ABSTRACT
The majority of humpback whales (Megaptera novaeangliae) undertake an annual migration from high latitude feeding grounds to tropical/subtropical breeding grounds. Suitable calving habitat for this species includes warm (typically 19°C to 28°C), shallow, sheltered waters in tropical and subtropical waters. Here, we investigated occurrence of calving beyond the primary recognised breeding grounds (16° to 24°S) of the east Australian humpback whale population (E1). We examined location, depth (m), and SST (⁰C) associated with newborn observations in Gold Coast Bay, in southern Queensland, Australia from 2013 to 2016. A total of 74 newborns were recorded in the study area, with the majority observed in July and August. These findings may signify that the Gold Coast Bay provides an apparently suitable habitat for calving for this humpback whale population. As the area has not been classified as calving habitat, these findings will assist conservation managers in making informed management decisions regarding this species.
Introduction
Humpback whales (Megaptera novaeangliae) undertake long-distance migrations between important habitats, typically from feeding areas to breeding and calving areas (Dawbin 1966; Rasmussen et al. 2007; Stevick et al. 2011; Franklin et al. 2012; Bortolotto et al. 2017; Irvine et al. 2018).
Studies from well-known breeding areas (e.g. Hawai`i: Cartwright et al. 2012; Craig et al. 2014; Currie et al. 2018; Ecuador: Félix and Haase 2005; Felix and Botero-Acosta 2011; Oña et al. 2017; Colombia: Félix and Guzmán 2014; Guzman and Felix 2017; Costa Rica: Oviedo and Solı´s 2008; Rasmussen et al. 2012; Brazil: Zerbini et al. 2004; Bortolotto et al. 2017; and Madagascar: Trudelle et al. 2016) concluded that breeding humpback whales prefer habitats between 19° and 22° latitude, warm sea surface temperatures (SST) (19° to 28°C), and shallow depths (15 to 60 m).
Results from recent studies suggest that calving humpback whales may be more capable to adjust their habitat selection than previously known, displaying plasticity, with some cow-calf pairs utilising offshore areas, shelfs and seamounts (Garrigue et al. 2015; Trudelle et al. 2016; Bortolotto et al. 2017; Derville et al. 2019). In Brazil, the highest density of cow-calf pairs was found in slow currents and in sheltered waters (Bortolotto et al. 2017). In Hawaii, Pack et al. (2017) recently concluded that young calves were found in shallow waters, while older calves were found in deeper waters with a rugged seabed. In Peru, Guidino et al. (2014) found cow-calf pairs in colder sea surface temperatures (lowest temperature: 18.2°C) in coastal waters leading them to suggest there was a southward extension of the breeding region of humpback whales in the Southeast Pacific.
Here in Australia, Bruce et al. 2014 found that cow-calf pairs preferred gentle slopes and calm waters. Irvine et al. 2017 found large numbers of neonate calves in shallow waters along the North West Cape of Western Australia, indicating a southward extension of the calving area for recovering population D.
Calving habitats (where birth and early maternal care occur), preferred by cow-calf whale pairs, maybe a sub-set of the breeding area habitats. Calving in shallow water may serve as an antipredator defense, placing vulnerable calves out of the range of killer whales (Orcinus orca) (Corkeron and Connor 1999; Pitman et al. 2015) and other predators found in colder (Forney and Wade 2006) and deeper waters (Herman and Antinoja 1977; Morete et al. 2007). Killer whales are a significant natural predator of humpback whales, with first-year calves being primarily targeted (Corkeron and Connor 1999; Janetzki and Patterson 2001; Pitman et al. 2015).
For the east Australian humpback whale population, known as the International Whaling Commission (IWC) breeding stock E1, the exact location of the breeding and calving grounds remains poorly defined and unclear. At this time, the primary breeding area is thought to be dispersed somewhere within the Great Barrier Reef (GBR hereafter) region (16° to 24° S latitude), possibly south of 21° S latitude (Simmons and Marsh 1986; Paterson 1991; Chaloupka and Osmond 1999; Smith et al. 2012). Exact knowledge of the intended migratory destination for breeding and calving is constrained by a paucity of research data due to the vastness of the region and the subsequent difficulty surveying the entire area (Chaloupka and Osmond 1999; Smith et al. 2012).
Newly born humpback whale calves can be distinguished by their pale colouration (light grey with white on the ventral region), light-coloured bands (foetal folds), and uncurled dorsal fins laterally compressed against their body (Ferreira et al. 2012; Faria et al. 2013; (Figure 1, 2, and 3)). Newborn calves are hindered by physiological constraints, having underdeveloped musculature, reduced breath-holding capacity, limited buoyancy control, and small body size: all of which limit their swimming performance (Cartwright and Sullivan 2009). Calf birth and development in warmer waters may also enhance fitness, as energy conserved in warm water can be devoted to growth, development, and survival (Whitehead and Mann 2000; Elwen and Best 2004). This strategy may result in a larger adult size with greater reproductive success (Clapham 2001; Rasmussen et al. 2007).
Figure 1. Mother and newborn calf observed in Gold Coast Bay, QLD, Australia. Photo: SeaPix Photographics, Ltd.
Figure 2. Mother and calf shown accompanied by an escort in Gold Coast Bay QLD, Australia. Photo: Laura Torre-Williams.
Figure 3. Mother humpback whale with a newborn calf displaying small size, pale colouration, foetal folds, and dorsal fin tilt in Gold Coast Bay, QLD, Australia. Photo: SeaPix Photographics, Ltd.
In the Southern Hemisphere, the east Australian humpback whale population, formerly part of IWC feeding Area V, 130° E to 170° W (Chittleborough 1965; Paterson 1991; International Whaling Commission. IWC 2006; Rock et al. 2006) exhibits a strong recovery from exploitation (Noad et al. 2011). This population migrates from their feeding grounds off Antarctica to their breeding grounds believed to be dispersed within the Great Barrier Reef region (Simmons and Marsh 1986; Paterson 1991; Chaloupka and Osmond 1999; Smith et al. 2012). However, this breeding area has proven difficult to clearly define, due in part to the region’s vastness, which prohibits broad-scale surveys (Smith et al. 2012). Thus, the location and habitat requirements for the calving area for this population remains undefined and poorly understood (Harwood 2001; Smith et al. 2012).
While this species is well studied, research effort has been mainly concentrated at well-known breeding and feeding grounds. In Queensland, Australia, the humpback whale migration pathway is close to the coast (e.g. within 10 km) facilitating land (Paterson 1984, 1991; Brown and Corkeron 1995; Noad et al. 2008, 2011), boat-based (Chaloupka et al. 1999; Franklin et al. 2011; Franklin 2014), and aerial studies (Bryden 1985; Noad et al. 2008). However, limited research has focussed specifically on cow-calf pods outside of known breeding grounds (e.g. Stockin and Burgess 2005; Franklin et al. 2011; Martinez et al. 2014; Franklin 2014) and in the Gold Coast Bay area (hereafter GCB; Meynecke et al. 2012). In particular, there is a paucity of empirical data on cow and newborn calf groups during the northern migration in the scientific record.
It is important to understand how newborn calves are utilising areas that are not defined as primary breeding grounds and what abiotic factors influence their distribution in these undocumented calving habitats. Newborn calves are not expected on the migration route. Consequently, there is no legislative protection to these vulnerable cohorts south of the perceived breeding grounds in the GBR region. As this species is vulnerable and recovering from depletion due to human exploitation, understanding calving habitat requirements, including what environmental factors can and cannot be endured, is important for successful conservation management.
The objectives of the present study were to examine the presence of newborn calves in GCB waters and more specifically to answer the following questions:
Are newborn calves present in GCB?
Where in the CGB (geographically) are newborn calves being sighted?
At what SST and water depths are newborn calves located at the study area?
Our study provides relevant data that will contribute to a better understanding of habitat requirements for cow-calf pairs. The outcomes will provide new information that will be useful to the marine mammal research community and the whale-watching tourism industry in the GCB area. It is hoped that data and recommendations herein will assist in sound management practice and will benefit conservation decision and management policymaking in Queensland. New information will assist tour vessel operators and conservation managers in making informed operational and conservation decisions.
Methods
Study site
The study area comprised the coastal waters of GCB, in southeastern Queensland, Australia (Figure 4). The search area covered by commercial whale-watching vessels in this study extended from Jumpinpin (27°45′14.2″ S; 153°26′15.9″ E), off South Stradbroke Island to the North to Tugun (28°14′31.2″ S; 153°49′54.7″ E) in the south. Tour vessels could venture 15 nautical miles offshore to search for whales in the allocated tour time, usually 3 hours total.
Figure 4. Map of Gold Coast Bay, Queensland, Australia. The shaded area on the map depicts the study area. Source: Geoscience Australia.
The study area is a shallow embayment with predominately south-easterly winds and annual SST ranging from 19.3°C to 28.0°C (Global Sea Temperatures 2016). The east Australian Current (EAC) is a warm boundary current dominating the continental shelf in the region (Cresswell et al. 2017). The EAC can move into the study area and, when it is present, humpback whales may alter their course and move closer to the coastal areas along the edge of this current (Meynecke, pers. comm. 2019; Reinke pers. comm. 2019).
Starting in 2013, the GCB had four commercial whale-watching operators (three large motorised vessels and one sailboat) offering weather dependent daily tours, during the humpback whale migration season (late May to early November). Regulation changes beginning in 2013 permitted whale-watching in Queensland state waters (zero to three nautical miles off the coast). This has resulted in an increase in whale-watching activity in nearshore waters because until then, operators were restricted to Commonwealth waters (3 to 15 nautical miles off the coast; State of Queensland (Department of Environment and Resource Management) 2011).
Data collection
Surveys were conducted on-board three commercial whale-watching vessels serving as platforms of opportunity from late May to early November (2013–2016). Vessels ranged from 12.5 to 30.8 m in length and operated from the Southport Seaway. Active search effort was dependent upon prevailing wind, sea conditions, and sighting reports (Corkeron 1995; Zaeschmar et al. 2014). Vessels communicated with one another to report whale sightings. Searches for whales were conducted by experienced crew members and a three-member research team from Humpback and High-Rises (HHR), a Gold Coast citizen science research group, using a continuous scanning method (Mann 1999) by naked-eye. Sighting cues included blows, the flank of the animal, and splashes or other water disturbance due to surface activity of animals.
Data collected included date, time, location, sea state, and weather conditions (Brown and Corkeron 1995) for all sightings. During each encounter, data collected included the species, pod size and group composition (Table 1), presence/absence of calves and/or newborns, and the general direction of travel (i.e. north or south) (Brown et al. 1995; Corkeron 1995). In accordance with the Australian whale-watching regulations (Australian National Guidelines for Whale and Dolphin Watching 2005: Department of Environment and Heritage 2006), all vessels were not permitted to approach whales closer than 100 m. When whales approached the vessel closer than 100 m, the engines were set to neutral.
Water depth data were recorded (±0.1 m) using the onboard depth sounder and within 100 m of the position of the pod at the beginning and end of the encounter. SST data for GCB were obtained from the Integrated Marine Observing System (IMOS) from the Australian Bureau of Meteorology (http://www.bom.gov.au/australia/satellite/). IMOS produce high-resolution satellite SST data sets in the Group for High-Resolution Sea Surface Temperature (GHRSST: www.ghrsst.org) file formats, with a spatial resolution of 1.1 km.
During the 2013 season, the location of sightings was determined using a handheld Global Positioning System GPS Holux 241 device (known accuracy within 2.2 m horizontally and less than 5.0 m vertically). GPS locations were recorded for all encounters within 100 m of the position of the pod at the beginning, throughout and at the end of the encounter. For the following seasons, a GPS X-Route XR-6100 logging device (known accuracy within 2.0 m) was attached in the helm via Velcro straps, and continuous tracks of vessels were recorded and later assigned to sighted pods.
Cow-calf pairs were identified by their close association (usually touching or less than one body length from each other), body size difference (length and girth), and the difference in blow height (Szabo and Duffus 2008). As each pod was encountered, the presence of a newborn calf was ascertained and the time, water depth (m), and GPS location were recorded (Szabo and Duffus 2008).
Photo-documentation of cow-calf pairs was performed by the research team, citizen scientists, and professional photographers from SeaPix Photographics using a Canon EOS 7D camera fitted with a 70 to 300 mm zoom lens or a Canon EOS 350D and 340D cameras equipped with a 70 to 200 mm zoom lens, respectively. All photographs from each contributor were labelled according to the date and time taken, vessel platform, and photographer. To distinguish between several newborn calves sighted on the same day, photographers focussed on obtaining images showing a) lateral body pigmentation patterns on the cow and calf (as per Glockner 1978; Katona et al. 1979; Katona and Whitehead 1981; Glockner and Venus 1983; Glockner-Ferrari and Ferrari 1985; Clapham and Mayo 1990; Felix and Botero-Acosta 2011); b) the dorsal fin region of the cow and calf (Glockner and Venus 1983; Chaloupka et al. 1999); c) a lateral view of the cow-calf pair together (to examine body size and colouration comparison, as per Glockner 1978; Katona et al. 1979; Katona and Whitehead 1981; Glockner and Venus 1983; Clapham and Mayo 1990; Cartwright 1999; Cartwright and Sullivan 2009; Felix and Botero-Acosta 2011); and d) caudal view of newborn to assess degree of dorsal fin tilt (Cartwright 1999; Cartwright and Sullivan 2009) for age-class determination.
Data analysis
Two environmental variables (SST and water depth) were selected for analysis. A number of studies have indicated that these variables are essential factors in the selection of suitable breeding, calving, and nursery habitat for humpback whales (Ersts and Rosenbaum 2003; Johnston et al. 2007; Rasmussen et al. 2007; Oviedo and Solı´s 2008; Smith et al. 2012; Guidino et al. 2014). Only sightings occurring in good visibility (≥1 km) and favourable sea conditions (Beaufort Sea State-BSS ≤ 4; Calambokidis et al. 2001) were included in the analysis. BSS 4 was considered appropriate as the upper limit for this study based on the large sizes of the vessels and their elevated platform height (3 to 6 m) (Hammond et al. 2002). The water depth was recorded at the start of each encounter as the ‘initial water depth’ for that sighting. The initial sighting time and location of each cow-calf pair was used to extract the local SST linked to that position in GCB from the IMOS generated SST data set. That temperature was then recorded as the ‘initial SST’ for that cow-calf pair. Descriptive statistics for SST and water depth including means, range, and standard errors were calculated. GPS data were extracted from the XRoute Manager GPS tracking software and tracks were downloaded into Excel 2016 Microsoft, where direction of travel could be ascertained by considering the start locations, subsequent locations, and the end of sighting location.
Prior to analyses, duplication of sightings collected from different vessels were removed by viewing all photographs taken by each vessel on a given date. When the same pod was observed by more than one vessel on any given date, the photographs with the best images were used for analysis. If the pod contained a newborn, that calf was only counted once for the day. The dataset was verified and checked for errors by the first author and senior researchers from HHR. If any discrepancies were detected, the data were omitted prior to analysis (Brown and Corkeron 1995).
The presence of newborn calves in GCB was determined by examining the best images taken during each survey throughout the season. When a calf was observed in a pod, the first image depicting the calf was considered the start of the encounter. The time associated with that first photograph was then used as the starting point for the calf track. The ‘start’ and ‘end track time’ from the last calf photo were also recorded so that the continuous GPS track could be represented.
Results
Survey effort
A total of 2274 h of survey effort were performed between May 2013 and November 2016. Highest survey effort occurred in 2016 (35.4%), followed by 2015 (23.1%) (Figure 5). Per month most effort featured in August and September. Effort variance can be attributed to the opportunistic nature of the study as well as weather conditions. A total of 74 newborn calves were sighted between June and September during the northern migration.
Figure 5. Study effort for 2013, 2014, 2015 and 2016 in Gold Coast Bay, Queensland, Australia.
Newborn calf presence by month
Although the first newborn calves were sighted in June on the northern migration, they only accounted for 4.0% (n = 3) of the total number of sightings (Table 2). In contrast, the months of July and August accounted for 51.4% (n = 38) and 35.1% (n = 26) of sightings, respectively. In September 9.5% (n = 7) of the newborns were sighted, with two heading north and five observed travelled south.
Table 2. Newborn calves sighted from opportunistic sighting platforms migrating north in Gold Coast Bay, Australia, from June 2013 to September 2016.
Newborn calf presence by year
Newborn calves were present in all years during the study period. 2016 had the highest number of sightings (33.8%, n = 25), followed by 2013 and 2015 (both with 27.0%, n = 20), and 2014 (12.2%, n = 9).
Newborn calf direction of travel
The GPS tracks collected indicated that 93.2% (n = 69) of individuals were travelling north through the GCB between June and August. This was evidenced by the start track latitude position during these encounters being further south than the end track latitude (Table 3). The remaining 6.8% (n = 5) newborns were sighted in September during the southern migration, travelling south through the bay.
Table 3. Latitudinal position of newborn calves (age class 1) for 2013 to 2016 from the Gold Coast Bay indicating northerly movement.
Water depth
Newborn calves were observed in GCB waters in varying water depths, with initial sighting depth ranging from 17.2 to 50.8 m (mean = 21.6, SD = 13.4, n= 64; Figure 6). On five occasions, the water depth was not able to be retrieved from the data set.
Figure 6. Monthly water depth (m) for newborn calf pods sightings in Gold Coast Bay, Queensland, Australia. Note: Bars represent the standard error of the mean.
Sea surface temperature
Newborn calves were observed in GCB waters with initial sighting SST ranging from 19.6°C to 22.8°C (mean = 20.4, SD = 2.9, n= 64; Figure 7). On the same five occasions, the SST data were not retrievable.
Figure 7. Monthly SST for newborn calf pods sightings in Gold Coast Bay, Queensland, Australia. Note: Bars represent the standard error of the mean.
Discussion
In this study, we successfully utilised platforms of opportunity to provide information on the youngest and most vulnerable cohorts in the recovering E1 whale population. Evidence that newborn calves were present with their mothers in GCB (28° S) during the recognised northern migration is presented. This result contrasts the general consensus that the breeding area is dispersed within the GBR region, most likely between 20° and 22° S (Smith et al. 2012) and that the GCB is only an aggregation area. Neither State or Commonwealth governments recognise waters south of 22° S as calving areas or maternal care areas. Additionally, newborn calves occurred in GCB as early as June and as late as September. These data also contradict the known historic timing known for calving, which is believed to mainly occur in July and August in GBR waters (Simmons and Marsh 1986; Paterson 1991; Chaloupka and Osmond 1999; Smith et al. 2012). Due to the opportunistic nature of this study and incomplete survey effort for the entire bay, our results likely underestimate the use of GCB waters by newborns.
Presence of newborn calves
The northern migration of humpback whales is well known to follow a specific age-class order, with a steady flow of cows with yearlings, sub-adults, adults, and finally pregnant females (Dawbin 1966; Clapham 2000). Pregnant females are typically the last members of the population to arrive in the breeding areas between 20° and 22°S (Dawbin 1966; Clapham 2000). Data herein, therefore, are in contradiction of the recognised distribution patterns of this species according to reproductive status on migration. Indeed, newborns are not typically expected on the northern migration as they tend to be born later in the season and at higher latitudes (Dawbin 1966; Clapham 2000; Paton 2016; Jackson et al. 2014).
One explanation for this early arrival and presence of newborn calves could be the influence of changing environmental conditions altering the timing of the east Australian humpback whale migration, as suggested by Paton (2016). Climate change induced impacts on the food supply of these whales may play a part in the earlier than expected calving at this location (Flores et al. 2012). If east Australian humpback whales are departing feeding areas earlier than typical, they could arrive and give birth before reaching the main breeding areas in GBR. However, as the known gestation period is 11 months, this would also imply that they are getting pregnant earlier than expected as well. Another possible explanation is that warming subtropical southern Queensland waters are now sufficiently warm enough for calving to occur (Lawler et al. 2007; Pásztor et al. 2016; Poloczanska et al. 2016). This warming effect can be attributed to ongoing climate change in the region (Evans et al. 2010; Pirotta et al. 2018) and pregnant females can tolerate these temperatures for calving and are beginning to utilise these warm inshore waters.
The data revealed most newborns observed in GCB were travelling north through the bay between June and August, indicating that they were continuing to migrate in that direction with their mothers. This continuing northward movement may be an unknown behaviour as newborn calves are thought to be poor swimmers, remaining in the warm, shallow waters until they acquire sufficient swimming skills to start the southward migration (Dawbin 1966; Clapham 2000; Craig et al. 2014). However, it remains unclear how far to the north the calves continued to swim.
According to the literature, a number of ‘suspected calving locations’ have been postulated (Chittleborough 1965; Paterson and Paterson 1984; Paterson 1984, 1991; Paterson et al. 1994). However, uncertainty remains regarding the location of the primary calving area for E1 whales with early sightings of newborns in June and July suggesting that migration patterns of E1 whales may not be as straightforward as previously reported (Chittleborough 1965; Dawbin 1966). Kaufman et al. (2010) suggested that a) birthing areas may be more widespread than thought and b) births were occurring south of the known calving area.
The presence of a number of newborn calves in GCB could signify that this strongly recovering population (Noad et al. 2011) is extending their calving habitat range to include suitable waters to the south of GBR. GCB may act as a ‘spillover’ area. Unknown breeding areas are being discovered where humpback whale populations are recovering around the globe (Mattila et al. 1994; Johnston et al. 2007; Guidino et al. 2014; Lucena et al. 2016).
Water depth and SST
Within GCB, newborn calves were initially observed in shallow water depths (mean = 21.6 m, SD = 13.4, range = 9.1 to 50.8 m). These results correlate with studies from known humpback whale breeding grounds that have concluded that cow-calf pods seek shallow waters (15 to 60 m deep: Whitehead and Moore 1982; Flórez-González 1991; Smultea 1994; Ersts and Rosenbaum 2003; Forestell et al. 2003; Félix and Haase 2005; Morete et al. 2007; Kaufman et al. 2010; Smith et al. 2012; Craig et al. 2014; Guidino et al. 2014).
This study recorded newborn calves in SST ranging from 19.6°C to 22.8°C (mean = 20.4, SD = 2.9). The lower range of these temperatures is cooler than the known preferred water temperatures for this species from other breeding areas (Whitehead and Mann 2000; Clapham 2001; Rasmussen et al. 2007) and suggests a higher tolerance to cooler SST than previously reported. Smith et al. (2012) study conducted in GBR waters suggests that east Australian humpback whales prefer waters temperature ranging from 21°C to 28°C . Although the results presented in this study are slightly colder than in other areas, Rasmussen et al. (2007) suggested that humpback whales might breedin areas with less than optimal water temperatures if those areas had other suitable conditions such as shallow and protected waters.
Recently, Clapham and Zerbini (2015) hypothesised that even though the East Australian coastal waters are historically considered ‘migratory pathways’, they may serve another function. The authors also suggested that the ‘widespread occurrence of newborn calves, singing and competitive behaviour in these areas leaves little doubt that they also represent major mating and calving grounds in their own right’. They further reported that many areas could provide suitable calving habitat (e.g. warm, shallow protected waters) for E1 whales. Therefore, there is a potential for considerable plasticity in east Australian humpback whales breeding distribution and they may seek suitable breeding habitats in other areas.
Confirmed sightings of newborn calves have been reported from whale-watching tour operators and researchers in New South Wales, from Byron Bay (28°64ʹ S, 153°63ʹ E) and Port Stephens (32°42ʹ S, 152°03ʹ E) (L. Maffesoni 2015–2017, pers. comm.). These sites are further south of the putative calving grounds in the GBR region.)
Finally, evidence from other mysticete species indicates that calf births occur along the migratory pathway before reaching the primary birthing and nursery area. Perryman et al. (2002) and Shelden et al. (2004), reported pods containing newborn gray whale (Eschrichtius robustus) calves heading south along the California coast in January towards the central nursery area in Baja California, Mexico.
Conclusions
Findings presented herein demonstrate that newborn calves are present in Gold Coast Bay from June until September. These results indicate that parturition occurs regularly along the northern migration, more than 1000 km outside the primary Great Barrier Reef calving grounds. We conclude that some humpback whales are utilising warm and shallow waters along south-east Queensland to birth their calves whilst migrating. The presence of newborn calves in the Gold Coast Bay signifies that this area is suitable habitat for calving. The Gold Coast Bay is currently not recognized as calving habitat and has no legislative protection in place. Understanding how cow-calf pairs are distributed and utilise the bay is an essential prerequisite for effective management. Concerns regarding ongoing development along this urban coastline, warrant a precautionary conservation approach. These findings will assist conservation managers in making informed management decisions to protect these vulnerable cohorts and enhance the survival rate and further recovery of this population.
Disclosure statement
No potential conflict of interest was reported by the authors.
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