Long-term variation in brown trout, Salmo trutta L., stocking success in a large lake: interplay between availability of suitable prey and size at release

Abstract –  Factors affecting long-term variation in brown trout, Salmo trutta L., stocking success were examined in a large lake, Lake Oulujärvi, in central Finland. Brown trout were stocked in spring (late May to early June) in 1974–1991 and in summer (late June to early July) in 1992–2001. The biomass of the vendace, Coregonus albula (L.), population (prey) at release time had the largest positive effect on stocking success within both periods: biomass of adult vendace in spring and both 0+ and adult vendace in summer. Increasing the size of stocked fish had a positive effect if the vendace available at release were only adults. The increasing trend of predator-catch-per-unit-effort (CPUE) [combined CPUE of northern pike Esox lucius L., burbot Lota lota (L.), and pike-perch Stizostedion lucioperca (L.)] through the study period and its negative effect on trout stocking success suggested an increasing effect of predation within the entire time series.     

Behavior of pike (Esox lucius L.) >50 cm in a turbid reservoir and in a clearwater lake

Abstract – Pike from two different waters were radio-tagged and released immediately upon recovery. In Bygholm Reservoir 19 pike (52–72 cm) and in Lake Ring 15 pike (53–77 cm) were tagged in late February and early March. Bygholm (58 ha) is a shallow eutrophic reservoir and Ring (22 ha) is a natural mesotrophic lake. The positions of the tagged fish were recorded through weekly trackings and a number of 3-day tracking sessions during a 9-month period. Diel activity patterns, home range sizes and habitat utilization by pike was compared between the reservoir and the lake. The pike in the lake occupied larger areas than the pike in the reservoir and were less associated with vegetation. In both waters pike were found more often in, or close to, vegetation during summer than during winter. No difference in average movement of pike was seen between the waters, but pike were more stationary in the reservoir than in the lake. There was no difference in the level of movement between different times of the day, but the diel rhythm of the pike changed significantly over the year. There were large behavioral differences between pike in the lake and in the reservoir and even more variation between individuals within each population.     

Pike predation on hatchery-reared Atlantic salmon smolts in a northern Baltic river

Abstract –  The effect of pike Esox lucius predation on the mortality of newly stocked Atlantic salmon Salmo salar smolts was investigated in the Pyhäjoki River, Finland. The number of smolts eaten by pike was assessed by estimating the size of the pike population (mark–recapture experiment) and studying the stomach contents of pike. Before recapturing the pike, approximately 39,700 smolts were stocked upstream of the 2.5-km-long (89-ha) research area. The estimated size of the >40-cm pike population was 1507 (95% CL 1012–4731) individuals (17 pike and 29.8 kg·ha⁻¹). Pike were estimated to eat 29% of the released smolts during 1 week. The diet of the pike in the research area consisted almost entirely of smolts, whereas in the reference area with no stocked smolts, the meal sizes were significantly smaller and the importance of smolts as prey was substantially lower. Pike <40 cm had not eaten any smolts, probably indicating a size refuge for the smolts, or alternatively fear of intraspecific interactions or cannibalism of pike.     

Do intracoelomic telemetry transmitters alter the post‐release behaviour of migratory fish?

Electronic tags have become a common tool in fish research, enhancing our understanding of how fish interact with their environment and move among different habitats, for estimating mortality and recording internal physiological states. An often‐untested assumption of electronic tagging studies is that tagged fish are representative of untagged conspecifics and thus show ‘normal’ behaviour (e.g. movement rates, swimming activity, feeding). Here, we use a unique data set for potamadromous walleye (Sander vitreus) in Lake Huron and Lake Erie tributaries to assess whether the lack of appropriate controls in electronic tagging could seriously affect behavioural data. We used fish tagged in previous years and compared their migratory behaviour during the spawning season to fish tagged in a current year at the same location. The objective of the study was to determine whether intracoelomic acoustic tag implantation altered downstream movement of walleye after spawning. Fish tagged in a given season travelled slower downstream from two river spawning sites than fish tagged in previous years. Fish tagged one or two years earlier showed no differences between each other in downstream travel time, in contrast to fish tagged in a given year. Our results support notions that standard collection and intracoelomic tagging procedures can alter short‐term behaviour (i.e. days, weeks, months), and as such, researchers should use caution when interpreting data collected over such time periods. Further, whenever possible, researchers should also explicitly evaluate post‐tagging effects on behaviour as part of their experimental objectives.     

Movements of pike, Esox lucius, in Lower Lough Erne, determined by mark–recapture between 1994 and 2000

Abstract Between 1994 and 1997, 508 pike, Esox lucius L., were tagged in Lower Lough Erne (LLE), Northern Ireland. By August 2000, 79 of these fish were recaptured. Ten of 27 pike recaptured and released a second time were then captured a third time. Distance from tagging to recapture site ranged from 0 to 16 km, with most recaptures within 10 km. Pike dispersed widely after spawning, an observation supported by netting survey data, and tended to return to the same spawning sites year after year. The usefulness of designated sanctuary areas free of commercial fishing, intended to maintain a stock of pike reserved for angling was evaluated. To protect angling stocks of pike from commercial fishing, sanctuary areas should be somewhat larger than at present.     

Spawning site fidelity and apparent annual survival of walleye (Sander vitreus) differ between a Lake Huron and Lake Erie tributary

Fidelity to spawning habitats can maximise reproductive success of fish by synchronising movements to sites of previous recruitment. To determine the role of reproductive fidelity in structuring walleye Sander vitreus populations in the Laurentian Great Lakes, we used acoustic telemetry combined with Cormack–Jolly–Seber capture–recapture models to estimate spawning site fidelity and apparent annual survival for the Tittabawassee River in Lake Huron and Maumee River in Lake Erie. Walleye in spawning condition were tagged from the Tittabawassee River in Lake Huron and Maumee River in Lake Erie in 2011–2012. Site fidelity and apparent annual survival were estimated from return of individuals to the stream where tagged. Site fidelity estimates were higher in the Tittabawassee River (95%) than the Maumee River (70%) and were not related to sex or fish length at tagging. Apparent annual survival of walleye tagged in the Tittabawassee did not differ among spawning seasons but was higher for female than male walleye and decreased linearly as fish length increased. Apparent annual survival of walleye tagged in the Maumee River did not differ among spawning seasons but was higher for female walleye than male walleye and increased linearly as fish length increased. Greater fidelity of walleye tagged in the Tittabawassee River than walleye tagged in the Maumee River may be related to the close proximity to the Maumee River of other spawning aggregations and multiple spawning sites in Lake Erie. As spawning site fidelity increases, management actions to conserve population structure require an increasing focus on individual stocks.     

Annual movement of adult pike (Esox lucius L.) in a lowland river

Abstract –  The movement of ten radio-tagged adult pikes (57–113 cm) in the River Gudenå, Denmark, was investigated from September 1998 to September 1999. The movements of pike were characterised by long resident periods in the submergent vegetation, interrupted by short excursions to nearby areas. Two periods with more intense movement were observed; one period during early winter; and one period during spring from mid-March to mid-May. The increased movement during early winter may have been initiated by a slight temperature increase at this time, whereas the increased movement during spring coincided with the spawning of pike. Despite suitable spawning areas nearby the areas where pike resided most of the year, several pike, mainly females, migrated to distant localities during spring.     

Spatial behaviour of young-of-the-year northern pike (Esox lucius L.) in a temporarily flooded nursery area

Abstract –  Unlike adult northern pike ( Esox lucius ), small-bodied young-of-the-year (YOY) individuals cannot be tracked by conventional telemetry, and virtually no data exist on their spatial behaviour. Here, we monitored 192 individuals released into a nursery area (0.47 ha, subdivided into 253 cells of 4 m × 5 m) that dried out progressively using a portable passive integrated transponder detector. Among them, 66 spent more than 5 days in the nursery area and were localised at least twice, allowing spatial behaviour analyses. The mean radial distance moved averaged 14.3 m (±8.4 SD, range 2.2–41.0) and the average daily movement was 8.0 m·day⁻¹ (±5.3 SD, range 0.6–31.1). Pike abundance in a cell significantly correlated with the abundance observed in adjacent cells within 32 m, confirming a patchy distribution. A selective use of the deepest area was measured while no effect of vegetation cover was observed at the cell scale. The existence of YOY pike aggregations and the positive correlation between water depth and their spatial distribution might, however, facilitate predation and/or cannibalism during this critical period. This also suggests that the choice of release habitats requires particular attention during restocking procedures.     

Seasonal and diel effects on the activity of northern pike studied by high‐resolution positional telemetry

Abstract – Temperate lakes can be ice covered for several months each year, yet little is known about the behaviour and activity of the fish during the cold season. As northern pike represents the top of the food web in many northern temperate lakes and may structure the ecosystem both directly and indirectly, a detailed understanding of the behaviour of this species during winter is important. We continuously monitored the activity of adult northern pike (Esox lucius) in a small temperate lake from late summer to winter for two consecutive years using an automatic acoustic positional telemetry system. Four subsample periods representing different temperature regimes from each year were chosen for further investigation. The results revealed that pike activity was similar between seasons. In all periods, a distinct diel pattern, showing increased activity during day as compared to night, was evident. Our findings indicate that the fish component of temperate lentic ecosystems can be more active during the cold season than previously assumed. This may have implications for the structuring effect of pike on the lower trophic levels.     

Protracted spawning of St Lawrence River northern pike (Esox lucius): simulated effects on survival, growth, and production

Abstract –  An individual-based early life history model demonstrated that the timing and distribution of St Lawrence River northern pike ( Esox lucius ) spawning could affect subsequent young-of-year (YOY) production during nursery and influence year-class formation. Three different spawning patterns have emerged from empirical studies, where egg deposition occurred along the entire littoral gradient beginning in seasonally flooded emergent habitats in tributaries, progressing to submerged aquatic vegetation in shallow bays, and ending in deep water littoral habitats (up to 6 m). The spawning period is protracted, and typically lasts 6–8 weeks due to the presence of a strong thermal gradient. The model used temperature as the driving variable to predict egg abundance, stage-specific development, growth, survival, and ultimately relative production of YOY northern pike within 1-ha plots representative of the three habitats. Earlier spawning (mean 21 days) and higher mean daily survival and growth yielded higher YOY net production for tributaries (mean = 3095.4 g ha⁻¹, SD = 2028.6) relative to the shallow bay habitat (202.5 g ha⁻¹, SD = 125.7). In contrast, deep littoral habitat represented an ecological sink with little production (<0.9 g ha⁻¹). The results demonstrate the importance of the linkage between spawning and nursery processes in determining reproductive success.     

Diet and growth of stocked and wild 0+ pikeperch, Stizostedion lucioperca (L.)

Wild and stocked 0+ pikeperch, Stizostedion lucioperca (L.), were sampled with a purse seine from Lake Oulujärvi, situated at the northern edge of the distribution range of the species. The stocked fry started immediate feeding on 0+ smelt, Osmerus eperlanus (L.) after their introduction into the lake in early August at about 50 mm length, whereas the smaller wild pikeperch fry continued to feed on zooplankton. Individual wet weight of the stocked pikeperch was about six-fold compared with the wild pikeperch throughout August. The length of the ingested smelt was as on average 50%, and maximum 66%, of the pikeperch length. Wild 0+ pikeperch were too small to forage on 0+ smelt. Predation by older conspecifics on 0+ pikeperch was observed.     

The effects of mechanically reducing northern pike density on the sport fish community of West Long Lake, Nebraska, USA

Abstract  Removal of piscivores may affect population size structure, abundance and growth rates of the remaining fish community. A total of 572 northern pike, Esox lucius L., was removed from 25-ha West Long Lake, Nebraska from 2003 to 2006. The northern pike population was reduced from 36 fish ha⁻¹ and 22 kg ha⁻¹ in 2002 to 20 fish ha⁻¹ and 9 kg ha⁻¹ in 2006. The northern pike population shifted to dominance by smaller individuals. Relative abundance increased for bluegill, Lepomis macrochirus Rafinesque, but remained similar between years for largemouth bass, Micropterus salmoides (Lacepède), and yellow perch, Perca flavescens (Mitchill). Bluegill and yellow perch size structure increased probably because of reduced predation by northern pike. The effects of reduced northern pike density on largemouth bass were less evident. The largemouth bass population may be returning to higher density with smaller size structure observed before pike were introduced. The sport fish community responded positively to the removal of northern pike in this small lake.     

Seasonal spatial distribution of juvenile lake sturgeon in Muskegon Lake,Michigan, USA

We examined seasonal spatial distribution and diel movements of juvenile lake sturgeon Acipenser fulvescens in Muskegon Lake, Michigan (a protected, drowned river mouth lake that links the Muskegon River to Lake Michigan). We surgically implanted ultrasonic tags in 20 juveniles (age 1–7) captured in gill nets to track their locations during August–December 2008/2009 and September 2010–October 2011. Most juveniles were observed ≤1.5 km from the mouth of the Muskegon River in Muskegon Lake at a mean depth of 7.5 m (SE = 1.3 m) during summer. In fall, juveniles moved away from the river mouth to the deepest part of Muskegon Lake and were observed at a mean depth of 15.8 m (SE = 1.3 m) during winter. The shift in spatial distribution coincided with fall turnover (i.e., loss of thermal stratification) and with changes in dissolved oxygen (DO) concentrations in the hypolimnion. During summer, DO concentrations in the hypolimnion were typically <4 mg·l^?1 in the deepest part of Muskegon Lake and DO concentrations at locations of tagged lake sturgeon were >7 mg·l^?1 in 94% of instances. Tracking in 2009 revealed no significant change in depth distribution or movement over the diel cycle. We only observed two tagged juveniles immigrating to Lake Michigan, suggesting that juveniles use Muskegon Lake for multiple years. Our results suggest that: (i) Muskegon Lake serves as an important nursery habitat for juvenile lake sturgeon that hatched in the Muskegon River before they enter Lake Michigan and (ii) seasonal changes in DO concentration in the hypolimnion likely affect the spatial distribution of juveniles in Muskegon Lake.     

Movements by adult cutthroat trout in a lotic system: implications for watershed-scale management

Abstract  Movements by adult cutthroat trout, Oncorhynchus clarkii (Richardson), were assessed from autumn to summer in the Salt River watershed, Wyoming-Idaho, USA by radio telemetry. Adult cutthroat trout were captured during September and October 2005 in the main stem of the Salt River, surgically implanted with radio transmitters, and tracked through to August 2006. Adult cutthroat trout were relatively sedentary and resided primarily in pools from October to March, but their movement rates increased during April. Higher movement rates were observed among tagged fish during May and early June. Among 43 fish residing in the Salt River during April 2006, 44% remained in the river, 37% moved into mountain tributaries and 19% moved into spring streams during the spawning season. Fish did not use segments of mountain tributaries or the upstream Salt River where fish passage was blocked by anthropogenic barriers or the channel was dewatered during summer. Almost all the fish that moved into spring streams used spring streams where pools and gravel–cobble riffles had been constructed by landowners. The results suggest that adult Snake River cutthroat move widely during May and early June to use spawning habitat in mountain tributaries and improved spring streams. Maintaining the ability of adult fish to move into mountain streams with spawning habitat, preserving spawning habitat in accessible mountain tributaries and removing barriers to upstream movements, and re-establishing summer stream flows in mountain tributaries affected by dams appear to be habitat management alternatives to preserve the Snake River cutthroat trout fishery in the Salt River.     

Potential reasons for the changes in the abundance of pike, Esox lucius, in the western Gulf of Finland, 1939–2007

Abstract  Pike, Esox lucius L., catch-per-unit-effort (CPUE) in rod and line fishing fluctuated considerably in the western Gulf of Finland between 1939 and 2007. Since the beginning of the 1980s, CPUE has been only 3–4% of the highest CPUE during the period, suggesting a drastic decrease in population size. The collapse of the population coincided with a rise in the nutrient level in the Baltic Sea and consequent changes in productivity, turbidity and vegetation. The differences in the food web that followed the environmental change may partly explain the variation both in CPUE and in the mean weight of pike caught. Long-term fluctuations in salinity and temperature, however, did not seem to affect the population size. The mean weight of pike fluctuated inversely with CPUE, indicating changes in the recruitment of pike to the study area.     

Extinction of a weakly armoured threespine stickleback (Gasterosteus aculeatus) population in Prator Lake, Alaska

Abstract –  Threespine stickleback ( Gasterosteus aculeatus ) samples from Prator Lake in southcentral Alaska consist of the relatively rare form of weakly armoured individuals with few lateral plates and no pelvic spines. Prator Lake has been sampled for threespine stickleback since 1983. Exotic northern pike ( Esox lucius ) were first observed in this lake in 1996. The appearance of pike corresponds with a dramatic decrease in stickleback numbers and apparent local extinction. The stickleback population may have been vulnerable to an exotic predator because Prator Lake lacks native piscivorous fishes, and this population had extreme armour reduction.     

High variability in spawning migration of sea trout,Salmo trutta,in two northern Swedish rivers

Abstract Telemetry was used to examine spawning migration of sea trout, Salmo trutta L. (n = 126), in two rivers in northern Sweden. The spawning areas defined by radio‐tagged fish differed between the river systems. In the River Vindelälven, sea trout spawned in the main stem and 80% of tagged individuals returned to areas where hatchery‐reared juveniles had been previously stocked. In the River Piteälven, 74% of tagged sea trout ascended tributaries for spawning. Tagged fish were categorised into three groups of migratory pattern. cart (classification and regression tree) analysis indicated that distance from tagging location to spawning site (S_dist) explained the migratory patterns. Large S_dist separated fish with stepwise upstream migration from those with up‐ and downstream migrations and one‐directional direct migration. Fish tagged early in the season migrated the longest distance to spawning areas. Stocking locations and sex explained the large search behaviour up‐ and downstream in the rivers. The findings are important for the sustainable management of sea trout in the Gulf of Bothnia.     

Prey selection and diets of bluegill Lepomis macrochirus with differing population characteristics in two Nebraska natural lakes

Abstract  Environmental prey samples and stomach contents of bluegill Lepomis macrochirus (Rafinesque) were collected in spring and summer 2000 from two Nebraska Sandhill lakes. Watts Lake contained a low-density bluegill population, whereas Cozad Lake contained a high-density bluegill population. Bluegill diets from both lakes were compared to determine if bluegill prey preference differed between the two populations. The highest median per cent (by calories) of zooplankton in the diet was 1.3%; the remainder was macroinvertebrates. Watts Lake bluegills preferred (based on Manly's alpha) amphipods in spring and chironomids in summer. Cozad Lake bluegills did not show a strong preference (compared with Watts Lake) for any macroinvertebrates, but still utilized amphipods and chironomids during both seasons. Larger bluegills in Watts Lake preferred chironomids in summer, but Cozad Lake bluegills did not exhibit this relationship. The higher density Cozad Lake bluegill population appeared to be more opportunistic than the lower density Watts Lake population, but both preferred macroinvertebrates.     

Northern pike (Esox lucius) growth and mortality in a northern Ontario river compared with that in lakes: influence of flow

Abstract –  We measured the growth and mortality characteristics of northern pike ( Esox lucius ) in a northern Ontario river and examined the influence of flow on these characteristics by comparing our measurements with those estimated for a lake at the same latitude based on published studies. Pike ranged in total length from 229 to 784 mm, in mass from 70 to 4250 g, and in age from 1 to 10 years. The population showed a preponderance of 2–5-year olds, with few fish surviving beyond 7 years of age. Growth, in terms of length increase, was similar to that reported for circumpolar populations. Mean total length at 5 years of age was 577 mm, growth rate of young adults was 62.5 mm year⁻¹, growth was isometric, longevity was 10 years of age, and the adult annual mortality rate was 49%. Growth and mortality characteristics of this riverine population were similar to those estimated for a lacustrine population at the same latitude. Flow thus had little measurable effect on the growth or mortality of pike possibly because of the overwhelming effect of other abiotic variables such as temperature, length of growing season and productivity. Consequently, growth characteristics of lacustrine populations can be used to assess the health and condition of riverine populations.     

Emigration and mortality of juvenile brown trout in a New Zealand headwater tributary

We investigated juvenile brown trout migration and mortality in a headwater tributary of the Motueka River, New Zealand, by tracking 1000 young‐of‐the‐year passive integrated transponder (PIT) tagged fish over autumn to summer to (i) partition total loss into emigration and mortality and (ii) determine the influence of season and flow on emigration. Fish were tracked using mobile and fixed PIT tag readers. Of the 1000 fish tagged, 173 remained within the Rainy River; emigration contributed 60% and mortality 29% to loss. Only 11% of fish tagged in autumn were predicted to remain in the upper reaches of the stream by early summer, and this agreed with density data collected in a parallel study. We identified a two‐phase downstream migration pattern with early movement of large young‐of‐the‐year fish in autumn (mainly during floods). This was followed by another substantial period of movement in spring (during floods and lower flows) by fish that were initially smaller at the time of PIT tagging. The management implications for damming and fish screening in headwater tributaries are discussed.