Evidence of the selection of tidal streams by northern rock sole (Lepidopsetta polyxystra) for transport in the eastern Bering Sea

Depth data from archival tags on northern rock sole (Lepidopsetta polyxystra) were examined to assess whether fish used tidal currents to aid horizontal migration. Two northern rock sole, out of 115 released with archival tags in the eastern Bering Sea, were recovered 314 and 667 days after release. Both fish made periodic excursions away from the bottom during mostly night-time hours, but also during particular phases of the tide cycle. One fish that was captured and released in an area of rotary currents made vertical excursions that were correlated with tidal current direction. To test the hypothesis that the fish made vertical excursions to use tidal currents to aid migration, a hypothetical migratory path was calculated using a tide model to predict the current direction and speed during periods when the fish was off the bottom. This migration included limited movements from July through December, followed by a 200-km southern migration from January through February, then a return northward in March and April. The successful application of tidal current information to predict a horizontal migratory path not only provides evidence of selective tidal stream transport but indicates that vertical excursions were conducted primarily to assist horizontal migration

A Mixed Optimal Control Approach for Upstream Fish Migration

This paper proposes a simple mathematical model forupstream fish migration along rivers. The model describes the fish migration along a river based on a mixed optimal control approach having swimming velocity, school size, and stopping time of migration as control variables. The optimization problem reduces to a variational inequality. Its explicit “viscosity” solution is presented with the dependence of the fish migration on river environment. To prove uniqueness of the solution to the variational inequality requires a constructive argument not based on the conventional theorems. A novel finite difference scheme for solving the variational inequality is also proposed with its convergence results. An application example of the model discusses the upstream migration of Plecoglossus altivelis (Ayu) in Japan, which evaluates the dependence of the fish migration on the habitat quality and provides recommendations for managing river environment. This is an interdisciplinary research between environmental and mathematical fields

A foraging cost of migration for a partially migratory cyprinid fish

Migration has evolved as a strategy to maximise individual fitness in response to seasonally changing ecological and environmental conditions. However, migration can also incur costs, and quantifying these costs can provide important clues to the ultimate ecological forces that underpin migratory behaviour. A key emerging model to explain migration in many systems posits that migration is driven by seasonal changes to a predation/growth potential (p/g) trade-off that a wide range of animals face. In this study we assess a key assumption of this model for a common cyprinid partial migrant, the roach Rutilus rutilus, which migrates from shallow lakes to streams during winter. By sampling fish from stream and lake habitats in the autumn and spring and measuring their stomach fullness and diet composition, we tested if migrating roach pay a cost of reduced foraging when migrating. Resident fish had fuller stomachs containing more high quality prey items than migrant fish. Hence, we document a feeding cost to migration in roach, which adds additional support for the validity of the p/g model of migration in freshwater systems

Marine reserves. A bio-economic model with asymmetric density dependent migration

A static bioeconomic model of a marine reserve allowing asymmetric density dependent migration between the reserve and the fishable area is introduced. This opens for habitat or ecosystem differences allowing different fish densities within and outside a reserve, not described in earlier studies. Four management scenarios are studied; a) maximum harvest, b) maximum current profit, c) open access and d) maximum sustainable yield (MSY) in the reserve. These are all analysed within the Induced Sustainable Yield Function (ISYF), giving the relationship between the fish abundance inside the reserve and the harvesting taking place outside. A numerical analysis shows that management focused on ensuring MSY within the reserve under the assumption of symmetric migration may be negative from an economic point of view, when the area outside the reserve is detrimental compared to the reserve. Furthermore, choice of management option may also have negative consequences for long run resource use if it is incorrectly assumed that density dependent migration is symmetric. The analysis also shows that the optimal area to close, either a more or a less attractive ecosystem for the resource in question, may differ depending on the management goal.bioeconomics; marine reserves; migration; management

MARINE RESERVES: WHAT WOULD THEY ACCOMPLISH?

A marine reserve is defined as a subset of the area over which a fish stock is dispersed and closed to fishing. This paper investigates what will happen to fishing outside the marine reserve and to the stock size in the entire area as a result of establishing a marine reserve. Three regimes are compared: (i) open access to the entire area, (ii) open access to the area outside the marine reserve, and (iii) optimum fishing in the entire area. Two models are used: (i) a continuous-time model, and (ii) a discrete-time model, both using the logistic growth equation. Both models are deterministic equilibrium models. The conservation effect of a marine reserve is shown to be critically dependent on the size of the marine reserve and the migration rate of fish. A marine reserve will increase fishing costs and overcapitalization in the fishing industry, to the extent that it has any conservation effect on the stock, and in a seasonal fishery it will shorten the fishing season. For stocks with moderate to high migration rates, a marine reserve of a moderate size will have only a small conservation effect, compared with open access to the entire area inhabited by a stock. The higher the migration rate of fish, the larger the marine reserve must be in order to achieve a given level of stock conservation. A marine reserve of an appropriate size would achieve the same conservation effect as optimum fishing, but with a smaller catch.Resource /Energy Economics and Policy,

Seasonal Migration Determined by a Trade-Off between Predator Avoidance and Growth

Migration is a common phenomenon in many organisms, terrestrial as well as aquatic, and considerable effort has been spent to understand the evolution of migratory behaviour and its consequences for population and community dynamics. In aquatic systems, studies on migration have mainly been focused on commercially important fish species, such as salmon and trout. However, seasonal mass-migrations may occur also among other freshwater fish, e.g. in cyprinids that leave lakes and migrate into streams and wetlands in the fall and return back to the lake in spring. In a conceptual model, we hypothesized that this is an adaptive behaviour in response to seasonal changes in predation (P) and growth (G) and that migrating fish change habitat so as to minimise the ratio between predation mortality and growth rate (P/G). Estimates from bioenergetic modelling showed that seasonal changes in the ratio between predator consumption rate and prey growth rate followed the predictions from the conceptual model and also gave more precise predictions for the timing of the habitat change. By quantifying the migration of more than 1800 individually marked fish, we showed that actual migration patterns followed predictions with a remarkable accuracy, suggesting that migration patterns have evolved in response to seasonally fluctuating trade-offs between predator avoidance and foraging gains. Thus, the conceptual model provides a mechanistic understanding to mass–migration in prey fish. Further, we also show that the dominant prey fish is actually absent from the lake during a major part of the year, which should have strong implications for the dynamics of the lake ecosystem through direct and indirect food-web interactions

Regulation of zooplankton vertical migrations by light, food, and fish

The regulation of zooplankton vertical migration has been attributed to the physical environment, and, more recently, to biological factors. This study evaluated the influence of light, food and fish on vertical migration. Laboratory experiments quantified changes in vertical migrations of Daphnia pulex in tall columns in response to short term changes in food concentration and the presence of a fish, under a wide range of natural light conditions. A stimulus-threshold model predicted the time of the start of migration from a threshold rate of relative light intensity change. Hypotheses that migrations follow isopleths of light intensity, and that velocity of migration is directly correlated to relative rate of light intensity change, were not supported. Concentrations of Chlorella sp. had little influence on the timing, amplitude, or velocity of migration. There was evidence of a sensory response of Daphnia pulex to the short term presence of a fish in the columns. With a fish present, pre-migration population depths were deeper. This response ceased within 24 hours after removing the fish. Juvenile Daphnia pulex started their migrations from shallower depths in the columns, and otherwise migrated similarly to adults. Field studies of zooplankton vertical migration were conducted on four New Hampshire lakes. The lakes varied in food concentrations, and all contained planktivorous fish. The field results were consistent with an avoidance of ultra-violet radiation by zooplankton. Pre-migration depths were deeper in waters more transparent to visible light. Food stratification was correlated with amplitude and direction of vertical migration, and the direction of migration was apparently influenced by the phytoplankton composition. Although planktivorous fish were present in the lakes, the zooplankton did not take advantage of possible light refugia. Fish density did not significantly affect vertical migrations. Invertebrate predation was not sufficient to explain reverse migrations

Influence of hydraulics on the dowsntream migratory route of Atlantic salmon (Salmo salar)

The interaction between hydrodynamics and the upstream migration of fish has been investigated in several studies over the past few years, but there has been a relative lack of investigation into the effects of hydraulics on the downstream migration of fish. In Norway, mortality associated with downstream migration is strongly related to hydropower production. However, there is a poor understanding of how fish choose their migratory routes, which limits the development of measures to mitigate the impact of anthropogenic structures on fish migration. The current study aimed to analyze the effect of hydraulics on the choice of downstream migration route of Atlantic salmon smolts (Salmo salar) in the proximity of an intake to a hydropower plant in Norway. We combined computational fluid dynamic modeling with 3-Dimensional acoustic telemetry positioning of a group of tagged smolts to investigate the interaction between fish and the flow dynamics, and to determine the influence of this interaction on fish migratory routes. A Hidden Markov Model was used to predict migratory routes based on the relations found between the hydraulic variables and fish behaviour. Results showed relationships between fish migratory routes and the different components of flow velocity. The knowledge acquired in this study is expected to inform opportunities and decision making in aquatic resources management and engineering design to increase fish survival past hydropower intakes and other anthropogenic structures

Interdisciplinary design of a fish ramp using migration routes analysis

The study presents several steps of a fish ramp geometry optimization performed with a 3D numerical model DualSPHysics, which is based on the smoothed particle hydrodynamics (SPH) method. The optimization process led to the design of a bottom ramp that is capable of providing suitable conditions for the migration of target fish species (Salmo truta, Phoxinus phoxinus, Cottus gobio, and Eudontomyzon vladykovi). Migration routes were determined as complex 3D volumes of fluid according to the simulated velocity field in various steady flow conditions. Including three categories of potential migration zones (rest, effort, and limit zones), migration routes were quantified in high detail in terms of the size and position of each zone, and in terms of the distance from a given fluid part to the nearest rest zone. The interdisciplinary approach of this study also led to the development of new tools for the DualSPHysics model, specifically suited to improve functionality in eco-hydraulics research. Fishway Ramp River restoration Smoothed particle hydrodynamics DualSPHysicspublishedVersio

Habitat Selection by Lacustrine Rainbow Trout within Gradients of Temperature, Oxygen, and Food Availability

Rainbow trout (Oncorhynchus mykiss [Walbaum]) in Castle Lake, California were concentrated at certain depths during day and evening hours. A fish bioenergetics simulation model based on vertical gradients of temperature, oxygen concentration, and food availability indicated that rainbow trout selected habitats that maximized growth rate. In 1 of the 2 years of study, a strong pattern of diel vertical migration of rainbow trout was evident and was associated with vertical migrations of daphnids in the lake. The simulation model correctly predicted the occurrence and magnitude of fish migration. During the day some trout resided at depths with little potential for feeding and growth but close to-regions of high food availability and low oxygen concentrations. Hydroacoustic sampling from stationary platforms suggested that fish briefly descended into anoxic layers to feed on abundant zooplankton