DATA REQUESTED BY THE MULTISPECIES WORKING GROUP .1 Mackerel

The catch of mackerel belonging to the North Sea stock has been included in the catches of the western stock since 1987.

While the total catch of mackerel in Sub-area IV declined in 1996 (206,675 tonnes) compared with 1995 (317,806 tonnes) no notable changes have taken place in the fishery in Division ilia in 1996 (6,164 tonnes) compared with 1995 (5,756 tonnes). Results of egg surveys carried out in 1996 (ICES 19971H:4) confimjed that t..lte stock is close to all historic.:.^l1y,IO'1.'/ level. The total catch of Nor-b' Sea stOCk IJI..ackerel was again assumed to be 10,000 tonnes or 4.7% of the tot~l 1996 catch.

12.1.1 Catch in numbers at age by quarter for the North Sea mackerel stock

The total catch in numbers of the North Sea stock for 1996. was calculated assuming a North Sea stock component of 10,000 tonnes and a mean weight in the catch equal to that ·of mackerel in Sub-area IV and Division IlIa (Tables 2.8 and 2.12) with additional mean weight at age data in the 2nd and 3rd quarter (Sub-area IV and Division IlIa) obtained from the 1996 egg survey (Table 12.1). The catch in numbers was partitioned across quarters in the same proportions observed for mackerel in Sub-area IV and Division ilia, and across ages using the proportion at age observed in samples taken during the 1996 egg survey (Table 12.2).

12.1.2 Weight at age in the stock

Ne\v data from egg su..-rveys (ICES 1997lH:4) on "Neight at age in t.lte stock for t.lte second and t.h.ird qua...rt..er ef 1996 ~e,pr~sente~ (Table 12.1): Remaining data are given in 1997 (ICES 1997!Assess:3).

12.1.3 Stock distribution by quarter

Although there appears to be some evidence suggesting a change in the distribution of mackerel in the North Sea, the working group did not have sufficient information to justify altering the distributions presented (Table 12.3) in previous reports (ICES 1997/Assess:3).

12.2 Horse Mackerel

12.2.1 Catch in numbers and weight at age by quarter for the North Sea horse mackerel stock

Since 1995 t.1te proportion of North Sea horse mackerel taken for human COIlSu..~ption has risen above 70%.

De-tails oft.l].e catch in nunlbe-rs a.'ld t..he· weight at age a.Te-given in Table 5.3.1.

12.2.2 Stock distribntion by quarter

The North Sea Horse Mackerel stock are known to migrate south to the Channel during the 4th quarter and to be back in the North Sea by the 2nd quarter of each year. The Working Group therefore considers that 50% and 10

% of the stock are in the North Sea during the 4th and 1st quarter respectively.

There is still no information about the numbers of western horse mackerel which migrate into the northern North Sea during the 3rd and 4th quarters of the year. From 1982 to 1986 catches of horse mackerel in Division IVa were low «1,000 tonnes) indicating very little migration. However, since then catches have increased to a maximu.--n of 113,OOOt in 1990, wbich was about 30% of ^Li;.c total western stock catch. Since 1994 catches rUive declined and in 1996 the provisional catch in Division IVa ,vas about 18,000 t (Table 4.3.1) or 4.6% oft.l:le total western stock catch.

Due to decreasing catches by Norway in Division IV a and a reduction in the modelled inflow of Atlantic water to the North Sea in 1996 (Iversen et al. WO 1997) the Working Group considers that 10% of the adult stock of the Western Horse Mackerel is available in Division IVa in the forth quarter, and 1 % in the fIrst quarters of the year (Table 12.4).

The Working Group noted the termination of the Multispecies Working Group in 1997.

E:IACFM\WGMHSA98\REPORT98.DOC 13/09/97

367

Table 12.1

Age I

Wt(g)117

Table 12.2

North Sea Mackerel: Mean weight at age (g) in 2nd and 3rdquarter of 1996 inStib:area N and Division IlIa.

2 3 4 S 6 7 8 9 10 11 12 13 14 IS+

194 . 333 456 469 41S 547' 600 630 650 642 680 673

Estimated catch.i1t numbers ('000) of N

Ortb

Sea mackerel stock in .1989-1986 by quarter, (This table is on the following page)

Table 12.3 Percentage of each mackerel stock assumed to be present in the North Sea, by quarter, in 1996.

North.SeaStock (%) Western Stock (%)

Quarrer . I 2 3 4

r

^{I 2 3 4}

I 100 100 100 100

I

^{20 30 30}

2 80 100 100 80 10 10 50 70

>2 90 100 SO 70 10 + 50 70

Tabie i2.4 Percentage of each hors~ mackerei stock

assumed

^{to be} present in the North Sea,'-by qoaIter. iri .'i9'Sl6.

North Sea Stock (%) Western Stock (%)

Q\l~r 1 2 3 4 1 2 3, 4

1-4 10 100 100 SO 0 0 0 0

S+ 10 100 100 50 1 0 0 10

E:\ACFM\ WGMHSA98\REPORT9KDOC 13109197 368

w

'"

'0

Table U.2 Estimated cateh in numbers ('000) of North Sea mack"rei (Sub-area

rv

and Division

mal by

quarter, 1989 -1996.

1989 ...2'1 92 03 .",0,,4_-;;_

e;\acfm\wQlmhlla98\ T -12-2.xls

~

13 : REQUEST FROM

THE

MACKERELIHORSE MACKEREL EGG SURVEY WORKING 'GROUP

13.1 Sampling for Maturity during Egg Surveys in 1998

The Mackerel/Horse Mackerel Egg Survey Working Group requested information on the distribution of 1, 2 and 3 year oid mackerel

ana

horse mackerel to be made available to this Working Group (ICJ:iS 1997/H:4). At this meeting charts should be made, which show where trawl hauls should be distributed over the egg survey area and the juvenile area for sampling fish for constructing maturity ogives based on histological analysis of the ovaries, because of uncertainties in the proportion mature of especially the younger age groups (see Section 1.4).

Based on: 'available

Ih.tii

on t.l!e distribution of eggs and

on-the

presented information on-the distribution of 1, 2 and 3 yeai old fish the following Si:lmpling scheme was accepted_ Half of t1!e tot~l sa.rnples per species should be collected: relatively close to the edge of the continental shelf, while the sampling was chosen to reflect the distribution of adultS (based on egg distribution). The other half of the samples should be taken in shallower water where relatively more juveniles are present and the sampling was chosen to reflect the distribution of the I, 2 and 3 year olds.

For mackerel a minimum of 20 samples of 100 fish eacb should be collected distributed over the western and southern area. For horse mackerel 14 samples of 100 fish each should be taken in the western and another 14 in the southern area (ICES 19971H:4). The scheme below is made for sampling in the western and southern area, and in the adult and juvenile area around peak spaWning time. Communications between countries I cruise leaders remain necessary to obtain this sampling scheme:

MACKEREL . HORSE MACKEREL

AREA Adult Juvenile AREA Adult Juvenile

.

Western 8 7 Western 7 7

I

~_

...

~_ _~

, I

^~_

... __

~ ~

I ...

^{vuu, .... J.1l ~ J}

I'

~V_U.L11vlll

, ,

Figures 13.1 and 13.2 show the charts where the trawl bauls should approximately be taken.

E:\ACFM\WGMHSA98\REPORT98.DOC 07110/97 12:07 370

ss 15 13 11 68

rn

66 65 64 63

S2

61 60

69 58

I

57 55 55 64 63 52 51 50 4,9 48 47 46

45 44

43 42 41 40 39

38 . S7

·36

~36

9 7 5 3 1 g 1 3 5 7

I I

In document Assess6(2)[1].pdf (6.558Mb) (sider 195-199)