Recent trends in the abundance of plaice Pleuronectes platessa and cod Gadus morhua in shallow coastal waters of the Northeastern Atlantic continental shelf – a review

Figures & data

Figure 1. Locations of the studies on trends in abundance of plaice and cod on the northeastern continental shelf. Numbers refer to studies listed in Tables I and II.

Table I. Trends and potential causes of changes observed in plaice abundance in various areas of the Bay of Biscay, North Sea and Skagerrak/Kattegat.

Area	Years of data	Trend	Identified or hypothesized cause	Reference
Bay of Biscay
Shallow, coastal
1 Bay of Vilaine, eastern shelf	1981–2001	↓ since 1990s	Increasing winter temperatures	Désaunay et al. (2006)
Deep, offshore
2 Eastern shelf	1987–2006	↓ since 1995	Recruitment failure related to temperature Amplification by fishing	Hermant et al. (2010)
North Sea
Shallow, coastal
3 Continental coast	1902–1909 1983–1987 1999–2003	↓ since 1983	Temperature in summer exceeding tolerance Increasing food requirements related to increased temperature Decrease in benthic productivity, e.g. Limecola balthica (Linnaeus, 1758)	van Keeken et al. (2007) Teal & van Keeken (2011)
4 Continental coast Wadden Sea	1970–2006	↓ since 1985	Increasing temperature (coast only) Oligotrophication, decreasing productivity Fishing on benthic prey, food reduction Increased predation Combination of factors, bioenergetics	Tulp et al. (2008), Tulp & Bolle (2009), Bolle et al. (2009a)
5 Wadden Sea (intertidal)	1975–2007	↓ since 1990s	Unexplained reduction in nursery function Decrease in offshore recruitment Interspecific competition	van der Veer et al. (2010, 2011)
Deep, offshore
6 Entire	1974–2006	↓ 1990	Not identified	Rijnsdorp et al. (2010)
7 East–central	1913–2007	↓ 1990–2000s	Temperature and climate effects Decreased productivity, prey resources Habitat modification (closure of nursery grounds)	Engelhard et al. (2011)
8 Central	2000–2006	↓ since 2000	Not identified	Poos et al. (2013)
Skagerrak/Kattegat
Shallow, coastal
9 Kattegat Belt Sea	1904–2007	No trend identified		Sparrevohn et al. (2013)
Deep, offshore
10 Skagerrak Eastern Kattegat	1901–2007	↓ since 1970, ↑ during 2000s	Increasing fishing mortality	Cardinale et al. (2010)
11 Danish Skagerrak Swedish Skagerrak SW Kattegat Swedish SE Kattegat	1901–2007	↓ since mid 1970s, ↑ during 2000s in Danish Skagerrak and SW Kattegat	Prolonged overexploitation Eradication of spawning aggregations	Cardinale et al. (2011)
12 Kattegat/Skagerrak	2002–2010	↓ since 2002 ↑ since 2007 in Skagerrak	No explanation	Ulrich et al. (2013)

Note: Downward arrow indicates decline, upward arrow indicates increase in abundance of plaice. Numbers in first column refer to the location of the study in Figure 1.

Table II. Trends and potential causes of changes observed in cod abundance in various areas of the North Sea and the Skagerrak/Kattegat.

Area	Years of data	Trend	Identified or hypothesized cause	Reference
North Sea
Shallow, coastal
13 British east coast	1983–2005	↓ since 1983	Environmental changes Fishing pressure	Holmes et al. (2008)
14 Continental coast	1971–2010	↓ since 1993	Predation by/competition with herring Temperature effects on recruitment	Hjermann et al. (2013)
4 Continental coast Wadden Sea	1970–2006	↓ since 1980s ↑ since 1995 in coastal zone	Seal predation Prey removal by beam trawl fishery Oligotrophication, reduced food Decreased cod recruitment offshore	Tulp et al. (2008); Tulp & Bolle (2009)
Deep, offshore
15 Entire	1970–2003	↓ since mid 1980s	Overfishing Temperature effects on production and recruitment	Brander (2007)
16 Entire	1983–2005	↓ since 1983	Environmental changes Fishing pressure	Holmes et al. (2008)
17 Entire	1929–1999	↓ since mid 1980s	Not identified	Lescrauwaet et al. (2010)
6 Entire	1973–2005	↓ since mid 1980s	Increased fishing effort Temperature/food effects on recruitment	Rijnsdorp et al. (2010)
Skagerrak/Kattegat
Shallow, coastal
18 Eastern Skagerrak	1968–1980 1975–1999 2000–2001	↓ since 2000	Increased fishery exploitation Lacking recruitment offshore	Svedäng (2003)
19 Inshore Skagerrak/inshore Kattegat	1955–1997/ 1975–1999	↓ since 1970s	Exploitation of local stocks and disappearance of spawning aggregations Variable recruitment from North Sea	Svedäng & Bardon (2003)
Deep, offshore
20 Eastern Skagerrak Eastern Kattegat	1978–1999	↓ since 1982 ↓ since 1978	High fishing pressure	Svedäng & Bardon (2003) Cardinale & Svedäng (2004)
21 Kattegat/Öresund	1981–2008 1981–2000, 2004–2008	↓ since 1981	High fishing pressure	Svedäng et al. (2010)
22 Skagerrak/Eastern Kattegat	1907–2007	↓ since 1980s ↑ since 1998	Fishery exploitation	Bartolino et al. (2012)

Note: Downward arrow indicates decline, upward arrow indicates increase in abundance of cod. Numbers refer to the location of the study in Figure 1.

Figure 2. Spawning stock biomass estimates from standard assessment (ICES 2015). (a) Estimates for plaice in the North Sea during 1963–2013. (b) Estimates for cod in the North Sea and Skagerrak/Kattegat for the years 1963–2014.

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