zyxwvutsrqp zyxwvutsrq zyxwvu zyxwvu ARCTIC VOL. 40, NO. 1 (MARCH 1987) P. 33-42 Aerial Surveys for Cetaceans in the Former Akutan, Alaska, Whaling Grounds B.S. STEWART,’ S.A. KARL,’ P.K. YOCHEM,’ S . LEATHERWOOD’ and J.L. LAAKE’ (Received 5 June 1985; accepted in revised form 7 August 1986) zyxwvuts ABSTRACT. Randomized aerial surveys were flown between 26 July and 26August 1984 to search for cetaceans in two areas of southwestern Alaska: one on both Bering Sea and Pacific Ocean sides of the Aleutian Islands near the defunct Akutan shore-whaling station, which operated from 1912 through 1939, the other overlapping continental slope and shallow continental shelf waters between the Aleutians and the Pribilof Islands. Surveys were made at altitudes between about 150 m and 245 m from a Partenavia P68 Observer with a plexiglass nose bubble, which permitted center-line viewing. Searches covered about 3940 nautical miles (nm), including some 2403 nm of random transects. Sightings were made of gray whales (10 sightings, 14 individuals), fin whales (3, 1 l), minke whales (1, l), unidentified beaked whales ( I , 6), Dall’s porpoises (47, 131), killer whales (8, 26), and harbor porpoises (4,7). A Fourier series model was used to estimate density of Dall’s porpoises as 115 individuals (CV = 0.263) per 1000 nm2 on the whaling grounds and 16.6 individuals (CV=O.O) per lo00 n m 2 in the Bering Sea north of the whaling grounds. These estimates are comparable to those previously reported for the same general areas (97.2 animals per lo00 nm2, SD=49.5). There were too few sightings of other cetaceans to permit calculation of meaningful density estimates. At least four species of great whales (blue, fin,humpback and sperm) were sufficiently abundant during the first four decades of this century to support significant whaling activities within about 100 nm of Akutan (more than 5300 whales were caught during 23 years of whaling, 1912-39). Although previous studies of the fisheries showed a downward trend in catch per unit of effort and an increase in distance traveled to take whales, whales were still being taken at relatively high rates (0.28-0.51 whales per gross catcher day) at the end of the fishery in 1939. Populations of fin, humpback, blue and sperm whales were probably significantly reduced by shore and pelagic whaling conducted widely in the North Pacific since 1939. The low number of sightings on the present surveys probably means that populations on and near the whaling grounds remain depressed from such activities. Key words: aerial surveys, cetaceans, Bering Sea, North Pacific Ocean, historical whaling RÉSUMÉ. Des relevis aeriens ont étt effectues au hasard entre le 26 juillet etle 26 août 1984, afin de determiner la presence de cetacts dansdeux régions du Sud-Ouest de l’Alaska: l’une située des deux côtes des îles Aldoutiennes (du côte dela mer de Bering et du côté del’océan Pacifique), près de ce qui fut jadisle port baleinier d’Akukan qui resta en op6ration de 1912 à 1939; l’autre couvrantà la fois les eaux du talus continental et celles,peu profondes, de la plate-forme continentale, entre les îles Aleoutiennes et les îles Pribilof. Les relevds furent effectues à des altitudes comprises entre 150 et 245 m, d’un appareil d’observation Partenavia P68, muni d’un nez de plexiglas, permettant de voir dans l’axe de déplacement. Les recherches ont été effectuees sur environ 3940 milles nautiques (mn), y compris 2403 mn de recoupements au hasard. On a relev6 la presence de baleines grises (10 relevés, 14 individus),derorqualscommuns(3, ll),depetitsrorquals(l, l),debaleinesàbecnonidentifi6es(l,6),demarsouinsdeDal1(47,131),d’épaulards(8, 26) et demarsouins communs. On a utilise un modble en series de Fourier pour determiner approximativement la densit6 de marsouins de Dall à 115 individus (CV = 0.263) aux 1000 dans les zones de pêche à l a baleine, età 16.6 individus (CV = 0.0) aux lo00 mnz dans la mer de B6ring au nord des zones de pêche. Ces evaluations sont comparables à celles rapportees prkcedemment pour ces mêmes zones en gbnéral(97.2animaux aux 1000 m2, DS = 49.5). Troppeu d’autres cetaces ont et6 aperçus pour justifier le calcul des densites approximatives. Durant les quarante premitres années de ce siècle, ily avait au moins quatre espi?ces de grandes baleines (rorquals bleus, rorquals communs, rorqualsàbosse et cachalots) en quantité suffisante pour alimenter une industrie baleinibre dans un rayon d’environ 100 mn d’Akutan. (Plus de 5300 aleines furent pêchees durant les 23 années que dura la pêche àla baleine, de 1912 1939). Bien que des etudes pdcedentes sur la pêche aient montr ne tendance à la baisse du nombre de prises par rapport au nombre d’unitésd’effort et une augmentation de la distance à parcourir pour capturer les baleines,,celles-ci étaient captudes àun taux relativement élevé (de 0.28 à 0.51 baleine par unit6 d’effort brute par jour) à la fin de la pêche en 1939. Les populations de rorquals communs, de rorquals à bosse, de rorquals bleus et de cachalots ont probablement eté dduites de façonsignificative par le pêche côtibre et la pêche pélagique, qui ont et6 pratiqu6es à grande tchelle dansle Pacifique Nord depuis 1939. Le petit nombre de cetacCs aperçus durant les présents relevds porte àcroire queles populations dans les zones de pêche et dans leur vicinite, restent peu Blevees en raison de ces activitts. Mots clés: relevé aerien, cetacts, mer de Bering, Pacifique Nord, ancienne pêche à la baleine Traduit pour le journal par N6sida Loyer. zyxwvuts n tn ’ A INTRODUCTION Between 1912 and 1939 whaling operations were conducted from a shore station on Akutan Island, in the eastern Aleutian Islands, Alaska (Fig. 1). Between May andOctober in the years 1912, 1914-20, 1922-30 and 1934-39 two to seven vessels hunted whales within anapproximately 100 nautical mile (nm) radius of the station on both BeringSea and Pacific Ocean sides of the Aleutian Islands and in Unimak Pass. Catches consisted mainly of fin (Bulaenopteraphysalus) (at least 2498), humpback (Meguprera novaeangliae) (15 lo), blue (B. musculus) (835) and sperm (Physeter catodon) (482) whales, with occasional takesof right whales (Eubalaena glacialis)(9) and other species (Reeves et al., 1985). Trends in availability to the whalers of the four key species within andamong years (Leatherwood et al., 1985), interpreted in the context of other data available for the area (Leatherwood et al., 1983), suggest that: 1) Finwhales formerly were present on both sides of the Aleutian Islands chain from April through early September. In July and August they were found primarily in the Bering Sea, where they wererelatively abundant nearUnalaska and Akutan islands. The southeast Bering Sea apparently was animportant spring-summer feeding ground. By Augustor early September, the population center had shifted to the North Pacific. Migration between the two areas apparently concentrated in Unimak and Akutan passes. 2) Humpback whales were present in greatest numbers from June through August, in the Pacific, in Unimak Pass and inthe Bering Sea just north of the pass. 3) Blue whales were most abundant from June through August, almost exclusively on the Pacific side of the islands. 4) Sperm whales, all adult males, were found in the Pacific near Akutan Island and rarely in the Bering Sea, largely in July. zyxwvut ‘Sea World Research Institute, Hubbs Marine Research Center, 1700 South Shores Road, San Diego, California 92109, U.S.A. ’San Diego State University, San Diego, California 92182, U.S.A. @The Arctic Institute of North America zy 34 B . S . STEWART er al. zyxwvutsrqponmlkjih zyxwvuts zyxwvuts Southwestern Alaskaand the eastern Aleutian Islands, showing the location of the shore whaling stationon Akutan and the threeblocks in which transects were flown. The adjoining photos show the station in about 1920 (lower right) and the site in early August 1984 (to left). (Photos courtesy of Alaska Historical Library, Juneau, bottom, and by S.A. Karl, top.) FIG. 1. Analysis of trends in the Akutan fishery (Leatherwood et al., 1985)indicatedsome depletion of the stocks. Both fin and humpbackwhalesweretaken at greater distances from the station in later than inearlier yeiirs, indicating reduced availability. Overall, there was a downward trend of catch per unit of effort, also taken to meanstockswere declining somewhat. Nevertheless, significant numbers of whales apparently were still available to the whalers between 1935 and 1939, as 0.280.51 whales per gross catcher day were taken in the last five years of operation. Whaling continued in the North Pacific after the closure of the Akutan station in 1939, and it is generally accepted that subsequent intense episodes of whaling in the northeastern Pacific from shore stations and pelagic fleets left most great whale stocks in the broader area depressed (e.g., Rice, 1974; Tillman, 1977; Braham, 1984). In 1982 and 1983, a series of eight aerial surveys of the southeastern Bering Sea and Bristol Bay (Ca. 185 O00 nm2) was flown to determine geographic and seasonal distribution and relative abundance of cetaceans. The transect lines in this enormous area werewidelyspacedand covered only about 1.93% of the areas during each survey. Furthermore, surveys were often flown in less than ideal survey conditions (see Leatherwood et al., 1983:Table 2, p. 9 and Table 4, p. 42). With the exception of gray whales (Eschrichtius robustus),for which it was possible to estimate density in portions of the southeastern Bering Sea in May andJune (Leatherwood et al., 1983:Table 10, p. 67), few great whales were seen (Leatherwood et al., 1983:Table 7, p.57). Several hypotheses were proposed to explain the apparent low density of whales in the area overall, and particularly in the portions of the surveyed area where some species formerly occurred in muchgreater abundance: 1) it was an artifact of sparse coverage and generally poor survey conditions; 2) whale distribution was highlylocalized near the Aleutian Islands where previous whaling effort had concentrated, but zyxwvuts zyxwvutsrqponm CETACEANS OFF SOUTHWESTERN ALASKA where aerial survey coverage was low; and 3) there were few great whales present in the eastern Bering Sea during survey periods in 1982 and 1983. To testthese hypotheses, in 1984 we flew intensive lowaltitude aerial surveysof the former Akutan whalinggrounds at preciselythetime of yearwhen the greatest abundance of whaleswasexpectedon the grounds, as determined from historical whaling records (see Reeves et al., 1985). We also flew a smaller number of transects in an area straddling the continental slope between the whalinggrounds and the Pribilof Islands, near scheduled oil and gas exploration and developments. 35 zyxwvutsrq zyxwvutsrq METHODS Survey Design, Transect Selection and Placement Surveys were designed using a stratified random sampling scheme to balance the need for a random sample with practical logistical and operational constraints. The former whaling grounds, defined by reference to Reeves et al. (1985:Figs. 11 and 12), were divided into two blocks, one south (block 1) and one north (block 2) of the Aleutian Islands chain but with a common southwest to northeast oriented boundary between them (Fig. 1). Blocks 1 and 2 covered about 14 400 nm2. Each block was subdividedinto three zonesof equal width. The sizes of blocks andzoneswere defined suchthat the amount of searching in each zone or combination of zones for which density estimates were to be reported (i.e., blocks 1 and 2 collectively and block 3 alone) was roughly proportional to its area. This feature permitted blocks and zones to be combined for density estimates. The boundary between blocks1 and 2 was scored at 0.25 nm intervals. Before beginningsurveys, eight sets of three numbers each were selected at random and without replacement. These represented the starting points of 48 transects (24 in each block, 8 in each zone) to be flown northwest to southeast or southeast to northwest, parallel to the zones’ long boundaries. A third block (block 3) was defined between Unimak Pass and the Pribilof Islands, in waters overlapping coastal, continental shelf and pelagic areas (Fig. 1) in which at least fin, sei (B. borealis), minke (B. acutorostrata), humpback, gray, right and bowhead (Baluena mysticetus) whales and various other smaller cetaceans had been reported recently (Leatherwood et al., 1983). This rectangular block, which covered 4000 nm2, was divided into two zones, each approximately 20 X 100 nm. The westernmargin of each zone was scored at 0.25 nm intervals, and eight sets of transects were selected for each, as described above. Transects were to be flown east to west, parallel to the long block and zone boundaries. FIG. 2 . ThePartenavia P 68 Observerusedinthe surveys. Note theclear plexiglass nose, permitting unobstructedviewing of the transect centerline, and thesidebubblewindowatthestarboardobserverstation.(Photoby S. Leatherwood.) Surveys were flown at altitudes between about 150 m and 245 m and at a ground speed of 100 knots (kts). As in our previous aerial surveys of cetaceans (e.g., Leatherwood, 1979; Leatherwood and Reeves, 1983; Leatherwood et al., 1987), transects were only initiated in sea surface conditions of Beaufort 3 and below, as rougher conditions are considered to significantly affect the probability of seeing cetaceans (e.g., Leatherwood and Show, 1980; Scott and Gilbert, 1982:Tables 6 and 7). If conditions deteriorated during a survey to Beaufort4 or higher andremained so for five minutes or morethe transect was terminated. If possible, such transects wereresumedwhen conditions improved or were reflown on subsequent days. Data on effort and sightings were collected from transects (the randomly selected lines that provided the basisfor density estimation; such periods were logged as ‘‘on effort”) and during transits (straight lines connecting transects with one another or with the shoreline, routes flown alongland masses and between the base of operations, Dutch Harbor, and starting or ending points of transects and any survey lines completed under unacceptable conditions; such periods werelogged as “off effort”). Data werealso recorded during the ferry flights between Anchorage and Dutch Harbor. All data were logged using an Epson HX-20 computer linked to the aircraft navigation system (Loran-C, Model AVA-100A, ARNAV Systems, Inc.) by means of an RS-232 connection. Location (latitude and longitude), local time, magnetic headingand ground speed were recorded automatically once each minute and whenever a report of a sighting was entered. Environmental conditions, including sea state (as Beaufort number), sun glare and characterizations of weather and visibility, were entered periodically, as they changed and when sightings were entered. For each marine mammal sighting the following information was recorded:the angle (y) formed between the horizon and a line to the animal(s) when the aircraft was perpendicular to the sighting (measured, to the individual or to the center of the group of individuals, with a hand-held Suunto clinometer, and later used to calculate perpendicular sighting distance); species; the cue prompting the sighting; behavior; total number of animals; swimming direction; and observer making sighting. Once the sighting angle wasmeasured, we left the transect and circled the animal(s) to confirm species identification, search for calves and count individuals. The time spent circling was considered “off effort.” Data were stored on microcassettes and later transferred to a WICAT computer atHubbs Marine Research Center for analysis. Perpendicular distance to each sighting was calculated as X = H tan (90 - y) (Equation 1) where H is aircraft altitude, in feet. zyxwvutsr zyxwvut Conduct of Surveys All surveys were flown in a Partenavia P68 Observer (Fig. 2), a high wing, twin engine aircraft with a clear plexiglass nose (which afforded a clear and continuous view of the transect center line) and a 61 cm plexiglass bubble window on each side adjacent to the observer’s seat. There were three observers. The forward observer, seated in the Co-pilot’s position, was dedicated to observing along the transect center line. Two side observers, who could also see the center line, searched outward from the line. Flights were sufficiently short that rotation of observers was unnecessary. zyxwvuts 36 zyxwvutsrqponmlk zy zyxwvutsrqp B.S. STEWART et a / . Data Analysis Density and abundance estimates were calculated using line transect techniques (following Burnham et al., 1980) and programTRANSECT (Laake et al., 1979). Highlights of the method as applied in thisinstance are summarized below. The probability density function (pdf) of the perpendicular distances, f(x), was estimated from calculated distances and evaluated at zero (f(0)). The result was used in the following expression for density D = - n f(0) (Equation 2) 2L where n is the number of observations and L is the length, in nautical miles, of the line(s) (i.e., the distance searched). The value of L was calculated from recorded positions and verified by comparison with time and speed calculations. In fact, distances calculated by the two methods differed by only three percent. Following Burnham etal. (1980), we selected a Fourier series model, a linear combination of cosine functions, which has proven generallyuseful and has been applied to a variety of recentsurveydata (e.g., Ratti et al., 1983; Hammondand Laake, 1983; Leatherwood et al., 1983; Leatherwood et al., 1987). It can be expressed as which is the product of the density of groups and an average group size (E). An estimate of the sampling variance for density, given by Burnham et al. (1980), is Var (D) = D2 (CV2(n)+ CV’(f(0)) + CV2(E)) (Equation 6) where CV2(n) = Var (n)/n2, (Equation 7) CV2(f(0)) = Var (f(O))/(f(O))’, and (Equation 8) CV2(C) = var (QE2 (Equation 9) zyxwvut E-! The variance of f(0) is from Equation 4; the variance of is the standard sampling variance; andthe variance of n, based as it is on replicate lines, can be expressed as Var(n) = L R- 1 R 2 4 (Equation IO) zyxwvutsrq zyxwvutsrqp zyxwvutsr + f(x) =- 1 W x m ak COS ( k d W ) (Equation 3) k= 1 where W is the half-width of the transect, in this case the largest observed perpendicular distance, m is the number of cosine terms used in the model, and ak is the kthparameter estimated from the data. The estimate of f(0) is m + 2 1 f(0) = W (Equation 4) ak i=l where R is the number of replicate lines, L is the total line length, and 4 and ni are the length and number respectively of observations for the ithreplicate. The validity of estimates of density from line transect sampling depends on how well the following underlying assumptions are satisfied: 1) the area of interest is sampled randomly or the population is distributed randomly within the area; 2) all animals on or near the transect center line are seen; 3) all measurements are made without error; 4) the animals do not move or sampling occurs instantaneously with respect to any movement; 5) sightings are independent events; and 6 ) the size of a group (herd) of animals does not affect its probability of being observed. For a detailed review of line transect theory and methodology see Burnhamet al. (1980). For details on the use of such techniques in censuses of cetaceans see contributors to Chapman (1982). k= 1 because when it is evaluated at x = 0 the cos (0) = 1. For marine mammals that occur in groups (herds), the group (herd), rather than the individual animal, must betreated as the observation (Hayes, 1977;Bumham etal., 1980; Quinn, 1980). Therefore, the number of sightings (n) is the number of groups observed. The estimate of density, therefore, is Z D=- n f(0) t (Equation 5) 2L , RESULTS On flights made between 26 July and 26 August 1984 we collected data along 3040.0 nmof survey track, including 2403.1 nm “on effort,” i.e., during random transects (Fig. 3, top; Tables 1 and 2), and 1819.5 nm “off effort” (Fig. 3, bottom; Tables 1 and 2). A total of about 23.6 hr was spent searching while on transect (i.e., “on effort”), at an average speed of 100 kts. The vast majority of effort on transect was zyxwvutsrq TABLE 1 . Distance searched by Beaufort class Transits Beaufort Areas 0-2 Blocks 1 & 2 combined Block 3 (12.5%) Ferry flights Total 1284.7 (58.6%) 183.8 (87.5%) 0.0 1468.5 (61.1%) Effort was assigned to the category Dutch Harbor. Transects (on effort) Beaufort 3-5 908.4 (41.4%) 26.2 0.0 934.6 (38.9%) (66.4%) (off effort) Total 2193.1 (31.4%) 210.0 0.0 2403.1 (26.6%) 0-2 1026.6 (68.6%) 40.0 3-5 470.3 (100%) 0.0 (0%) 269.3 13.3 (95%) (5%) 1335.9 (73.4%) 483.6 Total Beaufort 3-5 Total 1496.9 40.0 282.6 (5%) 1819.5 0-2 2311.3 (62.6%) 223.8 (90%) 269.3 (95%) 2804.4 Total 1378.7 (37.4%) 26.2 3690.0 250.0 (10%) 13.3 282.6 1418.2 (33.6%) 4222.6 “0-2” if whitecaps were absent, “3-5” if whitecaps were present. Ferry flights are those flights between Anchorage and zyxwvutsrqponm zyxwvutsrq CETACEANS OFF SOUTHWESTERN ALASKA 31 zyxw 58 BERING S E A 87 56 55 5. NORTH PACIFIC & ‘O 83 52 zyxwv zyxwvuts zyxwvutsrqponmlkjihgfedcb zyxwvutsrqpon 169 “ I 168 I ‘ 167 I ’ 166 I I 155 I I I I64 16s 162 1 1 161 1 1 160 I I t5s I 1 158 I I 157 I I56 FIG.3. The distribution of transects (top) and transits (bottom). Transects were logged as “on effort” and transits were logged as “off effort.” spent in blocks1 and 2, where 47 of 48 planned transects were completed. Inclement weather, mostly persistent low clouds and fog, whichsignificantlyaffectedsurvey conditions and safety, permitted us to completeonly 2 of 8 transects plannedfor block 3. TABLE 2. Distance searched (in nautical miles) by visibility class Transits effort) Visibility class Mostly obscured <1 nm obscured some Partially 1-10 nm 530.4 withUnlimited (53.1%) with (32.5%) Unlimited (100.0%) (10.4%) Total Overall, wesaw 77 groups (199 individuals) of cetaceans (Fig. 4). The only identified baleen whale seen on transect was a single minke whale located off western Unalaska Island (Fig. 4). The 11 fin and 14 gray whales recorded were all seen “off effort,” during transitor ferry flights. So also were 20 of the 26 killer whales (Orcinus orca) seen (Table 3). Only one species, Dall’s porpoise (Phocoenoides dulli), was observed withsufficient frequency to permit estimates of density (Table 4). Three such estimates were made: for blocks 1 and 2 combined; for block 3; and for blocks 1, 2 and 3 combined. There were too few “on effort” sightings of Dall’s porpoises to estimate f(0)reliably; so we combined “on” and “offeffort” sightings, as described below, to derive the sightability function. Such an approach is valid if the factors affecting f(0) are not significantly different between the sets twoof sightings. The factors most likelyto affect f(O), and their characterizations for the present surveys, are:1) sea state - theproportions of distance flown under various sea states were relatively consistent between alleffort in blocks 1 and 2 combined andeffort on transect in block 3. Sightings from remaining flights - i.e., those “off effort’’ in block 3 and those during ferries - were excluded from calculations to estimate f(0) because they were made almost entirely in the one category of good sea state conditions (Table 1); 2) visibility conditions-the proportions of distanceflownundervariousvisibility conditions were relatively consistent among all flights in blocks 1 and 2 combined and block 3 (Table l), so all sightings from them were included in calculationsto estimate f(0); 3) altitude -nearly all (91.8%) transects were flownat altitudes between about 225 m and 245 m; therefore, sightings from “offeffort” were included in calculations to estimate f(0) only if they were made while flying within this range of altitudes; and 4) effects of group size on sightability - group sizes were not substantially different between sightings “on effort” (X=2.5) and sightings “off effort” (jr = 3.8) andno differences were apparent between the sightabilityfunctions from the twocircumstances. Proceeding in thismanner, we were able to use 42 sightings of Dall’s porpoises to estimate f(0). Allof these 42 sightingsofDall’sporpoisesresultedin recording of clinometer angle. The distribution of distances calculated from those measured angles indicates little bias due to rounding. This does not imply that measurements are free from error, only that such error is random. Therefore, rather than being grouped into distance intervals, the calculated perpendiculardistanceswere usedas exact distances to estimate f(0) (23.0%) 1496.9 (23.5%) Blocks 1 and 2 combined Block Transects (on (off effort) 144.9 (6.6%) 706.6 (32.2%) (23.9%) 704.1 (32.1%) 637.543.3 (29.1%) 2193.1 129.0 (8.6%) 3 Transects effort) (on 0.0 (0.0%) 50.2 (35.4%) 487.0 111.5 350.5 210.0 Ferry flights Transits between Anchorage (offDutch effort) and Harbor 0.0 0.0 (0.0%) (0.0%) 29.6 (74.0%) 6.24 (15.6%) 4.16 282.6 40.0 282.6 0.0 (0.0%) 0.0 (0.08) 38 zyxwvutsrqponm zyx zy zy zyxwvutsrqpo B.S. STEWART et a1 167 162 166 163 161 167 163 I65 166 162 U zyxwvutsrqponmlkj BERING SEA 55 BERING SEA zyxwvutsrqponm UNIYAU I. c sowmd A * 54 A 4 A r.A &L” A A YILASKA I .. A 53 A A * A NORTH NORTH PACIFIC PACIFIC 62 167 166 I65 164 163 162 161 I67 I66 165 161 163 I62 161 56 56 I1 0 A Io l o 59 zyxwvutsrqpo i zyxwvu 1,. - MINKE ON EFFORT FIN OFF EFFORT UtlD. LAFGE Wll?LE ON EFFORT OFFEFFORT UNID. BEAKED WHALE OFF EFFORT OFF EFFORT WHALE OFF EFFORT ;GRAY HAR,pOR PORFOISE ON EFFORT 0 5s 55 BERINGSEA I 57 U N I U I K I. BERINGSEA C. SOriCm.1 56 54 55 53 NORTH PACIFIC . Ri il.‘ : 54 52 53 52 Locations of sightings of cetaceaiis during transects(“on effort”) and during transits (“off effort”). The numbers by the symbols indicate the number of sightings at that location. FIG. 4. and toderive a Fourier series fit for sightings of Dall’s porpoises (Fig. 5 ) . Density estimates weremadeusing the above described estimates of f(O), the number of “on effort” sightings (n), and in all “on effort” sightings the average group size (Fig. 6). We calculated an estimate for blocks 1and 2 combined and a separate estimate for block 3 because there was considerably more effort in proportion toarea in the former than in the latter. To construct an overall density estimate, we weighted the individual block estimates by the relative sizes of the areas as D = (A1 + A2) (Dl +D2) + A3D3 (Equation 11) Al+Az+A3 (e) where A,, A2 andA3 are the areas (in nm) andDl, D2 and D3 are the densities for blocks 1, 2 and 3 respectively. DISCUSSION The eastern North Pacific gray whale stock appears to have recovered from the effects of the most recent episode(s) of whaling, earlier this century, and is believed to be at or near its pre-exploitation size of 15 000-20 000 (Reilly, 1984). The vast majority of that population is north of Unimak Pass annually from April-June through November-December (Jones et al., 1984). With respect to our survey areas and times, gray whales are peripheral, moving through UnimakPass and then eastward close along the shores of Unimak Island and the Alaska Penin- zyxwvutsrqponm zyxwvutsrqpo zyx 39 CETACEANS OFF SOUTHWESTERN ALASKA TABLE 3. Number of sightings of marine mammals (number of individuals is shown in parentheses) Transects (on effort)Transits Species Blocks 1&2 Block 3 Fin Minke Gray Unid.1(1) Killer Unid. Dall’s porpoise Harbor porpoise Total (off effort) BlocksBlock 1&2 3(11) 1(1) 2(2) 4(6) Ferry Anchorage Dutch to Harbor transits) Total (all 3(11) 1(1) l 4(20) 1(6) l(1) 30(71) 2(4) 39(84) 8(26) 1(6) 16(59) 1(2) 25(93) 47(131) 4(7) 77(199) zyxwvutsrqp zyxwvutsrqpo l(1) sula during migrations. Gray whales were not takenby Akutan whalers (Reeves et al., 1985). All of our sightings were “off effort” and during transit along the north shore of the Alaskan peninsula, where gray whales were expected to beat this time of year. We did not expect to see many in our survey area. Minke whales of the northeastern Pacific have never been substantiallyexploited (a few were taken at Akutan -Reeves et al., 1985). They are at present regarded as an Initial Management Stock (IMS) and believed to be abundant overall (IWC, 1983:97).They werethe balaenopterids seen most frequently on recent aerial and vessel surveys in southeastern Bering Sea and Bristol Bay (Leatherwoodet al., 1983). Their population size is not known. TABLE 4. Summary of statistics used in density estimates of Dall’s porpoises and their coefficientsof variation (CV) in parentheses A n f(0) c D 14 400 (0.209) 4 000 (0.862) 30 (0.121) (0.450) (0.263) 1 - 6.957 3.30 115.0 Area Blocks 1&2 Block 3 3 whale whale whale 1(1) 12(21) The pre-1905humpback whale population in the North Pacific has been estimated as about 15 000, but the population was subjected to extreme modem whaling through the 1960s (Rice, 1978). Johnson and Wolman (1984) estimated the current population at about 1200, including 550-790 that winter in Hawaiian waters(Riceand Wolman, 1984). There are data suggestingthepopulationis much larger.Darling and McSweeney (1985) estimated that there are a minimum of 1500 humpback whales inthe northeasternPacific, and Darling ( 1983) has photoidentifiedas many as 2100 individuals in the Hawaiian population alone. Rice (1978) reports that humpbacks, though present in the Asian winter grounds, are now scarce in that area. Apparently, animals from both populations occur in Alaskan waters (Nishiwaki, 1966), but there are still only sporadic records in the southeastern Bering Sea and along the Aleutians et al., 1983). Humpbacks nearUnimakPass(Leatherwood were the second most important species to the Akutan whalers zyxwvutsrqpo 6.957 (0.0) 1.00 - 17.0 Density (D) is expressed as numberof animals per1000 nm2;A = the size of the areain nm; h = the number of sightings; f(0) = theprob_ailitydetection function evaluated atzero (see text for additional details); C = the average group (herd) size. .5 - ; A m W ; - .3 2 I g .2 a .I - 00.C t zyxwv zyxwv ‘793 )O 0.0 7 \ 0.15874 0.23811 0.31740 a39685 0.47622 0.5559 P E R P E N D I C U L A R DISTANCE ( x 1 0.5 I5 ( I N NAUTICAL MILES) RG.5. Illustrationsof the fit of the Fourier series to the perpendicular distances of the sightings of Dall’s porpoises (f(x) = 1/W + 2.994 Cos (IT x/W) + 1.289 Cos (27rxN) and W = 0.374). I 2 3 4 5 6 NUMBER OF ANIMALS RG.6 . Sizes of groups (herds) of Dall’s porpoises seen during transects (“on effort”), blocks 1, 2 and 3 combined. 40 zyxwvutsrqponm zyxwvutsrq zyxwvutsrq zyxwvuts zyxwvutsrq B.S. STEWART et al. numerically, constituting 30% of the total take (1510 of 5027 history of the fishery (Leatherwoodet a f . , 1985). If populations whales identifiedto species in 23 years) but being66.7%of the of these four species had been present on the Akutan grounds in total take at nearby Port Hobron (1573 of 2357 taken identified comparable numbers in July and August 1985, it is reasonable to 11 years)(Reeves et af., 1985). From their tospeciesin suppose, from Hay's (1982) experience, thatsomewhales apparent dispersal during recovery in various portions of the wouldhavebeen seen. Theappreciablenumberofsmaller North Atlantic (IWC, 1984: 135-6),one would predict that as animals detected suggests large numbers of whales were not their population grows, humpbacks would recolonize former missed simply by lack of vigilance. The results from sightings grounds in the North Pacific. et al. of Dall's porpoises are a useful case in point. Leatherwood The status oftheNorthPacificfinwhales has notbeen (1983) estimated that there were 97.20(SD = 49.50; CV = 0.5 1) adequately assessed. Stocks there have remained classified by Dall's porpoises perlo00 nm2 in study blocks between the north theInternationalWhalingCommission(IWC) as Protection side of the Aleutians and about the southern latitude of the Stocks for a decade(Gambell, 1985) and populations were most Pribilofs, from longitude 166"W to 170"w. From the present recently estimated to contain some 20 000 individuals, about surveys we estimated that there were16.6 (CV = 0.0) individu38% of the pre-exploitation stock sizeof 53 OOO (Allen, 1980). als per1000 nm2 in block3 and 115.0 (CV = 0.263) individuals This was the species most important to shore whalers atAkutan, per 1OOO nm2 in blocks1 and 2 during the period of the surveys constituting 49.7%(2498 of 5027 whales identified to species) (Table 4). The resultsof the present surveys bracket those from at Port of takes there in23 years and the second most important the previous work. Hobron, nearly 20% (464of 2357 whales identified to species) Results of the present surveys appear to support the hypotheof takes there in 11 years (Reeves et al., 1985). Further, fin sis that the relatively low numbers of baleen whales, other than whales were the balaenopterids seen second most often (after gray and minke whales, seen in the eastern Bering Sea and minke whales) in recent surveys (Leatherwood et al., 1983). northern North Pacific near Akutan actually do indicate low We expected to see them, especially on the continental shelf, density of these animals and are not merely artifacts of sparse during the present surveys. coverage and poor survey conditions. However, one must be The statusof sperm whales in the North Pacific is problematicautious when interpreting a scarcity of sightings of cetaceans cal and highly disputed. For the present, the species there is from aerial surveys as evidence of theirlow density inthe managed in two divisions, eastern and western (Gosho et al., area(s) under study, unless survey methods have been carefully 1984), which are at reducedlevels. There apparently are 61 OOO controlled to maximize the probability of sightings. Such was males over 10 years of age in the western North Pacific and the case. First, present surveys used anaircraft with downward 11 1 400 over 12 years of age in the eastern North Pacific, 47% visibility, permitting observersto see the transect center line and and 79% oftheoriginal(in 1910) stocksizesrespectively thereby more nearly satisfying the second assumption of line(Gosho et al., 1984:Table 4). Whatever the correct delineations transect methodology(i.e., that all animalson or near the track of stocks and actual numbers, adult males from theeastern and line are seen). Such increased visibility would result in larger western Pacific intermingle(d) in higher latitudes, and we would numbers of sightings near the center line. The absence of data in not have been surprisedto have encountered a few malesperm that strip couldsignificantlyaffectcredibility of estimates. whales in the deeper water portions of the surveyareas. There were few sightings of cetaceans during our surveys, but The other three northern North Pacific great whales are not whenallsightings(includingpinnipedsandsea otters, not commonly reported inor near any of the three study blocks and analyzed) werecombined, about 25%of them(51 of 206) were so were not expectedon these surveys. Bowheads may assemble within 0.04 nm of the transect center line. Second, present surveys were conducted only in acceptable et al., 1980; near St. MatthewIslandinspring(Braham conditions of sea state and visibility (91%of the survey effort Brueggeman et af., 1984) but are rarely reported farther south (Leatherwood et af., 1983); right whales are seriously endanwas in Beaufort 3 or below, 61% inthetwobestvisibility gered and rarely seen anywhere in the eastern North Pacific classes), when the probability of detecting animals is highest. (Rice, 1974; Brownell et al., 1986; Scarff, 1986; Reeves and This was made possible by the proximitylines of in blocks1 and Leatherwood, 1985); and sei whales are generally uncommon 2 to the operational base and the relatively short time required to north of the Aleutians, being found in pelagic regions farther complete a replicate setof transects ineach. Therefore, observsouth (Rice, 1974:181;Leatherwood et al., 1983). ers were afforded the luxuryof waiting at the operational base With the above mind, in there were surprisingly few sightings for acceptable weather conditions before departing for survey of great whales in or near the rou hly14 400 nm2 area of study and of surveyingon whichever side of the Aleutiansoffered the blocks 1 and 2 or in the 4000 nm!? area of block 3 during the 29 best weather conditions. The absence of anylee effect at block field days. By comparison, in surveys byaircraft of portions of 3, the greater distance to that block and the often significant an approximately 50 000 nm2 area within about100 nm ofshore differencesinweathernearthe chain andweather offshore off eastern Newfoundland-Labrador in August 1980, Hay (1982) (making difficult any decisions of when conditions would be observed 3 1 groups of humpback whales and 18 groups of fin 3) resulted in completion of only acceptable for surveying block whales,supporting his estimatesofpopulations of 738 one of four planned replicates in block 3 in 29 possible survey (SD = 221) and 478 (SD = 250) forthe two species respectively. days. Previous surveys ofthe Bering Sea (Leatherwood et af., 1983) hadcovered large areas, includingmany for which Hay's surveys were designed to cover essentially the whaling accurate weather reporting is not available. The result was a groundsusedbyCanadianwhalersfrom SouthDildo and high percentageof time in conditions of unacceptable visibility. 1964 through 1971 Williamsport,Newfoundland,between Third, the eight sets of replicates in blocks 1 and 2 were (Mitchell, 1974:Fig.5-1). From cumulativecatches, it has been completed within amonth, at a timeof year when peakcatches estimated there were populations of at least 1500 fin, lo00 of fin, humpback,blue and sperm whales were made (Leatherhumpback, 500 blue and 300 sperm whales available within a 100 nm radius of the Akutan whaling station at some point the inwood et af., 1985). Further, transects were spaced at narrow zyxwvutsrqp zyxwvutsr CETACEANS OFF SOUTHWESTERN ALASKA 41 of density from line transect sampling of biological populations. Wildlife distance intervals, affording higher coverage (per survey and overall, during the month) with concomitant higher probability Monographs 72. 202 p. CHAPMAN, D.G., chairman. 1982. Report of the workshop on the design of of detecting animals present than on previous surveys of the sightings surveys.Reports of theInternationalWhalingCommission area. 32531-549. DARLING, J.D. 1983. Migrations,abundance, and behavior of Hawaiian Fourth, special attention was paid to precision in distance humpbackwhales Megapfera novaeangliae. Ph.D. thesis, University of estimation (helped by the increase in proportion of sightings California, Santa CNZ, California. AM Arbor,Michigan,University close to the aircraft wherean error of afew degrees amounts to Microfilms. 147 p. an error <0.004 nm in the estimated perpendicular sighting -and McSWEENEY,D.J. 1985. Observations on themigrations of distance) and to remaining with groups long enough to confirm North Pacific humpback whales(Megapferanovaeangliae). Canadian Journal of Zoology 63:308-314. speciesandnumberofindividualspresent. The addedtime GAMBELL, R. 1985. Fin whaleBalaenopreraphysalus (Linnaeus, 1758). In: required for these last activities is notavailable on longer Ridgway, S.H., and Harrison, R., eds. Handbook of Marine Mammals. surveys, in which the aircraft is stretched to safety limitsjust to Volume 3: The Sireniansand Baleen Whales. 171-192. complete transects. GOSHO, M.E., RICE, D.W., and BRIEWICK, J.M. 1984. The sperm whale, One problemthatwillalways exist inaerialsurveysof Physefer macrocephalus.Marine Fisheries Review46(4):54-64. cetaceansisthatofestimatingnumbersofanimalsmissed HAMMOND, P.S., and LAAKE,J.L. 1983. Trends in estimates of abundance because they were submerged, and therefore not visible, during of dolphins (Sfenellaspp. and Delphinus delphis) involved in the purse-seine fishery for tunas in the eastern Pacific Ocean, 1977-1981. Reports of the et al., 1982). This the period of the overflight (Leatherwood International Whaling Commission33565-588. problem can only be corrected meaningfully withdata, preferHAY, K. 1982. Aerial line-transect estimatesof abundance of humpback, fin ably collected at the time of the surveys,on diving frequencies and long-finned pilot whales in the Newfoundland-Labrador area. Reports of the International Whaling Commission32:475-489. and times for each species seen and their resultant effects on HAYES, R. 1977. A critical review of line transect methods. M.S. thesis, visibility. Submergence is likely a more significant problemin University of Edinburgh, Scotland. attempts to estimate density of great whales (which usually INTERNATIONALWHALINGCOMMISSION (IWC). 1983. Thirty-third travel singly or in small groups and remain submerged for long report of theInternational Whaling Commission. Reports of the International periods), particularly when they occur in low densities, thanit is Whaling Commission 33. 782 p. -. 1984. Thirty-fourth reportof the International Whaling Commission. with animals such as Dall’s porpoises, which travel in larger Reports of the International Whaling Commission34. 752 p. groups and remain submergedfor shorter periods. zyxwvutsrqp zyxwvutsrq zyxwvut zyx JOHNSON, J.H., and WOLMAN, A.E. 1984. The humpback whale,Megaptera novaeangliae. Marine Fisheries Review46(4):30-37. JONES, M.L., SWARTZ, S.L., and LEATHERWOOD, S . , eds. 1984. The ACKNOWLEDGEMENTS Gray Whale. Orlando, Florida: AcademicPress. 600 p. LAAKE, J.L., BURNHAM, K.P., andANDERSEN, D.R. 1979. Users We thank the following:J.D. Hall provided generous assistance and manual for Program TRANSECT. Logan, Utah: Utah State University Press. support throughout the surveys; S . and T. Madsen (Aleutian Air, Ltd.) 26 p. radioedweatherreports to us fromDutchHarborwhilewewere LEATHERWOOD, S . 1979. Aerial surveyof the bottlenosedolphin, Tursiops conducting surveys offshore;K. Springer (Chevron Oil Corp.) allowed truncafus,and the West Indian Manatee,Trichechus manarus,in the Indian us access to SEDCO oil rig radio frequencies and MERISTAT Num77:47-59. and Banana Rivers, Florida. United States Fishery Bulletin REEVES, R.R. 1983. Abundanceof bottlenose dolphins in Corpus R. Landenberger (NORTEC) -and bers to obtain weather reports from them; communicated weather conditions us; to and employees at Air Pac and Christi Bay and coastal southern Texas. Contributions to Marine Science 26179-199. ReeveAirandresidentsofthe town of DutchHarborgavetheir S., and SHOW, I.T., Jr. 1980. Developmentof systematic assistance duringour stay at Unalaska Island. The Partenavia P68 was LEATHERWOOD, procedures for estimating size of “population(s)” of bottlenose dolphinsand owned by Dr. R. and Mr. W. Sutherland and was flown byD. Warth. estimates of sizes of “population(s)” of bottlenose dolphins in three geoS . Ingram and C. Hayashi prepared the figures. E. Garner typed the graphical areas; with incidental observations of West Indian manatees and manuscript. The project was sponsored by NOAA, National Ocean marine turtles. Final Report on contract NA-79-GAC-0038. Submitted to Service, Mr. L. Jarvella, Contract No. NA82RAC00039. U.S. Department of Commerce, NOAA, NMFS, Miami, Florida. 98 p. LEATHERWOOD, S . , BOWLES, A.E., and REEVES, R.R. 1983. Aerial Surveys of marine mammals in the southeastern BeringSea. U.S. Department of Commerce, NOAA, OCSEAP, Final Report.42(1986):147-490. REFERENCES LEATHERWOOD, S . , GOODRICH, K., IUNTER,A.L., and TRUPPO, R.M. 1982. Respirationpatternsand‘sightability’ofwhales.Reports ofthe ALLEN, K.R. 1980. Conservationand management of whales. Seattle: UniverInternational Whaling Commission32601-613. sity of Washington Press. 107 p. BRAHAM, H.W. 1984. The statusofendangered whales: anoverview. Marine LEATHERWOOD, S . , HAMMOND, P.S., and KASTELEIN, R.A. 1987. Fisheries Review46(4):2-6. 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