A length-based Bayesian stock assessment model for the New Zealand abalone Haliotis iris

2003 ◽  
Vol 54 (5) ◽  
pp. 619 ◽  
Author(s):  
Paul A. Breen ◽  
Susan W. Kim ◽  
Neil L. Andrew
Keyword(s):  
New Zealand ◽  
Stock Assessment ◽  
Assessment Model ◽  
Data Sets ◽  
Catch Per Unit Effort ◽  
Commercial Catch ◽  
Data Set ◽  
Future Directions ◽  
Common Component ◽  
Joint Posterior Distribution

We describe a length-based Bayesian model for stock assessment of the New Zealand abalone Haliotis iris (paua). We fitted the model to five data sets: catch-per-unit-effort (CPUE) and a fishery-independent survey index, proportions-at-length from both commercial catch sampling and population surveys, and tag–recapture data. We estimated a common component of error and used iterative re-weighting of the data sets to balance the residuals, removing the arbitrary data set weightings used in previous assessments. Estimates at the mode of the joint posterior distribution were used to explore sensitivity of the results to model assumptions and input data; the assessment itself was based on marginal posterior distributions estimated from Markov chain–Monte Carlo simulation. Assessments are presented for two stocks in the south of New Zealand. One may be recovering after recent catch reductions; the other is over-exploited and likely to decline further. Assessment for the first stock was robust; assessment for the second stock was sensitive to the CPUE data and may be too optimistic. We discuss future directions and potential problems with this approach.

Eels at the Edge: Science, Status, and Conservation Concerns

2009 ◽  
Keyword(s):  
New Zealand ◽  
Management System ◽  
Stock Assessment ◽  
Catch Per Unit Effort ◽  
Commercial Catch ◽  
The North ◽  
Anguilla Australis ◽  
Unit Effort ◽  
Access Rights ◽  
Quota Management

<em>Abstract.</em>—The New Zealand eel fishery comprises two species, the shortfin eel <em>Anguilla australis </em>and the New Zealand longfin eel <em>A. dieffenbachii</em>. A third species, the speckled longfin eel <em>A. reinhardtii</em>, is present in small numbers in some areas. Major fisheries in New Zealand are managed under the Quota Management System. Individual transferable quotas are set as a proportion of an annual total allowable commercial catch. The Quota Management System was introduced into the South Island eel fishery on 1 October 2000 and the North Island fishery on 1 October 2004. Freshwater eels have particular significance for customary Maori. Management policies allow for customary take and the granting of commercial access rights on introduction into the Quota Management System. Eel catches have remained relatively constant since the early 1970s. The average annual catch from 1989–1990 to 2001–2002 (fishing year) was 1,313 mt. Catch per unit effort remained constant from 1983 to 1989 and reduced from 1990 to 1999. Statistically significant declines in catch per unit effort for New Zealand longfin eel were found in some areas over the latter period. For management, an annual stock-assessment process provides an update on stock status.

scholarly journals Development and evaluation of catch per unit effort indices for southern blue whiting (Micromesistius australis) on the Campbell Island Rise, New Zealand

2005 ◽  
Vol 62 (6) ◽  
pp. 1131-1138 ◽  
Author(s):  
Stuart M. Hanchet ◽  
Ron G. Blackwell ◽  
Alistair Dunn
Keyword(s):  
New Zealand ◽  
Stock Assessment ◽  
Independent Data ◽  
Catch Per Unit Effort ◽  
Age Composition ◽  
Commercial Catch ◽  
Fourfold Increase ◽  
Fishing Strategies ◽  
Acoustic Surveys ◽  
Campbell Island

Abstract This paper develops standardized commercial cpue indices for a highly aggregated spawning fishery in New Zealand waters, and verifies the indices using fishery-independent data. Indices were calculated for all vessels using three different measures of effort, and for vessel subsets based on processing type (surimi and dressed), and relative experience in the fishery. Trends in cpue were consistent with trends in fishery-independent acoustic surveys, age composition of the commercial catch, and recent stock assessment results. In particular, the cpue indices tracked the more than fourfold increase in abundance from 1993 to 1996 associated with the recruitment of the strong 1991 year class, and the decline in relative abundance as this year class was fished down. Despite this being a highly aggregated spawning fishery, there was little evidence for hyperstability. There were also significant differences in fishing strategies of the fleets between periods of high and low fish abundance.

scholarly journals Correcting density-dependent effects in abundance estimates from bottom-trawl surveys

2014 ◽  
Vol 71 (5) ◽  
pp. 1107-1116 ◽  
Author(s):  
Stan Kotwicki ◽  
James N. Ianelli ◽  
André E. Punt
Keyword(s):  
Stock Assessment ◽  
Dead Zone ◽  
Walleye Pollock ◽  
Assessment Model ◽  
Bottom Trawl ◽  
Trawl Survey ◽  
Negative Consequences ◽  
Catch Per Unit Effort ◽  
Density Dependent ◽  
Index Of Abundance

Abstract Indices of abundance are important for estimating population trends in stock assessment and ideally should be based on fishery-independent surveys to avoid problems associated with the hyperstability of the commercial catch per unit effort (cpue) data. However, recent studies indicate that the efficiency of the survey bottom trawl (BT) for some species can be density-dependent, which could affect the reliability of survey-derived indices of abundance. A function qe∼f(u), where qe is the BT efficiency and u the catch rate, was derived using experimentally derived acoustic dead-zone correction and BT efficiency parameters obtained from combining a subset of BT catch data with synchronously collected acoustic data from walleye pollock (Theragra chalcogramma) in the eastern Bering Sea (EBS). We found that qe decreased with increasing BT catches resulting in hyperstability of the index of abundance derived from BT survey. Density-dependent qe resulted in spatially and temporarily variable bias in survey cpue and biased population age structure derived from survey data. We used the relationship qe∼f(u) to correct the EBS trawl survey index of abundance for density-dependence. We also obtained a variance–covariance matrix for a new index that accounted for sampling variability and the uncertainty associated with the qe. We found that incorporating estimates of the new index of abundance changed outputs from the walleye pollock stock assessment model. Although changes were minor, we advocate incorporating estimates of density-dependent qe into the walleye pollock stock assessment as a precautionary measure that should be undertaken to avoid negative consequences of the density-dependent qe.

A Ccomparison of sedigraph and pipette methods for soil particle-size analysis

Soil Research ◽  
1993 ◽  
Vol 31 (4) ◽  
pp. 407 ◽  
Author(s):  
GD Buchan ◽  
KS Grewal ◽  
JJ Claydon ◽  
RJ Mcpherson
Keyword(s):  
Particle Size ◽  
New Zealand ◽  
Particle Size Analysis ◽  
Size Analysis ◽  
Data Sets ◽  
Regression Equations ◽  
Total Iron Content ◽  
Data Set ◽  
X Ray ◽  
The Difference

The X-ray attenuation (Sedigraph) method for particle-size analysis is known to consistently estimate a finer size distribution than the pipette method. The objectives of this study were to compare the two methods, and to explore the reasons for their divergence. The methods are compared using two data sets from measurements made independently in two New Zealand laboratories, on two different sets of New Zealand soils, covering a range of textures and parent materials. The Sedigraph method gave systematically greater mass percentages at the four measurement diameters (20, 10, 5 and 2 �m). For one data set, the difference between clay (<2 �m) percentages from the two methods is shown to be positively correlated (R2 = 0.625) with total iron content of the sample, for all but one of the soils. This supports a novel hypothesis that the typically greater concentration of Fe (a strong X-ray absorber) in smaller size fractions is the major factor causing the difference. Regression equations are presented for converting the Sedigraph data to their pipette equivalents.

A simple model for ferret population dynamics and control in semi-arid New Zealand habitats

2001 ◽  
Vol 28 (1) ◽  
pp. 87 ◽  
Author(s):  
N. D. Barlow ◽  
G. L. Norbury
Keyword(s):  
Population Dynamics ◽  
New Zealand ◽  
Current Density ◽  
Average Density ◽  
Intrinsic Rate Of Increase ◽  
Data Sets ◽  
Data Set ◽  
Rate Of Increase ◽  
Semi Arid ◽  
Over Time

Introduced ferrets (Mustela furo) in New Zealand are subject to population control to reduce their threat to native fauna and the incidence of bovine tuberculosis (Tb) in livestock. To help in evaluating control options and to contribute to a multi-species model for Tb dynamics, a simple Ricker model was developed for ferret population dynamics in a semi-arid environment. The model was based on two data sets and suggested an intrinsic rate of increase for ferrets of 1.0–1.3 year–1 and a carrying capacity of 0.5–2.9 km–2. There was evidence for direct density-dependence in both data sets and the effect appeared to act mainly on recruitment. Dependence of the rate of increase of predators on the density of wild rabbits (Oryctolagus cuniculus) was exhibited in one of the two data sets, together with a numerical response relating current density of predators asymptotically to current density of rabbits, their primary prey. Predators in this data set included both cats and ferrets, estimated from spotlight counts, but the other data set demonstrated a direct proportionality between predator (cat and ferret) spotlight counts and minimum ferrets known to be alive by trapping. The model suggested, firstly, that populations are hard to suppress by continuous culling, with at least a 50% removal per year necessary to effect a suppression of 50% in long-term average density. Secondly, if control is episodic rather than continuous, culling in autumn gives a greater degree of suppression over time (280%, accumulated over time) than culling in spring (180%). A differential equation version of the model provides a component for a general Anderson/May bovine Tb/wildlife (possum/deer/ferret) model.

Distribution and abundance of freshwater eels (Anguilla spp.) in Tasmania

1984 ◽  
Vol 35 (4) ◽  
pp. 463 ◽  
Author(s):  
RD Sloane
Keyword(s):  
New Zealand ◽  
Coastal Lagoons ◽  
Catch Per Unit Effort ◽  
Commercial Catch ◽  
North Eastern ◽  
Coastal Streams ◽  
Catch Statistics ◽  
The 1960S ◽  
Density And Biomass ◽  
Freshwater Eels

The distribution of A. australis australis Richardson and A. reinhardtii Steindachner in Tasmania was determined from electrofishing surveys and commercial catch records. A. a. australis is abundant in coastal streams and extends far inland in the major drainage systems to the main lakes in Tasmania's Central Highlands. Density and biomass estimates for A. a. australis in streams, <0.01-1 .40 m-2 and 0.04-23.01 g m-2, respectively, are similar to those recorded for A. australis schmidtii Phillipps in New Zealand and for A. anguilla L. in Europe, A. reinhardtii is restricted to coastal lagoons and the lower freshwater reaches and estuaries of streams in north-eastern Tasmania including Flinders Island. Substantial populations of A. reinhardtii reside in these areas (0.05 m-2, 114.66 g m-2 in Douglas River). Analysis of commercial catch statistics indicates that the initial eel yields from standing waterbodies were high in the 1960s by world standards, although landings and catch per unit effort have subsequently declined.

scholarly journals What's in an elevation difference? Accuracy and corrections of satellite elevation data sets for quantification of glacier changes

2010 ◽  
Vol 4 (4) ◽  
pp. 2013-2077 ◽  
Author(s):  
C. Nuth ◽  
A. Kääb
Keyword(s):  
New Zealand ◽  
Regional Scale ◽  
Statistical Error ◽  
Data Sets ◽  
Methodological Framework ◽  
Data Set ◽  
Aster Gdem ◽  
Elevation Data ◽  
Elevation Changes

Abstract. There is an increasing number of DEMs available worldwide for deriving elevation differences over time, including vertical changes on glaciers. Most of these DEMs are heavily post-processed or merged, so that physical error modelling becomes impossible and statistical error modelling is required instead. We propose a three-step methodological framework for assessing and correcting DEMs to quantify glacier elevation changes: remove DEM shifts, check for elevation-dependent biases, and check for higher-order, sensor-specific biases. An analytic, simple and robust method to co-register elevation data is presented in regions where stable terrain is either plentiful (case study New Zealand) or limited (case study Svalbard). The method is exemplified using the three global elevation data sets available, SRTM, ICESat and the ASTER GDEM, and with automatically generated DEMs from satellite stereo instruments of ASTER and SPOT5-HRS. After three-dimensional co-registration, significant biases related to elevation were found in some of the stereoscopic DEMs. Biases related to the satellite acquisition geometry (along/cross track) were detected at two frequencies in the automatically generated ASTER DEMs. The higher frequency bias seems to be related to satellite \\emph{jitter}, most effective in the back-looking pass of the satellite. The origins of the more significant lower frequency bias is uncertain. ICESat-derived elevations are found to be the most consistent globally available elevation data set available so far. Before performing regional-scale glacier elevation change studies or mosaicking DEMs from multiple individual tiles (e.g. ASTER GDEM), we recommend to co-register all elevation data to ICESat as a global vertical reference system. The proposed methodological framework is exemplified for elevation changes on the Fox, Franz Joseph, Tasman and Murchison glaciers of New Zealand and the glaciers of central Spitsbergen, Svalbard.

Relationship between settlement of southern rock lobster pueruli, Jasus edwardsii, and recruitment to the fishery in Tasmania, Australia

2001 ◽  
Vol 52 (8) ◽  
pp. 1271 ◽  
Author(s):  
C. Gardner ◽  
S. D. Frusher ◽  
R. B. Kennedy ◽  
A. Cawthorn
Keyword(s):  
Interannual Variation ◽  
Stock Assessment ◽  
Catch Rate ◽  
Assessment Model ◽  
Rock Lobster ◽  
Commercial Catch ◽  
Jasus Edwardsii ◽  
Catch Rates ◽  
Additional Support ◽  
Northeast Coast

Puerulus catches on artificial collectors were measured monthly at four sites around Tasmania from 1991 to April 2000, with the aim of predicting future changes in recruitment to the fishery. Support for the potential of catch-rate prediction in Tasmania was provided at the two sites that have overlap of several years between indices of puerulus settlement and indices of the abundance of recruits to the fishery. At Bicheno, on the northeast coast, correlations between annual puerulus index and commercial catch rates were highly significant, with a lag of 5 years (P< 0.01). Similar interannual trends in puerulus index and estimates from a stock-assessment model of the biomass of recruits to the fishery provided additional support for a link with puerulus index. A 5-fold interannual variation in puerulus index detected at Bicheno, with a peak in 1995, was preceded by 3 years of relatively low puerulus catch. The peak in puerulus index appears to lead to an increase in the abundance of sublegal males in research sampling 3 years later. Correlation between annual measures of puerulus index and catch rate also appeared significant at King Island (P= 0.06) although data at this site had less contrast.

scholarly journals Consequences of variations in carrying capacity or migration for the perception of Atlantic bluefin tuna (Thunnus thynnus) population dynamics

2007 ◽  
Vol 64 (5) ◽  
pp. 827-836 ◽  
Author(s):  
Jean-Marc Fromentin ◽  
Laurence T Kell
Keyword(s):  
Population Dynamics ◽  
Carrying Capacity ◽  
Stock Assessment ◽  
Population Analysis ◽  
Bluefin Tuna ◽  
Assessment Model ◽  
Thunnus Thynnus ◽  
Commercial Catch ◽  
Atlantic Bluefin Tuna

Spectacular long-term cycles (around 110 years), independent of human exploitation, have been seen in historical catches of Atlantic bluefin tuna (Thunnus thynnus). Previous studies indicated that such variations could have been generated by contrasting but equally plausible dynamic processes, i.e., changes in carrying capacity or migration. A simulation framework was therefore used to test whether the International Commission for the Conservation of Atlantic Tuna stock assessment model, i.e., a virtual population analysis (VPA), can capture such dynamics. The main outcome is that knowledge of the underlying process is crucial, because distinct hypotheses lead to different population dynamics and contrasting performances of the stock assessment model. The VPA is indeed able to reconstruct accurately the historical stock parameters under the carrying-capacity hypothesis, but not under the migratory hypothesis, for which there is often strong bias (up to 500%) in absolute values and in trends of spawning stock biomass and F. Furthermore, it was shown that (i) different phases between exploitation and long-term cycle can induce contrasting terminal F for a same effort and (ii) that there was considerable confounding between the dynamics and increasing effort (as currently seen). We conclude that it is difficult to infer the actual dynamics on the basis of commercial catch data and that novel fishery-independent observation is needed.

scholarly journals Target-based catch-per-unit-effort standardization in multispecies fisheries

2018 ◽  
Vol 75 (3) ◽  
pp. 452-463 ◽  
Author(s):  
Hiroshi Okamura ◽  
Shoko H. Morita ◽  
Tetsuichiro Funamoto ◽  
Momoko Ichinokawa ◽  
Shinto Eguchi
Keyword(s):  
Stock Assessment ◽  
Catch Per Unit Effort ◽  
Target Variable ◽  
Traditional Methods ◽  
Data Set ◽  
Mixture Regression ◽  
Multispecies Fisheries ◽  
Unit Effort ◽  
Simple Simulation ◽  
Cpue Standardization

Standardized catch per unit effort (CPUE) is a fundamental component of fishery stock assessment. In multispecies fisheries, catchability can differ depending on which species is being targeted, and so the yearly trend extracted from the standardized CPUE is likely to be biased. We have, therefore, developed a method for predicting the unobserved variable related to targeted species from among multispecies composition data using a mixture regression model for the transformed residuals. In contrast with traditional methods, the proposed method predicts the target variable in CPUE standardization without removing a subset of the data. Keeping the entire data set avoids information loss, and so CPUE standardization with the predicted target variable should yield an unbiased estimate of the yearly trend. Simple simulation tests demonstrate that our method outperforms traditional methods. We illustrate the use of our method by applying it to CPUE data on arabesque greenling (Pleurogrammus azonus) caught in multispecies trawl fisheries in Hokkaido, Japan.

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