Long-term trends in the trophic structure of the North Sea fish community: evidence from stable-isotope analysis, size-spectra and community metrics

Abstract We investigate changes in the North Sea fish community with particular reference to possible indirect effects of fishing, mediated through the ecosystem. In the past, long-term changes in the slope of size spectra of research vessel catches have been related to changes in fishing effort, but such changes may simply reflect the cumulative, direct effects of fishing through selective removal of large individuals. If there is resilience in a fish community towards fishing, we may expect increases in specific components, for instance as a consequence of an associated reduction in predation and/or competition. We show on the basis of three long-term trawl surveys that abundance of small fish (all species) as well as abundance of demersal species with a low maximum length (Lmax) have steadily and significantly increased in absolute numbers over large parts of the North Sea during the last 30 years. Taking average fishing mortality of assessed commercial species as an index of exploitation rate of the fish community, it appears that fishing effort reached its maximum in the mid-1980s and has declined slightly since. If the observed changes in the community are caused by indirect effects of fishing, there must be a considerable delay in response time, because the observed changes generally proceed up to recent years, although both size and Lmax spectra suggest some levelling off, or even recovery in one of the surveys. Indeed, significant correlations between all community metrics and exploitation rate were obtained only if time lags ≥6 years were introduced.

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Comparing conceptual frameworks for a fish community MSY (FCMSY) using management strategy evaluation—an example from the North Sea

ICES Journal of Marine Science ◽

10.1093/icesjms/fsz015 ◽

2019 ◽

Vol 76 (4) ◽

pp. 813-823 ◽

Cited By ~ 3

Author(s):

Robert B Thorpe ◽

José A A De Oliveira

Keyword(s):

North Sea ◽

Management Strategy ◽

Fish Community ◽

Parameter Uncertainties ◽

Management Strategy Evaluation ◽

The North ◽

Strategy Evaluation ◽

The North Sea ◽

Definition Of

Abstract Maximum sustainable yield (MSY) is a well-established concept that is mandated by legislation, and has a clear theoretical meaning in terms of a single stock. However, its definition is problematic in a multispecies setting, which makes it more difficult to apply the MSY principle. In this study of the North Sea fish community, we consider several possible MSY candidates, and evaluate them in terms of their ability to produce optimum long-term yield whilst avoiding unacceptable risk of stock impairment. We perform this evaluation with an ensemble of size-structured models using a management strategy evaluation approach, in which harvest control rules (HCRs) are used to determine levels of fishing as a function of the proposed MSY target and stock status, taking account of recruitment and model parameter uncertainties. We find that HCRs of the type considered here are always useful in the scenarios we tested, as they reduce overfishing risk much more than average long-term yield. This is independent of the precise form of the HCR, so it is more important to implement one rigorously than obsess over the rule details. For a lax definition of overfishing, which accepts relatively severe stock depletion (B < 10% B0), and using HCRs, risks are “low” across all strategies, and the Nash equilibrium is the best performing MSY approach considered here. For more stringent definitions of “at risk” (e.g. likelihood of B < 20% of B0), the application of HCRs can allow a range of alternative formulations of MSY. Thus, the definition of MSY may be sensitive to judgements about acceptable levels of risk, and consistent application of a sensible management framework may be more important than developing the best possible theoretical definition of MSY.

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Long-term trends in the distribution, abundance and seasonal occurrence of larvae of mackerel (Scomber scombrus L.) around the British Isles, 1948–1978

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s0025315400046993 ◽

1981 ◽

Vol 61 (2) ◽

pp. 343-358 ◽

Cited By ~ 6

Author(s):

S. H. Coombs ◽

C. E. Mitchell

Keyword(s):

Surface Temperature ◽

North Sea ◽

Sea Surface ◽

Seasonal Occurrence ◽

British Isles ◽

Scomber Scombrus ◽

The North ◽

The North Sea ◽

Long Term Trends

The distribution, abundance and seasonal occurrence of larvae of mackerel (Scomber scombrus L.) are described from routine Continuous Plankton Recorder (CPR) sampling around the British Isles over the period 1948–78, and from more intensive CPR sampling in the Celtic Sea in 1977. There were two main areas of larval concentration: in the North Sea and over and adjacent to the Celtic Plateau; subsidiary aggregations were observed to the northwest of Ireland and to the west of Norway. There were some similarities between the distribution of larvae around the British Isles and that of adult Calanus spp. In the North Sea there was a southerly shift of larval distribution over the period 1948–77; over a similar period the abundance of larvae increased to reach high numbers by the late 1950s and subsequently declined after the mid-6os. To the south-west of the British Isles numbers of larvae showed a long-term decline. The long-term trends of distribution and abundance are discussed in relation to concurrent biological and environmental change. The clearest relationship was found between the numbers of mackerel larvae in the North Sea and sea-surface temperature in the North Atlantic, which suggests a common causative agent for both sets of observations; also, there was a weak relationship with both spawning stock biomass and sea-surface temperature at the spawning areas. In the North Sea the seasonal occurrence of larvae was from May to August, the majority being taken in June and July; over the period 1948–77 the seasonal time of occurrence of highest numbers of larvae has remained relatively constant. In the Celtic Sea the seasonal occurrence of larvae was spread over a longer period, from March to August, with relatively high numbers from March to June; over the period 1950–78 the time of occurrence has been variable, possibly with a tendency towards later timing in more recent years.

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Long Term Trends in the Occurrence of Phaeocystis Sp. in the North-East Atlantic

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s0025315400032185 ◽

1989 ◽

Vol 69 (4) ◽

pp. 813-821 ◽

Cited By ~ 35

Author(s):

N.J.P. Owens ◽

D. Cook ◽

M. Colebrook ◽

H. Hunt ◽

P.C. Reid

Keyword(s):

North Sea ◽

Plant Biomass ◽

Nitrogen And Phosphorus ◽

Sulphur Compounds ◽

North East ◽

The North ◽

The North Sea ◽

Long Term Trends ◽

Flagellate Algae

The effects of nutrient enrichment of natural water bodies range from small increases in plant biomass and production, to gross deterioration of water quality. The input of nutrients (e.g. nitrogen and phosphorus) to the sea off NW Europe (especially the North Sea) has increased dramatically over the last three or four decades (Folkard & Jones, 1974; Bennekom et al., 1975; Postma, 1978; Cadee, 1986a) but there is uncertainty about the effects on the ecosystem. One possible effect might be to induce changes in the phytoplankton community. Such an effect has been reported for the North Sea, where increases in flagellate algae have been observed (Gieskes & Kraay, 1977; Postma, 1985; Cadee, 1986b; Batje & Michaelis, 1986). Phaeocystis is one such alga, and its purported involvement in the formation of large quantities of foam, observed on European beaches (Batje & Michaelis, 1986; Weisse et al, 1986), together with evidence that the alga is a source of atmospheric sulphur compounds (Barnard et al, 1984) (with implications for atmospheric acidity), has attracted particular attention and concern

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Modelling the direct impact of bottom trawling on the North Sea fish community to derive estimates of fishing mortality for non-target fish species

ICES Journal of Marine Science ◽

10.1093/icesjms/fsp162 ◽

2009 ◽

Vol 66 (9) ◽

pp. 1985-1998 ◽

Cited By ~ 32

Author(s):

G. J. Piet ◽

R. van Hal ◽

S. P. R. Greenstreet

Keyword(s):

North Sea ◽

Fish Species ◽

Fish Community ◽

Direct Impact ◽

Fishing Mortality ◽

Bottom Trawling ◽

The North ◽

Target Fish ◽

The North Sea ◽

Sea Fish

Abstract Piet, G. J., van Hal, R., and Greenstreet, S. P. R. 2009. Modelling the direct impact of bottom trawling on the North Sea fish community to derive estimates of fishing mortality for non-target fish species. – ICES Journal of Marine Science, 66: 1985–1998. This study introduces a spatially explicit model that combines abundance data for all the main fish species in the demersal North Sea fish community with international effort data and estimates of gear-, species-, and size-dependent catch efficiency to determine the mortality of non-target fish species caused by bottom trawl fisheries and its spatial variation. Where necessary information was lacking, assumptions were made, and a sensitivity analysis performed to examine the impact of these issues on model results. Model outcomes were validated using international landings and discard data for five target species: cod, haddock, whiting, sole, and plaice. This showed that depending on its configuration, the model could reproduce recorded landings and discards of these species reasonably well. This suggests that the model could be used to simulate rates of fishing mortality for non-target fish species, for which few data are currently available. Sensitivity analyses revealed that model outcomes were most strongly influenced by the estimates of gear catch efficiency and the extent to which the distributions of fishing effort and each species overlapped. Better data for these processes would enhance the contribution that this type of model could make in supporting an ecosystem approach to fisheries management.

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Development of the EcoQO for the North Sea fish community

ICES Journal of Marine Science ◽

10.1093/icesjms/fsq156 ◽

2010 ◽

Vol 68 (1) ◽

pp. 1-11 ◽

Cited By ~ 87

Author(s):

Simon P. R. Greenstreet ◽

Stuart I. Rogers ◽

Jake C. Rice ◽

Gerjan J. Piet ◽

Emma J. Guirey ◽

...

Keyword(s):

North Sea ◽

Fish Community ◽

Environmental Influence ◽

Fish Stock ◽

Fishing Pressure ◽

Stock Management ◽

The North ◽

A Value ◽

The North Sea ◽

Sea Fish

Abstract Greenstreet, S. P. R., Rogers, S. I., Rice, J. C., Piet, G. J., Guirey, E. J., Fraser, H. M., and Fryer, R. J. 2011. Development of the EcoQO for the North Sea fish community. – ICES Journal of Marine Science, 68: 1–11. Development of the Ecological Quality Objective (EcoQO) for the North Sea demersal fish community is described. Size-based metrics were identified as the most effective indicators of the state of the community, but such metrics are also sensitive to environmental influence. Redefining the large fish indicator (LFI) produced a metric more sensitive to fishing-induced change and therefore more useful to managers. Fish stocks were thought to be exploited at a sustainable rate in the early 1980s, so in a process echoing the precautionary approach to fish stock management, this was considered the reference period for the LFI, suggesting a value of 0.3 as the appropriate EcoQO. The LFI declined from around 0.3 in 1983 to 0.05 in 2001, followed by a recovery to 0.22 in 2008. However, analyses of the longer-term groundfish survey data suggest that, even were fishing pressure to be reduced to early 20th century levels, the LFI would be unlikely to rise much above a value of 0.3. The response of the LFI to variation in fishing pressure suggested a more complex relationship than anticipated, underscoring the need for operational theoretical size-resolved multispecies fish community models to support management towards broader ecosystem objectives.

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Long-term trends in pelagic fish stocks of the North Sea and adjacent waters and their possible connection to hydrographic changes

Netherlands Journal of Sea Research ◽

10.1016/0077-7579(90)90024-b ◽

1990 ◽

Vol 25 (1-2) ◽

pp. 227-235 ◽

Cited By ~ 35

Author(s):

A. Corten

Keyword(s):

North Sea ◽

Pelagic Fish ◽

Fish Stocks ◽

The North ◽

The North Sea ◽

Long Term Trends

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Modelling the effects of fishing on the North Sea fish community size composition

Ecological Modelling ◽

10.1016/j.ecolmodel.2015.10.032 ◽

2016 ◽

Vol 321 ◽

pp. 35-45 ◽

Cited By ~ 4

Author(s):

Douglas C. Speirs ◽

Simon P.R. Greenstreet ◽

Michael R. Heath

Keyword(s):

North Sea ◽

Fish Community ◽

Size Composition ◽

Community Size ◽

The North ◽

The North Sea ◽

Sea Fish

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Trends in Daily Rainfall Intensity Over Israel 1950/1-2003/4

The Open Atmospheric Science Journal ◽

10.2174/1874282300903010196 ◽

2009 ◽

Vol 3 (1) ◽

pp. 196-203 ◽

Cited By ~ 22

Author(s):

Yizhak Yosef ◽

Hadas Saaroni ◽

Pinhas Alpert

Keyword(s):

Rainfall Intensity ◽

Daily Rainfall ◽

Water Shortage ◽

East Atlantic ◽

Teleconnection Patterns ◽

The North ◽

Rainfall Trends ◽

The North Sea ◽

Long Term Trends

The study focuses on long-term trends of daily rainfall in Israel as a function of their intensity in order to identify potential trends in rainfall extremity. The study period is the rainy season, October-May between 1950/1 and 2003/4. For the total rainfall, an increased trend is shown across Israel, especially for the central and southern regions, though non-significant. Daily rainfall intensity showed non-significant trends of increase in the heavy rainfall at the center and south and decrease at the north. The light to moderate rainfall trends increased in the north while they decreased at the center and south. Trends are significantly correlated with known teleconnection patterns, especially the East Atlantic- Western Russia and the North Sea-Caspian Sea patterns. Positive trends toward heavier rainfall are noted in Israel, which are significant in several specific locations. This finding has to be carefully followed since the region is a climatic border subjected to severe water shortage and is predicted to dry-up in most global warming scenarios.

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