Background: Assemblages of fishes in lakes and reservoirs in the western USA are dominated by non-native, large-bodied, piscivorous fishes that lack a shared evolutionary history. Top predators in these crowded systems are often characterized by unstable population dynamics and poor somatic growth rates. One such assemblage is in Fish Lake, located in southern Utah, USA, in which introduced lake trout (Salvelinus namaycush, Walbaum) exhibit a bimodal growth pattern. A few lake trout in Fish Lake grow rapidly to large size typical of the species; whereas, most never grow beyond 600 mm total length. Objective: To inform competitive interactions in this evolutionarily novel fish assemblage that might cause the low recruitment to large body size in lake trout, we characterized trophic niche (from stable isotope analysis of C and N) of all fishes in the lake. Methods: We used a Bayesian mixing model to describe the trophic niche and infer diet of lake trout and their potential prey, and we used Bayesian ellipse analysis to identify potential areas of high competition within the food web. Large lake trout feed mostly on small lake trout and splake (Salvelinus namaycush, Walbaum x Salvelinus fontinalis, Mitchill) despite availability of abundant yellow perch. (Perca flavescens, Mitchill). Small lake trout and splake feed mostly on zooplankton and exhibit substantial overlap of their trophic niche implying competition for food. Yellow perch and Utah chub (Gila atraria, Girard; formerly an important food item for lake trout in Fish Lake) exhibit extreme overlap of their trophic niche implying strong competitive interactions. Results: Our data suggest that lack of recruitment to large body size in lake trout may result from a reduction in availability of Utah chub resulting from competitive interactions with yellow perch, and increased competition from introduced splake for available prey. Conclusion: Management actions that may help ameliorate the poor somatic growth rates of most lake trout include efforts to reduce perch populations or increase vulnerability of perch to predation by lake trout, and removal of splake as a competitor of small lake trout.
Background:During 2005-13, at Osoyoos Lake, British Columbia, we investigated trophic relationships among fry ofOncorhynchus nerkaWalbaum (Sockeye and kokanee), a suite of limnetic planktivores includingMysis diluviana, and their zooplankton prey.Objectives:Our goal was to quantify the impacts that a recently introduced population ofMysiswould have on density, growth and survival of resident age-0 Sockeye Salmon.Methods:Evidence ofMysisimpact was based on (a) simple correlation analysis between various biophysical performance measures and (b) production and bioenergetics models used to identify the strength of bottom-up (i.e. production-driven) and top-down (i.e.consumption-driven) processes.Results:This nine-year study indicated that the Osoyoos Lake food web was strongly influenced by external events These included: large annual variations in river discharge, an earthen dam failure and effluent input from an Okanagan River tributary, and highly variable recruitment ofO. nerkafry given out-of-basin factors (harvest, marine survival) controlling adult salmon returns. Surprisingly, large annual variations inO. nerkarecruitment (0.63 - 7.0 million fry), did not induce significant “top-down” associations in growth, survival or subsequent production among the macro-planktivores (pelagic fish andMysis) and their zooplankton prey. A single significant correlation (p ≤ 0.05) betweenO. nerkafry abundance and their von BertalanffyW∞parameter emerged from a set of 14 potential top-down associations tested. By contrast, we identified several strongly positive “bottom-up” effects in which survival ofO. nerkafry was significantly associated (p ≤ 0.01) with annual variations in total zooplankton biomass,Daphniabiomass andEpischurabiomass. Our results indicate thatMysisplayed a dual role in the Osoyoos Lake pelagic food web. As predators, they accounted for an average (June-October) of 64% of the total prey biomass consumed by fish andMysis. As prey,Mysiscontributed an average of 35% of the prey biomass consumed by fish. Consumption by fish andMysistogether accounted for daily losses of only 4.5% of non-mysid zooplankton biomass and 34% of daily zooplankton production.Conclusion:We conclude that in all years, combined prey consumption byMysisand fish was never high enough, acting alone, to reduce the availability of their potential zooplankton forage base. However, we also estimate that in the absence ofMysis,O. nerkafry could experience a 43% increase in their daily food intake and that fish andMysismight control their principal prey taxa when exogenous factors (e.g.annual discharge) induced major reductions in zooplankton biomass. Finally, althoughMysishas clearly altered the energy flow pathways from plankton to fish in the Osoyoos Lake food-web, mysids have not precluded rebuildingO. nerkaabundance to levels at or exceeding historic maxima.
Introduction:The aim of the present study was to develop a trophic model characterizing simultaneously the structure and function of the two coastal marine ecosystems: Alvarado Lagoon, Mexico and adjacent continental shelf, important area for penaeid shrimps and demersal fish species.Method:The model was based on the assumption of biomass balance and describes the trophic relationships, flows of energy, and transfer efficiency of the food web, and includes 66 functional groups.Results:Results shows that 33% of the aggregate biological community biomass comes mainly second and third trophic levels. Size of aggregate flows as well as the transfer effectiveness among groups, results like those saw in other similar works. Connectance index (CI) was 0.12, meaning that there is only 12% only of the total theoretical connections exist. Results also shows that primary producers and detritus (lagoon and shelf) contribute with 60.1% of the total ascendency. Our work can be the basis for future research, which allow us to contrast alternate hypotheses about the functioning of the system.
Introduction:The growth in tourism in the Cape Verdean Sal Island has been a cause as well as a consequence of a number of investments (both by the State and the private entities) to create synergies for that sector, ensuring and promoting the island’s touristic attractiveness. Such increases in the number of visitors, allied with the island’s marine biodiversity - that make up much of its economic potential - have caused the growth of the diving industry, which has become one of the biggest attractions for tourists. In light of the scarcity of scientific studies on the impacts associated with this activity and means for diver engagement, the local diving operators have proposed the development of several tools.Method:An Underwater Species Identification Guide and four underwater routes were proposed for four popular scuba diving sites off Santa Maria Bay (Sal Island, Cape Verde): “Kwarcit”, “Sargo”, “Três Grutas” and “Tchuklassa”. To better understand how the diving industry could promote environmental education, conservation and enhance biodiversity awareness among divers, we also established the diver tourists’ profile using an online survey.Results:A total of 347 respondents, of which 85% have higher education, showed that 67% stay more than seven nights in Cape Verde. Moreover, natural reefs are the 1stdive site to be visited, while artificial reefs preference increases after a second dive on the man-made reefs. The majority would recommend the use of the Underwater Species Identification Guide and the underwater routes.The results showed that divers strongly embrace the use of new tools for better understanding of diving site biodiversity and that the diving industry can play an important role in the enhancement of biodiversity awareness.
Background:Close-up videos of sharks foraging on other live sharks are rare, especially when it comes to footage of the entire duration of an event.Objective:Our goal was to present an in-depth analysis involving a Galapagos shark,Carcharhinus galapagensis, foraging on a whitetip reef shark,Triaenodon obesus.Method:A frame by frame video examination was used to highlight the different aspects of this bout.Results:Several behavioral characteristics, including the somewhat cryptic approach, the extensive shaking once the Galapagos shark had the whitetip reef shark between its jaws, and devouring tail-first, stand out in this event.Conclusion:The entire act appeared very smooth, indicating that this bout, or at least parts thereof, may represent a common hunting strategy for Galapagos sharks.
Background: Reservoir communities in the intermountain west are typically dominated by a mix of introduced fishes. Due to the non-coevolved interactions present in these communities, energy flow and trophic interactions may not facilitate optimal growth and survival for all species. It is difficult to predict how well each species will survive in such novel communities. One such community is in Jordanelle Reservoir in northern Utah, USA. Recently, low survival and recruitment of stocked rainbow trout ( Onchorhynchus mykiss ) have been observed in Jordanelle Reservoir. Objective: We characterize the food web structure of the fish community in Jordanelle reservoir to infer competitive or predatory interactions that might lead to a poor return of stocked rainbow trout. Methods: We performed a stable isotope analysis on the fish community in Jordanelle Reservoir and carried out niche space analyses using the software package Stable Isotope Bayesian Ellipse (SIBER) in R. Results: Small rainbow trout exhibit high competitive overlap with brown trout ( Salmo trutta ), smallmouth bass ( Micropterus dolomieu ), and yellow perch ( Perca flavescens ). In addition, large brown trout and large smallmouth bass may feed heavily on small rainbow trout. Conclusion: Food web analysis suggests that rainbow trout encounter a highly competitive and potentially high predation environment in Jordanelle reservoir, leading to observed low return rates.
Determining when fish spawn has major implications for effective fisheries management, particularly in dam-controlled rivers where reproductive potential may be affected by an altered hydrograph. Three methods for estimating spawn timing in riverine broadcast spawners were compared for their precision, effort and potential impact on a population of Mountain Whitefish in the regulated Lower Duncan River, Canada. The first method is based on the Gonadosomatic Index (GSI), which is a measure of the relative mass of an individual’s gonads. The second method is based on counts of aggregating adults, while the third method is based on passive egg collection using egg mats. Analysis of the GSI data provided the most precise estimates. It estimated that spawning occurred between October 30th and November 26th in 2010 and between November 8th and November 27th in 2011. Collection of GSI data required moderate effort and had some impact due to the need for lethal harvest. Analysis of the spawner counts using a simple Bayesian Area-Under-the-Curve model provided less precise estimates of spawn timing but the method likely had negligible impact on the population and required only moderate effort. Deployment of egg mats required high effort and collected insufficient information to derive statistical estimates of spawn timing. We discuss how information from different methods could be combined together into a single integrated model to maximize the precision while minimizing the effort and impact.
Object:Landlocked fall Chinook SalmonOncorhynchus tshawytschain Lake Oahe, South Dakota, typically experience poor reproductive success.Introduction:Salmon diets consist of rainbow smeltOsmerus mordaxand other potentially thiaminase-containing fish that could impact reproduction.Methods:The thiamine levels of spawning female Salmon, eggs, and reproductive characteristics, were measured in 2000, 2001, 2002, 2003, and 2005.Results:Thiamine concentrations varied significantly from year-to-year, with the highest mean values recorded in 2001 at 8.70 nmol/g in maternal livers and 28.80 nmol/g in eggs. Most of the thiamine in the eggs was present as free thiamine, while most of the thiamine in maternal livers was present as thiamine pyrophosphate. The lowest recorded egg total thiamine level was 2.75 nmol/g in 2000. Egg survival to hatch ranged from 20.7% in 2005 to 35.4% in 2002, and was not correlated to egg thiamine levels. Twenty-two spawns experienced total mortality prior to hatch, and had significantly lower egg free thiamine and total thiamine concentrations than eggs from the 77 successful spawns. The eggs from spawns with total mortality were also significantly smaller than those eggs from spawns that did survive, and were produced by females that weighed significantly less. Several small, but significant, correlations were observed between egg size and egg thiamine levels, and female size and liver thiamine.There was also a significant negative correlation between the number of eggs per spawning female and egg thiamine pyrophosphate, liver thiamine monophosphate, and liver total thiamine levels.Conclusion:In general, Lake Oahe Chinook Salmon eggs show little indication of thiamine deficiency in the years sampled, indicating other factors are likely responsible for poor egg survival.
Lake Naivasha a shallow, freshwater body and a Ramsar site is found in the eastern arm of the Kenyan Rift Valley. This paper used published, unpublished and analyzed data to assess the status, challenges and management options for the fishery. Lake Naivasha fishery is based on exotic species that fluctuates depending on fishing regime, lake water level and aquatic plant concentrations. The fishery has been dominated by different species with the current catch contribution consisting mainly of common carp, Cyprinus carpio , Nile tilapia, Oreochromis niloticus, blue-spotted tilapia, O. leucostictus and African catfish, Clarias gariepinus. The minimum and maximum catch of 21 t yr -1 and 1181 t yr -1 was reported in 1997 and 2015, respectively. The main threats to the lake fishery are anthropogenic influences emanating from within the lake and its basin. The factors include intense fishing, exotic species introductions, water abstraction, lake level fluctuations, wetland utilization, eutrophication, and land degradation. There are also several conflicts of interest amongst the stakeholders in agriculture, fisheries, wildlife, tourism, conservation and geothermal electricity generation. There is fear that if the current trend persists, the lake and its fishery may be headed for extinction. The management measures instituted in the lake do not seem to have arrested reduction in fish catches nor reversed deterioration in water quality. For sustainable utilization of Lake Naivasha and its fishery, there is a need to consider a holistic ecosystem approach of the basin management. Additionally, all the relevant stakeholders should be involved in formulation and implementation of the decisions to manage the fishery.
We used information about hatchery rearing and release practices for 173 releases of age 0+ smolts between 1982 and 2012, as well as time series of early marine prey biomass and predator abundance/biomass, to investigate the biological basis of age-specific return variability of chinook salmon (Oncorhynchus tshawytscha) from the Robertson Creek Hatchery. We used survival rate as the response variable and considered the rate to be an apparent one because it is the product of the survival and maturation rates. Results of multiple regression analyses (adjusted R2 ranging between 0.43 and 0.59) showed that Pacific mackerel (Scomber japonicus) and Steller sea lion (Eumetopias jubatus) abundances accounted consistently for all of the explained variation in age-specific survival rate. We suggest that the persistence of the early marine (predation) effect with age shows that there is no effect of hatchery practice on age at maturity. Apparent survival rate variation was not explained when we used conventional physical oceanographic measurements (temperature, salinity, Pacific Decadal Oscillation Index, Northern Oscillation Index, Arctic Oscillation Index, Aleutian Low Pressure Index, Bakun Upwelling Index, timing of spring transition) in our analyses.
Softshell Dungeness Crabs have inferior meat quality and are vulnerable to handling by harvesters; therefore, knowing when softshell periods occur is important for managing Dungeness Crab fisheries. A computer simulation was used to study the effectiveness of several survey designs and statistical models for estimating softshell periods which normally would be construed from crab shell condition data obtained from trap surveys. Survey designs varied in the number of years of data collection (1, 3, 5 or 10 years) and by the number and arrangement of sampling events per year. Three statistical models, including standardized catch-per-unit-effort (SCPUE), hierarchical, and generalized additive, were tested using catch-per-unit-effort data (CPUEs) or CPUE- transformed data. CPUEs were standardised by dividing CPUE estimates by the maximum CPUE obtained in the sample year, and then transformed using the complementary log-log function. In the hierarchical model, CPUEs were modelled using a lognormal distribution, assuming the expected logarithms of CPUEs are a quadratic function of days plus a random normal error. CPUE-transformed data were modelled using a normal distribution, assuming expected values are a quadratic function of days in the SCPUE model or a spline smooth function of days in the generalized additive model. Results suggest the best survey design requires a relatively high number (6 or 11) of sampling events during several key consecutive months which contain the softshell period, and fewer sampling events during those months when softshell crab abundance is low. A minimum 3 years of data collection is required to produce reliable outputs. The hierarchical model performs best, slightly better than the SCPUE model. Use of the generalized additive model is not recommended.
Protecting an area from fishing by establishing a sanctuary is one possible management strategy that could protect adults during spawning, potentially enhancing recruitment in freshwater systems. From 2001-2006, Briery Creek Lake (342 ha), Virginia was characterized by high fishing pressure in spring when adults were spawning and low abundance of age-0 Largemouth BassMicropterus salmoides. Therefore, we created two sanctuaries in 2006 in Briery Creek Lake that were closed to angling and boats; these areas provided protection for nest-guarding male Largemouth Bass. However, the nest-success rate did not differ significantly between open areas and sanctuaries (30-40% nest success). Catch per unit effort of age-0 Largemouth Bass did not differ between areas open to angling (28.8/h and 39.0/h in 2006 and 2007, respectively) and sanctuaries (14.6/h and 22.2/h in 2006 and 2007, respectively). Similarly, mean length-at-capture was not different for age-0 Largemouth Bass between sanctuaries and open areas. Closing spawning areas to fishing may not be an effective management option to increase Largemouth Bass recruitment success in Briery Creek Lake.
June sucker, Chasmistes liorus , is an endangered lake sucker endemic to Utah Lake, Utah, USA. Over the last two decades, captive-raised June suckers have been stocked into Utah Lake to augment the wild population. However, it has become apparent that the fish stocked from captive stock may not always represent the typical June sucker morphology. To determine the utility of current captive brood lots to produce June sucker phenotypes, we characterized shape of the lip lobes on the lower jaw of each brood lot. We obtained offspring from within-lot crosses and characterized shape of the lower lips using geometric morphometrics. We compared shape of brood lots to reference samples of June sucker and reference samples of the co-occurring sister species, Utah sucker ( Catostomus ardens ). Mean shape of the lower lips among brood lots varies from typical June sucker morphology to shapes typical of Utah sucker. Three brood lots had mean shape scores somewhat similar to the reference June sucker mean, and five brood lots had mean shape scores more similar to the reference Utah sucker mean. All other brood lots were intermediate representing hybrid phenotypes. Utilization of all brood lots on a roughly equal basis for augmentation in Utah Lake will likely result in the loss of typical June sucker morphology in the lake within a few decades. We recommend use of brood lots that exhibit June sucker morphology and discontinuance of use of brood lots that represent Utah sucker morphology. In addition, selection on lower lip shape in captive brood lots may be required to recreate June sucker phenotypes from captive brood stock.
Fish implanted with acoustic transmitters are assumed to behave and grow after stocking similar to untagged fish. In this study, three groups (tagged, sham, and control) of rainbow trout Oncorhynchus mykiss [mean (SD) initial length = 277 (24) mm] range were maintained together in three raceways for 90 days, with each raceway containing 10 tagged, 10 sham, and 10 control fish. The fish in the tagged group were anesthetized and had an inert transmitter inserted via a ventral incision. Fish in the sham group were anesthetized and had an incision without transmitter implantation, while the control group was anesthetized only. In each raceway, trout with the inert transmitters were significantly lighter and shorter than fish from the other two groups at the end of the experiment. However, the reduction in weight, length, and specific growth rate occurred primarily during the first 38 days post-tagging, with tagged fish growing at similar rates to the other two groups for the final 52 days of the experiment. Mortality data indicated a survival threshold of 280 mm length in the tagged fish, with 100% survival of the Rainbow Trout greater than 280 mm and only 59.1% survival of trout less than 280 mm. Based on the results of this study, rainbow trout implanted with 9 x 24 mm, 3.6 g acoustic transmitters should be held prior to release for a minimum of 38 days to ensure similar growth rates as untagged conspecifics, and only trout with an initial length greater than 280 mm should be used to maximize survival.
Understanding the habitat requirements of salmonids in streams is an important component of fisheries management. We examined the summer and autumn habitat use of yearling Rainbow Trout Oncorhynchus mykiss in relation to available habitat in two streams in the Lake Ontario watershed. Little interstream variation in trout habitat use was observed; the variation that did occur was largely due to differences between streams in available habitat in the autumn. In both streams, yearling Rainbow Trout utilized pool habitat and during periods of high stream discharge were associated with larger substrate that may provide a velocity barrier. These findings may assist resource managers in their efforts to protect and restore habitat for migratory Rainbow Trout in the Lake Ontario watershed.
The capacity to sample otoliths of fish from commercial, recreational, artisanal or subsistence catches can be constrained if the dissection process results in alterations to their external appearance and thus reduces its value and/or shelf life. There can also be significant biases incorporated into the collection of otolith samples if access is only granted relative to the size of the fish (i.e. if smaller fish are sold whole). To reduce such limitations, we herein describe a rapid and simple method of lateral otolith extraction that maintains the integrity of the fish product, and thus reduces potential biases in sample collection for age structure data. Representative sampling is an important consideration for the collection of age structure data when it is intended to be used in fisheries stock assessments.
We filmed and analysed, in natural and field conditions, behaviours of large-bodied European catfish (Silurus glanis) individuals (body size ranging from 80 to 220 cm) exposed to a hook baited with 20 cm-long Carassius spp. Among a total of 95 individuals observed, 80 % of the catfish clearly demonstrated interest in the bait but attacks were performed only 25 % of the time and only 12.5 % of fish were hooked. More than half of the individuals (55 %) were observed swimming toward the bait and then turning around or tasting it without performing any attacks. These observations showed that individual fish motivation and behaviour are important factors in determining whether European catfish are attracted to bait and eventually hooked.
We designed and tested a novel otolith viewing apparatus termed the otolith illumination device (OID) to ascertain if its use would result in a reduction of interpretation error as determined by increased precision of age estimates obtained from otoliths of walleye Sander vitreus and smallmouth bass Micropterus dolomieu. Clarity of annuli on otolith sections viewed with the OID was generally greater than clarity of annuli on sections viewed with an alternative method. OID-based age estimates were equally as, and in some instance more precise than ages estimated using the alternative method. Additionally, no systematic differences in coefficients of variation across ages were detected between the OID and alternative methods of fish age estimation. Results suggest that the OID may be useful for inexperienced readers and is a viable option for reducing interpretation error, which may improve reader efficiency and accuracy and precision in estimating fish ages.
White sharks show a high degree of residency to specific aggregation sites, to which they return regularly over multiple years. Australian research has historically focused on single aggregation areas within each of the southern states where white sharks occur, but other key habitats likely exist and if so, will be important to identify to effectively monitor and protect threatened white shark populations. This study is the first to describe Liguanea Island as a second white shark aggregation site within South Australia, with residency periods and return visits recorded by multiple individuals. Eight sharks were detected at both Liguanea Island and the other known aggregation area in the state, the Neptune Islands, demonstrating movement between these locations. Sustained residency periods were recorded at both sites, although high periodic site fidelity was apparent with many individuals showing preference for the location at which they were tagged. Individual differences in site fidelity and residency patterns were found, although two sub-adult individuals were found to follow similar movement patterns. The implications of white shark movements, and the suggested identification of a second aggregation areas in close proximity are discussed.
Gill netting was carried out at 25 sites in Lake George, New York to determine if interbasin differences of yellow perch (Perca flavescens) exist. Fish relative weight, growth and diet were analyzed for 267 yellow perch. Yellow perch are known to be omnivorous in the lake eating zooplankton, benthos and small fishes in both the littoral and pelagic waters. The length-weight relationship exhibited a significant difference amongst the Narrows, North and South basins for condition constants (p < 0.05). Relative weights were consistently found to be below the general target range and had significant differences between the basins. Growth models of fish caught in the three basins showed variation in growth of yellow perch. The yellow perch from the North basin exhibited allometric growth, while those in the South and Narrows displayed isometric growth. The diets of yellow perch between the basins also were found to be different. Previous studies have noted differences between the basins with respect to chlorophyll a, chemistry, and biota. This study provides evidence of differences in the fishery amongst the basins that follow similar, previously defined, differences in chemistry.
