Production, Mortality, And Sustainable Yield Of Northwest Atlantic Harp Seals (Pagophilus groenlandicus)

1978 ◽  
Vol 35 (9) ◽  
pp. 1249-1261 ◽  
Author(s):  
G. H. Winters
Keyword(s):  
Population Size ◽  
Total Population ◽  
Historical Data ◽  
Maximum Sustainable Yield ◽  
Sustainable Yield ◽  
Natural Mortality ◽  
Northwest Atlantic ◽  
The Past ◽  
Relative Contribution ◽  
Pagophilus Groenlandicus

From recent and historical data the natural mortality rate of adult harp seals (Pagophilus groenlandicus) is estimated to be 0.10 which is within the range of previous estimates (0.08–0.11). New estimates of bedlamer and 0-group natural mortality rates were not significantly different from those of adult seals. Pup production estimates from survival indices agreed well with those from sequential population analyses and indicated a decline from about 350 000 animals in the early 1950s to about 310 000 animals in the early 1970s. Over the same period the 1+ population size declined from 2.5 to 1.1 million animals but has been increasing at the rate of 3%/yr since the introduction of quotas in 1972. The relative contribution of the "Front" production to total ("Front" plus Gulf) production during the past decade has fluctuated from 49 to 87%, the average of 64% being very similar to the 61% obtained previously. These fluctuations suggest some interchange between "Front" and Gulf adults and it is concluded that homing in the breeding areas is a facultative rather than obligatory aspect of seal behavior. Thus the heavier exploitation of the "Front" production is probably sufficiently diffused into the total population to avoid serious effects on "Front" production. The maximum sustainable yield of Northwest Atlantic seals harvested according to recent patterns is estimated to be 290 000 animals (80% pups) from a 1+ population size of 1.8 million animals producing 460 000 pups annually. The sustainable yield at present levels of pup production (335 000 animals) is calculated to be 220 000 animals which is substantially above the present TAC of 180 000 animals and coincides with present harvesting strategies designed to enable the seal hunt to increase slowly towards the MSY level. Key words: mortality, production, sustainable yield, population dynamics, marine mammal

scholarly journals Changes in the reproductive parameters of female harp seals (Pagophilus groenlandicus) in the Northwest Atlantic

2009 ◽  
Vol 67 (2) ◽  
pp. 304-315 ◽  
Author(s):  
Becky Sjare ◽  
Garry B. Stenson
Keyword(s):  
Environmental Factors ◽  
Population Size ◽  
Sexual Maturity ◽  
Reproductive Parameters ◽  
Northwest Atlantic ◽  
Pagophilus Groenlandicus ◽  
Long Term Trends ◽  
The Mean ◽  
The 1950S

Abstract Sjare, B., and Stenson, G. B. 2010. Changes in the reproductive parameters of female harp seals (Pagophilus groenlandicus) in the Northwest Atlantic. – ICES Journal of Marine Science, 67: 304–315. Changes in female harp seal (Pagophilus groenlandicus) reproductive parameters from 1980 to 2004, and long-term trends since the early 1950s, are evaluated. Estimates of the total number of seals in the Northwest Atlantic declined from ∼3.0 million in the 1950s to 1.8 million in the early 1970s, then increased steadily to 5.5 million in 1996, at which relatively stable level it has remained since. Pregnancy rates increased from ∼86% in the 1950s to a high of 98% in the mid-1960s, then declined to ∼65–70% by the early 1990s; the rate then varied between 45 and 70% from 2000 to 2004. Concurrently, the mean age at sexual maturity decreased from 5.8 (s.e = 0.02) years in the mid-1950s to 4.1 (s.e. = 0.02) in the late 1970s, increased to 5.5 (s.e. = 0.03) years by the early 1990s, and peaked at 5.7 (s.e. = 0.01) in 1995. From 2000 to 2004, mean age varied from 4.9 (s.e. = 0.01) to 6.0 (s.e. = 0.01) years. Although the direction of change in each of the parameters was consistent with a density-dependent response, changes in population size explained relatively little of the variability observed, suggesting that other ecological or environmental factors were influential.

Relationship of Fishing Mortality to Natural Mortality and Growth at the Level of Maximum Sustainable Yield

1982 ◽  
Vol 39 (7) ◽  
pp. 1054-1058 ◽  
Author(s):  
R. B. Deriso
Keyword(s):  
Logistic Model ◽  
Mortality Rates ◽  
Maximum Sustainable Yield ◽  
Sustainable Yield ◽  
Natural Mortality ◽  
Fishing Mortality ◽  
Difference Model ◽  
Relationship Of ◽  
Yield Per Recruit ◽  
Delay Difference

Fishing mortality constraints are derived for fishes harvested at the maximum sustainable yield (MSY) determined by a delay-difference population model. Those constraints depend upon rates of natural mortality and growth as well as a simple constraint placed on abundance of the exploited population. The results are generalized for a wider class of population models where it is shown that MSY fishing mortality is constrained often to be less than the fishing mortality which maximizes yield per recruit. Fishing mortality rates are lower in the delay difference model in comparison to MSY fishing rates in the logistic model, when a quadratic spawner–recruit curve is applied.Key words: delay-difference model, logistic model, fishing mortality, maximum sustainable yield, yield per recruit

scholarly journals THE BIOLOGICAL OPTIMAL LEVEL OF THE ARAFURA SHRIMP FISHERY

2017 ◽  
Vol 16 (2) ◽  
pp. 79 ◽  
Author(s):  
Purwanto Purwanto
Keyword(s):  
Optimal Level ◽  
Fishing Effort ◽  
Maximum Sustainable Yield ◽  
Sustainable Yield ◽  
Paper Briefly ◽  
Shrimp Fishery ◽  
Illegal Fishing ◽  
The Past ◽  
Arafura Sea ◽  
The Impact

This paper briefly describes the past development of the shrimp fishery in the Arafura Sea, including intensity of illegal fishing, and presents the impact of increasing fishing pressure on the quantity of catch and biomass. The maximum sustainable yield and the optimum fishing effort are estimated.

scholarly journals Tournament and non-tournament anglers have little effect on a largemouth bass population compared to natural mortality

2021 ◽  
Author(s):  
Andrea L Sylvia ◽  
Stephen J. Dinsmore ◽  
Michael J Weber
Keyword(s):  
Largemouth Bass ◽  
Total Population ◽  
Micropterus Salmoides ◽  
Population Level ◽  
Natural Mortality ◽  
Catch And Release ◽  
The Past ◽  
Population Mortality ◽  
Annual Mortality ◽  
Temperature Water

Popularity of bass Micropterus spp. catch and release and tournament angling during the past decade has resulted in increased potential for these activities to induce population level effects. Understanding capture rates and mortality sources relative to total population mortality is essential to focus of management. We conducted monthly electrofishing, solicited non-tournament angler tag returns, and censused largemouth bass Micropterus salmoides tournaments at Brushy Creek Lake, IA, USA from April 2015 to June 2018. We used a multistate mark-recapture model to evaluate the effects of air temperature, water temperature, tournament bass per angler, and tournament initial mortality on non-tournament and tournament angler capture probability and natural, non-tournament angling, and initial and delayed tournament mortality. Average total annual mortality was 0.66 with natural mortality representing the largest mortality source (0.57) followed by delayed tournament mortality (0.06), non-tournament angling mortality (0.02), and initial tournament mortality (0.006). Our results reveal both non-tournament and tournament angling mortality are low compared to natural mortality in some lakes. Therefore, cumulative angling mortality likely has minimal population level effects on some bass populations.

scholarly journals Explotación y evaluación de la pesquería de tilapia ( Oreochromis spp.) En el embalse “Zimapám” Fernando Hiriart Balderrama, Hidalgo, México

2012 ◽  
Vol 3 ◽  
pp. 105
Author(s):  
Mario A. Gómez-Ponce ◽  
María Isabel Gallardo-Berumen ◽  
Fabián Cervantes-Hernández
Keyword(s):  
Population Size ◽  
Fishing Effort ◽  
Maximum Sustainable Yield ◽  
Reproduction Rate ◽  
Sustainable Yield ◽  
Total Catch ◽  
Data Set ◽  
Biomass Dynamic ◽  
Annual Total ◽  
S Model

Oreochromis spp. fishing in the Fernando Hiriart Balderrama Reservior began in 1997 and its effects had never been studied before. Schaefer and Fox’s biomass dynamic model were used in order to obtain the first evaluation of this resource and to analyze the presence of record errors (or observation errors) in the annual total catch data set. The number of fishermen was used as the fishing effort unit. Schaefer´s model proved to be statically reliable: Oreochromis spp. was estimated at the maximum population size value of k = 9 000 tons and reproduction rate value at annual r = 0.730. Considering those ecological and biological strategies, Schaefer´s model showed that great biomass levels (predicted biomass) have been produced in the Zimapán reservior; however, only a small part of this biomass was exploited during the analyzed period. The results indicate that tilapia fishery in the Zimapán Reservoir was at equilibrium or was not over-fished between 1997 and 2006 because historical tilapia records observed in Schaefer´s model were far from the k parameter and below the MSY value. With this exploitation type, the fishing effort can increase to up to 7 203 fishermen (level of fishing effort at which the maximum sustainable yield is achieved (fMSY)). However, in order to avoid an increase of the non-controlled fishing effort a similar analysis is recommended with recent data. La pesca de la tilapia Oreochromis spp. en la presa hidroeléctrica Fernando Hiriart Balderrama comenzó en 1997, esta pesquería nunca ha sido evaluada. Fueron utilizados los modelos dinámicos de biomasa de Schaefer y Fox para obtener la primera evaluación de este recurso y para analizar la presencia de errores de registro (errores de observación) en la captura anual total. El número de pescadores fue usado como la unidad de esfuerzo de pesca. El modelo de Schaefer resultó estadísticamente confiable y para Oreochromis spp. fueron estimados el tamaño máximo de población en k = 9 000 tons y la tasa de reproducción en r = 0.730 anual. Considerando estas estrategias ecológicas y biológicas, el modelo de Schaefer sugirió que grandes niveles de biomasa (biomasa predicha) fueron producidas en la presa Zimapán, pero solo una pequeña parte de esta biomasa fue explotada durante el periodo analizado. Los resultados indicaron que la pesquería de la tilapia en la presa Zimapán estuvo en equilibrio o no fue sobreexplotada entre 1997 y el 2006, porque los registros históricos en el modelo de Schaefer fueron observados muy lejos del parámetro k y por debajo del valor MSY. Con este tipo de explotación, el esfuerzo de pesca podría incrementarse hasta alcanzar 7 203 número de pescadores (nivel de esfuerzo de pesca en el cual se activa el rendimiento máximo sostenible (fMSY)), pero para evitar un incremento no controlado del esfuerzo de pesca, se recomienda hacer un análisis similar integrando datos recientes.

Temporal Changes in the Reproductive Potential of Female Harp Seals (Pagophilus groenlandicus)

1981 ◽  
Vol 38 (5) ◽  
pp. 495-503 ◽  
Author(s):  
W. Don Bowen ◽  
Charles K. Capstick ◽  
David E. Sergeant
Keyword(s):  
Density Dependence ◽  
Population Size ◽  
Empirical Data ◽  
Reproductive Potential ◽  
Fertility Rate ◽  
Harp Seal ◽  
Northwest Atlantic ◽  
Pagophilus Groenlandicus ◽  
Age Of Maturity ◽  
Biological Sampling

The Northwest Atlantic harp seal (Pagophilus groenlandicus) population declined by more than 50% between 1952 and the early 1970s. Biological sampling of female reproductive tracts began in 1951 and has continued to the present. We reexamined the extent to which mean age of maturity and fertility rate have changed as population size declined. Mean age of maturity declined from ~ 6.2 yr in 1952 to 4.5 yr in 1979. During this same period fertility rate increased from 85 to 94%. Both parameters have changed concurrently with a decline in numbers. Although it is likely that density-dependent mechanisms are involved, empirical data are lacking.Key words: harp seals, Pagophilus groenlandicus; maturity, fertility, density-dependence

scholarly journals Estimating maximum sustainable yield of snow crab (Chionoecetes opilio) off Tohoku Japan via a state-space assessment model with time-varying natural mortality

2020 ◽  
Author(s):  
Yasutoki Shibata ◽  
Jiro Nagao ◽  
Yoji Narimatsu ◽  
Eisuke Morikawa ◽  
Yuto Suzuki ◽  
...  
Keyword(s):  
State Space ◽  
Maximum Sustainable Yield ◽  
Biological Characteristics ◽  
Assessment Model ◽  
Fish Stock ◽  
Snow Crab ◽  
Sustainable Yield ◽  
Natural Mortality ◽  
Time Varying ◽  
Chionoecetes Opilio

AbstractYield from fisheries is a tangible benefit of ecosystem services and sustaining or restoring a fish stock level to achieve a maximum sustainable yield (MSY). Snow crab (Chionoecetes opilio) off Tohoku has been managed by a total allowable catch since 1996, although their abundance has not increased even after 2011, when fishing pressure rapidly decreased because of the Great East Japan Earthquake. This implies that their biological characteristics, such as recruits, natural mortality coefficient (M), and terminal molting probabilities (p), might have changed. We developed “just another state-space stock assessment model (JASAM)” to estimate the MSY of the snow crab off Tohoku, Japan, considering interannual variations in M and p. The multi-model inference revealed that M increased from 0.2 in 1997 to 0.59 in 2018, although it was not different among the instars, sex, nor terminal molt of crabs. The parameter p also increased by 1.34–2.46 times depending on the instar growth stages from 1997 to 2018. We estimated the MSYs in three scenarios, which drastically changed if M and p were set as they were in the past or at the current values estimated from this study. This result indicated that the MSY of snow crab would also be time-varying based on their time-varying biological characteristics.

scholarly journals A Stochastic Model for the Management of the Northwestern Atlantic Harp Seal (Pagophilus groenlandicus) Population

1977 ◽  
Vol 34 (8) ◽  
pp. 1155-1187 ◽  
Author(s):  
Patrick F. Lett ◽  
Terje Benjaminsen
Keyword(s):  
Stochastic Model ◽  
Population Size ◽  
Management Strategies ◽  
High Arctic ◽  
Maximum Sustainable Yield ◽  
Future Research ◽  
Total Allowable Catch ◽  
Stock Size ◽  
Pagophilus Groenlandicus ◽  
Scientific Arguments

Advice from the scientific advisers under the auspices of ICNAF to the international commissioners for 1977 was that the total allowable catch (TAC) for harp seals (Pagophilus groenlandicus) should not exceed 170,000. This advice, in part, was based on the scientific arguments presented in this paper. A stochastic model is developed that takes into account the variations in natural mortality and the landsmen's high arctic and Greenland catches. The Canadian–Norwegian large vessel hunt is controlled under quota regulations. The model is nonlinear, a result of changes in fertility and fecundity rates in response to shifts in population size. The maximum sustainable yield (MSY) 1 + population size is determined to be 1.6 million seals, or a breeding stock size of 375,000 seals. The MSY is approximately 240,000 seals assuming the hunt continues its present pattern. The 240,000 can further be split into 200,000 pups and 40,000 1 + seals. Present stock size is approximately 1.2 million and a TAC of 170,000 seals will allow the population size to reach to MSY level in 10–15 yr. A number of other management strategies are considered, in addition to prospects for future research.

Status of southern elephant seals at South Georgia

1996 ◽  
Vol 8 (3) ◽  
pp. 237-244 ◽  
Author(s):  
I.L. Boyd ◽  
T.R. Walker ◽  
J. Poncet
Keyword(s):  
Population Size ◽  
Total Population ◽  
Breeding Habitat ◽  
World Population ◽  
Mirounga Leonina ◽  
Elephant Seals ◽  
South Georgia ◽  
The Past ◽  
Southern Elephant Seals ◽  
Complete Survey

Approximately 54% of the world population of southern elephant seals (Mirounga leonina) breeds at South Georgia. A partial survey in 1951 and a complete survey in 1985, together with counts at specific sites between these times, suggested that the population (around 100 000 breeding females) had not changed significantly in 34 years. This was in contrast to marked declines in most other populations. To examine this further, we conducted a third survey in 1995. This produced an estimate of 113 444 (se = 4902) breeding females. Taking into account improved information about the behaviour of female elephant seals since the survey in 1985, there was no significant change in the number of breeding female elephant seals between 1985 and 1995. When combined with information from the 1951 survey, this supports the view that the total population size has not changed significantly during the past 45 years. Evidence for regulation of the population by environmental factors is equivocal. We hypothesize that the lack of any net change in population size may be linked to a limited availability of high quality breeding habitat.

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