Testing Predictions of Marine Fish and Shellfish Landings from Environmental Variables

1987 ◽  
Vol 44 (9) ◽  
pp. 1568-1573 ◽  
Author(s):  
K. F. Drinkwater ◽  
R. A. Myers
Keyword(s):  
Environmental Variables ◽  
Environmental Effect ◽  
Degrees Of Freedom ◽  
Gulf Of Maine ◽  
Fishing Effort ◽  
Fish Stocks ◽  
Environmental Models ◽  
The Mean ◽  
Fish And Shellfish

Previous studies by Sutcliffe and co-workers using exploratory analysis found correlations between environmental variables and lagged annual catch for several Gulf of St. Lawrence and Gulf of Maine fish and shellfish stocks. The present study tests these relationships using recent data. For 6 of the 13 stocks investigated, correlations between the 9–14 yr of new catch data and that predicted from the environmental models remained high (r > 0.5) and of the same sign; however, individually none was statistically significant (p > 0.05) after accounting for the loss of degrees of freedom due to the high autocorrelation in the data. The hypothesis of an overall environmental effect on the landings was considered. It could not be substantiated as the correlation coefficient for 5 of the 13 stocks reversed sign using the new data, but changes in fishing effort are believed to mask detection of environmentally induced variability in the landings of many stocks. The utility of environmentally based predictions was also tested. Overall, the mean deviations of the predicted catch based on environmental regressions were similar to predictions based on the long-term means but were higher than predictions using lagged catch. Environmentally based predictions of landings for invertebrate stocks were generally more accurate than those for fish stocks.

Population fluctuations and recruitment in marine populations

1982 ◽  
Vol 297 (1087) ◽  
pp. 353-368 ◽  
Keyword(s):  
Oil Pollution ◽  
Fishing Effort ◽  
Background Information ◽  
Population Fluctuations ◽  
Japanese Sardine ◽  
Factors Affecting ◽  
Fish Stocks ◽  
The North ◽  
Natural Variations

This paper is not concerned with the effect of oil pollution as such, but sets out to consider the range of natural variation and the extent to which this might mask the effects of other factors such as possible pollutant effects. To detect the effect of a pollutant (or a change in fishing effort) it is necessary to allow for natural variations, both random and periodic. Some examples are given to illustrate the extent of natural variations, in a variety of marine populations. For Arcto-Norwegian cod, information is available on catches from about the middle of the last century to the present day. Large catches are about 3-6 times the size of small catches. The difference between large and small catches is about equal to the mean catch. Further, the time taken to change from a small to a large catch level is very variable. The Greenland cod provides an example of a stock that increased very considerably due to a northerly increase of the limits of distribution of the species. This increase was associated with a warm period in the North Atlantic and with increased catches. Many fish stocks and in particular many species of pelagic fishes, exhibit much larger fluctuations in stock size, e.g. the Hokkaido herring, the Japanese sardine, the Bohuslan herring, the Atlanto-Scandian herring and the Califonian anchovy and sardine. Fluctuations also occur in invertebrate species and evidence is given of changes that have occurred in North Sea phytoplankton and zooplankton. The Peruvian anchovy provides an example of a stock that decreased very considerably, due partly to fishing and partly to changes in the hydrographic regime that caused the fish to become more available for exploitation. Fluctuations in fish stocks are primarily due to fluctuations in recruitment. The factors affecting recruitment are not yet fully understood but are known to be determined during the first year of life and probably during the larval or early juvenile stages. Whatever the mechanism, however, it is the variations in recruitment that determine a very large part of the variations in adult fish stocks and hence it is variations in recruitment and the causes of these that are important. In conclusion, the examples show that natural communities can exhibit large natural fluctuations, of varying periodicity, in the long term. Apart from incidents where there is gross pollution, an effect of pollution can therefore only be convincingly demonstrated for those species for which background information is available for a long enough period to allow for long-term periodicity as well as for short-term and irregular variability.

Pronounced long-term juvenation in the spawning stock of Arcto-Norwegian cod (Gadus morhua) and possible consequences for recruitment

2008 ◽  
Vol 65 (3) ◽  
pp. 523-534 ◽  
Author(s):  
Geir Ottersen
Keyword(s):  
Time Series ◽  
Gadus Morhua ◽  
Experimental Studies ◽  
Reproductive Capacity ◽  
Fish Stocks ◽  
Stock Biomass ◽  
Clear Link ◽  
Spawning Stock ◽  
The Mean

The oldest and largest individuals are disappearing from many fish stocks worldwide as a result of overexploitation. This has been suggested to impair recruitment through decreasing the reproductive capacity of the spawners and increasing the mortality rate of the offspring. By using a time series on spawners biomass by age class for Arcto-Norwegian cod (Gadus morhua) from 1913–2004, I have documented pronounced changes in the spawning stock, including a trend towards younger fish, a less diverse distribution across ages, and a declining proportion of repeat spawners. Despite the total spawning stock biomass (SSB) being at similar levels now as in 1933, the mean age in the SSB has declined from 10–12.5 years to 7–8 years during the study period, and the percentage of fish of age 10 or above in the SSB has decreased from ~97% to ~10%. Contrary to earlier theoretical and experimental studies, no clear link between age structure and recruitment was found here. Recruitment to the Arcto-Norwegian cod stock may thus be more robust towards spawner juvenation than expected, possibly because of strong recruitment compensation.

scholarly journals MARINE CAPTURE FISHERIES POLICY FORMULATION AND THE ROLE OF MARINE PROTECTED AREAS AS TOOL FOR FISHERIES MANAGEMENT IN INDONESIA

2018 ◽  
Vol 30 ◽  
pp. 33-45
Author(s):  
D. G.R. Wiadnya ◽  
P. J. Mous ◽  
R. Djohani ◽  
M. V. Erdmann ◽  
A. Halim ◽  
...  
Keyword(s):  
Protected Areas ◽  
Marine Protected Areas ◽  
Scientific Evidence ◽  
Code Of Conduct ◽  
Fishing Effort ◽  
Policy Formulation ◽  
Maximum Sustainable Yield ◽  
Fish Stocks ◽  
Fisheries Policy

The FAO Code of Conduct for Responsible Fisheries states that conservation and management decisions for fisheries should be based on the best scientific evidence available. Studies show that most of Indonesia's capture fisheries are either full or over-exploited. However, the fishery sector is still expected to contribute to the increase of Indonesia's GNP through an increase in total catches. Furthermore, the current practice of using catch-effort data and Maximum Sustainable Yield models to inform Indonesia’s fisheries policies is flawed, putting sustainability and long-term profitability of Indonesia's fisheries at risk. In this paper, the authors argue that to ensure the survival of Indonesia's fish stocks and fisheries: fisheries policy must shift from development-oriented management towards management for sustainability. Furthermore, fisheries managers must accept that 'untapped resources' may not exist or cannot be exploited profitably, and that any transfer of fishing effort between fishing grounds may contribute to collapse of local fisheries. Also, fisheries managers should change the management paradigm from MSY models to eco-system based management, wherein Marine Protected Areas should play an important role.

scholarly journals A framework for modelling fish and shellfish responses to future climate change

2009 ◽  
Vol 66 (7) ◽  
pp. 1584-1594 ◽  
Author(s):  
Anne Babcock Hollowed ◽  
Nicholas A. Bond ◽  
Thomas K. Wilderbuer ◽  
William T. Stockhausen ◽  
Z. Teresa A'mar ◽  
...  
Keyword(s):  
Climate Change ◽  
Surface Temperature ◽  
Bering Sea ◽  
Environmental Variables ◽  
Future Climate ◽  
Future Climate Change ◽  
Climate Scenarios ◽  
The Mean ◽  
Fish And Shellfish ◽  
The Bering Sea

AbstractHollowed, A. B., Bond, N. A., Wilderbuer, T. K., Stockhausen, W. T., A'mar, Z. T., Beamish, R. J., Overland, J. E., and Schirripa, M. J. 2009. A framework for modelling fish and shellfish responses to future climate change. – ICES Journal of Marine Science, 66: 1584–1594. A framework is outlined for a unified approach to forecasting the implications of climate change on production of marine fish. The framework involves five steps: (i) identification of mechanisms underlying the reproductive success, growth, and distribution of major fish and shellfish populations, (ii) assessment of the feasibility of downscaling implications of climate scenarios derived from Intergovernmental Panel on Climate Change (IPCC) models for regional ecosystems to select and estimate relevant environmental variables, (iii) evaluation of climate model scenarios and select IPCC models that appear to provide valid representations of forcing for the region of study, (iv) extraction of environmental variables from climate scenarios and incorporation into projection models for fish and shellfish, and (v) evaluation of the mean, variance, and trend in fish and shellfish production under a changing ecosystem. This framework was applied to forecast summer sea surface temperature in the Bering Sea from 2001 to 2050. The mean summer surface temperature was predicted to increase by 2°C by 2050. The forecasting framework was also used to estimate the effects of climate change on production of northern rock sole (Lepidopsetta polyxystra) through projected changes in cross-shelf transport of larvae in the Bering Sea. Results suggest that climate change will lead to a modest increase in the production of strong year classes of northern rock sole.

Maximum Sustained Yields from Fluctuating Environments and Mixed Stocks

1958 ◽  
Vol 15 (5) ◽  
pp. 991-1006 ◽  
Author(s):  
W. E. Ricker
Keyword(s):  
Environmental Variability ◽  
Numerical Models ◽  
Fishing Effort ◽  
Optimum Level ◽  
Fish Stocks ◽  
Total Potential ◽  
Fluctuating Environments ◽  
Low Levels ◽  
Average Catch

Using numerical models, effects of environmental variability upon yield were tested for six single-age fish stocks characterized by different kinds and degrees of density-dependent reproduction potential. The two levels of variability examined had extremes of yield standing in the ratios 7:1 and 18:1, respectively. Close regulation of fishing to the optimum percentage for each year's stock improves the long-term average catch taken, the improvement being the greater, the more variable the environment. With the higher level of variability, improvement in average catch among five of the stocks ranged from 26% to 79% increase. However this increase in mean catch is achieved at the expense of increased variability in catch from year to year—in fact, for some kinds of stocks there must be complete cessation of fishing in some years in order to get the long-term maximum. The yield of stocks, in which reproduction per spawner declines at low levels of abundance, is particularly improved by a close adaptation of fishing effort to the supply of fish available.When two or more populations of a species, characterized by different reproduction potentials, are fished in common, total potential catch is less than when each can be fished separately at its optimum level. If a common fishery cannot be avoided, the achievement of maximum average yield may find one of two originally-equal stocks as abundant or even more abundant than before the fishery began, while the other may persist only at a low level or even be exterminated completely.

Correlations of Fish Catch and Environmental Factors in the Gulf of Maine

1977 ◽  
Vol 34 (1) ◽  
pp. 19-30 ◽  
Author(s):  
W. H. Sutcliffe Jr. ◽  
K. Drinkwater ◽  
B. S. Muir
Keyword(s):  
Gulf Of Maine ◽  
Species Abundance ◽  
Marine Species ◽  
Significant Degree ◽  
Fishing Effort ◽  
Individual Species ◽  
Species Variation ◽  
Total Biomass ◽  
Sea Temperature ◽  
Fish And Shellfish

In an investigation of catches of 17 commercial marine species of fish and shellfish from the Gulf of Maine, 10 showed statistically significant correlations with sea temperatures at St. Andrews, N.B., or Boothbay Harbour, Maine. Most fish records contained at least 40 yr of data. Descriptive equations are produced for four species based first on the correlation between catch and sea temperature and second on the correlation between catch and sea temperature allowing for fishing effort. Inclusion of fishing effort, not surprisingly, improved the correlations for all of the species so examined. The equations permitted the "prediction" of later parts of the records from earlier parts.Considering the fish species collectively, the Gulf of Maine system from 1940 to 1959 appeared to be in equilibrium with little fluctuation in the total commercial biomass. We interpret the large fluctuations in individual species abundance as resulting from a combination of fishing pressure and to a significant degree oceanic climate as represented by sea temperature. The small fluctuations in the total biomass displays the species variation, with their differing climatic "preferences," as well as possible predator (including man)–prey relationships. Environmentally imposed patterns underlie at least 50% of the fluctuations in catch of many species and the understanding of these fluctuations is basic to effective management.

scholarly journals Trends in the size and age structure of marine fishes

2018 ◽  
Vol 76 (4) ◽  
pp. 938-945 ◽  
Author(s):  
Julie A Charbonneau ◽  
David M Keith ◽  
Jeffrey A Hutchings
Keyword(s):  
Age Structure ◽  
Population Viability ◽  
Marine Fishes ◽  
Adult Survival ◽  
Average Weight ◽  
Fish Stocks ◽  
Size And Age Structure ◽  
Spawning Behaviour ◽  
The Mean

Abstract Size-selective harvesting is expected to reduce the average age and weight of commercially exploited fishes. The loss of larger, older fish has been hypothesized to negatively affect metrics of population viability, such as spawning behaviour, recruitment, and adult survival. Most studies to date have focussed on individual stocks. Here, we examine trends in average age and weight at broad taxonomic and temporal scales, using subsets of data compiled on 95 marine fish stocks. Following moderate declines between 1960 and 1990, we find that the average age has generally increased since 2000, such that 71% of 69 stocks are currently above their long-term average. However, the size of the oldest individuals has generally declined over time; the average weight is currently below average in 75% of 55 stocks. A temporal decline in the mean weight of the youngest constituents within 49 stocks is most evident in the Clupeiformes. Our results indicate that recovery of age structure need not be accompanied by recovery of weights-at-age, evidenced in part by a decline in the size of the oldest individuals within populations. Further study into the drivers of these patterns, and the consequences of declining weights-at-age for population viability, is warranted.

scholarly journals Measuring the strength of environment–recruitment relationships: the importance of including predictor screening within cross-validations

2006 ◽  
Vol 63 (4) ◽  
pp. 594-599 ◽  
Author(s):  
R.I.C. Chris Francis
Keyword(s):  
Environmental Variables ◽  
Cross Validation ◽  
Simulation Experiment ◽  
Large Set ◽  
Fish Stocks ◽  
The Mean

Abstract There has recently been considerable interest in establishing relationships between environmental variables and annual recruitment to fish stocks. Such relationships have the potential to reduce the uncertainty in the assessment of the stocks. When many environmental variables are considered, it is easy to draw conclusions that exaggerate the ability to predict recruitment. One technique to protect against this is cross-validation. This technique has usually been incorrectly applied, in that it has not included predictor screening (the selection from a large set of potential predictors of a smaller set to use in prediction). A simulation experiment is used to show that this omission can cause chance correlations to be wrongly identified as useful, and the reliability of useful predictors to be overestimated. It also shows that the mistaken use of chance correlations to predict recruitment can be worse than the use of the default predictor (the mean of previous recruitments), and that our ability to measure the reliability of recruitment predictors is typically poor.

The motion of a lunar orbiter

1966 ◽  
Vol 25 ◽  
pp. 373
Author(s):  
Y. Kozai
Keyword(s):  
Degrees Of Freedom ◽  
Dimensional Space ◽  
Artificial Satellite ◽  
Equations Of Motion ◽  
Triaxial Ellipsoid ◽  
The Moon ◽  
Secular Motion ◽  
The Earth ◽  
Close Satellite ◽  
The Mean

The motion of an artificial satellite around the Moon is much more complicated than that around the Earth, since the shape of the Moon is a triaxial ellipsoid and the effect of the Earth on the motion is very important even for a very close satellite.The differential equations of motion of the satellite are written in canonical form of three degrees of freedom with time depending Hamiltonian. By eliminating short-periodic terms depending on the mean longitude of the satellite and by assuming that the Earth is moving on the lunar equator, however, the equations are reduced to those of two degrees of freedom with an energy integral.Since the mean motion of the Earth around the Moon is more rapid than the secular motion of the argument of pericentre of the satellite by a factor of one order, the terms depending on the longitude of the Earth can be eliminated, and the degree of freedom is reduced to one.Then the motion can be discussed by drawing equi-energy curves in two-dimensional space. According to these figures satellites with high inclination have large possibilities of falling down to the lunar surface even if the initial eccentricities are very small.The principal properties of the motion are not changed even if plausible values ofJ3andJ4of the Moon are included.This paper has been published in Publ. astr. Soc.Japan15, 301, 1963.

Acute and Chronic Changes in Platelet Volume and Count After Cardiopulmonary Bypass Induced Thrombocytopenia in Man

1987 ◽  
Vol 57 (01) ◽  
pp. 55-58 ◽  
Author(s):  
J F Martin ◽  
T D Daniel ◽  
E A Trowbridge
Keyword(s):  
Platelet Count ◽  
Mean Platelet Volume ◽  
Artery Bypass ◽  
Bypass Graft ◽  
Control Group ◽  
Artery Bypass Graft ◽  
Platelet Volume ◽  
Young Males ◽  
The Mean

SummaryPatients undergoing surgery for coronary artery bypass graft or heart valve replacement had their platelet count and mean volume measured pre-operatively, immediately post-operatively and serially for up to 48 days after the surgical procedure. The mean pre-operative platelet count of 1.95 ± 0.11 × 1011/1 (n = 26) fell significantly to 1.35 ± 0.09 × 1011/1 immediately post-operatively (p <0.001) (n = 22), without a significant alteration in the mean platelet volume. The average platelet count rose to a maximum of 5.07 ± 0.66 × 1011/1 between days 14 and 17 after surgery while the average mean platelet volume fell from preparative and post-operative values of 7.25 ± 0.14 and 7.20 ± 0.14 fl respectively to a minimum of 6.16 ± 0.16 fl by day 20. Seven patients were followed for 32 days or longer after the operation. By this time they had achieved steady state thrombopoiesis and their average platelet count was 2.44 ± 0.33 × 1011/1, significantly higher than the pre-operative value (p <0.05), while their average mean platelet volume was 6.63 ± 0.21 fl, significantly lower than before surgery (p <0.001). The pre-operative values for the platelet volume and counts of these patients were significantly different from a control group of 32 young males, while the chronic post-operative values were not. These long term changes in platelet volume and count may reflect changes in the thrombopoietic control system secondary to the corrective surgery.

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