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.

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 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.

Changes in Western mackerel (Scomber scombrus) spawning stock composition during the spawning season

1986 ◽  
Vol 66 (2) ◽  
pp. 367-383 ◽  
Author(s):  
Wendy A. Dawson
Keyword(s):  
North Sea ◽  
Stock Assessment ◽  
East Atlantic ◽  
The West ◽  
Scomber Scombrus ◽  
North East ◽  
The North ◽  
Spawning Stock ◽  
The North Sea ◽  
Central North Sea

INTRODUCTIONTwo groups of mackerel (Scomber scombrus L.) are recognised by the International Council for the Exploration of the Sea (I.C.E.S.) for stock assessment purposes in the north-east Atlantic. The North Sea ‘stock’, which overwinters along the edge of the Norwegian Trench and spawns off the south coast of Norway, in the Skagerrak, Kattegat and the central North Sea (Hamre, 1980), and the Western ‘stock’, which overwinters and spawns along the edge of the continental shelf from the west of Ireland to the Bay of Biscay (Lockwood, Nichols & Dawson, 1981).

scholarly journals Opportunistically recorded acoustic data support Northeast Atlantic mackerel expansion theory

2015 ◽  
Vol 73 (4) ◽  
pp. 1115-1126 ◽  
Author(s):  
Jeroen van der Kooij ◽  
Sascha M.M. Fässler ◽  
David Stephens ◽  
Lisa Readdy ◽  
Beth E. Scott ◽  
...  
Keyword(s):  
North Sea ◽  
Stock Assessment ◽  
Detection Algorithm ◽  
Trawl Survey ◽  
Northeast Atlantic ◽  
Acoustic Data ◽  
The North ◽  
The North Sea ◽  
Northern North Sea ◽  
Feeding Grounds

Abstract Fisheries independent monitoring of widely distributed pelagic fish species which conduct large seasonal migrations is logistically complex and expensive. One of the commercially most important examples of such a species in the Northeast Atlantic Ocean is mackerel for which up to recently only an international triennial egg survey contributed to the stock assessment. In this study, we explore whether fisheries acoustic data, recorded opportunistically during the English component of the North Sea International Bottom Trawl Survey, can contribute to an improved understanding of mackerel distribution and provide supplementary data to existing dedicated monitoring surveys. Using a previously published multifrequency acoustic mackerel detection algorithm, we extracted the distribution and abundance of schooling mackerel for the whole of the North Sea during August and September between 2007 and 2013. The spatio-temporal coverage of this unique dataset is of particular interest because it includes part of the unsurveyed summer mackerel feeding grounds in the northern North Sea. Recent increases in landings in Icelandic waters during this season suggested that changes have occurred in the mackerel feeding distribution. Thus far it is poorly understood whether these changes are due to a shift, i.e. mackerel moving away from their traditional feeding grounds in the northern North Sea and southern Norwegian Sea, or whether the species' distribution has expanded. We therefore explored whether acoustically derived biomass of schooling mackerel declined in the northern North Sea during the study period, which would suggest a shift in mackerel distribution rather than an expansion. The results of this study show that in the North Sea, schooling mackerel abundance has increased and that its distribution in this area has not changed over this period. Both of these findings provide, to our knowledge, the first evidence in support of the hypothesis that mackerel have expanded their distribution rather than moved away.

scholarly journals Inaccuracies in routinely collected Atlantic herring (Clupea harengus) maturity data and correction using a gonadosomatic index model

2011 ◽  
Vol 91 (7) ◽  
pp. 1477-1487 ◽  
Author(s):  
Lindsay R. McPherson ◽  
Konstantinos Ganias ◽  
C. Tara Marshall
Keyword(s):  
North Sea ◽  
Low Cost ◽  
Gonadosomatic Index ◽  
Clupea Harengus ◽  
Implicit Assumption ◽  
Multinomial Regression ◽  
Index Model ◽  
The North ◽  
Spawning Stock ◽  
The North Sea

Macroscopic maturity staging data are widely used to distinguish between reproductive and non-reproductive individuals. The implicit assumption is that these data are accurate. The accuracy of macroscopic maturity staging of North Sea herring (Clupea harengus) has not been checked since the macroscopic scale was produced in 1961. The aim of this study was to assess the accuracy of macroscopic maturity staging of female North Sea herring by comparison to histological staging and the gonadosomatic index (GSI). Ovary samples were collected during the North Sea Herring Acoustic Survey in 2006 on-board FRV ‘Scotia’ (Scotland) and in 2007 on-board FRV ‘Scotia’ and RV ‘Johan Hjort’ (Norway). Commercial samples were also collected by Marine Scotland, Aberdeen in both years. The maturity staging error was relatively low in 2006 (21% error) but was much higher on-board FRV ‘Scotia’ (57%) and RV ‘Johan Hjort’ (47%) in 2007. There was estimated to be a 27% under-estimation of the spawning stock biomass (SSB) in 2007 due to the differences in the proportion mature but no change in SSB estimates in 2006. GSI cut-off scores, estimated by means of multinomial regression models were successfully able to separate immature females from both mature-active and recovering females; however, there was some overlap between the mature-active and recovering individuals. We conclude that an effective and low-cost means of reducing error in herring maturity studies is the combined use of a four-point macroscopic maturity scale with routinely collected GSI data, the latter acting to validate and fine tune macroscopic staging.

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.

scholarly journals Modelling combined harvest and effort regulations: the case of the Dutch beam trawl fishery for plaice and sole in the North Sea

2008 ◽  
Vol 65 (6) ◽  
pp. 822-831 ◽  
Author(s):  
A. Hoff ◽  
H. Frost
Keyword(s):  
North Sea ◽  
Stock Assessment ◽  
Beam Trawl ◽  
Trawl Fishery ◽  
The North ◽  
Feedback Model ◽  
Economic Operation ◽  
The North Sea ◽  
Fishing Fleets ◽  
Fleet Dynamics

Abstract Hoff, A. and Frost, H. 2008. Modelling combined harvest and effort regulations: the case of the Dutch beam trawl fishery for plaice and sole in the North Sea. – ICES Journal of Marine Science, 65: 822–831. Currently, several European fishing fleets are regulated through a combination of harvest and effort control. The two regulation schemes are interrelated, i.e. a given quota limit will necessarily determine the effort used, and vice versa. It is important to acknowledge this causality when assessing combined effort and harvest regulation systems. A bioeconomic feedback model is presented that takes into account the causality between effort and harvest control by switching back and forth between the two, depending on which is the binding rule. The model consists of a biological and an economic operation module, the former simulating stock assessment and quota establishment, and the latter simulating the economic fleet dynamics. When harvest control is binding, catch is evaluated using the biological projection formula, whereas the economics-based Cobb–Douglas production function is used when effort is binding. The method is applied to the Dutch beam trawl fishery for plaice and sole in the North Sea.

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.

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