detected by both methods amounted to almost a third of the number of species in each method’s catch, and that 90% of these species are candidates for cross-calibration. 74% of the species at BRUV and 50% at trammel had occurrence probabilities above 10%, a reasonable threshold allowing stock assessment of these species. The sampled and predicted total species richness, extrapolated from the species accumulation curves, were almost identical across methods. We conclude that cross-calibrating the two methods and eventual replacement of the trammel method with non-destructive BRUV is feasible. The most effective areas of improvement are increased BRUV night-sampling effort and increased total sampling size to increase the statistical power of BRUV as a monitoring tool. This work has been supported under the Croatian Science Foundation under the project COREBIO (3107).

Assessment of Fish Health Status Under Long-Term Water Pollution : Vygozero Reservoir , North-West Russia

Environmental pollution and its effects on the health of aquatic ecosystems is a great problem that has been studied intensely in the last years. The Vygozero reservoir is one of the largest water bodies of the Karelian Republic. Its ecosystem has undergone significant changes since the 1930s mainly due to anthropogenic influence from the development of pulp and paper mill industry leading to accumulation of toxic contaminants and eutrophication. At present, the water body has been shown to be also polluted by hydrocarbon products and heavy metals. Among the huge changes in Vygozero ecosystem is the decrease of some fish populations and partial loose of commercial fishing importance. Despite the obvious changes in fish population the chronic biological effects of the Vygozero reservoir pollution on fish organism are poorly studied. This study is concerned with the evaluation of pollution influence on fish health status and establishment relation between fish health and environmental quality. The parameters selected for this aim were the occurrence of gills, liver and kidney alterations, as histopathological changes are widely used as biomarkers in the evaluation of the health of fish exposed to contaminants. Our findings confirm chronic pollution of the Vygozero reservoir. Histological analysis of fish tissues revealed a variety of progressive, regressive, inflammatory, circulatory disturbances and neoplastic changes. Observed histological alterations indicate that organism of fish from Vygozero reservoir responses to the impaired environment quality. Revealed histopathologies are sings of metabolic disorders, immunity suppression, compensatory reactions development and functional abnormalities in vital organs of studied fish. The results of the study correspond to the prior research devoted to ascertain tissue changes in different fish species taken from an area with chronic multiple anthropogenic impact. So it can be concluded that histopathological lesions are result of long-term effect of toxic xenobiotics.

The Pacific decadal oscillation and changes in anchovy populations in the Northwest Pacific

The Pacific decadal oscillation (PDO) has been identified as an important driver for fluctuation of fish populations on the eastern Pacific Ocean. However, the relationship between changes in fish population and climate oscillations on a decadal time scale in the Northwest Pacific is still unclear due to the lack of reliable long-term time series data. In the present study, a time series of Engraulis japonicus (Japanese anchovy) populations was reconstructed using the density of sedimentary fish scales in the Yellow Sea basin. E. japonicus populations and the PDO index showed similar patterns on a decadal time scale. Our results confirm that climate is a major driver of ecological changes on a decadal time scale, and indicate that suitable sea water temperature might be the main forcing of anchovy migration. This work also demonstrates the potential of predicting changes in fish population based on climate records.

Differences in the metabolic rates of exploited and unexploited fish populations: a signature of recreational fisheries induced evolution?

Non-random mortality associated with commercial and recreational fisheries have the potential to cause evolutionary changes in fish populations. Inland recreational fisheries offer unique opportunities for the study of fisheries induced evolution due to the ability to replicate study systems, limited gene flow among populations, and the existence of unexploited reference populations. Experimental research has demonstrated that angling vulnerability is heritable in Largemouth Bass Micropterus salmoides, and is correlated with elevated resting metabolic rates (RMR) and higher fitness. However, whether such differences are present in wild populations is unclear. This study sought to quantify differences in RMR among replicated exploited and unexploited populations of Largemouth Bass. We collected age-0 Largemouth Bass from two Connecticut drinking water reservoirs unexploited by anglers for almost a century, and two exploited lakes, then transported and reared them in the same pond. Field RMR of individuals from each population was quantified using intermittent-flow respirometry. Individuals from unexploited reservoirs had a significantly higher mean RMR (6%) than individuals from exploited populations. These findings are consistent with expectations derived from artificial selection by angling on Largemouth Bass, suggesting that recreational angling may act as an evolutionary force influencing the metabolic rates of fishes in the wild. Reduced RMR as a result of fisheries induced evolution may have ecosystem level effects on energy demand, and be common in exploited recreational populations globally.

Simplification of Caribbean reef-fish assemblages over decades of coral reef degradation.

Caribbean coral reefs are becoming structurally simpler, largely due to human impacts. The consequences of this trend for reef-associated communities are currently unclear, but expected to be profound. Here, we assess whether changes in fish assemblages have been non-random over several decades of declining reef structure. More specifically, we predicted that species that depend exclusively on coral reef habitat (i.e., habitat specialists) should be at a disadvantage compared to those that use a broader array of habitats (i.e., habitat generalists). Analysing 3727 abundance trends of 161 Caribbean reef-fishes, surveyed between 1980 and 2006, we found that the trends of habitat-generalists and habitat-specialists differed markedly. The abundance of specialists started to decline in the mid-1980s, reaching a low of ~60% of the 1980 baseline by the mid-1990s. Both the average and the variation in abundance of specialists have increased since the early 2000s, although the average is still well below the baseline level of 1980. This modest recovery occurred despite no clear evidence of a regional recovery in coral reef habitat quality in the Caribbean during the 2000s. In contrast, the abundance of generalist fishes remained relatively stable over the same three decades. Few specialist species are fished, thus their population declines are most likely linked to habitat degradation. These results mirror the observed trends of replacement of specialists by generalists, observed in terrestrial taxa across the globe. A significant challenge that arises from our findings is now to investigate if, and how, such community-level changes in fish populations affect ecosystem function.

Evaluation of geostatistical estimators and their applicability to characterise the spatial patterns of recreational fishing catch rates

Western Australians are heavily engaged in recreational fishing activities with a participation rate of approximately 30%. An accurate estimation of the spatial distribution of recreational catch per unit effort (catch rates) is an integral component for monitoring fish population changes and to develop strategies for ecosystem-based marine management. Geostatistical techniques such as kriging can provide useful tools for characterising the spatial distributions of recreational catch rates. However, most recreational fishery data are highly skewed, zero-inflated and when expressed as ratios are impacted by the small number problem which can influence the estimates obtained from the traditional kriging. The applicability of ordinary, indicator and Poisson kriging to recreational catch rate data was evaluated for three aquatic species with different behaviours and distribution patterns. The prediction performance of each estimator was assessed based on cross-validation. For all three species, the accuracy plot of the indicator kriging (IK) showed a better agreement between expected and empirical proportions of catch rate data falling within probability intervals of increasing size, as measured by the goodness statistic. Also, indicator kriging was found to be better in predicting the latent catch rate for the three species compared to ordinary and Poisson kriging. For each species, the spatial maps from the three estimators displayed similar patterns but Poisson kriging produced smoother spatial distributions. We show that the IK estimator may be preferable for the spatial modelling of catch rate data exhibiting these characteristics, and has the best prediction performance regardless of the life history and distribution patterns of those three species.

Disentangling the effects of climate, abundance, and size on the distribution of marine fish: an example based on four stocks from the Northeast US shelf

AbstractClimate change and fishing can have major impacts on the distribution of natural marine resources. Climate change alters the distribution of suitable habitat, forcing organisms to shift their range or attempt to survive under suboptimal conditions. Fishing reduces the abundance of marine populations and truncates their age structure leading to range contractions or shifts. Along the east coast of the United States, there have been major changes in fish populations due to the impacts of fishing and subsequent regulations, as well as changes in the climate. Black sea bass, scup, summer flounder, and winter flounder are important commercial and recreational species, which utilize inshore and offshore waters on the northeast shelf. We examined the distributions of the four species with the Northeast Fisheries Science Center trawl surveys to determine if the along-shelf centres of biomass had changed over time and if the changes were attributed to changes in temperature or fishing pressure through changes in abundance and length structure. Black sea bass, scup, and summer flounder exhibited significant poleward shifts in distributions in at least one season while the Southern New England/Mid-Atlantic Bight stock of winter flounder did not shift. Generalized additive modelling indicated that the changes in the centres of biomass for black sea bass and scup in spring were related to climate, while the change in the distribution of summer flounder was largely attributed to a decrease in fishing pressure and an expansion of the length–age structure. While the changes in ocean temperatures will have major impacts on the distribution of marine taxa, the effects of fishing can be of equivalent magnitude and on a more immediate time scale. It is important for management to take all factors into consideration when developing regulations for natural marine resources.

Potential loss and rehabilitation of stream longitudinal connectivity: fish populations in urban streams with culverts

Riverine connectivity is important to the persistence of fish communities, but culverts may impede fish movements to varying degrees and in both directions. Baffles can be installed in culverts to mitigate upstream connectivity loss; however, evaluation of their effectiveness is limited. To examine the potential impacts of culverts and their potential rehabilitation with baffles, we sampled fish populations in 26 streams that contained either (i) nonbaffled culverts or (ii) baffled culverts or (iii) lacked culverts (reference streams) in Metro Vancouver, British Columbia, Canada. Using mixed effects models, we compared fish responses across these three stream types to infer effects at the whole-stream scale (i.e., over both upstream and downstream positions equally), the within-stream scale (i.e., upstream versus downstream of culverts), and the interaction of scales. Densities (n·m−2) of coastrange sculpin (Cottus aleuticus) and prickly sculpin (Cottus asper) were significantly lower in nonbaffled and baffled stream types than in reference stream types, while densities of cutthroat trout (Oncorhynchus clarkii) and rainbow trout (Oncorhynchus mykiss) were significantly lower in reference stream types, indicating whole-stream differences. Using multivariate statistics, we similarly found that fish community compositions were significantly different across stream types. For our various fish responses, we found no interaction between stream type and upstream or downstream position. Further, we found reaches directly downstream of baffled culverts had greater fish biomass and that overall species richness increased with age of baffles. These data suggest that culverts may drive changes in fish populations at whole-stream scales, and restoration of these effects with baffles may take decades.

How a millennium of fishing changed fish populations: a case study of Lake Peipus and the Velikaya River (NW Russia)

The Velikaya River is the principal river flowing into the southern part of Lake Peipus, which is situated in the basin of the Gulf of Finland, an arm of the Baltic Sea. Lake Peipus is one of the largest and most productive freshwater bodies in Europe. An important population center in ancient Russia, the town of Pskov sits on the downstream part of the Velikaya. Here fisheries resources have been exploited for millennia. Local archaeological materials and historical documents provide unique opportunities for examining the historical ecology of this river and lake ecosystem. This study describes millennium-long changes in fish populations in the Velikaya River and Lake Peipus and discovers the factors responsible for them. We analyzed 5,981 fish remains dating from the 4th to the 18th centuries collected at two archaeological sites in Pskov and its surroundings. During this 1500-year period, three species predominated: pike, perch and bream together composed about three-quarters of identified bone elements. Fish sizes estimated from bone remains showed that target species, particularly bream and perch, tended to be larger before 1800 than in 20th century landings. Catch composition also changed over this long period, with increased contribution from smaller species such as whitebait, ruffe and vendace, especially in the 20th century. The main driver of the observed changes was fishing, with other human-induced factors and climate change being less important.

Putting pharmaceuticals into the wider context of challenges to fish populations in rivers.

The natural range of fish species in our rivers is related to flow, elevation, temperature, local habitat and connectivity. For over 2000 years, humans have altered to varying degrees the river habitat. In the past 200 years, we added to the environmental disruption by discharging poorly treated sewage, nutrients and industrial waste into our rivers. For many rivers, the low point arrived during the period of 1950s–1970s, when rapid economic development overrode environmental concerns and dissolved oxygen concentrations dropped to zero. In these more enlightened times, gross river pollution is a thing of the past in the Developed World. However, persistent legacy chemical contaminants can be found in fish long after their discharge ceased. Changes in habitat quality and morphology caused and continue to cause the disappearance of fish species. The range of fish stressors has now increased as temperatures rise, and non-native fish introductions bring new diseases. The threat from pharmaceuticals to fish populations remains hypothetical, and no studies have yet linked change in fish populations to exposure.

Aspects of Fishery Management, Job Satisfaction, and Well-Being among Commercial Fishermen in the Northeast Region of the United States

The complexity and rapid changes in fishery management approaches have forced fishermen to adopt strategies that may not be congruent with the original appeal of fishing as an occupation. Changes in fish populations and resulting efforts to manage stocks can impact job characteristics that influence job satisfaction (social–psychological needs, basic needs, and self-actualization) and potentially well-being. This hypothesis is addressed through examination of job satisfaction and well-being among 478 fishermen in three subregions of the northeastern United States. The results demonstrate that differences between the mix of regional fisheries and attitudes toward regulations affect two components of job satisfaction and well-being but not self-actualization. Management's attempts to reduce fishing effort therefore need to account for the persistence of self-actualization by either developing appropriate alternative occupations or preparing for the consequences of lower job satisfaction on the well-being of fishermen forced to leave the occupation.