Agenda Item 8
Paper 8.1
For Discussion
Mortality Trends in the North East Atlantic
Extract from ICES Advice 2011
1.6
General trends in the Northeast Atlantic
As an indication of the general trend of fish stocks in the Northeast Atlantic,the overall trend in the 46so-called “data
rich” stocks assessed by ICES,is considered (Figure 1.6.1). “Data rich” means in this case that there are longtime series
available of fishing mortality, F, and of spawning stock biomass (SSB), and that Fmsy is defined. The landings from
them was 5.5million t compared to a total catch of fish in the Northeast Atlantic of 8.3 million tin 2010(2011 landings
statistics were not yet available from Eurostat in December 2012).The stocks were grouped into categories: benthic
(megrim, plaice, and sole), demersal (cod, haddock, whiting, and saithe) and pelagic (blue whiting,herring, horse
mackerel, and mackerel). Figure 1.6.2 shows the number of stocks within each category by year.
For each category of stocks the fraction of stocks having Fbelow Fmsyin a given year is shown in Figure 1.6.3.Ideally,
about 50% of the stocks should have F below Fmsy and 50% F above Fmsy in a given year,if the stocks are managed at
a target fishing mortality of Fmsy. This is seen to be the case only for the pelagic stocks and only if the periods 19701977 and 1995-2004 are disregarded. The benthic and demersal stocks have been overexploited in the entire time
period. However, some improvements are apparent in recent years and in 2011 the demersal stocks reached the situation
where 50% were above and 50% below.
The trend in fishing mortality over time is illustrated in Figure 1.6.4. It can be seen that F for benthic stocks gradually
increased over time until about year 2000 and have since reduced substantially. For demersal stocks the increase was
steeper in the beginning of the time period, peaked around year 2000 and has reduced since. The pelagic stocks have
had a very different development over time. F increased significantly in the late 1960s and early 1970s. This resulted in
the well known collapse of several important herring and mackerel stocks. Since then, F has been quite low and stable
and like for the other two types of stocks, has decreased since year 2000.
For a subset of these stocks also the SSB reference point MSY-Btrigger has been defined. Figure 1.6.5 shows the
present situation (using F and SSB in 2011) in terms of stockstatus above or below this reference point and Fmsy. It can
be seen that there are still several benthic and demersal stocks in the undesirable upper left corner of the plot, while the
pelagic stocks are all more or less in a desirable area.
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Time series length (in years) by stock
Cod in Subdivisions 22 - 24
Cod in Subdivisions 25 - 32
Cod in Subarea IV (North Sea), Divison VIId (Eastern Channel) and IIIa West (Skagerrak)
Cod in Divisions VIIe-k (Celtic Sea cod)
Cod in Subareas I and II (Northeast Arctic cod)
Cod in Subdivision Vb1 (Faroe Plateau)
Cod in Division VIIa (Irish Sea)
Cod in Division VIa (West of Scotland)
Haddock in Subarea IV (North Sea) and Division IIIa West (Skagerrak)
Haddock in Subareas I and II (Northeast Arctic)
Haddock in Division Vb
Haddock in Division Va (Icelandic haddock)
Haddock in Division VIb (Rockall)
Haddock in Division VIa (West of Scotland)
Herring in Subdivisions 25 - 29 (minus Gulf of Riga) and 32
Herring in Subdivision 30 (Bothnian Sea)
Herring in Division IIIa and Subdivisions 22 - 24 (Western Baltic spring spawners)
Herring in Subarea IV and Divisions IIIa and VIId (North Sea autumn spawners)
Herring in Division VIIa South of 52° 30’ N and VIIg,h,j,k (Celtic Sea and South of Ireland)
Herring in Division VIIa North of 52° 30’ N (Irish Sea)
Herring in the Northeast Atlantic (Norwegian spring-spawning herring)
Herring in Subdivision 28.1 (Gulf of Riga)
Herring in Division Va (Icelandic summer-spawners)
Herring in Division VIa (North)
Hake in Division IIIa, Subareas IV, VI and VII and Divisions VIIIa,b,d (Northern stock)
Hake in Division VIIIc and IXa (Southern stock)
Horse mackerel (Trachurus trachurus) in Divisions IIa, IVa, Vb, VIa,, VIIa-c, e-k, VIIIa-e (Western stock)
Mackerel in the Northeast Atlantic (combined Southern, Western and North Sea spawning components)
Megrim (Boscii) in Divisions VIIIc and IXa
Megrim (Whiffiagonis) in Divisions VIIIc and IXa
Plaice in Division VIId (Eastern Channel)
Plaice in Division VIIe (Western Channel)
Plaice Sub-area IV (North Sea)
Saithe in Subarea IV (North Sea) Division IIIa West (Skagerrak) and Subarea VI (West of Scotland and Rockall)
Saithe in Division Vb (Faroe Saithe)
Saithe in Division Va (Icelandic saithe)
Sole in Divisions VIIIa,b (Bay of Biscay)
Sole in Divisions VIIf, g (Celtic Sea)
Sole in Division VIId (Eastern Channel)
Sole in Division VIIe (Western Channel)
Sole in Division VIIa (Irish Sea)
Sole in Division IIIa (Skagerrak-Kattegat)
Sole in Sub-area IV (North Sea)
Sprat in Subdivisions 22 - 32 (Baltic Sea)
Blue whiting in Subareas I-IX, XII and XIV (Combined stock)
Whiting in Divisions VIIe-k
0
10
20
30
40
50
60
70
Number of years
Figure 1.6.1
The length of the time series of the various stocks used in the present analysis.
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50
45
40
Number of stocks
35
30
25
Pelagic
Demersal
20
Benthic
15
10
5
0
Figure 1.6.2
200
Number of stocks within each of the categories: benthic, demersal and pelagic stocks.
Accumulative plot.
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201
Figure 1.6.3
202
Fraction of stocks with F below Fmsy.
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0.9
Trends in F
0.8
Fishing mortality
0.7
0.6
0.5
Pelagic
0.4
Demersal
Benthic
0.3
0.2
0.1
0
1950
Figure 1.6.4
1970
1990
2010
2030
Trends in fishing mortality. Mean F by year and type of stock. This plot includes additionaldatarich stocks, which do not have an Fmsy defined: Anchovy in Subarea VIII (Bay of Biscay), Cod in
Division Va (Icelandic cod), Saithe in Subareas I and II (Northeast Arctic) and Sardine in
Divisions VIIIc and IXa.
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Figure 1.6.5
Status of stocks in 2011 in terms of Fin relation to Fmsy and SSB in relation to MSY-Btrigger. Xaxis represents stock size and Y-axis fishing pressure.
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