Voluntary Speed restriction in Tīkapa Moana; saving endangered Bryde’s Whales

Marine Science & Cetacean Ecology | Danielle Lucas

Sixteen Bryde's whales are alive today that would have otherwise succumbed to vessel strike in Tīkapa Moana had the Hauraki Gulf Transit Protocol not been introduced in September 2014. Many individuals are stunned to learn that we have some incredible marine species including Cetaceans such as Brydes whales (Balaenoptera brydei) and common dolphins (Delphinus delphis) in our very own backyard, Tīkapa Moana (Hauraki Gulf), Tāmaki Makaurau.

Bryde's whale in the Hauraki Gulf. Photo by the author.

Currently Bryde’s whales, pronounced 'broo-des’ are endangered, classified as Nationally Critical with only an estimated 135 left in the Tīkapa Moana population. Bryde’s whales are a year-round resident in the gulf as part of only a handful of global whale populations not to partake in migrations.

Unfortunately, it was discovered that ship-strike by vessels ≥70 m were killing on average 2.4 whales per annum in Tīkapa Moana, and between 1996 and 2014, 44 Bryde’s whales died in the Hauraki Gulf [1]. “85% of whale deaths in the gulf were definitely or most likely the result of injuries sustained during a collision” [1]. In a small, isolated population of only 135 individuals, this rate of mortality is unsustainable and would likely contribute to a collapse of the population if protocols were not put in place to interfere. Lethal ship strike is a relatively new example of humanwildlife conflict and is especially threatening to large cetaceans. Bryde’s whales typically spend more than 80% of their time in the top 10 metres of the ocean [1]. This makes them incredibly susceptible to strikes as the average draft (height of the part of the ship which is underwater) of a vessel is about 8.4m. A vessel sailing at 15 knots (around 28 kmh-1) has an approximately 80% chance of killing a whale when they collide, whereas at 8.6kt (~16kph-1) this was reduced to 20% [4]. When a vessel is travelling at a speed above 10kt (~18.5kph-1), the potential risk of ship strike is measurably increased.

The Hauraki Gulf embayment has an area of around 4000km². It is the gateway into Aotearoa’s largest port, Ports of Auckland, and there are three major shipping channels: Colville channel, Jellicoe channel, and Craddock channel, whereby vessels will enter the gulf en route to the port (Fig. 1) [2].

In September 2013, Ports of Auckland introduced the Hauraki Gulf Transit Protocol for commercial shipping. This is a voluntary protocol in which vessels slow down to 10kt as they travel throughout the gulf. Mandatory measures require the lengthy formation of laws and regulations and enforcement, which takes time, money and resources [2]. In an interview with Dr Rochelle Constantine, a researcher at the Institute of Marine Science, University of Auckland, and a crucial member of the research team whose work contributed to the implementation of this protocol, Dr Constantine states that in regard to this voluntary speed reduction, “I’m really proud that every day the ships and their crew go slow. Even though many of them have no idea why, it’s just the new normal.”

Figure 1: Map and location of the study site, the Hauraki Gulf. The Ports of Auckland is located within Auckland city, shown by the black dot. Dotted lines indicate where the voluntary Transit Prorocal comes into effect.

Bryde’s whale population distribution in Tīkapa Moana was mapped from October 2014 to September 2016. The shipping traffic was also monitored in the gulf from October 2014 to September 2016, using Automatic Identification System (AIS) shipping data which provides information about a vessel according to a unique Maritime Mobile Service Identity (MMSI) number (Fig. 2).

The median speed of ≥70 m long vessels transiting through Tīkapa Moana was 10 kt in 2014–2015 (range = 1–27 kt; IQ = 9–12.4 kt), and 10.2 kt in 2015–2016 (range = 1–26.9 kt; IQ = 9–11.7 kt); these speeds represent a 25% decrease from the 13.2 kt reported from July 2012 – June 2013 prior to the implementation of the Transit Protocol [1] (Fig 3).

At lower travel speeds through the gulf, the risk of death via direct strike or hydrodynamic forces that pull the whale toward the ship are considerably reduced [3]. The voluntary Hauraki Gulf Transit Protocol recommendation to reduce speeds to ~10 kts directly resulted in a ~25% decrease in ship speeds, thereby nearly halving the threat of lethal ship strike to Bryde’s whales within two years of implementation [1]. Since the Protocol was introduced in 2013, there has not been a single report of a Bryde’s whale death in Tīkapa Moana caused by ship-strike. No vessel has reported on any collisions resulting in injury either. “As long as they continue to go around that 10kts, the risk to the whales of vessel strike mortality is very low,” says Dr Rochelle Constantine.

Figure 2: a) Density of ship transits per 100m2 grid cell with a search radius of 100 m. b) Sighting per unit effort (SPUE) of Bryde's whales in the Hauraki Gulf, October 2014 - September 2016. The values represent the chances of seeing a whale within a 1,500 m radius.

Figure 3: Median speeds of vessels 70 m in length transiting through the Hauraki Gulf in a) July 2012 - June 2013 (from Riekkola, 2013), October 2014 - September 2015, and c) October 2015 - September 2016, calculated within 250 x 250 grid cell.

Effective environmental management is imperative to decreasing the threats to biodiversity [3]. When asked how it feels to know you’ve made a positive impact on the population of Bryde’s whales in Tīkapa Moana Dr Rochelle Constantine responded: “It was really a collective that found this solution, the thing I think was most important, for me as a scientist, is that it was science informed. Conservation solutions are never about one person, and we made a real conscious decision in the beginning to have an inclusive process, bringing lots of people together who saw this issue through different eyes, industry, legal, scientists, government and Mana Whenua. I’m proud of us, and it was a really good example of how to get conservation wins.”

Dr Constantine mentioned that there will be an abundance estimate of the whale population done next year, a decade since the Hauraki Gulf Transit Protocol implementation. “There are at least 16 whales alive now that would have been dead, had ships continued with their previous speeds. We are anticipating that the abundance estimate will go up.” The Hauraki Gulf Transit Protocol is a great example of how a small social change can garner incredible results. The next population estimate for Bryde’s whales in Tīkapa Moana will be an imperative statistic that showcases the capacity for effective environmental management by users of the gulf. An increase in the Bryde’s whale population will be an absolute win for conservation efforts. There is no end date on the reduced-speed protocol, and it is now the new normal when entering the gulf. This effort has made a lasting impact on the health of Bryde’s whale populations in Tīkapa Moana.

[1] Constantine, R., Johnson, M., Riekkola, L., Jervis, S., KozmianLedward, L., Dennis, T., Torres, L.G., Aguilar de Soto, N., 2015. Mitigation of vessel-strike mortality of endangered Bryde’s whales in the Hauraki Gulf, New Zealand. Biol. Conserv. 186, 149–157. https://doi.org/10.1016/j.biocon.2015.03.008.

[2] Ebdon, P., Riekkola, L., & Constantine, R. (2020). Testing the efficacy of ship strike mitigation for whales in the Hauraki Gulf, New Zealand. Ocean & Coastal Management, 184, 105034.

[3] Silber, G.K., Adams, J.D., Bettridge, S., 2012. Vessel operator response to a voluntary measure for reducing collisions with whales. Endanger. Species Res. 17 (3), 245–254. https://doi. org/10.3354/esr00434.

[4] Vanderlaan, A.S., Taggart, C.T., 2007. Vessel collisions with whales: the probability of lethal injury based on vessel speed. Mar. Mamm. Sci. 23 (1), 144–156. https://doi. org/10.1111/ j.1748-7692.2006.00098.x.

Figure retrieved from: • Ebdon, P., Riekkola, L., & Constantine, R. (2020). Testing the efficacy of ship strike mitigation for whales in the Hauraki Gulf, New Zealand. Ocean & Coastal Management, 184, 105034

Danielle Lucas - Bsc, Marine Science, Biological Sciences

Danielle is a second-year student majoring in Marine Science and Biological Science. She is incredibly interested in cetacean and crustacean ecology and conservation. She plans to do a Masters in Marine Science after undergrad. She is a passionate kaitiaki and prioritises Mātauranga Māori in all areas of study and life.