Long-term changes in life history characteristics and reproductive potential of northern Gulf of St. Lawrence cod (Gadus morhua) and consequences for the stock productivity

2013 ◽  
Vol 138 ◽  
pp. 5-13 ◽  
Author(s):  
Yvan Lambert
Keyword(s):  
Life History ◽  
Gadus Morhua ◽  
Reproductive Potential ◽  
Life History Characteristics ◽  
Long Term Changes

scholarly journals Long-term changes in trophic patterns of Iceland cod and linkages to main prey stock sizes

2011 ◽  
Vol 68 (7) ◽  
pp. 1488-1499 ◽  
Author(s):  
Ólafur K. Pálsson ◽  
Höskuldur Björnsson
Keyword(s):  
Gadus Morhua ◽  
Atlantic Water ◽  
Type I ◽  
Feeding Response ◽  
Total Consumption ◽  
Stock Size ◽  
Main Prey ◽  
Northern Shrimp ◽  
Long Term Changes

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.

Environmental and fishing limitations to the rebuilding of the northern Gulf of St. Lawrence cod stock (Gadus morhua)

2011 ◽  
Vol 68 (4) ◽  
pp. 618-631 ◽  
Author(s):  
Yvan Lambert
Keyword(s):  
Life History ◽  
Gadus Morhua ◽  
Life History Traits ◽  
Atlantic Cod ◽  
Negative Impact ◽  
Reproductive Potential ◽  
Reproductive Rate ◽  
Fishing Mortality ◽  
Recent Period ◽  
Instantaneous Rate

Time series of life history traits determining the reproductive potential and productivity of Atlantic cod ( Gadus morhua ) in the northern Gulf of St. Lawrence (nGSL) were obtained for the period covering the collapse and failure of the stock to recover. Decreasing trends in these traits were observed under unfavourable oceanographic conditions, with lowest values reached in the early 1990s. These changes had a negative impact on reproductive rate and instantaneous rate (r) of population growth. Estimates of r used as a proxy of stock productivity were negative when the stock collapsed, indicating that the biomass would have decreased even without fishing. Population abundance projections for the recent period suggest a potential increase in population size of 7.3% per year, with a doubling time of 10.5 years in the absence of exploitation and a near 0% rate with current fishing mortality, indicating that present harvesting does not allow any rebuilding of the stock. Given the similarities in environmental conditions and key life history traits, the situation in the nGSL might reflect the state of many northwest Atlantic cod stocks.

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

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.

scholarly journals Long-term trends in the occupancy of ants revealed through use of multi-sourced datasets

2021 ◽  
Vol 17 (10) ◽  
Author(s):  
Julie K. Sheard ◽  
Carsten Rahbek ◽  
Robert R. Dunn ◽  
Nathan J. Sanders ◽  
Nick J. B. Isaac
Keyword(s):  
Life History ◽  
Science Data ◽  
Occupancy Modelling ◽  
Habitat Changes ◽  
Participatory Science ◽  
Long Term Changes ◽  
Biodiversity Change ◽  
Long Term Trends ◽  
Insect Decline

We combined participatory science data and museum records to understand long-term changes in occupancy for 29 ant species in Denmark over 119 years. Bayesian occupancy modelling indicated change in occupancy for 15 species: five increased, four declined and six showed fluctuating trends. We consider how trends may have been influenced by life-history and habitat changes. Our results build on an emerging picture that biodiversity change in insects is more complex than implied by the simple insect decline narrative.

Life-history characteristics of the yakka skink, Egernia rugosa, indicate long-term social structure

2016 ◽  
Vol 64 (5) ◽  
pp. 335 ◽  
Author(s):  
Stephen Peck ◽  
Michael G. Gardner ◽  
Jennifer M. Seddon ◽  
Greg Baxter
Keyword(s):  
Life History ◽  
Life Expectancy ◽  
Genetic Analysis ◽  
Social Structure ◽  
Litter Size ◽  
Sexual Maturity ◽  
Age Cohorts ◽  
South West ◽  
Life History Characteristics

One lineage of squamates, the Egernia group, has received particular study due to stable aggregations identified in many of the species. Egernia rugosa is a large, terrestrial, viviparous skink and has been reported living communally. To investigate whether this species lives in social aggregations, we examined life-history characteristics in one population within the Mulga Lands bioregion of south-west Queensland. We found this skink used both active and inactive rabbit burrows. Parturition occurred in January/February and took several days to complete, with a mean litter size of 2.4 and a mean snout–vent length (SVL) of 84.5 mm. Six subadult age cohorts were identified. Juveniles took at least five years to reach sexual maturity and lizards had a life expectancy of >12 years. Lizards were found clustered in aggregations of up to 21 individuals (mean = 7.21) of multiple ages. An average of 50% (range = 31–67%) of all individuals within each of the age cohorts were located at their original location for two or more seasons. Dispersal was recorded for older subadult lizards. These characteristics support the hypothesis that E. rugosa aggregations comprise long-term family units; however, genetic analysis would be needed to confirm kin-based associations.

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