Bustamente, Rodrigo H.

Collins, Ken

Jennings, Simon

Mallinson, Jenny

English

Aquatic Commons

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Noticias de Galápagos Oecember 1999No. 60
REEF FISH BEHAVIOR DURING A TOTAL SOLAR ECLIPSE
AT PINTA ISLAND
Simon Jennings, Rodrigo H. Bustamante, Ken Collins, and Jenny Mallinson
At 10.59 hours (Ecuadorian Time) on 26 February
1998 there was a solar eclipse at Pinta Island, Calápagos
(Espenak and Anderson 1997; Figure 1). The eclipse
began when the sun was at an altitude of 68° and the
period of totality (sun completely obscured by the
moon) lasted 3.5 mino Light levels during totality were
equivalent to those at night, and planets and stars were
visible to the human eye. The eclipse provided an
opportunity to observe the effeds of changes in light
intensity on the behavior of reef fishes.
Reef fishes can be categorised as diurnal, nocturnal,
al' crepuscular (Hobson 1965, 1972, McFarland 1991).
In late morning, on reefs clase to the equator, only diur-
nal fishes are active and nocturnal or crepuscular fishes
are sheltering within crevices or caves. The behavior
and abundance of reef fishes was recorded before, dur-
ing, and after the eclipse in an area of 10 m by 2 m at a
depth of 7- 10 m on the reef slope north of Pinta Island
(Figure 1, 00° 37.77' N, 90° 45.32' W). The study area
consisted of a volcanic boulder slope with C. 15%
massive coral and 2% branching coral cover. All fishes
>5 cm LT swimming in open water above the reef were
1°N
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Figure 1. Map of Galápagos sllOWillg limits of total eclipse.
counted at 5 min intervals from 10.20 until10.45 hours
and then counted before, during, and after totality.
Each census took 2-3 mino Divers also made behavioral
observations at depths of 2-15 m on the same reef.
Eight diurnal species: the anthias (Serranidae)
Paranthias colonus (Valenciennes), the wrasse (Labridae)
Bodianus diplotaenia (Cill), the damselfish
(Pomacentridae) Stegastes beebei (Nichols), the hawkfish
(Cirrhitidae) Cirrhitichthys oxycephalus (Bleeker), the
angelfish (Pomacanthidae) Holocanthus passer
Valenciennes, the butterflyfish (Chaetodontidae)
Johnrandallia nigrirostris Cill and the grunt (Haemulidae)
Anisotremus interruptus (Cill) were observed in the 20 m2
studyarea. The nocturnal squirrelfishes (Holocentridae)
Myripristis leiognathos Valenciennes and Adioryx subor-
bitalis (Cill) were sheltering in crevices.
Clear changes in the behavior of diurnal fishes
were observed at 10.55 hours, 4 min before totality. At
this time light levels had fallen to < 1 % of those in
unobstructed sunlight at the same time of day.
Plankton-feeding P. colonus started to descend from the
shallow study area towards the reef edge and other
species stopped feeding and retreated to crevices
between the boulders and corals. Hawkfishes sheltered
within branching corals. When the area was censused
during totality (Figure 2), no diurnal fishes were swim-
ming above the reef.
All species within the study area remained in shel-
ter during totality, with the exception of some P. colonus
which formed tight schools on the reef edge. There was
no sign of nocturnal squirrelfishes emerging from the
reef and they shared crevices and caves with diurnal
species. Totality ended shortly after 11.02 hours and
diurnal fishes returned to areas above the reef within 3
mino At this time fishes were as abundant above the
reef as they had been 14-39 min prior to the eclipse
(Figure 2). Seven minutes after totality, all species in
the study area had been observed feeding.
The behavior of other species was observed outside
the 20 m' study area. In deeper water (12-15 m), some
nocturnal species such as the glasseye Heteropriacanthus
cruentatus (Lacepede) and Myripristis spp. started to
leave the shelter of caves and crevices. The diurnal par-
rotfishes (Scaridae) Scarus ghobban ForsskaI and Scarus
rubroviolaceus Bleeker stopped feeding 3 min before
totaJity and resumed feeding 4 min after totality.
During totality the parrotfishes sheltered in the reef as
at night. The only diurnal species which did not exhibit
typical night-time behavior during the eclipse was the
surgeonfish (Acanthuridae) Prionurus laticlavius
9
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December 1999
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2.0
Noticias de GalápagosNo. 60
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10.46 10.51 10.56 1101 11.06 11.11 11.16
Time of day
Figure 2. Abundance of fishes prior, during, and after the eclipse.
Valenciennes, which stopped grazing on algae in the
surge zone approximately 4 min before totality and
formed large tight schools, which swam with alarm and
rapid changes in direction throughout the eclipse periodo
Prionurus continued this disturbed shoaling behaviour
for 2 min after totality and did not resume grazing for
another 5 mino All other species of planktivorous, her-
bivorous, and invertebrate-feeding fishes appeared to
have adopted normal day-time behavior before this time.
The relatively slow rate of descent of fishes towards
the reef at dusk is considered to be a function of the rel-
atively slow decrease in light level (Hobson 1991,
McFarland 1991). The rate of descent is governed by
the trade-off between maximizing feeding rate and
minimizing the risk of being attacked by predators
(Hobson 1991). Our observations support the hypothesis
that the behavior of diurnal reef fishes at dawn and
dusk is a direct response to light leveJ. The rapid
decrease in light level during the brightest period of the
day did not elicit a response noticeably different from
that usually observed at dusk, but movement towards
shelter provided by the reef was simply accelerated.
The only species which did not respond as if subjected
to a normal day-night cycle was the grazing surgeon-
fish Priollurus. Their alarmed shoaling response may
have resulted from the presence of sea lions in the surge
zane. The sea lions swam actively in this area throughout
the eclipse, whereas they would do so rarely at night.
Studies of other animals during eclipses also
demonstrate a direct response to decreased light inten-
sity and the rapid adoption of night-time behavior.
Ransome (1927) reported that brown trout Salmo trutta
1. stopped feeding for approximately 20 min after an
eclipse in the United Kingdom and Uetz et al. (1994)
demonstrated that colonial orb-weaving spiders began
to take down their webs (as they do at night) during the
Mexican eclipse in 1991. Similarly, lizards reverted to
typical night time behavior during this eclipse
(Ortegarubio et al. 1994). The next total solar eclipse
will occur on 11 August 1999. The path of the moon's
umbral shadow will cross marine and freshwater sites
from south-west England to the Bay of Bengal.
ACKNOWLEDGEMENTS
We thank David Day and Heidi Snell for informa-
tion on the solar eclipse, the captain and crew of the RV
Beagle for logistic support, tne Galápagos National Park
Service for research permits, and the Department of
Environment, Transport and Regions (DETR) Darwin
Initiative for funding.
LITERATURE CITED
Espenak, E and J. Anderson. 1997. The total solar eclipse of
1998: February 26. National Aeronautics and Space
Administration Reference Publication 1383, 5pp.
Hobson, E.S. 1965. Diurnal-nocturnal activity of some inshore
fishes in the Gulf of Ca] ifornia. Copeia 1965: 291-302.
Hobson, E.s. 1972. Activity of Hawaiian reef fishes during
the evening and morning transitions between daylight
and darkness. Fishery Bulletin 70: 715-740.
Hobson, E.s. 1991. Trophic relationships of fishes specia!ised
to feed on zoooplankters above coral reefs. In P.E Sale,
ed., The EcoJogy of Fishes on Coral Reefs, pp. 69-95,
Academic Press, San Diego.
McFarJand, W.N. 1991. The visua] world of coraJ reef fishes.
In P.E Sale, ed., The Ecology of Fishes on Coral Reefs, pp.
16-38, Academic Press, San Diego.
Ortegarubio, A., P. Galinatessaro, and S. Alvarezcardenas.
1994. Behavior of the zebra tailed !izard during a total
solar eclipse. Texas JournaJ of Science 46: 121-126.
Ransome, A. 1927. Fish and the eclipse. Manchester
Guardian June 29, 1927.
Uetz, G. W., CS. Hieber, E.M. Jakob, R.S. WiJcox, D. Kroeger,
and A. McCrate. 1994. Behavior of colonial orb-weaving
spiders during a solar eclipse. Ethology 96: 24-32.
Simon Jennings, Centre for Environment, Fisheries, and
Aquaculture Science, Lowestoft Laboratory, England
(e-mail: S.Jennings@cefas.co.uk). Rodrigo H.
Bustamante, Charles Darwin Research Station,
Galápagos, Ecuador (e-mail: rbustama@fcdarwin.org.ec).
Ken Collins, University of Southampton,
Oceanography Centre, Southampton, England (e-mail:
Kenneth.J.Collins@soc.sotan.ac.uk). Jenny Mallinson,
University of Southampton, Oceanography Centre,
Southampton, England.
This article is reprinted with modificatiolls from the
Journal 01Fish Biology (1998, Vol. 53: 683-686), Academic
Press Limited, London.
10


Reef fish behavior during a total solar eclipse at Pinta Island

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Reef fish behavior during a total solar eclipse at Pinta Island

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