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C.M.1973/J:20Pelagio Fish (southern) Committee

OBSERVATIONS ON THE BIOLOGY OF SOOMBER JAPONICUS

OFF NORTHWEST AFRICA

xBahgat HABASHI and' Jan WOJClECHOWSKI

xAoademy of Agrioulture

Faoulty of Marine Fisheries

ul~Kazimierza Kr61ewioza .3

71-550 SZOZECIN~

POLAND

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Introduction

African mackerel - Scomber japonicus /Scomber collas/,

family Scombridae, i8 of great importanoe in the commercial

catohes off northwest Afr1oa. It smounts nearly to 15 per

cent of the Polish oatches in this area. Duri.og the recent

years, PoliSh trawlers fished 1t mainly off Mauritania and

Senegal ooasts, and small quantities off Spanish Sahara and

Marocco ooasts. Soomber japonicus oceur in the trawl oatclles

throughout the year, but mostly in the period of September ­

Maroh. Diurnal vert10al m1g;-at1ons of the Afr1can mackerel

iDfluenoes the oatches to some extent. The b1ggestones

were noted during the d8y-ti~e near the bottom and 10 the

deeper layers. Our f1shermen use mostly pelagio trawls.

As it 1s observed in the reoent years, oatches of Soomber

japonious fluotuate from year to year. The present status

of knowledge about this speoies does not prov1de an

explanation of this phenomenon.

The present paPer attempis to give aO characteristics of

the composition of the oommerc1al oonoentrations of Soomber

japonious off northwest Afrioa. The authors studied many

phases of lile history and habits of maokerel, whioh had

to be understood in order to interpret the ohanges in

oatohes.

Our observations oonoerned length and age composit1on,

maturity stage and feedlng. The material for this study,

oomprising 26562 specimens of Scomber japonicus, was partly

obtained from commercial catches in the area investigated

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in the 1ears 1970/197'. 'rho majority of 111 stigations

were oarrled out on board of two oommeroial f1sh1:og vessels

within the period Augu.st - Deo mber 1971 and January - May

1973.

Length oompos1t10n

The study' of the length ocmposit10~ i b sed on

measurements of 26562 spaoim ns. Tb length data were

grouped into 1 om /total longth and forle length! aize

groups. The results of thes inv8stigations are presented

in Figu:re 1. The maximum total 1 ngth was 50 om and the

minimum. as 150m. 'rhe length oompo81tion of the mackerel

oatohes var1ed in 4!fferent ar 8 a:od different years.

~ngth class 38-40 om /t.l./ dominated in the catches of

1969-1972, while in the yaar 19'73 the 30 cm length olass

preva1led. Th1s differenoe may be conneoted w1th the faot

that in 1973 the majority of the Poliah catohes was carried

off the Span1sh Sahara, while in the years 1969-1972 on the

Mauritania ahelf.

Por exampla t maokerel length of 38-40 om dominated in

the oatohes off Senegal and Mauritania, while in the area

of Span1sh Sahara and Marocoo - maokerel length of 25-30 cm

preva11ed~

The presenoe of some seasonal ohanges in the length

oompos1tion of Scomber japonious was observed. During the

. spawning time /December - April/, the larger fishes prevailed

in the oatcheSt when in other seasonS t smaller ones.

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- ~ -This peoies spawn in the inter time in the !nshON

grounds. After spavming it probably migrate towards the

open sea to the f'eeding areas. Smaller f'ishes probably do

not undertake the large di tanoe migration.

It must be noted here that t Oepth of' the ater also

has some tteot on the length oompo 1tion or the eatohes.

Allour oat he W 1'0 at the depth tram 50 to 250 matres.

Pelagte trawl t kat f' sh trom surfao to the botto •

In the day-time fisbing takes p ee near the bottom as

00 pared with neal'-surtaoe oatchea in the night time. It was

observed, the sp otmen "tdth length above 25 em made ve1!3

distinot diurnal ertical migrations. Smaller one8 live

rather ne to t bottom. This i8 probabl,. oonneoted with

the teediDg habits or larger and smaller rishes. Generall,.

emall r fishe were 0 ught at larger depths than th larger

olies.

The to~l length/tork length relationsh1p of' Scomber

japonicus 1s g1ven in the J'igure 2. No signitioant difterenoe

between the length ot males aDd temales was f'ound•

Age and grt\wth

Observations on the age oanposition 01' the catohes are

based on ageing of 3544 pairs of' otoliths oollected in the

years 197 -1972. Allotoliths were immersed in olearing

agent such as glycerine, xylol or water end tbe readings

were made against a black back-ground. In some otoliths

hyaline and opaque zones can be seen clearly around the

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whole otolith. They can b di t· gu had r a binoc

mioroscope by altering the degrae of hadiDg.

Ou.r investigations show that hyaline zones ware formed

mostly in the per10d of s e~ and opaqu zones in winter

time. It ooino1des probably wi h f diDg and apawniDg

seaSODS respeot1vely. Diffioulti iDt rpratatio f the

zones of the otol~ths are caus d by h format

bands, and also by hyaline ban s hieh a not annual ring

The age oomposition of all t ample 1s given in

Figura 3. In the area of observa.t on the f1ah belollging

to 3 and 4 aga groups were the most numerou • Maximum ~

noted was 8 yaars.

Figura 4 shows the growth rate of the Af~ican mac eral.

Tha growth rate 1s nearly the e in the fir t 3 year of

life. It decreases after the hird y ar.

The mean weight of the partie ar age groups is shown

in the Figura 5. Af'rieaD mackerel aohieves good weight

inerements up to the last y ars of their lire.

Matur1ty stage and spaw'nin@i

Maturity stage was determined according to the Maier's

scale on the base of analysing 3554 speoimens. Spa.wning of

Scomber japon1ous 1s partial and prolonged in time. The peak

1s observed in winter time /stage IV-VI. Spawning takes

'place in shallower waters. After spawning mackereI probably

disperse to find the feeding areas.

On the spawning grounds, male s prevailed up to 38-40 cm

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gwc~gu" from this length upwards.

em part of the area /Spanish Sah.ara and

/ pawning takes plaoe later than in the

and senegal ooasts/. This seems

w ter temperature '-nfluenoed by the oold

on

show: d that spawning has DO infiueDoe

abits of this fiah~ Speo1meDs in the ripen1Dg

oblgex~ed to ha,ve tul1 stomaohs.

S 0 food hab!ts of Scomber japoDious are .

servations cf stomach contents Of about }?8

•Gen ~ 17 this fieh feeds ohief1y OD Oopepoda and

Eupha~siacea. These items were found in tne stomaehs of 811

1 ngth c1asses specimens oaught in different areas, seasODS

and d pths.

The Iargest speoimens of Scomber japoDicus reeds also

on Decapo ,Oh etognatha, Tunioata, Oephalopoda and small

fiehe a. Ceph 1 poda prevailed in the northern part of the

ar a examiDated.

Small fishes like Sardina pilohardus, Branohiostoma

~anoea.atum an some others were found to be the food oompo­

nant of specimena oaught inahore, while Maurolious m\:hleri

as foun to be the food oomponent of specimens oaught

offshore.

There are some differenoes in the food .oompos1tioD

cf African mackerel oaught in w:Lnter end summer time.

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