Table Of ContentSOUTHERN HEMISPHERE GROUP IV HUMPBACKWHALES: THEIR STATUS
FROM RECENTAERIAL SURVEY
JOHN L. BANNISTERAND SHARON L. HEDLEY
Bannister, J.L. & Hedley, S.L. 2001 12 31: Southern Hemisphere Group IV humpback
whales: theirstatus fromrecent aerial survey. Memoirs ofthe QueenslandMuseum 47(2):
587-598, Brisbane. ISSN 0079-8835.
From 1976to 1994, aerial surveys ofSouthern Hemisphere 'Group IV1humpbackwhales,
Megapteranovaeangliae.wereundertakentoproviderelativeabundanceindicesofanimals
migratingnorthwardalongtheWestern Australiancoast. Thesedemonstratedahighrateof
population increase, at least between 1982 and 1991, of -10% per year. Surveys were
conductedover 10 'good'days inmid-Julyin an area offSharkBay, WA, wherehumpback
whales were taken in the last years of Australian whaling, to 1963. The 1994 survey
confirmedtheincreaseratewithanestimatedpopulationof4-5,000.Themostrecentsurvey,
in 1999,plannedtoobtain anestimateofabsoluteabundance,wasconsiderablyaffectedby
poorweather(only 15 'good'days'flyingwerepossibleoutof30plannedovertwomonths).
Nevertheless, applying a correction factor for animals missed while submerged to the
estimated number ofanimals sighted gives the 1999 population size within 8,207-13,640.
Theresultisdependenton 'deepdiving'timeandwouldbeproportionallylowershouldthis
divetimebe lessthantherangeused(10-15 minutes). Wereviewreportedratesofincrease
and population estimates for this stock in the Antarctic, as well as preliminary Southern
Hemisphere population estimates that take accountofmuch largerthan officiallyreported
catches in the 1950s-60s. Plans for future surveys are discussed. The population's
exploitation history is briefly reviewed. Humpback whale, aerial survey, population
estimate, recovery, WesternAustralia.
John L. Bannister, c/- The Western Australian Museum, Francis Sreet, Perth 6000,
Australia;SharonL.Hedley,SouthwestFisheriesScienceCenter,POBox271,LaJolla, CA
92038, USA; 5 October2001.
Since 1976aerialsurveyshavebeenconducted HISTORY OF EXPLOITATION
offShark Bay, Western Australia, to investigate
possible increase in numbers in the Southern Humpback whales were the first Southern
Hemispherehumpbackwhale,Megaptera novae- Hemisphere whale species to be taken during
aqgticte, Group IV population. That population, 'modern'whaling,using steamcatcherboats and
summering in the Antarctic between ~80°E- explosive harpoons. Starting in 1904 at South
120°E, and wintering offthe coast ofWA, was Georgia, large catches were obtained in the early
severely depleted by whaling twice in the 20th years, followed by a rapid decline (Mackintosh,
Century, in 1934-1939 and 1949-1963. When 1965). By 1916 some 38,000 animals had been
Australian humpback whaling ceased in 1963, taken in the western South Atlantic (Find!ay et
the population was calculated to have been al, 2000), with -8,000 in 1910 and 1911. Over
reduced to 3.5-5% ofits pre-1935 state. 16,000 were also taken from 1909-1914 on the
westcoast ofSouth Africa.
Following increasing reports of humpback
whale sightings off the WA coast in the early- 'Modern' whaling of humpback whales off
mid-1970s, surveys of animals during their Australia began in 1912 (Dakin, 1963). Before
northward migration were undertaken from that, as elsewhere, 19th Century 'open boat'
whalers (using hand harpoons and based on
Carnarvon (24°52'S, 113°38'E) in an area off
SharkBay. Thesefindingsservedforcomparison pelagic sailing vessels or from shore), had taken
withaerial spotterandotherdatafromoperations humpback whales but not generally as the
there in the lastyearofwhaling. preferredprey. Although coastal inhabit, at least
duringtheirwintermigrations,humpbackwhales
Thispaperreviewstheresultsofaerial surveys were harder to catch than slower moving right
from 1976-1999 in the context of estimates of whales (Eubalaena australis). Their oil was not
initial population size, recent results from as sought after as that from right or sperm
Antarctic surveys and preliminary estimates of (Physeter macrocephalus) whales, and their
current Southern Hemisphere stock sizes. relatively short and inflexible baleen was not as
MEMOIR! HEQI ENS! A 5WJM
I I '
n ,!'' 'Alimit's. Ne* erik-less, C h.ttleborough, 1965); :lI 1935-193*. pelagic
Kos were taIken| by pelagic whalers on the PTtheWcoast(Chjttlcfaorough, 1%5);
breeding grouNndWs* for example off Datflpfcr and iiit 1949-1963, shore-based i ! &Wi
tAhueliurpmeilgangiol.nmalonuAVuVsAtirna:liisal,s(iain;idnMissoicmie, Id9m86i. Pum5i0-1(9l6o3a)ieosn (di1e94W9-1co9a5s5t,)aannddboCamrnAalrbvaonny
1952- 963) on the S coast (Chtttleborough.
iistrnlian* humpback whales have bfietl gen- f
Bannister. "64).
eralIv regarded as belonging to two populations, : I
rated during the fi crding m by the The major eaiehes w : taken in the pre-
I i
Australiancontinent,and,despiteasmall amount pd -WWII periods 1935 1939 and L949
I
of miving, feeding on generally separated Chiuleborough 1196$) records 7.744 anin
AthnetaWrcAticcoarsetedbienlgonggrotuondthse.SAonuitmhaelrsn bIrfeetendiispnhgtioff ih,,e \l\aQttfetr.WAA ifnutrhtehetroi^meiwaenrde 1c2a.u3g1h2tto I u<
'Group IV population while Chose oil' the east (Bannister, 1964),
coast belong to 'Group V. These appellations in addition, between 1928-1938andfrom1048
i! .1 used by Mackintosh ( i942), die word ma! least 1963, therewas pelagic whalingonthe
'Group' denoting a population occupying a Group IV population at the Mhei cud of the
tropical breeding ground and a feeding area (in migration, iW the Antarctic feeding grounds
the Antarctic] to the south. These were based on Prior tO WWII 6.000 an-mak vvere |akgn
awnhiamlaelsm,ariknidnivgidrueasullsts:mairnktehde ewahsieleQffGeredoiunpg IiVn post-WWI-Ihiasbiemtiwleaernnum95b0e-r1v9*6a2so(fCfhiictiatlllcybortcVcWogrhd-.
scc(aKuoaummygmnhmeetorr.niinn19wwt4hii0ent)thAenrTtoahtorehfcfetaristcshSubeomeputWttwAiehoeennrconlBaisOatsHM,ebOemftteiPnsBptbIhiJe3re c1a9it6c5h)..i.-nBgt|hyaatt19wb6ho3al,lhitnheegndssht1uoodcfkbdteehcceloirmnweeg|ruens'eu.lctoinngo,miftscraoslmo
and Australian humpback whaling ceased
humpback whales. (heGroup IV bicedingground
i; COfKefttrated close to the coast (in this case o\' I hittlcborough (lOofo calculated that ..-
WA). In temperate and tropica! ^aier, catchee Orowp iv stock depletion to 1962 could h
and sightings in both the 1*>th and 20th Cenmnes been tromahighoi'17.000animalspriorto 19 I'S
were eoii.il Miggesling thai the anunals ooi - 10,000 in 1949, and to fewer than 800
|
concentrated near shore and were not evenly animals at the end Of 1962 Including the 1963
distributed across open pecans (Dawbin, 1966). catch, the decline was calculated as to 601
Mackintosh originally recognised five groups the end ofthat year(Bamlistei 1964),
will) animal,-, migrating between Antarctic feed- Revelations of unreporled illegal Souti.
ing grounds and wanner-water breeding grounds Hemisphere pelagic catches by Soviet fleets
offChile, inthe South Atlantic, offSouth Africa, before and after 1963 (Yablokov |994) have led
oil'western Australia and ofT eastern Ausiralie1 to a considerable revision of the catch figures.
New Zealand. Their formal longitudinal limits The overall Group IV eateh is now estimated as
TgwrheoreuenGdrtsoa,kuepinnIciVlruopdnoiipnugklnattohiowosnne wobaafslehetuhnmupswbdhaeasclikegnw(ahfteieeddinags 'I-bfIrm7ed,el0d4ai0yngfoelrst1oa9lc4k,7-L2V109060is3,,edqtau^bidlvea-s4le8nI0tafntoodr 1G9IrI6,o4uwphIeIrVie,
occurring between 70°E-13GPE. In 1965, excep! lhai for eaiehes south of40*5, those for
Mackintosh amended his five groups to six to Group IV have been taken as occurring between
include two in the South Atlantic, one wintering 60°1 -i-Mn- |IW( I998an. ihe revision ofthe
sorfuelgcgeBenrstatlzeyidl,,(stIehnetveeronntahtemiroanjoafolfrWwhegasrltoeiurnpngsAIfhoramicvuanessbWieooerune, CIjrQirUnotduhlpayofVel4pmaolp'.Su\l2a0it0si0,o,envbeutni' bh'iebgihrweeere.edninCghti2su0ll°oeEcb-ko1r7Eotu1FgWih,n
1998a), including, one in the central South (1965) believed thai to explain the very high
Pacific, bin the distinction beiween animals mortality poeffieients be obtained Um- thai
wintcringoffthewestandeastcoastsofAustralia population o\ei thcshorl period 1959-1962there
reman musthavebeen unreportedcatches m dieordetof
Twentieth Century humpback whaling on the 5,000 in 1961 and 1962. In fact, foi theGroupV
ip iv population offthe WA coasi occurred in population the true total catch for 1959-1962 is
three main phases: i) 1912-1916, 1922-1928,with nated as 15,975 (fmdlav ci al . 201 I
shot. btiS d onrelieNs Wmainly from Norwegian compare^ with 3,918 reported at the time
Bay/Point CToatcs, Australia [Dakin,1963; (Chiuleborough 1965); for fteyears 1961-1962
.
GROUP IV HUMPBACK WHALE STATUS 589
5001) Group IV coveringthehumpbackwhales'north
4000 and south migration routes. From
S 3000 then until the early 1970s there were
few, ifany, reports ofsightings along
2000 WA
the coast, in line with the
1000 conclusion of Findlay et al. (2000)
jl. that Southern Hemisphere stocks
!
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 were at their lowest level in about
year(0=1930) 1968 -- perhaps less than 1,000
animals.
9000 Inwintersofthemid-1970'sreports
8000 GroupV begWanAofhumpback whale sightings
off in formerconcentration areas
7000
such as Shark Bay. Aerial surveys
6000 were conducted there annually from
5000 1976-1978 and repeated in 1980, 1982
and approximately every three years
4000
thereafter (Bannister, 1985). Surveys
:('0iJ were designed to cover the area
2O00 searched by the whaling operations,
particularlyoutside Shark Bay,where
1000
uu. catching had been concentrated in
• a.* I. I 1963, the last year ofwhaling there.
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 From 1982 each survey covered the
year(0=1930) same area, with the same flight path,
typeofaircraftand,asfaraspossible,
FIcGo.luIm.nC)omcaptacrhiessonfroomf 'tohfefiGciraol'up(liIgVhtacnodluGmrno)upanVd pacotpuuallat(idoanrsk, the same pilot and observer. Each
tookplaceoverten 'good'flyingdays
1930-72.
in mid-July when the maximum
number ofanimals would be moving
it is 3,549 compared with 1,483. For that stock,
and for Group IV, considerable illegal catching northward through the area.
hboardoubgehensuopcpcousrerdi.ngItesvheonuledarbleiernottheadnhCohwiettvleer- sigRneisfuilctasnttloy1m9o8r8e(Bhaunmnpisbtaecrketwahl.a,le19s9i1g)htsihnogwseidn
that at least two Group V substocks have been the area in the 1980's than in 1963. Further
recognised, from their breeding ground dis- surveys, in 1991 and 1994, demonstrated annual
tribution, one centred on the Australian east increase rates of -10% (instantaneous rates,
coast, the other on Fiji/Tonga (Dawbin, 1966). obtained from the regression of Log n of the
Chittleborough's Group V population estimate averagenumberseenperflyingdayeach year, of
was based largely on a breeding component on 10.09±3.0%, 10.00±4.6%respectively; Bannister,
the east Australian coast and a feeding com- 1994, 1995). Using a log-transformation of the
ponent between 130°E-170°W. A comparison of number seen on each flying day in each year,
reported and actual catches for both stocks is 1982-1994, the annual rate was 10.15 ± 4.6%
given in Fig. 1 (Fig. 2). Such high population growth rates, i.e.
AERIAL SURVEYS >10%,areconsideredtobewithinthemaximum
biologically possible (IWC, 1998b) and are
1976-1994 SURVEYS. Anindicationofthe very feasible if: the average pregnancy rate is 0.5;
low humpback whale stock levels in the survival rates are high(atleast0.96); andtheage
mid-1960's was given by the results ofa survey at first parturition is relatively low, i.e. at a
for sperm whales off the WA coast, flown at maximum of8 years (Brandao et al., 2000).
monthly intervals from April 1963 to March By comparison with the estimated population
1965 (Bannister, 1968). Only ten humpback
of568 at the end of 1963 (Bannister, 1964), the
whale contacts were recorded. The flight path size in 1994 was estimatedat4-5,000 (Bannister,
coveredanareaseawardsofthecontinentalshelf,
1995).
but observations were made from the shoreline
offSharkBay, Geraldton, Perth andAlbany,thus The 1994surveyresultsindicatedthattodetect
590 MEMOIRS OF THE QUEENSLAND MUSEUM
To allow for comparability with
earlier results, the same transect grid
was flown asinall surveys since 1982,
i.e. approximatelyW80 x 30 nautical
miles immediately ofBernier, Dorre
andDirkHartogIslandsonthewestern
boundary of Shark Bay, between
112°30,-113o10'Eand24o46,-26o09'S
(Fig. 3). The N-S distance between
gridlines varied between 7-8nm.
Toexaminetheextentofcoverageof
the humpback whale migration path.
transects were extended seawards of
the area on two occasions, out to the
operational limits of the aircraft (to
W
FIG 2. Aerial survey, outside Shark Bay, 1982-94: regression of 112°14.rE), 50nm oftheWnorthern
sightingratesperflyingday(log-transformed,i.e.Log/;)peryear. tip of Bernier I., i.e. 20nm of the
normal seaward limit ofthe survey at
a significant difference in population size in that latitude.
futureyears, atanannualrateof10%, an interval To examine the distribution of humpback
ofthreeyearswouldberequiredbetweensurveys whales within Shark Bay, which earlier surveys
(N. Caputi, in Bannister, 1995). Given funding suggested was a 'resting area' for migrating
constraints, that survey was carried out in 1999. individuals, flights were conducted in an area
-70 x 30nm between 113o04,-113°35,E and
1999 SURVEY. Previous surveys, originating in
24°58'-25°32,S, within the bay. All analyses in
1976 and modified in 1982, were designed to
this paper, however, refer to animals in the area
provide a relative index of abundance over a
relatively shortperiod (ten 'good1 flyingdays) in "outside the bay', where they are assumed to be
mid-July, during the animals' northward actively migrating.
migration. That period was chosen on con- Based on a review of migration patterns off
siderationofexpectedweatherconditionsandfor western and eastern Australia (Chittleborough,
cspoomtptaerridsaotna,wiatnhdawvhaielnabmleosctom(m7e0r%c)iahluwmhpablaicnkg 1965; Bryden etal., 1996; Dawbin 1997)thetwo
month period between 15 June and 15 August
whales would be moving northwards.
Bycontrast,the 1999survey(Bannister&Burton, wmaajsorcihtoyseonffnoorrtthhewasrudr-vmeiy,gradutriinngg hwuhmipchbatchke
2000) was designed to provide an absolute
whalescouldbeexpectedtotraversethearea.For
abundance estimate of northward-moving
animals, in the same area, but over a longer logistical reasons (availability ofobservers and
(-2-month)periodthan earliersurveys. It used a aircraft) the period was later amended to 21
ParlenaviaP68B high-wing, twin-engineaircraft June-20August. Thirtyflights(oneeverysecond
(Tropicair Services Pty Ltd) flying at 120 knots day) were proposed, but it was decided to allow
and 1500 feet, with two observers, one on either forpossible comparison with earlier survey data
side of the aircraft, seated behind the pilot. (i.e. to 1994), by including aperiod offlights on
Bubble observation windows were fitted to ten consecutive days over 9-18 July (the 'com-
maximisetheareaswept,particularlytocoverthe parable ten-day period'). On that basis, taking
area immediately below the aircraft. A GPS and account of the probable changing density of
OD-baard computer system were available. To whalesoverthetwomonths, avariable sampling
measureanglestosightingsaclinometer(industry regime was planned. This required sampling
standard Suunto PM-5/360PC) was used for everytwodaystowardsthebeginningandendof
declination, and an angleboard for horizontal the two months (when number—s could be
angles. expectedto be relatively low) and apart fr—om
Difficulties with the availability and fitting of the mid-July 'comparable ten-day period'
thebubblewindowsandassociatedairworthiness every three days towards the middle (when
led to the first two flights taking place without numbers should be higher), while still providing
them. 30 flying days overall.
GROUP IV HUMPBACKWHALE STATUS 591
Carnarvon
movenortheast n=28 movesouthwest n=4 moveeast n=1 non-directional n=257
-- 21 mo•ve2southeast n=3 — 2 • 3
movenorth n=211 V 2 movewest n=2 • *
i 1 movesouth n=15 «- 2
t 2 u 1
2
t 3
FIG. 3. Aerial Survey, outside Shark Bay, 1999: flight path, sighting positions, numbers and directions of
humpbackwhale movement forthe sixcompleted flightswithinthe 'comparable ten-dayperiod', 9-18 July.
RESULTS theproportionoffcgood' flyingdays, particularly
consecutive ones, was low. Survey days were
FIELDWORK. The planned start date (21 June restrictedtothosewithwindspeedsof<15knots.
1999) was delayed to 24 June, through observer Only 18 flights could be attempted in those
availability and for fitting of bubble windows.
The finishing date (20 August) was brought conditions, and ofthose, 15 were completed, the
forwardto 19 August, againbecause ofobserver remaining 3 being terminated early because of
availability. deteriorating weather. For the first of the 15
Planned coverage of 30 flying days was n—ot completed days the bubble windows were not
achieved because ofpoor weather conditions available. For the 'comparable ten-day period',
592 MEMOIRS OF THE QUEENSLAND MUSEUM
B
12 12
3 4 5 3 4 5
Perpendiculardistance(km) Perpendiculardistance(km)
FIG. 4. Aerial survey, outside Shark Bay, 1999: estimation ofstrip-width. Fitted detection function forchosen
Hazard Rate) model: A, based on exact perpendiculardistances; B, based on selected cut-points.
(
9-18July,onlysixcompleteflightswerepossible distances(Fig.4A)forthecandidatemodelchosen.
due to bad weather. The extended legs seawards Clearlytheobservers,evenwithbubblewindows
ofthemainsearchareawereflownasplanned,on fitted, either could not see directly beneath the
two occasions, 4 and 27 July. aircraft, or found it preferable to scan out to the
An example ofthe results obtained is given in horizonand focusonareas furtheraway fromthe
Fig.3,whichshowstheflightpathanddistribution trackline. As a result, for the analysis the data
of sightings for the combined 'outside the bay' weregrouped(Fig.4B). Estimatedmeanpodsize
data for the six completed flights within the was 1.87(95%CI 1.7894, 1.9588);becausethere
'comparable ten-day period*, 9-18 July. was evidence that recorded pod size decreased
with perpendicular distance from the transect
DATA ANALYSIS. Population Size. Data from line,the estimatewasobtained from aregression
the 14 'good' days flown (excluding the one oflog (pod size) against perpendiculardistance.
withoutbubblewindows)wereanalysedbycom-
bining standard aerial line transect methodology In fitting migration models to the daily pod
with a migration count approach (Bannister & counts, itwas assumedthattherateofpassage of
Hedley, 2000). Effective strip width was thewhales through the survey areawas such that
estimated by pooling data from all flights using no whale seen on one daywouldbe available for
DISTANCE software (Laakeetal„ 1995),which detection on the subsequent day. With the
also gave an estimate of mean pod size. The northern and southern boundaries -90nm apart,
number of pods passing through the surveyed an animal would have to travel at an average
area was then estimated from the daily counts speed ofless than 3.78 knots for the assumption
usinga FORTRAN program, GWNORM(Buck- not to hold. Four alternative scenarios were
land, 1992), which fits a density function based considered (Fig. 5A-D) to allow for analyses of
onakey function (usuallyaNormal distribution) two sets ofdata (from E-W legs only; from all
and Hermite polynomial adjustment terms, by transects,i.e. includingN-S legs) intwodifferent
maximum likelihood methods. Outputs from the migration periods (80 days, 1 1 June-1 Sept.; 100
line transect analysis and the migration days, 1 June-8Sept.).Themigrationperiodswere
modelling were combined to obtain an estimate based on Group V Australian coastal surveys
of the number of individual whales passing wherethere has been some variation in length of
through the survey area during the migration the observed northward migration (75-85 days,
period. Paterson et al., 2001; up to 110 days, Bryden et
Estimatedstrip half-widthwas 3.34km, froma al., 1996). While adding the N-S transects
hazardratemodelchosenasthe'best'model from increases the data available for analysis, the use
four fitted, using Akaike's Information Criterion of E-W legs only is preferred, because the
(Akaike. 1973). Difficulty was experienced analysis relies on the random placement of
initially through significant lack-of-fit for small transectswithrespectto thewhales'distribution.
GROUP IV HUMPBACK WHALE STATUS 593
North-bound whales; all legs B North-bound whales; E/W legs
20 40 60 80 100 20 40 60 80 100
Dayssince1stJune Dayssince1stJune
North-bound whales; E/W legs D North-bound whales; E/W legs
20 40 60 20 40 60
Dayssince1stJune Dayssince11thJune
FIG. 5. Aerial survey, outside Shark Bay, 1999: A-D, pods sighted on 'completed' days, together with fitted
curves, forcombinations oftransects (legs) andmigrationperiods.
The E-W transects, being perpendicular to the by wind speed, was generally worse than later.
marked density gradient (with higher densities Modal wind speed for the first three completed
near the coast and being latitudinally system- flights (3, 4, 7 July) was -12 knots (range 10-16
atically spaced throughout the area [Fig. 3]), knots) comparedwith 8 knots (range0-12 knots)
provide representative coverage; that is not the thereafter; thus it is likely that there was some
case for the N-S transects, use ofwhich gives a undercounting in the earlierpart.
biased estimation. Results for the four scenarios ii) Estimate ofg(0). The probability ofdetecting
(Table 1)givepointestimatesrangingfrom3,249 animals onthetrackline, g(0), was nottaken into
to 3,441 with 95% CI, with a lower bound of account in earlier surveys where relative
2,706 andupperbound of4,294. abundance indices were the objective. For the
Two major factors influenced the 1999
estimate, one operational, the other analytical: TABLE 1. Aerial surveyestimatesofpopulation size,
'outside' Shark Bay, Western Australia, 1999,
i) Data quality. Given the 60 days allocated for northbound animals only. *Number ofanimals; **
thesurveyandtheplannedcoverageof30flights, 95% C.I.
thenumberofcompleted flights (14) is small for
fitting to a migration model, particularly given 80dayperiod 100dayperio
theunevennessofthecoverage. Also,theexpected Legs (1 1 June-1 Sept) (1 June-8Sept)
peak of the migration (around mid-July) was Estimate* Range** Estimate* Range**
inadequately sampled. In addition, the weather E-W 3,365 2,706-4,185 3,441 2,757-4,294
early in the period ofcompleted flights, judged All 3,249 2,720-3,881 3,434 2,864-4,117
594 MEMOIRS OF THE QUEENSLAND MUSEUM
120- ~10-15mins, bearing in mind
that d, at least, may be
-^m overestimated.
To obtain /, a subset of
so observations ofdeclination and
horizontal angles, comprising
66 those obtained during the west
coast 1999 survey 'comparable
ten-day period', 9-18 July, has
40
been used to provide inform-
ation on the distance from the
20 aircraft at which sightings were
made. In this case the distance
calculated was parallel to the
10
7 6 5 4 3 2 -1 -2 -3 -4 -5 -6 -7 cruise track, and not perpen-
distance, by 1km (+=ahead, - aft), planeflying rightto left dicularto it as in the calculation
ofstrip-widthabove.Theresults
FIG. 6. Aerial survey, outside Shark Bay, 1999: distribution ofsighting (Fig. 6) show that a high
distancesahead,abeamandaftoftheobservers,overthesix'good'days. proportion of sightings was
9-18 July. made directly abeam; that may
be lessafunction ofthedistance
1999survey,wherethe intentionwastoobtainan atwhichtheanimalsoccurredthanthetimetaken
absolute estimate, and given that whales to make the measurements. From the results as
generallyspendaconsiderably longertimeunder presented, a maximum value for the sighting
water than at the surface, a knowledge ofg(0) is 'window' can be estimated at -8km, comprising
essential. Barlow et al. (1988) derived a animalsseenahead(generallyupto5km),abeam
correction factor for the probability of missing
and aft (up to 3km).
submerged animals during aerial surveys of
eastern Pacific harbour porpoises as: However, estimation of g(0) by this method
Pr{being visible) = (s+t)f(s+d) requires the assumption of a rectangular
s(iu.rwef.haec'red,eeedsp=-=diaavvvieenrrgaa'g)ge,ettiaimnmedespaten=ntanbwieimlnaoldwostwthaeyossfuarttfiatmcheee gws'uiaivrvnafedianolcawepb,eiarlitip.teea.ynnpdwyaiircandulidllsoeatlrwa'tndociietsnhteaawlnhtocrienacgnhissetcaehtqewulhailanleelln.ygeAtlhlpitokohdefolyauttghthaeo
duringwhichan animal iswithinthevisual range sightings were clearly peaked abeam (thus
ofan observer. violating the assumption), that seems likely to
Applying the above for humpback whales, have been caused by the way the measurements
valuesfors,/and</canbeestimatedwithvarying were obtained, as noted above. Smoothing the
degrees of precision. Migrating humpback data by eye to obtain a more appropriate idea of
WA
whales off the coast are reported to blow the likely rectangular sighting window suggests
severaltimes atthe surface overaperiodof-2-5 its length might be less than 8km, i.e. forward to
minutes and then dive for -10-15 minutes (C. 3.5km and back only to 1km, giving a 'window'
Jenner, C. Burton, pers. comm.). Those observ- of 4.5km, which can be taken as a minimum
ations correspond with the ionger, presumably estimate. At 120 knots, 8km wouldbecoveredin
deeper, dives of 8 to 15 minutes [surfacing] 2.2 minutes, and4.5km in 1.2 minutes.
...
ArbWeueigstnutwlnreaarel&lniya'Rndeiirveceaehpssoltreftycoeord(a1sa9tfb8,o5or)uh.tohwuI4enmvfpemobrira,nmuacttkseiusogw,nghefasbrltloesosmwtithbnhayget tvhaerMitiarbnuleiemmsiuanmreiamtnhuedmn:mvaaslx=uie2m,mua5m;ydbvea=l<u11e00s,);f1o5tr—(tah1le.t2ht,o2hu.r2ge.he
divingintervalsmaybeshortenwithdeeperdives The longer the time the whale spends at the
ranging from as little as 2 or3 minutesto 5 or 10 surface (s), and the shorter the time spent deep-
minutes (M. Bryden, R. Paterson, pers. comm.), diving(d),thegreatertheprobabilityofseeingall
with larger groups of animals, i.e. 3 or more, animals present; the converse is true for the
diving more frequently than single animals or sighting 'window1 (t). The most conservative
pairs (M. Brown, pers. comm.). We have takens population estimate is that derived by using the
for west coast animals as -2-5mins and d as highest probability of detecting animals, while
GROUP IV HUMPBACK WHALE STATUS 595
the least conservative is that derived using the range calculated with a diving time of 10-15
corresponding lowest probability. However, minutes.
theseprobabilities are unknown,and thedata are In all the above it has been assumed that an
insufficient to estimate them accurately. Given estimate of the number of animals passing
wt=(hiPet1rh.mu2n,sacxa=en)r2td,hatiadhns=etbilee1ise5k,,neltteyh=se't2lil.oim2wk,aeetsnletoyd't'ipuhnrsigoigbnhtagehbasait*tl=1oiptt5rhy,oe(bdrPav—rbaimll1iu0in,et)syt Ggn'rooreuroattutshipwdmeaIa'rjVdoSprhomipaiturgylrkaaottfBiiaootynnheswfiipozlorelpautsbhleeaatawifuholtonlrluemee,ixgteiers.enat.ttitemhsaoatftepttaohhseetf
forthese parameters are also potentially feasible Shark Bay each year. That does not take into
(e.g. d <10) and may thus extend the range of account the possibility of sex-biased migration
detection probabilities. (Brown et al., 1995), nor that in any one year
ThenPrmax=(5+1.2)/(5+10)i.e.0.4l;whiie someanimalsmay notmigrateas farnorthupthe
Prmin =(24- 2.2)/(2 + 15) i.e. 0.25. WAcoastasSharkBay.Giventhosepossibilities,
any figure obtained forGroup IVpopulation size
Applying those factors to the more conserv-
pateirvieoodfaesntdimaEt-esWinleTgasbleonl1y(,tha3t,3fo6r5)thegi8v0esdaya fmrionmiameurimalesstuirmvaetyes.offShark Bay is likelytobea
minimum adjusted population estimate of8,207 RECENTANTARCTIC ESTIMATES
and amaximum of13.460. Ifdwere indeed <10,
theminimumestimatecouldbelower,butit isnot Independent estimates ofpopulation size and
possible to say by how much. If, for example, d increase rate for the Group IV population have
were as low as 5, theprobability ofdetecting the been derived from sightings obtained during the
animals on the trackline would be increased to Japanese Research Programme in the Antarctic
0.62, and the adjusted population size would be (JARPA) in -Area IV, which includes the Group
reduced to 5,427. IV feeding grounds (Matsuoka et al., 2000).
It seems appropriate to conclude that the Sightings south of 60°S from two sources
population passing through the survey area in (dedicated sightings vessels and sighting and
1999 would have numbered more than the most samplingvessels)giveestimatesofabundance in
conservative estimate unadjusted for g(0), i.e. the 1999/2000 Antarctic summer of 12,664
3,365. With 'deep diving time', d. of 10-15 (coefficientofvariation=0.28)and 11,138(CV=
minutes, the 1999 population size lies within the 0.29) respectively. Density estimates from six
range 8,207-13,640. However, should d indeed seasons'data,between 1989/1990and 1999/2000.
be closer to 5 minutes than 10, the lower bound give an instantaneous increase rate of 12.41%
could be 5,427. (Matsuoka et al.: fig. 5), equivalent to an annual
From the most recent survey results (Paterson rate of 13.2%. It should be noted, however, that
et ah, 2001) of animals migrating along the there isa small amountofinterminglingbetween
animals from each population on the feeding
Australian east coast past Stradbroke Island.
Queensland, GroupV population size (at leastas grounds (Chittleborough, 1965; Dawbin 1966),
ritalrieafneresasttocoaansitm)ailns1m9i9g9rawtaisng3,a6l0o0ng± 4th4e0A(u9s5t%- peasrttiimcautleasrloyfinabAurnedaanIcVetboatsheedeoanstAorfea11I5V°E,assoa
CI). Another east coast survey, in 1999, did not whole(i.e. to 130°E)arelikelytobeoverestimates
yield conclusive results (M. Brown, pers. ofthe Group IV population.
comm.): poor weather led to a lack of observ- The Area IV-based population sizes quoted
ations at the migration peak. But based on a above lieinthe upperpartoftherangecalculated
successful surveyin 1996. andatan increaserate for the 1999 Australian west coast survey. In
of 12.3% (Bryden et al., 1996), that part ofthe addition to the intermingling already noted,
Group V population size in 2000 would be differential migration, where not all animals
-4,600. The Group IV (Antarctic Area IV and migrate northward each year, would result in a
Australian west coast) population has generally higher estimate in the Antarctic. Similarly, the
been considered larger than that ofthe Group V increase rate, although within the 95%
(Antarctic Area V and Australian east coast) confidence interval forthe Australian west coast
population, by some 20-70% (Chittleborough, estimate (10.15 ± 4.6%), is higherthan the point
1965). On that basis the two recent Group V estimate, and of the order of that recorded
results would implya 1999 Group IV population recently for animals on the east coast (e.g.
size of4.300-7,800, i.e. somewhat less than the Paterson et al., 2001).
596 MEMOIRS OF THE QUEENSLAND MUSEUM
RECENT SOUTHERN HEMISPHERE iii) To 'ground-truth' the aerial survey
POPULATION ESTIMATES sightings, andto provide estimates ofswimming
speed and diving interval, a program of land-
Preliminary assessments of Southern based sightings should be undertaken over at
Hemisphere population size based on Antarctic least ten 'good* days from an appropriate
catches, adjusted to account for the previously location,possiblythesouthernpartofDirkHartog
unreported illegal Soviet take and usingreported Island. This should occur towards the middle of
increase rates and target stock sizes (Findlay et thesurveyperiod, i.e. atthe expected peakofthe
al.. 2000). placethe 1999Group IVpopulationat migration. It is important that flying and land-
7.686 using the 1977-1991 Australian westcoast based observations occur on the same days.
annual increaserateof10.9%and 1991 stocksize Timing ofsurveys beyond the next one should
of3,300(fromBannister, 1994). Themajoreffect be determined from its results, using a power
ofthe greatly increased catches is to increase the analysis similar to that undertaken previously
estimates of initial population size. Various (Caputi, in Bannister. 1995) on which thesurvey
combinationsofcatchesapportionedbetweenthe planned forthree years after 1994 was based. At
relevantstocksareused; theaboveusesthe 'Base an annual increase rate of -10%, 60% initial
Case' scenario, with a 'naive' catch apportion- population level (i.e. 12.600) might be reached
mentandnooverlapbetweenGroups. ForGroup
very soon: from a 1999 level of 8,000, for
IV, rather than the earlier estimate of 12-17.000 example, it would be reached by the year 2002,
(Chittleborough, 1965), initial population size is and from 5,000 by the year 2006. It is clearly
preliminarily estimated as -21,000. While the important that the next survey should be
Group IV stock has so far shown encouraging
undertaken as soon as possible.
recovery, itisstill estimatedassome4,900(39%)
below Maximum Sustainable Yield Level ACKNOWLEDGEMENTS
(MSYL, 60% ofinitial stock size) of 12,600. By
contrast, the Group V stock is still considerably Advice on the 1976-94 surveys was provided
depleted, despite a high recent increase rate of intheearlystagesbyR.G.Chittleboroughandthe
12.3%; the preliminary estimate of 1999 stock late W.H. Dawbin, and later by G.P. Kirkwood
sizeof4,615 is-11,500(71%)belowMSYL.The and N. Caputi. Field work was largely the
lowest point for either population would have responsibilityofthelateJ. Bell(pilot), the lateK.
been reached in 1968, with an estimated 268 Godfrey, and A. Murdoch (observers). Analyses
animals in the Group IV population and 104 in wereundertakenbyG.R Kirkwood, S. Wayteand
Group V. N. Caputi.
Forthe 999survey,thehardworkanddedicat-
FUTURE AERIAL SURVEYS 1
ionofthepilots(M. Whyte, R. Easter)andobservers
Given the disappointing 1999 aerial survey (wMo.rkBrawsasseuru,nCd,erJactohbes)suispearcvkinsoiwolnedogfedC..FLi.eKl.d
results off Shark Bay, particularly the small Burton. G.R Donovan and D.S. Butterworth
number ofdays' coverage, plans are in hand to
advised on survey methodology and regression
undertake another survey in the same area and analysis; G.R Donovan supplied relevant data
over the same period as soon as possible. The
forms. G.R Donovan, RB. Best and L. Petersen
following considerations will be taken into
advised on the use of bubble windows. For
account.
migration and dive times, C. Jenner and C.L.K.
i) The survey should again have the objective Burtonprovided informationfromthewestcoast,
ofproviding an estimate ofabsolute abundance M.R. Brown, M.M. Bryden, D.H. Cato and R.
ofnorthward migrating animals in the Group IV Paterson from the east coast. K.R Findlay
population. advisedonobservationsoffeasternSouthAfrica.
beiir)epTlhaecefdorbmyear''sbaowx--tsoeoatrhc'h'(zfilgi-gzhatgp)aftohrmsahto,ultdo SS..LT..HBedulcekyl'asndde.taiJl.edBaanrallyoswiscwoasmmreevniteewdedobny
provide unbiased,representative, coverage. Legs estimation of the sighting 'window*. C.L.K.
shouldextendseawards from thewestern limitof Burton generated Fig. 4 and D. Elford assisted
the bay, i.e. the western shores shore ofBernier. with Figs 1, 2 and 6.
Dorre and Dirk Hartog Is, to allow for migrating The 1999 surveywas fundedby the Australian
animals apparently concentrated close to the Natural Heritage Trust through Environment
coast there (Fig. 3). Australia(ProjectOfficerR. McCulloch). Earlier
