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Marine Heatwaves

According to the National Institute of Water and Atmospheric Research (NIWA), New Zealand’s coastal waters are set to experience longer and more severe marine heat waves. Our coastal waters have seen the most extended marine heatwave ever recorded in New Zealand. The past seven years have been the hottest in recorded history, with ocean temperatures hitting record highs for consecutive years, compounded by back-to-back La Niña events. This has resulted in New Zealand contending with ongoing marine heatwaves, with the ocean being plagued by warming waters. New research indicates that marine heatwaves (periods of five days or more of increased ocean temperatures above the 90th percentile) are expected to increase in intensity by 20% in the best-case scenario and 100% in the worst-case scenario. New Zealand experienced one of its most intense marine heatwaves in 2017, with the ocean being 7C warmer than average. These climatic effects on the marine environment result in increased sea surface temperatures, affecting marine life and impacting survival. The country experienced its most intense marine heatwave in 2021 and research indicates that this will start to become the norm, with severe consequences for marine wildlife. NIWA states that the odds of marine heatwaves becoming a permanent fixture is alarming, given the significant impacts they have both at sea and on land. Looking to the future, average sea temperatures could increase by 1.4 degrees by 2060 and by almost three degrees by the end of the century. This has wide implications for marine life and means that by mid-century we may be facing 260 days of marine heatwaves per year, increasing to 350 days by 2100. Seabird Survival Seabirds are the most threatened group of vertebrates in the world and are declining faster than any other group of birds, with 90% of seabirds in New Zealand threatened with extinction. Seabirds are barometers of ocean health and plummeting populations are a red flag. Seabirds face an abundance of threats including overfishing, by-catch, plastic pollution, predation by introduced mammals, and more recently - climate change. Climate change is now considered a primary threat to seabird survival, with the impacts of marine heat waves worsening every year. This is not a natural phenomenon and is a direct result of human-induced global warming.

Warming sea surface temperatures suppress prey by driving krill and shoaling fish to cooler depths, out of reach of surface feeding and diving seabirds. As a result, many seabird species are unable to forage effectively, increasing foraging effort and reducing foraging success. This leads to poor body condition and increased parasite loadings, driving mortality rates. The effects of this are particularly pronounced during the breeding season when adults must also forage for their chicks; while inexperienced fledglings struggle to forage in challenging conditions. Marine heatwaves not only impact the survival of individual birds but also reduce overall breeding potential. As many seabirds are long-lived we are seeing ageing populations with low juvenile recruitment. This means few chicks survive to adulthood and there are not enough young birds in the population to replace ageing individuals. With long-lived species such as albatrosses, which have lifespans of over 70 years, declines are not always immediately apparent until populations suddenly crash. An alarming number of inshore and pelagic seabirds are affected by marine heatwaves, with many found beach cast in poor body condition. Starvation results in emaciation, lethargy, anaemia, dehydration, hyperglycaemia, hypothermia, and high parasite burdens; leading to progressive organ failure and ultimately death. This is unprecedented as it is occurring year after year and cannot be simply attributed to certain periodic conditions. Across bird rescue centres and wildlife hospitals, there has been an increase in seabird patient numbers. For example, last season five times the number of penguins were in care nationally due to starvation, parasites and disease. Kaikōura Seabirds Kaikōura is a biodiversity hotspot, marine mecca and one of New Zealand’s seabird capitals. In Kaikōura starvation is the primary reason that seabirds are found unwell or deceased, with many requiring rescue and rehabilitation. Seabird die-offs due to marine heatwave-related starvation were first notable in Kaikōura in 2016, and have continued to become a growing threat every year. Initially, the impacts of this were worst during the summer period (peak temperature), which concerningly coincides with the breeding season. In subsequent years seabird die-offs began in early spring, continuing into late summer. 2021 was the first year in which Kaikōura seabirds were suffering from starvation in all seasons - including winter, the coolest time of year. Die-offs of threatened red-billed gulls have become apparent; while emaciated shags, penguins, shearwaters, prions, petrels, albatrosses and gannets (particularly juveniles) are frequently found. Marine heatwaves are also resulting in the displacement of marine life, with migrations south to cooler waters. Displacement is generally not an option for seabirds, which have site fidelity to natal colonies(highly philopatric) and are generally restricted to forage within the same range during the breeding season (i.e. are unable to avoid the impacts of reduced prey availability). Research has shown that seabird species are having to travel further during the breeding season, resulting in adults in poor body condition which cannot source enough food for their chicks. At managed seabird colonies (e.g. endangered Hutton’s shearwater/Kaikōura tītī) chicks are underweight, with delayed development and increased mortality rates. More recently this has resulted in human intervention via supplementary feeding at the artificial insurance colony to ensure fledging. With delayed fledging timeframes later in the season many young shearwaters in poor body condition that are still partially downy, are forced to take flight due to starvation, before being ready to fledge from the mountain breeding colonies. For an endangered species which is already faced with many compounding threats (predation by introduced mammals, uprooting of burrows by feral pigs, post-earthquake induced landslides at breeding colonies, light disorientation and crash landing), climate change could be the final nail in the coffin.

Threatened Red-Billed Gulls Red-billed gulls/tarāpunga are often wrongly perceived as overly abundant or a nuisance by the general public. What most people do not realise is that populations are plummeting, and this gull is now classified as a threatened species. Red-billed gull numbers have fallen so rapidly that the species is now listed as Nationally Vulnerable. Numbers have dropped sharply at the three main breeding colonies (Kaikōura, Three Kings and Mokohinau Islands), and are expected to plummet by 50-70% over the next three decades. Experts state the threatened red-billed gull is severely at risk with just 27,800 breeding pairs remaining nationwide, and the main offshore breeding colonies suffering population declines of 80-100%. Generally, populations on predator-free offshore islands fare better than those on the mainland, due to a lack of mammalian predation on breeding pairs, chicks and eggs. The fact that offshore island populations have plummeted regardless, highlights that it is the swiftly changing marine ecosystem that is primarily driving declines. Climatic impacts and depletion of the marine environment are apparent, with limited access to natural food sources resulting in decreased prey upwellings at the sea surface. Climate-induced fluctuation in the availability of krill, the principal food of red-billed gulls, has a major impact on breeding success and survival. Gulls are non-diving seabirds which can only feed on readily available prey at the sea surface and have no means to access krill if there are no naturally occurring upwellings or workups. As red-billed gulls are a long-lived species, decades passed before significant population declines were evident. Few fledglings survive, while even fewer juveniles survive to adulthood and become part of the breeding population. With low juvenile recruitment

and future reproductive potential, there are not enough young birds to replace ageing adult birds. This results in an ageing population of relatively long-lived birds (30-year lifespan) which die without succession, resulting in a sudden and inevitable population crash. This is how local colonies become extinct within a relatively short time span and how a species diminishes in distribution nationwide until it is at the point of being critically endangered.

At present, the Kaikōura Peninsula supports the largest remaining, and fastest declining, red-billed gull colony on the New Zealand mainland. The colony is a rarity in that it has been studied for over 60 years and benefits from ongoing predator control, which has ensured the survival of breeding birds. Without predator control (in particular cats), this colony would vanish within two years. Despite this management, significant numbers of gulls die every year of starvation. Loss of body condition from emaciation leads to high parasite loadings (ectoparasites such as ticks, endoparasites such as gape and tapeworm), resulting in severely compromised birds which are then susceptible to Aspergillosis. Progressive organ failure from starvation, and respiratory distress from Aspergillosis, lead to prolonged suffering and eventual death. Starving birds are also less likely to evade other human-related threats, leading to a notable increase in injuries and deaths. For example, an increased occurrence in vehicle strike incidences as starving gulls will desperately scavenge for food scraps in urban areas and not evade oncoming traffic; and an increase in dog attacks in coastal areas as weakened gulls will not evade approach.

Starving gulls are becoming more apparent in urban environs, regarding an increased reliance on humans (e.g. roosting at eateries). To some, this increased visibility equates to an increase in gull numbers (with misinformed calls in the media for ‘culling’), when the opposite is true. The species continues to decline rapidly and we are merely witnessing adaptive behaviour and a shift to unnatural habitats. Some resourceful adult birds may persist with limited scavenging success - but with fewer krill upwellings and low juvenile recruitment becoming the status quo, population declines will hasten.

With the current rate of decline red-billed gulls are at risk of extinction. Increased management is needed, with wildlife hospitals being a critical conservation tool to offset declines. Rehabilitation gives individual birds a second chance at life and enables future breeding potential. Advocacy and outreach is vital, ensuring the public understands and respect these birds, which are often wrongly perceived as ‘pests’ and victims of wildlife crimes.

This article was written by

Sabrina Luecht

Kaikōura WildlifeHospital & Conservation Centre Project


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