The Diel Behaviour of Small Demersal Fish on Soft Sediments on the West Coast of Scotland using a Variety of Techniques: with Special Reference to Lesueurigobius friesii (Pisces; Gobiidae)

P.S.Z.N.1: Marine Ecology, 3 (2): 161-178 (1982) 0 1982 Paul Parey Scientific Publishers, Berlin and Hamburg ISSN 0173-956YInterCode: MAECDR

Accepted: 7. G. 1982

The Die1 Behaviour of Small Demersal Fish on Soft Sediments on the West Coast of Scotland using a Variety of Techniques: with Special Reference to Lesueurigobius friesii (Pisces; Gobiidae) R. D. M. NASH*

University Marine Biological Station, Millport, Isle of Cumbrae, Scotland, KA 28 OEG.

Scottish Marine Biological Association, Dunstaffnage Marine Research Labotatory, P. 0. Box 3, Oban, Argyll, Scotland, PA34 4AD.

With 13 figures and 1 table

Key-words: Fish, demersal, goby, burrowing, behaviour, daily, techniques, Scotland

Abstract. The diel behaviour of communities of small demersal fishes was studied in situ on the west coast of Scotland using trawling, diving, underwater television and underwater time-lapse photography techniques. Lumpenus lamprctacformis and Pomatoschisrus norvegicus were shown to have crepuscular behaviour patterns. Lesueurigobius friesii was a day active fish, spending the night close to or within its burrow and feeding through the day. Disruptions to this behaviour pattern occurred at high abundances of gadoids and during the spawning season. The fish community as a whale showed a crepuscular periodicity. The various observational methods are discussed. There did not appear to be any close association between Lesueurigobius friesii and the decapod Neplirops norvegicus.

Problem

Rhythmic activities in fish are well reviewed (see WOODHEAD, 1966; BLAXTER, 1970; SCHWASSMAN, 1971; THORPE, 1978): Classically the timing of the rhythmicity is controlled by environmental factors such as variations in light intensity (solar rhythms), tides (tidal or lunar rhythms), and temperature and day length (mainly seasonal fluctuations).

The environmental factors impose behavioural patterns in fish such as: diel activity (increased activity either during the day or night), crepuscular activity (dawn and dusk active), vertical migrations (a vertical movement in the water column), lateral movements (with tides in the littoral region) and horizontal

* Present address: Institutt for Marinbiologi og Limnologi, Universitetet i Oslo, Postboks 1064 Blindern, Oslo 3, Norway.

U.S. Copyright Clearance Center Code Statement: 0173-9565/82/0302-0161$02.50/0

162 NASH

migrations (a seasonal activity pattern). The last two are not dealt with in this paper.

Various research workers have investigated the diel behaviour of cornmercial- ly exploited demersal fish around Britain, using trawl samples and echosounder surveys (e. g. KRUUK, 1963; HEMPEL, 1964; WOODHEAD, 1964; BEAMISH, 1966; MACER, 1966; BAILEY, 1975). In general, these species tend to migrate off the bottom during the night and return to the bottom at dawn. These vertical migrations enable the fish to exploit more than one environment within each day. The relative visual powers of both prey and predatory species synchronize

~ the patterns of feeding and evasive behaviour. Amongst the demersal fish there is a wide diversity in vertical migration patterns. Various factors modify these vertical movements e. g. light, temperature, age, season and depth ( B ~ X T E R , 1970).

On the smaller, non-commercial species, GIBSON & EZZI (1978) used a 24 h trawling survey to show that the burrowing Lesueurigobius friesii was more abundant on the mud surface at night than during the day. They did, however, suggest that the catches at night may have been due to a diurnal variation in capture efficiency of the net. The results from an analysis of stomach ‘fullness’ did not, however, agree with suggestions of increased feeding activity at night. Another soft sediment burrowing species, Cepola rubescens, has been studied using completely different techniques (SCUBA, underwater television and underwater time-lapse photography) (ATKINSON et al., 1979; R. J. A. ATKINSON, pen. comm.) to show the activity rhythms and other behavioural sequences in situ.

The present work looks at the daily behavioural patterns of small demersal fish on the west coast of Scotland using a combination of observational and sampling techniques. Each of the methods showed slightly different aspects of the behavioural patterns. Of the fish species within these fish communities Lesueurigobius friesii was selected as the most amenable to detailed study.

As the behaviour of L. friesii is centred around its burrow underwater television (UTV) and underwater time-lapse (UTL) techniques were possible for detailed behavioural recording. In the Lynn of Lome (Nr. Oban, Scotland, U. K.) and Loch Riddon (Firth of Clyde, Scotland, U. K.) the populations of L. friesii were at < 35 m, which allowed SCUBA techniques to be employed. A population of L.friesii in Irvine Bay (Firth of Clyde) (at 60m) was sufficiently large to allow 24 h trawling surveys to be undertaken. The diel synchronization of feeding times of L. friesii was measured from stomach ‘fullness’ from the trawling surveys. The seasonal variation in behaviour was obtained from UTL photography.

An overall view is taken of the small species in the soft sediment fish community and anomalies in regular behaviour patterns are analysed with respect to both biological and physical parameters.

Material and Methods 1. 24 h beam trawl studies

Three separate 24 h experiments (December 1977, November 1978, March 1979) were conducted in Irvine Bay at 60 m (Firth of Clyde) using a 3 m beam trawl with a 20m mesh net, which reduced to

Die1 behaviour of demersal fish 163

8 mm at the cod end. The nei was towed for 1 km, which lasted 10-15 min, every 2 h over a 24 h period. Bad weather conditions interrupted sampling on 7-8th November 1978 but the missing samples were obtained on the 27-28th November 1978.

The samples were sorted on deck and each species counted. Lesueurigobius friesii was immedi- ately stored in 70 % alcohol and the rest of the catch deep frozen. In the laboratory the L. friesii were measured to the nearest mm below. The fish were aged (see NASH, in press), sexed and their stomachs removed. An assessment of the stomach ‘fullness’ was made using a points method (see HYNES, 1950).

2. Underwater television (UTV)

A TC 125, Hydroproducts camera, mounted in a rectangular frame, with two 500 W lights (covered with red filters Kodak Safelight Filter No. 1 A) was placed on the seabed. The pictures were viewed on a Sony monitor and recordings made on a Sony video recorder. Notes were made on behavioural sequences and used for cross referencing with analysis from the tape recordings. Due to the continuous nature of the data an arbitary index was used to describe the abundance patterns of each species.

3. 24 h diving

Diver observations were made at two hour (Lynn of Lorne) and three hour (Loch Riddon) intervals along a 2 x 50m belt transect. Two parallel marker ropes were marked at 2.5 m intervals, with cross lines at 10 m intervals. Divers recorded the positions of each species on the mud surface on diving slates which were marked in an identical pattern to the transect. The Lynn of Lome site was at 20m and Loch Riddon at 18-24 m.

Each dive took approximately 15 rnin. At night all observations were made using standard underwater battery operated lights. Additional lighting for recording was supplied by underwater safety helmet lights. The times of dusk and dawn were made from visual observations.

4. Underwater time-lapse photography (UTL)

An underwater time-lapse camera, on loan from DAFS (Aberdeen), was used in the Lynn of Lorne at 20m. The UTL consisted of a Nikon ‘F’ camera with a 240 frame, 34mm, film capacity, motor drive, automatic timer and a Mecablitz flash unit. The camera system was mounted in a cast aluminium casing with two ‘windows’ (one for the camera and the second for the flash). The whole UTL unit was supported in a steel frame, at 45’ to the sediment surface. In general, either Ilford Mk V or HP 5 (black and white) film was used. The camera was on a six minute cycle at either f 8.0 or 5.6 with 1/60 th second exposure. On one occasion a 20min cycle was used over three days. The camera was usually deployed from a ship and then positioned by divers in front of an occupied Lfriesii burrow. The camera was then switched on and the time of the first flash recorded. When the weather was unsuitable for diving the camera was switched on at the surface, the time of the first flash on deck recorded and then i t was lowered to the bottom.

The films were analysed by recording the presence of animals on the mud surface during each hour.

Results

1. 24 h beam trawl studies

Using the data from the three experiments each of the four small demersal species, Lumpenus lampretaeformis, Callionymus maculatus, Pomatoschistus

164 NASH

Table 1. Overall catch composition of 24 h trawling experiment in November 1978 and March 1979 in Irvine Bay at 60m. n = number of individuals, N = total number of individuals. Nomenclature follows WHEELER (1978)

Porna tosc histus nor vegicus Lesueurigobius f r icsi i Callionyrnus rnaculatus Lumpenus lampretaetormis

Argentina sphyraena Meriuccius rnerluccius Gadus rnorhua Trisopterus rninutus Trisopterus esmarki i Trisopterus luscus

Merlangius rnerlangus Melanogrammus aeglefinus Pollachius virens Enchelyopus cirnbrius Call ionymus ly ra fu t r i g la gurnardus Cepola rubescens Hippoglossoides platessoides Limanda fimanda Pleuronectes platessa Platichfhys f l esus Microstornus k i l t Syngnalhus sp. Conger conger

November 1978 n .I.

235 7.1 1 453 13.70 7L 2.24 1L 0.42

I

23.5 '1-

158 4.78 11 0.33 0 0 0 0

309 9.35 0 0

390 11.80 2 0.06 1 0.03

12 0.36 6 0.18 0 0

35 0.09 1505 45.52

132 3.99 0 0 0 0 0 0 0 0 1 0.03

'4 = 3306

ss I

SR

' r t 500

March 1979 n I

1 1.30 132 12.34 78 1.2L 44 1.08

24.9 "la

5 0.46 1 0.09 5 0.46

179 16.60 5 0.46 1 0.09

31 2.88 0 0 2 0.19 7 0.65 5 0.46 1 0.09 0 0

507 47.03 58 5.47

5 0.46 1 0.09 1 0.09 1 0.09 0 0

N = 1078

ss SR - I I r I

Fig. 1. Die1 fluctuations in the number 10 50 of fish species and individuals over soft

sediments at 60m in Irvine Bay, Firth of Clyde a) November 1978. 0 = 7-8th Nov., 0 = 27-28th Nov. b) March 1979. SS = sunset. SR = sunrise.

11 13 15 1 7 1 9 21 23 01 03 05 07 01 1 1 Greenwich Mean Time


norvegicus and Lesueurigobius friesii is dealt with separately. The overall community fluctuations are covered as are the other relevant species.

Fish community - The overall catch compositions, over 24 h, are shown in Table 1 for November 1978'and March 1979. The four small demersal species constitute between 23.5 and 24.9 % of the total catch. In November 1978 there were 3306 individuals from 16 species caught whereas in March 1979, 1078 individuals were from 22 fish species. The fluctuations in number of individuals and species per haul showed a trend towards less species and individuals caught during the night in November 1978 (Fig. 1). However there was no clear trend in March 1979.

The numbers of individuals of each species caught in each sample are shown in Fig. 2.

Lumpenus lampretaeformis - This species was not caught in December 1977 thus only November 1978 and March 1979 are considered. There were increased catches of L. lampretaeformis in both experiments one hour before surface light dusk and at surface light dawn. Very few to no fish were caught two hours after dusk and throughout the night but a few were present throughout the day.

December 1977 November 1978 March 1979

40

20

131721010509

Lumpenus lampretaeforrnis

Callionymus macula tus

Poma toschistus norvegicus

L esueurigobius friesii

Trisopterus spp. , - - - - - , Merlangius merlangus (- 1

Nephrops norvegicus

Greenwich Mean Time

Fig. 2. Die1 variations in the abundance of small demersal fish species in Irvine Bay at 60m for December 1977, November 1978 and March 1979. Also included are the gadoids and Nephrops norvegicus. The black band indicates the night period. The 7-8th November 1978 sampling programme (solid line) was interrupted by bad weather conditions and was completed on 27th-28th November 1978 (dotted line). N. R. = not recorded.

166 NASH

Callionymus rnucu1utu.s - This species was never abundant although there was a greater number caught after dusk in December 1977 and March 1979. The only persistent feature was the low numbers caught during certain periods of the night. The timing of the low number of individuals caught was not consistent amongst the three experiments.

Pomatoschistus norvegicus - Over the three experiments P. norvegicus was consistently scarce during the night. In the daylight period prior to dusk (December 1977) the number of P. norveggicus fell and reached a minimum at the onset of dusk. In November 1978 the number of individuals caught reached

. a maximum one hour before dusk and then fell to a low value at dusk. No P. norvegicw were caught in this period in March 1979.

The numbers of individuals increased again two hours before dawn in December 1977 and at the onset of dawn in November 1978 and March 1979. In the latter cases the number of individuals caught returned to a low value three hours after dawn.

Lesueurigobius friesii - In both December 1977 and November 1!978 the number of L.friesii caught decreased at the onset of dusk. The low numbers of individuals continued through the night until dawn, when there was an increase (November 1978, dotted line Fig. 2). However, during the 7-8th November samples the number of individuals decreased after dawn. In all cases the fall in number of individuals caught was not marked. No such trend was noted in March 1979.

A more detailed analysis of the November samples showed the adult population (> 50mm standard length SL) (see NASH, in press) remained at the same abundance until two hours after dusk, after which the number of individuals decreased (Fig. 3). The curves then followed the population curve. The number of juveniles (< 50mm SL), however, began to decline two hours before dusk and maintained a low level throughout the rest of the sampling period. Over the whole sampling period the sex ratio was 1 : 1 (x' = 0.002; 1 d. f.; P > 0.05) and

December 1917

50 - 72 mm (SL)

- 2

30 - 49 mm (SL) z L

0 7 - 8 November o 27 - 28 November

b.. 50 - 72 mr i-7 n ISL)

1 0 4 1 I L.---- I I I I I I I I /t 1 1 - 1 30 - 49 m m (SL)

11 13 15 17 19 21 23 01 03 05 07 09 11

1978 1978

Fig. 3. Die1 variations in the catches of adult (50-72mm SL) and juvenile ( 3 M 9 mm SL) Lesueurigobius friesii in Irvine Bay (60 m) for a) December 1977, b) November 1978.7-8th Nov. = 'solid line, 27-28th Nov. = broken

Greenwich Mean Time line. S S = sunset. SR = sunrise.

Diel behaviour of dernersal fish 167

did not deviate from this throughout the 24 h period (x’ = 14.33; 14 d. f.; P > 0.05). In December 1977 there were more males than females (0.732 : 1; x2 = 4.46; 1 d. f.; P < 0.05). However, this sex ratio was maintained throughout the 24 h period (x‘ = 3.58; 8 d.f.; P > 0.05).

An analysis of the mean stomach ‘fullness’ indicated only minor differences over the 24 h period for December 1977 and November 1978 (Fig.4). In the latter samples (Fig. 4 b) there was a trend towards a minimum mean ‘fullness’ at 0700 h. By 0900 h the ‘fullness’ had returned to the daytime level noted for the previous day (1100-1300 h).

Fig. 4. Diel variations in the mean stomach ‘fullness’ (HY- NES (1950) points method) of Lesueurigobius friesii in Ir- vine Bay (60m). a) De- cember 1977, b) November 1978. 7 4 t h Nov. = solid line, 27-28th Nov. = broken line. Two standard errors are shown for each mean stomach ‘fullness’. SS = sunset. SR = sunrise.

ss I

14

SR I

December 1977

el ,- 0 ss SR

D 0 7 - 8 November 1978 n E b) 0 27 - 28 November 1978

._

0

Q I I c :I 6 *.?-i$ I \

I

1 1 1 1 1 1 1 1 1 1 13 15 17 19 21 23 01 d3 d5 d7 d9 111

Greenwich Mean Time

Gadoids - These were not recorded for December 1977. In November 1978 the numbers of Merlungius merlungus fell at dusk and reached a maximum just after dawn. Trisopterus minutus and T. esmarkii showed a similar trend although it was not as marked. In March M. merlangus was scarce and did not show a trend. The Trisopterus species declined in numbers caught just after dusk but steadily rose through the night until two hours before dawn, whereupon the catch stabilized at the previous days level.

Nephrops norvegicus - This burrowing crustacean was most abundant in the December 1977 samples at dusk (1500 h) and again at 2130 h. In March 1979, however, there was only one peak in abundance, two hours before dawn (0400 h). A subjective assessment in November 1978 indicated they were present before dusk, abundant at dusk, absent in the night and reappeared at dawn (0700 h) .

168 NASH

2. Underwater television (UTV)

In December 1977 in Loch Riddon at 30m (10th; 1800 h - 12th; 0800 h) there was a higher level of abundance of gobies on the mud surface during the day than the night (Fig. 5) . Instances of gobies on the mud surface at night may have been caused by raised light levels from the lighting system. Identification of the

X

TI -

SR ss SR I I Gobies 4 -

3 -

2 -

1 -

-

I I I I I I I 1

1 I I Gadoids

I l l I I I I I , , I I I I I r f , , I I 1 1 , , , I I , I , I, 19 21 23 01 03 05 07 09 11 13 15 17 19 21 23 01 03 05 07

10 I 1 2 11 I 1 2 Greenwich Mean Time

1 2 / 1 2

Fig. 5. Variations in the abundance of gobies and gadoids on the mud surface in Loch Riddon at 34m (10-12th December 1977). Data from underwater television observations. S S = sunset. SR = sunrise.

3 4--$

ss SR I I Lesueurigobius

friesii

4 Nephrops norvegicus

Fig. 6. Die1 variations in the - abundance of Lesueurigobiur

friesii and Nephrops nor- vegicur on the mud surface in Loch Riddon (25 m) (2627th June 1979). Data from under-

13 15 17 19 21 23 01 03 05 07 09 11 water television observa- 26 I 6 2 7 1 6 tions. S S = sunset. SR = sun-

1

:: Greenwich Mean Time rise.


individual goby species was difficult, hence the general term used. During the same period the gadoids were lower in abundance during the day than at night.

Of a number of other UTV studies only the observations from the 26-27th June in Loch Riddon at 25 m gave any further data on Lesueurigobius friesii. This species was present during the 26th until dusk, whereupon it disappeared. However, it did not return for the remaining period of observation (Fig. 6). The burrowing crustacean, Nephrops norvegicus was present at around dusk and then again approximately two hours before dawn.

3 -

2 -

1 -

3. 24 h diving

SS SR a )

I

.A. I - '.. '. .A. A D ' -Q.

4' . . I*

I i i r i I T I I Y I I r i 1 1 1 1 1 I I T I I I

I I

In Loch Riddon (October 1978), Lesueurigobius friesii was not abundant but did appear in increased numbers on the mud surface after dawn. L. friesii was noted close to burrow entrances during the night (Fig. 7 a). Gadoids were present after 0000 h although numbers slowly diminished towards dawn. The recorded

Fig. 7. Die1 variations in the abundance of Lesueurigobiis friesii, Nephrops norvegicus and gadoids on the mud surface from diving observations. a) Loch Riddon (18-24111) (2625th Oc- tober 1978). b) Lynn of Lome (20 m) (25-26th July 1979). Solid line = on the mud surface, broken line = at a burrow entrance. SS = sunset. SR = sunrise.

._ > 5 09 11 13 15 17 19 21 23 01 03 05 07 09 - .- c 24 J 10 2 5 / 1 0

P 0

QJ L

b) 5 z

ss S R I I 4


Neplirops norvegicus

Gadoidr

Lesueurigobius friesii

6 - I I Nephrops norvegicus

09 11 13 15 17 19 21 23 01 03 05 07 09 25 1 7 26 1 7

Greenwich Mean time

170 NASH

presence of these fish was probably very susceptible to observational error. The burrowing crustacean, Nephrops norvegicus was most abundant on the mud surface between 1800 and 2100 h (after dusk) and then at 0600 h (2.5 11 before dawn). The chelae of this species were visible at burrow entrances throughout the 24 h period.

In the Lynn of Lorne (July 1979) L.friesii was present on the mud surface throughout the day and night (Fig. 7 b). Due to the presence of a large number of burrows belonging to other species (Nephrops norvegicw, Calocaris macun- dreae and Callianassa subferrunea) it was not possible to discern the distance of an individual from its burrow. Nephrops norvegicus was most numerous on the mud surface at 2200 h (3 h after dusk) and then at 0400 h (dawn). This species was noted moving at least 2 m across the sediment surface although this may be an underestimate of the distance travelled.

4. Underwater time-lapse photography (UTL)

Due to individual variability within the data and the peaks of presence on the mud surface of L.friesii not being clear (i. e. double peaks or extended high frequencies), the first period after dusk where the fish was absent for one hour (Po dusk) and the last period before dawn where the fish was absent for one hour

0 2 4 a ’ 0 0 00

22 Po dusk

16

14

0 0 0

0 r = 0.747

o o o o n - 14

0 - 14 16 18 20 22 Time of dusk (G.M.T.)

08

(G.M.T.) 02

00

22

0

r = 0.938 n - 1 4

0

7722ZF70 Time of dawn (G.M.T.)

Fig. 8. The presence of Lesueurigobiusfriesii on the mud surface (at 20m) in relation to a) dusk b) dawn in the Lynn of Lorne (data from underwater time lapse photography). Po dust = first period after dusk where L. friesii was absent for one complete hour. P, = last period before dawn when 1.. friesii was absent for one complete hour; r = correlation coefficient; n = no. of observations.

(Po dawn) were chosen for analysis. There was a positive correlation between the time of Po and either dusk or dawn (r = 0.75; 12 d. f.; P < 0.01 and r = 0.94; 12 d. f.; P < 0.001) (Fig. 8). The number of hours that L. friesii was absent from the mud surface during the night was also positively correlated with the number of hours of darkness (r = 0.84; 14 d. f.; P < 0.001) (Fig. 9).

During 72 h continuous UTL observation a period between 2300 and 0200 h (10-13th August) was identified where L. friesii was consistently absent from the mud surface (Fig. 10).

Diel behaviour of demersal fish

14- E - a 12- 5 - E 10- e - F 8- r

8 - n m 6- 0 - 0 L

f ig . 9. Seasonal variations in the number of hours Lfriesii was absent from the mud surface at night in the Lynn of Lorne at 20m. Data from underwater time

8 41 2-

171

r = 0.838 a n=16

a *

a

Fig. 10. Diel variations in the presence of Lfriesii, Nephrops norvegicus and gadoids on the mud surface in the Lynn of Lome at 20m (10-13th August 1979). From underwater time lapse photography. SS = sunset, SR = sunrise, G = 1 gadoid. GS = > 2 gadoids.

ss SR

~ Nephrops 1 I


L

3 0 L

L

al m L L

3 VI

'D

i 03

5 C

norvegicus

- ' 9 - 1 1 1 I I I I I T I T 1 1

3 m 0 3 3 G G G I n 2- r

1- 3 a 5

- 1 5

m

VI

m

I ,,,,, , , l ~ l : , l , , , , , l l l l I , t R 1

13 15 17 19 21 23 01 03 05 07 09 1 1 Greenwich Mean Time

The photographs also indicated that L. friesii spent considerable periods of time close to its burrow (Fig. 11). Laboratory and diver observations confirmed the UTL data. In many cases the fish was less than eight body lengths away from its burrow (Fig. 12).

The UTL photographs also showed the presence of Nephrops norvegicus and gadoids on or near the mud surface. In general, N . norvegicus was on the mud

172 NASH

Y

presence of L. friesii on the mud surface and proximity to its burrow for the Lynn of Lome at 20 rn. From underwater time lapse

5 photography. Broken line indicates the L. friesii was < 2 body lengths from its burrow entrance. a) 22-23rd February 1978, b) 1617th May 1979, c) 18-19th June 1979, d)

09 1 1 1 3 15 17 19 21 23 01 03 05 07 09 11 13 2-3rd July 1979, e) 2-3rd November 1977. 1 ° k Greenwich Mean Time S S = sunset, SR = sunrise.

surface after dusk and before dawn (Fig. 13) and probably traversed quite large distances (the full width of a photographic frame, approximately 2m). There was, however, very little overlap between this species and L. friesii (see Fig. 10). The gadoids were present around dusk in January (Fig. 13 a) and also in December (Fig. 13 e). In the latter case they occasionally occurred up to 2300 h.

Discussion

In Britain, work on diurnal periodicity in fishes in siru has mainly been restricted to commercial or littoral species. Except for GIBSON & EZZI (1978), ATICINSON et al. (1979), and R. J. A. ATKINSON (pers. comm.) very little is known about diurnal periodicities in British sublittoral burrowing fish species.

This study utilized a variety of in situ methods of observing demersal fish behaviour, because no single method can provide a complete answer to the


Fig. 12. Underwater time lapse sequence showing the distance maintained by Lesueurigobiw friesii from its burrow entrances (arrows in a) and a conspecific. Loch Riddon, 20m depth, February 21, 1979. a) 1248 h b) 1300 h c) 1306h d) 1324 h GMT.

problem. Although the beam trawl samples provided information on the change which occurred in the population they only suggested individual behaviour patterns. The 24 h diving studies combined a study of individuals with a population study. Unfortunately the area studied was less than for the beam trawl and there was also a reduction in the density of Lesueurigobius friesii. However, it was not possible to investigate stock structure or feeding variations with the diving study. From the UTL and UTV observations the behaviour of one individual was studied. Individual variability and actual behaviour sequences involved were shown. These specific behaviour patterns were indicated by the beam trawl and diving studies but needed confirmation from UTL and UTV investigations. Each of these methods looks at a specific part of a behaviour pattern and must be considered when undertaking such a study.

174

SR fries;; a) SS - 5 - - - - -

h

NASH

norvegicus L- - - - ) Gadoidr (. ........... J

- - 3

a 0

5 v a B 0

0 a ?+ 3 c ) SS SR zr

SS d e’

3 ... . . . .

09 1 1 13 15 17 19 21 23 01 03 05 07 09 11 Greenwich Mean Time

Fig. 13. Die1 and seasonal variations in the presence of L. friesii, N. nor- vegicur and gadoids on the mud surface for the Lynn of Lome at 20m. From underwater time lapse photography. a) 2425th January 1980, b) 16-17th May 1979, c) 6-7th June 1978, d) 25-26th July 1979, e ) 1516th December 1978. SS = sunset, SR = sunrise.

The beam trawl samples are subject to gear selectivity (see NASH, 1980). The selectivity also changes with light levels (BLAXTER et al., 1964). A reduced reaction time of fish to nets at very low light intensities may partially explain increased night catches (PARRISH et al., 1964) noted by many researchers (tabulated in BLAXTER, 1970: pp. 263-264).

The observational area of both UTL and UTV is restricted, thus fish which make long excursions move out of the field of view. UTL photographs do not give any indication of transient behavioural actions and an absence from a photograph could indicate a lateral or upward movement or, in the case of burrowing species, into a burrow. The equipment can, however, be placed on site and retrieved at some later date. UTL systems with large film capacities


have been designed (FEDRA & MACHAN, 1979) which can provide more information at a smaller time interval. The major problem with smaller time intervals at present is an inability to quantify the observations. A similar problem is found with UTV data. UTV has been used extensively in fisheries research and for in situ animal behaviour studies around Britain e. g. Nephrops norvegicus (COLE, 1967; CHAPMAN & PRIESTLEY, 1972; CHAPMAN & HOWARD, 1979), MYRBERG (1973) reviewed the application of this equipment. In British waters UTV usually necessitates the use of some lighting which, even though covered by red filters, may cause disturbance to the animal under study. However, the use of silicon intensified target tube (SIT) cameras (e. g. Hydroproducts TC 125 SIT camera) which are vastly more sensitive than vidicon cameras may alleviate part of this problem. If ships are necessary for the work undertaken then the use of this equiqment becomes expensive. However, the continuous record of behaviour is invaluable for studying burrowing fish.

The 24 h diving programmes allow observations to be made over a much wider area, although the frequency of observations needs to consider diver decompression times. During the night it is necessary to use light sources although the effect of the light has not been quantified. The effect of a moving diver on the behaviour patterns of fish is also unknown. HEMMINGS (1971) has shown an avoidance reaction to the noise generated by divers’ exhalent air whilst CHAPMAN et al. (1974) showed that in some cases aggregations occurred.

By combining these methods it was possible to deduce the die1 behaviour of some of the fish species. The trawling results indicated a crepuscular activity pattern for Lumpenus lampretaeformis and Pomatoschistus norvegicus. The presence of L. lampretaeformis in the catch could be explained by a movement out of their burrows at dawn and dusk. Their presence in the daytime catches may suggest that not all individuals return to their burrows or avoid the net during the day. A reduction in numbers at night, together with a nocturnal absence from mid-water (J. GORDON, pers. comm.), suggests this species probably does return to its burrow at night.

The reasons for the marked increases in catches of Pomatoschistus norvegicus at dawn and dusk are unclear. This species has been caught in mid-water trawls at night in the Lynn of Lorne (J. GORDON, pers. comm.) and plankton hauls at night in the Firth of Clyde (A. GEFFEN, pers. comm.). The low abundance during the night is therefore caused by a vertical migration. Recent work on the related Pomatoschistus minutus suggests that this intertidal goby may have a similar movement (GIBSON & HESTHAGEN, 1981). Previous work on sublittoral P. mi- nutes also suggested an ‘off bottom’ stage at night (HESTHAGEN, 1973; RUMOHR, 1979).

Callionymus maculatus did not show any periodicity in catch rate. This species will bury itself in sediment in aquaria at random intervals (pers. obs.). However, its low catch rate made any trends difficult to discern.

Generally Leseueurigobius friesii was present on the mud surface during the day and its appearance and disappearance was synchronized to dawn and dusk. When it was present on the mud surface after dusk the majority of the time was spent close to a burrow entrance. This pattern was, however, disrupted during the spawning season (June and July). Similar disruptions were noted by AN- DREASSON (1969) for two Cottus species. Another disruption to the pattern was

176 NASH

caused by a very rapid increase in the abundance of gadoids, especially Merlangius merlungus, after dawn, which was synchronized with a decline in the L. friesii caught. UTL photography has shown that L. friesii will escape into its burrow when gadoids approach. The burrow acts as a refuge for L.friesii on what is essentially a flat plain. GIBSON & Ezzr (1978) have shown that the eggs are laid in the burrow.

The position of the fish in relation to its burrow at night (from UTL, UTV and diving observations) explained the presence of L. friesii in trawl catches at night. Reduced visibility at night prevented these fish from reacting to the trawl to escape down their burrows. This was probably the case in the results reported by GIBSON & EZZI (1978) and March 1979 in the Firth of Clyde but the reasons for an increased susceptibility during these periods of the year is uncertain.

Within the L. friesii population there were no behavioural differences between the sexes but the adult population (> 50mm) was more abundant on the mud surface at night than the juveniles. The disappearance of the juveniles may have reflected a greater need for predator protection in smaller individuals. A similar suggestion was put forward for parrott fishes (WINN & BARDACH, 1959; HOBSON, 1965, 1975). In general the stomach ‘fullness’ observations of November 1978 agreed with GIBSON & EZZI (1978), food being taken through the day with relatively little or none taken at night. JENKINS & GREEN (1977) have pointed out the problems of inferring a feeding time from stomach fullness and stressed the importance of individual variation in feeding patterns. How- ever, stomach ‘fullness’ was adequate for the purpose of this investigation in distinguishing between day and night feeding of the population as a whole. Unfortunately the reasons for this feeding pattern cannot be fully explained as the behaviour of the food organisms is unknown.

All the small demersal fishes are part of a fluctuating ecosystem and many of the daily behaviour patterns are a compromise to fit in with the community as a whole. The diurnal fluctuation can cause serious errors when estimating population sizes, as pointed out by KONSTANTINOV (1964) and PARRISH et al. (1964). The majority of fluctuations in number of individuals and species are caused by the vertically migrating fishes e. g. Merlangius rnerlungus. However, these perturba- tions within the community are variable and often cause little change in the number of species caught. The slight increases in both number of individuals and species at dawn and dusk suggests a crepuscular nature for the Clyde fish community but gear avoidance during the day may mask a day active community.

A species which is also found on these soft sediments is Nephrops norvegicus. It has been suggested that this species is associated with Lesueurigobius friesii. Their occurrence has been noted by RICE & JOHNSTONE (1972) and WHEELER (1978) has suggested that L. friesii acts as a ‘watch dog’ for N . norvegicus. The bchavioural data indicates that N . norvegicus is dawn/dusk active to nocturnal in the Lynn of Lorne (20m) and dawn/dusk active in the Clyde (60m). This is in agreement with CHAPMAN et al. (1975) and ATKINSON & NAYLOR (1976). In many cases L. friesii is absent or in reduced numbers during these periods. A full discussion on this topic can be found in NASH (1980). In addition, analysis of behaviour and spatial considerations did not reveal any close associations between these two species but the topic merits further investigation.


Summary

A community of small demersal fish on soft sediments on the west coast of Scotland (at 60 m depth) showed a crepuscular activity pattern. Four species of small demersal fish constituted between 23 and 25 % of the sampled populations. Lumpenus lampretaeformis and Pomatoschistus norvegicus were most abundant on the mud surface at around dawn and dusk. There were no patterns to the catchability of Callionymus maculatus. The catches of Lesueurigobius friesii were greatest during the day. The average stomach fullness was high during the day and reached a minimum just prior to dawn (November 1978 experiment). The sex ratio was maintained through all diel abundance fluctuations. L. friesii tended to be either in its burrow or very close to its burrow entrance during the night. There were positive correlations between the time of emergence from the burrow and dawn, disappearance from the mud surface and dusk and absence from the mud surface and the number of hours of darkness per day. The presence of large numbers of gadoids caused a reduction in the number of L. friesii caught with the beam trawl. There was no substantial evidence to suggest a strong relationship between Lesueurigobius friesii and the Dublin Bay Prawn (Nephrops norvegicus).

Acknowledgements

The author acknowledges: Drs. R. J. A. ATKINSON and R . N. GIBSON for their help and reassurance throughout this work; the skippers and crews of MFV Leander (Millport), RV Calanus (Oban) and RV Seol Mara (Oban); Mr. A. GALE (Oban, chief diver), Mr. I. DRUMMOND (Oban, boatman), Mr. P. MORGAN (Millport) and all the members of the S. M. B. A. diving team who assisted in this work; Mr. R. PRIESTLEY and Mr. C. SHAND (DAFS, Aberdeen) for the loan of the UTL system; the directors, Professor J. A. ALLEN (U. M. B. S., Millport) and Professor R. I. CURRIE (S. M. B. A , , Oban) for facilities at the respective laboratories. The author was in receipt of a NERC CASE award. The underwater television (UTV) and diving work was in conjunction with Dr. R. J. A. ATKINSON and Mr. P. MORGAN who were supported by a separate NERC grant.

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Documents

The Diel Behaviour of Small Demersal Fish on Soft Sediments on the West Coast of Scotland using a Variety of Techniques: with Special Reference to Lesueurigobius friesii (Pisces; Gobiidae)