A pike management strategy for a trout fishery

The efficiency of pike removal from a chalkstream trout fishery, by an angling society using electrofishing, was estimated over five successive autumns using mark-recapture methods. It averaged c . 50% for pike aged 1+ years or more. Numbers of 3+ and older pike decreased from 3.7 ha^-1 (1980) to 1.4 ha^-1 (1984), but there was no corresponding reduction in recruitment success. Both pike immigration and an inverse relationship between natural and fishing mortality could have reduced the effect of the pike culls. The mean weight of 0+ pike increased from 19.4 g to 48.2 g over the 5 years, but there was no change in the growth rates of older pike. Only the larger pike were able to eat the larger trout stocked, and the reduction in numbers of 3 + and older pike appears to have reduced the predation pressure on the trout population. Angling effort increased more than three-fold over the 5 years studied and rod-catches more than doubled, but catch-per-unit-effort was extremely variable between years. The increased rod catch occurred despite the decrease in numbers of large (> 33 cm) trout stocked in the spring and early summer. Compared with pre-cull years, the angling society saved about ş850 (present day prices) by stocking fewer trout.     

Predation Threat Affects Behaviour and Habitat Use by Hatchery Brown Trout (Salmo Trutta L.) Juveniles

The effect of predation threat on behaviour and habitat use by brown trout (Salmo trutta L.) juveniles were studied in four indoor and six outdoor experimental channels. Northern pike (Esox lucius L.) was used as a predator. Brown trout were more active during the night compared to day, but in the presence of pike the increase in activity was less than in treatments without predator. Aggressive interactions between trout were higher during the day when pike was absent. In the presence of pike trout tended to use more coarse substrate classes as subdominant habitat suggesting increased use of cover and also higher or lower water depths. Our results increase knowledge of the effects of predation threat on habitat selection and behaviour by brown trout.     

The critical-period concept for juvenile survival and its relevance for population regulation in young sea trout, Salmo trutta

An example of density-dependent regulation is provided by a long-term investigation (1966-present) of a population of migratory trout (estuarine and sea trout), Salmo trutta L., in a Lake District stream. Evidence for the concept of a critical period for the survival of young fish is briefly reviewed and found to be rather equivocal. The concept is, however, relevant to the trout population. Loss rates were high before but low after a critical survival time ( t_c days after fry emergence) that varied between year-classes (range 33-70 days) and was inversely density-dependent on egg density. Survivor density and loss rates were strongly density-dependent on egg density before t _c, but proportionate survival with stable loss-rates occurred after t _c. Some trout established feeding territories soon after emergence and the number of fish without territories decreased from a high initial value to a negligible value at t _c. Fish size at t_c was not constant but increased as t _c increased. The range of t _c for the different year-classes was similar to that for survival times of unfed fry in the laboratory. A new stock-recruitment model, incorporating t _c, has been developed for the trout population and shown to be related to the model (Ricker curve) used in the long-term study. The critical time can also be regarded as the critical age for survival in young trout; this concept may be relevant to other fish species.     

Experimental manipulations of the fish populations in Windermere

A large scale experiment has been carried out on the perch and pike populations of Windermere in the English Lake District for nearly 40 years, and the objectives have changed over this period. Initially the aim was to manage the trout population, but the work has produced data of interest in predator-prey relationships and pike management. Perch were first heavily fished and then monitored for size, and numbers by trapping. Large pike have been culled by gill netting. The effects of pike gill netting have been to increase the growth rate and decrease the average age in the population. These changes in the pike population structure, together with climatic variations, have modified the perch population. The perch did not recover from the heavy fishing for many years and the population numbers remained low due to pike predation supressing recruitment. It was not until a large cohort, mainly controlled by the weather, was produced that the population increased. Cannibalism by these perch later combined with the pike predation to suppress future cohorts. There have also been as yet unexplained changes in the perch mortality rates. The experiments have led to a greater understanding of the relationship between pike and perch populations, but the use of this knowledge for management depends on what the objectives are.     

Reproduction effort versus the environment; case histories of Windermere perch, Perca fluviatilis L., and pike, Esox lucius L.

The theoretical limits of net reproduction rates for perch, Perca fluviatilis L. and pike, Esox lucius L, have been estimated from the upper and lower limits of fecundity, growth, mortality, age of maturity and biomass of parental stock, observed in Windermere over 40 years. Differences in egg numbers due to changes in fecundity were for perch × 1.5, for pike × 2. Assuming the same mortality, a fast growing cohort would produce more eggs during its lifespan than a slow growing, for perch × 2, for pike × 9. Changes in mortality from high to low resulted in more eggs, for perch × 7, and for pike (where high mortality includes natural and fishing mortality) × 10. Change in age at first maturity from 3 to 2 years was unimportant. Biomass of parental stock varied by × 6 for perch and × 3 for pike, and number of eggs laid varied by x2 for perch and × 5 for pike. The number of recruits at age 2 years varied by × 300 for perch and × 7 for pike. It was concluded that temperature in the first summer of life and predation were of major importance in regulating the number of recruits. Ricker recruitment curves and a simple model showed that perch, but not pike, could produce maximum recruitment from minimum parental stock. For perch, but not pike, compensatory density dependent mortality increased with increased parental stock. It was concluded that responses by the perch and pike populations to a changing environment can not be of sufficient magnitude to prevent wide fluctuations in recruitment.     

The ecology of brown trout Salmo trutta in English chalk streams

SUMMARY. .1. Chalkstream trout are fast-growing, short-lived with a stable age structure that is a consequence of the lack of extremes in the abiotic environment, especially of water temperature and flow.
2. Levels of secondary (invertebrate) production arc high and there is no evidence that interspecific or intraspecific competition for food resources limits growth.
3. Dietary studies show a broad similarity between trout and other species, but indicate differences that reflect variations in the micro-habitat distributions between fish species.
4. Trout numbers appear to be limited initially by the availability of gravel spawning areas, and then by areas suitable for newly-emerged fry. Reduction in stream discharge in the spring, either naturally or by man, can lower the number of 0+ trout that survive.
5. Eels are not important predators on trout eggs or fry. but a reduction in pike numbers can lead to a decrease in the mean weight of pike. Small pike do not pose a serious threat to stocked yearling trout.     

Transmission of Tetracapsuloides bryosalmonae (Myxozoa: Malacosporea) to Fredericella sultana (Bryozoa: Phylactolaemata) by various fish species

Tetracapsuloides bryosalmonae is a myxozoan parasite of salmonids and freshwater bryozoans, which causes proliferative kidney disease (PKD) in the fish host. To test which fish species are able to transmit T. bryosalmonae to bryozoans, an infection experiment was conducted with 5 PKD-sensitive fish species from different genera. Rainbow trout Oncorhynchus mykiss, brown trout Salmo trutta, brook trout Salvelinus fontinalis, grayling Thymallus thymallus and northern pike Esox lucius were cohabitated with T. bryosalmonae-infected Fredericella sultana colonies and then subsequently cohabitated with statoblast-reared parasite free Bryozoa. Statoblasts from infected colonies were tested by PCR to detect cryptic stages of T. bryosalmonae, which may indicate vertical transmission of the parasite. In this study, brown trout and brook trout were able to infect Bryozoa, while there was no evidence that rainbow trout and grayling were able to do so. Few interstitial kidney stages of the parasite were detected by immunohistochemistry in brown trout and brook trout, while rainbow trout and grayling showed marked proliferation of renal interstitial tissue and macrophages with numerous parasite cells. Intraluminal stages in the kidney tubules were only detected in brown trout and rainbow trout. In contrast to previous observations, pike was not susceptible to PKD in these trials according to the results of T. bryosalmonae-specific PCR. No DNA of T. bryosalmonae was detected in any statoblast.     

Serine proteinase inhibitors of seminal plasma of teleost fish: distribution of activity, electrophoretic profiles and relation to proteinase inhibitors of blood

Anti-proteinase activity has been found in seminal plasma of eight teleost fish species: brown trout, rainbow trout, brook trout, lake whitefish, bream, northern pike, Danube salmon and burbot. This activity correlated with seminal plasma protein and sperm concentrations. Using a mammalian (bovine) trypsin for detecting proteinase inhibitors it was found for the first time that there are species-specific electrophoretic profiles of anti-proteinase activity. One to three bands could be identified by this method. However, additional proteinase inhibitors could be identified by using fish (cod) trypsin. These inhibitors were detected in seminal plasma of salmonids and coregonids and have a slow migration rate. Fast-migrating proteinase inhibitors were present in rainbow, brown and brook trout, northern pike, whitefish and burbot. These inhibitors could be detected in brook and brown trout by using either trypsins. However, they were detected only with bovine trypsin in rainbow trout, northern pike, whitefish and burbot. These results suggest that multiple forms of serine proteinase inhibitors exist in seminal plasma of teleost fish and they differ in their affinity toward serine proteinases. Seminal plasma serine proteinase inhibitors of rainbow trout migrated during electrophoresis similarly to blood plasma proteinase inhibitors, and suggests that the two inhibitors may be similar or the same. Anti-proteinase specific activity was similar in blood and seminal plasma. Proteinase inhibitors of fish seminal plasma seem to be an important part of sperm physiology, possibly related to protection of spermatozoa. Staining for detection of serine proteinase inhibitors also allowed detection of presence of nonspecific esterase in seminal plasma of most species.     

Effects of predation, trout density and discharge on habitat use by brown trout, Salmo trutta, in artificial streams

1. The effects of predation risk, fish density and discharge on habitat use by juvenile brown trout, Salmo trutta, in four artificial streams were studied. Each stream contained three habitats, riffles, runs and pools, the latter two each being further divided into shallow margins and deeper mid-regions. 2. The presence of northern pike, Esox Indus, caused trout to decrease use of pool midregions, where pike also occurred, and to increase use of other habitats. Increasing the number of trout caused trout to increase use of pools and the shallow margins of runs. Decreasing discharge reduced the area of the run and pool margins covered by water, thereby reducing use of these areas by trout. 3. Habitat selection indices for the different treatments were calculated. The data indicated that riffles and the mid-regions of runs were preferred habitats, whereas run margins and pools were inferior habitats used when intraspecific fish densities were high. 4. Despite density- and discharge-dependent habitat use by trout, the number of trout consumed by pike was independent of trout density and discharge. 5. The results reveal the flexibility of habitat use by trout and illustrate the potential danger of applying data on habitat use in one stream to others where habitat availability and bioric interactions may differ.     

Antibodies against Discocotyle sagittata (Monogenea) in farmed trout

The relationship between Discocotyle sagittata intensities and host length, weight and specific anti-parasite antibody titres was studied in 3 year-classes of farmed rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta at the end of the annual transmission cycle. Antibody titres were significantly higher in infected farmed fish than in naive controls, indicating that infection elicits immunoglobulin production. No correlation was found between host size and parasite burdens, nor between infection intensities and antibody titres.     

Fish introductions reveal the temperature dependence of species interactions

A major area of current research is to understand how climate change will impact species interactions and ultimately biodiversity. A variety of environmental conditions are rapidly changing owing to climate warming, and these conditions often affect both the strength and outcome of species interactions. We used fish distributions and replicated fish introductions to investigate environmental conditions influencing the coexistence of two fishes in Swedish lakes: brown trout (Salmo trutta) and pike (Esox lucius). A logistic regression model of brown trout and pike coexistence showed that these species coexist in large lakes (more than 4.5 km²), but not in small, warm lakes (annual air temperature more than 0.9–1.5°C). We then explored how climate change will alter coexistence by substituting climate scenarios for 2091–2100 into our model. The model predicts that brown trout will be extirpated from approximately half of the lakes where they presently coexist with pike and from nearly all 9100 lakes where pike are predicted to invade. Context dependency was critical for understanding pike–brown trout interactions, and, given the widespread occurrence of context-dependent species interactions, this aspect will probably be critical for accurately predicting climate impacts on biodiversity.     

A nondestructive,rapid, reliable and inexpensive method to sample,store and extract high‐quality DNA from fish body mucus and buccal cells

A rapid, nondestructive, reproducible and cheap DNA extraction method from body mucus and buccal cells of northern pike and brown trout is described. Buccal cells and body mucus were sampled on FTA Cards; the captured DNA was used directly for microsatellite and polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) analyses. A complete concordance with control DNA was found. The genotyping error rate for microsatellite ranged from 1.9% to 3.3% for the northern pike and brown trout, respectively. This methodology, using for the first time these materials as a fish DNA source, combines speed of sampling and processing, with a twofold to a threefold time and costs saving.     

Temperature dependence of predation depends on the relative performance of predators and prey

The temperature dependence of predation rates is a key issue for understanding and predicting the responses of ecosystems to climate change. Using a simple mechanistic model, we demonstrate that differences in the relative performances of predator and prey can cause strong threshold effects in the temperature dependence of attack rates. Empirical data on the attack rate of northern pike (Esox lucius) feeding on brown trout (Salmo trutta) confirm this result. Attack rates fell sharply below a threshold temperature of +11°C, which corresponded to a shift in relative performance of pike and brown trout with respect to maximum attack and escape swimming speeds. The average attack speed of pike was an order of magnitude lower than the escape speed of brown trout at 5°C, but approximately equal at temperatures above 11°C. Thresholds in the temperature dependence of ecological rates can create tipping points in the responses of ecosystems to increasing temperatures. Thus, identifying thresholds is crucial when predicting future effects of climate warming.     

A 27-year study of brown trout population dynamics and exploitation in Lake Songsjøen, central Norway

From 1968–1984 (period I), a brown trout Salmo trutta , population in a 70-ha oligotrophic lake in central Norway was exploited using larger mesh gill-nets selectively removing the larger fish. From 1985–1994 (period II), intermediate sized fish were removed using smaller-mesh sizes gill-nets. Fishing mortality and CPUE were correlated positively with effort and numbers of fish >3 years old for period II. The gill-net catchability was correlated negatively with spawner biomass and number of trout >3 years old. The significant positive correlation between natural mortality and stock biomass and spawning stock biomass indicated density-dependent mortality. The significant correlation between spawning stock and recruitment described by the Ricker model, indicated density-dependent recruitment of 1-year-old trout. The fishing regimes in the two periods affected the population dynamics and density differently. Selective removal of smaller fish permitted the larger fish to survive, and was beneficial in reducing fish density and maintaining stocks at low levels, consequently, achieving the expected increase in fish growth rates.     

Long-term studies on the Windermere populations of perch (Perca fluviatilis), pike (Esox lucius) and Arctic charr (Salvelinus alpinus)

SUMMARY. 1, Windermere is a glacial valley lake with two basins separated by shallows and a total area of 14.8 km². Perch, pike and charr are the dominant fish species and have been studied on a continuous basis for over 45 years.
2. The initial slow-growing stocks of numerous small perch and moderate numbers of large pike were subjected to a heavy initial fishing pressure that was subsequently relaxed for perch but not for larger (>550 mm) pike. The number of charr in the lake has increased 6–8-fold during the study, probably due to the sustained reduction in the abundance of the larger pike that heavily predate the autumn spawning race of charr when it enters the shallow littoral areas to spawn.
3. The biomass of perch did not recover from the initial fishery until the late 1950s when strong year-classes occurred in warm summers. However, it was now composed of larger and faster growing individuals. In 1976, disease killed over 98% of all adult perch in the lake and the subsequent recovery has again been slow.
4. Existing models have explained the variation in perch year-class strength for the years 1959–74 in terms of adult perch biomass, pike cohort strength and temperature in the year of hatch. A new. more generally applicable model, incorporating a stock-recruitment expression, gives a better fit to the earlier data, particularly from the North Basin, where there have been periods of extremely low adult biomass.
5. The importance of continuing to extend these long-term data sets and the scope for future modelling work are discussed.     

Trophic relationships of two species of grebe on a prairie lake based on stable isotope analysis

Loch Leven, U.K., contains brown trout (Salmo trutta), eel (Anguilla anguilla), minnow (Phoxinus phoxinus), perch (Perca fluviatilis), pike (Esox lucius) and three-spined stickleback (Gasterosteus aculeatus), with brook lamprey (Lampetra planeri) and stone loach (Barbatula barbatula) also present in its tributaries. Arctic charr (Salvelinus alpinus), Atlantic salmon (Salmo salar) and flounder (Platichthys flesus) are now extinct. The brown trout population has supported a world-renowned recreational fishery for over a century, although a decline in fishery performance led to extensive stocking between 1983 and 2006, including with non-native rainbow trout (Oncorhynchus mykiss). This review combines historical information with contemporary gill-net and hydroacoustic surveys. In 2008, brown trout, perch and three-spined sticklebacks were abundant, but pike and stone loach were rare. The obstruction of migratory routes was probably responsible for the loss of Atlantic salmon and flounder, while a lowering of water level likely caused the extinction of Arctic charr and contributed to a reduction in pike abundance. Perch abundance has fluctuated markedly, being influenced by disease and eutrophication, although a reduction in nutrients and associated recovery of macrophytes are likely to have benefitted this species. Although the brown trout population has undoubtedly shown a long-term decline, individuals are currently in excellent condition.     

The dynamics of the abundance of the walleye pollock <Emphasis Type="Italic">Theragra chalcogramma</Emphasis> (Pallas, 1814) (gadiformes: gadidae) in the Sea of Japan

The biomass of the walleye pollock (Theragra chalcogramma) stock in waters of Primorskii krai, Sea of Japan, during the 1976–2015 observation period ranged from 48000 to 373000 tons; their number ranged from 99 to 1115 million fish. Four very strong year-classes born in 1975, 1981, 1997, and 2006 have been identified. It has been shown that the duration of the sexual-maturity period is determined by the periodicity of the dynamics of the year-class strength close to the 9-year cycle. According to the results of numerical modeling, an increase in the walleye pollock stock in Primorye is expected from 2017 to 2020.     

Proteolytic activity and electrophoretic profiles of proteases from seminal plasma of teleosts

Using gelatin-SDS-PAGE, proteolytic activity was found in the seminal plasma of 10 teleosts: common carp Cyprinus carpio , bream Abramis brama , ide Leuciscus idus , chub Leuciscus cephalus , rainbow trout Oncorhynchus mykiss , grayling Thymallus thymallus , perch Perca fluviatilis , pike Esox lucius , goldfish Carassius carassius and pikeperch Stizostendion lucioperca . This activity was also measured, using azoalbumin as a substrate, in the seminal plasma of these species, with exception of pikeperch and goldfish. When azoalbumin-hydrolysing activity was expressed per volume, it was highest in common carp. Otherwise, as expressed per g of protein, the activity was highest in pike. The lowest proteolytic activity (expressed per g and volume) was observed in perch seminal plasma. Using gelatin containing polyacrylamide gels for detecting gelatinolytic activity, species-specific electrophoretic profiles were found. For all cyprinids two similar bands with a molecular mass of 68 and 74 kDa were found. The seminal plasma of grayling and rainbow trout showed similarities in the 41 kDa band. Perch and pikeperch had one similar main band with a molecular mass of 61 kDa. Proteolytic enzymes of seminal plasma from pike showed high individual variability. These results suggest that multiple forms of proteolytic enzymes exist in seminal plasma of teleosts and they differ among fish families and species.     

Influence of hydrologic attributes on brown trout recruitment in low-latitude range margins

Factors controlling brown trout Salmo trutta recruitment in Mediterranean areas are largely unknown, despite the relevance this may have for fisheries management. The effect of hydrological variability on survival of young brown trout was studied during seven consecutive years in five resident populations from the southern range of the species distribution. Recruit density at the end of summer varied markedly among year-classes and rivers during the study period. Previous work showed that egg density the previous fall did not account for more than 50% of the observed variation in recruitment density. Thus, we expected that climatic patterns, as determinants of discharge and water temperature, would play a role in the control of young trout abundance. We tested this by analyzing the effects of flow variation and predictability on young trout survival during the spawning to emergence and the summer drought periods. Both hatching and emergence times and length of hatching and emergence periods were similar between years within each river but varied considerably among populations, due to differences in water temperature. Interannual variation in flow attributes during spawning to emergence and summer drought affected juvenile survival in all populations, once the effect of endogenous factors was removed. Survival rate was significantly related to the timing, magnitude and duration of extreme water conditions, and to the rate of change in discharge during hatching and emergence times in most rivers. The magnitude and duration of low flows during summer drought appeared to be a critical factor for survival of young trout. Our findings suggest that density-independent factors, i.e., hydrological variability, play a central role in the population dynamics of brown trout in populations from low-latitude range margins. Reported effects of hydrologic attributes on trout survival are likely to be increasingly important if, as predicted, climate change leads to greater extremes and variability of flow regimes.