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... Þessi aðferð er enn notuð, ásamt ýmsum leiðréttingum, við mat á stofnstaerð íslenskra refa. 13,[17][18][19] Á tímabilinu sem rannsóknir Páls stóðu yfir, árin 1979-2011, voru veiddir 118.656 refir, þar af 51.877 yrðlingar. 20 Fjöldi maeldra og aldursgreindra dýra nálgaðist 9 þúsund þegar aevi Páls lauk en þegar þetta er skrifað er fjöldinn komin yfir 12 þúsund, og er þetta eitt staersta gagnasafn sem til er um þessa tegund í heiminum. ...
... Aldursgreining veiddra dýra er forsenda fyrir því að haegt sé að meta stofnstaerð með viðurkenndri aðferð sem kallast aldurs-afla-greining (e. age-cohort analysis). 17 Páll Hersteinsson hafði kynnt sér aðferðir til aldursgreiningar sem byggjast á að taka röntgenmyndir af tannholi og þunnsneiða og lita raetur tannanna (2. mynd). ...
... Forsendur þessarar aðferðar eru þaer að veiði sé reglubundin, dánardagur þekktur og að haegt sé að aldursgreina veidd dýr. 17,19 Íslenska tófan fellur vel að þessu stofnlíkani á meðan reglubundnar veiðar eru stundaðar, aflatölur þekktar og hluti felldra dýra skilar sér til aldursgreiningar. Reikniaðferðin byggist á bakreiknaðri lágmarksstaerð hvers árgangs í árlegri veiði, eins langt aftur og elstu dýr lifa (12 ár). ...
Tímarit Hins íslenska náttúrufraeðifélags 97 Ritrýnd grein / Peer reviewed Ester Rut Unnsteinsdóttir TÓFAN er eitt af flaggskipum rannsókna á áhrifum hlýnunar á lífríki norðurslóða og landfraeðileg einangrun tegundarinnar gerir Ísland mikilvaegt sem samanburðarsvaeði. Þekking á lífsháttum og líffraeði íslenska refsins er því mikilvaeg, og sem betur fer liggur fyrir talsverður efniviður sem varpar ljósi á stöðu tegundarinnar hérlendis og í alþjóðlegu samhengi. Íslenski melrakkinn-fyrsti hluti Stofnbreytingar, veiðar og verndun Náttúrufraeðingurinn 91 (3-4) bls. 97-111, 2021 Ljósmynd/Photo: Gyða Henningsdóttir.
... Two methods of virtual population analysis by Fry (1949Fry ( , 1957 and Gulland (1965), both cited after Skalski et al. (2005), were initially applied. These methods use age-atharvest data to back-calculate the cohort sizes. ...
... The spatial dispersion of randomly sampled adult lynx appeared to slow down, reaching a threshold of 20 individuals. Our biggest sample contained During the study period, the estimated lynx abundance in Latvia according to the age-structured population reconstruction model (Fry 1949(Fry , 1957; cited from Skalski et al. 2005) increased from 300 to 882 lynx (Fig. 5). Since the population parameters for calculations were obtained by a single sampling each season, confidence intervals are not applicable for these estimates. ...
... The mean value was higher in the western population compared to the eastern population: 0.060 vs. 0.002 (total population pairwise mean, Fig. 4 Relationship between the number of harvested lynx and their distribution across the 75 management units during the process of quota fulfilment. Samples are divided into juveniles and adults and summarise the entire study period Fig. 5 Estimated lynx population size according to the agestructured population reconstruction model (Fry 1949, 1957, cited from Skalski et al. 2005) and reported annual harvest in Latvia compared to the estimated minimum and maximum carrying capacity (after Kawata 2008) Mamm Res −0.002). These regional mean pairwise relatedness values were both significantly higher than the overall mean pairwise relatedness calculated for all analysed lynx samples. ...
The Eurasian lynx is managed as a game species in Latvia. A variety of demographic parameters were used to assess the current status of the Latvian lynx population and recruitment after annual harvest. Population age–gender structure and female prenatal fecundity were determined in 530 legally hunted animals over a 9-year period. Average prenatal fecundity was 3.2 ± 0.1, and evidence of reproduction was found in 87 % of the examined adult females. We found a disproportionally low number of 1- and 2-year-old lynx in the hunting bags and therefore constructed an age–gender pyramid, adjusting the survival curves to the proportions of the remaining age classes. Two hundred and eighty-eight tissue samples were analysed using 12 autosomal microsatellite loci. Groups of related individuals were identified using a group approach and supported by pairwise relationship analysis. Thirteen potential maternal–offspring relationship groups and 30 related groups of lynx individuals based on potential full-sib and half-sib relationships between the individuals within the research period were identified. Evidence from this study shows that the population is not only stable but also likely growing and that there currently appear to be no barriers preventing gene flow. We can conclude that, in general, the lynx population was sustainably maintained. The previous harvest intensity has not obstructed the conservation aim for lynx in Latvia, which is to maintain the population as stable or growing. Combining demographic and molecular analyses, this study reveals relevant reference indices that can be used in future monitoring of the lynx population in Latvia.
... An efficient method to track relative abundance of cervids over time may be through spring spotlight counts, at least in mountainous environments (Garel et al. 2010;Corlatti et al. 2016). Alternatively, the use of individual age-at-harvest data (catch-at-age data) in cohort population analysis can also be employed to track variations in population abundance (Fry 1949;Pope 1972;Fryxell et al. 1988). ...
... The age at death can then be used to reconstruct population size, as the number of individuals of a specific age will correspond to the sum of the number of individuals from that age and of the individuals in subsequent years (Ueno et al. 2009). The reconstruction of population size through cohort analysis was originally developed in fishery (Fry 1949), but it has been extended to other taxa, including ungulates such as red deer Cervus elaphus (Lowe 1969;Mysterud et al. 2007), white-tailed deer Odocoilenus virginianus (Fryxell et al. 1991) and chamois Rupicapra rupicapra (Reiner et al. 2020). In its simplest form, this deterministic method assumes that the population is closed, all mortality events are recorded and that, for each dead animal, exact age is known. ...
Reliable and cost-effective monitoring tools to track population size over time are of key importance for wildlife management and conservation. Deterministic cohort analysis may be used to this aim, especially in hunted populations, but it requires that all mortality events are recorded and that individual age at death is known exactly. In this study, we investigated the reliability of cohort analysis as a relative index to track overtime variation in red deer (Cervus elaphus) abundance, in the absence of exact information about natural mortality and age. Visual tooth inspection was used to age 18,390 individuals found dead or hunted between 1982 and 2020 within the Trentino sector of the Stelvio National Park and the Val di Sole hunting district (Central Italian Alps). Temporal trend of reconstructed population size was checked using spring spotlight counts as a benchmark, through the Buishand range test and a linear model. Our results showed a significant and positive relationship between reconstructed population size and spring spotlight counts between 1982 and 2013, suggesting that cohort analysis could reliably track red deer population trend up to 7 years in the past. With a relative error of + 1.1 (SD = 1.5) years in the estimation of age, and fairly stable hunting pressure, our results support the use of deterministic cohort analysis as a relative index of abundance for monitoring red deer over time, even in the absence of exact information about natural mortality. Under violation of assumptions, however, the performance of deterministic reconstruction should be carefully inspected at the management scale.
... Este modelo se originó en la URSS donde Derzhavin (1922) fue tal vez el primero en combinar datos de edad con las capturas. Redescubierto por Fry (1949) y posteriormente modificado por varios autores, incluyendo a Gulland (1965) y . La modificación hecha por Pope es conocida por Análisis de Cohortes de Pope (AC). ...
... Los siguientes modelos estructurados por edades, no son modelos matemáticos que contengan la noción de estados de equilibrios, en su formulación básica: Análisis de Poblaciones Virtuales (APV) (Fry, 1949(Fry, , 1957Gavaris, 1988); Análisis de Cohortes (AC) ; Análisis de Cohortes Modificado (ACM) (Hernández y Perrotta, 2008); Modelo Secuencial Simplificado (MSSIM) (Aubone, 2010); Modelo Secuencial Mixto (MSMix); Modelo de Producción estructurado por edades (ASPM) (Hilborn, 1990;Punt et al., 1995;Restrepo, 1996). Todos estos modelos suelen utilizarse para el describir la dinámica poblacional estructurada y diagnosticar el estado presente. ...
Modelos de dinámica de poblaciones de peces con estructura. Orientados a la evaluación de recursos pesqueros
... Retrospective life tables (i.e., age pyramids) for wild populations might be a useful tool to better understand demographic changes after extreme events, which may be interesting under the current context of climate change. This technique was first proposed by Fry (1949) to analyze minimum population size of lake trout (Salvelinus namayacush) in North America. This method allowed the retrospective estimation of the minimum number of individuals alive for each trout cohort and year using harvest data from subsequent years, and thus allowing the estimation of several demographic parameters through the construction of age pyramids. ...
In Mediterranean areas, severe drought events are expected to intensify in forthcoming years as a consequence of climate change. These events may increase physiological and reproductive stress of wild populations producing demographic changes and distribution shifts. We used retrospective life tables to understand demographic changes on a wild population after severe drought events. We studied the impact of two extreme events (2003 and 2005) on the population dynamics of our model species, the red deer (Cervus elaphus). During both years, population density was high (40 and 36 ind/100 ha, respectively). Thus, we reconstructed retrospectively the age structure of the female part of the population for the period 2000–2010 by using data of known-age individuals culled during the period 2000–2019 (n = 4176). Also, based on previous study results, we aimed to validate this methodology. Both extremely dry years, 2003 and 2005, produced marked and lasting cohort effects on population demography. Age pyramid the following years (2004 and 2006) revealed that the extreme drought caused the female fawn cohort to be similar or even smaller than the yearling cohort. Furthermore, these cohort effects were still perceptible 3 years after these severe events. Results agree with previous findings that showed a negative effect of severe drought events on female pregnancy rates and conception dates. Although simple, this study provides an empirical quantification of the demographic effects of severe drought events for a wild population which might be useful to understand future demographic changes under the context of climate change.
... Basicamente, esse modelo analisa as capturas da pesca comercial, combinadas com informações detalhadas sobre qual a contribuição de cada coorte para o rendimento e a biomassa total do estoque. A palavra virtual, introduzida por Fry (1949), é baseada em uma analogia com a imagem virtual, derivado da física. Uma população virtual não é a população real, mas é a única que é mensurável. ...
O subfilo Crustacea (do Latim “crusta” = carapaça dura) está entre os animais mais conhecidos e apreciados pela população em geral e representam o grupo mais abundante, com maior diversidade e maior distribuição nos oceanos. Vivendo
amplamente em ambientes marinhos, dulcícolas e terrestres, os crustáceos representam um dos grupos mais bem-sucedidos nos processos de adaptação às condições desses ambientes. São encontrados desde o supralitoral até às maiores profundezas dos oceanos (11.000 m de profundidade). Atualmente, existem aproximadamente 52 mil espécies marinhas descritas de um total de cerca de 72 mil (incluindo formas fósseis) distribuídas em mais de 1.000 famílias, com uma estimativa que possa existir entre
5 a 10 vezes mais espécies para serem descobertas, especialmente nos ambientes de mar profundo. Representam, portanto, um grupo muito diverso e com grande plasticidade morfológica, podendo medir desde 10 μm (Tantulocarida) até 4 m de envergadura de patas. Sua amplitude morfológica supera a dos insetos, como destacou Martin e Davis
(2001): “nenhum grupo de plantas ou de animais no planeta apresenta a amplitude de diversidade morfológica observada entre os crustáceos”.
... The t0 value was taken as zero. The method was first developed by Fry (1949) and subsequently modified by many authors. Pauly (1984) and Jones (1984) gave practical reviews of VPA methods. ...
... The estimated length structured virtual population analysis (VPA) and cohort analysis were done according to the FiSAT routine following the method of Fry (1949). Pauly (1984) and Jones (1984) gave the practical reviews of VPA. ...
... Taking into account the previous factors, age-structured population reconstruction methods [34][35][36][37][38], summarized and demonstrated by Skalski et al. [39], were considered. All of these methods use age-at-harvest data to back-calculate cohort sizes before harvesting. ...
Large carnivores are essential components of natural ecosystems. In populated areas, their conservation depends on preserving a favorable status in coexistence with humans, which may require the elimination of excess carnivores to minimize public concerns. As the Baltic region currently hosts a thriving wolf population, locally sustainable management of wolves is important for preserving biodiversity at a European scale. In this paper, we provide a dynamic assessment of the Latvian wolf subpopulation from 1998 until 2020. This study is based on age composition and fecundity data from teeth, uteri, and ovaria inspections obtained from samples of legally culled or accidentally killed individuals. The abundance estimates indicated population growth that exceeded the previously predicted carrying capacity. The proportion of juveniles among the culled individuals increased in recent years, but the mean age of culled adults exhibited a stable trend. In presumably nonselective hunting, the juveniles and individuals older than 3 years had greater culling mortality estimates in comparison with other age classes, and the culling rates for adult females of particular age classes were higher than for males of the same age. While creating significant hunting pressure, wolf management in Latvia may have contributed to the population growth by affecting its demographic processes.
... Basicamente, esse modelo analisa as capturas da pesca comercial, combinadas com informações detalhadas sobre qual a contribuição de cada coorte para o rendimento e a biomassa total do estoque. A palavra virtual, introduzida por Fry (1949), é baseada em uma analogia com a imagem virtual, derivado da física. Uma população virtual não é a população real, mas é a única que é mensurável. ...
... Basicamente, esse modelo analisa as capturas da pesca comercial, combinadas com informações detalhadas sobre qual a contribuição de cada coorte para o rendimento e a biomassa total do estoque. A palavra virtual, introduzida por Fry (1949), é baseada em uma analogia com a imagem virtual, derivado da física. Uma população virtual não é a população real, mas é a única que é mensurável. ...
This book aims to further contribute to the study of the practical and sustainable use of marine resources, balancing the demands for development with the those of critical environment protections. The objective of Volume 2 and it’s 18 chapters is to examine emerging topics related to the Bioecology, aquaculture and fishing. It will offer professors and students from various areas of discipline within the Sea Sciences in Brazil with the newest theoretical and scientific research to help us better contextualize the understanding of our seas and oceans.
... Basicamente, esse modelo analisa as capturas da pesca comercial, combinadas com informações detalhadas sobre qual a contribuição de cada coorte para o rendimento e a biomassa total do estoque. A palavra virtual, introduzida por Fry (1949), é baseada em uma analogia com a imagem virtual, derivado da física. Uma população virtual não é a população real, mas é a única que é mensurável. ...
... The length-weight measurements of the individuals examined according to their ages are presented in Table 2. The length and weight data obtained are consistent with the studies conducted on trout species in different water sources by Fry (1949), Geldiay (1968), Baltacı et al. (2007), Tanır and Fakıoğlu (2017), Yüksel et al. (2020). ...
In the present study, the length-weight relationship of black sea trout (Salmo labrax) captured from the tributaries of the Ilgaz Stream was investigated. A total number of 36 individuals were captured during 2014-2015 and transported to the laboratory. Here, the length and weight values of the fish were measured and the age determination was performed. Afterward, the condition factor and length-weight relationship parameters were calculated. The age of the fish ranged between 1+ and 4+. The mean condition factor was found to be 1.30 ± 0.13 for all fishes. The total length of the fish ranged between 12.80 and 23.90 cm whereas the weight ranged between 20.52 and 203.46 g. The “b” value was calculated as 3.4 and the growth of the fish was determined to be isometric. It was inferred that the Ilgaz stream is rich in food and the black sea trout inhabiting the stream is well-nourished. The stream is a convenient source in terms of nutrition and future studies should explore other aspects of aquaculture to benefit from the source to grow fish.
... Deterministic models [e.g. VPA (Fry, 1949), ADAPT (Gavaris, 1988), and XSA (Shepherd, 1999)] subtract the observed total catches-at-age each year, so the selectivity is simply what is given by the relative observed catches, which are assumed known without error. For deterministic models, it is not important for the analysis of the stock dynamics if the catch is divided into one or more fleets. ...
The state-space assessment model (SAM) is increasingly used to assess fish stocks in International Council for the Exploration of the Sea. One unique feature of the SAM class is that it allows the fishing selectivity to vary over time, and the degree to which it varies is not subjectively assigned, but estimated within the model. Selection may vary over time due to changes in the spatial pattern of the fish stock or fishing fleet, but a direct cause of selectivity change can be changed in fishing technology or other measures that target specific segments of the fish stocks. If the relative catches from fishing fleets which target different age or size classes of a species are changing over time, then the overall selectivity will also change—even if the selectivity within each fleet is fairly constant. A recent extension of the SAM model allows multiple fleets to be defined. It has been applied to two herring stocks to allow more detailed and fleet-specific management options in forecasts. For both stocks, the assessment from the multi-fleet models was consistent with the results from the single-fleet models, which strengthens confidence in the estimated time-varying selectivity for these and other stocks.
... Lake charr may not reproduce every year once they attain puberty (development of reproductive competency), a phenomenon previously referred to as "intermittent spawning" (Martin and Olver 1980) or as "infertile" fish (Fry 1949), but now commonly as "skipped spawning" (Rideout et al. 2005). In lake charr populations in several Canadian lakes, 8-87% of females in a population skipped spawning in a given year (Cuerrier and Schultz 1957;Johnson 1972Johnson , 1973Kennedy 1954;Miller and Kennedy 1948;Rawson 1961). ...
Lake charr Salvelinus namaycush are typically fall spawners although one ecotype has populations that spawn during spring and fall (siscowets in Lake Superior). Lake charr are iteroparous (reproduce more than once in a lifetime) with group-synchronous ovarian development and typically spawn once per year. However, lake charr may not reproduce every year, a phenomenon known as skipped spawning. Free embryos are active on spawning reefs, make diurnal vertical movements from spawning substrate, and feed exogenously much earlier than previously assumed. The abundance of food and predators strongly affects the rate of development, yolk sac absorption, and duration of residence on spawning sites. The necessity for, and timing of, gas bladder inflation, and mechanisms for inflation without access to the surface, need further study. The low survival of free embryos due to thiamine deficiency has likely contributed to the lack of recruitment of lake charr in the Laurentian Great Lakes for decades. Thiaminase, a thiamine-degrading enzyme, appears to be the causal agent for thiamine deficiency in Great Lakes lake charr.
... Most standard assessment methodologies were developed for application to temperate finfish stocks. Nevertheless, many have been applied to cephalopods, including stock-recruitment models based on the methods of Ricker (1954) and Beverton and Holt ( 1957 ), depletion estimates (De Lury, 1947 ), cohort analysis (Fry, 1949;Jones, 1961;GuUand, 1965;Murphy, 1965;Tomlinson, 1970;Pope, 1972 ), yield-per-recruit (Ricker, 1958 ) and production models (Schaefer, 1954;Pella and Tomlinson, 1969;Fox, 1970). ...
Cephalopods are of increasing importance as a fishery resource and many species are taken in directed and bycatch fisheries around the world. Owing to the short life-cycles and variable growth rates of most cephalopods, stocks may be highly volatile, both highly susceptible to recruitment overfishing and, conversely, capable of rapid recovery. Many species have protracted spawning seasons so that multiple microcohorts may be present in the population at any one time.
Many assessment methods have been applied to cephalopod stocks, including stock-recruitment relationships (e.g. the Japanese Todarodes pacificus stock), recruitment indices (e.g. Saharan Bank cephalopod stocks), swept-area biomass estimates (e.g. Northwest Atlantic stocks of the squids Loligo pealei and Illex illecebrosus), production models (e.g. Saharan Bank cephalopod stocks), cohort analysis (e.g. Illex argentinus in the Falkland islands), yield-per-recruit models (e.g. Northwest Atlantic squid stocks), length-based cohort analysis (e.g. Dosidicus gigas in the Gulf of California), and depletion estimates of stock size (e.g. Illex argentinus in the Falkland islands).
Despite the widespread application of assessment methods, few stocks are rigorously managed, and the best example of a regulated fishery is the Falkland islands squid fishery. In contrast, although a number of assessment methods are used in the Japanese Todarodes fishery, management activities are designed to ensure harmonious operation on the industry rather than maintain stock size. Fisheries for Loligo forbesi and Loligo vulgaris in the Northeast Atlantic are mainly based on by-catches, although there is some directed fishing, particularly artisanal jig fishing in coastal waters. There is currently no assessment and minimal management for these species, and available management options are constrained by the nature of the fishery and the generally poor quality of available data.
... Originally given as age-structured model by Fry (1949Fry ( , 1957 and Pope (1972), the length structured model was given by Jones (1984). This method utilizes basically the same approach as the age-structured VPA but is adapted to accommodate length frequencies. ...
The present study is based on morphometry, length-weight relationship, food and feeding habits, reproductive biology and stock assessment of Otolithoides pama (Hamilton, 1822) collected from three landing centers namely Godakhali, Diamond Harbor and Frasergunj under Hooghly-Matlah estuarine system of West Bengal, India during November 2016 to April 2018. A total of 618 samples with the size range of 101-384 mm total length and 7.29-470.71 g total weight were studied. Analysis of fourteen morphometric characters in O. pama revealed that standard length has fastest growth rate compared to total length while eye-diameter has the lowest growth rate compared to head length. Among meristic characters, fin formula of O. pama occurring in Hooghly-Matlah estuarine system can be written as: B. 7, D. 9-10/1/44-45, P. i/16-17, V. 1/5, A. 2/7-8, C. 19-21, L. 48-52. The length-weight relationship for the species is estimated as W = 0.0000158 L 2.85848 from the pooled samples while ‘t’ test indicated that the species exhibited negative allometric growth. The gut content analysis of O. pama revealed that the species is highly carnivorous in nature, mainly feeding on prawns, small teleosts, crabs and other crustaceans. Throughout the year specimens with empty stomach were noticed in high proportion. For both the sexes, the lowest monthly mean GaSI values were observed during July/August while highest values were recorded during February. The values of RLG for both the sexes were found less than one throughout the year indicating that the species is highly carnivore in nature. The total length at which 50% of the species attained maturity was estimated to be 183 mm and 196 mm for males and females respectively. Occurrences of matured ovaries in three different phases indicated that there are three peak spawning seasons for the species, one during February-March, second during June and third during September-November. The month-wise distribution of sex ratio indicated the marginal dominance of females over males except in the months of March-June with an overall sex ratio of 1:1.07. The absolute fecundity ranged from 4,652 to 1, 70,688 eggs with an average of 24,950 eggs. The relative fecundity varied from 96 to 808 eggs/g body weights (average 382). The von Bertalanffy growth equation in length is derived as Lt = 418 [1-e -0.58 (t+0.1356)]. The length attained by employing VBGF for O. pama were 202, 297, 350, 380 and 397 mm at the end of 1, 2, 3, 4 and 5 years of its lifespan respectively. In the present study, the maximum size recorded was found to be 384 mm, and the corresponding age was estimated at 4.19 years. The total, natural and fishing mortality were estimated at 4.16, 1.14 and 3.02 yr-1 respectively. The exploitation rate (U) was calculated as 0.72 and exploitation ratio (E) was 0.73. From the knife-edge selection, the value of Emax obtained was 0.586 and from selection ogive the value was 0.584. The virtual population analysis (VPA) indicated that the highest fishing mortality of 6.7602 was observed at 220-230 mm length group, followed by 5.9216 from 200-210 mm length groups. On average, sciaenids production contributed 20.2% to the total demersal catch and 5.08% of the total marine capture production during 2008-2017 in India. The total marine fish catch of West Bengal during the year 2015-16 was estimated at 1, 73,771 t and sciaenids contributed 11.45% of it.
... Population reconstruction methods are based on the idea that age-at-death can be used to back-calculate year-and agespecific abundance. These methods, also known as cohortor virtual population analyses, were originally developed in fisheries (Fry 1949) and later extended to other wildlife (Lowe 1969). In its simplest form, deterministic population reconstruction (DPR) allows to assess minimal population size, and the minimum number of individuals alive in one cohort for a given year is the sum of all individuals from that cohort found dead in subsequent years (Roseberry and Woolf 1991). ...
Knowledge of population trends is of key importance for sustainable management of wildlife and finding reliable and cost–effective monitoring methods is therefore of great interest. In two populations of Alpine chamois Rupicapra rupicapra, we collected data on mortality from 12424 individuals hunted or found dead and population size data based on ground counts over a period of 28 years. Our study had three aims: 1) we investigated if changes in population size obtained with a simple deterministic population reconstruction (DPR) approach using hunting and natural mortality covary with population size estimates obtained from ground count data. 2) We investigated if the performance of DPR is affected by the removal of natural mortality data. 3) We assessed how many years of mortality data are needed to obtain consistent population trends using DPR. Our results suggested that 1) population abundance from mortality data using DPR significantly and positively correlated with population abundance obtained with ground counts. 2) DPR without natural mortality data performed similarly as compared to DPR using full data (hunting and natural mortality). 3) Consistent estimates of population trends can be obtained with ≥10 years of mortality data, however, this time span was influenced by the mean age at death, which in turn was affected by the local hunting regime. Our results suggest that DPR and ground counts perform similarly for the estimation of temporal trends in Alpine chamois abundance. The consistence of ground counts and DPR supports the use of these methods as reliable tools for tracking abundance of chamois populations over time. However, the reliability of abundance estimates using DPR may vary between populations and the influence of different hunting regimes must be considered for the correct interpretation of results.
... Marten population estimates were derived using cohort analysis (Ricker 1940, Fry 1949. The principle behind this population estimator is based on use of a backward recursion formula to reconstruct specific contemporaneous cohorts of harvested animals to estimate minimum population abundance at various points in time. ...
... Cohort analysis (also known as virtual population analysis, VPA) is a method for population reconstruction applied to age-specific harvest data (catch-at-age data) that was originally developed in fisheries sciences (Ricker, 1940;Fry, 1949;Gulland, 1965;Pope, 1972), but since has also been applied to terrestrial species including ungulates (e.g. red deer, Lowe, 1969;white-tailed deer, McCullough, 1979;moose, Fryxell et al., 1988;Ferguson, 1993;roe deer, Lowe and Thompson-Schwab, 2003;reindeer, Eberhardt and Pitcher, 1992; and sika deer Cervus nippon, Ueno, 2008). ...
... Рис. 1. Районы проведения исследований на территории Ненецкого автономного округа (а) и Республики Коми (б) Обработка статистической информации проводилась на персональном компьютере IBM с применением стандартных программ. При определении коэффициентов общей, естественной и промысловой смертности, а также расчёте численности и промыслового запаса печорских сиговых использованы общепринятые методы, изложенные в ряде монографий и методических руководств [Fry, 1949;Рикер, 1979;Малкин, Борисов, 1987;Сечин, 1990, 2010Бабаян, 2000]. ...
Dynamic of stocks of whitefish species in it correlation to environment in the Pechora river and inflow was reviewed. At population level there is a violation of migratory ways and a mode of natural reproduction of whitefish species, change of their number and a condition of stocks. At the organisms level degradation of a physiological condition of concrete individuals and strengthening of epizootiya is observed.
... Age-at-harvest data commonly collected at hunter check stations often provides the only information on catch per unit effort and overall age-structure of a population across broad spatial extents (Gove et al. 2002, Broms et al. 2010, Skalski et al. 2012b. Early on, these data were used simply to estimate minimum population size based on cohort-specific sums of harvested animals (Fry 1949, Skalski et al. 2007). In rare cases, age-at-harvest data were also used to estimate state-level abundance under restrictive assumptions of stable and stationary populations (Millspaugh et al. 2009, Broms et al. 2010). ...
The mathematical modeling of ecological interactions is an essential tool in predicting the
behavior of complex systems across managed landscapes. The literature abounds with examples of models used to explore predator-prey interactions, resource selection, population growth, and the relationship between population density and disease transmission. These models provide managers with an efficient alternative means of testing new management and control strategies without resorting to empirical testing that is often costly, time-consuming, and impractical. However, because models are abstractions of reality that make a large number of simplifying assumptions, their results are substantially less accurate than those of empirical testing. This illustrates a fundamental challenge in conservation biology – the trade-off between effort and the validity or impact of results. Because wildlife managers and researchers have a limited number of resources with which to conserve and study wildlife populations (e.g., time, funding, number of field technicians), this trade-off is a matter of efficiency. Using mathematical models to test a hypothesis, for example, requires substantially less effort and fewer resources than empirically testing, but at the expense of the validity of the results. Understanding the dynamics of this trade-off in different situations and landscapes can help managers and researchers better allocate their limited resources. My intention is to explore this trade-off in addressing questions on individual-level resource selection, state-level estimates of population abundance, and population-level assessments of alternative management strategies in controlling the spread of infectious diseases.
... VPA is conducted to obtain the information on a fish population that should have been in water to produce the current catch. According to Fry (1949) virtual population is a population that is analyzed from the methods based on real catch data with the assumptions of natural mortality (M) and final fishery mortality. This method is used by the calculation of the total recruitment in the first cohort. ...
Southern Bluefin Tuna in spawning area of the Eastern Indian Ocean where the Indonesian’s longliners operated has a specific character in term of size, age, sex-specific growth rate and the population. The aims of this study are to determined changes in size/age, sex-specific growth rate and virtual population analysis of Southern Bluefin Tuna (SBT) in the spawning area. This study is important to find out the successful management of SBT in spawning area by looking at the catch at age/size movement, sex-specific growth analysis and the estimation of the population by virtual population analysis. In this study, we were used 452 pairs of otolith with fish sized from 134-196 cmFL and fish aged from 8-20 years. The growth equation was Lt = 191 (1-e-0,167(t+1,081)). Catch at age structure was distributed from 5-22 years with mean and mode of age were 9.63 and 9 years. The distribution of mode changed from year to year shifting to a younger fish. In 2012, the mode was 10 years but entering 2013-2014 the mode was shifted to 6 years. In 2015-2017, the mode was increased from 7 years (2015) to 8 years (2016) and 9 years (2017). The fishing pressure happened in the age group under 20 years. In 2012 to 2014, the highest fishing pressure respectively obtained in the age group of 13 to 11 years with an average length of 167 to 174 cmFL. Entering 2015 and 2016, the highest fishing pressure obtained in the age group of 6 years with an average length of 138 cmFL. The exploitation rate ranged from 0.14/year to 0.25/year meaning that the exploitation was in optimal condition.
... The relative abundances of different SMB year classes were inferred from 'virtual population estimates' based on age data of fish in anglers' creels. The 'virtual population method' had been applied at Lake Opeongo to Lake Trout data by F.E.J. Fry (1949) and then also applied to SMB. In the late 1960s mark-and-recapture methods were adapted to estimate the proportion of SMB actually captured and retained by anglers during the summer open season that were intercepted by the creel census clerks (Shuter et al., 1987). ...
Late in the 20th Century, participants in a trans-jurisdictional fisheries research network in the Great Laurentian Basin collaborated with participants of other research networks (waterfowl, piscivorous birds, benthic insects, plankton, bacteria, meteorology, hydrology, etc.) in a mega-scale happening during the years 1967 to 1992 that I call ‘The Great Laurentian Spring’. With a basin-wide version of adaptive management, the scientific researchers collaborated with citizen activists, private entrepreneurs, commission facilitators and governmental administrators in remediating harm done to the natural living features of the Great Laurentian Basin, particularly in the preceding 150 years. Like the degradation process that preceded it, the remediation process had features of a self-organizing movement that became complex beyond the ability of participants and observers to fully describe and explain it. Here I offer as an hypothesis, a rough sketch of how fisheries networkers in the Great Laurentian Basin came to play a role of helping to conserve valued fisheries and preserve vulnerable species during the degrading pre-Great Laurentian Spring period and then to help remediate harmful stresses, rehabilitate fisheries and prevent further degradation during the Great Laurentian Spring period and since then. In general fisheries researchers performed empirical science in responsible ways, with emphasis on the fish and on their habitats, and thus on the health of the aquatic ecosystems. Occasionally, the strongly modified natural system could be managed to produce major fisheries benefits, at least temporarily. The Scot T. Reid’s Common Sense science contributed to the American C.S. Peirce’s Pragmatism and together they informed the German A. Thienemann’s Limnology and the Canadians W.E. Ricker’s and F.E.J. Fry’s Fisheries Science. All along, mathematics of increasing sophistication played a role. Reputable criticisms of scientific inferences as well as untested and disreputable rhetoric of science deniers were taken seriously by the researchers.
... Because the number of animals harvested from each cohort each year is related to the size of the previous year's cohort, the harvest rate, and the nonharvest mortality rate, these harvest data provide some information about abundance, harvest mortality, and natural survival (i.e., 1 − non-harvest mortality; Clawson et al. 2013Clawson et al. , 2016. However, harvest data alone are not adequate to estimate all the desired parameters without either strong assumptions (e.g., no non-harvest mortality (Fry 1949), or non-harvest mortality is known and constant (Gulland 1965) or incorporating auxiliary data (Gove et al. 2002). Therefore, we incorporated auxiliary data from GPS-collared mountain lions, published kitten survival estimates, and hunter effort data. ...
Directly monitoring abundance of cryptic species, such as mountain lions (Puma concolor), over large areas is a challenge for wildlife managers because traditional population estimation techniques may be impractical and expensive. We generated annual estimates of mountain lion abundance in Arizona, USA, for 2004–2018 by employing statistical population reconstruction methods, which use available age‐at‐harvest data and auxiliary information such as estimated survival rates, harvest probabilities, and hunter effort. Using PopRecon 2.0 software, we estimated that the statewide abundance of all mountain lions including kittens ranged from 1,848 (95% CI = 650–3,046) to 4,661 (95% CI = 393–9,030) during 2004–2018. Abundance for subadults and adults was more stable and precisely estimated, ranging from 1,166 (95% CI = 622–1,709) to 1,715 (95% CI = 872–2,558). Our results suggest a stable statewide mountain lion population. This approach provides a practical and cost‐effective option for monitoring Arizona's mountain lion population, and will improve the ability of managers to monitor the population annually to respond to changes in abundance and to evaluate factors that influence mountain lion abundance. © 2019 The Authors. Journal of Wildlife Management published by Wiley Periodicals, Inc. on behalf of The Wildlife Society. Statistical population reconstruction provides a practical and cost‐effective option for estimating statewide mountain lion abundance in Arizona. The ability to update abundance estimates quickly with relatively little effort using PopRecon 2.0 improves the ability of managers to monitor Arizona mountain lion populations annually and respond to changes in abundance.
... Cohort analysis, or virtual population analysis, has its roots in fisheries population assessment (Fry 1949;Pope 1972). Age-at-harvest data are combined with the known number of animals that die from other causes to reconstruct the population by backcalculating the number of animals in a specific age-sex cohort (Ueno et al. 2009). ...
Monitoring abundance of black bears (Ursus americanus) is critical, as this information is required to inform sustainable management of a harvested black bear population. In Ontario, black bears have been monitored using a combination of direct and indirect measures, including determining if harvest is sustainable by examining annual harvest statistics; estimating survival, mortality, and abundance through telemetry studies; modelling population viability using the RISKMAN program; and estimating abundance and density through genetic capture-recapture methods.
Many jurisdictions in the United States reconstruct the hunted population of black bears using harvest and age-at-harvest data to estimate population size and trend. Our objectives were to: 1) Determine whether population reconstruction models could be used as an alternative to direct measures of population size, such as capture-recapture methods 2) Summarize the main data requirements and assumptions common to many population reconstruction models 3) Determine the extent to which those requirements can be met by data available in Ontario
We also provide recommendations to improve the reliability of black bear harvest and age-at-harvest data, which would be required to implement population reconstruction as a viable management tool in Ontario.
Population reconstruction is based on an estimate of the number and age distribution of harvested animals, as well as other auxiliary data, such as hunter effort, to determine the original size, age distribution, and recruitment rate of the harvested population of a wildlife species. To calculate total population size, annual mortality due to other causes must also be known or estimated. We present and discuss six methods of population reconstruction, and describe the data and assumptions required to run the models. We conclude that no population reconstruction model can replace direct estimates of abundance, but such models can provide managers with accurate, important population trend information between years of other surveys.
For accurate and precise population estimates via population reconstruction, harvest and effort data must be complete, accurate, and unbiased. Age-at-harvest data from annual tooth submissions must be accurate and representative of the harvested population. Independently collected auxiliary data, such as mortality or abundance, should be available at regular intervals and be representative of the bear population. Finally, immigration and emigration should be negligible, and harvest mortality should be the main cause of death. If other causes of death are common, the rate of that mortality should either be constant and known, or measured annually for each region.
Ontario harvest and age-at-harvest data for 1985 to 2014 violated the main assumptions of population reconstruction.
* Harvest and effort surveys for non-residents were completed by most non-resident hunters; therefore, they can be considered to be accurate. However, corresponding data for resident hunters were likely more biased through time and across space. Resident hunters may hunt in any wildlife management unit (WMU) with an open season, so if spatial biases in the data exist, we could not account for them because we did not know where non-replying hunters hunted. Harvest and effort data were biased to hunters who replied voluntarily and likely to those who were successful.
* Survey methods changed through time, making reported success rates and projected annual bear harvests inconsistent through time.
*Total bear harvest was estimated using a provincial correction factor instead of a local factor, potentially biasing WMU-specific harvest estimates.
* Non-resident hunters submitted an adequate sample of bear teeth for ageing, but resident hunters did not. As a result, it is unlikely that the sample of age-at-harvest data from residents was representative of the harvested population.
* In some WMUs, especially those surrounding protected areas, seasonal immigration may significantly outweigh seasonal emigration during the hunting season in Ontario (Obbard et al. 2017), which introduces differential biases in the population estimate.
* Harvest mortality is the main cause of death for black bears in Ontario, but many bears die from other natural and human-induced causes. We have poor estimates of these mortalities. Therefore, estimated population size can be viewed only as an indicator of total population size. Trends in the proportion of mortality due to factors other than hunting, which may occur over time, could bias population estimates.
* Independent bear abundance estimates from regularly conducted telemetry or capture-recapture studies (every 5 to 10 years) are necessary to calibrate estimates from population reconstruction. Currently, vital rate information for bears in Ontario is dated and may not be available at appropriate spatial scales.
If population reconstruction is to be considered a viable method for estimating population size and population trends in Ontario in the future, consistent survey methods, greater compliance with mandatory reporting, and higher rates of tooth submission are needed. Population reconstruction should not be used in isolation to obtain accurate abundance estimates. Other jurisdictions conduct independent abundance estimates using alternate methods every 5 to 10 years to confirm and correct population reconstruction trends and estimates. Therefore, Ontario requires upto-date vital rate information from capture-recapture programs, such as collaring (physical capture-recapture) or barbed-wire hair-trap (genetic capture-recapture). Without these auxiliary data, population reconstruction models may produce trends or estimates that are unrealistic or incorrect. Ontario manages bear populations at the WMU scale; therefore, accurate and precise data are required at that scale to provide meaningful estimates. We present specific recommendations to improve data collection and meet the assumptions of the model. When assumptions and data requirements are met, population reconstruction could be a valuable tool for local bear managers, especially as population estimates are available each year, allowing managers to respond immediately to local problems or socioeconomic opportunities.
... Derzhavin (1922) applied the Baranov catch equation (1) to catch-at-age data in order to assess population size while assuming negligible mortality from sources other than fishing. A similar method was used in Fry (1949), where a "virtual population" was introduced to represent the initial population size (assumed to be at least as big as what was later caught). Notice that this concept of a virtual population size is reminiscent of state-space terminology, as it refers to an unobserved random variable. ...
Fisheries science is concerned with the management and understanding of the raising and harvesting of fish. Fish stocks are assessed using biological and fisheries data with the goal of estimating either their total population or biomass. Stock assessment models also make it possible to predict how stocks will respond to varying levels of fishing pressure in the future. Such tools are essential with overfishing now reducing stocks and employment worldwide, with in turn many serious social, economic, and environmental implications. Increasingly, a state-space framework is being used in place of deterministic and standard parametric stock assessment models. These efforts have not only had considerable impact on fisheries management but have also advanced the supporting statistical theory and inference tools as well as the required software. An application of such techniques to the North Sea cod stock highlights what should be considered best practices for science-based fisheries management.
... Aussi, à des fins de comparaison une approche globale tout sexe confondu a été réalisée en utilisant la moyenne des valeurs des différents paramètres biologiques des 2 sexes. Baranov (1914), Fry (1949), Beverton et HoIt (1956) et Jones (1961, la méthode générale de cette méthode se base sur l'analyse de la structure démographique de la population ; elle a été développée par Murphy (1965), Gulland (1965) et Pope (1972. ...
... The L∞, K, M, F, a (constant) and b (exponent) values were inputs in a VPA analysis and the t 0 value was assumed to be zero. This method was first published by Fry (1949) and subsequently modified by Jones (1984) and Pauly (1984). ...
... We used a Downing (1980) adaptation of the Virtual Population Analysis developed by Fry (1949) to reconstruct the northwestern South Carolina black bear population through backward summation of cohorts. This technique is suitable for analysis of age-and sex-specific harvest data that are typically collected by managers (Warburton 1996, Bender 1997, Jones 2005, Noyce 2011b). ...
As American black bears (Ursus americanus) reoccupy portions of the eastern United States, it is important to implement sustainable management practices based in a strong understanding of the dynamics of these recovering populations as they expand into areas with increasing anthropogenic pressures. We used the Downing population reconstruction technique on harvest records to establish baseline abundance and population growth-rate trends over 15 years for a population of black bear in northwestern South Carolina, USA. The total population in 2013 was estimated to be a minimum of 412 black bears, increasing from approximately 97 bears in 1998. We established age structure and sex structure in harvest, which were consistent with sustainably harvested bear populations. We recommend using these data as a baseline to determine the maximum sustainable harvest rate for this population. We also recommend future investigation into the development of research priorities and harvest management decisions for the population to maintain desired levels of black bear recovery. © 2017 International Association for Bear Research and Management.
... only the most advance oocytes were counted). ACCs were estimated according to the Thorsen and Kjesbu (2001) protocol based on Fry (1949) for each study area and lab: ...
The autodiametric method is a highly streamlined method for estimating fecundity of fish with a determinate oocyte development pattern. Greenland halibut is a deepwater flatfish presenting a very peculiar reproductive strategy, with ovaries showing the simultaneous presence of both a cohort of large vitellogenic oocytes (developing for the current year) and a cohort of small vitellogenic oocytes (developing for the subsequent year). The first objective of this study was to determine if the autodiametric method could be reliably used for estimating fecundity of Greenland halibut, and the second one was to test spatial differences in the autodiametric calibration curve (ACC) and potential fecundity in the Northwest Atlantic (Div. 3M, Div. 3LNO, Div. 3Ps and Div. 4S). Results showed that the autodiametric method can be applied to estimate fecundity in Greenland halibut. Spatial differences in ACCs (3M = 3LNO ≠ 3Ps ≠ 4S) were observed, but did not translate into differences in fecundity at length. This is the first time that differences between ACCs of the same species but from different areas have been reported. These differences could be the result of (1) the unusual oocyte development pattern, or (2) spatial differences in oocyte biochemistry, however interpretation is complicated by differences in sampling methodology between laboratories. More research on the relative dynamics of oocyte cohorts simultaneously present in Greenland halibut ovaries and the factors (endo- or exogenous) that influence oocyte packing density could lead to a better understanding of the observed geographical differences.
... Age-at-harvest data commonly collected at hunter check stations often provide the only information on catch per unit effort and overall age structure of a population across broad spatial extents (Gove et al. 2002, Broms et al. 2010, Skalski et al. 2012b. Early on, these data were used simply to estimate minimum population size based on cohort-specific sums of harvested animals (Fry 1949, Skalski et al. 2007). In some cases, age-at-harvest data were also used to estimate state-level abundance under restrictive assumptions of stable and stationary populations (Millspaugh et al. 2009). ...
Statistical population reconstruction using age-at-harvest and catch-effort data has recently emerged as a robust and versatile approach to estimating the demographic dynamics of harvested populations of wildlife. Although there are clear benefits to incorporating radio-telemetry data into reconstruction efforts, these data are costly and time-consuming to collect. Managers that consider collecting these data alongside existing efforts could benefit from a comprehensive examination of how such benefits are influenced by the amount of radio-telemetry data collected. Using a harvested population of American marten (Martes americana) in northeastern Minnesota, USA as a case study, we investigated the performance of population reconstruction using information on natural, harvest, or combined mortality derived from radio-telemetry data collected over different numbers of years and with different numbers of animals collared each year. We simulated populations under a range of conditions and determined that incorporating radio-telemetry data on natural and harvest mortality significantly improved model precision, and that each additional animal collared per year yielded a 0.50 ± 0.14% (SE) improvement in precision, whereas every additional year of radio-telemetry data resulted in a 2.42 ± 0.70% improvement. Thus, including another year of radio-telemetry resulted in similar gains in precision as including approximately 5 additional animals collared per year. In our applied marten example, incorporating radio-telemetry data resulted in a significantly higher estimate of trapping vulnerability (0.20 vs. 0.058) and an overall smaller population size than reconstruction based solely on age-at-harvest and trapper effort data. These results illustrate the benefits of performing auxiliary studies, caution against relying on the results of population reconstruction based solely on age-at-harvest and hunter-effort data, and demonstrate that improvements from incorporating radio-telemetry data become evident even after as few as 2 years of data collection.
... By adding the catches removed in the future years to the existing the year-classes alive in a given year, he estimated the minimum number of sturgeon alive in the reference year. This was named utilized stock by Voevdoin (1938) and virtual population by Fry (1949)". The equations of VPA were lately formalized by Gulland (1965). ...
... The Downing model is a special case of the Fry model, which estimates only minimum abundance, and is subject to the assumption of constant harvest and survival rates (Fry 1949, Downing 1980, Davis et al. 2007). Alternatively, managers will populate population dynamics models with parameter estimates from the literature to guide their management decisions (Connelly et al. 2005). ...
Historically, management agencies in the United States have monitored most
game populations through an ad hoc approach which combines indices, harvest data,
hunter surveyed data, and occasional demographic evaluation. However, changing
management priorities and increased scrutiny require more informative and defensible
means of monitoring harvested populations. Statistical population reconstruction (SPR) is
a flexible modeling system which simultaneously analyzes age-at-harvest data, hunter
effort data and any additional demographic data which are available, producing estimates
of abundance, natural survival and harvest rate, as well as their associated variances. An
SPR based monitoring framework provides comprehensive analysis of commonly collected data and represents a statistically rigorous and defensible alternative to the
currently popular approaches. However, applications of SPR have previously been
limited to small scale, highly monitored populations, primarily due to a lack of formal
evaluation of data requirements and guidance for management application. In this
dissertation I provide the guidance necessary for broad scale application of SPR modeling
to monitor harvested species. I rigorously evaluate the relative utility of auxiliary data
sources as well as minimum harvest and hunter effort data requirements for SPR models,
providing necessary guidance for resource managers seeking to apply SPR. I present a
historic population reconstruction based on SPR parameter estimates as an illustrative
example of the management application potential of SPR output. I comprehensively
evaluate models to project reconstructed abundance into the future in order to further
increase the management utility of statistical population reconstruction. I provide a
detailed explanation of model structure and assumptions, allowing resource managers to
critically evaluate SPR models. Finally, I offer guidance on the customization of SPR
models necessary to adequately model the harvest regimes and data collection
methodologies which are unique to each harvested population, thus increasing the
number of populations which can be modeled. This dissertation will facilitate the broad
scale management application of SPR, thus increasing the rigor and efficiency with
which harvested game populations are monitored.
... Taille virtuelle des cohortes La taille virtuelle (ou le «stock utilisé») est une estimation de l'abondance minimale d'une cohorte de poissons (Ricker 1975). Exprimée en nombre total d'individus capturés, la taille virtuelle d'une cohorte donnée est calculée en faisant la somme des poissons capturés appartenant à cette cohorte, dès leur recrutement jusqu'à leur élimination (Fry 1949). Du fait que l'on ne tient pas compte de la mortalité naturelle, cette méthode sous-estime la taille réelle de la population. ...
NACEUR N., BÜTTIKER B., 1999. The «palée» of the Lake de Joux: breeders' fishing statistics; age, growth and fertility. Bull. Soc. vaud. Sc. nat. 86.4: 273-296. The population of the vvhitefish Coregonus palaea (local name: «palée») of Lake Joux has been monitored from 1980 to 1996. This study has shown that whitefish population strength and harvest follow cyclic variations. The length of the cycles is about 7 years. More or less distinct annual variations can be observed for age, length and weight structures. Productivity of vvhitefish population tends to decrease since the beginning of the investigations. In the same time, the annual variations have also decreased. This reduction of productivity may possibly be an effect of the algae Oscillatoria rubescens or intraspecific competition. This study reveals that management of the whitefish should tend to exploit fish up to an age of about four years. Mesh size should therefore be chosen for an optimal exploitation of 3 to 4 years old fish.
... The term Virtual Population was introdueed by FRY(1949) and was defined as the sum of the eatehes of a year-class whieh has passed through fishery. BEVERTON & HOLT(1957), GULLAND (1965GULLAND ( ,1983 developed a method of estimating fishing mortality and abundanee from eatch at age data, whieh is now ealled Virtual Population Analysis or in the modification of POPE(1972) named as Cohort Analysis. ...
Virtual Populations Analysis (VPA) of the data on catch number by age and year, is used to estimate fishing mortality, abundance and biomass of the fishable stock of pikeperch in Lake Võrtsjärv (270 km2, mean depth 2.8 m), Estonia. The catch rate of the fishery is rather low, finishing mortality (F) of the dominant age group (4-10 years) was 0.21-0.63 during 1978-1990. Natural mortality (M) was 0.13. During the last 14 years there were no major fluctuations of abundance, owing to the strict regulation of fishery. However, changes in pikeperch catches have been 80-fold during the history of the fishery. The causes of such abundance fluctuations are discussed. Optimum annual catch ought to constitute 40-50% of fishable stock (F = 0.65).
... The t 0 value was taken as zero. The method was published by Fry (1949) and subsequently modified by many authors. Practical reviews of VPA methods were, among others given by Pauly (1984) and Jones (1984). ...
Estimates of growth, mortality and relative yield per recruit of the sergestid shrimp, A. intermedins in the coastal waters of Malacca, Peninsular Malaysia were obtained from the monthly length-frequency data. The von Bertalanffy growth function (VBGF) estimates were: L∞ = 34.65 mm total length; K = 1.5 yr-1 and t0 = -0.1004 years. Natural mortality rate (M) was 1.5 yr-1. Total mortality coefficient (Z) was estimated as 4.15 yr-1 and the exploitation ratio (E = F/Z) was 0.43. The recruitment pattern was continuous throughout the year with one major peak. The relative yield per recruit analysis predicted the maximum allowable limit of exploitation (Emax) = 0.65. The current exploitation rate E is less than the predicted Emax). Thus, the stock of A. intermedius was found to be below optimum fishing pressure (E < 0.50) in the coastal waters of Malacca, Peninsular Malaysia.
... El APV es una técnica que reconstruye el paso de cada cohorte por la pesquería, esto es para un conjunto de individuos nacidos en un momento dado y que pasarán por las mismas vicisitudes (cohorte), estima su abundancia y biomasa, así como la mortalidad por pesca que sufre para cada clase de edad, a lo largo del periodo considerado y partiendo de datos de la última edad del último año. El desarrollo de esta técnica se deba a Gulland (1965) quién se basó en otras técnicas empleadas por otros autores (Fry, 1949), aunque el pionero fue Baranov (1914): Este autor asumió que, como mínimo, los integrantes de una clase de edad eran la suma de los capturados, obteniendo con éstas sumas un tamaño mínimo de la población, aunque muy sesgado. Posteriormente, Fry (1949) y Gulland (1965), corrigieron esta estimación considerando los vectores de mortalidad natural (M) y de mortalidad por pesca (F). ...
This thesis presents a study of the biology of the red shrimp Aristeus antennatus and its exploitation as a renewable resource was analyzed in three neighbouring areas of the Spanish Mediterranean: the Gulf of Alicante, Ibiza Channel and the Gulf of Vera. Specimens were gathered monthly during a period of 8 years, from 1992 until 1999, from the fish markets used for landings by the commercial fleets of various representative ports in each area (Villajoyosa, Santa Pola and Garrucha), as well as from on board vessels that visited the different fishing grounds. In addition, data from the fishery (e.g. landings, effort) were compiled for each area during the study period. The exploitation areas and their depths were identified, and a total of 17 fishing grounds were characterised. The exploitation ranges between depths of 350 and 1,153 m were characterised by the influence of the Levantine Intermediate Water (LIW) down to 700 m and the Deep Water (DW) below this depth. A. antennatus could be defined as a stenothermic and stenohaline species, with a wide bathymetric and geographical distribution. Although the structure of the exploited population did not show large differences between the areas, with the females dominating in the sexual proportion of the catches (SP = 0.80), significant differences existed in their average sizes and growth, both between sexes and areas. In general, the females were more robust and larger than the males, being able to reach five years old, whereas the males only achieved three years old. Differences in reproduction, which occurred in the summer months, also existed between sexes, although this had the same pattern in the three areas. The sizes at first maturity found for both sexes (17 mm Cl and 22 mm Cl in males and females, respectively), were less than those reported by other authors in neighbouring areas, and were attributed to a larger contribution of small sizes in the catches. The exploitation patterns and activity groups of the fleets were identified and characterised. Standardised abundance indexes were obtained for both activity groups identified. The exploitation state of the resource was analysed by means of length cohort analysis (LCA), yield per recruit (Y/R) and virtual population analysis (VPA), calibrated with abundance indexes derived from standardised catches per unit of effort, as well as those obtained on survey cruises. No changes in the exploitation patterns were found with time, and the recruitments were very stable. By areas, the resource was more important in the Gulf of Vera, which represented the sum of the other two areas (Ibiza Channel and Gulf of Alicante). It was concluded that the resource was in a state of overexploitation not detected previously by other authors in neighbouring areas, with the maximum sustainable yield being around 50% of the current effort, and certain recommendations were established for its management.
Objective
Cormack–Joly–Seber (CJS) mark–recapture analysis was used to estimate the effect of travel distance and fuel costs on angling party persistence (i.e., survival = probability of remaining in the Lake Trout Salvelinus namaycush fishery from year‐to‐year) and visitation (i.e., detection = probability of detection at the access point) over a 14‐year period (2006–2019) for the Lake Trout recreational fishery in Lake Opeongo, Ontario, Canada.
Methods
Boat identification numbers, positioned near the bow and present by law, were used as “tags” in the CJS analysis. Complete trip creel interviews at the sole access point provided information on trip characteristics.
Result
The long‐term mark–recapture analysis of individual angling parties showed travel distance had a significant negative effect on party persistence among years and visitation within years. The distance effect was strongest for visitation, with visitation having a more negative relationship with distance than persistence. Persistence in the Lake Trout fishery was insensitive to fuel costs while the fuel cost covariate had a small though significant and negative effect on visitation. Time‐varying CJS models were ranked low with little model weight indicating the distance effect estimated for Lake Opeongo was a general phenomenon and not year dependent.
Conclusion
Cormack–Joly–Seber mark–recapture analysis cleanly separated effects of travel distance and fuel cost between visitation versus persistence for Lake Trout angling parties. Prior to this analysis, travel costs were typically associated with visiting a recreational fishery, while here we have shown that travel costs can be associated with persisting as anglers in a fishery independent of visitation patterns. Long‐term monitoring of angling parties provides unique insights into angling patterns that can aid in travel cost estimation.
Multispecies, multigear fisheries occur in most ecosystems in the world, but are typical in tropical ecosystems and especially in emerging economies. However, much of fishery science has been developed from a single-species perspective. Management schemes based on single-species reference points often ignore the trophic link among species and the technical interaction between gears, essentially disconnecting management objectives from the context of an ecosystem—or socioecological system—where fisheries operate. Using the Gulf of Thailand fishery as an example, we demonstrate how aggregate production models can be used to estimate system-level fishery reference points for multispecies fisheries. Our results show that the multispecies maximum sustainable yield changes with ecosystem state—the systemic productivity level due to species composition and ecological (trophic/habitat, etc.) structure—under various development levels of fishing and varies with management objectives such as biodiversity, system resilience, total catch, total value, and employment. Aggregate approaches are a tractable way of estimating sustainable ecosystem-scale extraction for multispecies fisheries, avoiding the dilemma of facing conflicting advice derived from single-species methods and providing a practical, operational step toward ecosystem-based management. However, these methods are sensitive to the ecosystem states over time and decision makers need to make informed decisions on which state they want to maintain (or recover) and thus which system-level reference points to use. Consequently, management of multispecies fisheries must be clear on their system-level fisheries policy objectives.
Lake charr Salvelinus namaycush life history and population dynamics metrics were reviewed to evaluate populations inside (n = 462) and outside (n = 24) the native range. Our goals were to create a database of metrics useful for evaluating population status and to test for large-scale patterns between metrics and latitude and lake size. An average lake charr grew from a 69-mm length at age-0 (L0) at 89 mm/year early growth rate (ω) to 50% maturity at 420 mm (L50) at age 8 (t50), and then continued to grow toward a 717-mm asymptotic length (L∞). L50 was positively correlated to ω, whereas t50 was inversely correlated to ω. Lake charr grew slower toward larger size and older age in northern latitudes and larger lakes than in southern latitudes and smaller lakes. Population density (number/ha) and yield density (kg/ha) decreased with lake size, and yield and total annual mortality (A) decreased with latitude. Native populations grew slower (ω), were heavier at 500 mm (W500), matured at shorter L50, grew to a shorter L∞, and suffered lower annual mortality A than non-native populations. Our review and database should be useful to managers and researchers for quantifying lake charr population status across the species range.
Ergodic Analysis of Biological Sustainability of an Age-Structured Fish Population
A focus on post-war reconstruction and development superseded the earlier prioritization of the conservation of fisheries and other resources. It is within this context that a largely-forgotten international gathering, the Symposium on Fish Populations, was held in Toronto in January of 1947. Many participants arrived at this meeting armed with conventional pre-Second World War conservation ideals. This meeting shook their certainty in their concepts of ‘overfishing’, jolted their confidence in their ability to clearly link reduced catches to overfishing, and undermined support for effective conservation measures.
Stock assessment models and predictions of catch and biomass are handmaidens to fisheries management. Their primary purpose is to help manage fisheries rationally. They also help us understand the biology of fish stocks by quantifying the key factors, such as spawning potential and recruitment that lay at the heart of reproductive biology. This chapter describes the approaches that fisheries scientists use to understand stock dynamics, to estimate past-present stock states, and to predict future states and catches. It focuses on the prediction of stock abundance and stock biomass, and lays emphasis on the need to estimate and predict the recruitment and spawning potential of stocks. The methods by which stock dynamics are understood and by which estimates are made are usually described in mathematical terms. As mathematics are a barrier to understanding for many people, the chapter, as far as possible, uses words and pictures rather than mathematics.
Cohort reconstructions (CR) currently applied in Pacific salmon management estimate temporally variant exploitation, maturation, and juvenile natural mortality rates but require an assumed (typically invariant) adult natural mortality rate (dA), resulting in unknown biases in the remaining vital rates. We explored the sensitivity of CR results to misspecification of the mean and/or variability of dA, as well as the potential to estimate dA directly using models that assumed separable year and age/cohort effects on vital rates (Separable Cohort Reconstruction, SCR). For CR, given the commonly assumed dA = 0.2, the error (RMSE) in estimated vital rates is generally small (≤ 0.05) when annual values of dA are low to moderate (≤ 0.4). The greatest absolute errors are in maturation rates, with large relative error in the juvenile survival rate. The ability of CR estimates to track temporal trends in the juvenile natural mortality rate is adequate (Pearson’s correlation coefficient > 0.75) except for high dA (≥ 0.6) and high variability (CV > 0.35). The alternative SCR models allowing estimation of time-varying dA by assuming additive effects in natural mortality, fishing mortality, and/or maturation rates did not outperform CR across all simulated scenarios, and are less accurate when additivity assumptions are violated. Nevertheless an SCR model assuming additive effects on fishing and natural (juvenile and adult) mortality rates led to nearly unbiased estimates of all quantities estimated using CR, along with borderline acceptable estimates of the mean dA under multiple sets of conditions conducive to CR. Adding an assumption of additive effects on the maturation rates allowed nearly unbiased estimates of the mean dA as well. The SCR models performed slightly better than CR when the vital rates covaried as assumed. These separable models could serve as a partial check on the validity of CR assumptions about the adult natural mortality rate, or even a preferred alternative if there is strong reason to believe the vital rates, including juvenile and adult natural mortality rates, covary strongly across years or age classes as assumed.
Leopard shark tag covery data, obtained from a 1979-88 study in San Francis00 Bay, were analyzed to determine temporal and geographic distribution of the tagged population. V i population analysis of the tag recovery data was used to derive fishing mortality rates, which in turn were used to obtain yield-per-recruit and stock replacement values, and to estimate the effect of management by size limit on stock replenishment and yield per recruit. Of the tagged population, 11% was recovered by sport anglers and commercial fishermen, and the distribution of recoveries indicates that leopard sharks are mostly resident in San Francisco Bay, although a portion of the population moves out of the Bay during fall and winter. An unusually high number of recaptures was made in 1983, a year of El Nifio conditions and high river runoff. After obtaining mortality, yield, and stock replacement values, it was proposed that a viable management strategy for the San Francisco Bay leopard shark would be a size limit of 100 cm or 40 inches to ensure maintenance of the stock and provide a yield per recruit not too far below a maximum.
This research spans a variety of research topics with a common theme, providing decision support through the development and analysis of methods that assist decision making for natural resource and wildlife management. I used components of structured decision making and decision analysis to address natural resources management problems, specifically monitoring and estimating the status of harvested populations, as well as data collection decisions for landscape conservation.
My results have implications for the way populations are monitored and their status is estimated. I find that the inclusion of error in data collection can have a substantial impact of the performance of abundance and growth rate estimates of harvested species and that the selection of estimation methods depends on what management objectives are most important. For example, the Sex-Age-Kill population estimation method best estimates the size of populations, while the Downing population reconstruction method better estimates trends in population growth rates. I provide a framework to support selection of the best estimation method while considering a monitoring program as a whole. Based on this framework the Vermont Fish and Wildlife Department will obtain the most benefits from a monitoring program including necropsy analysis that uses the Downing method to track population status. Finally, I demonstrated the use of value of information analysis as a tool to determine the relative expected benefits of addition spatial data collection for use in landscape mapping and conservation. This type of analysis can provide conservation agencies with a planning tool to direct budgets and mapping efforts.
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