scholarly journals Spawning origins of pelagic juvenile cod Gadus morhua inferred from spatially explicit age distributions: potential influences on year-class strength and recruitment

2000 ◽  
Vol 202 ◽  
pp. 193-217 ◽  
Author(s):  
GA Begg ◽  
G Marteinsdottir
Keyword(s):  
Gadus Morhua ◽  
Spatially Explicit ◽  
Class Strength ◽  
Pelagic Juvenile

Offshore spawning and year-class strength of northern cod (2J3KL) during the fishing moratorium, 1994-1996

2001 ◽  
Vol 58 (7) ◽  
pp. 1386-1394 ◽  
Author(s):  
John T Anderson ◽  
George A Rose
Keyword(s):  
Gadus Morhua ◽  
Juvenile Fish ◽  
Late Summer ◽  
Rapid Decline ◽  
Natural Mortality ◽  
Potential Fecundity ◽  
Larval Stages ◽  
Northern Cod ◽  
Class Strength ◽  
Pelagic Juvenile

Two new surveys have been conducted in recent years to assess the status of the northern cod (Gadus morhua) stock (2J3KL). An offshore acoustic survey in spring sampled concentrations of spawning adults and estimated potential fecundity. A pelagic juvenile fish survey carried out in late summer measured cod year-class strength prior to settlement. Spawning biomass of offshore cod decreased from 11 700 t in 1994 to 2000 t in 1995 to 900 t in 1996 with a corresponding decrease in eggs spawned. This decline was mirrored in the distribution and abundance of pelagic juvenile cod. Natural mortality estimated between the egg and pelagic juvenile stages increased from –0.068·day–1 in 1994 to –0.084·day–1 in 1995 to –0.112·day–1 in 1996. The decline in year-class strength of cod appeared to result primarily from a reduction in the number of offshore spawners compounded by an increase in natural mortality during the egg and larval stages. The decline in spawners occurred 2 years after the implementation of a fishing moratorium and cannot be linked to fishing. The rapid decline in abundance of adult fish combined with increased natural mortality during the egg and larval drift is consistent with depensation.

scholarly journals Egg production of Baltic cod (Gadus morhua) in relation to variable sex ratio, maturity, and fecundity

2002 ◽  
Vol 59 (12) ◽  
pp. 1908-1920 ◽  
Author(s):  
Gerd Kraus ◽  
Jonna Tomkiewicz ◽  
Friedrich W Köster
Keyword(s):  
Sex Ratio ◽  
Egg Production ◽  
Gadus Morhua ◽  
Reproductive Potential ◽  
Relative Fecundity ◽  
Spawning Stock ◽  
Class Strength ◽  
The Difference ◽  
Eastern Baltic ◽  
Baltic Cod

Observed fluctuations in relative fecundity of Eastern Baltic cod (Gadus morhua L.) were related to food availability during the main feeding period and were used to develop a predictive model that explained 72% of the interannual variations in fecundity. Time series of sex ratios, maturity ogives, and relative fecundity were combined with mean weights-at-age and stock sizes from an analytical multispecies model to estimate the potential egg production (PEP). Relationships between PEP and independent estimates of realized daily and seasonal egg production from egg surveys were highly significant. The difference between estimates of potential and realized seasonal egg production was of a magnitude corresponding to the expected loss of eggs as a result of atresia, fertilization failure, and early egg mortality. The removal of interannual variability in sex ratio, maturity, and fecundity on estimates of PEP deteriorated the relationships in all three cases. PEP proved to be superior to spawning stock biomass as measure of the reproductive potential in a stock-recruitment relationship of Eastern Baltic cod. PEP in combination with the reproductive volume explained 61% of the variation in year-class strength at age 2.

The early life-history dynamics of Northeast Arctic cod: levels of natural mortality and abundance during the first 3 years of life

2016 ◽  
Vol 73 (2) ◽  
pp. 246-256 ◽  
Author(s):  
Bjarte Bogstad ◽  
Natalia A. Yaragina ◽  
Richard D.M. Nash
Keyword(s):  
Life History ◽  
Early Life ◽  
Egg Production ◽  
Gadus Morhua ◽  
Early Life History ◽  
Natural Mortality ◽  
Arctic Cod ◽  
Stock Assessments ◽  
Class Strength ◽  
New Generation

Recruitment at age 3 of the Northeast Arctic cod (Gadus morhua) is highly variable. It has generally been believed that year-class strength for this stock is determined prior to settlement to the bottom after about 6 months. However, newer observations indicate that year-class strength may change considerably between settlement and recruitment at age 3. Our analyses cover the 1983–2009 year classes where comprehensive data from total egg production (TEP), surveys, and stock assessments were available for a thorough examination of these cohorts. On average, only 6 out of 1 million of a new generation at the TEP stage reaches the age of recruitment to the fishery. The between-cohort variability in abundance is greatest at the ages 0–1 stage. Although the mortality is highest during the first months of life, the year-class strength can also be affected considerably by processes taking place between the 0-group stage (∼6 months) and age 3. The mortality in this period of life seems to be strongly density-dependent, and cannibalism is an important source of mortality.

scholarly journals Diet and prey preferences of larval and pelagic juvenile Faroe Plateau cod (Gadus morhua)

2020 ◽  
Vol 167 (8) ◽  
Author(s):  
Sólvá Jacobsen ◽  
Kristoffer Klitgaard Nielsen ◽  
Rune Kristiansen ◽  
Peter Grønkjær ◽  
Eilif Gaard ◽  
...  
Keyword(s):  
Gadus Morhua ◽  
Prey Preferences ◽  
Pelagic Juvenile

Inter-Annual Distributions of Larval and Pelagic Juvenile Cod (Gadus morhua) in Southwestern Nova Scotia determined with two Different Gear Types

1989 ◽  
Vol 46 (4) ◽  
pp. 591-602 ◽  
Author(s):  
Iain M. Suthers ◽  
Kenneth T. Frank
Keyword(s):  
Nova Scotia ◽  
Gadus Morhua ◽  
Empirical Support ◽  
Single Type ◽  
Sampling Effort ◽  
Limited Sampling ◽  
Inshore Waters ◽  
Made In ◽  
Spawning Sites ◽  
Pelagic Juvenile

Ichthyoplankton surveys conducted during 1979 on the Scotian Shelf have shown coincident egg and larval distributions for cod (Gadus morhua) and other related groundfish species. These data have been used by other investigators to support the larval retention hypothesis, in spite of three limitations: the exclusive use of a single type of small sampling gear, limited sampling landward of the 50-m isobath, and analysis of data collected in a single year. During May of 1985, 1986, and 1987 two gear types were used, from the shelf to coastal waters in southwestern Nova Scotia to assess the horizontal distributions of larval and pelagic juvenile cod. Tucker trawl collections made in each year revealed a cohort of cod [Formula: see text] that was not evident in the smaller gear, which effectively sampled cod larvae < 10 mm. During 1985 and 1986, when both larvae and juveniles were abundant, their distributions coincided. The mixture of sizes of cod from 3–45 mm reduced the importance of using multiple gear types. The interannual location of young cod shifted markedly between the nearshore and offshore demonstrating that a single year of sampling effort is inadequate to assess their distribution. Nearshore sampling revealed high densities of young cod as much as three-fold greater than offshore. The inshore waters may serve as a nursery area for young cod originating from offshore spawning sites. Our results confirm the existence of two important sampling limitations of previous cod ichthyoplankton surveys that reduce their utility as empirical support for the retention hypothesis.

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