Coupling age-structured stock assessment and fish bioenergetics models: a system of time-varying models for quantifying piscivory patterns during the rapid trophic shift in the main basin of Lake Huron

2015 ◽  
Vol 72 (1) ◽  
pp. 7-23 ◽  
Author(s):  
Ji X. He ◽  
James R. Bence ◽  
Charles P. Madenjian ◽  
Steven A. Pothoven ◽  
Norine E. Dobiesz ◽  
...  
Keyword(s):  
Alternative Energy ◽  
Lake Trout ◽  
Stock Assessment ◽  
Time Varying ◽  
Rainbow Smelt ◽  
Trophic Shift ◽  
Fish Bioenergetics ◽  
Age Structured ◽  
Time Varying Models ◽  
Energy Pathways

We quantified piscivory patterns in the main basin of Lake Huron during 1984–2010 and found that the biomass transfer from prey fish to piscivores remained consistently high despite the rapid major trophic shift in the food webs. We coupled age-structured stock assessment models and fish bioenergetics models for lake trout (Salvelinus namaycush), Chinook salmon (Oncorhynchus tshawytscha), walleye (Sander vitreus), and lake whitefish (Coregonus clupeaformis). The model system also included time-varying parameters or variables of growth, length–mass relations, maturity schedules, energy density, and diets. These time-varying models reflected the dynamic connections that a fish cohort responded to year-to-year ecosystem changes at different ages and body sizes. We found that the ratio of annual predation by lake trout, Chinook salmon, and walleye combined with the biomass indices of age-1 and older alewives (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax) increased more than tenfold during 1987–2010, and such increases in predation pressure were structured by relatively stable biomass of the three piscivores and stepwise declines in the biomass of alewives and rainbow smelt. The piscivore stability was supported by the use of alternative energy pathways and changes in relative composition of the three piscivores. In addition, lake whitefish became a new piscivore by feeding on round goby (Neogobius melanostomus). Their total fish consumption rivaled that of the other piscivores combined, although fish were still a modest proportion of their diet. Overall, the use of alternative energy pathways by piscivores allowed the increases in predation pressure on dominant diet species.

scholarly journals Looking in the rear-view mirror: bias and retrospective patterns in integrated, age-structured stock assessment models

2014 ◽  
Vol 72 (1) ◽  
pp. 99-110 ◽  
Author(s):  
Felipe Hurtado-Ferro ◽  
Cody S. Szuwalski ◽  
Juan L. Valero ◽  
Sean C. Anderson ◽  
Curry J. Cunningham ◽  
...  
Keyword(s):  
Life Histories ◽  
Temporal Change ◽  
Stock Assessment ◽  
Model Misspecification ◽  
Assessment Model ◽  
Time Varying ◽  
Simulation Framework ◽  
Zero Values ◽  
Age Structured ◽  
Management Advice

Abstract Retrospective patterns are systematic changes in estimates of population size, or other assessment model-derived quantities, that occur as additional years of data are added to, or removed from, a stock assessment. These patterns are an insidious problem, and can lead to severe errors when providing management advice. Here, we use a simulation framework to show that temporal changes in selectivity, natural mortality, and growth can induce retrospective patterns in integrated, age-structured models. We explore the potential effects on retrospective patterns of catch history patterns, as well as model misspecification due to not accounting for time-varying biological parameters and selectivity. We show that non-zero values for Mohn’s ρ (a common measure for retrospective patterns) can be generated even where there is no model misspecification, but the magnitude of Mohn’s ρ tends to be lower when the model is not misspecified. The magnitude and sign of Mohn’s ρ differed among life histories, with different life histories reacting differently from each type of temporal change. The value of Mohn’s ρ is not related to either the sign or magnitude of bias in the estimate of terminal year biomass. We propose a rule of thumb for values of Mohn’s ρ which can be used to determine whether a stock assessment shows a retrospective pattern.

Predator responses to prey population dynamics: an empirical analysis based on lake trout growth rates

1995 ◽  
Vol 52 (7) ◽  
pp. 1564-1571 ◽  
Author(s):  
Lisa A. Eby ◽  
Lars G. Rudstam ◽  
James F. Kitchell
Keyword(s):  
Growth Rates ◽  
Prey Density ◽  
Lake Trout ◽  
Energy Content ◽  
Stock Assessment ◽  
Lake Superior ◽  
Average Density ◽  
Rainbow Smelt ◽  
Search Volume ◽  
Consumption Rates

Lake trout (Salvelinus namaycush) growth rates were lower in Lake Superior (with the lowest prey density) than in Lakes Michigan and Ontario. In contrast, consumption rates (estimated using bioenergetics models) of lake trout were similar in Lakes Superior, Michigan, and Ontario because the primary prey in Lake Superior, rainbow smelt (Osmerus mordax), have a lower energy content than the primary prey in Lakes Michigan and Ontario, alewife (Alosa pseudoharengus). Estimated consumption rates did not respond to three-to five-fold changes in prey density within lakes and were similar across a 100-fold difference in prey density among lakes. These results demonstrate that lake trout are able to sustain high predation rates at low prey densities and a type II functional response fitted to these data rises very steeply at low prey densities. Two factors are implicated: the large search volume of these predators and disparity between the average density estimates of prey stock assessment and the spatial and temporal scaling appropriate for understanding predator–prey interactions. If prey are highly aggregated or predators can search large areas, then a decrease in whole-lake prey abundance will not necessarily result in a lower predation rate until prey populations are severely reduced.

Dynamics of lake trout production in the main basin of Lake Huron

2020 ◽  
Vol 77 (3) ◽  
pp. 975-987
Author(s):  
Ji X He ◽  
James R Bence ◽  
Charles P Madenjian ◽  
Randall M Claramunt
Keyword(s):  
Fishery Management ◽  
Lake Trout ◽  
Stock Assessment ◽  
Round Goby ◽  
Lake Huron ◽  
Prey Fish ◽  
Total Consumption ◽  
Age Structured ◽  
Population Mortality ◽  
Ecosystem Changes

Abstract To inform lake trout (Salvelinus namaycush) fishery management in Lake Huron that has undergone rapid ecosystem changes, we quantified lake trout production dynamics by coupling age-structured stock assessment and fish bioenergetics models. Our approach revealed the connection between piscivore production and prey consumption, included growth compensation to reproduction losses, and allowed comparisons between long-term dynamics of fishery harvests and fish production. We found that, despite the collapse of alewives, a major non-native pelagic prey fish, lake trout production appeared to be sustainable. To a certain degree, the effect of recent recruitment declines on lake trout production was offset by the release of harvest pressure from subadult lake trout and reduction in fishing and sea lamprey-induced mortality on adult lake trout. Evidence for sustainability also included the finding that no changes in average ratios of annual production to beginning-of-the-year biomass. Juvenile P:B ratio remained as high as 2.1. The effect of growth declines on adult and subadult production was offset by reduction in population mortality. Body growth and condition did not continue to decline when lake trout became more and more reliant on round goby as food, and the dynamics of total consumption of prey fish continued to be recipient controlled.

Integrated multi-timescale modeling untangles anthropogenic, environmental, and biological effects on catchability

2019 ◽  
Vol 76 (11) ◽  
pp. 2045-2056 ◽  
Author(s):  
Shota Nishijima ◽  
Shigenori Suzuki ◽  
Momoko Ichinokawa ◽  
Hiroshi Okamura
Keyword(s):  
Population Dynamics ◽  
Stock Assessment ◽  
Biological Effects ◽  
Predictive Ability ◽  
Fishing Effort ◽  
Estimation Accuracy ◽  
Takifugu Rubripes ◽  
Time Varying ◽  
Population Dynamics Model ◽  
Age Structured

Catchability plays a central role in fisheries stock assessment. Since catchability often varies with time depending on population density, environmental factors, and anthropogenic effects, assuming constant catchability in population models can lead to biased abundance estimates. Here we present a novel way to simultaneously estimate time-varying catchability and abundance by integrating a short-term (month-based) removal method and a long-term (year-based) age-structured population dynamics model. We applied this approach to commercial fishery data for a Japanese pufferfish (Takifugu rubripes) population and found that the models with time-varying catchability greatly outperformed the models with constant catchability in terms of predictive ability and model consistency. The temporal variation in catchability was parsimoniously predicted by fishing effort and population size, indicating the existence of effort- and density-dependent catchability. Our approach, integrating population dynamics at different timescales, will help avoid inadvertent overexploitation and contribute to sustainable harvesting by enhancing the estimation accuracy of time-varying catchability and abundance.

scholarly journals Simultaneous inference for time-varying models

2021 ◽  
Author(s):  
Sayar Karmakar ◽  
Stefan Richter ◽  
Wei Biao Wu
Keyword(s):  
Simultaneous Inference ◽  
Time Varying ◽  
Time Varying Models

scholarly journals Stock assessment and projections incorporating discard estimates in some years: an application to the hake stock in ICES Divisions VIIIc and IXa

2010 ◽  
Vol 67 (6) ◽  
pp. 1185-1197 ◽  
Author(s):  
C. Fernández ◽  
S. Cerviño ◽  
N. Pérez ◽  
E. Jardim
Keyword(s):  
Time Series ◽  
Stock Assessment ◽  
Reference Points ◽  
Assessment Model ◽  
Marine Science ◽  
Fishing Mortality ◽  
Change Over Time ◽  
Age Structured ◽  
Available Information ◽  
Over Time

Abstract Fernández, C., Cerviño, S., Pérez, N., and Jardim, E. 2010. Stock assessment and projections incorporating discard estimates in some years: an application to the hake stock in ICES Divisions VIIIc and IXa. – ICES Journal of Marine Science, 67: 1185–1197. A Bayesian age-structured stock assessment model is developed to take into account available information on discards and to handle gaps in the time-series of discard estimates. The model incorporates mortality attributable to discarding, and appropriate assumptions about how this mortality may change over time are made. The result is a stock assessment that accounts for information on discards while, at the same time, producing a complete time-series of discard estimates. The method is applied to the hake stock in ICES Divisions VIIIc and IXa, for which the available data indicate that some 60% of the individuals caught are discarded. The stock is fished by Spain and Portugal, and for each country, there are discard estimates for recent years only. Moreover, the years for which Portuguese estimates are available are only a subset of those with Spanish estimates. Two runs of the model are performed; one assuming zero discards and another incorporating discards. When discards are incorporated, estimated recruitment and fishing mortality for young (discarded) ages increase, resulting in lower values of the biological reference points Fmax and F0.1 and, generally, more optimistic future stock trajectories under F-reduction scenarios.

Fish community change in Lake Superior, 1970–2000

2003 ◽  
Vol 60 (12) ◽  
pp. 1552-1574 ◽  
Author(s):  
Charles R Bronte ◽  
Mark P Ebener ◽  
Donald R Schreiner ◽  
David S DeVault ◽  
Michael M Petzold ◽  
...  
Keyword(s):  
Great Lakes ◽  
Native Species ◽  
Fish Community ◽  
Lake Trout ◽  
Community Change ◽  
Osmerus Mordax ◽  
Rainbow Smelt ◽  
Additional Species ◽  
Community Agencies ◽  
Natural Reproduction

Changes in Lake Superior's fish community are reviewed from 1970 to 2000. Lake trout (Salvelinus namaycush) and lake whitefish (Coregonus clupeaformis) stocks have increased substantially and may be approaching ancestral states. Lake herring (Coregonus artedi) have also recovered, but under sporadic recruitment. Contaminant levels have declined and are in equilibrium with inputs, but toxaphene levels are higher than in all other Great Lakes. Sea lamprey (Petromyzon marinus) control, harvest limits, and stocking fostered recoveries of lake trout and allowed establishment of small nonnative salmonine populations. Natural reproduction supports most salmonine populations, therefore further stocking is not required. Nonnative salmonines will likely remain minor components of the fish community. Forage biomass has shifted from exotic rainbow smelt (Osmerus mordax) to native species, and high predation may prevent their recovery. Introductions of exotics have increased and threaten the recovering fish community. Agencies have little influence on the abundance of forage fish or the major predator, siscowet lake trout, and must now focus on habitat protection and enhancement in nearshore areas and prevent additional species introductions to further restoration. Persistence of Lake Superior's native deepwater species is in contrast to other Great Lakes where restoration will be difficult in the absence of these ecologically important fishes.

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