Tidal movements of shallow water fishes in Kuwait Bay

Journal ofFish Biology (1990) 37, 959-974

Tidal movements of shallow water fishes in Kuwait Bay

J. M. Wright*")", D. A. Clayton"!" and J. M. BishopJtZoology Department, Kuwait University, P.O. Box 5969, Safat, 13060, Kuwait and

%Mariculture andFisheries Department, FoodResources Division, Kuwait Institute forScientific Research, P.O. Box 1638, Salmiya, 22017, Kuwait

(Received 18 April 1990, Accepted29 July 1990)

The intertidal migrations of shallow water fishes in Kuwait Bay were studied during two 24 hperiods using an otter trawl. Most specieswereconcentrated at a location corresponding to LowLow Water mark. At the other tidal levels some fishes migrated with the tide to High High Watermark through a horizontal distance of up to 2 km. Any effect of day and night on the catch wasmasked by the effect of tidal condition.

Leiognathus decorus (de Vis)was typically concentrated at Low Water but a proportion of thepopulation followed the rising tide toward the shore. There was a diet effectwhich may have beendue to fish moving to shallower water at night compared with the day. Length-frequency distribution changed slightly with tidal state so that larger fish were not captured at High Water duringthe day. Of the fishescaptured at high tide, the largest individuals of L. decorus were captured at adepth of 20 m deep. Soleaelongate: Day did not migrate with tidal fluctuations and was capturedin large numbers only at Low Water. Ariustenuispinis Day was captured in shoals at or aroundLow Water.

Keywords: trawl; semi-diurnal tides; diel; intertidal fishes; Leiognathus decorus; length-frequency; Arabian Gulf.

I. INTRODUCTION

The intertidal zone of Kuwait Bay has been shown to be an important nurseryground for several speciesof shrimp (Al-Attar, 1984; Bishop & Khan, in press)andfish (Wright, 1988). This area consists of extensive mud flats that, in addition tospecies that migrate with the tide, support large populations of resident mud-skippers (Clayton & Vaughan, 1986; Clayton & Wright, 1989) and crabs (Jones &Clayton, 1983; Jones, 1986). Height differences between Kuwait Bay's unequalsemi-diurnal high and low tides range between 1-7 and 4-2 m (Marine OperationsDepartment, 1989). The horizontal distance between the Mean Higher HighWater and Lowest Astronomical Tide edges in Kuwait Bay is over 5 km (Ministryof Communication, 1986).

The tidal migrations of fish on temperate soft sediments has been extensivelyreviewed(Gibson, 1982). Relatively little work has been completed in sub-tropicaland tropical environments (Quinn & Kojis, 1987; Abou-Seedo et ah, 1990).Onshore movements offish are considered to be feeding migrations and a mechanism to avoid piscivorous fishes (Gibson, 1982). Tidal currents are utilized byPleuronectes platessa Linnaeus for migrations (Jones et ah, 1979; Walker et al,1979).

*Author to whomcorrespondence should be addressed at Metocean Consultancy Ltd, Hamilton House,Kings Rd, Haslemere, Surrey GU27 2QA, U.K.

959

0022-1112/90/012959+ 16S03.00/0 © 1990 The Fisheries Society of the British Isles

Table I. Numbers for each species captured in the different tidalsampling period 1 ranked by total abundance. Low Low Water (LLW),Low High Water (LHW), Falling Tide 1 (F1), High Low Water (HLW),

High High Water (HHW), Falling Tide 2 (F2)

conditions duringRisingTidel(Rl),Rising Tide 2 (R2),

Family/species

1. LeiognathidaeLeiognathus decorus(de Vis)2. Soleidae

Solea elongata Day3. Ariidae

Arius tenuispinis Day4. EngraulidaeThryssa hamiltoniiGray4. Sciaenidae

Otolithes ruber(Schneider)5. Sciaenidae

Johniops aneus (Bloch)6. Haemulidae

Pomadasys stridens(Forsskal)7. Tetraodontidae

Chelonodon patoca(Hamilton-Buchanan)8. ScorpaenidaePseudosynanceiamelanostigma (Day)9. TeraponidaeTeraponputa (Cuvier)10. CynoglossidaeCynoglossus arel(Schneider)11. ClupeidaeNematolosa nasus (Bloch)12. Gobiidae

Acentrogobius ornatus(Ruppel)13. CallionymidaeCallionymus hindsiRichardson

14. SillaginidaeSillago sp.15. SillaginidaeSillago sihama(Forsskal)16. Trichuridae

Eupleurogrammusglossodon (Bleeker)17. MugilidaeLiza carinata

(Valenciennes)18. Triacanthidae

Pseudotriacanthusstrigilifer (Cantor)

Tidal state

LLW Rl LHW Fl HLW R2 HHW F2

36 0 5 51 121 46 54 148

19 17 3 13 10 3 0 13

74 4 1 1 40 1 0 3

42 22 16 10 7 4 0 3

46 4 4 12 14 0 0 24

39 14 2 11 2 1 0 9

57 1 0 1 0 0 0 1

0 8 19 2 4

22 7 0 2 4 0 0

0 0 5 8 5 11 4 4

7 5 2 2 4 1 0 4

1 0 0 8 2 9 2 2

1 4 3 10 1 3 0 7

27 0 0 0 0 0 0

2 4 6 2 0 2 1 8

11 3 1 3 1 2 0 2

2 0 0 1 5 2 0 5

1 2 0 1 0 2 4 0

0 2 0 3 1 0 0

Family/species

18. HemiramphidaeHemiramphus marginatus(Forsskal)19. Soleidae

Euryglossa orientalls(Bloch & Schneider)20. DasyatididaeDasyatis imbricatus(Bloch & Schneider)21. PolynemidaePolynemus sextarius(Bloch & Schneider)22. GymnuridaeGymnura poecilura (Shaw)23. ClupeidaeIlisha melastoma(Schneider)23. CarangidaeTrachinotus mookaleeCuvier

24. ApogonidaeApogonichthys uninotatusSmith & Radcliffe

24. Plotosidae

Plotosus lineatus(Thunberg)24. PlatycephalidaePlatycephalus indicus(Linnaeus)24. PlatycephalidaeGrammoplites scaber(Linnaeus)24. Bothidae

Pseudorhombus arsius(Hamilton-Buchanan)24. Haemulidae

Pomadasys macula turn(Bloch)24. Gobiidae

Acentrogobius cyanomos(Bleeker)24. Gobiidae

Scartelaos viridis(Hamilton-Buchanan)24. Carcharhinidae

Scoliodon laticaudatus

Muller&Henle

24. SparidaeAcanthopagrus berdaForsskal

24. Gobiidae

Periophthalmuskoelreuteri Pallas

Table I. (Continued)

Tidal state

LLW Rl LHW Fl HLW R2 HHW F2

0 0 0 0 2 4 1

0 3 0 2 10 0

4 0 0 1 0 0 0

2 0 2 0 0 0 0 0

2 0 0 1 0 0 0 0

10 0 0 0 0 0 1

0 0 0 0 110 0

0 0 0 0 0 0 0

0 0 0 0 0 0 0

0 0 0 0 0 0 0

0 0 0 0 0 0 0

0 0 0 0 0 0 0

0 10 0 0 0 0 0

0 0 10 0 0 0 0

0 0 10 0 0 0 0

0 0 0 1 0 0 0 0

0 0 0 0 0 10 0

0 0 0 0 0 0 1 0

Table II. Numbers for each species captured in the different tidal conditions duringsampling period 2 ranked by total abundance. High Low Water (HLW), Rising Tide 2(R2), High High Water (HHW), Falling Tide 2 (F2), Low Low Water (LLW), Rising Tide 1

(Rl), Low High Water (LHW), Falling Tide 1 (Fl)

Family/species

1. LeiognathidaeLeiognathus decorus2. Ariidae

Arius tenuispinis3. Soleidae

So lea elongata4. CynoglossidaeCynoglossus arel5. Sciaenidae

Johniops aneus5. Tetraodontidae

Chelonodonpatoca6. Sciaenidae

Otolithes ruber7. TeraponidaeTeraponputa8. MugilidaeLiza carinata

9. EngraulidaeThryssa hamiltonii9. ScorpaenidaePseudosynan ceiamelanostigma10. Haemulidae

Pomadasys stridens11. ClupeidaeNematolosa nasus

12. CallionymidaeCallionymus hindsi13. Gobiidae

Acentrogobius ornatus14. SillaginidaeSillago sp.15. PolynemidaePolynemus sextarius15. Sciaenidae

Johnius belangerii16. SillaginidaeSillago sihama17. GymnuridaeGymnura poecilura18. Gobiidae

Scartelaos viridis18. CarangidaeCaranx sexfasciatus(Quoy & Gaimard)19. TriacanthidaePseudotriacan th usstrigilifer

Tidal state

HLW R2 HHW F2 LLW Rl LHW Fl

66 18 33 54 195 10 25 37

18 0 1 87 33 4 33 1

3 1 1 21 70 6 0 8

13 6 0 17 31 5 1 12

5 3 3 26 25 1 1 4

2 15 18 3 1 18 5 6

8 3 3 13 24 10 0 4

3 4 5 8 17 8 2 2

5 7 2 7 1 3 0 14

6 1 1 10 6 4 6 1

9 2 0 12 6 1 0 5

2 0 0 2 20 1 0 1

2 0 2 7 2 2 0 4

0 0 0 0 15 0 0 1

1 2 1 0 5 1 0 1

0 0 2 0 0 2 4 1

0 0 0 3 1 1 2 0

0 0 0 0 5 1 0 1

0 0 0 2 1 1 0 2

0 2 1 1 0 0 0 1

0 1 1 0 0 1 1 0

0 0 0 2 0 1 1 0

0 0 0 0

TIDAL MOVEMENTS OF FISHES IN KUWAIT BAY

Table II. (Continued)

963

Tidal state

Family/speciesHLW R2 HHW F2 LLW Rl LHW Fl

20. Soleidae 1 0 0 1 0 0 0 0

Euryglossa orientalis20. Hemiramphidae 0 0 0 0 0 0 0 2

Hemiramphus marginatus21. Haemulidae 1 0 0 0 0 0 0 0

Pomadasys macula turn21. Trichuridae 1 0 0 0 0 0 0 0

Eupleurogrammusglossodon21. Sparidae 1 0 0 0 0 0 0 0

Acanthopagrus berda21. Scatophagidae 0 1 0 0 0 0 0 0

Scatophagus tetracanthusLacepede21. Gobiidae 0 0 1 0 0 0 0 0

Acentrogobius cyanomos21. Sparidae 0 0 0 1 0 0 0 0

Acanthopagrus latus(Houtyn)21. Clupeidae 0 0 0 1 0 0 0 0

llisha melastoma21. Apogonidae 0 0 0 0 1 0 0 0

Apogonichthys uninotatus21. Carcharhinidae 0 0 0 0 1 0 0 0

Scoliodon laticaudatus21. Rhynchobatidae 0 0 0 0 0 1 0 0

Rhynchobatus djiddensis(Forsskal)21. Gobiidae 0 0 0 0 0 0 0 1

Apocryptes madurenesisBleeker

21.Bothidae 0 0 0 0 0 0 0 1

Pseudorhombus arsius21. Dasyatididae 0 0 0 0 0 0 0 1

Dasyatis imbricatus

This study was undertaken as an attempt to assess the effects of both unequalsemi-diurnal tides and the diel cycle on the distribution of the shallow water fishassemblage. The programme was designed to sample eight tidal states in each offour diel conditions over the necessary number of 24 h periods. Due to unpredictable weather, however, it was not possible to complete the programme. Herewe report the results offish catches with respect to tidal condition, diel period andwater depth during two 24 h periods in June 1989. Total numbers, numbers ofindividual species and total lengths of all fish were determined for each catch.Catch was related to each oftidal condition, diel period and water depth for the two24 h periods.

964

4 r

-I

J. M. WRIGHT ETAL.

Sulaibikhat BayJO km

Fig. 1. Map of Kuwait showing location of sampling site.

Hours

18.00 20.00 22.00 00.00 02.00 04.00 06.00 08.00 10.00 12.00 I4O0 16.00 18.00

HHW••O

Fig.2. Kitediagrams showing meantotal numerical catchoffishes and that ofSoleaehngata (shaded) at 0-6,10 and 20 m for each of eight tidal states during 4^5 June 1989. Height in metres refers to ChartDatum. Tidal height from tide tables (•), calculated tidal height (O). Low Low Water (LLW),Rising Tide 1(Rl), Low High Water (LHW), Falling Tide 1(Fl), High Low Water (HLW), RisingTide 2 (R2), High High Water (HHW), Falling Tide 2 (F2).

TIDAL MOVEMENTS OF FISHES IN KUWAIT BAY 965

10.00 12.00 14.00 16.00 18.00 20.00 22.00 00.00 02.00 04.00 06.00 08.00 10.00 hours

1 ' ' " ' ^

-2L

I I I

50 0 50

N

Fig. 3. Kite diagrams showing mean total numerical catch of fishes and that ofSolea elongata (shaded) at 0-6,1 0 and 20 m for each of eight tidal states during 25-26 June 1989. Height in metres refers to ChartDatum. Tidal height from tide tables (•), calculated tidal height (O). High Low Water (HLW),Rising Tide 2 (R2), High High Water (HHW), Falling Tide 2 (F2). Low Low Water (LLW), RisingTide 1 (Rl), Low High Water (LHW), Falling Tide 1 (Fl).

18.00 20.00 22.00 00.00 02.00 04.00 06.00 08.00 10.00 12.00 14.00 16.00 18.00 hours

4p

3 -

2 -

Q.CD

Q

0 ••O LLW

-2L

1 I 1

20 0 20

N

• •O HHW

Fig. 4. Kite diagrams showing mean numerical catch of Leiognathusdecorusat 0-6, 1 0 and 2-0 m for each ofeight tidal states during 4-5 June 1989. Height in metres refers to Chart Datum. Tidal height fromtide tables (•), calculated tidal height (O). Low Low Water (LLW), Rising Tide 1 (Rl), Low HighWater (LHW), Falling Tide 1 (Fl), High Low Water (HLW), Rising Tide 2 (R2), High High Water(HHW), Falling Tide 2 (F2).

966 J. M. WRIGHT ETAL.

18.00 hours

LW -

LLW -

R1 -

HW

LHW

F1 -

LW

HLW

R2 -

HW

HHW

F2

18.00 hours J L

/

57-

•

'

O

\

6

J L J I I I

30 40 50 60 70 80 90 I00 NO I20

Length (mm)

Fig. 5. Length-frequency histogram of Leiognathus decorus from water depths 0-6, 1 0 and 20 m for each ofeight tidal states during 4-5 June 1989. Height in metres refers to Chart Datum. Tidal height fromtide tables (•), calculated tidal height (O). Low Low Water (LLW), Rising Tide 1 (Rl), Low HighWater (LHW), Falling Tide 1 (Fl), High Low Water (HLW), Rising Tide 2 (R2), High High Water(HHW), Falling Tide 2 (F2).

II. MATERIALS AND METHODS

Three transects were established in an area of north Kuwait Bay characterized by extensive mud flats (Fig. 1) and sampled on 4-5 and 25-26 June 1989. Starting at low tide, trawltows were made at depths of0-6,1 0 and 20 m every three hours for 24 h resulting in a totalof72 5-min tows. An oar marked at 0-5,1 -0and 2-0 m was used prior and during each tow tomaintain depth. Each tow of the 4 m mouth width trawl, 13 mm stretch mesh, from a 6 moutboard motorboat covered a distance of 223 m (s.d. = + 10 m, n = 6). Distance coveredduring a trawl tow was estimated by trawling immediately adjacent to a straight shoreline inanother part of Kuwait Bay and marking the boat's bow position from shore before andafter 5 min. The 3 h sampling periods coincided with the following tidal states: Low LowWater (LLW), Rising 1 (Rl), Low High Water (LHW), Falling 1 (Fl), High Low Water


90 r

80

Period I

o

o

70P«P

-g 18.00 LLWE hours

=& I00r Period 2

90 -

80

70

10.00 HLW

hours

R2

R1 LHW F1 HLW R2 HHW

HHW F2 LLW R1

F2

LHW

967

18.00

hours

F1 10.00

hours

Fig. 6. Geometric means of total lengths of Leiognathusdecoruscaptured on 4-5 June and 25-26 June 1989at0-6(#). 10 (O) and 20 m (D). Low Low Water (LLW), Rising Tide 1 (Rl), Low High Water(LHW), Falling Tide 1(F1), High Low Water (HLW), Rising Tide 2 (R2), High High Water (HHW),Falling Tide 2 (F2).

10 00 1200 14 00 16 00 18.00 20.00 22.00 00.00 02.00 04.00 06.00 08.00 10.00 hours

4r

3 -

Q.a>

O

-21-

20 0 20

N

Fig. 7. Kite diagrams showingmean numericalcatch of Leiognathus decorus at 0-6, 10and 20 m for each ofeight tidal statesduring 25-26June 1989. Height in metresrefersto Chart Datum. Tidal height fromtide tables (•), calculated tidal height (O). High Low Water (HLW), Rising Tide 2 (R2), High HighWater (HHW), Falling Tide 2 (F2). Low Low Water (LLW), Rising Tide 1 (Rl), Low High Water(LHW), Falling Tide 1 (Fl).

968

10.00 hours LW -

HLW -

R2

HW

HHW

F2

LW

LLW

R1

HW

LHW

F1

10.00 hours

J. M. WRIGHT ETAL.

Depth (m)

I 2

J L

20 30 40 50 60 70 80 90 I00 NO I20

Length (mm)

Fig. 8. Length-frequency histogram of Leiognathusdecorusfrom water depths 0-6,1 0 and 20 m for each ofeight tidal states during 25-26 June 1989. Height in metres refers to Chart Datum. Tidal height fromtide tables (•), calculated tidal height (O). High Low Water (HLW), Rising Tide 2 (R2), High HighWater (HHW), Falling Tide 2 (F2). Low Low Water (LLW), Rising Tide 1 (Rl), Low High Water(LHW), Falling Tide 1 (Fl).

(HLW), Rising 2 (R2), High High Water (HHW) and Falling 2 (F2). Diel conditions wereday, dusk, night and dawn.

The catch from each trawl was frozen until processed. Total lengths ofall fishes from eachtrawl tow were recorded after identification (Fischer & Bianchi, 1984) and enumeration.The mean total number offish capture for each depth was plotted as kite diagrams againstcalculated tidal condition as were length-frequency histograms and geometric means oftotal length for the most abundant species captured.

III. RESULTS

A total of 1484 fishes from 37 species in 29 families were captured in the 24 hsampling (period 1) beginning on 4 June (Table I). In the second sampling (period


Table III. Geometric means of total length (mm) with 95% confidence limits for Leiognathus decorus inthe different tidal states in sampling periods 1 and 2. Low Low Water (LLW), Rising Tide 1 (Rl), LowHigh Water (LHW), Falling Tide 1 (Fl). High Low Water (HLW), Rising Tide 2 (R2), High High

Water (HHW), Falling Tide 2 (F2)

Sampling period 1 Sampli ng period 2

Tide 0-6 m l-0m 2-0 m Tide 0-6 m 10m 2-0 m

LLW 82,77-89 77,64-94 81,79-84 HLW 82,76-88 83,79-88 82,77-88Rl — — — R2 — 89,74^108 82,79-85LHW — — 82,64-104 HHW 81 80,77-83 82,78-86Fl 83,74-94 76,71-82 81,81-81 F2 96,89-102 — 84,82-87HLW 78,74-83 78,76-81 81,79-83 LLW 79,67-93 72,54-97 84,82-85R2 78,63-96 77,75-78 80,77-83 Rl — — 82,75-90HHW 74,72-75 74,73-76 76,74-77 LHW — 92,85-98 80,77-84F2 78,76-80 77,75-79 84,82-86 Fl —

77 80,75-86

2) beginning on 25 June, 1303 fishes were captured representing 38 species and 29families (Table II).

The catches from the two periods were broadly similar although diel conditionsfor the two periods corresponded to different tidal states and tidal range differedmarkedly. Period 1 sampling began at dusk on a LLW, and was characterized bylarge catches in all three water depths at LLW (Fig. 2). All subsequent catches wereless, but catches on Fl, HLW and F2 exceeded those on Rl, LHW, R2 and HHW.There was no marked difference between catches in the night (Rl, LHW) and day(R2, HHW; Fig. 2). Becausetidal effects could not be isolated, comparison of duskand dawn catches was avoided.

During period 2, initiated on HLW during the day, the largest catches were takenin all three depths at LLW (Fig. 3). Large catches were taken on HLW, F2 andLLW. Catches taken in daylight on HLW were less than night catches at LLW, butday catches at R2 werenot very differentfrom night catches at Rl (Fig. 3). As inperiod 1,it wasnot possibleto compare dusk and dawn catches becauseof unequaltidal effects.

Leiognathus decorus (de Vis) was the commonest species with 461 and 428 inperiods 1and 2, respectively (TablesI and II). In period 1,this species wascapturedin greatest numbers on HLW and F2 with relatively few captured at LLW (Fig. 4).Also, very few were captured on Rl and LHW in the night compared to R2 andHHW in the day. The length-frequency distribution showed an attenuated rangeof lengthson R2 and HHW during the day so that no large fish werecaptured (Fig.5). The geometric mean total lengths for the three water depths showed that largerfish were typicallycaptured in 20 m compared to 1-0 and 0-6m during tidal statesfrom Fl to F2 (Fig. 6 and Table III).

In period 2 the largestcatchesweretaken at LLW with largecatchesat HLW, F2and Fl. Daytime catches at HLW were less than night time catches on LLW,whilst R2 catches in the day were slightly greater than Rl catches at night (Fig. 7).The length frequencyhistogram showed no reduction in sizedistribution at HHW,but a number of young of the year (< 40 mm t.l.) were captured on HLW, LLW

970

18.00 hours

LW

LLW

R1

HW -

LHW -

F1

LW

HLW

R2 -

HW

HHW

F2 -

18.00 hours L

J. M. WRIGHT ETAL.

-I 0

Depth (m)

1 2 3 4

I I I 1 1 1

0-1 0-2 0-3 0-4 0-5 0-6 0-7 0-8 09 1-0

Proportional lengthH

-i 100

-1 0

Fig. 9. Proportional lengths for all species at 0-6, 1-0and 20 m for each of eight tidal states during 4-5 June1989. Height in metres refers to Chart Datum. Tidal height from tide tables (•), calculated tidalheight (O). Low Low Water (LLW), Rising Tide 1 (Rl), Low High Water (LHW), Falling Tide 1(F1), High Low Water (HLW), Rising Tide 2 (R2), High High Water (HHW), Falling Tide 2 (F2).

and F1. Few fish were captured in water depths 0-6and 1-0m so that the geometricmean total lengths were very variable (Fig. 6 and Table III).

Ariustenuispinis Day was the second most abundant species with 124captured inperiod 1 and 177 in period 2 (Tables I and II). Large numbers of the fish wereyoung of the year (< 60 mm t.l.). Greatest catches were taken at LLW and HLWin period 1 and F2, LLW and LHW in period 2 with most fish taken at only onewater depth, typically in one trawl, suggesting the capture of shoaling fish.

Solea elongata Day was the third most abundant species with 178 captured inperiod 1 and 110 in period 2 (Tables I and II). This species showed a similar


10.00 hours LW r

HLW

Depth (m)

I 2

R2

HW

\•

HHW KJ

/^F2

. ' *'

/ _nLW

LLW 0

R1

HW

LHW

F1 -

_10.00 hours

•

I I I I L J L

0 01 0-2 0-3 0-4 0-5 0-6 07 08 09 10 NProportional length

971

I00

Fig. 10. Proportional lengths forallspecies at 0-6, 10 and 20 mforeach ofeight tidal states during 25-26June1989. Height inmetres refers toChartDatum. Tidalheight from tidetables (•), calculated tidalheight (O). Low Low Water (LLW), Rising Tide 1(Rl), Low High Water (LHW), Falling Tide 1(Fl), High Low Water (HLW), Rising Tide2(R2), High High Water (HHW), Falling Tide 2(F2).

distribution in both sampling periods with greatest catches taken at LLWirrespective of diel conditions (Figs 2 and 3).

IV. DISCUSSION

The intertidal width of the study area in north Kuwait Bay covers a distanceexceeding 2 km (Ministry of Communication, 1986). The sampling programmefollowed theedge of the tideso that samples takenat HHWwere at a considerablehorizontaldistance from samplestaken at LLW. The data showthat fish migrate,

972 J. M. WRIGHT ET AL.

to some extent, with the rising and falling tides. In both periods, however, theassemblage was compressed at a location at or below the LLW mark, irrespectiveof diel condition, with a lesser congregation at or below the location of HLWmark. The majority of the assemblage remained at a location corresponding to theLLW mark or lower so that fewer fish were captured at higher tidal states. Therefore, only a proportion of the assemblage moved with the tides in and out of theintertidal area. Tidal, rather than diel, condition appeared to be the dominantfactor affecting the distribution of the assemblage. Where comparisons werepossible catches were similar in both day and night. During low tide the intertidalarea ofKuwait Bay between Mean High High Water and Mean High Low Water isdominated by several species of mudskipper (Clayton & Vaughan, 1986). Thesemudskippers were captured in low numbers by the trawl suggesting these fish werein their burrows when covered by the tide.

In order to determine if smaller individuals of the fish assemblage dominatedcaptures at higher tidal states, histograms of their proportional lengths werecompiled. For each species, proportional lengths were calculated using the largestindividuals as the standard (1-0). These were then summed for all species andplotted against tidal state (Figs 9 and 10). Results show movement in and out withthe rising and falling tide was undertaken by the whole size range of all speciesmaking up the assemblage. Small fish did not dominate the assemblage at LHWand HHW, and large fish did not dominate at LLW and HLW (Figs 9 and 10).

Tidal movements by fish have been found in a number of studies using variouskinds of gear. In estuarine environments, a preference for particular salinities hasbeen shown (Robin & Marchand, 1986; Quinn & Kojis, 1987). Avoidance ofstranding during low water by moving into drainage channels has been suggestedby Shenker & Dean (1979) and van der Veer & Bergman (1986). Tidal relatedfeeding migrations have also been reported (Reis & Dean, 1981). Migration on seagrass beds in Florida were considered to be anti-stranding movements due to tidaleffects and feeding movements due to diel effects (Sogard et al, 1989).

Using a beam trawl in an equatorial estuary in Papua New Guinea, Quinn andKojis (1987) captured greater numbers of fishes at night due to either or bothincreased abundance and decreased net avoidance. Otter trawl catches weregreater at night compared to the day in Sulaibikhat Bay, a semi-enclosed areawithin Kuwait Bay (Wright, 1989a) and similar results were obtained in KuwaitBay although this relationship was affected by season and shore type (Abou-Seedoet al.9 1990).

The distribution ofL. decorusreflected that of the entire assemblage so that mostspecies were captured at LLW. The length-frequency distribution over the varioustidal states suggested some length-dependent migrations with larger fish avoidingHHW during the day. Previous work has shown that larger fish are typical of thesubtidal zone compared to the intertidal zone (Wright, 19896). A proportion of theL. decorus population made considerable horizontal migrations during high tide,presumably as a feeding migration and to avoid predation (Gibson, 1982). There issome evidence for an unequal migration to high water depending on light conditions with few fish captured at high water during the night. These fish may be inshallower water than sampled in this study. An asymmetrical migration was suspectedfor this species in a lesscomprehensivesampling programme in Kuwait Bay,with fewer fish captured in sampled shallower water at night when compared to


the day (Abou-Seedo et aL, 1990). P. platessa on a sandy beach near Oban,Scotland, of intertidal width 120 m, showed a movement into shallower water atnight compared with the day (Gibson, 1973).

The present sampling programme has shown that L. decorus was not depthspecific, but the majority of the population remained in a location corresponding toan area at or below the position of the LLW mark. On a sandy beach at Loch Ewe,Scotland, P. platessa tended to be concentrated at the location of Low WaterSprings when sampled during high tide (Edwards & Steele, 1968). A proportion ofthe L. decorus population made the migration, but these fish were not markedlysmaller members of the population, although the largest fish appeared not to movewith the tide to HHW.

At Oban a positive correlation was observed between length of P. platessa anddepth of water sampled (Gibson, 1973)and a similar relationship was observed atLoch Ewe (Edwards & Steele, 1968). This relationship was maintained as the tiderose and fell (Gibson, 1973). During sampling period 1, when L. decorus wascaptured in all three water depths between Fl and F2, larger fish were captured in20 m of water than in 0-6and 1 0 m. In sampling period 2 fewfish were captured inwater depths 0-6 and 1 0 m so that no meaningful comparison could be made. Thisdifference in distribution over water depths between sampling periods suggests thatsome factor other than tidal or diel condition is affecting the distribution of thisspecies.

S. elongata was captured for the most part at LLW and showed little evidence oftidal migration. L. limanda (Linnaeus) at Oban hardly penetrated the intertidalzone (Gibson, 1973) and similar results were obtained at Loch Ewe (Edwards &Steele, 1968). S. elongata showed a similar distribution and remains in the samearea relative to the bottom as the tide rose. A. tenuispinis was captured in schoolswhich tended to be at or around LLW and HLW.

The intertidal width of Kuwait Bay may be up to 5 km (Ministry of Communication, 1986). This distance, in combination with the pronounced unequalsemi-diurnal tides in a subtropical environment produce an unusual marineenvironment. The migrations of fishes into the intertidal zone of Kuwait Bay areinfluenced predominantly by tidal state, by diel condition to a lesser extent, and inthe absence of estuaries, not by salinity gradients.

References

Abou-Seedo, F., Clayton, D. A. & Wright, J. M. (1990). Tidal and turbidity effects on theshallow water fish assemblage of Kuwait Bay. Marine Ecology Progress Series 65,213-223.

Al-Attar, M. H. (1984). Kuwait Bay: a nursery area for penaeid shrimps. 1. Penaeussemisulcatus. In Proceedings of the Third Shrimp and Fin Fisheries ManagementWorkshop, Vol. I (Mathews, C. P., ed.), pp. 85-105. Kuwait: Kuwait Institute forScientific Research.

Bishop, J. M. & Khan, M. H. (in press). Depth as a factor of abundance and size ofjuvenilepenaeid shrimps in the absence of estuaries and marshes. Marine Biology.

Clayton, D. A. & Vaughan, T. C. (1986). Territorial acquisition in the mudskipperBoleophthalmus boddarti (Teleostei, Gobiidae) on the mudflats in Kuwait. Journal ofZoology, London 209, 501-519.

Clayton, D. A. & Wright, J. M. (1989). Mud walled territories and feeding behaviour ofBoleophthalmus boddarti (Pisces: Gobiidae) on mudflats of Kuwait. Journal ofEthology 7(2), 91-95.

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Edwards, R. & Steele, J. H. (1968). The ecology of O-group plaice and common dabs atLochewe. I. Population and food. Journal of Experimental Marine Biology andEcology 2, 215-238.

Fischer, W. & Bianchi, G. (eds), (1984). FAO Species Identification Sheets for FisheryPurposes. Western Indian Ocean (Fishing Area 51). Rome: Food and AgriculturalOrganization.

Gibson, R. N. (1973). The intertidal movements and distribution of young fish on a sandybeach with special reference to the plaice (Pleuronectes platessa L.). Journal ofExperimental Marine Biology and Ecology 12, 79-102.

Gibson, R. N. (1982). Recent studies on the biology of intertidal fishes. Oceanography andMarine Biology Annual Review 20, 363-414.

Jones, D. A. (1986). A Field Guide to the Sea Shores ofKuwait and the Arabian Gulf. Poole,Dorset: Blandford Press.

Jones, D. A. & Clayton, D. A. (1983). The systematics and ecology ofcrabs belonging to thegenera Cleistostoma de Haan and Paracleistostoma de Man on Kuwait mudflats.Crustaceana 45, 183-199.

Jones, F. R. H„ Arnold, G. P., Walker, M. G. & Scholes, P. (1979). Selective tidal streamtransport and the migration of plaice in the southern North Sea. Journal du Conseil,Conseil International pour VExploration de la Mer 38, 331-337.

Marine Operations Department (1989). Tide Table, Year 1989, Shuwaikh Port. State ofKuwait: Ports Public Authority.

Ministry of Communications (1986). Khalij Al-Kuwait, Chart KU6E, State of Kuwait.Quinn, N. J. & Kojis, B. L. (1987). The influence of diel cycle, tidal direction and trawl

alignment on beam trawl catches in an equatorial estuary. Environmental Biology ofFishes 19,297-308.

Reis, R. R. & Dean, J. M. (1981). Temporal variation in the utilization ofan intertidal creekby the Bay Anchovy (Anchoa mitchilli). Estuaries 4, 16-23.

Robin, J. P. & Marchand, J. (1986). Preliminary observations on the feeding activity offishes during tidal and diel cycles in the Loire Estuary: The Bib Trisopterus luscus L.1758. Pubblicazioni delta Stazione zoologica Napoli (I. Marine Ecology) 7, 181-189.

Shenker, J. & Dean, J. M. (1979). The utilization of an intertidal salt marsh creek bylarval and juvenile fishes: abundance, diversity and temporal variations. Estuaries 2,154-163.

Sogard, S. M., Powell, G. V. N. & Holmquist J. G. (1989). Utilization by fishes of shallow,seagrass-covered banks in Florida Bay: 2. Diel and tidal patterns. EnvironmentalBiology ofFishes 24, 81-92.

Veer, H. W. van der & Bergman, M. J. N. (1986). Development of tidally related behaviourof a newly settled 0-group plaice (Pleuronectes platessa) population in the westernWadden Sea. Marine Ecology Progress Series 31, 121-129.

Walker, M. G., Jones, F. R. H. & Arnold, G. P. (1979). The movements of plaice(Pleuronectes platessa L.) tracked in the open sea. Journal du Conseil, ConseilInternationalpour TExploration de la Mer 38, 58-86.

Wright, J. M. (1988). Recruitment patterns and trophic relationships offish in SulaibikhatBay, Kuwait. Journal ofFish Biology 33, 671-687.

Wright, J. M. (1989#). Diel variation and seasonal consistency in the fish assemblage of thenon-estuarine Sulaibikhat Bay, Kuwait. Marine Biology 102, 135-142.

Wright, J. M. (1989/?). Biology of Leiognathusdecorus(Leiognathidae) in Sulaibikhat Bay,Kuwait. Australian Journal ofMarine and Freshwater Research 40, 179-185.

Tidal movements of shallow water fishes in Kuwait Bay

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