Status and behaviour of southern right whales (Eubalaena australis) in the Uruguayan Atlantic coast.

Transcription

1 Status and behaviour of southern right whales (Eubalaena australis) in the Uruguayan Atlantic coast. Gabriela Jorge, Federico Riet-Sapriza, Paula Costa *. Francaaustral Project/ Cetáceos Uruguay. Sección Etología Facultad de Ciencias, Universidad de la Republica (UdelaR). *corresponding author: Abstract Between 2001 and 2009, a total of 38 aerial surveys were conducted in the Uruguayan Atlantic coast (30-35 º S) with the aim to study the general behaviour and habitat use patterns of southern right whales. A total of 489 whales were sighted, of which 95.5% were unaccompanied whales while 4.5% were cow-calf pairs. We photo-identified 54.4% of the whales sighted and nine were re-identified within a season and six were re-identified between seasons. Unaccompanied whales were observed in groups of two to 10 individuals and most of them involved in surface active groups. The results of the current study suggested that there is a high frequency of movements between the coast and offshore, and/or a constant renewal of individual in the study area. In addition, the low proportion of cow-calf pairs in the Uruguayan Atlantic coast differs from that of southwestern calving grounds. The high proportion of whales in surface active groups, comparable to courtship behaviour, suggests that the Uruguayan coast should consider as a social and breeding ground. It also suggests that the species may make a differential use of areas in the Southwest Atlantic, where some sites seem to be preferred by females with calves and others by the rest of the population. 1

2 Introduction In the XVIII and XIX centuries southern right whales populations (Eubalaena australis) were severely under pressure due to the commercial hunt (IWC, 2001), such that in the middles 1840 the species was considered commercially extinct (Patenaude and Baker, 2001). After decades of protection, populations increased at an annual rate of 7-8% (Bannister, 2001; Best et al. 2001; Cook at al. 2001). Currently, the species is categorized as least concern (UICN, 2011). The calving grounds for the species are Península Valdés (42-43º S, Argentina) ( Payne, 1986; Rountree et al. 2001) and Santa Catarina (27-25º S, Brasil) in the Southwestern Atlantic Ocean, Tristan da Cunha and Isla Gough Island in the middle of the Atlantic Ocean (38ºS, 12ºE), Angola and Namibia (16-27º S, Africa), Mozambique (20º S, Africa) (IWC, 2001), South Africa (32º S) (Best 1990; 2000), Australia (Bannister,2001; Burnell, 2001) and New Zeland ( Patenaude and Baker, 2001). In some of these grounds, where long-term research has taken place, the behavioural patterns of whales with calves are shared: most of the sighted calves were probably born there, females produce calves at 3-5 year intervals, they return every three years to give birth and there is a high females phylopatry and high residency (Rowntree et al. 2001; Best et al. 2003; Burnell, 2001). Southern right whales occur in Uruguayan coasts in winter and spring, mainly in August and October (Costa et al. 2007), seasonality which match that of Peninsula Valdés in Argentina and Santa Catarina in Brazil (Best 1986; Palazzo and Flores, 1998). Despite Uruguayan coasts are located between the two calving grounds in the Southwestern Atlantic Ocean, the first studies suggest that the structure and population dynamics in the former differ from those of the latter (Costa et al. 2005; 2007). Most individuals observed were part of surface active groups, and a low percentage of cow-calf pairs was observed, as compared to calving grounds in the southern hemisphere. These observations suggest that the Uruguayan coast could be an area of socialization and breeding for southern right whales (Costa et al. 2007). The current study aims to describe the information obtained in the Uruguayan Atlantic Coast from 2001 to

3 Methods The study area comprised 220km of the 250km of the Uruguayan Atlantic coast, from Punta Ballena (35º02 S) to Cerro Verde (33º54 S) (Figure 1). The aerial surveys were conducted from July to November, for the years 2001 to 2003 and from August to November for the years Forty-five aerial surveys (two to six per year, see figure 2) were carried out in a single engine aircraft, Cessna 172 in and Cessna 182 in The study area was surveyed twice along the same track at a constant distance from the coast of 500m, and at a constant altitude of 400m. The sighting effort was mainly inside the 1,000m strip following the coastline, but some whales sighted beyond 1,000m up to 2,000m from the coast were also recorded. The number of right whales and group size along with the position taken from a GPS were recorded. For full description of survey methodology see Costa et al. (2007). To obtain the number of whales per flight only the highest number of individuals counted during one of the two replicate surveys was used for the analyses, considering this number as a relative abundance index (Bannister, 1990; Costa et al. 2007). The number of whales per year was calculated as the sum of the number of whales recorded in each survey within a year. Two whales were considered to be in a group if they were less than two body lengths apart from each other. Group composition was divided into cow-calf pairs and unaccompanied whales. A cow-calf pair was defined as any pair of whales in which the length of one individual was greater than half that of the other, and the maximum distance between them was not greater than the length of the cow. Unaccompanied whales were defined as any right whale, solitary or in groups, not accompanied by a calf. Solitary whales were defined as individuals not accompanied by any other whales. Photo-identification (photo-id). When whales were sighted the airplane descended to an approximate altitude of 150m. Photographs were taken using 35mm cameras (Nikon 6006 and F65) equipped with AF Nikkor zoom lens and negative color film 400 ISO in 2001 to A digital camera (Nikon N200) with zoom lenses was used in 2006 to An automated system was used for matching the callosity patterns depicted on photographs (Hiby and Lovell, 2001). Further details are described in Costa et al. (2007). We also analyzed pigmentation variation using five phenotypes (black-morph, white spot morph, grey-morph, partial-grey-morph, partial-grey-morph with white spots) and skin lesion produced by sea gull attacks, however, the later information were update until Behavioral aspects. Residence time, movement and relative individual site fidelity were analyzed through matching individuals within and between seasons. Residence time was estimated for each whale and defined as the time (days) between the first and the last identification of an individual in any given season (Rowntree et al. 2001). Movement was estimated as the minimum distance between the first and the second time the same individual was photo-identified. Relative individual site fidelity was determined and defined as whales that showed some degree of fidelity to the Uruguayan coast if they were recorded at least in two seasons (Burnell, 2001). Three whale behavioral states were recorded, defined as: (i) rest, when one or more individuals were motionless; (ii) travel, when the animal was moving from one location to another leaving surface footprints ; and (iii) surface active group (SAG) defined by their apparent courtship 3

4 behavior as described in Kraus et al. (2001) and Best el at. (2004). The relationship among months, group size and the three behavioral states was analyzed by a multivariate Principal Components Analysis (PCA). Components were considered significant if they were higher than one and their cumulative variance represented at least 70% of the total variance. ). Although, we did not differentiated by sex or age of class, our result that SAGs tended to be larger than other groups, and that SAG increased through the season appear to be agree with findings in South African waters (Best et al. 2003). Results During the study period ( ) a total of 489 whales were sighted. Out of the total, 95.5% (n = 445) were categorized as unaccompanied whales, while 4.5% (n=22) were cow-calf pairs. A total of 256 were identified from photo-id. Of them, 15 (5.9%) were re-identified within and between seasons (Table 1). The proportion between the number of sighted whales and the number of individuals that were identified from -photos_id and the number of aerial surveys per year is shown in Figure 2. The lack of re-identifications betwene seasons is well depicted in the exponential discovery curve observed (Figure 3). Variation in the dorsal pigmentation pattern. Nearly 7.3 % (n=36) of right whales sighted presented variation in their dorsal pigmentation pattern. Out of the five dorsal pigmentation patterns reported for the species, four were observed in the current study. We identified 29 unaccompanied whales with variation in their dorsal pigmentation. Six females showed white spot on their dorsal and a calf showed grey morph. The proportion for each phenotype was calculated from out of the unaccompanied whales and out of the total cow-calf pairs and not from the total number of whales sighted (Table 2). We detected skin lesions caused by sea gulls in 11 out of 150 photo-id whales in 2001 to Behavioural aspects. Nine individuals were re-identified within seasons, one of which was a cow-calf pair (Table 1). The residency ranged from 20 to 41 days for unaccompanied whales. A cow-calf pair was re-identified by the presence of a dorsal white spot, and showed a residency of 10 days. The greatest movement showed by unaccompanied whales was 110 km while the shortest was 2 km. The cow calf pair showed a movement of 30 km. Six individual were reidentified between seasons showing a relative fidelity to the Uruguayan coast (Table 1). One individual was re-identified in three consecutive seasons. Solitary whales occurred with greater frequency, while most of the whales were sighted in groups (Figure 4a,b). The three behavioral states were observed in smaller groups, whereas all bigger groups were described as SAG (Figure 4c). Groups from two to four whales did not vary within the season. However, groups of six to ten whales were observed only from September onwards (Figure 5). The results presented in Figures 2 and 3 were supported by PCA: a strong relationship was found among group size and behavioral state in the first component, and a weaker relationship was found among the month and group size in the second component. Both components explain the 77% of the total variance (Table 4, Figure 6). 4

5 Discussion In the current study we updated the Uruguayan southern right whales photo-id catalogue ( ) and analyzed some aspects of their behavior. Our results suggested that: i) southern right whales sighted in the Uruguayan Atlantic coast were predominately unaccompanied whales in surface active groups; and ii) cow-calf pairs were observed in low frequencies in comparision with the reported in calving grounds in the Southern hemisphere. Hence, the former suggests that the Uruguayan coast could be considered a social, and probably a breeding, ground but not a calving ground. Callosity patterns. Most whales identified by photo-id, with the exception of one individual, showed a callosity pattern that agrees with what has been described in right whale aggregation areas. However, one whale showed a callosity pattern described for the northern hemisphere, where half of the photo-id population has a unique callosity extending from the bonnet to behind the blowhole (IWC, 2001). Dorsal pigmentation and leson caused by sea gulls. For the entire population surveyed we found similar proportion of unaccompanied whales that presented pigmentation patterns, other than black morph, than those found in Argentina (6.9%, Shaeef et at. 1999). However, we observed a very high proportion of cow with dorsal pigmentation other than black morph whales, particularly theses cow showed with-spot morph and the proportion was similar to the proportion observed in South Africa but not to Argentina (Shaeef et at. 1999). A low proportion of our observation were cow-calf pair, this bias cannot be discarded. Most dorsal skin lesions (5-20 cm) observed in right whales off Peninsula Valdes in Argentina are caused by kelp gulls attack (Larus dominicanus) that feed on their blubber and skin. Kelp gull attacks were first recorded in 1979, and in % of right whales sighted showed wounds produced by kelp gulls increasing to 76.8% by the year 2008 (Sironi et al. 2009). In the present study, we did not record any sea gull attack, but 11 whales photo -ID (until the year 2006) showed scars caused by these injuries. The whales presented between two to four scars along their backs, suggesting that these whales were common visitors to Peninsula Valdes. Behavioral aspects. Only nine whales were re-identified within a season, making it difficult to obtain any estimation of the mean residence time for southern right whales off the Uruguayan Atlantic coast. Furthermore, this suggests that there is a constant renewal of individuals in the study area (Costa et al. 2007). Nevertheless, we estimated the residence time of a cow-calf pair (10 days) and observed that these can stay from 2 to 5 days in the area. But we were unable to record this short residence time with photo-id because intervals between aerial surveys were of more than 5 days. The low return record rate is depicted by the discovery curve, which did not reach a plateau, strongly suggesting that southern right whales in Uruguayan coast are part of an open population. A total of nine unaccompanied whales were re-identified across years, suggesting that some individuals show relative site fidelity to the Uruguayan coast. Further, one individual was reidentified in the nearby area 6 km apart. 5

6 Cow-calf pair. Studies conducted in Argentina have shown that the majority of sexually mature females return to Peninsula Valdes mainly in the years they give birth (Payne and Dorsey, 1983; Best et al. 1993; Payne, 2000; Rowntree et al. 2001; Best et al. 2003). Sightings of cow-calf pairs have been recorded since 1975 (21 cow-calf pairs between 1975 and 1990, Costa et al. 2005). The low percentage of cow-calf pairs (5%) observed in the period , the short residence time within seasons and no re-identification of females in calving years among seasons, indicate that the Uruguayan Atlantic coast may constitute a site with different characteristics of that described for calving grounds in the southern hemisphere (Rowntree et al. 2001). Our results support the idea that, for cow-calf pairs, the Uruguayan coast could constitute a bi-directional north-southward route between Santa Catarina and Peninsula Valdes as previously suggested by Costa et al. (2007). Three cows identified in South Brazil had been identified in Argentina with different calves in previous years (Best et al. 1993). This study supports the hypotheses proposed by Best et al. (1993) that some females could move between two nursery grounds in the year their calves are born. Unaccompanied whales. The IWC (2001) defines four categories for right whales habitat that are not necessarily exclusive: (i) feeding areas of seasonal use and rich in copepods and krill; (ii) calving grounds, areas used traditional for neonatal care and calving; (iii) nursery grounds, areas of whale aggregation where cow feed and nurse their calf, and (iv) breeding grounds areas in which courtship behavior and mating are predominant and in which copulation occurs. The development of long-term photo-id research programs in calving areas have allowed the estimation of the gestation period for this species in 11 to 13 months, indicating that conception and mating occur around mid-winter (Payne, 2000; Best et al. 2003). Unaccompanied whales show greater dispersion, shorter residence times and less fidelity to calving grounds than cow-calf pairs. In fact, the areas where unaccompanied southern right whales occur during austral winter are unknown (Burnell, 2001), which implies that unaccompanied whales present behavior patterns less predictable than cows with calves (Costa et al. 2007). The low frequency of courtship behaviors observed (IWC, 2001), the absence of the majority of cows in previous years of giving birth and the low proportion of unaccompanied whales (juveniles, males and receptive females) in calving grounds suggest that breeding areas could be located near these areas (Best et al. 2003). To further our argument, the high proportion of unaccompanied right whales (92.5%), of which 66% were observed in SAG, may indicate that the Uruguayan coast could constitute a socializing area and breeding grounds for the species in the southwestern Atlantic Ocean. It is possible that southern right whales have a differential habitat use along the southwestern Atlantic Ocean, where some areas are preferred by pregnant females and others by the rest of the population. This agrees with the results and suggestions of early studies on southern right whales in Uruguay (Costa et al. 2007). Final Remarks The major findings of the current work were that the Uruguayan coast is not a calving ground as it has been described in the Southern hemispheres; instead, it is likely to be a social and/or breeding ground. Hence, we hypothesize that cow-calf pairs and unaccompanied right whales would have differential habitat uses along the southwestern Atlantic Ocean. If this case we suggest that southern right whales off the southwestern Atlantic Ocean belong to a single genetic stock. 6

7 Acknowledgment We are indebted to those who collected field data during this study Carolina Abud for made valuable suggestions to the present manuscript and to Rafael Alvarez for his dedication to this work. Financial support was gratefully received from the Whale Dolphin Conservation Society (UK) and Cetacean Society International and Cleveland Metro Zoo Park. References Bannister, J.L Southern right whales off western Australia. Rep.int. Whal. Commn (special issue) 12: Bannister, J Status of southern right whales (Eubalaenaaustralis) off Australia. J. Cetacean Res. Manage. (special issue) 2: Best, P.B., Payne, R., Rowntree, V., Palazzo, J.T., Both, M.D Long-range movements of South Atlantic right whales, Eubalaena australis. Mar. Mammal Sci. 9(3): Best, P.B Coastal distribution, movements and site fidelity of right whales Eubalaena australis off South Africa, S. Afr. J. Mar. Sci 22: Best P.B., Brandão, A., Butterworth, D.S Demographic parameters of southern right whales off South Africa. J. Cetacean Res. Manage. (special issue) 2: Best, P.B., Schaeff, C.M., Reeb, D.,Palsbøll, P Composition and possible functions of social groupings of southern right whales in South African waters. Behaviour. 140: Burnell, S.R Aspects of the reproductive biology, movements and site fidelity of right whales off Australia. J. Cetacean Res.Manage. (special issue) 2: Cooke, J.G., Rowntree, V., Payne, R Estimates of demographic parameters for southern right whales (Eubalaena australis) observed off Península Valdés, Argentina. J. Cetacean Res.Manage. (special issue) 2: Costa, P., Praderi, R., Piedra, M., Franco-Fraguas, P Sightings of southern right whales, Eubalaena australis, off Uruguay. Latin Amer. J. Aquatic Mammals. 4(2): Costa P, Piedra M, Franco P, Paez E Distribution and habitat use patterns of southern right whales, Eubalaena australis, off Uruguay. J. Cetacean Res. Manage. 9(1): Groch, K.R., Fabian, M.E., Adler, F.R., Palazzo, J.T. and Flores, P.A.C Recent rapid increases in the right whale population off southern Brazil. The Latin American Journal of Aquatic Mammals. 4(1): Hiby, L., Lovell, P A note on an automated system for matching the callosity patterns on aerial photographs of southern right whales. J. Cetacean Res. Manage. (special issue) 2: International Whaling Commission Report of the workshop on status and trends of western North Atlantic right whales. J. Cetacean Res. Manage. (special issue) 2:

8 IUCN IUCN Red List of Threatened Species. Version < Downloaded on 16 June Kraus, S.D., Hatch, J.J Mating strategies in the NorthAtlantic right whale (Eubalaena glacialis). J. Cetacean Res. Manage. (special issue) 2: Palazzo, J.T., Flores, P.A Right whales (Eubalaena australis) in southern Brazil: A summary of current knowledge and research needs. Paper SC/M98/RW14 presented to the IWC Special Meeting of Scientific Committee towards a Comprehensive Assessment of Right Whales Worldwide, March, Cape Town, South Africa (unpublished). 7pp. [Paper available from the Office of this Journal]. Patenaude, N.J.,Baker, C.S Population status and habitat use of southern right whales in the sub-antarctic Auckland Islands of New Zealand. J. Cetacean Res. Manage. (special issue) 2: Payne, R., Brazier, O., Dorsey, E.M., Perkins, J.S., Rowntree, V.J., Titus, A External features in southern right whales (Eubalaena australis) and their use in identifying individuals. pp In: Payne, R. (eds). Communication and Behavior of Whales. AAAS Selected Symposia Series 76. Westview Press,Colorado. 643pp Payne, R Long term behavioral studies of the southern right whale (Eubalaena australis). Rep. int. Whal. Commn (special issue)10: Rowntree, V.J., Payne, R. and Schell, D.M Changing patterns of habitat use by southern right whales (Eubalaena australis) on their nursery ground at Península Valdés, Argentina, and in their long- range movements. J. Cetacean Res. Manage. (special issue) 2: Schaeff, C.M.,Best P, Rowntree, V.J. Payne R, Jarvis C, Portway VA Dorsal skin color patterns among southern right whales (Eubalaena australis): genetic basis and evolutionary significance. The genetic American association 90: Sironi, M., Rowntree, V.J. Charles, Snowdon, T., Valenzuela L., Marón, C Kelp gulls (Larus dominicanus) feeding on southern right whales (Eubalaena australis) at Península Valdés, Argentina: updated estimates and conservation implications. SC/61/BRG19. 8

9 Figure 1. Map of the showing study area and survey areas at the Uruguayan Atlantic coast. 9

10 Absolute Frecuency SC/S11/RW Years Sigthed whales Photo-ID whales Fligths Figure 2. Number of southern right whales (Eubalaena australis) that were sighted (white bars), identified from photo-id (dark grey bars) and the number of flight made per season from 2001 to 2009 in the Uruguayan Atlantic coast. 10

11 Table 1. Southern right whales (Eubalaena australis) re-identification within and between seasons from 2001 to 2009 in Uruguayan Atlantic coast. Residency is given in days and movement is given in km. Direction represents the direction follow by a whale between the photo-id and Re-photo-ID date. Unaccompanied whales: U, cow-calf: CC. Re-identification within season ID date Re-ID date Residency Movements Direction U 03/09/ /10/ N U 22/09/ /10/ N U 22/08/ /10/ N U 30/09/ /10/ N U 30/09/ /10/ N U 30/09/ /10/ N U 08/10/ /10/ N U 03/10/ /10/ N CC 14/09/ /09/ S Re-identification between season ID date Re-ID date 2 nd Re-ID date U 03/09/ /09/2005 U 08/10/ /10/2006 U 12/10/ /10/2006 U 08/10/ /10/2007 U 08/10/ /10/2008 U 23/10/ /10/ /10/

12 No. Photo-ID whales SC/S11/RW Years Figure 3. Discovery curves of southern right whales (Eubalaena australis) in Uruguayan coast form Number of new individuals identified during the field season (years). 12

13 Table 2. Percentage of five dorsal pigmentation patterns recorded for southern right whales (Eubalaena australis) in the Uruguayan coast. Phenotypes: BM; black-morph; WSM, white spot morph; GM, grey-morph; PGM, partial-grey-morph. Morphotype Unacompained Females Calves WSM GM GPM

14 Percentage P ercentage of whales Percentage SC/S11/RW8 a) b) Group Size Group size c) SAG R T Group size Figure 4. Southern right whales (Eubalaena australis) proportion of a) group size; b) number of whales involved in each group size ; and c) behavioral state groups from two to ten individual recorded in Uruguayan Atlantic coast ( ). 14

15 Group size SC/S11/RW Number of days from 1 of July Figure 5. Group sizes of southern right whales (Eubalaena australis) registered between first of July and November (2001 to 2009) in the Uruguayan coast. 15

16 Second Component SC/S11/RW8 Table 3. Principal component analysis results. The firsts two component (1 st C, 2 nd C) were higher than one (Eigenvalue > 1). Cum. Prop. Represent the Cumulative variance proportion. Group size and behavior are strong related on the first component. 1 st C 2 nd C Months Group Size Behavior Eigenvalue 1,28 1,03 Cum. Prop Biplot of Months.... Behaviour 2 1 Months Group Size 0 Behaviour First Component Figure 6. Southern right whales(eubalaena australis) relationship among Month Group size and Behavior are represented by vector on the Principal component analysis. Group size and Behavior showed strong dependence (closer vectors) and Month and Group size showed weaker dependence (angle less than 90 ). 16