Changes in the North Sea fish community: evidence of indirect effects of fishing?

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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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 large fish indicator and associated target for a Northeast Atlantic fish community

ICES Journal of Marine Science ◽

10.1093/icesjms/fsu101 ◽

2014 ◽

Vol 71 (9) ◽

pp. 2403-2415 ◽

Cited By ~ 28

Author(s):

Larissa Modica ◽

Francisco Velasco ◽

Izaskun Preciado ◽

Maria Soto ◽

Simon P. R. Greenstreet

Keyword(s):

North Sea ◽

Fish Community ◽

Ecosystem Approach ◽

Time Lags ◽

Bay Of Biscay ◽

Large Fish ◽

Biodiversity Indicator ◽

Eu Member States ◽

The North ◽

The North Sea

AbstractThe large fish indicator (LFI) was developed to support the North Sea fish community Ecological Quality Objective (EcoQO) pilot study, intended to establish an operational ecosystem approach to management. Subsequently, procedures established in the North Sea were applied to the Celtic Sea to derive an LFI and target specific to this region. The Marine Strategy Framework Directive (MSFD) requires EU Member States sharing marine regions to cooperate using the Regional Seas Conventions, and using indicators already adopted by them. The MSFD explicitly suggests the LFI as a foodweb indicator, but it could equally well be used to monitor biodiversity. Here, we apply the established rationale to develop an LFI and target specific to the southern Bay of Biscay. Despite declining in the 1990s, the LFI subsequently recovered to near original values in 2008. Previously, relationships between the LFI and fishing pressure have involved lengthy time-lags. We observe a similar relationship, but with shorter lag. The nature of the larger species responsible for much of the change in the LFI may explain this difference, and might also suggest that, in the Bay of Biscay, the LFI is more appropriately used as a biodiversity indicator, rather than a foodweb indicator.

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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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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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Reconstructing three decades of total international trawling effort in the North Sea

10.5194/essd-2019-90 ◽

2019 ◽

Author(s):

Elena Couce ◽

Michaela Schratzberger ◽

Georg H. Engelhard

Keyword(s):

North Sea ◽

Large Scale ◽

Information Source ◽

Marine Ecosystem ◽

Fishing Effort ◽

Anthropogenic Pressures ◽

The North ◽

The North Sea ◽

Long Term Impact

Abstract. Fishing – especially trawling – is one of the most ubiquitous anthropogenic pressures on marine ecosystems worldwide, yet very few long-term, spatially explicit datasets on trawling effort exist; this greatly hampers our understanding of the medium- to long-term impact of trawling. This important gap is addressed here for the North Sea, a highly productive shelf sea which is also subject to many anthropogenic pressures. For a 31-year time span (1985–2015), we provide a dataset on the spatial distribution of total international otter and beam trawling effort, for all ICES rectangles (0.5° latitude by 1° longitude) of the North Sea. The dataset was largely reconstructed using compiled effort data from 7 fishing effort time-series, each covering shorter time spans and some of the countries fishing the North Sea only. For the years where effort data for particular countries were missing, the series was complemented using estimated (modelled) effort data. This new, long-term and large-scale trawling dataset may serve the wider scientific community, as well as those involved with policy and management, as a valuable information source on fishing pressure in a Large Marine Ecosystem which is heavily impacted, but which simultaneously provides a wealth of ecosystem services to society. The dataset is available on the Cefas Data Hub at: https://doi.org/10.14466/CefasDataHub.61 (Couce et al., 2019).

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

Marine Biology ◽

10.1007/s00227-002-0905-7 ◽

2002 ◽

Vol 141 (6) ◽

pp. 1085-1097 ◽

Cited By ~ 177

Author(s):

Jennings S. ◽

Greenstreet S. ◽

Hill L. ◽

Piet G. ◽

Pinnegar J. ◽

...

Keyword(s):

Fish Community ◽

Trophic Structure ◽

Isotope Analysis ◽

Size Spectra ◽

The North ◽

Community Metrics ◽

The North Sea ◽

Long Term Trends ◽

Sea Fish

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Reconstructing three decades of total international trawling effort in the North Sea

Earth System Science Data ◽

10.5194/essd-12-373-2020 ◽

2020 ◽

Vol 12 (1) ◽

pp. 373-386 ◽

Cited By ~ 3

Author(s):

Elena Couce ◽

Michaela Schratzberger ◽

Georg H. Engelhard

Keyword(s):

North Sea ◽

Large Scale ◽

Information Source ◽

Marine Ecosystem ◽

Fishing Effort ◽

Anthropogenic Pressures ◽

The North ◽

The North Sea ◽

Long Term Impact

Abstract. Fishing – especially trawling – is one of the most ubiquitous anthropogenic pressures on marine ecosystems worldwide, yet very few long-term, spatially explicit datasets on trawling effort exist; this greatly hampers our understanding of the medium- to long-term impact of trawling. This important gap is addressed here for the North Sea, a highly productive shelf sea which is also subject to many anthropogenic pressures. For a 31-year time span (1985–2015), we provide a gridded dataset of the spatial distribution of total international otter and beam trawling effort, with a resolution of 0.5∘ latitude by 1∘ longitude, over the North Sea. The dataset was largely reconstructed using compiled effort data from seven fishing effort time series, each covering shorter time spans and only some of the countries fishing the North Sea. For the years where effort data for particular countries were missing, the series was complemented using estimated (modelled) effort data. This new, long-term and large-scale trawling dataset may serve the wider scientific community, as well as those involved with policy and management, as a valuable information source on fishing pressure in a large marine ecosystem which is heavily impacted but which simultaneously provides a wealth of ecosystem services to society. The dataset is available on the Cefas Data Hub at: https://doi.org/10.14466/CefasDataHub.61, version 2 (Couce et al., 2019).

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