Evaluating potential competitive bottlenecks between invasive common carp and native bluegill and yellow perch

Processes influencing fish recruitment are often highly complex and inherently difficult to understand. Invasive species may complicate recruitment through habitat and food web modifications resulting in competitive bottlenecks. Common carp Cyprinus carpio have been distributed worldwide, and their introductions have resulted in destructive effects on aquatic ecosystems and food web dynamics. Common carp are highly fecund, and high densities of age‐0 carp may occur in some years that may reduce invertebrate prey resources and adversely affect native age‐0 fishes. We used enclosures and field observations to examine potential effects of age‐0 common carp on growth and survival of age‐0 yellow perch Perca flavescens and bluegill Lepomis macrochirus. Yellow perch and bluegill were stocked into enclosures with and without common carp (31 fish/m³) using a substitution experimental design, and fish growth and survival and invertebrate prey resources were assessed. Common carp reduced growth of yellow perch but not bluegill and did not affect survival of either species in mesocosms. Next, we used patterns of common carp, bluegill, and yellow perch abundance and total length across 38 lake‐years to evaluate potential interspecific interactions in natural systems. Age‐0 common carp abundance was not negatively related to size or abundance of bluegill or yellow perch. However, adult common carp and age‐0 yellow perch abundance were inversely related, suggesting a potential competitive bottleneck. Thus, age‐0 common carp may suppress growth of yellow perch when prey is limited, but adult common carp may have larger effects than early life stages on native juvenile fishes.     

Hydroacoustic assessment of young-of-year perch, Perca fluviatilis, population dynamics in an oligotrophic lake (Lake Annecy, France)

Abstract  A cohort of perch, Perca fluviatilis (L.) was monitored from hatching to first winter in the oligotrophic Lake Annecy, France, by combining hydroacoustic and direct capture methods (fish plankton net and pelagic trawl). The total stock of pelagic fish increased by a factor of 10 during the season, reaching a maximum in August and decreasing in autumn. Juvenile perch were mainly pelagic, being aggregated into schools in the daytime and dispersed at night. Migration of young-of-year (Y-O-Y) perch to the pelagic zone of Lake Annecy in late spring did not significantly affect zooplankton population abundance. It did, however, result in changes in zooplankton vertical distribution, with Daphnia remaining deeper in the water column. The increase in Y-O-Y biomass during summer was possibly associated with collapse of the Daphnia population by late July, and copepods one month later.     

Early life history and recruitment of black crappie (Pomoxis nigromaculatus) in two South Dakota waters

Abstract— We compared the early life history of black crappie ( Pomoxis nigromaculatus ) in Richmond (an impoundment) and Brant (a natural lake) lakes during 1994-1996. We expected variable recruitment (i. e., missing year classes) in the natural lake and more consistent recruitment in the impoundment. Larval black crappie abundance was always higher in Richmond Lake than Brant Lake. Peak abundance of larval black crappie was highest during 1994 in both waters. However, peak larval abundance did not correspond with fall trap-net catch per unit effort (CPUE) of age-0 black crappie, which was highest during 1995. Thus, recruitment of black crappie was not simply a function of the number of larvae hatched. Similar trends in catches of age-0 black crappie with the ichthyoplankton trawl and trap nets for both water bodies during 1994-1996 suggest that broad environmental factors similarly affected reproduction and recruitment in Richmond and Brant lakes.     

Emergence of larval yellow perch, Perca flavescens, in South Dakota lakes: potential implications for recruitment

Abstract  Temporal patterns in length frequency distributions and hatch dates were described for larval yellow perch, Perca flavescens (Mitchill), captured in surface ichthyoplankton trawls from late April to mid-June 2000 to 2002 in six South Dakota, USA lakes. Fewer than 15 larval yellow perch were collected in four of six lakes during 2002, suggesting that in some cases factors prior to, during or immediately after hatching likely play a critical role in the perch recruitment process. When larval yellow perch were encountered in larger numbers, temporal trends in total length (TL) frequencies indicated that only a single cohort was produced annually in each lake. Most yellow perch in these lakes hatched between 29 April and 17 May, and most hatching occurred during 5–11 days each year. Larval TL was not related to hatch date. The apparent prevalence of relatively short hatch periods in these yellow perch populations probably increases the risk of catastrophic losses resulting from periods of poor environmental conditions.     

Changes in yellow perch length frequencies and sex ratios following closure of the commercial fishery and reduction in sport bag limits in southern Lake Michigan

Abstract  The closure of the Indiana commercial fishery in Lake Michigan in 1997 provided the opportunity to examine the effects of commercial exploitation on the yellow perch, Perca flavescens (Mitchill), population. Data from annual gillnet and trawl sampling, recreational angler creel surveys and commercial fishing harvest were used to determine whether changes in length–frequency distributions and sex ratios were altered following closure. The proportions of large, adult yellow perch were significantly greater after the closure of the commercial fishery. Overexploitation of fish >200 mm by commercial harvest likely truncated the size distribution, but recreational harvest was comparatively small and did not appear to be a factor influencing size distributions. This post-closure period also had a greater proportion of females in trawl catches, and the mean length of harvested fish increased in the recreational fishery. These findings suggest commercial exploitation influenced yellow perch population dynamics in far southern Lake Michigan.     

Copepods and salmon: characterizing the spatial distribution of juvenile salmon along the Washington and Oregon coast,USA

Yearling Chinook (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) were sampled concurrently with physical variables (temperature, salinity, depth) and biological variables (chlorophyll a concentration and copepod abundance) along the Washington and Oregon coast in June 1998–2008. Copepod species were divided into four different groups based on their water‐type affinities: cold neritic, subarctic oceanic, warm neritic, and warm oceanic. Generalized linear mixed models were used to quantify the relationship between the abundance of these four different copepod groups and the abundance of juvenile salmon. The relationships between juvenile salmon and different copepod groups were further validated using regression analysis of annual mean juvenile salmon abundance versus the mean abundance of the copepod groups. Yearling Chinook salmon abundance was negatively correlated with warm oceanic copepods, warm neritic copepods, and bottom depth, and positively correlated with cold neritic copepods, subarctic copepods, and chlorophyll a concentration. The selected habitat variables explained 67% of the variation in yearling Chinook abundance. Yearling coho salmon abundance was negatively correlated with warm oceanic copepods, warm neritic copepods, and bottom depth, and positively correlated with temperature. The selected habitat variables explained 40% of the variation in yearling coho abundance. Results suggest that copepod communities can be used to characterize spatio‐temporal patterns of abundance of juvenile salmon, i.e., large‐scale interannual variations in ocean conditions (warm versus cold years) and inshore‐offshore (cross‐shelf) gradients in the abundance of juvenile salmon can be characterized by differences in the abundance of copepod species with various water mass affinities.     

Abiotic and biotic correlates of yellow perch recruitment to age‐2 in southern Lake Michigan, 1984–2007

Abstract Seven abiotic and biotic variables were tested to determine whether they influence the recruitment to age two of yellow perch, Perca flavescens (Mitchill), in waters of southern Lake Michigan, USA. Recruitment was analysed using a Ricker stock‐recruitment relationship that accounts for density dependency. Significant model variables tested individually and ranked by total variance explained included the abundance of sexually mature yellow perch, alewife, Alosa pseudoharengus (Wilson) and spottail shiner, Notropis hudsonius (Clinton). Variables found unrelated to recruitment or generally less explanatory included the abundance of round goby, Neogobius melanostomus (Pallus), mean water temperature, variation in water temperature and water clarity. The best‐fitting multivariable model explained 69% of the recruitment variability and included abundances of sexually mature yellow perch, alewife and spottail shiner. These results suggest that yellow perch recruitment in southern Lake Michigan is regulated in part by biotic interactions with other species of the near‐shore community, including alewife and spottail shiners, in addition to the abundance of reproductively mature yellow perch.     

Distribution, abundance and biological interactions of the cutlassfish Trichiurus lepturus in the southern Brazil subtropical convergence ecosystem

The distribution, abundance and biological interactions of the cutlassfish Trichiurus lepturus in the southern Brazil subtropical convergence ecosystem were studied from demersal trawl surveys conducted along the continental shelf and upper slope from Cape Santa Marta Grande (28 °36′S) to Chui (34 °45′S) between 1981 and 1987. Trichiurus lepturus was more abundant at bottom water temperatures of over 16 °C and in the 40–120 m depth range. From late spring to fall, juveniles of 5–30 cm total length (TL) were found in coastal waters, subadults (TL 30–70 cm) mainly in inner shelf waters and adults (TL > 70 cm) in coastal, inner and outer shelf waters. Higher catches of subadults and adults were found associated with thermal fronts in the western boundary of the Subtropical Convergence or with a shelf break upwelling observed in summer. The standing stock in a 58 000 km² shelf area estimated by the swept area method, ranged from 3066 t (±46% CI) in September 1981 to 37814 t (±22% CI) in January 1982. Correlation between occurrences of different size groups of cutlassfishes and other fishes caught in 250 bottom trawl hauls was analyzed. A positive correlation between cutlassfish and juvenile weakfish, Cynoscion guatucupa, was associated with similar spatial distribution but also indicated trophic competition.     

The influence of abiotic factors on gillnet catch rates of yellow perch in southern Lake Michigan, 1989–2006

Abstract The difference in yellow perch, Perca flavescens (Mitchill), catch rates were evaluated for gillnets set on the bottom at 10‐ and 15‐m depths in southern Lake Michigan during June, July and August from 1989 to 2006. More yellow perch were captured in gillnets set at 10 m than at 15 m. Differences in water temperature were significant in explaining variation in catch rates, but differences in Secchi depth and wave height were not significant. These results suggest that yellow perch may associate with habitat based on water temperature during the summer and move in response to thermal changes. In addition, this portion of the lake lacks noticeable heterogeneous structural habitat features that normally influence yellow perch behaviour. Fisheries managers should consider sampling based on temperature in addition to depth or other habitat features when designing sampling protocols.     

Night sampling improves indices used for management of yellow perch in Lake Erie

Abstract  Catch rate (catch per hour) was examined for age-0 and age-1 yellow perch, Perca flavescens (Mitchill), captured in bottom trawls from 1991 to 2005 in western Lake Erie: (1) to examine variation of catch rate among years, seasons, diel periods and their interactions; and (2) to determine whether sampling during particular diel periods improved the management value of CPH data used in models to project abundance of age-2 yellow perch. Catch rate varied with year, season and the diel period during which sampling was conducted as well as by the interaction between year and season. Indices of abundance of age-0 and age-1 yellow perch estimated from night samples typically produced better fitting models and lower estimates of age-2 abundance than those using morning or afternoon samples, whereas indices using afternoon samples typically produced less precise and higher estimates of abundance. The diel period during which sampling is conducted will not affect observed population trends but may affect estimates of abundance of age-0 and age-1 yellow perch, which in turn affect recommended allowable harvest. A field experiment throughout western Lake Erie is recommended to examine potential benefits of night sampling to management of yellow perch.     

Pikeperch, Stizostedion lucioperca (L.), catch in relation to juvenile density and water temperature in Pärnu Bay, Estonia

Abstract The abundance of 0+ pikeperch, Stizostedion lucioperca (L.), in trawls was compared with water temperature, water level and commercial catches 6–9 years later. The abundance of juveniles in autumn was positively correlated with the water temperature but not with water level in May or in June. The sum of a year abundance of juveniles showed a strong correlation with the catch years later. This abundance and the cumulative water temperature between August and October inclusive in five consecutive years one year prior to recruitment into the commercial fishery explained 86% of the variation in catches. This empirical model indicates that catches of pikeperch depend on both juvenile abundance and water temperature.     

Factors influencing recruitment and growth of age‐0 yellow perch in eastern South Dakota glacial lakes

Variation in recruitment and growth of age‐0 yellow perch, Perca flavescens (Mitchill), was modelled across a range of nine eastern South Dakota glacial lakes to: (i) estimate factors influencing recruitment and growth dynamics during early ontogeny; and (ii) determine the relative importance of biotic versus abiotic processes in regulating recruitment and growth dynamics. Results provide a framework for future investigations and suggest that abiotic factors were more important in regulating recruitment of age‐0 yellow perch, whereas biotic factors were more important in regulating growth. Recruitment was positively related to springtime water levels and temperature and negatively related to spawning stock biomass and springtime wind conditions. By contrast, growth was negatively related to abundance of conspecifics and potential competitors (i.e. bluegill, Lepomis macrochirus Rafinesque) and positively related to abundance of potential predators [i.e. walleye, Sander vitreus (Mitchill) and northern pike, Esox lucius Linnaeus].     

Use of first‐order tributaries by brown trout (Salmo trutta) as nursery habitat in a cold water stream network

Many investigators have examined the importance of suitable in‐stream habitat and flow regime to salmonid fishes. However, there is much less known about the use of small (<5 l·s^?1 discharge) first‐order streams within a larger stream network by salmonids. The purpose of this study was to evaluate the use of small headwater streams by juvenile brown trout Salmo trutta in the Emmons Creek stream network in Wisconsin, USA, and to determine whether abundance was related to habitat variables in these streams. Fishes in eight spring‐fed first‐order streams were sampled during a 7‐month period using a backpack electroshocker and measured for total length. Habitat variables assessed included stream discharge, water velocity, sediment composition and the abundance of cover items (woody debris and macrophytes). Densities of YOY trout ranged from 0 to 1 per m² over the course of the study and differed among first‐order streams. Stepwise multiple regression revealed discharge to be negatively associated with trout density in spring but not in summer. All other habitat variables were not significantly related to trout density. Our results demonstrate the viability of small first‐order streams as nursery habitat for brown trout and support the inclusion of headwater streams in conservation and stream restoration efforts.     

Factors influencing the abundance of three common nearshore fishes in south‐west Lake Michigan

Variation in the distribution and abundance of nearshore fishes is critical to understand food web processes and fishery management issues in Lake Michigan. This study characterised patterns in abundance of three common nearshore species, yellow perch Perca flavescens (Mitchell), round goby Neogobius melanostomus (Pallas) and alewife Alosa pseudoharengus (Wilson), in relation to spatio‐temporal, abiotic and biotic factors using gillnet sampling conducted across 5 years at multiple locations representing different substrates. Significant variations were observed in alewife and round goby catches between locations. A negative relationship between round goby and age‐0 yellow perch catch was observed, indicating potential competition between the two species. This study demonstrates that variability in nearshore fish communities can be driven by factors including substrate and interspecific interactions. Given the prominent role these species play in Lake Michigan's food web and thus their importance to fishery production, a thorough understanding of these factors is warranted.     

Body size trends along vertical and thermal gradients of chum salmon in the Bering Sea during summer

Relationships between the vertical distribution and thermal habitat, and body size of chum salmon Oncorhynchus keta were studied in the Bering Sea in summer using trawl surveys at various depths. Chum salmon abundance decreased with increasing depth, but the patterns of decrease differed between size groups. The abundance of small salmon fell rapidly with depth, whereas that of large salmon decreased gradually to 40 m depth, and abruptly below that. The average fork length of chum salmon collected from each trawl correlated positively with trawl net depth and negatively with water temperature. Since the optimal temperature for growth decreases with body size in this species, the observed body size‐related vertical habitat use by chum salmon may indicate size‐dependent thermal preferences.     

Habitat use of lake trout (Salvelinus namaycush) following species introduction

Abstract – Although introductions of prey species have the potential to significantly alter habitat use by top predatory fish, this aspect has rarely been directly quantified. Introduction of yellow perch (Perca flavescens), a littoral–pelagic prey species, to a small boreal lake previously dominated by littoral cyprinids provided a unique opportunity to examine how a change in forage base influenced habitat use by the sole top predator, lake trout (Salvelinus namaycush). We monitored lake trout pelagic and spatial distribution using acoustic telemetry before (2001) and after (2008) the introduction of perch to determine whether habitat use reflected a deeper, offshore prey community. After accounting for differences in water temperature and dissolved oxygen concentrations between years and the inclusion of a control lake, our data suggest that lake trout habitat use changed after the introduction of yellow perch. Lake trout, on average, were 1.4 m deeper (P < 0.01), reduced their use of littoral habitat by 55% (P = 0.03) and experienced a 71% decrease in home range size (P < 0.01), consistent with a greater offshore habitat overlap between predator and prey after the introduction of yellow perch. This study illustrates how introduced prey species may have a significant influence on habitat use by top predatory fish, while also showing the importance of using direct measurements to quantify behavioural changes.     

Associations of fish with various types of littoral habitats in reservoirs

Fish associations with different types of littoral habitats were studied in four canyon‐shaped reservoirs in the Czech Republic in years 2010 and 2011 by gillnets. Two to three habitats per reservoir–beaches (former meadows), stump fields (former forest) and rubble slopes–were defined and sampled along the longitudinal axis of reservoirs. Effects of reservoir, habitat and locality (position along longitudinal axis) on fish biomass, abundance and species structure were tested for juvenile and adult fish separately. Hierarchical analysis of variance revealed that habitats differed significantly in fish biomass and abundance. Redundancy analysis showed that analysed environmental variables had significant influence on fish community structure. Most variability in community structure was explained by reservoir and then by combination of habitat and slope steepness. Locality position had the smallest influence on community structure. For both adult and juvenile fish total abundance and biomass, the most inhabited habitat was beaches; rubble slopes were the least inhabited. Habitat associations differed among species. Among adults, bream Abramis brama, white bream Blicca bjoerkna and roach Rutilus rutilus were associated with beaches and stump fields, whereas perch Perca fluviatilis, ruffe Gymnocephalus cernuus, asp Aspius aspius and pike Esox lucius were associated with rubble slopes. Bream, white bream, bleak Alburnus alburnus, roach, ruffe and pikeperch Sander lucioperca were associated with beaches among juveniles, whereas the only juvenile associated with rubble slopes was perch. We showed that most common species are associated with distinct habitats and also that utilisation of various littoral habitats differs in general.     

Fyke-netting and coarse fisheries in lowland Britain: practical advice for fishery owners and managers

Abstract  The by-catches of fish, mammals and birds from a fyke-net survey of eel, Anguilla angilla (L.), stocks (total effort 1593 end days) at 45 sites in rivers and lakes in the Thames catchment and tidal river were examined. Sizes and compositions of by-catches varied between sites, yielding a total of 21 fish species representative of the types of water body sampled. The largest catches were of shoaling juvenile perch (especially in lakes). Small roach, perch and ruffe were also fairly frequent in running waters (especially the tidal and non-tidal Thames). Carp, tench and pike were less frequently caught (mainly in still waters and upper tributaries). Juvenile flounders and smelt were fairly common in the tidal Thames. Salmonids were rarely caught and fish mortalities overall were very low. Few mammals, wildfowl or crustaceans were trapped, but it is important that nets are set below water level to avoid trapping birds swimming on the surface, and the use of otter guards is recommended. Fouling of fishing tackle was rare. Recommendations are made for practical steps that can be taken to minimize undesirable impacts of commercial fyke-netting, whilst realizing the potential financial and management benefits. The cost-effective uses of fyke-nets for sampling and culling fish for management purposes are discussed.     

Effects of food supply and stream physical characteristics on habitat use of a stream‐dwelling fish

Identifying the environmental factors that affect freshwater fish can be crucial for their conservation and management. Despite the widespread investigation of relationships between fish habitat use and environmental variables, there is a paucity of knowledge on how abiotic and biotic factors jointly influence stream fish habitat use. Three New Zealand South Island streams were selected to investigate the habitat preference of a stream‐dwelling galaxiid, banded kokopu (Galaxias fasciatus). Fish abundance in several permanent pools was determined by spotlighting at night once a month from June 2008 to May 2009. Drifting invertebrates and key physical features of each pool were measured at the time of fish sampling. An information‐theoretic approach (AIC) indicated that the most parsimonious candidate model to predict banded kokopu biomass was the one that included pool area, undercut banks, water velocity, overhanging vegetation, invertebrate drift density and an interaction term between invertebrate drift density and water velocity. Banded kokopu biomass was positively related to pool area, undercut banks, overhanging vegetation and invertebrate drift density. Our study suggests that fish resource use patterns need to be understood in the context of multiple interacting ecological factors, including prey abundance.