Cook Islands Humpback Whales – Part 1

Gerald McCormack, CINHT

The dedicated researchers in the South Pacific Whale Research Consortium, including Nan Hauser, have made a large contribution to the recent explosion of information about Humpback Whales. Although science is always a “work in progress” this seems like a good time to review 34 papers up to 2014.

Humpback vitals

Humpback breeching

The vernacular name humpback refers to the arching of the back as they dive. The unusual Latin name, Megaptera novaeangliae translates to “big-wings of New England”. They were first described around 1750 as the “baleen whale of New England” after the area where they were common, along the northeast coast of the US. A hundred years later, around 1850 they were separated from the other baleen whales and given the name Megaptera or “big wings”, because of their unusually long pectoral fins.

Mother and calf

At birth humpbacks are about 4.5m and weigh around one tonne. They feed on mother’s milk for about six months, then increasingly feed themselves on krill, and are weaned at about a year. Females mature at about five years and eventually reach an average of 15 metres and 35 tonnes; males are usually around 14 metres. Females breed every 2-3 years and pregnancies last about 11 months. They can live 50-100 years.

Humpbacks are famous for their long migrations between summer feeding areas around Antarctica and winter breeding areas in the subtropics, about 5,000km apart. At a typical migration rate of 3-6km/hr or 70-140km/day (Horton et al. 2011) it takes them 35-70 days to cover the 5,000km. For comparison, people typically walk at about 5km/hr, about the same speed as whales migrate.

Antarctic krill – photo from Wikipedia

Around Antarctica they feed on tiny shrimp-like animals called krill that form immense swarms, and adult whales can consume about 1.5 tonnes-a-day. During this time they develop an immense layer of fatty tissue known as blubber upon which they live during the 6-8 months of migration and breeding.

In their subtropical breeding grounds humpbacks are famous for their spectacular leaping out of the water (“breaching”) and for the long songs of the males.

Yankee whalers

Life in the Cook Islands was transformed by the non-sectarian London Missionary Society missionaries arriving in the 1820s with the Gospel and a plethora of new plants and animals.

They encouraged people to raise the new crops and animals to sell to visiting ships and traders. In addition to provisioning the whaling ships, young men often joined as replacement crew. Rarotonga sailors were tattooed with the Rau Teve pattern on the side of their necks so they could recognise each other in distant places.

The main islands for provisioning were Rarotonga and Aitutaki. Richards (2014) reported that Yankee whalers called at Rarotonga as follows: one (1820s), 16 (’30s), 82 (’40s), 134 (’50s), 39 (’60s), 13 (’70s), 7 (’80s) and none thereafter. The analysis was based on a partial collection of logbooks and Richards concluded that the actual number of visiting whalers was probably 2-3 times greater.

These whalers were known as Yankee whalers because they came from coastal towns in the New England area, especially from Nantucket and New Bedford in Massachusetts.

Yankee whaling began around 1650 killing Right and Humpback Whales feeding near the New England coast. A Sperm Whale was killed in 1712 and the superior “sperm oil” from its blubber and the much-prized spermaceti or “head oil” lead to whalers sailing further and further to find them.

By 1780 they were whaling everywhere in the north and south Atlantic, along with a few British whalers. They entered the Pacific around 1790 and within a few years were whaling throughout the ocean, except around Antarctica which was too cold and inhospitable.

Humpback kills by American Sailing Whalers

The Yankee whaling industry peaked around 1850 when there were about 740 ships under the US flag. The industry went into steady decline after about 1860 and finished around 1920.

Townsend’s (1935) analysis of whaler logbooks showed that between Fiji and French Polynesia they killed very few Sperm Whales, and humpbacks as follows: two in Fiji; none in Samoa; 297 in Tonga; three in Cook Islands; and none in the Societies. He analyzed about 10% of the voyages and concluded that actual kills were probably 5-10 times more than shown. He also found that nearly all the humpbacks were killed in August and September. See Figure 1.

The relative number of whales killed in each area is particularly interesting because it provides the earliest data on the distribution of humpback across the South Pacific. It is very obvious that they bred mainly around Tonga and rarely elsewhere.

Smith et al. (2006) re-analyzed Townsend’s data and other information to discover that all whaling in Tonga occurred within the ten years of the 1870s and they estimated that about 2,837 whales were killed. Humpbacks were a last resort for the Yankee whalers because the blubber gave the least valuable whale oil, they were relatively fast and difficult to catch, and they often sank before they could be secured.

As a result of Yankee whaling there was a development of shore-based whaling in Tonga and the Cook Islands. It is not known when it started in the Cook Islands. Powell (1979) reported that the last whale killed on Rarotonga was in 1914 by a gang working for Makea Nui Tinirau Ariki.

This might be mistaken, because the PIM 1930 reported that “Recently there have been numerous whales … and the natives spent endless hours chasing after them….. with no luck but on two occasions managed to scratch the whales with harpoons. However, Aitutaki natives …. landed two whales…” (PIM 1930Dec.  v.1(5):9).  It is not known when local whaling ceased, although there was no further mention of whaling in 1930s PIM.

The July onset of flowering of the indigenous Ngatae or Coral Tree (Erythrina variegata) was the sign to prepare the equipment and put lookouts on the hills. Upon sighting a whale or To’ōra the lookouts blew their Pū or Triton Conch (Charonia tritonis) trumpets and the rowboats were launched. Whale carcasses were brought ashore into Ngātangi’ia Harbour where the blubber was cooked in large metal pots to extract the oil, which was put in wooden barrels for export.

In Tonga the industry started in the 1890s in the Ha‘apai Group using locally constructed longboats; the oil was sold to trading ships. In 1912 the operation moved to Tongatapu where Tongans soon developed a taste for whale meat and this became the main focus of the industry. (Reeves 2002)

During the 1950s and ’60s they were taking 10-20 whales-a-year, and in the 1970s eleven small operators were taking 3-8 whales-a-year. The industry was banned under the Whaling Act 1979, pending an improved stock assessment. Today, Tonga has a significant whale watching industry, which includes swimming with whales.

Tonga, Cook Islands and French Polynesia

In the last twenty years there has been great progress on monitoring whales with photographic and genetic identification and satellite tracking. These tools have enabled scientists to learn much more about whales moving between island groups, both within breeding seasons and between breeding seasons.

Resighting data to 2004 enabled it to be estimated that Tonga had about 2,300 whales, and French Polynesia about 1,000. At that stage, Cook Islands had no resightings and therefore no population estimate (Baker et al. 2006). The authors concluded that the Cook Islands was “not a primary migratory destination, but rather a part of a migratory corridor used by one or more breeding stocks”.

Genetic research in 2007 (Olavarria et al.) showed Cook Islands whales to be nearly indistinguishable from those of Tonga.  In 2007 the six Rarotonga whales with satellite tags all departed to the west or northwest (Hauser et al. 2010, Horton et al. 2011), which further supported the idea that Cook Islands’ whales are part of the Tonga group. In 1993 one whale was recorded in Mo‘orea and a month later in Palmerston which showed that sometimes whales move direct from French Polynesia to the Cook Islands (Poole 2006). See Figure 2.

To 2015, after eighteen years of monitoring, there had been only two resightings in the Cook Islands (Hauser, unpublished), which showed that whales rarely reuse the corridor.

The 2009 (Albertson-Gibb et al.) estimate for French Polynesia was 850-1,850 whales. The sub-stock is genetically distinct (Olavarria et al. 2007) with occasional sharing with other sub-stocks to the west. There has been one intra-seasonal match to the Cook Islands in 1993, and several inter-seasonal matches: Tonga (5), American Samoa (2), and New Caledonia (1) (Poole 2006). The whales of French Polynesia are most common in the Societies and northern Australs, less common in the Tuamotus and very rare in the Marquesas (Poole pers.comm.). The occurrence of this large population in French Polynesia was unexpected considering the lack of whales killed in the area by the Yankee whalers, even though they often provisioned their ships in Tahiti.

 

Author’s notes
First published Cook Island News, October 2015 to CI News
Contact Cook Island Natural Heritage Trust for full Bibliography.
Photos by Michael Poole, Kirby Morejohn and Wikipedia.
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Is Mangaia the oldest island?

Gerald McCormack, CIHT

A view of Mangaia north to south. The outer green belt is the raised fossil reef (makatea), which surrounds the inland volcanic hills. (Photo Ewan Smith)

In the Quarantine Quiz (CINews 29 May) the oldest island in the Pacific was listed as Mangaia at 18 million years (Ma). This idea gained popularity with the 2010 publication entitled “Tangi ke – Welcome to Mangaia – The oldest island in the Pacific”, by the Mangaia Historical and Cultural Society and the University of the South Pacific.

It is simply not true, there are many islands in the Pacific much older, and, within the Cook Islands, all the Northern Atolls are more than twice as old as Mangaia.

The Hotspots

The Southern Group islands formed from two long-lived “hotspots” to the southeast. The oldest dated-island in this complex chain is Mangaia at around 19.5Ma (million years). This makes Mangaia the oldest dated-island in the Cook-Austral chain. (See the illustration)

Mangaia originated 1,900km to the southeast at the Macdonald Hotspot, which is growing yet another island, presently within 50m of the surface. The Pacific Plate carries islands to the northwest, away from their hotspots, at about 10cm/year which accounts for the distance from Mangaia to the Macdonald Hotspot.

Showing the hotspot tracks

The Cook-Austral hotspot chain. The tracks of the Macdonald and Arago hotspots for more than 50 million years.

Other islands with evidence of a Macdonald origin are Rapa, Raivavae, Tubuai, Rurutu and Rimatara. In addition, some geologists conclude there was another undiscovered hotspot southeast of Raivavae that played a later role in the formation of Raivavae, Tubuai and various seamounts. The story is still unfolding.

The Southern Group atoll of Palmerston is of unknown age and origin. It might be a very old island like the Northern Group atolls, or it might be the most westerly member of the Cook-Austral hotspot chain.  In the latter case, it probably originated at the Arago Hotspot, which is now a small seamount 130km southeast of Rurutu. If this is the case, would Palmerston be older than Mangaia?

The islands formed by the Arago Hotspot include Aitutaki, Ātiu, Ma‘uke and Miti‘āro. Of these islands, only Ātiu is well-dated. It is 850km from Arago and dated at 8Ma. Palmerston is 1,400km from Arago giving it an estimated age of 13Ma. If Palmerston formed at Arago, Mangaia would still be the oldest island in the Cook-Austral chain.

In recent years scientists have shown that the Macdonald and Arago hotspots also made seamounts and islands in the Tokelau chain and in the Tuvalu-Gilbert chains, respectively. There the islands are an amazing 60-80Ma, and there is more speculative evidence that these hotspot tracks continue into western Micronesia to islands older than 100Ma.

Mangaia, as a child of the Macdonald Hotspot, is the oldest in the island-dense Cook-Austral archipelago. However, compared to the Macdonald’s oldest offspring in the Tokelau, Mangaia is a teenager.

The Manihiki Plateau

The Northern Group islands are all much older than Mangaia.  The massive Manihiki Plateau formed between 125-120 million years ago. It soon broke into separate sections, three of which drifted away: one to Colombia; one to Antarctica; and, one to New Zealand as the Hikurangi Plateau. The remaining section, the Manihiki Plateau, became partially divided by deep troughs.

Between 100Ma and 60Ma there were a number of small eruptions on the plateau, forming a few seamounts along with the islands of Suwarrow, Pukapuka, Nassau, Manihiki and Rakahanga. When Penrhyn grew to the east of the plateau is unknown, but is it probably more than 50Ma. All Northern Group islands are much older than Mangaia.

Since its formation near the surface the plateau has been slowly sinking. The highest section is presently about 2,500m above the surrounding seafloor, which is typically about 5,000m below sea level.

The Pacific Tectonic Plate

The Pacific Ocean overlies two main tectonic plates, the largest being the Pacific Plate. This plate started to grow about 180Ma and it has pushed other plates away to become the largest tectonic plate in the world. The edge of this plate is known as the “Ring of Fire” because it is associated with intense volcanism and earthquakes. In our area, the Pacific Plate’s western boundary is the Tonga Trench, where it subducts under the Australian Plate.

Like the Cook Islands, islands on the Pacific Plate have grown by within-plate volcanism, mainly over “hotspots”. In the western South Pacific, on the Australian Plate there are many large islands in Fiji, Vanuatu, Solomons and New Caledonia, which usually have much older foundations than Mangaia. Fiji, for example, has rocks dated to around 40Ma; the oldest in the Solomons are around 60Ma.

Comparing islands on the Australian Plate with islands on the Pacific Plate, such as Mangaia, is like comparing apples with oranges. We will leave the Australian Plate and focus on Pacific Plate, where many of the islands are more than twice as old as Mangaia.

Another contest?

The wave eroded coastal cliff of the uplifted fossil reef (makatea). Cliff is approximately 15 meters high.

While Mangaia is not the oldest island on the Pacific Plate, it can win a restricted contest for the oldest island with exposed volcanic rocks.

When volcanic islands grow on the Pacific Plate their volcanic cores are soon surrounded by an ever-thicker limestone reef, grown by corals. Within about 10Ma the volcanic core sinks below sea level, leaving a lagoon surrounded by a coral reef – an atoll. For example, when Eniwetok atoll in the Marshall Islands was drilled in 1952 there was 1,300m (4,200ft) of limestone before they hit the volcanic core. While the sinking of an island is incredibly slow, given 70Ma the effect can be very dramatic.

All but a few of the old islands on the Pacific Plate have limestone caps completely covering their original volcanic cores. The few exceptions just happen to be six islands in the Australs (Rimatara and Rurutu) and Southern Cooks (Mangaia, Ātiu, Ma‘uke, Miti‘āro). These are the uplifted makatea islands.

Cross-section of Mangaia showing inland volcanic hills, swampy gulch and uplifted limestone fossil reef. The coastal image above shows the cliff on the inside of the reef flat. The steps on the outer uplifted reef formed a different times when the sea level was much than at present.

The makatea islands subsided until they were low volcanic hills surrounded by a wide fringing reef of limestone. At that stage, they stopped sinking and were uplifted so that today each has a dry fossil reef surrounding inland volcanic hills. In our case, the uplift started about 2Ma and Mangaia is the most spectacular, with its fossil reef to 75m elevation and the central hill of Rangimotia at 170m.

Mangaia is the oldest of these six makatea islands, and I believe this makes it the oldest island on the Pacific Plate with exposed volcanic rocks.

What about other uplifted islands, such as Niue, Makatea (Tuamotu) and Henderson? While Niue and Makatea are much older islands than Mangaia they have no exposed volcanic rocks, because they were atolls at the time of their uplift.

Although Mangaia is not the oldest island in the Pacific or the Cook Islands, it is definitely the oldest dated island in the Cook-Austral archipelago. And, it is probably the island with the oldest exposed volcanic rocks on the Pacific Plate.

Mangaia is neither the oldest island in the Pacific nor on the Pacific Plate. But, it can be first in two lesser contests. It is the oldest island in the Cook-Austral archipelago; and, it is most likely the oldest island on the Pacific Plate with exposed volcanic rocks.

Author’s notes
First published CI News (04 June 2020 condensed) and CI Herald (10 June 2020 in full). This article is the full version.
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Cook Islands Humpback Whales – Part 2

Gerald McCormack, CINHT

Soviet illegal whaling

I came to Rarotonga in 1980 and over the next few years periodically saw a humpback or two. At that time Ron Powell and George Cowan told me that humpbacks were not seen for many years and they were keen to make a documentary to tell people that whales used to visit the Cook Islands.

During the 1980s, whale sightings slowly became more frequent and this trend continues. Why did they disappear?

The Soviet Union formally collapsed in 1991. In 1993 the Russian biologist, Alexey Yablokov revealed that Soviet whalers had implemented an immense global campaign of illegal and unreported whaling from 1948 to 1973. This was despite the legal protection given whales in 1966 by the International Whaling Commission (IWC) of which the Soviet Union was a foundation member. The 1966 protection evolved into an international moratorium on commercial whaling in 1985 which was binding on all signatory nations.

Since its discovery in 1993, the details of Soviet whaling have been clarified and show that the populations of several species of whale around Antarctica were decimated during the 1950s and ’60s (Rocha et al. 2014).

To understand the past and predicted future of Cook Islands whales we need to look at the Oceania sub-population to which they belong.

The Oceania sub-population

The whales that breed in the subtropics of the South Pacific migrate about 5,000km southward to feed on krill around Antarctica in a band about 500-1,000km wide north of the sea ice.

In 1998 the IWC identified seven breeding stocks (A-G) in the Southern Hemisphere and linked them directly southward to six feeding areas (I-VI) around Antarctica. This simple linkage of breeding stocks to feeding areas is known as the Naïve Population Model and it provided an initial hypothesis to start assessing discrete populations and their recovery.

Humpback Whale Migration

In the South Pacific the three IWC breeding stocks were E, F and G. The complex and widely dispersed nature of the breeding areas lead to Stock E being divided into three sub-stocks: east Australia (E1); New Caledonia (E2); and Tonga (E3). Stock F was divided into two sub-stocks: Cook Islands (F1); and French Polynesia (F2). The last stock was the Southeast Pacific stock (Stock G) breeding mainly off Colombia, but extending from 6°S (north Peru)  across the Equator to 12°N (Costa Rica). See figure 3.

To assess population recovery of sub-stocks it is necessary to discover where each feeds around Antarctic so the impacts of Soviet whaling can be accurately assigned and original populations estimated.

Genetic analysis to 2008 (Albertson-Gibb et al.) indicated that 80% of the whales in Area VI were from Tonga; 80% in Area I were from Colombia; and Area IV was 30% from west Australia and surprisingly 30% from New Caledonia; they did not include data for east Australia whales. The overlapping of sub-stocks in the feeding area shows that the Naïve Population Model is in need of further development.

In general terms the Soviet whalers killed 22,570 in Area V, 7,195 in Area VI, and 649 in Area I (Clapham et al. 2009). Scientists break this data into smaller areas to better link it to the subtropical sub-stocks.

Genetic analysis in 2011 (Pastene et al.) gave further support for putting Tonga and Cook Islands whales together and feeding in Area VI. Although there was also evidence that whales from New Caledonia were mainly east of 135°E in Area V and might form a single stock with the Tonga and Cook Islands whales in Area VI. The only tagged Cook Islands whale tracked to Antarctic waters was in 2007 and it ended up in the far east section of Area VI (Hauser et al. 2010).

Pastene et al. found no evidence of French Polynesia whales in Area VI. It is surprising that there are more than 1,000 humpbacks nearby east of the Cook Islands that rarely interact during the breeding season or during the feeding season – is there a language barrier? The feeding area of the French Polynesia whales remains a mystery with very few being found in Area I. (Pastene et al. 2011, Poole pers.comm.).

Some whales undertake unexpected migrations. One remarkable migration involved two whales that bred in American Samoa and fed at the Antarctic Peninsula (eastern Area I), a distance of 9,400km apart. One made a return journey to the same area of Antarctica: Area 1 in Jan 2002; American Samoa in Oct 2005; and Area 1 in May 2009 (31km from its 2005 position!). (Robbins et al. 2011).

Areas around Antarctica are not equally good feeding areas. Extensive surveys under the IWC IDCR/SOWER programmes around Antarctica reported in 2011 (Branch) showed high concentrations of humpbacks south of NZ in Area V and around the Antarctic Peninsula south of South America in the eastern section of Area I. There were only moderate densities through Area VI and most of Area I. See Figure 3. If one compares this distribution with the distribution of Antarctic Krill on KRILLBASE it can be seen that whales have higher densities in areas with high densities of krill.

Recovery to 2008 – IUCN

The International Union for the Conservation of Nature (IUCN) has elaborate criteria to assign species to categories of threat or risk of extinction for their famous Red List. Extinct (EX) is totally gone, Extinct in the wild (EW) means it survives only in captivity; and, in descending order of threat, there is Critically Endangered (CR), Endangered (EN), Vulnerable (VU), Near Threatened (NT) and Least Concern (LC).

The Humpback Whale was listed as Endangered in 1986 and 1988, and downgraded to Vulnerable for 1990, 1994 and 1996, and in 2008 it was further downgraded to Least Concern. Least Concern was based on evidence that the population continued to increase and that it was more than 50% of the 1940s population, which was the threshold to be considered Vulnerable.

While assessing the humpback as a species to be of Least Concern, IUCN singled out the Oceania sub-population as being at a greater risk because it was only 27% recovered.

They categorised the Oceania sub-population (including the east Australia sub-stock) as Endangered because it had suffered a decline of  73% over the last three generations of 21.5 years each. This decline spanned criteria for Vulnerable and Endangered, and the latter was selected based on a balance between “precaution and credibility”. (Childerhouse et al. 2008)

Recovery to 2014 – IWC

In 2014 IWC undertook a detailed assessment of the population trends of the Oceania sub-population, from which they excluded the east Australian sub-stock E1 (IWC 2014 Annex H). See Figure 4 for a graphical summary of the assessment.

The graph shows that before 1949 there were about 14,000 Oceania humpbacks; under intense whaling pressure the sub-population declined gradually to 1960 when it suddenly collapsed. In 1966 there was probably only about 140 humpbacks coming into Oceania. It is little wonder people rarely saw any whales off Rarotonga during the 1970s, although dive operator Greg Wilson (pers.comm.) reports that they usually saw three or four whales each year during the 1970s.

As of 2014 the sub-population had recovered to about 5,200 which was about 37% of the number in the 1940s, and it will probably take them another 20 years to recover their pre-Soviet whaling numbers. The Oceania recovery has been slower than west Australia and east Australia, 90% and 63% respectively.

It is not clear when IUCN will re-assess the Oceania sub-population. However, if the IWC estimates are correct the sub-population should reach 50% of its 1940s number around 2020 and then be categorized as of Least Concern.

In a separate assessment by NOAA in 2015 (Bettridge et al.) it was concluded that the east Australia sub-population is not at risk of extinction with high certainty (>80% votes), while the Oceania sub-population (New Caledonia to French Polynesia) is not at risk of extinction with moderate certainty (68% votes).

Now that IWC is accepting that the east Australian E1 sub-stock does not belong in Oceania with sub-stocks E2 and E3 it is probably time to revise the naïve model notation system. Most data also shows that the Cook Islands F1 sub-stock belongs with Tonga E3 and not with sub-stock F2 in French Polynesia.

 Feeding in the cold

During the southern Summer humpbacks are near Antarctica in near freezing water (about 2°C) feeding on the shrimp-like Antarctic Krill. Krill are only 3-5cm body-length, but they form immense swarms outside the sea ice around Antarctica; they are estimated to be one of the most abundant animals on earth.  The humpbacks lunge through the swarms of krill with their mouths wide to take an immense volume of water into their greatly extended mouth-cavity. They then expel the water through their comb-like baleen plates to retain the krill to swallow.

A detailed study of humpback feeding in May near Antarctica showed that during the daylight hours (8am-3pm) they rested at the surface with occasional dives to 50m. The krill migrated to the surface around 4pm (dusk) and the humpbacks dived up to 10 dives-per-hour throughout the night. They usually dived from 50-150m, although some dived to about 300m and one was recorded at 370m. In the dawn twilight the krill started to sink and feed-diving stopped around 7am.(Nowacek et al. 2011, Friedlaender et al. 2013) During each dive the whales made brief accelerated lunges after which they closed their mouths and expelled the water to sieve the prey to swallow. During feeding dives of less than 50m they typically did 2-3 lunges, while during 100m dives they often performed 6-8 lunges. (Ware et al. 2011)

Dietz et al. (2002) found a similar pattern diving for whales feeding near Greenland. The deepest accurately recorded dive was 395m, and there was some indirect evidence that a few dived to near 500m.

Starving in paradise

The South Pacific humpbacks migrate from their feeding grounds near Antarctica to the warmer subtropical waters to give birth and nurse their calves, court and mate. Ratios of males to females of 1.5-to-1 in French Polynesia and of 2.4-to-1 in east Australia indicate that many females do not migrate every year (Branch 2011). It is thought they migrate every two or three years.

During migration and in the subtropics there is not enough krill or small fish to cover the high energy cost of lunge feeding – so they starve for 6-8 months and live entirely off the fats in their blubber. This is especially true in places like Tonga and the Cook Islands which are in one of the most plankton poor areas of the South Pacific. The exception, is some opportunistic feeding off New South Wales where krill or small fish sometimes congregate when nutrient levels are higher than usual (Silva et al. 2011).

In the winter breeding grounds humpbacks spend most of their time in the shallow near-shore environment where the seabed is less than 100mbsl (metres below sea level). Research on male humpbacks in Hawai‘i (Baird et al. 2000) showed they spent 80% of their time within 30m of the surface, 15% between 30-100mbsl and about 5% deeper than 100mbsl with a maximum depth of 180mbsl involving dive times of up to 25 minutes. Of the 13 tagged whales, seven spent time in water greater than 100m depth and seven dove to more than 100mbsl. The authors used descent and ascent rates and dive duration to estimate that the whales could theoretically dive to about 650mbsl, although no such dives were recorded.

In the Cook Islands, humpbacks spend most of their time cruising, shallow diving and breaching on the leeward side of islands. Females make various sounds but not songs, while males spend a considerable amount of time singing their long and complex songs. The songs are stereotyped within a population but evolve over time. New “songs have been documented radiating repeatedly across the region from east to west, from east Australia to French Polynesia, usually over a period of two years” (Garland et al. 2013). While singing for hours on end is the norm in the breeding grounds, they sing only sometimes during migration and infrequently in the feeding grounds. Despite the infrequency of singing around Antarctica, Garland et al. showed that in one case it was there that New Caledonian whales acquired a song from east Australia whales.

People have an auditory range from a low of about 20Hz to a high of around 20,000Hz, being most sensitive from 1,000-5,000Hz.  Humpback males sing in the range 20-3,000Hz, which is all within the range of human hearing. It has been estimated that they can hear calls as quiet as 60dB (in water) which is nearly equivalent to the quietest sound we can hear in air.

Their songs are loud at around 170dB (in water at 1m) which is four times “louder” than a 12m fishing boat moving at 7kt or a typical motorboat.  Over what distance can they hear the songs?

It is known that Blue Whales and Fin Whales can send low frequency calls over distances of several thousand kilometres in the Deep Sound Channels (700-1,500mbsl), but there is no evidence that humpbacks use this channel.

I have not managed to find scientific information on how far humpbacks can communicate and can only offer a loose theoretical value. Outside the Deep Sound Channel sounds decrease by 6dB for each doubling of distance. A call of 170dB (at 1m) would decrease to 60dB by 500km and be inaudible to a whale. In reality the background noise from ships and boats would reduce the effective distance of communication.

Threats

Humpback populations have been recovering since Soviet whaling ceased in 1973. The Oceania sub-population, from New Caledonia to French Polynesia, is one of the slowest to recover. The IWC assessment of 2014 put it at 37% recovered and predicted around 50% recovery by 2020. What could prevent the continued recovery?

The most obvious direct threat would be a resumption of commercial whaling and we should all support the countries and organisations that oppose commercial whaling regardless of the level of recovery. A more subtle threat could come from the establishment of a krill fishery around Antarctica. Although such a fishery has so far proven to be uneconomic, a large krill fishery could seriously impact whale health by making feeding more difficult.

Author’s notes
First published CI News Oct 2015 
Photo from Google
Contact Natural Heritage Trust for a full list of the Bibliography
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The spread of the “farmers friend” – the myna

The spread of the “farmers friend” – the myna

Gerald McCormack, CINHT

The myna is locally much loathed as a pest, yet it arrived in the early 1900s with such high hopes as the “farmer’s friend”. We follow its triumphant march from India to many countries, including the Cook Islands.

The “farmer’s friend”

A couple of common myna birds competing for the right to feed on the fruit of the pawpaw.

The Common Myna is indigenous to southern Asia, primarily India. It lives in open woodlands but is strongly associated with people in agricultural and urban areas. It is known as the “farmer’s friend” because it helps control insects.

It was probably the first animal introduced to another country as a biocontrol, when the French took some from southeast India to Mauritius and Réunion islands in 1763 to control locusts/grasshoppers in the sugarcane fields. The French colonists called them “Martin” after Captain Martin of the ship “Gracieuse” that had brought them. The locusts were soon much reduced and the Martin was given the credit.

A little later, in 1766 Linnaeus considered this bird to be a bird of paradise and named it Paradisea tristis, meaning the dull  bird of paradise. In 1816 Vieillot made the genus Acridotheres meaning grasshopper-hunter,and our myna became Acridotheres tristis; literally meaning the dull grasshopper-hunter. An obvious misnomer for a bird that is not dull in behaviour or appearance.

These birds and their relatives are Asian starlings and they are known in Hindi as Mainā, meaning “delightful”, referring to their varied calls and speech mimicry. Mainā is rendered into English as mynah or myna, while the French name is martin. Our particular myna is the Common Myna or Indian Myna, and it is identified in French as Martin triste.

Introductions continued

A hundred years later the myna became very popular and it was introduced in 1862 to Melbourne for no known reason, and thence to Queensland in 1883 to control Plague Locusts and insects in sugarcane. In the Pacific they were first introduced to Hawai‘i (1865 from India for insect control in sugarcane), then New Caledonia (1867 from Réunion for locusts and insects in sugarcane), New Zealand (1870 from Melbourne to enhance the fauna), Fiji (c.1890 or earlier for insects in sugarcane), and Tahiti (unknown date but pre-1904 for paper wasps and cattle ticks).

Cook Islands introductions

Visiting Rarotonga in 1904, Clement Wragge wrote that “Bird life was most meagre, and this was especially striking on our drive around the island” and therefore insect pests were abundant. He wrote that on other Pacific islands the “mina” had been introduced to control insects with happy results, but that here the Resident Commissioner feared “to try the experiment, lest the birds should destroy the fruit.” Wragge’s round-island guide told him that “If insect-eating birds are not soon introduced, the pests will ruin us.”

A Common Myna holding a Coconut Stick-insect having beaten off the legs.

Two years later, in March 1906, Sidney Davis, the manager of Cook Islands Trading Company, wrote to his trading partner in Tahiti, Mr. H. Meuel, to obtain some “Indian Minahs”. Mr Meuel replied that he knew of them as the Merle des Moluques (“thrush of the Moluccas”) and could obtain them at about 4 shillings a pair (about $30 today). He noted that they had been “imported to help in the destruction of wasps, but it was found in practice that they also fed with preference on native fruit, such as Bananas, they multiply pretty fast…..”.

The first colony of about 20 birds arrived in late June. They were released on the Davis farm in Tītīkāveka and were known as Manu Tēve, Davis’s Bird. On the 12th of  July Gudgeon showed Government support by protecting the “Minahs imported from Tahiti” which “are likely to benefit the island by keeping the insect pests in check.” Any conviction for shooting or injuring the birds carried a fine of £5 (about $700 today).

The Cook Islands Trading Company (CITC) imported more mynas in 1907 and 1909 and also around this time Jean Peyroux brought mynas from Tahiti to Matavera where they were known as Manu Piru – Peyroux’s bird.

At the time of these introductions there is no known mention of a particular insect to be controlled. It was not until January 1914 that the Fruit Inspector, Mr E.A. Reid, reported that the mynas were increasing rapidly and “were putting a severe check on the stick insect which attacks the leaves of the coconut palms.” And in 1933 biologist Whitley was told that mynas had been introduced to “cope with the large introduced wasps” [Paper-wasps, Rango Patia, Polistes spp.].

Coconut Stick-insect

The humongous female Coconut Stick insect munches a coconut leaflet while the puny male starves to perform his duty.

The Coconut Stick-insect (‘Ē, Graeffea crouanii) was an accidental introduction of the ancient Polynesians. In the 1800s the missionaries and other visitors reported that these insects were often in plague proportions and could rapidly destroy coconut plantations. People often made smoky fires in a usually futile attempt to control the insect.

In April 1915 Brian Morris, the Resident Agent of Ma‘uke wrote to the administration on Rarotonga requesting that mynas be sent because he feared that a plague of Coconut Stick-insects might destroy all their coconut palms. The Government arranged for mynas to be sent from Tahiti to Mangaia and Aitutaki in 1915 and to Ma‘uke and Ātiu in 1916.

Mr. Russell was the Resident Agent on Ātiu at that time and mynas were initially called Manu Rataro, Russell’s bird. In time the national name standardised to Manu Kavamani, Government Bird. The initial Mangaia colony failed and the Ministry of Agriculture successfully introduced mynas from Rarotonga in 1958 to help the depressed copra production.

 Number 1 alien invasive bird

The winners of a territorial dispute immobilise a challenger while its partner looks on in dismay. Such battles are highly ritualised and, despite their intensity, the combatants are rarely injured.

In 2000 the International Union for the Conservation of Nature (IUCN) declared the Common Myna the number 1 invasive alien bird in the world, and the third most invasive alien species behind the Australian Black Wattle and the Giant African Snail. In Australia in 2004 the Myna was voted the number 1 pest in a national-wide survey by the Australian Broadcasting Association, ahead of the ecologically devastating Cane Toad.

In the Cook Islands the myna is the most abundant bird on Rarotonga, Aitutaki, Ātiu, Ma‘uke and Mangaia – it was not introduced to Miti‘āro and it has not invaded from the neighbouring islands.

Although mynas are known to eat many insects they are widely disliked because they harass nesting native birds, attack fruits the day before people pick them, steal food from within houses, make a very loud noise at dusk in roosts, mob and embarrass cats in their own homes, and build untidy nests in holes in houses – and, their rowdiness and territorial aggression are embarrassing reminders of ourselves. Many people kill mynas on their properties and most people wish the myna had not been introduced or would now disappear.

The Ātiu eradication project

Atiu birdman George Mateariki retrieves a trapped myna at night.

In the last 25 years many communities around the world have started attacking mynas to reduce their numbers or eradicate them. In Canberra alone more than 30,000 mynas had been trapped by the end of 2010 and Fregate Island (220ha) in the Seychelles established a record by eradicating a thousand mynas in 2010.

In May 2009 the Natural Heritage Trust started a project with the Island Council to reduce their mynas and this became an eradication project in November 2010. The 3-pronged attack of poisoning, community trapping and shooting, and non-resident shooters has been very successful and we estimate there are now less than a thousand to go – the most difficult thousand!

If successful, this eradication will eclipse the record set on Fregate Island, because Ātiu had six times more mynas (about 6,000) and it is twelve times larger (2900ha). The eradication of mynas on Ātiu will allow us to evaluate the effect the myna has had on native birds, insects and the quality of life of residents.

 

Author’s notes

First published CINEWS (June 23, 2012). Original article with the history of the species name corrected (January 2024).

Posted by Gerald in Agriculture, Animals, Biocontrol Species, Biodiversity, Invasive Species, Uncategorised, 0 comments

Black Shouldered Lapwings – a rare vagrant

Gerald McCormack, CINHT

The 2023 Maureen Goodwin lapwings in Muri.

On the 30th of August, Maureen Goodwin saw two unusual birds on her inland Muri lawn. She Googled and identified them as Australian Southern Lapwings rather than the Northern due to the black ‘ei kakī (collar). Over the next few days, the birds fed, ran over the lawn, and flew around the area.  Unexpectedly, one died after eight days and the other after ten, apparently of natural causes. This was only the third time lapwings have been reported on Rarotonga in thirty years.

They are in the same bird family as the well-known Tōrea (Pacific Golden Plover), which breeds in Alaska and migrates yearly to spend the southern summer here and elsewhere in the South Pacific. Birds that visit yearly are known as migrants, while birds that arrive at erratic intervals are known as vagrants.

On Rarotonga, the first record of the Black-shouldered Lapwing was by the author on the grass at the western end of the Airport in 1993 on the 7th and 28th of October. It was nine years to the next record.

In 2002, on the 19th of October, Eddie Saul reported a similar lapwing on the field near Nikao Video, and Geoff Stoddart saw two birds in the same area on the 25th, of which he photographed one. On the 29th, the author saw one on the grass at the eastern end of the Airport.

There was a twenty-year gap to August 2023, when the Goodwin lapwings were reported. By any definition, the lapwing is a very rare vagrant on Rarotonga.

On Aitutaki, the first Black-shouldered Lapwing was reported with a photograph (eBird) in 2003 at the airport on the 28th of August by Eric VanderWerf, and presumably, the same bird was reported near the terminal on 12th October by Gary Turtle and Ruth Vomund.

The Ma‘uke lapwings in 2011 by Keiti Tuakana.

Ma‘uke is a special case because it has a resident pair of Black-shouldered Lapwings. The two birds were first reported in 2011 on the 25th of August when Keiti Tuakana photographed them at the harbour. Basilio Kaokao monitored the birds and two years later reported a fledgling on the 28th of June 2013. In September this year, he reported that the young bird was still alive, and the three live mainly on the grass around the inland Water Protection Zone (No‘o‘anga Atua) and regularly visit the airport area.

Native range expansion

In the 1800s, the Black-shouldered Lapwing was native to the Australian mainland from central Queensland south to Victoria and eastern South Australia. It is widely considered a subspecies (Vanellus miles novaehollandiae), with its plain-necked sibling, the Northern Masked Lapwing (Vanellus miles miles), native to Northern Queensland, Northern Territory and New Guinea.

In a contrary opinion, Birdlife International treats the two forms as separate species. However, regardless of whether it is a subspecies or a species, we focus on the form with the black collar and use BirdLife’s descriptive name, the Black-shouldered Lapwing.

In 1888, the Black-shouldered Lapwing spread south of mainland Australia to establish itself in Tasmania.

In New Zealand, more than 1700km from Australia, the first lapwings were recorded in 1886 near Wanganui and 1892 near Hokitika. There were no more reports for thirty years!

In 1932, a pair bred at Invercargill Airport; by 1950, there were over a hundred in the immediate area. By 1970, they were very common up to 100km from the airport, with isolated groups throughout the island. In 1973, they were reported in the southern part of the North Island, and by 1990, they were everywhere, including the Far North.

In 1981, they flew 700km east from one of the main islands to breed on the Chathams. And by 1993, they had flown 1,000km north of North Island to breed on Raoul Island in the Kermadecs.

In New Zealand, they are known as Spur-winged Plovers, and although they are recent settlers, they are classified as native birds because they introduced themselves without human assistance. They are protected along with all Aotearoa native birds, although many consider them invasive.

The rapid spread of the Spur-winged Plover in New Zealand is particularly interesting regarding the genetic viability of small founding populations.  When 30 Kākerōri (Rarotonga Flycatcher) were moved from Rarotonga to Ātiu in 2001-2003, and 27 Kura (Rimatara Lorikeet) were moved from Rimatara to Ātiu in 2007, there were concerns that such small founding numbers would lack the genetic variability to enable them to flourish in the future.  The spread of the lapwing throughout New Zealand from a founding pair seems to mock such concerns, despite the expectation that a few more genetic packages probably arrived from Australia during the expansion.

Pacific islands exploration

New Caledonia is about 1,300km east of Australia, and the first Black-shouldered Lapwings were reported in 1994, and they were breeding there by 1998.

Fiji is about 1,200km east of New Caledonia, and the first lapwings were reported on Viti Levu near Suva in February 1997 and July 1999 – one Black-shouldered and one unknown. While it is reasonable to think these birds came from New Caledonia or Australia, we cannot rule out the North Island or the Kermadecs.

The Rarotonga 1993 Black-shouldered Lapwing arrived before any were recorded in New Caledonia or Fiji, which makes its origin in the Kermadecs or North Island reasonably likely. This source for the Cook Islands is further reinforced by the Aitutaki 2003 and Ma’uke 2011 birds, which arrived before any had been reported in Tonga or the “Samoas”. However, the few reported sightings could be misleading because, without a doubt, most lapwings landing on tropical islands would not have been reported, so we will never know their early distribution in our region.

In more recent years, reporting has increased. Although no breeding reports exist in Fiji, it has had new sightings of vagrants. In March 2018, there were four Black-shouldered Lapwings near Suva (eBird), and on Kadavu Island, two indeterminate birds were recorded in April 2016 (eBird) and a Black-shouldered in March 2023 (iNat).

Single birds were reported in American Samoa in December 2018 (eBird) and in Tonga in February 2023 (iNat). Both were Black-shouldered.

Map of known records of Black-shoudered Lapwings. Arrows starting with a question mark show the general location of origin, The Fiji and Rarotogan origins are speculative.

Trans-oceanic flights

Lapwings are strictly land-birds and cannot land or feed in the ocean. General information indicates they can sustain a flight speed of about 65km/h. This means that the 1,700km trans-oceanic flight from Australia to New Zealand would have taken about 26 hours, with a tailwind, much less.

For our Cook Islands vagrant lapwings, the 3,000km flight from North Island would have taken about 46 hours or two days, and we know our migratory Karavia (Long-tailed Cuckoo) does this non-stop flight every year. On the other hand, if our lapwings came non-stop 4,500km from Australia, it would take them about 70 hours or three days. Even this is not unreasonable because their relative, the Tōrea (Pacific Golden Plover), does a 5-7day non-stop flight from Alaska to islands around Rarotonga each year. The main difference in both cases is that the migrant adult birds know where they are going, while vagrant lapwings are just cruising over the ocean on the off-chance of finding land.

I wonder where the two Goodwin lapwings started their trans-oceanic flights?

Author’s notes
First published CINEWS (October 7, 2023), Minor update (January 2024)
Posted by Gerald in Uncategorised, 0 comments
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