scholarly journals Maturity and growth population dynamics of Norway pout (Trisopterus esmarkii) in the North Sea, Skagerrak, and Kattegat

2009 ◽  
Vol 66 (9) ◽  
pp. 1899-1914 ◽  
Author(s):  
Gwladys Lambert ◽  
J. Rasmus Nielsen ◽  
Lena I. Larsen ◽  
Henrik Sparholt
Keyword(s):  
Population Dynamics ◽  
North Sea ◽  
Stock Assessment ◽  
Age Group ◽  
Commercial Catch ◽  
The North ◽  
Stock Biomass ◽  
Spawning Stock ◽  
The North Sea ◽  
Immature Fish

Abstract Lambert, G., Nielsen, J. R., Larsen, L. I., and Sparholt, H. 2009. Maturity and growth population dynamics of Norway pout (Trisopterus esmarkii) in the North Sea, Skagerrak, and Kattegat. – ICES Journal of Marine Science, 66: 1899–1914. The population dynamics of the Norway pout stock in the North Sea are investigated by statistical analyses, and GIS of ICES International Bottom Trawl Surveys (IBTS) and Danish commercial catch data from 1983 to 2006. The stock spawns mainly around mid-February along the northeastern English and Scottish coasts and between Shetland and Norway. Sex ratios indicate that males, which mature younger than females (age-at-50%-maturity, respectively, 1.2 and 1.5 years), migrate out of the Skagerrak–Kattegat to the spawning grounds before females. There is a decrease in the 2+-group maturity ratios as well as in weight and female length from before to after spawning. The results indicate spawning mortality. Only some 20% of the 1-group reaches maturity in the first quarter, which is higher than assumed in the stock assessment. Although the maturity ogives are variable over time, this difference should be taken into account when estimating spawning-stock biomass in routine assessments. Growth is also variable, with a tendency for male maximum length to be smaller than that of females, and immature fish to be smaller than mature ones in each age group. The juvenile growth rate is higher when the stock density is low and results in a reduced age-at-50%-maturity. Besides these intraspecific patterns, the growth rates show interspecific links to stock sizes of the important predators: cod, haddock, and whiting.

scholarly journals Gadoid dynamics: differing perceptions when contrasting stock vs. population trends and its implications to management

2014 ◽  
Vol 71 (6) ◽  
pp. 1433-1442 ◽  
Author(s):  
Steven J. Holmes ◽  
Colin P. Millar ◽  
Robert J. Fryer ◽  
Peter J. Wright
Keyword(s):  
North Sea ◽  
Stock Assessment ◽  
Research Vessel ◽  
Vital Rates ◽  
The North ◽  
Depth Contour ◽  
Spawning Stock ◽  
Population Structures ◽  
The North Sea ◽  
Local Pressures

Recent research suggests that ICES stock definitions for cod, haddock, and whiting of “west of Scotland” and “North Sea”, do not reflect underlying population structures. As population responses to different vital rates and local pressures would be expected to lead to asynchrony in dynamics, we examined trends in local spawning-stock biomass (SSB) among putative subpopulations of the three species. Delineation of subpopulation boundaries around spawning time was made based on genetic, tagging, and otolith microchemistry studies together with density distributions of species based on research vessel survey data. Subpopulation specific indices of SSB were derived using numbers-at-age and maturity observations from the same research vessel data and asynchrony was assessed by fitting a smoother to log SSB for each subpopulation and testing whether the smooths were parallel. Results for cod support the hypothesis of distinct inshore and larger offshore subpopulations and for whiting for northern and southern North Sea subpopulations with a boundary associated with the 50 m depth contour. In haddock, no difference in SSB trends between the North Sea and west of Scotland was found. For cod and whiting, subpopulation SSB trends differed substantially within current stock assessment units, implying reported stock-based SSB time-series have masked underlying subpopulation trends.

A reanalysis of North Sea plaice spawning-stock biomass using the annual egg production method

2009 ◽  
Vol 66 (9) ◽  
pp. 1999-2011 ◽  
Author(s):  
Cindy J. G. van Damme ◽  
Loes J. Bolle ◽  
Clive J. Fox ◽  
Petter Fossum ◽  
Gerd Kraus ◽  
...  
Keyword(s):  
North Sea ◽  
Egg Production ◽  
Stock Assessment ◽  
Population Analysis ◽  
Spatial Dynamics ◽  
Production Method ◽  
Southern Bight ◽  
The North ◽  
Stock Biomass ◽  
Spawning Stock

Abstract van Damme, C. J. G., Bolle, L. J., Fox, C. J., Fossum, P., Kraus, G., Munk, P., Rohlf, N., Witthames, P. R., and Dickey-Collas, M. 2009. A reanalysis of North Sea plaice spawning-stock biomass using the annual egg production method. – ICES Journal of Marine Science, 66: 1999–2011. Uncertainty about the quality of current virtual population analysis-based stock assessment for North Sea plaice (Pleuronectes platessa) has led to various abundance indices. We compared biomass estimates from the annual egg production (AEP) method with current stock assessments based on catch-at-age to validate the current and historical perception of exploitation. The AEP method was also used to investigate the dynamics of the spatial components of plaice in the North Sea. We corrected for fecundity down-regulation and changes in sex ratio. Estimates from both methods were similar in trend and absolute biomass. On the Dogger Bank, there was a dramatic decline in biomass from 1948 and 1950 to 2004, and in the Southern Bight, the stock appeared to increase from 1987 and 1988 to 2004, although not reaching the historically high levels of 1948 or 1950. The timing of spawning of North Sea plaice does not appear to have changed throughout the period of high exploitation. We conclude that the AEP method is a useful way to hindcast the spatial dynamics of heavily exploited flatfish stocks.

Decadal changes in the North Sea food web between 1981 and 1991 — implications for fish stock assessment

2006 ◽  
Vol 63 (11) ◽  
pp. 2586-2602 ◽  
Author(s):  
Alexander Kempf ◽  
Jens Floeter ◽  
Axel Temming
Keyword(s):  
Food Web ◽  
North Sea ◽  
Fish Stock ◽  
Fish Diet ◽  
Data Set ◽  
The North ◽  
Stock Biomass ◽  
Spawning Stock ◽  
The North Sea ◽  
The Impact

The North Sea ecosystem of the early 1980s differed substantially from that of the early 1990s. The current North Sea multispecies fisheries assessment models are parameterized by fish diet data sets that reflect both ecosystem states, as the stomachs were sampled in 1981 and 1991. In this study, multispecies virtual population analysis (MSVPA) was parameterized with either diet data set, leading to different model food webs, each representing the predator's diet selection behavior and spatiotemporal overlap with their prey in the two respective ecosystem states. The impact of these changes in predator preferences and spatiotemporal overlap on recruitment success and on stock developments could be demonstrated by using either stomach data set to estimate historic and future spawning stock biomass and recruitment trajectories. The observed changes in the food web mainly impacted the hindcasted recruitment trajectories, whereas spawning stock biomass estimates were quite robust. In the prediction runs, the differences in the survival rate of the recruits decided whether fish stocks of commercially important species (e.g., Gadus morhua, Merlangius merlangus) would recover or collapse in the near future.

Recent Changes in the Central and Southern North Sea Herring Stocks

1985 ◽  
Vol 42 (S1) ◽  
pp. s192-s206 ◽  
Author(s):  
A. C. Burd
Keyword(s):  
North Sea ◽  
Maximum Yield ◽  
Total Allowable Catch ◽  
Underlying Assumption ◽  
Southern North Sea ◽  
The North ◽  
Management Procedure ◽  
Stock Biomass ◽  
Spawning Stock ◽  
The North Sea

Since 1980 there has been a sudden recovery of recruitment to the central and southern North Sea herring stocks (Bank and Downs, respectively). In contrast, recruitment to the northern North Sea has continued at a low level and spawning stock biomass has even declined since 1979. These events underline the independence of the substocks in the North Sea, each of which has reacted differently to the cessation of the directed herring fishery in the North Sea since 1977. A precondition to the reopening of a herring fishery in the North Sea was that the severely depleted spawning stock biomass should have recovered to 800 000 t, the underlying assumption being that all components would respond in a similar manner and that a reopening of the whole North Sea would be possible. This has not happened and it may well be that management of the North Sea as a single unit is not a viable management procedure. The paper examines the historic changes in sizes of the Bank and Downs stocks, with particular emphasis on the most recent period. Evidence of density-dependent growth change is considered together with the recent data on fecundity and larval herring production. It is concluded that if the separate stocks are to be managed individually for maximum yield, then global North Sea regulations such as a total allowable catch and size regulation are inappropriate. Regulations must also take into consideration the seasonal distributions of the stocks. Indeed, this would lead, in particular, to more restrictive and specific regulation of the industrial fisheries.

scholarly journals Evaluation of the quality of the North Sea herring assessment

2009 ◽  
Vol 66 (8) ◽  
pp. 1814-1822 ◽  
Author(s):  
E. John Simmonds
Keyword(s):  
North Sea ◽  
Management Strategy ◽  
Fishing Mortality ◽  
The North ◽  
Stock Biomass ◽  
Spawning Stock ◽  
The North Sea ◽  
Acoustic Surveys ◽  
One Year

Abstract Simmonds, E. J. 2009. Evaluation of the quality of the North Sea herring assessment. – ICES Journal of Marine Science, 66: 1814–1822. The assessment of North Sea herring has been used to give advice on catch quota for more than 20 years. The data sources comprise acoustic surveys, International Bottom Trawl Surveys, Methot Isaacs–Kidd net post-larval surveys, larval surveys, and catch-at-age data. These sources and their uses are briefly reviewed, and the changes in the weighting attached to each index in the assessment over time are discussed. The performance of the assessment is examined both in historical and analytical retrospectives of spawning–stock biomass and fishing mortality, and in retrospective assessments of numbers by cohort. Increased length of the time-series, the use of a statistical model with appropriate weighting, and a more consistent management strategy have all contributed to the assessment becoming highly stable from one year to the next. The results presented lead to the conclusion that the assessments provide an excellent basis for the management of this stock.

scholarly journals Population dynamics and stock assessment of grey sharpnose shark Rhizoprionodon oligolinx Springer, 1964 (Chondrichthyes: Carcharhinidae) from the north-west coast of India

2017 ◽  
Vol 64 (3) ◽  
Author(s):  
G. B. Purushottama ◽  
Gyanaranjan Dash ◽  
Thakur Das ◽  
K. V. Akhilesh ◽  
Shoba Joe Kizhakudan ◽  
...  
Keyword(s):  
Population Dynamics ◽  
Stock Assessment ◽  
Total Mortality ◽  
North West ◽  
The North ◽  
Stock Biomass ◽  
Spawning Stock ◽  
Yield Per Recruit ◽  
Peak Phase

The life history and exploitation parameters of Rhizoprionodon oligolinx Springer, 1964 were assessed using commercial landing data of 2012-2015 from Mumbai waters of India to understand the population dynamics and stock status of the species. The average annual landing of the species was estimated to be 383 t, which formed about 9.1% of the total shark landings of Maharashtra. L∞, K and t0 estimated were 97.1 cm, 0.47 yr-1 and -0.79 yr respectively. Total mortality (Z), fishing mortality (F) and natural mortality (M) rates were estimated as 2.16 yr-1, 1.48 yr-1 and 0.69 yr-1 respectively. The length at capture (L50), length at female maturity (Lm50) and male maturity (Lm50) were estimated as 49.7, 62.3 and 59.5 cm respectively, which indicated that most of the sharks entered peak phase of exploitation before attaining sexual maturity. Length-weight relationship indicated allometric growth (b>3) for the species. The species was found to be a continuous breeder and showed peak recruitment during April. The current exploitation rate (Ecur) was found to be 0.68, which is lower than Emax estimated for the species using Beverton and Holt yield per recruit analysis. Thompson and Bell prediction model showed that at current exploitation level, the biomass (B) has reduced to 32% of virgin biomass (B0) where as, the spawning stock biomass (SSB) has reduced to 16% of the virgin spawning stock biomass (SSB0). Hence the exploitation level for the species should be reduced by 40% that will ensure the availability of SSB at a relatively safer 30% level to rebuild the stock for long term sustainability of the resource.

scholarly journals The implications of warming climate for the management of North Sea demersal fisheries

2005 ◽  
Vol 62 (7) ◽  
pp. 1322-1326 ◽  
Author(s):  
R.M. Cook ◽  
M.R. Heath
Keyword(s):  
North Sea ◽  
Reference Points ◽  
The North ◽  
Stock Biomass ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
The North Sea ◽  
State Of The Environment ◽  
Negative Relationships ◽  
Positive Effect

Abstract Since the 1950s, records from the North Sea show a gradual increase in temperature. Using temperature as a proxy indexing the state of the environment, relationships between recruitment, spawning-stock biomass, and temperature are investigated for major North Sea stocks. Cod, plaice, and sole exhibit significant negative relationships between temperature and recruitment, while there is evidence of a positive effect for saithe and whiting. Stock-recruitment models that incorporate temperature are developed and used to examine implications for the management of these stocks with small increases in mean winter sea surface temperature. These suggest that for cod, minimum safe biomass reference points are unlikely to be achieved even at fishing mortality rates that are considered safe. The same analysis suggests that sustainable fishing for cod is still possible with higher yields than have been experienced in recent years.

scholarly journals Spatial patterns and trends in abundance of larval sandeels in the North Sea: 1950–2005

2013 ◽  
Vol 70 (3) ◽  
pp. 540-553 ◽  
Author(s):  
Christopher P. Lynam ◽  
Nicholas C. Halliday ◽  
Hannes Höffle ◽  
Peter J. Wright ◽  
Cindy J. G. van Damme ◽  
...  
Keyword(s):  
Spatial Patterns ◽  
North Sea ◽  
Wadden Sea ◽  
Larval Fish ◽  
Stock Assessment ◽  
Commercial Catch ◽  
The North ◽  
Stock Assessments ◽  
The North Sea ◽  
Early Recruitment

Abstract Lynam, C. P., Halliday, N. C., Höffle, H., Wright, P. J., van Damme, C. J. G., Edwards, M., and Pitois, S. 2013. Spatial patterns and trends in abundance of larval sandeels in the North Sea: 1950–2005 – ICES Journal of Marine Science, 70: 540–553. Early recruitment indices based on larval fish data from the Continuous Plankton Recorder (CPR) have the potential to inform stock assessments of Ammodytes marinus in the North Sea. We evaluate whether the CPR data are reliable for sandeel larvae. Spatially, CPR larval data were comparable with catches by dedicated larval samplers (Gulf and bongo nets) during ICES coordinated surveys in 2004 and 2009. ICES data are also used to explore environmental influences on sandeel distributions. Temporally, CPR data correlate with larval data from plankton surveys off Stonehaven (1999–2005), with sandeel 0-group trawl data at the east Fair Isle ground (since 1984), and with recruitment data (since 1983) for the Dogger Banks stock assessment area. Therefore, CPR data may provide an early recruit index of relative abundance for the Dogger Banks assessment area, where the majority of the commercial catch of A. marinus is taken, and the Wee Bankie area that is particularly important for seabird foraging. While warm conditions may stimulate the production of sandeel larvae, their natural mortality is typically greater, in the Dogger Banks and Wadden Sea areas, when the larvae are hatched in warm years and/or with abundant 1-year-old sandeel that are likely to be cannibalistic.

scholarly journals Emergence of a new predator in the North Sea: evaluation of potential trophic impacts focused on hake, saithe, and Norway pout

2016 ◽  
Vol 73 (5) ◽  
pp. 1370-1381 ◽  
Author(s):  
Xochitl Cormon ◽  
Alexander Kempf ◽  
Youen Vermard ◽  
Morten Vinther ◽  
Paul Marchal
Keyword(s):  
North Sea ◽  
Negative Impact ◽  
Stock Assessment ◽  
Single Species ◽  
Bottom Up ◽  
The North ◽  
Spatial Shift ◽  
Spawning Stock ◽  
The North Sea ◽  
Indirect Impacts

Abstract During the last 15 years, northern European hake (Merluccius merluccius) has increased in abundance, and its spatial distribution has expanded in the North Sea region in correlation with temperature. In a context of global warming, this spatial shift could impact local trophic interactions: direct impacts may affect forage fish through modified predator–prey interactions, and indirect impacts may materialize through competition with other resident predators. For instance, North Sea saithe (Pollachius virens) spatial overlap with hake has increased while saithe spawning-stock biomass has decreased recently notwithstanding a sustainable exploitation. In this context, we investigated the range of potential impacts resulting from most recent hake emergence in the North Sea, with a particular focus on saithe. We carried out a multispecies assessment of North Sea saithe, using the Stochastic MultiSpecies (SMS) model. In addition to top-down processes already implemented in SMS, we built in the model bottom-up processes, relating Norway pout (Trisopterus esmarkii) abundance and saithe weight-at-age. We simulated the effects, on all North Sea species being considered but focusing on Norway pout and saithe, of combining different hake abundance trends scenarios with the inclusion of bottom-up processes in SMS. North Sea saithe FMSY was then evaluated in a multispecies context and contrasted with single-species value. The different scenarios tested revealed a negative impact of hake emergence on saithe biomass, resulting from an increase of predation pressure on Norway pout. These results confirm the competition assumption between saithe and hake in the North Sea and might partially explain the most recent decrease of saithe biomass. This study also highlighted that taking into account bottom-up processes in the stock assessment had a limited effect on the estimation of saithe FMSY which was consistent with single-species value.

scholarly journals Evidence for substock dynamics within whiting (Merlangius merlangus) management regions

2013 ◽  
Vol 70 (6) ◽  
pp. 1118-1127 ◽  
Author(s):  
Carlos de Castro ◽  
Peter J. Wright ◽  
Colin P. Millar ◽  
Steven J. Holmes
Keyword(s):  
North Sea ◽  
Metapopulation Dynamics ◽  
Current Management ◽  
The North ◽  
Stock Biomass ◽  
Spawning Stock ◽  
The North Sea ◽  
Merlangius Merlangus ◽  
Northern North Sea ◽  
Eastern Channel

Abstractde Castro, C., Wright, P. J., Millar, C. P., and Holmes, S. J. 2013. Evidence for substock dynamics within whiting (Merlangius merlangus) management regions. – ICES Journal of Marine Science, 70: 1118–1127. Whiting in the North Sea and Eastern Channel is currently assessed as a single management unit. However, several studies suggest that this stock may be comprised of more than one subpopulation within a larger metapopulation. A key characteristic of metapopulations is asynchrony in the dynamics of component subpopulations. In this study, indices of recruitment and spawning–stock biomass (SSB) were developed to test for asynchrony across putative subpopulations in the North Sea and west of Scotland. Differences in SSB and recruitment trends were detected, consistent with expectations from metapopulation dynamics. At least three different subpopulation components (southern and northern North Sea, and west of Scotland) were indicated on the basis of differing trends. Analysis of spatial distribution suggested that the boundary between the northern and southern North Sea subpopulations was associated with the change in bathymetry that extended from the coast of Norfolk in England to the southern tip of Norway. The current management system for whiting in the North Sea assumes a unit stock, which is contrary to current sources of biological evidence and seems inappropriate. Consideration of a north–south split along the boundary detected should be beneficial for both assessment and management of the resource.

Sign in / Sign up

Export Citation Format

Share Document