Population Dynamics of the Arcto-Norwegian Cod

1967 ◽  
Vol 24 (1) ◽  
pp. 145-190 ◽  
Author(s):  
D. J. Garrod
Keyword(s):  
Gadus Morhua ◽  
Barents Sea ◽  
Fishing Effort ◽  
Catch Per Unit Effort ◽  
Group Iii ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
Post War ◽  
The One ◽  
Definition Of

By reason of its geographical distribution, the Arcto-Norwegian cod (Gadus morhua) supports three distinct fisheries, two feeding fisheries in the Barents Sea and at Bear Island–Spitsbergen, and a spawning fishery off the Norway coast. In the past this diversity of fishing on the one stock has made it difficult to unify all the data to give an overall description of post-war changes in the stock. In this contribution three modifications of conventional procedures are introduced which enable this to be done. These are: (i) a system of weighting the catch per unit effort data from each fishery to a level of comparability; (ii) a more rigorous definition of the effective fishing effort on each age-group; (iii) a method of estimation of the effective fishing effort on partially recruited age-groups.Using these methods the analysis presents the effects of fishing on each fishery in the context of its effect on the total stock, and at the same time it indicates ways in which factors other than fishing may have influenced the apparent abundance of the stock. The treatment of the data is also used to derive estimates of spawning stock and recruitment of 3-year-old cod for subsequent analysis of stock–recruitment relationships.

scholarly journals Direct and indirect effects of minke whale abundance on cod and herring fisheries: A scenario experiment for the Greater Barents Sea

2000 ◽  
Vol 2 ◽  
pp. 120 ◽  
Author(s):  
Tore Schweder ◽  
Gro S Hagen ◽  
Einar Hatlebakk
Keyword(s):  
Gadus Morhua ◽  
Barents Sea ◽  
Minke Whale ◽  
Clupea Harengus ◽  
Prey Abundance ◽  
Balaenoptera Acutorostrata ◽  
Time Step ◽  
Minke Whales ◽  
Spawning Stock ◽  
Capelin Mallotus Villosus

To study the pattern of interaction between minke whale (Balaenoptera acutorostrata) abundance and the main fisheries in the Greater Barents Sea, a simulation experiment was carried out. The population model involves 4 species interconnected in a food web: cod (Gadus morhua), capelin (Mallotus villosus), herring (Clupea harengus) and minke whales. Minke whales are preying on cod, capelin andherring; cod are preying on (young) cod, capelin and herring; herring in the Barents Sea are preying on capelin; while capelin is a bottom prey in the model. The consumption function for minke whales is non-linear in available prey abundance, and is estimated from stomach content data and prey abundance data. The model is dynamic, with a time step of one month, and there are two areas: the BarentsSea and the Norwegian Sea. Minke whale abundances are kept on fixed levels, while recruitment in fish is stochastic.Cod and herring fisheries are managed by quotas targeting fixed fishing mortalities, while capelin is managed with a view to allow the cod to have enough food and leaving a sufficient spawning stock of capelin. The model is simulated over a period of 100 years for a number of fixed levels of minke whaleabundance, and simulated catches of cod, herring and capelin are recorded.The experiment showed interactions between whale abundance and fish catches to be mainly linear. For cod catches, both the direct effect of whales consuming cod, and the indirect effect due to whales competing with cod for food and otherwise altering the ecosystem, are linear and of equal importance. The net effect on the herring fishery is of the same magnitude as the net effect on the cod fishery, witheach extra whale reducing the catches of both species by some 5 tonnes. These conclusions are conditional on the model and its parameterisation.

Improving the stock-recruitment relationship in Icelandic cod (Gadus morhua) by including age diversity of spawners

1998 ◽  
Vol 55 (6) ◽  
pp. 1372-1377 ◽  
Author(s):  
Gudrun Marteinsdottir ◽  
Kristjan Thorarinsson
Keyword(s):  
Gadus Morhua ◽  
Extended Period ◽  
Shannon Index ◽  
Age Composition ◽  
Stock Size ◽  
Age Diversity ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
Mature Fish

The size of the Icelandic cod stock has been gradually declining since the middle of this century. Recruitment has been poor over an extended period of time and much below the long-term average since 1985. Except for the concurrent decrease in stock size and recruitment during this period, the stock size - recruitment relationship is weak. This relationship is improved by including the age composition of the spawning stock. Spawning stock age diversity in each year from 1955 to 1992 was estimated with the Shannon index using the number of mature fish in each age group. By including information on age composition, 31% of the total variation in recruitment was accounted for by the model with stock size, age diversity, and the interaction between the two, compared with less than 15% by single factor models of either age diversity or stock size. These results indicate that age diversity is an important component in stock-recruitment models and that one of the management goals for fish species should be to maintain high age diversity in the spawning stocks.

Effect of Assumptions about the Stock–Recruitment Relationship on a Lobster (Homarus gammarus) Stock Assessment

1986 ◽  
Vol 43 (11) ◽  
pp. 2353-2359 ◽  
Author(s):  
R. C. A. Bannister ◽  
J. T. Addison
Keyword(s):  
Carapace Length ◽  
Stock Assessment ◽  
Fishing Effort ◽  
Yield Curves ◽  
Recruitment Curve ◽  
Homarus Gammarus ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
Yield Per Recruit ◽  
Marked Tendency

Stock assessment of the European lobster (Homarus gammarus) has involved yield per recruit analysis based on the established length cohort methodology of Jones (1974. ICES C.M. 1974/F:33; 1981. FAO Fish. Circ. 734) which assumes that recruitment to the fishery is independent of spawning stock. The Shepherd (1982. J. Cons. Int. Explor. Mer 40: 67–75) model has been used to simulate a range of assumed stock–recruitment relationships, and the resulting sensitivity analysis describes how these affect the relation between yield or biomass and four management variables, namely fishing mortality, minimum carapace length, maximum carapace length, and the capture or noncapture of egg-bearing females. Yield curves show a clear maximum with a marked tendency to stock collapse when fishing effort is high. For the range of simulations considered, the probability of an early recruit failure is greatest for asymptotic stock–recruitment curves, which generate yield curves with maxima at an effort substantially lower than the present level. Only with a highly overcompensatory stock–recruitment curve is there a case for increasing effort to maximise yield, but such a relationship tends to reduce the benefit of increasing minimum carapace length or of setting a maximum carapace length. The model predicts that the assumption made about the stock–recruitment relationship also has a marked effect on the results expected from a ban on the landing of egg-bearing females. Overall the results confirm the unsatisfactory prognosis of the yield per recruit model and emphasise the need to gain an understanding of the biological factors determining the shape of the lobster stock–recruitment curve.

scholarly journals Cod catches taken by the German recreational fishery in the western Baltic Sea, 2005–2010: implications for stock assessment and management

2012 ◽  
Vol 69 (10) ◽  
pp. 1769-1780 ◽  
Author(s):  
Harry V. Strehlow ◽  
Norbert Schultz ◽  
Christopher Zimmermann ◽  
Cornelius Hammer
Keyword(s):  
Baltic Sea ◽  
Gadus Morhua ◽  
Stock Assessment ◽  
Mail Survey ◽  
Fishing Effort ◽  
Commercial Fishery ◽  
Catch Per Unit Effort ◽  
Yearly Variation ◽  
Fish Stocks ◽  
Recreational Fishery

Abstract Strehlow, H. V., Schultz, N., Zimmermann, C., and Hammer, C. 2012. Cod catches taken by the German recreational fishery in the western Baltic Sea, 2005–2010: implications for stock assessment and management. – ICES Journal of Marine Science, 69: 1769–1780. Next to the commercial fishery, the recreational fishery plays an important role in the removal of biomass from fish stocks. In this study, we present estimates of German recreational cod (Gadus morhua) catches in the western Baltic Sea between 2005 and 2010. Fishing effort was estimated using a stratified mail survey and annual sales of fishing licences. Catch per unit effort was estimated by stratified random sampling of access points and interviews about completed trips. Length distributions of cod catches were acquired by sampling recreational cod catches from charter boats and data from community fishing events. Estimates of the total cod biomass removed by the recreational fishery fluctuated between 2159 t in 2009 and 4127 t in 2005. Annual recreational fishery cod harvests accounted for a significant share of the total landings, with a yearly variation from 34 to 70% of the German commercial cod landings from the western Baltic Sea. The majority of recreational fishery cod catches were taken from private boats and charter vessels. Because of the amount and specifically the variability of the recreational catches, they are important for the assessment and management of the resource and, therefore, need to be surveyed annually.

Vacant inheritance, heirless inheritance and claims from Warsaw Decree (part II)

2019 ◽  
Vol 3 (3) ◽  
pp. 11-28
Author(s):  
Kamil Zaradkiewicz
Keyword(s):  
Civil Code ◽  
The State ◽  
The Other ◽  
Inheritance Law ◽  
Other Hand ◽  
Current Article ◽  
The Law ◽  
Post War ◽  
The One ◽  
Definition Of

The second part of the article concerns the interpretation and application in the central parts of Poland of the provisions of the Napoleonic Code on vacant inheritances. The Code does not provide a definition of the vacant inheritance. The key to the interpretation of the provisions on the acquisition of vacant inheritances by the state is the term “is presumed to be” (a vacant inheritance) used in the former Article 811 of the Napoleonic Code (French: est réputée vacante), see the current Article 809 of the French Civil Code which omits the term “is presumed to be”).This indicates that, in the absence of suitable heirs, the law introduced a specific rebuttable presumption of a vacant inheritance, belonging to the state. Only after an appropriate period of time did the presumption turn into certainty, i.e. it resulted in the inability to invoke the inheritance title. In practice, this meant that thirty years after the time necessary to draw up an inventory of the inheritance and to deliberate (ad deliberandum), the inheritance ultimately fell to the State. The mechanism adopted in the Napoleonic Code made it possible, on the one hand, for the heir to acquire the inheritance, which remained under the supervision of a curator for the period when it was presumed vacant, and on the other hand, it prevented the existence of inheritances without a claimant, i.e. inheritances devoid of the persons entitled to take them over. In the post-war period, when the communist authorities passed subsequent legal acts concerning the provisions of the inheritance law, the deadlines for heirs to apply for inheritance changed. Ultimately, the legislator did not adopt the model of vacant inheritances in the regulations harmonising the inheritance law on the Polish lands since 1947; instead, a solution analogous to the one provided for in the German Civil Code of 1986 (BGB) was adopted. The “shortening” of the statute of limitations also influenced the assessment of the admissibility of further application of the provisions of the Napoleonic Code in regard to vacant inheritances during the period of the People’s Republic of Poland regime (despite the existence of different inheritance law solutions).

Potential effects of maternal factors on spawning stock–recruitment relationships under varying fishing pressure

1999 ◽  
Vol 56 (10) ◽  
pp. 1882-1890 ◽  
Author(s):  
Beth Scott ◽  
Gudrun Marteinsdottir ◽  
Peter Wright
Keyword(s):  
Gadus Morhua ◽  
Reproductive Output ◽  
Atlantic Cod ◽  
Reproductive Potential ◽  
Fishing Pressure ◽  
Age Composition ◽  
Standard Population ◽  
Stock Biomass ◽  
Spawning Stock ◽  
Stock Recruitment

The use of spawning stock biomass as a direct measure of reproductive potential may not be valid because of age- or size-specific differences in fecundity and the effect of maternal size and condition on offspring viability. In this study, we examine the potential significance of these effects using modelled Atlantic cod (Gadus morhua) populations. We quantify how changes in the age composition of the spawning stock, due to a range of fishing pressures and under different stock-recruitment relationships, could influence the reproductive output. Quantitative comparisons were made between a "standard" population where all age-classes only suffer natural instantaneous mortality (M = 0.2) and populations that suffer increasing levels of fishing pressure (F = 0.0-1.0). The results of the modelling exercise suggests that if the effects of the loss of more fecund older/larger individuals in the population are not considered, the number of potential recruits produced by populations under higher levels of fishing mortality could be overestimated by as much as 60%. When age/size-related maternal effects on egg viability are also considered, the amount of potential recruits can be overestimated by a further 10% in the heavily exploited populations.

scholarly journals A review of early life history dynamics of Barents Sea cod (Gadus morhua)

2014 ◽  
Vol 71 (8) ◽  
pp. 2064-2087 ◽  
Author(s):  
Geir Ottersen ◽  
Bjarte Bogstad ◽  
Natalia A. Yaragina ◽  
Leif Christian Stige ◽  
Frode B. Vikebø ◽  
...  
Keyword(s):  
Early Life ◽  
Gadus Morhua ◽  
Barents Sea ◽  
Atlantic Cod ◽  
Prey Availability ◽  
Life Stage ◽  
Early Life History ◽  
Sea Temperature ◽  
Spawning Stock ◽  
Long Time

Abstract The Barents Sea stock of Atlantic cod (Gadus morhua) is currently the world's largest cod stock. It is also a stock for which long time-series are available and much research has been carried out. With this review, we wish to present an overview and evaluation of the knowledge on Barents Sea cod early life dynamics. The focus is on the effects of the biotic and abiotic drivers, which jointly determine the strength of a year class. A stage-by-stage approach is employed. We summarize and assess the significance of the different processes described in the literature to be at play during each specific life stage, from spawning stock, through eggs, larvae, and pelagic juvenile, to demersal juvenile and recruitment at age 3. Also Russian work is included, some of which until now has not been available to non-Russian readers. Physical drivers examined include sea temperature, advection and dispersal, wind-induced turbulence, and light. Biotic mechanisms studied range from maternal effects and skipped spawning in the adult stock through egg quantity and quality, to prey availability for the larvae and effects of cannibalism on the juveniles. Finally, we evaluate the main hypotheses put forth by Johan Hjort a hundred years ago in the light of our synthesis of present knowledge. A main conclusion is that it is unlikely that there is any one single life stage during which recruitment with any generality is determined.

scholarly journals Effect of a fish stock's demographic structure on offspring survival and sensitivity to climate

2017 ◽  
Vol 114 (6) ◽  
pp. 1347-1352 ◽  
Author(s):  
Leif Christian Stige ◽  
Natalia A. Yaragina ◽  
Øystein Langangen ◽  
Bjarte Bogstad ◽  
Nils Chr. Stenseth ◽  
...  
Keyword(s):  
Gadus Morhua ◽  
Barents Sea ◽  
Condition Index ◽  
Wide Distribution ◽  
Commercial Fishing ◽  
Demographic Structure ◽  
Data Set ◽  
Spawning Period ◽  
Spawning Stock ◽  
Eggs And Larvae

Commercial fishing generally removes large and old individuals from fish stocks, reducing mean age and age diversity among spawners. It is feared that these demographic changes lead to lower and more variable recruitment to the stocks. A key proposed pathway is that juvenation and reduced size distribution causes reduced ranges in spawning period, spawning location, and egg buoyancy; this is proposed to lead to reduced spatial distribution of fish eggs and larvae, more homogeneous ambient environmental conditions within each year-class, and reduced buffering against negative environmental influences. However, few, if any, studies have confirmed a causal link from spawning stock demographic structure through egg and larval distribution to year class strength at recruitment. We here show that high mean age and size in the spawning stock of Barents Sea cod (Gadus morhua) is positively associated with high abundance and wide spatiotemporal distribution of cod eggs. We find, however, no support for the hypothesis that a wide egg distribution leads to higher recruitment or a weaker recruitment–temperature correlation. These results are based on statistical analyses of a spatially resolved data set on cod eggs covering a period (1959−1993) with large changes in biomass and demographic structure of spawners. The analyses also account for significant effects of spawning stock biomass and a liver condition index on egg abundance and distribution. Our results suggest that the buffering effect of a geographically wide distribution of eggs and larvae on fish recruitment may be insignificant compared with other impacts.

Stock-recruitment relationships of the tiger prawns (Penaeus esculentus and Penaeus semisulcatus) in the Australian northern prawn fishery

1996 ◽  
Vol 47 (1) ◽  
pp. 87 ◽  
Author(s):  
YG Wang ◽  
D Die
Keyword(s):  
Population Model ◽  
Fishing Effort ◽  
Maximum Sustainable Yield ◽  
Production Model ◽  
Commercial Catch ◽  
Penaeus Semisulcatus ◽  
Spawning Stock ◽  
Tiger Prawn ◽  
Stock Recruitment ◽  
Northern Prawn Fishery

This paper investigates the stock-recruitment and equilibrium yield dynamics for the two species of tiger prawns (Penaeus esculentus and Penaeus semisulcatus) in Australia's most productive prawn fishery: the Northern Prawn Fishery. Commercial trawl logbooks for 1970-93 and research surveys are used to develop population models for these prawns. A population model that incorporates continuous recruitment is developed. Annual spawning stock and recruitment indices are then estimated from the population model. Spawning stock indices represent the abundance of female prawns that are likely to spawn; recruitment indices represent the abundance of all prawns less than a certain size. The relationships between spawning stock and subsequent recruitment (SRR), between recruitment and subsequent spawning stock (RSR), and between recruitment and commercial catch were estimated through maximum-likelihood models that incorporated autoregressive terms. Yield as a function of fishing effort was estimated by constraining to equilibrium the SRR and RSR. The resulting production model was then used to determine maximum sustainable yield (MSY) and its corresponding fishing effort (fMSY). Long-term yield estimates for the two tiger prawn species range between 3700 and 5300 t. The fishing effort at present is close to the level that should produce MSY for both species of tiger prawns. However, current landings, recruitment and spawning stock are below the equilibrium values predicted by the models. This may be because of uncertainty in the spawning stock-recruitment relationships, a change in carrying capacity, biased estimates of fishing effort, unreliable catch statistics, or simplistic assumptions about stock structure. Although our predictions of tiger prawn yields are uncertain, management will soon have to consider new measures to counteract the effects of future increases in fishing effort.

scholarly journals New Perspectives on the II CIAM onwards: How Does Housing Build Cities?

2019 ◽  
Vol 4 (3) ◽  
pp. 76-82
Author(s):  
Alessandro Porotto ◽  
Chiara Monterumisi
Keyword(s):  
Rational Design ◽  
Town Planning ◽  
Present Issue ◽  
Collective Work ◽  
90Th Anniversary ◽  
Post War ◽  
War Production ◽  
The One ◽  
Definition Of ◽  
The Town

Far from nostalgically celebrate the 90th anniversary of the second CIAM, which indeed opened in October 1929 in Frankfurt, the present issue is intended as collective work, a springboard which aims to widen the debate over housing experiences beyond geographical and temporal frameworks. The focus of that event, the Existenzminimum, has often been cited as representing a fundamental contribution to the rational design of the modern dwelling. But the debates during that event went beyond the definition of this concept, because demonstrated, on the one hand, how the responsibility of architects would imply the resolution of multiple technical aspects, starting from the typological concern stretching towards the town planning aspects, and on the other hand, the calling to develop a multifaceted intellectual vision of society. Though the title selected for the present issue, namely ‘Housing Builds Cities’, denotes the different scales of the project, the aim is to achieve a something more. First and foremost, the objective is not strictly confined to a historical understanding of facts around the 1929 congress. Today a critically objective approach is useful to examine past contributions and, if applicable, their actualization. Secondly, this special issue intends to address the CIAMs’ theoretical and architectural legacy. The hypothesis on their interpretation suggests that these are still topical issues today. The issue comprises fourteen articles which investigate, through different applied methodologies, the years from the first steps of the CIAMs to the 1929 aftermath, analyze the post-war production and explore many case-studies, of which some are also geographically far from a Euro-centric vision as well as contemporary realities.

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