ORCID Profile
0000-0001-8956-5638
Current Organisations
University of Adelaide
,
South Australian Research and Development Institute
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Publisher: CSIRO Publishing
Date: 2010
DOI: 10.1071/MF08289
Abstract: Sedentary benthic invertebrates exhibit clustering at a range of spatial scales. Animal clustering reduces the precision of er surveys and can accelerate overexploitation in e fisheries. Dive harvesters target the densest aggregations of males and females that produce the highest rates of egg fertilisation during mass spawning events. By quantifying these effects of harvesting on fertilisation success, measuring animal clustering can inform stock management for reproductive sustainability. We present a method to measure the spatial extent of density aggregations down to 1 m, extending a previously described leaded-line survey design. Applying this method to abalone, research ers counted in iduals in successive 1 × 2 m2 quadrats lying along adjoining pairs of 1 × 100 m2 transects. Clusters were observed as neighbouring quadrats of high animal density. Spatial autocorrelations at inter-quadrat distances of 1 to 100 m were calculated for four surveys, with eight pairs of transects swum in each survey. For all four surveys, inside two survey regions, spatial autocorrelation declined to non-significant levels at a distance of ~20 m. Quantified by the distance within which density counts are correlated, this quadrat-within-transect method provides a er survey measure of the scale of spatial aggregation for sedentary invertebrates such as abalone, sea cucumbers and urchins.
Publisher: CSIRO Publishing
Date: 2001
DOI: 10.1071/MF01172
Abstract: In length-based lobster stock-assessment models where the population is sub ided into discrete length classes, growth is represented as a matrix of length-transition probabilities. At specific times during the model year, the length-transition probabilities specify the proportions growing into larger length classes. These probabilities are calculated by integration of gamma or normal distributions over the length intervals of each larger length class. The mean growth from any given length category is commonly modelled by a von Bertalanffy or other continuous growth curve. The coefficients of variation, describing variance among in iduals, are modelled by functions constant or linear with length. These approaches have yielded good descriptions of growth for males and juveniles, but the von Bertalanffy curve does not capture the rapid decrease in mean growth rate after maturity for females. We generalized this length-transition model by writing the parameters of the growth distributions as polynomial functions of carapace length. This generalization procedure increases the number of parameters depending on the degree of polynomial employed. In fits to South Australian rock lobster (Jasus edwardsii) tagrecovery data, each increase in polynomial degree yielded a significantly better fit for females and successfully represented the decrease in growth at maturity. For males, the von Bertalanffy description was little improved by higher polynomials.
Publisher: Oxford University Press (OUP)
Date: 05-02-2009
Abstract: McGarvey, R., Matthews, J. M., and Feenstra, J. F. 2009. Estimating mortality from times-at-large: testing accuracy and precision using simulated single tag-recovery data. – ICES Journal of Marine Science, 66: 573–581. Single tag-recovery data are available for many commercial and recreational fish stocks. However, the use of tag-recovery data has been limited by the unknown proportion of tagged recaptured animals that fishers report back to researchers. Tag underreporting causes underestimation bias in commonly applied Petersen-based estimators of fraction harvested. Using simulated data, we tested the claim that estimates of total instantaneous mortality rate (Z) based on mean time-at-large are unbiased by tag non-reporting, and by short-term (type 1) tag shedding and tag-induced mortality. The Chapman time-at-large estimator produced unbiased estimates of Z. Non-reporting and short-term tag losses produced no detectable bias in estimates of Z. Standard errors of the Chapman Z-estimate decreased with , as predicted. Non-constant-Z scenarios of fishery closure and seasonal cycling gave time-at-large Z-estimates that closely approximated the true population time averages when tag releases were spread evenly across time. Ongoing (type 2) tag shedding and tag-induced mortality biased Z-estimates upwards by the respective ongoing loss rates. When tag-recovery experiments are cut short, accurate estimates of Z are provided by Deemer and Votaw's ‘truncated’ estimator, which had wide standard errors for short experimental length, precision becoming acceptable for tag-recovery experiments run longer than approximately two or three times Z−1.
Publisher: Canadian Science Publishing
Date: 06-2002
DOI: 10.1139/F02-080
Abstract: Tag-recovery data are commonly used to estimate movement rates of fish stocks. Fishers report tagged fish found in their catch however, not all recoveries are reported to fishery researchers and the rate of nonreporting is usually not known or is imprecisely estimated. To obviate the problem of nonreporting, an estimator of movement rates is proposed that does not use the number originally tagged but is fitted to the relative proportions recaptured in each cell in each time step subsequent to release. Rates of processes that occur in the tag-release spatial cell, such as short-term tagging mortality and survival, cancel from the predicted likelihood probabilities. Similarly, rates in the recapture cell for processes of ongoing tag loss, natural mortality, and tag nonreporting, if they can be reasonably approximated as uniform across cells, also cancel. Estimators are presented assuming one of two levels of auxiliary fishery inputs: (i) total mortality by cell or time step, or (ii) if mortality can be approximated as spatially uniform, effort totals in each cell, by time step. Yearly movement transition matrices were estimated for King George whiting (Sillaginodes punctata) in South Australia among 11 spatial cells from tag recoveries gathered over a period of three decades.
Publisher: Elsevier BV
Date: 07-2017
Publisher: Informa UK Limited
Date: 20-12-2018
Publisher: Wiley
Date: 07-05-2014
DOI: 10.1111/FOG.12069
Publisher: Elsevier BV
Date: 2013
Publisher: Elsevier BV
Date: 07-2010
Publisher: Elsevier BV
Date: 11-2016
Publisher: Wiley
Date: 19-08-2011
Publisher: National Shellfisheries Association
Date: 08-2005
Publisher: Canadian Science Publishing
Date: 09-2008
DOI: 10.1139/F08-101
Abstract: Abalone surveys worldwide measure relative stock abundance. However, important advantages accrue if er surveys measure absolute numbers or biomass per square metre. Principally, absolute biomass permits quota setting from a single survey using a decision table. Although relative abundance surveys have permanently fixed s ling protocols and locations, absolute abundance survey designs can be improved with technology over time. Furthermore, surveys can be directed to areas of principal management focus, and absolute survey population numbers by length with confidence intervals provide informative model input. We propose and test a transect survey design to estimate and map absolute density and biomass of abalone or other sedentary invertebrates. Divers count and measure all abalone within 1 m of a 100 m, boat-deployed leaded rope line. Semi-systematic transect locations provide spatially representative s ling inside bounded survey regions and geostatistical data for contour maps of abalone density and mean size. The effectiveness of the design for estimating change in population size under harvesting and for locating areas of fishable density was tested by a fish-down experiment, using surveys run before and after commercial harvest. The leaded-line survey design estimates of population change and spatial distribution showed agreement with the fish-down experimental harvest.
Publisher: Canadian Science Publishing
Date: 09-2007
DOI: 10.1139/F07-080
Abstract: Fishery processes of selectivity and recruitment to legal size vary with fish length and are mediated by fish growth. Yet most fishery models are age-based. To model length-dependent change within each cohort, fish numbers must vary dynamically with length as well as with age in the model population array. The fishery model formalism described here achieves this by a partition of the continuous length-at-age distribution. This method is computationally efficient and cleanly differentiates legal from sublegal fish. Fish numbers within each cohort are partitioned into length bins, called slices. A slice is defined and calculated as the fish in each cohort length-at-age distribution that have grown into legal size since the start of the previous time step. When growth is estimated from catch length and age s les separately from the stock assessment, biases result from the implicit assumption that catch s les are representative of the population and from ignoring length-dependent change within cohorts. These biases are avoided by integrating recruitment, growth, and selectivity estimation into a stock assessment likelihood that represents changing population numbers by both age and length. Size dependence also permits a natural extension of fishery models to trophic interactions with the surrounding ecosystem.
Publisher: Elsevier BV
Date: 03-2012
Location: Australia
No related grants have been discovered for John Feenstra.