GLM-based standarization of the catch per unit effort series for South African west coast hake, focusing on adjustments for targeting other species

Catch per unit effort (cpue) data for the South African west coast Cape hakes Merluccius capensis and M. paradoxus were standardized by applying the Generalized Linear Modelling (GLM) technique. The resulting standardized series indicated that resource abundance declined at a rate of 0.4% per annum over the period 1978–1994. Further investigation revealed that the model applied did not adequately adjust for effort being directed away from hake towards other species. This was because, for low bycatch cpue, there was a positive rather than the expected negative correlation with hake catch rates. A method to correct for this inadequate adjustment, taking account of an assumed underlying reason of positively correlated fluctuations in catchability of hake and bycatch species, was developed and tested by simulation. This resulted in a more optimistic view of resource status, indicating a 0.6% per year increase in abundance over the period considered. This result remained contrary to general perceptions in the industry that there was a substantial improvement in resource abundance over the 17-year period considered, as suggested by a 4% increase in abundance per year in nominal cpue. The reasons that the GLM indicated a lesser increase in resource abundance were that the effective average power of the fleet increased, the fleet moved over time to deeper water, where catch rates were higher, and the increase in fish density in deeper water was more than offset by a simultaneous decrease in density in shallower waters. The inadequate bycatch adjustment arose from the analyses inappropriately including bycatch species that co-occur with hake, and hence are taken incidentally in hake-directed fishing, instead of only species whose capture requires a different targeting of effort.Keywords: bycatch corrections, Cape hakes, catch per unit effort, Generalized Linear ModellingAfrican Journal of Marine Science 2002, 24: 323–33

Evaluation of a class of possible simple interim management procedures for the Namibian hake fishery

During 1997, considerable scientific differences arose about the status of the Namibian hake (Merluccius capensis and M. paradoxus) resource, and as to whether the hake Total Allowable Catch (TAC) should be substantially decreased or increased. These differences revolved primarily around whether or not abundance estimates from the swept-area trawl surveys by the Norwegian research vessel Dr Fridtjof Nansen should be considered as reliable measures of biomass in absolute (as distinct from relative) terms. The paper relates the computations underlying the Interim Management Procedure (IMP) approach that was put forward at that time as a basis to resolve this impasse. The anticipated performance, in terms of catch and risk of resource depletion, of a number of simple candidate IMPs for the Namibian hake resource is evaluated. The IMPs depend on two parameters, whose values are to be chosen by decision-makers, and adjust the TAC up or down from one year to the next according to whether trends in recent commercial catch rate and survey indices of abundance are positive or negative. Performances are evaluated across the then current wide range argued for resource abundance and status. Trade-offs in performance across the candidates considered are discussed. One of the candidates was subsequently selected by a joint meeting of scientists, industry and Ministry officials in February 1998 and served as the basis for scientific recommendations for the TAC for the hake resource for the following three years. Keywords: abundance, Cape hake, Management Procedure, Namibia, performance, surveys, trade-offAfrican Journal of Marine Science 2001, 23: 357–37

Towards adaptive approaches to management of the South African abalone haliotis midae fishery

The South African abalone Haliotis midae resource is widely perceived as being under threat of overexploitation as a result of increased poaching. In this paper, reservations are expressed about using catch per unit effort as the sole index of abundance when assessing this fishery, particularly because of the highly aggregatory behaviour of the species. A fishery-independent survey has been initiated and is designed to provide relative indices of abundance with CVs of about 25% in most of the zones for which Total Allowable Catchs (TACs) are set annually for this fishery. However, it will take several years before this relative index matures to a time-serieslong enough to provide a usable basis for management. Through a series of simple simulation models, it is shown that calibration of the survey to provide values of biomass in absolute terms would greatly enhance thevalue of the dataset. The models show that, if sufficient precision (CV 50% or less) could be achieved in such a calibration exercise, the potential for management benefit is improved substantially, even when using a relatively simple management procedure to set TACs. This improvement results from an enhanced ability to detect resource declines or increases at an early stage, as well as from decreasing the time period until the survey index becomes useful. Furthermore, the paper demonstrates that basic modelling techniques could usefully indicate which forms of adaptive management experiments would improve ability to manage the resource, mainly through estimation of the level of precision that would be required from those experiments. The results of this study are particularlyapplicable to fishing zones for which there are insufficient other data to perform a standard stock assessment

Cephalopod fisheries: A future global upside to past overexploitation of living marine resources? Results of an international workshop, 31 August – 2 September 1997, Cape town, South Africa

Management strategies for cephalopod fisheries present similar challenges to those encountered in fisheries for finfish. Peculiarities of cephalopod life cycles and the fact that cephalopod fisheries can benefit frommanagement experiences gained in other fisheries may help to preclude mistakes and management failures. During a three-day workshop, features of cephalopod biology, recommended areas of research and key conclusions for management were identified and points of differences between cephalopods and fish were highlighted. Among these, life-cycle understanding, spatial distribution, stock-recruitment relationship and agedetermination/growth studies were identified as key priorities for research. Physiological and genetic approaches to understanding basic aspects of the life cycle, and their importance for understanding populationdynamics, were stressed. Similarly, theoretical ecology has a role to play in management, e.g. the role of a spatial distribution strategy in survival. Environmental studies are also emerging as being important in thepossible prediction of population trends through links that operate at the level of spawning biology. In the interim, cephalopods can be managed using similar principles to those applied to short-lived fish species.Among these, constant proportion harvest strategies were identified as the most effective

The application of a management procedure to regulate the directed and bycatch fishery of South African sardine sardinops sagax

The South African sardine Sardinops sagax resource is subjected to both directed fishing that targets adult fish, and bycatch of both juvenile and adult fish taken in the directed fisheries for anchovy Engraulis capensisand round herring Etrumeus whiteheadi. Two separate TACs (Total Allowable Catch) for sardine are calculated in the management procedures considered. The first is a directed TAC linked to sardine abundance, and the second is a bycatch TAC with an “anchovy” component coupled to the anchovy population dynamics as a proportion of the anchovy TAC, plus a “round herring” component reflecting a fixed tonnage independent of round herring abundance. Requirements from the pelagic industry, such as a minimum economically viable annual directed catch and a maximum percentage decrease in the directed TAC that could be tolerated from year to year are also incorporated. The selection of a single management procedure for implementation is based on the comparison of performance statistics such as risk of severe depletion and average annual catch, which incorporate the consequences of random error in survey estimates of abundance and random fluctuations in recruitment from year to year. Sensitivity tests are carried out to ensure robustness over a range of alternative assumptions concerning resource dynamics. A description is given of the development of the management procedure for sardine thatwas implemented in 1994, and the rationale for its selection. A wide range of variants to this procedure, including those that consider alternative approaches for handling bycatch, are investigated. Performance of the management procedures considered demonstrates extreme sensitivity to the choice of the proportion of the anchovy TAC used in the sardine bycatch TAC calculation. A lack of robustness of the selected management procedure to possible bias in estimates of spawner biomass from hydroacoustic surveys, and poor precision of recruit survey estimatesare argued as justification for adopting a conservative approach for managing sardine

The dependence of dijet production on photon virtuality in ep collisions at HERA

The dependence of dijet production on the virtuality of the exchanged photon, Q^2, has been studied by measuring dijet cross sections in the range 0 < Q^2 < 2000 GeV^2 with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb^-1. Dijet cross sections were measured for jets with transverse energy E_T^jet > 7.5 and 6.5 GeV and pseudorapidities in the photon-proton centre-of-mass frame in the range -3 < eta^jet <0. The variable xg^obs, a measure of the photon momentum entering the hard process, was used to enhance the sensitivity of the measurement to the photon structure. The Q^2 dependence of the ratio of low- to high-xg^obs events was measured. Next-to-leading-order QCD predictions were found to generally underestimate the low-xg^obs contribution relative to that at high xg^obs. Monte Carlo models based on leading-logarithmic parton-showers, using a partonic structure for the photon which falls smoothly with increasing Q^2, provide a qualitative description of the data.Comment: 35 pages, 6 eps figures, submitted to Eur.Phys.J.

Observation of associated near-side and away-side long-range correlations in √sNN=5.02 TeV proton-lead collisions with the ATLAS detector

Two-particle correlations in relative azimuthal angle (Δϕ) and pseudorapidity (Δη) are measured in √sNN=5.02  TeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1  μb-1 of data as a function of transverse momentum (pT) and the transverse energy (ΣETPb) summed over 3.1<η<4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|Δη|<5) “near-side” (Δϕ∼0) correlation that grows rapidly with increasing ΣETPb. A long-range “away-side” (Δϕ∼π) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ΣETPb, is found to match the near-side correlation in magnitude, shape (in Δη and Δϕ) and ΣETPb dependence. The resultant Δϕ correlation is approximately symmetric about π/2, and is consistent with a dominant cos⁡2Δϕ modulation for all ΣETPb ranges and particle pT

Search for new phenomena in final states with an energetic jet and large missing transverse momentum in pp collisions at √ s = 8 TeV with the ATLAS detector

Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses 20.3 fb−1 of √ s = 8 TeV data collected in 2012 with the ATLAS detector at the LHC. Events are required to have at least one jet with pT > 120 GeV and no leptons. Nine signal regions are considered with increasing missing transverse momentum requirements between Emiss T > 150 GeV and Emiss T > 700 GeV. Good agreement is observed between the number of events in data and Standard Model expectations. The results are translated into exclusion limits on models with either large extra spatial dimensions, pair production of weakly interacting dark matter candidates, or production of very light gravitinos in a gauge-mediated supersymmetric model. In addition, limits on the production of an invisibly decaying Higgs-like boson leading to similar topologies in the final state are presente

Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb^-1. The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet cross-section is measured as a function of the dijet invariant mass in the range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets and the angular variable chi in two dijet mass regions. The results are compared with next-to-leading-order QCD predictions. Good agreement is observed between the measured cross-sections and the predictions obtained using POWHEG + Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final version published in European Physical Journal

Search for direct pair production of the top squark in all-hadronic final states in proton-proton collisions at s√=8 TeV with the ATLAS detector

The results of a search for direct pair production of the scalar partner to the top quark using an integrated luminosity of 20.1fb−1 of proton–proton collision data at √s = 8 TeV recorded with the ATLAS detector at the LHC are reported. The top squark is assumed to decay via t˜→tχ˜01 or t˜→ bχ˜±1 →bW(∗)χ˜01 , where χ˜01 (χ˜±1 ) denotes the lightest neutralino (chargino) in supersymmetric models. The search targets a fully-hadronic final state in events with four or more jets and large missing transverse momentum. No significant excess over the Standard Model background prediction is observed, and exclusion limits are reported in terms of the top squark and neutralino masses and as a function of the branching fraction of t˜ → tχ˜01 . For a branching fraction of 100%, top squark masses in the range 270–645 GeV are excluded for χ˜01 masses below 30 GeV. For a branching fraction of 50% to either t˜ → tχ˜01 or t˜ → bχ˜±1 , and assuming the χ˜±1 mass to be twice the χ˜01 mass, top squark masses in the range 250–550 GeV are excluded for χ˜01 masses below 60 GeV