Age and growth of larval cod and haddock on Georges Bank during 1995 and 1996

Self Cite

The egg and larval stages of the Atlantic cod Gadus morhua and haddock Melanogrammus aeglefinus populations on Georges Bank, northeastern USA, were sampled monthly from February through July in 1995 and January through June in 1996 to 1999 as part of the US GLOBEC Georges Bank program. The eggs were staged by means of microscopic examination. Larvae were aged by otolith increment analysis. Seasonally averaged rates of egg mortality were estimated for both species and ranged from 9.9 to 20.4 % d -1 for cod and 7.8 to 13.4% d -1 for haddock. From the results of a simple drift model, the interannual variability in egg mortality rate is believed to be due largely to wind-driven transport off the southern side of the bank. The estimated number of hatched eggs is strongly correlated with the subsequent recruitment for both the Atlantic cod and haddock stocks. Mortality during the early larval period was estimated for 10 d cohorts within each year, based on the decrease in abundance from egg hatching to the first sampling of the cohort on a survey, when the larvae were on average about 15 d old. For both species, these rates were slowly varying between cohorts within a season, but showed large variation between years. For the 1995 to 1996 period, the annual average mortality rate was about 6.3% d -1 for cod and 10.1% d -1 for haddock, whereas in 1998 to 1999 the values were 3.9% d -1 for cod and 5.4% d -1 for haddock. The lower mortality rates in 1998 to 1999 are believed to be due to higher prey abundance for the larvae in those years. From the larval stage to stock recruitment, haddock appeared to have a survival rate (recruits per larvae) 3 times higher than that for Atlantic cod.

Section: Introductionmentioning

confidence: 71%

“…The ages of alcohol preserved larvae were estimated following the procedures of Green et al (2004). Otolith microstructure (enumeration of daily growth increments) was used to determine larval age in days (Bolz & Lough 1988).…”

Section: Methodsmentioning

confidence: 99%

Growth and mortality of Atlantic cod Gadus morhua and haddock Melanogrammus aeglefinus eggs and larvae on Georges Bank, 1995 to 1999

Mountain¹,

Green²,

Sibunka³

et al. 2008

Self Cite

“…This problem was resolved by measuring the diameter (µm) of the amorphous area for each juvenile otolith across the long axis of the transverse section, and by estimating the number of daily increments in that area using an equation relating otolith diameter and ring counts in larval haddock collected on GB. Otoliths were removed from larvae and processed without sectioning (Green et al 2004). For larvae, otolith diameter was measured across the shortest axis to correspond with the long axis viewed in the transverse section of the juvenile otolith.…”

Section: Methodsmentioning

confidence: 99%

Hatch date distributions of young-of-year haddock Melanogrammus aeglefinus in the Gulf of Maine/ Georges Bank region: implications for recruitment

Lapolla¹,

Buckley²

2005

We determined the hatch dates of young-of-year (YOY) juveniles from the 1995 to 1999 year-classes of haddock Melanogrammus aeglefinus collected in the Northeast Fisheries Science Center fall groundfish surveys in the Gulf of Maine/Georges Bank region. Hatch dates were based on age estimates made by counting otolith daily rings. The average YOY haddock was > 200 d old at the time of capture, with estimated hatch dates ranging from mid November to early June. Haddock collected in the Gulf of Maine had mean hatch dates about 1 mo later than fish collected on Georges Bank. Each year on Georges Bank, hatch date frequencies (HDF) of survivors peaked between February and mid March, considerably earlier than the peak in HDF estimated from late-stage eggs. The ratio of the relative HDF of survivors collected in the fall to the relative HDF estimated from late-stage eggs was used to calculate relative survivorship of different cohorts. These data suggest that haddock hatched early in the season had a survival advantage over those hatched later in the year. The 1998 year-class, the largest produced on Georges Bank in the past 20 yr, had one of the latest peaks in HDF of juveniles among the 5 years examined. More survivors were produced in each month of 1998 compared to the monthly averages of the remaining years. In particular, the 1998 year-class benefited from enhanced survival of individuals hatched in the mid and latter portions of the hatch curve, although survival was still highest for individuals originating from the early portion of the hatching curve. KEY WORDS: Georges Bank · Hatch date distributions · Juvenile haddock · Otolith microstructure · RecruitmentResale or republication not permitted without written consent of the publisher

“…Estimates of size-at-age of Georges Bank cod and haddock larvae based on our SPPDG models tend to be lower that those based on otolith daily-ring counts (Bolz & Lough 1988, Green et al 2004. A number of factors likely contribute to this difference.…”

Section: Role Of Photoperiod and Temperature In Determining Larval Grmentioning

confidence: 61%

“…This suggests that the 2 models are in good agreement when the effect of photoperiod is considered. A reference growth model for well-fed larvae that incorporates the effects of both temperature and photoperiod is needed to predict the maximum growth potential of larvae over the range of temperatures and photoperiods encountered in the sea.Estimates of size-at-age of Georges Bank cod and haddock larvae based on our SPPDG models tend to be lower that those based on otolith daily-ring counts (Bolz & Lough 1988, Green et al 2004. A number of factors likely contribute to this difference.…”

mentioning

confidence: 61%

Ontogenetic and seasonal trends in recent growth rates of Atlantic cod and haddock larvae on Georges Bank: effects of photoperiod and temperature

Buckley¹,

Caldarone²,

Lough³

et al. 2006

Growth rate is a key demographic factor affecting survival and recruitment of marine fishes. Yet in the field, the patterns of change in growth rate with development and the effects of environmental variability on growth are poorly understood. We examined several factors that may contribute to the observed variability in recent (i.e. 2 to 4 d before sampling) growth and survival of Atlantic cod Gadus morhua and haddock Melanogrammus aeglefinus larvae on the southern flank of Georges Bank for the years 1995 through 1999. For both species, strong ontogenetic and seasonal trends in larval growth rates were apparent. A rapid initial increase in specific growth rate with larval size was observed in both species, followed by a stanza with little change in specific growth rate and finally a gradual increase with size to a maximum specific growth rate. For larva of any given size, growth rate increased as the season progressed. A variety of models were used to explore and describe the relations among growth rate, larval size, photoperiod, temperature and other variables. Generalized additive models (GAMs) with both larval size (protein content) and photoperiod terms explained 48% and 61% of the variability observed in recent growth of cod and haddock, respectively. Residuals from these models were used to examine the effects of other factors on estimated growth rates. Salinity, water density (sigma-t, σ t ), distance along the Bank, bottom depth, temperature (T) and residual T (observed T minus the long-term mean for a given day of the year) explained small but significant portions of the residual variability in larval growth rates. These data and other considerations suggest that, while both increasing photoperiod and temperature contribute to the increase in larval growth rates observed each spring, photoperiod rather than temperature was the better proxy for the seasonal trend in larval growth rates between March and May on Georges Bank. Feeding conditions and growth of larval Atlantic cod and haddock were poor during the late winter and spring of 1995 compared with those from 1997 to 1999.KEY WORDS: Atlantic cod · Haddock · Larvae · Growth · Photoperiod · Temperature · Diel trends Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 325: 2006 agreement, however, that knowledge of the factors affecting growth and survival during the first year of life is key to understanding the linkages between the physical and biotic environment and fish production (Leggett & Deblois 1994).Rapid growth and high mortality characterize the larval stage of most marine fishes. The rare survivor increases in mass by 1 to 2 orders of magnitude from hatching through metamorphosis to the juvenile stage. The rates of growth and mortality together determine the rate of change in the biomass of a cohort. Interannual variability in these rates coupled with fluctuations in egg production can lead to large fluctuations in recruitment and year-class size (Houde 1989). While larval mortality...