Humpback Whale Distribution and Abundance in the Near Shore SW
Total Page:16
File Type:pdf, Size:1020Kb
Field Report A Description of Humpback Whale and other Mega fauna Distribution and Abundance in the Western Pilbara Using Aerial Surveys – 2009/2010 Prepared by Curt and Micheline Jenner Centre for Whale Research (WA) Inc. PO Box 1622 Fremantle WA 6959 [email protected] 1. Abstract Aerial surveys were conducted across a 12 month period in the coastal region of the proposed Anketell Point Iron Ore Port facility in order to determine mega fauna distribution and abundance for development purposes. A total of 1069 humpback whales were sighted in 22 aerial surveys over the western Pilbara offshore region during mid August 2009 to late July 2010. The aerial surveys also reported regular sightings of dolphins, manta rays and turtles throughout the survey. A useful humpback whale baseline dataset has been established prior to establishment of the new port facility so that managers and key stakeholders can proceed with an understanding of where potentially important areas to humpback whales may be monitored. 2. Objective The primary purpose of this study is to determine the seasonal distribution and relative abundance of humpback whales and other mega fauna along the western Pilbara coast near Anketell Point during a 12 month seasonal cycle. Aerial surveys were considered the most effective means of detecting spatial and temporal species clusters in the time window assigned and which could be used for preliminary environmental assessment purposes. This report describes a 12 month dataset collected at approximately two week intervals during the predicted peak whale period (June to November) and at 3 week intervals during off-peak periods(December to May). 3. Introduction The Centre for Whale Research (CWR) was commissioned by API Ltd in October 2009 to design, conduct and analyse, a series of aerial surveys that would best compliment existing datasets and fill knowledge gaps in great whale and other mega fauna distribution and abundance along the inshore and offshore western Pilbara coastline (Figure 1). This is the final report which documents the complete 12 month monitoring programme (in total 22 aerial surveys) and provides contextual interpretation of the results for future management purposes. It forms the first step in a systematic process to address the question: Does Anketell Point and the surrounding off-shore area represent a biologically important area for humpback whales? 1 | P a g e 3.1 Survey Relevance CWR has been conducting independent studies into the population dynamics and migratory habits of humpback whales in Western Australia since 1990. CWR has confirmed Chittleboroughs’ (1953) theory that Exmouth Gulf, 325 km to the southwest of the study area (2-4 days swim-time, based on speeds of 2.4 – 4.6 km/hr, Dawbin (1956) and Chittleborough (1965)), is a nursery area for humpback whales (Jenner et. al. 2001). As such, Exmouth Gulf represents the closest known biologically important area for humpback whales to the study site and here is used as a comparison basis for this study program. The understanding of Exmouth Gulfs’ role for humpback whales is more advanced than that at Anketell Point. CWR has conducted a variety of boat-based (including photo-id, genetic, behavioural and satellite tracking) and aerial survey studies in Exmouth Gulf since 1995. Humpback whales are expected to be the most frequently encountered protected species in the Anketell study area although direct study programs have not been conducted in this general area since 1994 (at Dampier, Jenner and Jenner( 1994)). Chittleborough (1953) first described Exmouth Gulf as a possible “nursery” for humpback whales based on aerial surveys over the area in 1951 and 1952. These flights were a regular part of an exploratory process designed to maximise returns for the commercial whaling industry. A whaling station operated at Norwegian Bay near Pt Cloates (Lat S 22˚ 36’) from 1912 to 1916 and then from 1922 to 1928, and finally from 1949 to 1955. By 1963, when a moratorium on humpback whaling commenced, there was thought to be less than 800 whales left in Breeding Population “D”, or the Western Australian population (Chittleborough 1965). Now, over forty years on since the cessation of whaling, this population of whales is thought to have been recovering at an annual rate of between 7 and 12% (Hedley et al., 2009; Salgado Kent et al., 2010). By extrapolating this recovery rate forward to 2010, the population could reach 30-35,000 individuals. If, as suggested, approximately 10% of this population is represented by cow/calf pairs, then as many as 3,500 pairs could use nursing areas like Exmouth Gulf by 2010. How this population increase is progressing and how it relates to other nursing or resting areas is of great interest to industry and regulatory managers. 2 | P a g e Figure 1. Aerial survey flight paths for the Anketell 2009/2010 study period showing proximity to the 2000–2009 CWR aerial survey flight paths near North West Cape and the Exmouth Gulf series from 2004/2005. 3 | P a g e 3.2 Background Research – Humpback Whales at Exmouth Gulf/North West Cape Exmouth Gulf is the nearest area on the WA coast to Anketell Point that detailed migration data for humpback whales exists. Timing of migration and off-shore distribution patterns of whales from the two adjacent, but separate, study sites will be compared. The migration of humpback whales both north and south past Exmouth Gulf follows predictable but complicated patterns each season. The northern migration of this species near Albany, Western Australia, has been described by Chittleborough (1965) as being segregated by age and sex class. It is likely that this same pattern, where subadults and mature females terminating lactation are in the vanguard of the northern migration, followed by mature males and females and then later pregnant females (carrying near-term foetuses), is present off North West Cape and the broader south western Pilbara offshore region. The southern migration follows a similar order, with addition of cows and their newly born calves at the tail end of the migration. The cow/calf portion of the migration congregates in greatest numbers inside Exmouth Gulf, but their spatial/temporal distribution has not previously been described near the Anketell study area. Spatially, the northern migratory path is consistent for all age and sex classes off North West Cape and centres on about the 250 m depth contour (Figure 2). Whales rarely enter Exmouth Gulf during the northern migration (June to early August), perhaps due to the 3˚C or more temperature difference between the open ocean and the shallow Gulf during June to early August. A transition phase between the northern and southern migrations occurs from early August to early September (Figure 3). This time period coincides with peak numbers of whales each season (Figure 5) and results in the migratory path spreading spatially to include a much wider depth range than is observed during the northern or southern migration. Sightings of whales inside the northern warmer part of the Gulf increase during early September and by mid-late September the main southbound migratory peak passes by west of North West Cape with some animals entering the Gulf (Figure 4). 4 | P a g e Northern Migration (June to early August) Exmouth Gulf Figure 2. Aerial survey sightings of humpback whales during the northern migratory period (June to early August) in 2000 and 2001. Data from CWR aerial surveys in Woodside Energy EIS Document (2002) section 2.3.2.5. Peak of Migration (mid August to early September) Exmouth Gulf Figure 3. Aerial survey sightings of humpback whales during the Transition Phase (mid August to early September) in 2000 and 2001. Data from CWR aerial surveys in Woodside Energy EIS Document (2002) section 2.3.2.5. 5 | P a g e Southern Migration (mid September to December) Exmouth Gulf Figure 4. Aerial survey sightings of humpback whales during the southern migratory period (mid September to December) in 2000 and 2001. Data from CWR aerial surveys in Woodside Energy EIS Document (2002) section 2.3.2.5. 140 120 106 100 80 60 45.5 40 32 32.5 24 17 15 16 20 9.5 12.5 5 7.5 9 6.5 6.5 2 0.5 1.5 0 Jul4-13 Oct 2-11Oct Aug3-12 Sep2-11 Mean number of pods / 10 day block Jul 14-23Jul 1-10Nov June4-13 12-21Oct 22-31Oct Aug13-22 Sep12-21 Nov 11-20Nov 21-30Nov June14-23 Jul 24-AugJul 2 Sep22-Oct 1 June24-Jul 3 Aug23-Sep 1 Sample period Figure 5. Mean number of humpback whale pods recorded during aerial surveys in 10 day sample blocks per sampling season during the months of June to October ( X 1 SE). Data from CWR aerial surveys west of, and not including, Exmouth Gulf for Woodside Energy 2000/2001, Woodside Energy EIS Document (2002) section 2.3.2.5. It is likely that water temperature plays a role in determining when whales, particularly cow/calf pairs trying to minimise metabolic expenditures, enter Exmouth Gulf, however it is also possible that 6 | P a g e the northward facing opening to the Gulf acts to trap whales migrating southwards along the coast. Cow/calf numbers inside the Gulf peak during the first two weeks of October (Figure 6), at a similar time annually that the sea surface temperature inside the Gulf becomes equal to that found offshore at the same latitude (Figures 7 & 8). 35 30 25 20 15 10 Number of Calves of Number 5 0 Figure 6. Numbers of cow/calf pod sightings from 2005 aerial surveys inside Exmouth Gulf (CWR unpubl. data).