Subject: Case Study: Wages of Captivity (marine mammals)

Michael Williamson (whe_william)
Mon, 1 Feb 1995 21:15:03

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From: Michael Williamson <WHE_WILLIAM@FLO.ORG>
Subject: Case Study: Wages of Captivity (marine mammals)
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Subj:	Wages of captivity
 
Date:         Wed, 1 Feb 1995 13:49:30 -0400
Reply-To:     Marine Mammals Research and Conservation Discussion
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From:         David M Lavigne <dlavigne@uoguelph.ca>
Subject:      Wages of captivity
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To:           Multiple recipients of list MARMAM <MARMAM@UVVM.BITNET>
 
 
We would like to address some of the queries that have been raised with
regard to "Wages of Captivity".
 
The International Marine Mammal Association Inc. was asked by several
organizations, including HSI, to compare survival rates of captive
bottlenose dolphins and killer and beluga whales with their wild
counterparts.  A draft report (A comparison of survival rates for captive
and free-ranging bottlenose dolphins, killer whales and beluga whales)
was produced and distributed to contracting parties, as well as to a
number of marine mammal scientists for comment.  The ms is currently
being revised and a final version will be available shortly.
 
To summarize findings of the draft report, we followed DeMaster and
Drevenak (1988; Mar. Mamm. Sci. 4#4) and calculated annual survival rates
(ASR) of captives using the animal-days survived method.  ASRs from the
entire data base and a post-1980 subset were calculated to establish
whether the two samples would lead to different conclusions.
 
Not surprisingly, overall ASRs derived for captive bottlenose dolphins,
killer whales and beluga whales were similar to those reported by
DeMaster and Drevenak (1988) and Small and DeMaster (1994; Galveston
poster).  No significant differences between ASRs from the entire sample
and post-1980 subsets were found for any species and conclusions drawn
from either data base would be similar.
 
Comparable data for deriving animal-day ASRs of wild populations is
limited: Wells and Scott (1990; Rep. Int. Whal. Commn. Special Issue 12)
was used for bottlenose dolphins and Bigg (1982; Rep. Int. Whal. Commn.
34) and Olesiuk et al. (1990; Rep. Int. Whal. Commn. Special Issue 12)
were used for killer whales.
 
Estimated ASRs from the wild population of bottlenose dolphins (Sarasota,
Florida) were significantly higher than those of captives for calves,
non-calves and all-animals combined.  Because of limitations in the wild
killer whale data, we deemed the best comparison was between captive
non-calves and all (age 0.5+) wild killer whales and the wild ASR was
significantly higher.  Results from models for hypothetical stable
populations were consistent with these results.  Small and DeMaster
(1994) also reported higher survival rates for wild non-calf bottlenose
dolphins and killer whales than for their captive counterparts.
 
Data for wild beluga whales were deemed unsuitable for comparisons with
captive animals and the hypothetical models provided equivocal results.
Although based on small samples with wide confidence limits, first-year
ASRs of captive-born belugas were lower than would be expected for a
mammal with similar longevity.
 
Potential biases and limitations of the study were also discussed.
 
The draft study did not report on life spans although, as is reported in
DeMaster and Drevenak (1988), the expected number of years that an animal
will survive can be estimated from ASRs [E = -1/ln(ASR)] where it is
assumed that survival is constant over time and across ages.  NB - small
differences in ASRs result in large differences in life expectancy.
 
>From the average survival rates calculated for captives of each species,
DeMaster and Drevenak (1988) got life expectancies of 14 yr for
bottlenose dolphins, 13 yr for killer whales and 16 yr for beluga whales;
our captive ASRs give essentially the same life expectancies for
bottlenose dolphins and killer whales but give 14 (entire data base) and
12 (post-1980) yr for belugas.  The ASRs we derived for wild bottlenose
dolphins from Wells and Scott (1990) give overall life expectancies of 20
and 22 yr; our ASRs for non-calf killer whales in captivity give a life
expectancy of 16 yr, while the all-animal wild estimates from Bigg (1982)
and Olesiuk et al. (1990) give 58 and 50 yr, respectively.  (The latter
figure is best since it includes data from the former.)
 
We are now out of copies of the draft report but preprints of the revised
ms will be available in the not too distant future from IMMA (3 Paisley
St., P.O. Box 515, Guelph, Ontario, Canada N1H 6K9).
 
Any recent empirical data on survival rates of wild populations of killer
whales, beluga and Tursiops would be appreciated.
 
Thom Woodley, Jan Hannah and Dave Lavigne
International Marine Mammal Association Inc. and
Dept. of Zoology, University of Guelph