Australian sea lion populations at Seal Bay and the Seal Slide (Kangaroo Island): continuation of the monitoring program Photo: R McIntosh Report to the Department for Environment & Heritage Wildlife Conservation Fund Project No. 3723 Simon D Goldsworthy 1 , Peter D Shaughnessy 2 , Rebecca R McIntosh 3 , Clarence Kennedy 4 , Janet Simpson 4 and Brad Page 1 1 South Australian Research and Development Institute (SARDI), 2 Hamra Avenue, West Beach SA 5024 2 South Australian Museum, North Terrace, Adelaide, SA 5000 3 Zoology Department, La Trobe University, Bundoora, Victoria, 3086 4 Department of Environment and Heritage, Kingscote, Kangaroo Island, SA
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Australian sea lion populations at Seal Bay and the Seal Slide (Kangaroo Island): continuation of the monitoring program
Photo: R McIntosh Report to the Department for Environment & Heritage
Wildlife Conservation Fund Project No. 3723
Simon D Goldsworthy1, Peter D Shaughnessy2, Rebecca R McIntosh3, Clarence Kennedy4, Janet Simpson4 and Brad Page1 1South Australian Research and Development Institute (SARDI), 2 Hamra Avenue, West Beach SA 5024 2South Australian Museum, North Terrace, Adelaide, SA 5000 3Zoology Department, La Trobe University, Bundoora, Victoria, 3086 4Department of Environment and Heritage, Kingscote, Kangaroo Island, SA
Australian sea lion populations at Seal Bay and the Seal Slide (Kangaroo Island): continuation of the monitoring program SD Goldsworthy, PD Shaughnessy, RR McIntosh, C Kennedy, J Simpson, B Page South Australian Research and Development Institute SARDI Aquatic Sciences 2 Hamra Avenue West Beach SA 5024 Telephone: (08) 8207 5400 Facsimile: (08) 8207 5481 http://www.sardi.sa.gov.au/ Disclaimer The authors warrant that they have taken all reasonable care in producing this report. The report has been through the SARDI Aquatic Sciences internal review process, and has been formally approved for release by the Chief Scientist. Although all reasonable efforts have been made to ensure quality, SARDI Aquatic Sciences does not warrant that the information in this report is free from errors or omissions. SARDI Aquatic Sciences does not accept any liability for the contents of this report or for any consequences arising from its use or any reliance placed upon it. Copyright South Australian Department for the Environment and Heritage and South Australian Research and Development Institute 2008. This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without prior written permission from the author. Printed in Adelaide, July 2008 SARDI Aquatic Sciences Publication Number F2008/000645-1 SARDI Research Report Series No. 293 Authors: SD Goldsworthy, PD Shaughnessy, RR McIntosh, C Kennedy, J
Simpson, B Page Reviewers: J. Nichols, Ib Svane Approved by: J Tanner
Signed: Date: 11 August 2008 Circulation: Public Domain
TABLE OF CONTENTS...........................................................................................................1 1 EXECUTIVE SUMMARY....................................................................................................2 2 INTRODUCTION ................................................................................................................3
AIMS AND OBJECTIVES .........................................................................................................6 3 PUP PRODUCTION ESTIMATES FOR THE 2007 BREEDING SEASON AT SEAL BAY
Field site.............................................................................................................8 Pup production estimates...................................................................................8 Cumulative births and deaths surveys................................................................8 Mark-recapture...................................................................................................9
RESULTS............................................................................................................................11 Cumulative births and deaths surveys..............................................................11 Mark-recapture estimates of pup production ....................................................11 Trends in pup abundance and pup production at Seal Bay ..............................12 Pup mortality ....................................................................................................13
DISCUSSION .......................................................................................................................19 4 PUP PRODUCTION ESTIMATES AT THE SEAL SLIDE................................................22
5 MAINTENANCE OF MICRO-CHIPPING PROGRAM ........................................................27 INTRODUCTION ...................................................................................................................27 METHODS...........................................................................................................................27 RESULTS............................................................................................................................27 DISCUSSION .......................................................................................................................28
6 FUTURE OF POPULATION MONITORING AND RESEARCH PROGRAM AT SEAL BAY..........................................................................................................................................30
subcutaneously. This procedure was only undertaken when pups were at least two months of
age. Pups were captured by hand when unattended by their mother. Clip marks were visible
on pups up until the end of the breeding season. As the number of marked animals in the
population increased, mark-recapture procedures were used to estimate the number of live
pups in the Seal Bay colony. Mark-recapture surveys were incorporated into the colony
surveys conducted between 11 September and 30 December 2007, and included all areas
with the exception of Pup Cove.
During each survey of the colony, the number of marked and clear pups was recorded, taking
care not to double count individuals. On most surveys the identity of marked pups was
determined by scanning with a hand-held RFID PIT tag reader.
Pup Production Estimates at Seal Bay 10
Mark-recapture estimates of pup numbers ( ) were calculated using a variation of the
Petersen method (formula attributed to D.G. Chapman by Seber 1982), with the formula
N̂
1)1(
)1)(1(ˆ −+
++=
mnMN ,
where M is the number of marked pups at risk of being sampled during recapture operations
(based on the number of pups given clip-marks/micro-chips to date), n is the number of pups
examined in the recapture sample, and m is the number of marked (clipped/micro-chipped)
pups in the recapture sample.
The variance of this estimate is calculated as
)2()1())()(1)(1()ˆvar( 2 ++
−−++=
mmmnmMnMN
.
Where several mark-recapture estimates ( ) are undertaken (one from each recapture
session), they are combined by taking the mean (N) using formulae from White and Garrott
(1990, pp. 257 & 268):
jN̂
∑=
=q
j
j
qN
N1
ˆ
where q is the number of estimates for the colony (i.e., the number of recapture sessions).
The variance of this estimate is calculated from
)ˆ(var1)var(1
2 j
q
jN
qN ∑
=
= .
Following Kuno (1977), the square root of var(N) gives the standard error (SE) for the
estimation, and the 95 % confidence limits calculated as
. )*96.1( SEN ±
As mark-recapture surveys were made throughout the breeding season, individual surveys
estimated the number of pups alive in the colony on a given day. In order to use these data to
provide multiple estimates of total pup production, individual survey estimates were adjusted
as follows:
jj
q
jjjj PCbbdNAdjN −⎟⎟
⎠
⎞⎜⎜⎝
⎛−++= ∑∑∑
=1
ˆ
Pup Production Estimates at Seal Bay 11
Where AdjNj is the adjusted total estimate of pup production for each (jth) survey, ∑dj is the
cumulative number of dead pups counted up to the jth survey, ∑b is the cumulative number
of new pups observed during the breeding season, ∑bj is the cumulative number of new pups
counted up to the jth survey and PCj is the number of pups counted in Pup Cove on the jth
survey. In this way multiple estimates of total pup production could be made and a mean
(AdjN), and 95% confidence limits calculated as detailed above.
Results
Cumulative births and deaths surveys
A summary of the birth and death surveys undertaken during the 2007 breeding season at
Seal Bay is presented in Table 3.1. Details of all the survey results for each area within the
colony are given in Appendix 1. The breeding season lasted seven months, commencing in
May and ending in December. 90% of births occurred over 120 days (3.9 months), between
28 June and 26 October (Table 3.2). The median pupping date was 27 August (sd = 36 days)
(Table 3.2). The mean interval in median pupping date between four consecutive breeding
seasons was 542.7 days (range 541-545, sd = 2.1, n = 3), or 17.8 months (based on the
median pupping dates in Table 3.2).
The cumulative number of births recorded for the 2007 breeding season at Seal Bay was 245
(Table 3.1, Figure 3.1). Most pups were born in the Main Beach area (97, 39.6%) (outside
public access), and the WPA (63 pups, 25.7%), with 47 pups reported for the EPA (19.2%)
and 38 pups for Pup Cove (15.5%)(see Appendix 1). As Pup Cove could only be surveyed
from along the cliff-line at various vantage points above the Cove, the number of cumulative
births there may be under estimated.
Of the 245 births, 51 (20.8%) were reported dead by the end of the breeding season (Table
3.1). The highest live pup count was 145 on 3 November 2007 (Table 3.1, Figure 3.1).
Mark-recapture estimates of pup production
Details of 29 mark-recapture Petersen estimates are provided in Table 3.1. For the AdjN
values (estimates of total pup production), estimates ranged between 222 and 338 (Table
3.1, Figure 3.1). There was little pattern to this variability, with the exception that between 8
November and 30 December, estimates were consistently high. This may have been due to
Pup Production Estimates at Seal Bay 12
temporary dispersal of large (marked) pups away from the survey area, reducing the
percentage of marked pups in recapture samples, and hence producing higher than expected
(biased) Petersen estimates. These six recapture estimates, and the first two estimates (on
11 and 16 September, that were based on only 9 marked pups in the population) were
omitted, leaving 21 recapture estimates to calculate the Adj N estimate of total pup
production. The estimate of pup production based on this approach was 260 (with 249-271
95%CL) (Table 3.1 and 3.2). This is 15 more pups than that estimated from the cumulative
survey of new births. These additional pups are likely to be uncounted pups from Pup Cove
that were not able to be observed from the cliff-top vantage points. For the 21 mark-
recapture estimates used, there was no significant relationship between the estimate and
date of the survey (F1,20=1.259, P = 0.276).
Following the breeding season, an additional 27 pups were micro-chipped up until 12 May
2008, giving a total of 203 micro-chipped pups (Chapter 5). Adding this total to the cumulative
dead pups (51 all non-micro-chipped), gives a minimum estimate of pup production (total
micro-chipped + cumulative dead) of 254, 6 less than estimated from Adj N (Table 3.2). This
minimum estimate enables the lower confidence limit of Adj N to be increased slightly, giving
a final estimate of pup production for the 2007 breeding season at Seal Bay of 260 (254-272
95%CL).
Trends in pup abundance and pup production at Seal Bay
The surveys undertaken during the 2007 season at Seal Bay represent the fourth
consecutive breeding season when mark-recapture procedures have been used to provide
Petersen estimates of pup production. Comparison of the timing of breeding, estimates of
pup production, highest live pup counts and cumulative births and pup deaths between these
four breeding seasons are given in Table 3.2. In addition, trends in live pup counts between
1985 and 2007 (16 breeding seasons), and Petersen estimates of pup production and
mortality rates of pups between 2003 and 2007 are presented in Figure 3.2.
As detected by Shaughnessy et al. (2006), an examination of the trends in maximum live pup
counts between 1985 and 2007 identified an apparent oscillation in pup numbers between
high and low seasons (Figure 3.2). Following the approach of Shaughnessy et al. (2006),
trends in maximum live pup counts were analysed using a general linear model (GLM)
incorporating backwards stepwise inclusion of the three predictor variables (year, inter-
breeding interval and their interaction, with probability P set at 0.15 to enter or remove a
predictor) which produced a significant model that included all predictor variables (F3,12 =
5.407, P = 0.014, r2 = 0.575). As detected by Shaughnessy et al. (2006) for the 1985 to
Pup Production Estimates at Seal Bay 13
2002-03 analysis, results indicate that year, inter-breeding interval and the interaction
between year and interval, all significantly contribute to explaining variance in the numbers of
pups counted at Seal Bay over the 16 consecutive breeding season between 1985 and 2007.
The negative coefficients of the terms indicate that both year and inter-breeding interval have
a significant negative effect on the maximum numbers of live pups counted.
Trend analyses in maximum live pup counts for the 16 pupping seasons between 1985 and
2007, demonstrated an annual decrease of -0.54% per year, or -0.78% per breeding cycle,
which amounted to a decrease of -11.1% over the 16 year period.
Examination of the four consecutive breeding season estimates of pup production based on
mark-recapture and Petersen estimates, supports the same oscillation in pup numbers
between high and low pup production seasons observed above, with 2002-03 and 2005-06
being low pup production years and 2004 and 2007 being high pup production years. There
is also a general decline in pup numbers between the two successive low and high pup
production breeding seasons (Table 3.2, Figure 3.2). The rate of decline in pup production
between these successive low and high pup production seasons was -1.8% and -4.9% per
breeding season (mean -3.3%), or between -1.2% and -3.3% per year, respectively (mean -
2.3%).
Pup mortality
Based on a pup production estimate of 260 pups for the 2007 breeding season at Seal Bay,
and a total of 51 cumulative pup deaths, the mortality rate for the breeding season was
estimated to be 19.6% (Table 3.2). This compares to 32.2% for 2002-03, 24.3% for 2004 and
34.2% for the 2005-06 breeding season, an average of 27.6% (sd = 6.8) over the four
seasons (Table 3.2). Mortality rate appears to oscillate between high and low seasons and
vary inversely with estimated pup production (r2=0.63), although not significantly (F1,2=3.40,
P=0.206, Figure 3.2).
14
Figure 3.1 Map of Seal Bay breeding colony, Kangaroo Island, extended to Bay 2 (EPA 2), of the Eastern Prohibited Area (EPA). Western Prohibited Area (WPA), Main Beach and EPA comprise the main areas of the site.
Pup Production Estimates at Seal Bay
Pup Production Estimates at Seal Bay 15
Table 3.1 Summary of surveys undertaken for new births and dead pups, cumulative births and deaths, and counts of brown (BP), moulted (MP) and total live Australian sea lion pups at Seal Bay during the 2007 breeding season. Details of Petersen mark-recapture estimate are also given, where N refers to total estimate of live and cumulative dead pups and counts in Pup Cove on the day of survey, Adj N is the same as N but includes the remaining new births to occur in the population. The shaded values are those used to calculate mean Adj N (and its 95% CL).
Date New New Cumulative Counts Petersen M-R estimates
No. Births Dead Born Dead Alive BP MP Total live M n m N Adj N SE
Table 3.2 Summary of the timing and spread of four consecutive Australian sea lion breeding seasons at Seal Bay, and pup abundance estimates including: cumulative births and pup deaths; maximum live pup count; total numbers of micro-chipped pups and minimum pup production (micro-chipped + cumulative pup deaths); adjusted mark-recapture Petersen estimates (Adj N); and the overall estimate of pup production. Estimated mortality rate is also included. Comparative data for the 2002-03, 2004 and 2005-06 breeding seasons are from McIntosh et al. (2006) and McIntosh (2007), unless otherwise indicated.
2002-03 2004 2005-06 2007
Month breeding season commenced Dec-02 Jun-04 Dec-05 May-07
Duration of breeding season (months) 9 7 6 7
Median pupping date 13-Mar-03 5-Sep-04 28-Feb-06 27-Aug-07
± s.d. (days) 42 39 36 36
90% births (5%- 95%) 2 Jan—21 May1 3 Jul -1 Nov 4 Jan-18 Apr 28 Jun- 26 Oct
90% births (days) 1391 121 104 120
Cumulative births - 200 207 245
Cumulative pup deaths 73 70 75 51
Maximum live pup count 122 148 125 145
At months since beginning of BS 6 7 6 6
Max live pup count + cumulative dead2 185 208 197 198
Total live pups micro-chipped 148 202 144 203
Minimum pup production3 221 272 219 254
Adj N 227 288 203 260
( 95% CL) (216-239) (273-302) (199-207) (249-272)
No. recapture estimates 3 2 3 21
Overall estimate of pup production 227 288 219 260
Confidence limit (min est. to 95% CL) (221-239) (273-302) (254-272)
Mortality rate 32.2% 24.3% 34.2% 19.6%
1Shaughnessy et al. 2006 2at time of maximum live count 3total micro-chipped + cumulative dead
Pup Production Estimates at Seal Bay 17
Figure 3.1 Changes in the number of cumulative pup births, deaths, minimum alive, and number of live pups counted during twice weekly surveys of Australian sea lion pups at Seal Bay between 30 May and 30 December 2007. Values of Adj N (± SE) are also given.
Pup Production Estimates at Seal Bay 18
Figure 3.2 Trends in the abundance of Australian sea lion pups at Seal Bay based on maximum live pup counts, for 12 breeding season between 1985 and 2007. Trends in the estimated total pup production (based on Adj N mark-recapture estimates, with 95% CL) and pup mortality rate are also presented.
Pup Production Estimates at Seal Bay 19
Discussion The 2007 survey at Seal Bay is the fourth consecutive breeding season at Seal Bay where
‘modern’ methods have been used to estimate total pup production. Between 1973-74 and
2002-03 (20 breeding seasons), maximum counts of pups during each breeding season
where used to provide an index of pup abundance (reviewed by Shaughnessy et al. 2006).
The introduction of modern survey methods in the 2002-03 breeding season using mark-
recapture techniques, identified that visual counts of pups may only census a little over half of
those actually present (McIntosh et al. 2006). Additional mark-recapture surveys undertaken
in the 2004 and 2005-06 breeding seasons reinforced this pattern, with mark-recapture
surveys averaging 1.58 times those of visual counts (range 1.10 to 2.05, McIntosh 2007).
Given the large variance in the correcting factor between estimated and counted pups, the
degree of confidence that can been placed in trend analyses using count data is questionable
(Shaughnessy et al. 2006).
Modern censusing methods are not free from problems either. McIntosh (2007) identified that
although results from the 2002-03 and 2004 mark-recapture surveys satisfied the
assumptions of equal capture and recapture probability, the 2005-06 results did not,
questioning the accuracy of the latter survey estimates. Access restrictions to parts of the
colony at Seal Bay, were considered to be the most likely cause for violating the assumption
of the Petersen estimate (McIntosh 2007). The physical access restrictions to Pup Cove with
its steep limestone cliffs were not considered a major problem. Because pups leave Pup
Cove to join the rest of the colony when old enough, and movement of pups is only from west
to east, lack of access could be corrected for by excluding the area from the mark-recapture
survey and adding a direct count of pups remaining in Pup Cove onto the mark-recapture
survey result. However, lack of access to the EPA as a consequence of site management
and Local Area Policy, meant that pups were not captured and marked evenly throughout the
colony. Although there is some movement of pups between the EPA and other areas of the
colony, the ratio of marked pups to unmarked pups was lower in the EPA at the time of the
mark-recapture surveys compared to the Main Beach and WPA areas, and this may have led
to a failure to meet the assumptions of mark-recapture in the 2005-06 breeding season
(McIntosh 2007). In this season the cumulative birth count and total number of micro-chipped
pups plus cumulative dead pups also exceeded the mean estimate of pup production based
on mark-recapture methods (McIntosh 2007).
Access restrictions to the EPA were lifted for the 2007 breeding season, and although testing
for the assumption of equal capture and recapture probability was beyond the scope of this
study (although data are available to test for this), we expect the assumptions were satisfied
Pup Production Estimates at Seal Bay 20
because, with the exception of Pup Cove, the marking and survey efforts for the remainder of
the colony were consistent during the breeding season. Overall, there has been a
progressive improvement in the application of the modern survey methods over the past four
breeding seasons at Seal Bay, with the 2007 survey providing the most supported estimate
(cumulative births ~94% Adj N). Further, due to very comprehensive efforts to micro-chip
pups following the breeding season, the combined estimate of pups based on the addition of
micro-chipped and cumulative dead pups was only 6 less (98.5%) than the Adj N estimate of
pup production.
If it were not for the physical access restrictions into Pup Cove, cumulative birth counts (if
undertaken at least twice-weekly throughout the breeding season), would provide the best
means of estimating pup production. Based on Petersen estimates during the 2007 breeding
season, about 15 additional births to those reported occurred; most of these were likely to
have occurred in obscured parts of Pup Cove. As such, the Petersen estimate provides an
important check against estimates of pup production based upon cumulative new births, and
importantly provides confidence limits around estimates. Further, by being able to report on
the physical location and timing of almost all births in the population, the twice-weekly
surveys also provide an accurate means to monitor the timing and duration of pupping, and
importantly to accurately determine rates of mortality throughout the breeding season.
Despite improvement in estimating pup production at Seal Bay, there is still some uncertainty
in the degree to which the survey of pup production throughout the breeding season using
mark-recapture, meets all the assumptions of the Petersen estimate. The five assumptions
are that: i) every animal, marked and unmarked, must have the same probability of capture
and recapture; ii) animals must be marked uniformly throughout the survey area; iii) every
animal must have the same probability of mortality or of leaving the sampling area for the
duration of the experiment; iv) marks must not be lost and must be correctly reported; and v)
no animal is born or immigrates to the study area between marking and recapturing
(Caughley 1977; Seber 1982). Most of these assumptions have been assessed by McIntosh
(2007). Most uncertainty surrounds assumption iii). Because of the extended breeding
season, pup age can vary by between 6-9 months within each breeding season. Younger
pups are less mobile and less likely to leave the colony area, have a greater probability of
mortality (McIntosh 2007) and are less likely to be marked compared to older pups (pups are
marked when older than two months). As such, the likelihood of re-sighting younger and
unmarked pups is likely to be greater than for older and marked pups, and therefore they
have different likelihoods of re-sightability and mortality (McIntosh 2007). This may explain
progressive changes in the estimates of adjusted N throughout the 2007 breeding season,
Pup Production Estimates at Seal Bay 21
with greater dispersal of larger (marked) pups away from the survey area towards the end of
the breeding season, leading to a reduction in the percentage of marked pups in recapture
samples and higher than expected estimates (Figure 3.1). Further research needs to be
undertaken to assess the importance of differences in the recapture probabilities relating to
age, mortality and marking to the assessment of pup production using the Petersen estimate.
Despite these remaining challenges, three factors have improved the accuracy and precision
of pup production estimates at Seal Bay: the removal of access restrictions to the EPA for
pup surveys, multiple mark-recapture estimates undertaken throughout the breeding season
and increased micro-chipping efforts.
Trends in pup production
The 2007 survey provides additional support for the continuing decline in pup production and
population size at Seal Bay. Based upon three more seasons of maximum live pup counts
from those reported by Shaughnessy et al. (2006), pup abundance is still declining
significantly. There is also additional evidence for the oscillation between high and low pup
production years, both in maximum live pup counts and total pup production estimates. Given
that the most accurate data of changes in pup production are derived from the last four
pupping seasons, rates of change detected between the two high and low pup production
years suggest the actual rates of decline in pup production are much greater than those
observed using maximum live pup counts (-3.3 to 4.5% vs. -0.8% per breeding season,
respectively). Although the time series for pup production estimates is too short to provide
confidence in these rates, they are close to the rate of decline estimated by McIntosh (2007),
based upon a demographic model developed for the population. This model incorporated all
the available data from tagged and micro-chipped seals in the Seal Bay population to provide
estimates of survival, recruitment, fecundity and longevity, and model outputs suggested a -
4.5% decline per breeding season. Given the large uncertainty in the degree to which
maximum live pup counts mirror real changes in total pup production, and the corroboration
between rates of decline estimated from changes in total pup production over the last four
breeding seasons and a demographic model development from vital rates determined for the
Seal Bay population (McIntosh 2007); the best assessment of the current status of the Seal
Bay population is that it is declining by 3.3 to 4.5% per breeding season. This rate of decline
would see the population more than halve within 24-32 years (16-21 breeding
seasons)(McIntosh 2007).
Pup production estimates at the Seal Slide 22
4 PUP PRODUCTION ESTIMATES AT THE SEAL SLIDE
Introduction
This chapter details results from the survey of the Australian sea lion colony at the Seal Slide
(Kangaroo Island), using an approach developed by Goldsworthy et al. (2007a), termed the
cumulative mark and count (CMC) method that was used for the 2005-06 season. This
represents the second survey for the Seal Slide using this methodology.
Methods
The Australian sea lion colony known as the Seal Slide (-36°.028 S, 137°.539 E, Figure 2.1)
is located in the Cape Gantheaume Conservation Park, south-east Kangaroo Island. The
colony can be accessed by 4WD vehicle and was visited on five occasions during the 2007
breeding season (3 September, 18 September, 5 October, 22 October and 23 October).
The methodology to survey these sites followed that describe by Goldsworthy et al. (2007a)
for small colonies, termed the cumulative mark and count (CMC) method. During each visit,
attempts were made to mark a number of pups, by clipping a small patch of fur on the head
using scissors, and pups were also micro-chipped by implanting Passive Integrated
in the rump. As pups at Seal Bay (~24km away) were clip-marked on the rump, any
dispersing pups from either colony could be readily identified.
The number of marked, unmarked and dead pups sighted was recorded on each visit to the
colony, and where possible, additional pups marked. Marked pups at the Seal Slide were
also scanned for a microchip with a hand-held RFID PIT tag reader to confirm they were born
at the Seal Slide and not Seal Bay. Dead pups were covered with rocks to avoid repeat
counting on subsequent surveys. Pup numbers were estimated for each visit from the
numbers of marked pups and accumulated dead pups, plus the number of live unmarked
pups. The last item was estimated in several ways, and the maximum number was used to
estimate number of pups born to date. For the first visit, it was simply the number of
unmarked live pups seen. For the latter surveys it was the maximum number of unmarked
pups seen in one of the previous surveys, less pups marked since then.
Pup production estimates at the Seal Slide 23
In addition, the Petersen estimate was used to provide a mean estimate, with confidence
limits, following methods detailed in Chapter 3. The lower bounds in confidence limits were
determined by the minimum estimate of pup abundance based upon the CMC method.
Results
A total of 8 pups were marked over the five visits to the colony. Details on the number of
unmarked, marked and dead pups sighted on each survey are presented in Table 4.1. The
minimum number of marked, dead and unmarked pups present in the population, based on
the re-sight and marking history is also presented. Based on these data, the minimum
number of pups estimated to have been born in the subpopulation was 15, based on two
consecutive surveys undertaken on the 22 and 23 October (Table 4.1). This estimate is
greater than the 11 maximum live plus cumulative dead pups sighted on two of the surveys
(Table 4.1).
Petersen estimate results for the second to fifth surveys are given in Table 4.2. The surveys
conducted on 22 and 23 October were used to calculate a mean estimate of 16 pups (with
95% CL 14-18), as these two estimates were on consecutive days and undertaken when all
pups had been born. The minimum estimate of pups based on the CMC method bounds the
lower limit of the estimate, providing an over estimate of pup production for the Seal Slide of
16 pups (range 15-18).
Discussion
This is the second season for which the cumulative mark and count (CMC) method has been
used to estimate pup production at the Seal Slide. In both seasons the method has
demonstrated that not all pups were present or visible during any of the surveys. In the 2005-
06 survey, based on the CMC estimate, between 10-40% of pups were not sighted on each
survey (Goldsworthy et al. 2007a). Similarly, during the 2007 breeding season about one-
third (33%, SD = 4.8) of pups estimated to have been born based on the CMC method, were
not sighted on each survey (2nd 33%, 3rd 38%, 4th 33% and 5th 27%, based on results
presented in Table 4.1).
Pup production estimates at the Seal Slide 24
Trends in abundance
Although records of pups born at the Seal Slide go back to 1975 (Dennis 2005), the quality of
some surveys relative to the timing of breeding is uncertain, and as such there is the potential
that many of the pups recorded in the past at the Seal Slide may represent dispersed pups
from Seal Bay. To this end, Shaughnessy et al. (in press) restricted counts of pups to those
observed within four months of the beginning of the breeding season at Seal Bay. Although
controlling for dispersed pups from Seal Bay, this adjustment is likely to result in an
underestimate of actual pup production as it will omit pups born during the last third of the
breeding season. Surveys undertaken in the 2002/03 and 2004 breeding season differ from
earlier ones in that they included monthly surveys where only pups <1 month age (and
therefore assumed to have been born at the Seal Slide) were counted on each survey by
experienced observers. The cumulative number of pups <1 month old observed on each
survey was used to estimate the number of pups born in that season. Estimates based on
this method from these two seasons (2002/03 9 pups, 2004 11 pups), including the two using
the CMC methods (2005/06 10 pups, range 10-11 based upon Peterson estimate; 2007 16
pups, range 15-18) provides four consecutive breeding seasons with estimates of pup
production with a high level of confidence (Shaughnessy et al. in press, Goldsworthy et al.
2007a, this report). Although there is a general trend for an increase in pup production over
these four seasons, the rate of increase is not significant (F1,3=7.894, P = 0.1068, Figure 4.1).
Until data from more breeding seasons become available, the Seal Slide population appears
to be stable.
Pup production estimates at the Seal Slide 25
Table 4.1 Details of pup surveys undertaken at the Australian sea lion colony at the Seal Slide (Kangaroo Island) between September and October 2007. The number of clear (unmarked), marked, dead and total pups seen on each survey is indicated, in additional to the number of new marks applied. The number of marked pups available to be re-sighted at each survey is presented, along with the cumulative number of dead pups recorded. The maximum number of pups at each visit is estimated by summing the number of pups marked, maximum number of unmarked pups and cumulative dead pups.
Date Clear Marked Dead Dead Total Total live & New Cum. Min Cum. Min
Table 4.2 Details of Petersen mark-recapture procedures undertaken at the Seal Slide between September and October 2007. M = number of marked pups in the population, n = the total number of pups sampled and m = the number of marked pups in each recapture sample. N = the estimated pup population size, ‘Dead’ is the cumulative number of unmarked dead pups, SE = standard error and V = variance. %m = the percentage of marked pups in each sample. The SE, CV (coefficient of variance), and Nlo (lower 95%confidence limit) and Nup (upper 95%confidence limit) are estimated from the last two surveys (22-23 October 2007). The overall mean estimate (in bold) is for the two final surveys (22-23 October) undertaken when the breeding season had ended.
Mean 22-23 Oct 13.1 16.1 1.03 50% 6.4% 14.1 18.1 (95% CL) (11-15) (14-18)
Pup production estimates at the Seal Slide 26
Figure 4.1 Trends in the abundance of Australian sea lion pups born at The Seal Slide (Kangaroo Island) over four consecutive breeding seasons between 2002-03 and 2007. Upper (95%) and lower (absolute minimum) confidence limits are given for the 2005-06 and 2007 breeding seasons.
Maintenance of the micro-chipping program 27
5 MAINTENANCE OF MICRO-CHIPPING PROGRAM
Introduction
Micro-chipping of pups with implanted radio-frequency identification (RFID) tags was
introduced in 1991 by Terry Dennis (former DEH employee). 50-60 pups of both sexes were
chipped each breeding season up to 2001 (Table 5.1). Nick Gales micro-chipped adult and
juvenile animals in 1989. The numbers of pups micro-chipped increased during the 2002-03,
2004 and 2005-06 breeding seasons, as part of R. McIntosh’s PhD research project (Table
5.1). During these seasons, pups were not captured in Pup Cove or the EPA, but some were
captured on the fringes of the EPA. At the end of the 2005-06 pupping season, at least 947
pups had been micro-chipped at Seal Bay, as well as some older animals. Here we describe
the methods used to micro-chip sea lion pups and detail the number of pups micro-chipped
during the 2007 breeding season at Seal Bay.
Methods
Pups less than two months of age and attended by an adult female were not considered
suitable for capture. Pups were captured by hand, and weighed (kg) in a canvas bag with the
aid of a spring balance to the nearest 0.1 kg. They were sexed and the standard length (cm)
from nose to tail was measured to the nearest 0.5 cm. Pups were marked externally by
clipping the fur of the rump and also by implanting Passive Integrated Transponder tags (PIT
were inserted in the clipped area, parallel to the spine and close to the tail to minimise
gravitation. To successfully identify a pup, a PIT tag reader was held at a distance of up to
10cm from the insertion site.
Results
A total of 203 pups born in the 2007 breeding season at Seal Bay were micro-chipped. The
first pups were captured and micro-chipped on 7 September 2007, the last pups were micro-
chipped on 12 May 2008. Based on a total pup production estimate of 260 for the 2007
breeding season, and a minimum of 51 pup deaths, an estimated 209 live pups were
available at the end of the breeding season to microchip. The number micro-chipped
represents 98.5% of the estimated available pups and the largest number and proportion of
pups micro-chipped in a single cohort.
Maintenance of the micro-chipping program 28
Table 5.1 Numbers of sea lion pups micro-chipped with RFID tags at Seal Bay (1989-2007).
(1989-2006 data from McIntosh 2007).
Breeding season No. pups micro-
chipped
1989-90 15
1991 58
1992-93 62
1994 49
1995-96 50
1997 57
1998-99 58
2000 51
2001-02 53
2002-03 148
2004 202
2005-06 144
2007 203
Discussion
Data from Seal Bay and other Australian sea lion colonies indicate that a high level of
variability in pup production between breeding seasons may be typical in this species. As
such, changes in pup production across successive breeding seasons may not provide
accurate measures of population status. Changes in population vital rates, such as age-
specific and cohort survival and recruitment rates provide better measures of the longer-term
demographic vulnerability of populations, and provide a better means to forecast future
population trajectories.
The benefits of having an individually-marked, known-aged population at Seal Bay have been
embraced by DEH and previous researchers that have undertaken studies at Seal Bay. In
1991, the tagging of pups using implantable RFID or PIT tags commenced, in conjunction
with a regular re-sight (scanning) program. Between 1991 and 2001, 50-60 pups were micro-
chipped each breeding season. Since 2002-03, the number micro-chipped increased to
between 144 and 202 per season, and in this most recent season 203 pups were micro-
chipped (Table 5.1). In addition to regular hand-held scanning, a number of automated
Maintenance of the micro-chipping program 29
recording stations comprising RFID flat-bed aerials have been placed in the sand along major
sea lion paths between the beach and dune areas (Figure 5.1). This has greatly increased
the number of re-sight records of tagged animals, and improvements to these passive
recording systems are proposed, pending funding commitments.
McIntosh (2007) has undertaken the most comprehensive demographic analyses of the
species, principally from re-sight records of marked animals at Seal Bay. Important
information relating to the maintenance of the Seal Bay sea lion population can be gained
from maintaining this demographic program. It provides a context for pup abundance data,
and provides a means to examine the role of environmental factors in regulating sea lion
survival and fecundity, and for developing population models, from which future changes in
population trajectories can be predicted. With large numbers of pups being tagged within
each cohort, and the increased re-sighting probability as a consequence of passive receivers
placed within the colony, high quality re-sight data can be obtained readily and cost-
effectively and form the basis for assessing population status and health, and for further
demographic analyses.
Figure 5.1 Map of Seal Bay breeding colony, Kangaroo Island, extended to Bay 5, EPA. Western Positions of the automated scanners (AS) and the antenna type are noted by the coloured diamonds.
Future of population monitoring and research program at Seal Bay 30
6 FUTURE OF POPULATION MONITORING AND RESEARCH PROGRAM AT SEAL BAY
In 2007 Goldsworthy et al. (2007 c) produced a report that provided detailed
recommendations for a population monitoring and research program to be implemented to
assist management of the Australian sea lion population at Seal Bay. The report included a
historical summary of research and monitoring of the sea lion population, an evaluation of the
current status of the population, a detailed appraisal of the ongoing monitoring and research
needs, what an ongoing population monitoring and research program should consist of and
cost, and potential funding sources to support such a program. They concluded that during
the last 30 years, the focus at Seal Bay has been on visitor management and commercial
operations, and there has been limited and variable funding and human resources allocated
to monitor the sea lion population. As a consequence, the effort and consistency in
monitoring methods has varied considerably. For example, data on pup abundance has been
collected for most breeding seasons since 1973-74 (see Dennis 2005, McIntosh et al. 2006,
Shaughnessy et al. 2006). However, analysis of these data by Shaughnessy et al. (2006)
identified significant limitations and much of the data could not be used meaningfully.
Most of the data collected have been on live pup counts, and it is now known that such
indices of abundance significantly underestimate pup production, by as much as 187%
(McIntosh et al. 2006). The lack of focus and commitment of resources to population
monitoring have resulted in limited ongoing methodological evaluation to ensure that the data
are providing adequate monitoring of the status and trends in abundance of the population.
Such evaluation has only been done recently by University and Government based
researchers. Given the vagaries in the data available to date, the best appraisal of indices of
pup abundance over the last 20 plus years is that the population has been in steady decline
(Shaughnessy et al. 2006, McIntosh 2007).
Goldsworthy et al. (2007c) concluded that that investment in population monitoring over the
last 30 years has been inadequate and ill-directed, and resulted in:
• inappropriate survey methods being developed and used,
• no ongoing evaluation and analysis of data or methodologies,
• no formal assessment process to evaluate and report on the status and trends in
abundance in the population,
• a failure to detect systemic population decline, and
• limited implementation of research findings into day-to-day management activities.
Future of population monitoring and research program at Seal Bay 31
Since the 2002-03 breeding season, considerable efforts have been made to develop more
appropriate methods to monitor the Seal Bay population (McIntosh et al. 2006, McIntosh
2007, Shaughnessy et al. 2006, this report).
Goldsworthy et al. (2007c,b) noted that in order to meet the long-term management needs of
Seal Bay to ensure that the sea lion population remains viable and economically sustainable
as a tourism destination into the future, a population monitoring and research program needs
to be established to monitor changes in the status, health and trends of the population, and to
identify, measure and mitigate threats. Such a program would provide critical performance
measures to assess whether or not the population is being appropriately managed, and
provide an effective insurance policy for the regional tourism industry.
Goldsworthy et al. (2007c) determined that a population monitoring and research program
should include both long-term monitoring and targeted research. Long-term monitoring
should focus on the assessment of pup production and mortality each breeding season, and
the monitoring of age-specific and cohort specific fecundity and survival rates. Targeted
research should focus on specific management needs. The most critical of these would be
those that aim to identify the cause(s) of decline in the population, and those that more
broadly target the monitoring and mitigation of threatening processes. The suggested
program is summarised below.
Long-term monitoring
Population status and trends in abundance The number of pups born per breeding season that survive to weaning is the most critical and
perhaps readily measured reproductive performance parameter in sea lion populations. It
provides an instantaneous measure of the number and quality of offspring able to be
produced by a population, and integrate information of the size, age-structure and fecundity
of populations, and the environmental conditions during the gestation and lactation period.
However, pup production and weaning rates are not straightforward to measure. The
Australian sea lion breeding season is lengthy, lasting up to 9 months in duration, and to
adequately estimate number of births and deaths requires some level of ongoing survey
throughout the breeding season to ensure that appropriate estimates can be calculated. A
problem with past monitoring programs has been that surveys of pup abundance by direct
counting have only estimated part of the pup production, and retrospective analyses have
identified that counting significantly underestimates the number of pups present in the colony
(McIntosh et al. 2006, McIntosh 2007, Shaughnessy et al. 2006).
Future of population monitoring and research program at Seal Bay 32
Mark-recapture methods using the Petersen estimates, in conjunction with cumulative counts
of new births and deaths in the remainder of the colony during twice-weekly surveys of the
colony (as detailed in this report), provide the best methods to estimate pup production in the
population. Efforts to micro-chip all remaining live pups also provides a means to determine
the minimum pup production and fix the lower confidence limit of the estimate, ultimately
improving the precision of pup production estimates.
Monitoring of pup production and mortality would involve:
• Twice-weekly surveys of new births (with their location) and deaths (number and
cause) during the breeding season.
• Hair-clip marking, micro-chipping (internal PIT, RFID tags), sexing and measuring
(mass & length) of pups.
• Regular re-sighting efforts to determine which individuals are alive.
• Regular mark-recapture surveys undertaken throughout the breeding season.
• Strong scientific management and coordination of surveys.
• Results reported upon and reviewed shortly after each breeding season.
Population demography – monitoring of vital rates Data from Seal Bay and other Australian sea lion colonies indicate that a high level of
variability in pup production between breeding seasons may be typical in this species. As
such, changes in the pup production across successive breeding seasons may not provide
accurate measures of population status over short time periods. Changes in population vital
rates, such as age-specific and cohort survival and recruitment are likely to provide better
measures of the longer-term demographic vulnerability of populations, and provide a better
means to forecast future population trajectories.
The principal aims of an on-going demographic program should be to determine breeding
season and cohort-specific survival rates; and determine breeding season and cohort-
specific fecundity rates (as outlined in Goldsworthy et al. 2007c).
The achievement of these goals would require:
• RFID tagging (micro-chipping) of all live pups of each cohort;
• ongoing passive re-sighting from a network of aerials and data-loggers;
• active re-sighting program (using a hand-held aerial), especially for females and
mother-pup pairs during each breeding season (to monitor fecundity and maternity);
• strong scientific leadership and management with results reported upon and reviewed
regularly.
Future of population monitoring and research program at Seal Bay 33
Targeted projects To complement long-term monitoring programs, there will be a need for targeted research to
support ongoing population management. The most critical of these will be those that aim to
identify the cause(s) of decline in the population, and understand more about threatening
processes with a view to monitor and mitigate them. The management of key anthropogenic
factors, such as fisheries interactions of sea lions, is a priority. Natural causes of mortality,
particularly the role and significance of disease and parasites, are poorly understood.
Knowledge of basic biological and ecological aspects of the species is still poor. Given that
the reproductive biology of Australian sea lions is unique among pinnipeds, the factors that
are important in maintaining populations of other species may not be the same for Australian
sea lions, hence a better understanding of the selective processes and environmental factors
that have shaped their unusual reproductive biology are important. Ensuring the long-term
sustainability of the Seal Bay population will require management of their foraging habitat and
prey resources (which may involve spatial and temporal management of fishing effort).
Knowledge of the species’ foraging habitats and prey, especially sex and age differences,
and how diet and foraging locations vary with season and year is poor. There is also a need
to ensure that visitor disturbance and commercialisation are ecologically sustainable and
sensitive.
There is an important role that research can play in educating the public about the biology
and ecology of Australian sea lions, and more broadly about the management of threatened
marine species. Given that Seal Bay is Australia’s largest sea lion tourism site, that South
Australia has about 80% of the sea lion population, and that the Australian Government Sea
Lion Recovery Plan is due to be released in 2009, there is an opportunity for the public focus
of the recovery of this species to be at Seal Bay. This provides unique educational and
marketing opportunities.
In summary, targeted research could include:
• studies on foraging habitats and diet, including sex and age differences, and season
and year differences;
• studies on the role of disease and parasites;
• threatening processes: identification, monitoring and mitigation (eg. fisheries
interactions);
• reproductive ecology;
• visitor interaction issues.
Future of population monitoring and research program at Seal Bay 34
Recommendations
This report has provided additional support for the observation of an ongoing decline in the
Seal Bay Australian sea lion population. The current rate of this decline is estimated to be
between 3.3-4.5% per breeding season. Although there is some corroboration in these
values based on estimates of pup production over the last four breeding seasons and from a
model of the Seal Bay population (McIntosh 2007), both the time-series of pup production
estimates and the demographic factors upon which the population model was developed are
limited. As such there is a high degree of uncertainty in the actual and current rates of
decline, and in the expected trajectory of the population into the near future. This provides
significant challenges for State and Commonwealth threatened species managers, managers
of the Seal Bay Conservation Park, and presents sustainability issues for the Kangaroo
Island regional tourism industry.
The aims of this project were to ensure that continuity in monitoring of the Seal Bay
population is maintained until the resources required to implement an ongoing research and
monitoring program can be secured. Based upon the results presented in this report, the
need for a secured, fully funded research and monitoring program is pressing. Several
scenarios of research and monitoring programs were proposed by Goldsworthy et al.
(2007c). All of these fall well outside the funding presently available to monitor the Seal Bay
sea lion population.
The next breeding season at Seal Bay is scheduled to commence in October 2008. At
present there are no plans or funding dedicated to support a survey of pup production and
maintain the micro-chipping program in this season or any following seasons.
We make the following recommendations:
• A population monitoring and research plan needs to be developed and implemented.
This would aim to ensure that the status and health of the population are adequately
monitored and facilitate identification of the cause(s) of population decline;
• A population monitoring and research program should include both a long-term
monitoring program (monitoring of pup production, pup mortality and vital
demographic rates) and targeted projects that address specific data gaps and
management needs;
Future of population monitoring and research program at Seal Bay 35
• The population monitoring and research program will require strong scientific
leadership and management, and results and methodologies should be reported upon
regularly, and reviewed;
• The absence of ongoing funding to support a population monitoring and research
program remains a critical issue for the future management and sustainability of Seal
Bay. The current level of State funding, and funding through competitive grants have
all been proven to be inadequate. A monitoring and research levy on visitor fees and
tourism operator licence fees should be investigated (Goldsworthy et al. 2007c).
Acknowledgments 36
7 ACKNOWLEDGMENTS
The work was conducted under an animal ethics permit from SA Department for Environment
and Heritage and the PIRSA Animal Ethics Committee. We thank Kate Lloyd and Peter
Canty (SA Department for Environment and Heritage) for provision of SA DEH Permits. We
thank Bill Haddrill for providing both staff and financial support to this program, and to the
DEH staff at Seal Bay for support of this work. We thank the Wildlife Conservation Fund for
funding support. Dr Ib Svane and Jason Nichols (SARDI) provided constructive review of this
report.
References 37
8 REFERENCES
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the Galápagos Islands. pp 495-519. In ‘Sea Lions of the World’. (Eds A. W.
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M. Wynne). Alaska Sea Grant College Program, University of Alaska: Fairbanks,
Alaska.
Campbell, R. A. (2003) Demography and genetic population structure of the Australian
sea lion (Neophoca cinerea). Unpublished PhD Thesis. Department of
Zoology. University of Western Australia, Perth.
Campbell, R.A., Gales, N.J., Lento, G.M., Baker, C.S. (2008) Islands in the sea: extreme
female natal site fidelity in the Australian sea lion, Neophoca cinerea. Biology
Letters 4: 139-142.
Carretta, J.V., K.A. Forney, M.M. Muto, J. Barlow, J. Baker, and M. Lowry. (2004) U.S.
White, G. C., and Garrott, R. A. (1990) 'Analysis of Wildlife Radio-tracking Data'.
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Appendix 41
9 APPENDIX
Appendix 1 Results from 54 pup surveys of the Seal Bay Australian sea lion population undertaken between 30 May and 300 December 2007. Observers include Clarence Kennedy (CK), Rebecca McIntosh ( RM), Rachael Gray (RG). BP = Brown Pup, MP = moulted pup, New = new live pup, Chip = micro-chipped pup, Dead = new dead pup.
Accumulated count Total for day of survey Survey Observers Cumulative Cumulative Total live New Chipped New
No. Date Dead Born Alive count BP MP Births Total Dead 1 CK 30-May 0 1 1 1 0 0 1 0 0 2 CK 6-Jun 0 2 2 1 1 0 1 0 0 3 CK 12-Jun 0 2 2 1 1 0 0 0 0 4 CK 15-Jun 1 3 2 2 2 0 1 0 1 5 CK 19-Jun 1 5 4 3 3 0 2 0 0 6 CK 21-Jun 2 6 4 3 3 0 1 0 1 7 CK 26-Jun 2 9 7 6 6 0 3 0 0 8 CK 29-Jun 2 12 10 10 10 0 3 0 0 9 CK 5-Jul 2 13 11 9 9 0 1 0 0
Survey West Cove WU WE Dunes West No. BP MP New Chip Dead BP MP New Chip Dead BP MP New Chip Dead 1 2 1 1 3 1 4 1 5 1 1 1 6 1 1 7 2 1 2 1 8 1 1 3 1 3 9 1 2 2