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On the Reaction of Captive Sea Lions to
Live Fish
Katherine Karlis, Rebecca Russo and Michael Noonan
Aquarium of Niagara and Canisius College, Buffalo, New
York
Presented at the Animal Behavior Society, College Park, Maryland,
June, 1997.
Introduction
It has been noted elsewhere that captive individuals of a number of
carnivore species (such as domestic cats) show considerable variability in their reaction
to live prey items. While nearly all individuals will pursue animate prey items, many will
not go on to kill and eat them. It has been suggested that this variability may derive in
part from the age at which the individual predators are initially introduced to live prey.
It has been proposed that while the pursuit of prey items may be more firmly
"pre-programmed", each individual must acquire the experience of killing and
eating live animals during a critical developmental period in order for it to demonstrate
the consumption of live prey as an adult.
Within this context, we tested the reaction of five captive
California sea lions to live fish. The subjects had been raised in captivity and had never
before encountered live prey. We wanted to know whether sea lions reared under such
conditions would pursue and consume live fish items if given the opportunity.
Procedure
The subjects were five female California sea lions (Zalophus
californianus). Each had been reared in captivity on a diet of recently thawed commercial
"fish" (herring, capelin, mackerel, smelts and squid). None had prior experience
with tinfoil barbs or with any live fish.
The test food items were tinfoil barbs (Barbus schwanenfeldi), 6-8cm
in length. They were presented to the sea lions under three circumstances
- alive in free swim (sea lion allowed to "discover" fish in
26,500 liter pool)
- alive hand fed (in the manner in which their normal food is
presented)
- thawed hand fed (in the manner in which their normal food is
presented)
All testing took place at 7 am after the sea lions had undergone a
normal twelve-hour overnight fasting period.
Results
Our findings are summarized in Table 1. Four of our five subject
noticeably oriented to the live fish when they encountered them in the free-swim condition
(Figure 1) Three of the sea lions repeatedly pursued the live fish, approached them within
1-2 cm and nuzzled them with extended vibrissae (Figure 2). Two of the sea lions
repeatedly took the fish into their mouths and released them still alive (Figure 3)
When live fish were offered to the subjects in the manner in which
thawed fish are normally presented (Figure 4), none of the sea lions ate the fish, either
spitting them out or refusing take them into their mouths in the first place.
Later, when individuals of the same fish species were frozen and
then thawed and presented to the sea lions as part of an otherwise-normal feeding, two of
the sea lions readily ate the fish. One other sea lion ate the first thawed fish offered
but thereafter refused.
Table One: Reactions of subjects to tinfoil barbs
under different circumstances.
Subject |
Age |
History |
Live Fish/ Free Swim |
Live Fish/ Hand Fed |
Thawed Fish/ Hand Fed |
| |
|
|
|
|
|
Sq |
9 |
Captive born |
Sustained
pursuit and mouthing |
Spit out |
Ate |
Ca |
15 |
Captive born |
Sustained
pursuit and nuzzling |
Spit out |
Refused |
Di |
8 |
Captive born |
Brief
orientation |
Refused |
Ate |
Jo |
19 |
Beach stranded
as newborn; hand raised |
Sustained
pursuit and mouthing |
Refused |
Refused |
Ju |
9 |
Captive born, hand raised |
Ignore |
Refused |
Ate one,
refused rest |
Discussion
In general, our sea lions appeared to be
initially attracted to the live fish when they first encountered them. Most of them
engaged in pursuit and brought their mouths into close proximity of the fleeing fish.
However, none of the sea lions actually ingested the fish. This strikes us as reminiscent
of behavior described for domestic cats in which captive-reared adults will pursue and
pounce upon live prey items but often not kill or eat them. It is tempting to speculate
that sea lions, like cats, have a critical period during their adolescence during which
time they need to capture, kill, and consume live prey in order for such events to become
part of the behavioral repertoire. Perhaps a developmental sequence of this nature is a
widespread characteristic within the carnivora/pinnipedia taxonomic cluster. Of course,
this can only be tested directly by conducting similar observations on sea lions that had
prior experience with consuming live prey.
We recognize that our introduction of live tinfoil barbs was the sea
lions' first experience with that species of fish. It is worth questioning whether they
would have responded the same way had they been presented with live individuals of one of
their customary food species (e.g., herring), and we encourage studies of this type to be
carried out in the future.
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