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- Norrström, Niclas, et al.
(författare)
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Selection against Accumulating Mutations in Niche-Preference Genes Can Drive Speciation
- 2011
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 6:12, s. 29487-
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Tidskriftsartikel (refereegranskat)abstract
- Our current understanding of sympatric speciation is that it occurs primarily through disruptive selection on ecological genes driven by competition, followed by reproductive isolation through reinforcement-like selection against inferior intermediates/heterozygotes. Our evolutionary model of selection on resource recognition and preference traits suggests a new mechanism for sympatric speciation. We find speciation can occur in three phases. First a polymorphism of functionally different phenotypes is established through evolution of specialization. On the gene level, regulatory functions have evolved in which some alleles are conditionally switched off (i.e. are silent). These alleles accumulate harmful mutations that potentially may be expressed in offspring through recombination. Second mating associated with resource preference invades because harmful mutations in parents are not expressed in the offspring when mating assortatively, thereby dividing the population into two pre-zygotically isolated resource-specialist lineages. Third, silent alleles that evolved in phase one now accumulate deleterious mutations over the following generations in a Bateson-Dobzhansky-Muller fashion, establishing a post-zygotic barrier to hybridization.
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- Holmgren, Noél M. A.
(författare)
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MSY analyses for herring and sprat in the Baltic Sea, methods and suggested reference points
- 2011
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Ingår i: ICES report of the Baltic Fisheries Assessment working Group (WGBFAS). - Copenhagen : ICES. ; , s. 798-804
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The concept of maximum sustainable yield (MSY) rests on the notion that an intermediately sized stock exists at which the biomass production is at its maximum. the maximum is a result of density-dependent negative feedback on percapita production with increasing stock size. the harvesting is sustainable if it equals the stock productivity. the stock productivity depends on environmental variables, typically food-availability but also temperature and salinity may be important. Predation does not affect the productivity directly, but it is important to consider how the annual surplus production is shared with predators and hence affects the fishing yield. In the stock model we use for MSY analyses we differentiate between internal factors affecting density-dependence and external factors that either drive productivity or represent predation.To estimate MSY reference points we modelled some stocks with Monte-Carlo simulations (see WD6 for details). The stochastic properties of the stock are estimated and implemented in the stochastic behaviour of the model in order to find the natural range of stock ariables under MSY management. This can be a basis for B trigger in ICES framework, the SSB at which the F MSY is re-evaluated or an adjusted F is adopted according to the harvest control rule. Under some conditions, stochastic simulations will have F MSY that are different from deterministic runs, i e yields are asymmetrical around their means.The stock model has two variables, NAA (numbers at age) and WAA (weight at age). The functions and their parameters to update the variables annually were obtained from statistical analyses of the data and results from XSA runs provided by the WGBFAS stock coordinators. Four functions were estimated statistically:1) Number of recruits per SSB as a linear function of SSB2) Age-specific natural mortality as a linear function of predator abundance ( e. g. Cod SSB)3) Weight of recruits as a linear function of average parent weight4) Average weight increase as a linear function of WAA and year-specific growthThe MS errors of the regressions were used as variances of the normal distributions from which a random parameter was generated. If body growth is negatively correlated with weight it indicates a Von Bertalanffy type of growth. Also, if number of recruits per SSB is negatively correlated with SSB, there is a density-dependence required for a maximum production to exist.There are also two external variables that affect the analyses: predator abundance and year-specific growth (named year-growth). The year-growth is a statistical variable tha t encapsulates all year-specific growth common for all age-classes. The year-growth is externally linked driver for variation in productivity of the stock. A Fourier function including the four longest wave-lengths was fitted to the predator abundance and the year-growth respectively. The Fourier functions were representing long term changes in the external conditions, and the residuals as uncorrelated inter-annual variation. The MS of the residuals was also used or generating randomscatter in the external variables between years.The stock model was run for 10 500 (for sprat 40 500) years, under which the first 500 years were not generating data and were only used to release the dependence on the initially set conditions. The time series of yields and SSB were collected. The runs were repeated for intervals of F to frame the maximum average yields with a step of 0.01. A weighted catchability (as estimated for each species) was applied so that the F denoted the average for a given range of age-classes. We also present F MSY max and F MSY min which frames the range in which the average yields within 95% of the MSY (WKFRAME-2 2011). The B trigger is set as the lower 2.5 % percentile of the SSBs from the simulation.
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- Holmgren, Noél M. A., et al.
(författare)
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MSY-orientated management of Baltic Sea herring (Clupea harengus) during different ecosystem regimes
- 2012
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Ingår i: ICES Journal of Marine Science. - : Oxford University Press. - 1054-3139 .- 1095-9289. ; 69:2, s. 257-266
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Tidskriftsartikel (refereegranskat)abstract
- The Baltic Sea ecosystem has undergone dramatic changes, so-called ecosystem regime shifts, during the past four decades. Baltic Sea herring (Clupea harengus) spawning-stock biomass has declined to a third, and weight-at-age has halved as a result of food shortages and competition with sprat (Sprattus sprattus). The management objective for the herring stock is currently in transition from precautionary to maximum sustainable yield (MSY). The main basin Baltic Sea herring was modelled under the current ecosystem regime and the effect of a recovery of the cod (Gadus morhua) stock and the availability of planktonic food to levels found in the early 1980s analysed. A target of F-MSY = 0.16 for herring, which should decline to F-MSY = 0.10 with recovery of the cod stock, is proposed. An increase in the availability of planktonic food is estimated to more than double the yield at F-MSY = 0.27, overriding the negative effects of cod predation should there be a simultaneous increase in both cod and availability of planktonic food. The estimated net increase in yield is 40% at F-MSY = 0.20. Functions are presented to calculate FMSY and to estimate the expected yield depending on the abundance of cod and food availability. Retrospective application of the functions is indicative of overfishing of herring in the 1990s and early 2000s, and a net loss in yield, with a landing value of some E440 million.
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| 6. |
- Holmgren, Noél M. A., et al.
(författare)
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MSY oriented management of the Baltic Sea herring under regime shifts
- 2011
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Ingår i: ICES report of the Baltic Fisheries Assessment working Group (WGBFAS). - Copenhagen : ICES. ; , s. 752-798
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The ecosystem of the baltic sea has undergone dramatic changes, perhaps a regime-shift, during the last four decades. The Baltic Sea Herring SSB has declined to a third and weight-at-age has halved due to plankton prey deficits. The management objective of the herring is currently in the transition to a cautionary maximum sustainable yield (MSY). We modelled the main basin Baltic Sea herring under the currernt regime, and analysed the effect of a ercovery of the cod stock and the food availability as they were in the early 1980s. We recommend a target F MSY of 0.16, but with a recovery of the cod, recommended target F MSY is is 0.10. A simultaneous increase in both cod and food availability is estimated to increase the yield with 40% at the target F MSY is 0.20. We present functions to calculate F MSY and estimate the expected yield depending on the abundance of cod and food-availability. A retrospective application of our functions indicates over-fishing in the 1990s and early 2000s, and a net loss in yields with a landing value of about E440 Millions.
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| 8. |
- Norrström, Niclas, et al.
(författare)
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Nash equilibrium can resolve conflicting maximum sustainable yields in multi-species fisheries management
- 2017
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Ingår i: ICES Journal of Marine Science. - : Oxford University Press. - 1054-3139 .- 1095-9289. ; 74:1, s. 78-90
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Tidskriftsartikel (refereegranskat)abstract
- The current fisheries management goals set by the European Commission states that fish stocks should be harvested to deliver maximum sustainable yields (MSY) and simultaneously, management should take ecosystem considerations into account. This creates unsolved trade-offs for the management of the stocks. We suggest a definition of a multi-species-MSY (MS-MSY) where no alternative fishing mortality (F) can increase yield (long term) for any ecologically interacting stock, given that the other stocks are fished at constant efforts (Fs). Such a MS-MSY can be solved through the game theoretic concept of a Nash equilibrium and here we explore two solutions to this conflict in the Baltic Sea. We maximize the sustainable yield of each stock under two constraints: first, we harvest the other stocks at a fixed F (FNE); second, we keep the spawning stock biomasses of the other stocks fixed [biomass Nash equilibrium (BNE)]. As a case study, we have developed a multi-species interaction stochastic operative model (MSI-SOM), which contains a SOM for each of the three dominant species of the Baltic Sea, the predator cod (Gadus morhua), and its prey herring (Clupea harengus), and sprat (Sprattus sprattus). For our Baltic Sea case, MS-MSYs exist under both the FNE and the BNE, but there is no guarantee that point solutions exists. We found that the prey species’ spawning stock biomasses are additive in the cod growth function, which allowed for a point solution in BNE. In the FNE, the herring MSY was found to be relatively insensitive to the other species’ fishing mortalities (F), which facilitated a point solution. The MSY targets of the BNE and the FNE differ slightly where the BNE gives higher predator yields and lower prey yields.
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