Long-term changes in age at sexual maturity of Northeast Arctic cod (Gadus morhua L.)

Abstract Pálsson, Ó. K., and Björnsson, H. 2011. Long-term changes in trophic patterns of Iceland cod and linkages to main prey stock sizes. – ICES Journal of Marine Science, 68: 1488–1499. Data on the diet composition of Iceland cod (Gadus morhua) were collected in March of the years 1981–2010 and in autumn of the years 1988–2010. Capelin, northern shrimp, and euphausiids dominate the diet in all years and may be classified as the stable food of Iceland cod. Overall, total consumption by the smallest cod (20–29 cm) remained stable over the three decades, whereas that of larger fish has declined since the mid-1990s. This decline may explain the reduced growth rate of cod in recent years. Long-term, prey-specific patterns were identified in consumption, and significant trophic links were found between cod consumption and stock sizes of capelin and northern shrimp. In March, the correlation between cod consumption on capelin and capelin stock size was highly significant, a type I functional feeding response, but not significant in autumn. The correlation deteriorated in the early to mid-1990s and in the early 2000s. Increased inflow of Atlantic water into north Icelandic waters, and associated changes in capelin distribution, may have contributed to this trend. The interaction between cod consumption on northern shrimp and shrimp stock size showed a highly significant type I functional feeding response in both seasons.

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Long term changes in the sexual maturity and in the reproductive biomass of the southern king weakfish Macrodon atricauda (Günther, 1880) in southern Brazil

Fisheries Research ◽

10.1016/j.fishres.2014.05.012 ◽

2014 ◽

Vol 160 ◽

pp. 120-128 ◽

Cited By ~ 11

Author(s):

Luis Gustavo Cardoso ◽

Manuel Haimovici

Keyword(s):

Sexual Maturity ◽

Southern Brazil ◽

Long Term Changes ◽

Reproductive Biomass

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The code of the long-term biomass cycles in the Barents Sea

ICES Journal of Marine Science ◽

10.1016/s1054-3139(03)00152-8 ◽

2003 ◽

Vol 60 (6) ◽

pp. 1251-1264 ◽

Cited By ~ 10

Author(s):

Harald Yndestad

Keyword(s):

Gadus Morhua ◽

Barents Sea ◽

Temperature Cycle ◽

Biomass Growth ◽

Sea Temperature ◽

Arctic Cod ◽

Temperature Cycles ◽

Large Fluctuations ◽

Capelin Mallotus Villosus

Abstract Barents Sea capelin (Mallotus villosus), Norwegian spring-spawning herring (Cluea harengus), and Northeast Arctic cod (Gadus morhua) have been associated with large fluctuations of biomass growth. The cause of these large fluctuations has been poorly understood and led to problems in biomass management. The identification of a deterministic cause would provide the possibility of forecasting future biomass fluctuations. In this investigation, the Kola Section sea temperature and the biomasses of capelin, herring, and cod have been analyzed by a wavelet transform to identify the source of the long-term cycles. The wavelet analysis shows that the Kola Section temperature has dominant cycles at the lunar-nodal tide cycles of 3×18.6=55.8, 18.5 and 18.6/3 = 6.2 years. The recruitment of Barents Sea capelin, Norwegian spring-spawning herring, and Northeast Arctic cod has adopted an optimal recruitment cycle close to the stationary 6.2 years Kola temperature cycle. Long-term biomass growth is correlated to the phase relation between the biomass eigen-frequency cycle and the Kola temperature cycles. The biomasses of capelin, herring and cod have long-term growth when the 6.2 and 18.6 years Kola temperature cycles are positive at the same time. There is a long-term biomass reduction when the temperature cycles are not positive at the same time, and a biomass collapse when the temperature cycles are negative at the same time. The deterministic property of the 18.6 years lunar-nodal tide provides a new way of long-term biomass forecasting over periods of 50–80 years or more.

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Long-term interplay between harvest regimes and biophysical conditions may lead to persistent changes in age-at-sexual maturity of Northeast Arctic cod (Gadus morhua)

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/cjfas-2021-0068 ◽

2021 ◽

Author(s):

Carl Jakob Rørvik ◽

Bjarte Bogstad ◽

Geir Ottersen ◽

Olav Sigurd Kjesbu

Keyword(s):

Gadus Morhua ◽

Dynamic Range ◽

Age Groups ◽

Fishing Mortality ◽

Sea Temperature ◽

Arctic Cod ◽

Trawl Fishery ◽

Stock Biomass ◽

Total Stock

This investigation commenced by constructing principal maturation schedule equations as a function of fishing mortality (F), key biophysical factors and a term attributed to fisheries-induced adaptive change (FIAC). Following the onset of industrial trawl fishery on the model stock, Northeast Arctic cod (NEAC) (1934-2020), F on immature age groups 5-8 years (F5-8) increased and mean age at 50% maturity (A50) decreased from ≈10 years in the late 1940s to ≈7 years today. Large annual fluctuations in total stock biomass (TSB), sea temperature (KolaT) and F5-8 were used to better understand A50 responses. In the model, the annual accumulation of F5-8 drives FIAC. The model includes the option that NEAC may sustain F5 8 up to a certain level (F_bal) before FIAC becomes statistically evident, with F_bal falling between 0.00 and 0.40 for A50. This dynamic range in F_bal indicates a sophisticated, underlying adaptive response. Independent of F_bal, our analysis clarifies that FIAC is necessary to explain the observed changes in A50.

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Time-variant productivity in biomass dynamic models on seasonal and long-term scales

ICES Journal of Marine Science ◽

10.1093/icesjms/fsz154 ◽

2019 ◽

Author(s):

Tobias K Mildenberger ◽

Casper W Berg ◽

Martin W Pedersen ◽

Alexandros Kokkalis ◽

J Rasmus Nielsen

Keyword(s):

Gadus Morhua ◽

Dynamic Models ◽

Ecological Factors ◽

Fish Populations ◽

Reference Levels ◽

Real World Data ◽

Long Term Changes ◽

Biomass Dynamic ◽

Management Advice

Abstract The productivity of fish populations varies naturally over time, dependent on integrated effects of abundance, ecological factors, and environmental conditions. These changes can be expressed as gradual or abrupt shifts in productivity as well as fluctuations on any time scale from seasonal oscillations to long-term changes. This study considers three extensions to biomass dynamic models that accommodate time-variant productivity in fish populations. Simulation results reveal that neglecting seasonal changes in productivity can bias derived stock sustainability reference levels and, thus, fisheries management advice. Results highlight the importance of biannual biomass indices and their timing relative to the peaks of the seasonal processes (i.e. recruitment, growth, mortality) for the estimation of seasonally time-variant productivity. The application to real-world data of the eastern Baltic cod (Gadus morhua) stock shows that the model is able to disentangle differences in seasonal fishing mortality as well as seasonal and long-term changes in productivity. The combined model with long-term and seasonally varying productivity performs significantly better than models that neglect time-variant productivity. The model extensions proposed here allow to account for time-variant productivity of fish populations leading to increased reliability of derived reference levels.

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