Author Name: Daisy Harrison, BSc (Hons) Animal Behaviour and Welfare
Two centuries of intensive whaling have reduced whale populations worldwide by up to 99%. While most whales are granted protection as endangered species, there are still human activities regularly carried out that negatively affect the recovery of whales. Whale watching has grown in popularity since the fall in commercial whaling. The presence of humans in the natural habitat of species such as the Humpback Whale can evoke unnatural behaviours that interfere with the mating and breeding habits of these animals. This can hinder population regrowth. The connection between the two practices is discussed in this review.
Data on whale numbers are often taken from the records of whaling boats in order to compare whale population numbers pre, during and post whaling. However the accuracy of these records could be increased by acknowledging instances of hit and miss. Through this, the low numbers of Northern Bottlenose and Right Whales could be better understood and the impact of whaling could be discussed and analysed with increased accuracy.
The loss of such vast numbers of whales has impacted the ecosystems they once occupied in abundance. This is partially by way of knock on effect as their role as a top down predator has led to the ‘Krill surplus hypothesis’, resulting in a rise in Krill and Mink Whale populations. Their absence has also led to a decrease in nitrogen distribution to areas of lower productivity and a decrease in carbon levels in the ocean. Whales also benefit the ocean with their carcasses which provide habitats for deep-sea animals and encourage both biodiversity and adaptive radiation. The impact of their reduced numbers and the quality of the literature within this research area is discussed in this review.
The commercial whaling of the nineteenth century and illegal whaling carried out by the Soviet Union in the twentieth century resulted in dramatic declines in whale numbers from which populations are still struggling to recover (Jackson et al., 2008). These declines have made the monitoring and recovery of whales a priority in wildlife conservation attempts (McCauley et al., 2012). For whales such as the Humpback, rates of recovery are so low that they are not currently measurable (Schaffar et al., 2013). Data are therefore often calculated from whaling records (Torres et al., 2013). Catch data are used to estimate historical abundance in contrast to present day numbers (Jackson et al., 2008; Torres et al., 2013). In addition, exploring the impact that the decline of these marine mammals has had on the environments they once inhabited in abundance has been of great interest to marine biologists (Kuo, Chen and McAleer, 2011; Schaffar et al., 2013). A consequence of this loss to the oceans is a substantial reduction of mtDNA haplotype richness (Jackson et al., 2008) which enables chemical energy to be absorbed as a substance of nutrition. Other contributions derived from whales include whale fall carcasses (Smith et al., 2015). These provide nourishing and ideal habitats for small ocean floor life (Butman, Carlton and Palumbi, 1995; Roman et al., 2014). This wide scale removal of whale populations is evident throughout the species affected and the many ecosystems they supported. By understanding the impact of whaling better, rehabilitation and rebuilding of reduced species may be encouraged.
2.0 To What Extent are Whales and Their Surrounding Environments affected by Whaling?
2.1 The Effect of Whaling on Whale Populations
Post intensive whaling, some populations are estimated to have been reduced by 99% (Clapham, 2016). After sustainable whaling was derailed for profit, large-scale illegal whaling was carried out by the Soviet Union (Jackson et al., 2008; Clapham, 2016). Data on whaling numbers has been drawn in most cases from catch records in order to assess numbers of Whales pre, during and post whaling (Jackson et al., 2008; Torres et al., 2013). It should be noted however that not all data can be assumed to be accurate given the high abundance of whales in the past and the use of the medium to give approximate figures (Jackson et al., 2008; Torres et al., 2013). Sperm Whales have been a protected species for approximately 25 years but to date there is no clear evidence for their recovery in any exploited area of their habitat (Carroll et al., 2014). The data presented for this particular study were collected over only three months and therefore may not show the full extent of population trends if the behaviour and migration patterns of the whales vary throughout the year.
In some areas, particularly Scandinavian regions, The Humpback Whale does not currently have an increased population trend due to low numbers and slow paced recovery (Schaffar et al., 2013). Those whales that currently reside in the South Pacific Ocean are threatened by the highly popular and economically valuable activity of whale watching (Schaffar et al., 2013; Bertulli et al., 2016). Whale watching has long been engrained into the tourism culture of many Scandinavian countries and offers those visiting the chance to experience whales in their natural environments and at a much closer proximity than they may be viewed on land. This is an appealing and popular activity for many tourists. The decline of whaling may also have made countries previously known for whaling more attractive to tourists (Kuo, Chen and McAleer, 2011; Schaffar et al., 2013; Bertulli et al., 2016). It is hypothesised that whaling and whale watching cannot coexist and that tourists may have boycotted countries who participated in whaling on moral grounds or else been unable to enjoy the activity in those areas due to practical issues and the conflict of whaling and whale watching boats (Kuo, Chen and McAleer, 2011).
When approached by the whale watching boats, Humpback Whales were found to significantly change their behaviour and path predictability (Kuo, Chen and McAleer, 2011; Schaffar et al., 2013). This is thought to be an avoidance strategy upon being approached by the whale watchers and also a method of energy preservation (Schaffar et al., 2013). It is unknown to what extent whaling and whale watching have influenced one another but this regular and stressful interruption to their normal behavioural patterns may have a negative effect on the growth and survival of the already vulnerable Humpback Whale. Their risk of extinction puts them in a position where they cannot afford further human interference during their attempts to recover. However it should be noted that this same study (Kuo, Chen and McAleer, 2011) presenting a correlation between the decline of whaling and the rise of whale watching also indicated that 31% of the tourists who participated in the study were unaware of the country’s history of whaling (Kuo, Chen and McAleer, 2011). These tourists may have supported the country’s whale watching industry regardless of on-going whaling if they were ignorant to the activities. It is also unclear if the remaining 69% of tourists who participated in the study who were aware of the history of whaling in the country would have refused to visit and ceased to contribute to the tourist economy if whaling were on-going. This calls into question how far whaling has really influenced whale watching and the strength of the correlation between the two in regards to the Humpback Whale population growth.
Along the east coast of Brazil, Humpback Whales are beginning to re-occupy areas which have been identified as conservation priorities as they include important breeding areas that were previously overtaken by human activity (Martins et al., 2013). This study exclusively documents this trend along the Brazilian Coast, which is limiting to understanding how widespread are these changes. In recent years the Humpback Whale has experienced conservation success in Australia, bringing its population number in that region to 50% of what it was pre whaling and an estimated 80,000 worldwide (Bejder et al., 2016). The world wide population trends of the Humpback Whale currently show no signs of diminishing despite a slow recovery and several scientists have suggested it ought to be down-listed on the official endangered species list (Bejder et al., 2016). This report does not fully disclose the methods of data collection, citing only the Australian monitoring of the whales (Bejder et al., 2016). Full discussion of the methods would improve the validity of this study.
Prior to intensive whaling, approximately 1000,000 Northern Bottlenose Whales existed worldwide but by 1920 this number had been heavily reduced (Whitehead and Hooker, 2012). Similarly, Right Whales around New Zealand and Australia also struggle to recover after having been the focus of world wide whaling from the 1500’s to the 1900’s (Carroll et al., 2014). Data gathered from log books show an increase on previous kill estimates as this records incidences of struck and loss rates where the whale was supposedly killed but not successfully retrieved by the Whaling boat (Carroll et al., 2014). The commercial extinction of Southern Right Whales appears to have occurred between 1830 and 1849, indicating an intensive period of whaling in the New Zealand and East Australian areas (Carroll et al., 2014).
2.2 The Environmental Effects of Whaling
Marine mammals are credited with enhancing primary production within ecosystems due to the great abundance in which they occur (Estes, 2009; Roman and McCarthy, 2010). One effect of intensive whaling on ecosystems is thought to be an excess of Krill, often called the ‘Krill surplus hypothesis’ (Surma, Pakhomov and Pitcher, 2014). This puts forward the plausible but unproven theory that intensive whaling has led to an abundance of other smaller ocean life due to a competitive release for smaller Krill eating species caused by the reduction of the top down predator (Ruegg et al., 2010; Wiedenmann et al., 2011). While samples are often drawn from a limited geographic area, they have been estimated to reflect genetic diversity through the ocean due to the variety of samples from the Japanese meat market where the data were gathered (Ruegg et al., 2010). However there is no evidence put forward from this study that the markets from which the samples were collected were particularly diverse or that the meat they sold reflected various areas of ocean diversity equally in order to provide data that can be applied globally. The study may be improved by collecting samples from various locations worldwide or by providing detail and evidence that the samples from the market are as diverse as suggested.
As the structure of the ocean continues to change with the increase of whale populations, similarly as it did in response to their decline, an effect on PH Biomass has been observed as Humpback and Fin whales slowly grow in numbers. This is thought to be due to the top down effects of increased predation by the recovering whale populations (Heithaus et al., 2008; Surma and Pitcher, 2015).
The alterations of deep sea biodiversity brought on by whaling is thought to have diminished a prime source of organic matter for chemosynthetic based communities that are associated with hydrothermal vents and other organic sources of input (Butman, Carlton and Palumbi, 1995; Gibson and Atkinson, 2003). Marine mammals enhance primary productivity in their feeding areas by distributing recycled nitrogen near the surface through the release of flocculent faecal plumes to facilitate the transference of nutrition (Roman and McCarthy, 2010; Roman et al., 2014). The physical changes to the ocean that occurred during the period of intensive whaling could have brought about a decline in biodiversity contributing to a decline of southern ocean productivity (Surma, Pakhomov and Pitcher, 2014).
Despite being only a small portion of the ocean’s biomass, the loss of whale abundance has impacted the ocean’s ability to store and sequester carbon (Pershing et al., 2010). Carbon management is often considered an environmental responsibility to maintain for the sake of biodiversity. Whale conservation to rebuild their numbers would provide a similar attempt to restore and manage carbon in the ocean (Pershing et al., 2010). Even in reduced numbers, whales sustain productivity in the regions they occur. Their reduced numbers and possible extinction would have an extreme effect on other marine life in these locations (Roman and McCarthy, 2010).
Research has only developed sufficiently to allow the relationship between whales and ocean carbon levels to be explored in approximately the last few decades as seen by the publication dates of the papers surrounding the topic. This discussion is therefore relatively recent and the full extent of the connection may not be apparent yet. These findings gain validity by the fact that they are extensively tested and recently published with such sponsors as the Marine Mammal Commission of the Fulbright scholar program (Pershing et al., 2010). The results and conclusions they have suggested are most likely of the highest quality currently available. It is important for the sake of validity to note that recent scientific research is often subject to change as new findings and methods come to light though.
Whale carcasses produce an organic and sulphide rich habitat on the sea floor due to their high bone lipid content that allows them to support heterotrophic and chemosynthetic microbial assemblages in the low energy environment of the deep sea (Smith et al., 2015). The communities the carcasses support contain many new species, allowing for adaptive radiation and high trophic diversity (Baco and Smith, 2003; Smith et al., 2015). This study presented evidence supported elsewhere (Smith, 2015) but is limited by its sample sizes. Only 1-7 bones of the 356 bones whales can possess were used and the samples were collected from just three whale carcasses, which may not accurately represent the average whale. The paper also acknowledged that fauna may have fallen from the bones during the initial collection, thus hindering how far the samples reflect those found in the ocean (Baco and Smith, 2003). Larger scale research that protects the samples from damage would strengthen and improve knowledge of whale carcass biodiversity.
Two studies have specifically recorded nematode communities in the remains of an implanted whale carcass (Debenham et al., 2004; Pavlyuk, Trebukhova and Tarasov, 2009). The organic enrichment of the carcasses saw an increase in nematode density, demonstrating the abilities of whale falls to facilitate increased life on the ocean floor (Debenham et al., 2004; Pavlyuk, Trebukhova and Tarasov, 2009). It has been speculated that low numbers of nematodes in recent years can be attributed to the reduced whale numbers (Pavlyuk, Trebukhova and Tarasov, 2009). Data between the studies conflict slightly as one study (Pavlyuk, Trebukhova and Tarasov, 2009) showed nematode density in the context of mink whales, which have been in abundance as a result of whaling (Ruegg et al., 2010; Wiedenmann et al., 2011). While neither of the papers suggest that the results would be different with another whale not in abundance since whaling, the impact of those carcasses removed from the ocean due to whaling ought to be further considered.
Current conditions for the regrowth of whales are often not ideal despite most whale species occupying a place on the endangered species list. Whale watching may have increased in popularity since the decline of whaling but this human interference can cause abnormal behaviour which can conflict with breeding and mating behaviours. However in some areas along the Brazilian and Australian coast, Humpback whale populations thrive to almost 50% of what they were pre-whaling. This has brought about hope for future whale recovery and suggestions that Humpback whales ought to be down-listed as an endangered species.
The decline of whales has also seen a shift in ecosystem structure due to their effect on the PH Biomass. The consequences of this are a surplus of Krill and the Mink Whale. Deep-sea biodiversity has also reduced as a result of whaling due to the whale’s ability to distribute nitrogen and enhance productivity. The reduced role of whales as facilitators of primary productivity has impacted and reduced the ocean’s ability to store carbon. Whale carcasses are another loss to ocean life as they provide ideal resources for a multitude of species and the decline of carcasses due to whaling has resulted in a loss of deep-sea trophic diversity, biodiversity and adaptive radiation. Overall the removal of so many whales from the ecosystems they once inhabited in abundance has resulted in reduced deep-sea biodiversity and a less enriched ocean.
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