The contribution of Cox et al. Other studies suggest a decline in krill within the SW Atlantic sector and/or shifts in distributional range or mean size 37,38,[73][74][75][76] [77] [78] . Ironically, the journal article below from a 1991 study claimed that the chinstrap penguin population increased during the 1900s *because* of global warming. Some 300,000 tons are harvested annually. “You could potentially have some significant decline in the number of predators – particularly for penguins – caused by climate change,” said Watters. Tarling, G.A., Klevjer, T., Fielding, S., Watkins, J., Atkinson, A., Murphy, E., Korb, R., Whitehouse, M. & Leaper, R. Watters, G.M., Hill, S.L., Hinke, J.T., Matthews, J. This will be more useful to policy makers and other stakeholders than polarised opinions. Last month, Greenpeace launched a campaign in support of the sanctuary. There have been spatial shifts in sampling effort over time, including a contraction of effort into three main study areas where krill are most abundant (Atkinson et al., 2004, 2008, 2017). (2018) will reduce the slope of any decline (issue F in our Fig. Firstly, the precision of GAMs declines towards the extreme values of the independent variable (i.e. The caption to their Figure 1 suggests that linear regressions were fitted to transect means. Simeon L Hill, Angus Atkinson, Evgeny A Pakhomov, Volker Siegel, Evidence for a decline in the population density of Antarctic krill Euphausia superba  still stands. This is because their main food source – krill – has declined by up to 80 percent. Find out why these tiny animals have enormous importance in the ocean's food chain. Atkinson et al. We intend KRILLBASE to be a useful resource for investigating Southern Ocean ecology. Cox et al. The functions used in this standardisation, accompanying sensitivity analyses, and guidelines identifying key bias issues are published in the literature (Atkinson et al., 2008, 2017), while the database itself includes warnings about problematic data (Atkinson et al., 2017). An iceberg in the western Antarctic Peninsula where krill populations – vital food source for seals, whales and penguins – are declining. These filters can be very fine in species (such as Euphausia spp.) Last updated on 15 February 2018. Prof Alex Rogers, who is a specialist in sustainable oceans at the Oxford Martin School, Oxford University, said: “Climate change is having an impact [on the krill population] at the same time as a resurgence in krill fishing, with increasing numbers of fishing vessels and changes in technology that are causing increasing krill catches.”. Winter data or data from deeper strata (> 200 m) are not reliable indicators of summer density in the upper strata (0 to 200 m). KRILLBASE does not identify transects and Cox et al. (2004) also performed a range of supplementary analyses to ensure that their conclusions were robust to spatial, temporal, and methodological shifts in the data. From 1970–1990 climate-change effects were becoming evident in this highly altered ecosystem, with marked declines in sea ice, episodic recruitment in krill populations, and declining krill density. Type II error). net type, time of year, and time of day). Marine crustaceans provide a variety of important ecosystem services, several of which are exemplified by Antarctic krill (Euphausia superba Dana, 1850) (Grant et al., 2013). The population of Antarctic krill, the favorite food of many whales, penguins, fish and seals, shifted southward during a recent period of warming in their key habitat, researchers report. This is the equivalent biomass of 28.5 million human beings, approximately 4 times the population of Greater London or the entire population of Canada, averaging 70kg each, in area a third that of Greater London - or 12 times the human biomass density of London (which is a busy place!). Distribution, Biomass and Demography of Antartcic krill, Environmental correlates of Antarctic krill distribution in the Scotia Sea and southern Drake Passage, Long term (1993–2013) changes in macrozooplankton off the Western Antarctic Peninsula, Deep Sea Research Part I: Oceanographic Research Papers, Variability and predictability of Antarctic krill swarm structure, Decision‐making for ecosystem‐based management: evaluating options for a krill fishery with an ecosystem dynamics model, Rapid warming of the ocean around South Georgia, Southern Ocean, during the 20th century: forcings, characteristics and implications for lower trophic levels. The report describes an Antarctic penguin population that is down nearly 7 percent, compared to 2019, with 5.8 million breeding pairs identified nesting … Cox et al. (2018) analysed 1976–2016. Of these six regression analyses, five supported a widespread decline in density with P values < 0.05. These fishing fleets are feeding a growing global demand for krill-based health products which are claimed to help with a range of ailments from heart disease to high blood pressure; strokes to depression. We thank the editors for the opportunity to write this comment, and Jaume Forcada for helpful advice and comments. Each of these sources will reduce the slope of any decline and therefore increase the risk of failure to detect a real decline. Grant, S.M., Hill, S.L., Trathan, P.N. Secondly, 2016 is not representative of the region as a whole, since the last 5 years of data in the Cox dataset come exclusively from the two cells in the extreme Southwest of the study region, and there are no post-2003 data from anywhere north of 58°S. 3 Optimistic scenario: If conditions improve (reliable sea ice, more krill) and the probability of “poor” years decreases, the penguin population will recover. We validated this dataset by comparison with the number of records stated in Table S1 of Cox et al. Silk, J.R., Thorpe, S.E., Fielding, S., Murphy, E.J., Trathan, P.N., Watkins, J.L. Firstly, while linear models are useful for detecting trends, non-linear models, including the type used by Cox et al. Avoid linear extrapolation of population trajectories. Long-term, climate-driven declines in krill abundance are evident in this region. These factors maximise the chances of failure to detect a real decline. (2018) twice extrapolate the 1976–2003 rate of decline found by Atkinson et al. Since the Southwest Atlantic sector has warmed rapidly over the last century (Whitehouse et al., 2008) and Antarctic krill is an important species, clear information on its population status and trends is a major requirement for policy makers and scientists alike. The effect on mean density of A, exclusion of data from net types with fewer than 30 presence records; B, the inclusion of winter data; and C, the inclusion of deep stratum data. Records with a deeper top sampling depth will generally underestimate density compared to those with a more appropriate sampling depth range, for example 0 to 200 m. The Cox dataset included 40 records based on sampling only at depths below 200 m. Thirty-two of these occurred in 1982 and the rest in 1976, 1978, and 1985. Atkinson et al., 2004; 2014, 2019; Forcada & Hoffman, 2014; Loeb et al., 1997; Watters et al. In the years following such abnormalities, there are usually a lower number of juvenile krill, leading to a population decline. 2011; Rose & Kulka 1999) and of baleen whale populations (Heazle, 2012). (2018) and the percentage of data and sign of slope by grid cell in their Figure 1. Without sufficient krill, penguins among many the krill’s many other predators will decline (Wayne Z. Trivelpiece, 2010)e too. & Beaulieu, C. Hewitt, R.P., Watkins, J., Naganobu, M., Sushin, V., Brierley, A.S., Demer, D., Kasatkina, S., Takao, Y., Goss, C., Malyshko, A. In simple terms, if a coin was tossed 1,000 times and it came up heads at least 526 times, then one could reasonably conclude that the coin favour heads (a decline). For example, Atkinson et al. the probability of an erroneous result given the assumptions of the analysis). Nonetheless we caution that faith in the ability of fishery catch rate data to indicate population declines in aggregating species, as promoted by Cox et al. Antarctic krill (Euphausia superba Dana, 1850) exemplifies the key role of marine crustaceans in fisheries, foodwebs, and biogeochemical cycles. the first and last years), as indicated by the widening confidence intervals in Figure 3 of Cox et al. Although Cox et al. Instead, their approach removes potentially useful data based on consistent basic net designs (e.g. This combination of factors led Cox et al. Gleiber, M.R., Steinberg, D.K. So apparently global warming can both increase and decrease the penguin population. The opinion of Cox et al. (2018), that there has been no decline in krill density, is clear. 2013). The population of Antarctic krill, the favorite food of many whales, penguins, fish and seals, shifted southward during a recent period of warming in their key habitat, researchers report. This is illustrated in our Table 2 and in Figure 3 of Fielding et al. “The decline in the krill population is … While penguin populations did decline in the northern Scotia Sea, where impacts on krill were strongest, areas with relatively minor reductions in krill biomass also saw some of the greatest declines in penguin populations (e.g. This decision to log transform individual net hauls impacts the results shown in Figure 1 of Cox et al. As a result, a large krill stock ultimately leads to a longer starvation period and becomes an obstacle rather than an advantage for successful overwintering and the recruitment of a new generation. Holmes added that “protecting the Antarctic ecosystem” was critical to Aker BioMarines long-term operation. & Reiss, C. Atkinson, A., Hill, S.L., Pakhomov, E.A., Siegel, V., Anadon, R., Chiba, S., Daly, K.L., Downie, R., Fielding, S., Fretwell, P., Gerrish, L., Hosie, G.W., Jessopp, M.J., Kawaguchi, S., Krafft, B.A., Loeb, V., Nishikawa, J., Peat, H.J., Reiss, C.S., Ross, R.M., Quetin, L.B., Schmidt, K., Steinberg, D.K., Subramaniam, R.C., Tarling, G.A. The 2001 and 2011 figures are not completely comparable because of boundary differences between the sub places of … The issue is therefore simply whether there is any statistical evidence of a decline, as the title of Cox et al. They feed on marine algae and are a key source of food for whales, penguins and seals. The mean predicted krill densities in Figure 3 of Cox et al. Many krill are filter feeders: their frontmost appendages, the thoracopods, form very fine combs with which they can filter out their food from the water. & Everson, I. Cleary, A.C., Durbin, E.G., Casas, M.C. (2018) do not explain how they did so. A number of penguin species found in western Antarctica are declining as a result of a fall in the availability of krill, a study has suggested. "Autumn saw the greatest decline in habitat quality and area, mainly in sub-Antarctic regions. (2004). The decline in krill, however, is not due to the disappearance of sea-ice alone, according to the report, which also cited commercial fishing for krill by specialised trawlers beginning nearly 40 years ago and growing competition for krill by recovering whale and fur seal populations. This in turn affected other species: the shearwater population dropped. Krill populations in the area, as well as populations of krill-dependent Adélie penguins, are declining. The close predator-prey relationship between Adélie penguins and krill is important when considering the potential causes for Adélie population decline. (2018). Hear about the threats that could collapse krill populations. over the past few decades. 1. Krill, which grow to about six centimeters, or two inches, occurs in vast schools and is the major source of food for whales, seals, penguins and sea birds. Antarctic krill (Euphausia superba) is a species of krill found in the Antarctic waters of the Southern Ocean.It is the dominant animal species of Earth. One-sample t-test of whether the regression slopes of cells differ from zero. Type: Media Watch. Some suggest that these declines are linked to declines in penguin populations, and that fishing on krill is a cause of both declines. (2018) suggest that the conclusions of Atkinson et al. It contains no post-2003 data for the most northerly grid cells (405, 406, 505, and 506 in Table 2). Atkinson, A., Siegel, V., Pakhomov, E.A, & Rothery, P. Atkinson, A., Siegel, V., Pakhomov, E.A., Rothery, P., Loeb, V., Ross, R.M., Quetin, L.B., Schmidt, K., Fretwell, P., Murphy, E.J. (2018) to identify surveys is not reliable. “I am not advocating removing fishing entirely from Antarctic waters,” said Watters. We therefore evaluate the null hypothesis using the assumption that 569 samples indicated a decline, and then we test whether our conclusion is robust to fewer samples indicating a decline. Hill, S.L., Atkinson, A., Darby, C., Fielding, S., Krafft, B.A., Godø, O.R., Skaret, G., Trathan, P. & Watkins, J. Hill, S.L., Watters, G.M., Punt, A.E., McAllister, M.K., Quéré, C.L. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide, This PDF is available to Subscribers Only. The health of these Southern Ocean species depends heavily on healthy krill populations. While the researchers say that ice loss does affect penguins, they say the more important problem appears to be a decline in the population of Antarctic krill (Euphausia superba), tiny shrimplike crustaceans that dwell in vast schools. & Turner, J. Henson, S.A., Sarmiento, J.L., Dunne, J.P., Bopp, L., Lima, I.D., Doney, S.C., John, J.G. The null hypothesis is that the number of samples indicating a decline is no higher than chance and therefore that the model is not consistent with a decline. IAP2 … The minimum and maximum of parametric bootstrap confidence intervals were about 1.7 and 3.3 krill.m–2 respectively. (2018). Atkinson et al. The existence of KRILLBASE, which compiles data from ten nations, shows the potential for scientific collaboration. As the krill population declines so does that of the chinstrap penguin since krill is their favorite food. (2018) who dispute the evidence for a late twentieth-century decline in krill density (number per unit area) in the Southwest Atlantic sector of the Southern Ocean and claim to overturn “much of recent thinking about climate-driven change in krill populations.” They support this claim with an analysis which reaffirms one non-significant result from an earlier paper but does not challenge the five significant results from that paper or those of other studies which support a decline. Some studies have indicated (2004) that stocks of krill in Antarctica may have declined in recent years at least in some areas. The Antarctic, one of the world’s last great wildernesses and home to animals such as whales, penguins and leopard seals, is being threatened by the plight of an animal just a few centimetres long, according to scientists. Log transformation of individual net hauls down-weights very high values to a much greater extent than log transformation of annual averages (columns d to f in our Table 2). The onus is now on the scientific community to provide useful advice on how the krill stock has changed over time. Check that conclusions are robust to the effects of data transformation and unavoidable biases such as shifts in sampling method and location. 2018: fig. Oxford University Press is a department of the University of Oxford. The shift in the Cox dataset toward areas where krill are abundant and density has been relatively stable (Steinberg et al., 2015) will reduce the slope of any decline. Krill, which grow to about six centimeters, or two inches, occurs in vast schools and is the major source of food for whales, seals, penguins and sea birds. Antarctic krill population has declined by 80% The Antarctic krill population has declined by 80% since the 1970s, and without them the entire ecosystem of the Southern Ocean will collapse. (2016). For example, female krill need access to plentiful food during the summer in order to spawn. Cox et al. Spatio-temporal linear mixed model with random year and cell-by-year effects. Their Figure 3 shows predicted density rising slightly from 1976 before falling to about 84% of its 1976 level in the early 2000s and then recovering slightly to about 88% of its 1976 level by 2016. The West Antarctic Peninsula, which is one of the most rapidly warming areas in the world, has experienced a measurable loss of sea ice. The assertion of Cox et al. In particular the Cox dataset shifts into shallower water and southwards over time (issues D and E in our Figure 1). Summary of results in Atkinson et al. We suggest that a collaborative effort is needed to identify appropriate standards of evidence and to ensure that such advice is based on informed use of the available data. Krill decline is often put as being first caused by global warming then after industrial fishing is added to the list of causes. Ensure that data coverage is appropriate for the intended analysis. (2018) excluded this latter category of nets and presented a mixed model analysis which was similar but not equivalent to analysis 2a. Global warming has been blamed for part of that decrease because the ice that is home to the algae and plankton they feed on is retreating. ... Krill cannot feed on the smaller coccolithophores, and consequently the krill population (mainly E. pacifica) in that region declined sharply. Researchers and environmental campaigners warn that a combination of climate change and industrial-scale fishing is threatening the krill population in Antarctic waters, with a potentially disastrous impact on larger predators. Polar Regions are among the most sensitive areas to climate change (Hagen et al., 2007), which will affect the flow of energy from lower trophic leve… This criterion clearly selects against zero-density records. Annual mesoscale (≤ 125,000 km2) acoustic surveys conducted since the 1990s monitor krill biomass in about 5% of this area (Hill et al., 2016) and two large scale (471,000 km2 and 2,065,000 km2) surveys were conducted in 1981 and 2000 (Siegel & Watkins, 2016). The decline in the reproductive capacity of the krill population, associated with the overall decline in sea ice, suggests that food resources for penguins and other predators may continue to decline in the near future. (2018) we aim to identify these errors and provide recommendations which will enable readers to avoid repeating them. Humans also fish for krill, which is used for aquarium food, fishing bait, pharmaceuticals and in some foods consumed by humans. We make this point not to endorse the approach of comparing two years, but to demonstrate that the interpretation of their own results in Cox et al. Thirdly, this approach is not suitable for datasets with high inter-annual variability, which may influence between-year comparisons more than any underlying trend. Within the Atlantic sector of the Southern Ocean where 50% of the circumpolar krill population occurs, observations suggest that their abundance, recruitment success, and population structure already are changing with an overall decreasing trend since the 1970s, although there is also marked interannual variability (Murphy et al., 2007b; Atkinson et al., 2008). Andrea Kavanagh, director of the Pew Charitable Trust’s Protecting Antarctica’s Southern Ocean campaign which funded the latest study, said the findings showed the importance of creating a network of sanctuaries. (2018) applied very limited filtering according to net sampling depth, excluding only those nets with a sampling depth range of less than 10 m, but they did not include sampling depth as an explanatory variable in their models. There will be uncertainties associated with any assessment, especially because there is no large-scale, long-term direct monitoring of the krill stock. A loss of sea ice, or change in seasonal timings, could hurt krill populations and those that depend on them. (2017) and support future use: Composite datasets such as KRILLBASE may need some correction for differences in sampling methods. CALIFORNIA / U.S. may ban krill fishing for sea's sake / West Coast decline in population means other species die Jane Kay , Chronicle Environment Writer March 8, … (2004). Understanding how krill demography is affected by changes in the physical environment poses an outlook to predicting future changes in marine ecosystems. British Antarctic Survey, High Cross, Cambridge, UK. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, Biodiversity and host specificity of sponge-associated barnacles (Cirripedia: Thoracica) in Thailand, Salinity acclimation alters acid and alkaline phosphatase expression and histological changes in the hepatopancreas of the oriental river prawn, http://creativecommons.org/licenses/by/4.0/, Receive exclusive offers and updates from Oxford Academic, Clarifying trends in the density of Antarctic krill. (2017). Atkinson et al. Antarctic krill feed on algae and phytoplankton that are suspended in the water column. 1 5 2 4 3 Check your understanding. Do not assume that the KRILLBASE data fields contain any information that is not stated in Table 2 of Atkinson et al. (2018) argue that the decreasing trend in their Figure 3 is not consistent with a “massive” decline. Campaigners say recent developments in fishing technology are exacerbating the problem, allowing ‘suction’ harvesting by large trawlers which are now able to gather up vast quantities of krill. On the one hand their study reaffirms the one non-significant result in Atkinson et al. Projected future changes in physical features such as ocean temperature, ice conditions, stratification, and currents will have further and considerable impacts on marine ecosystems (Hays et al., 2005; Doney et al., 2012). Atkinson, A., Hill, S.L., Barange, M., Pakhomov, E.A., Raubenheimer, D., Schmidt, K., Simpson, S.J. An alternative approach of modelling the effect of net mouth area, as in the KRILLBASE standardisation, would have allowed Cox et al. AS KRILL DECLINE – SO DO PENGUIN POPULATIONS As Antarctic temperatures warm, the penguins’ main food source is plummeting. How can we manage fisheries to prevent the competition with penguins ? We followed the criteria in Table S1 of Cox et al. The Cox dataset excludes most of the KRILLBASE net types but includes negatively biased data from winter and deep strata. & Reid, K. Whitehouse, M.J., Meredith, M.P., Rothery, P., Atkinson, A., Ward, P. & Korb, R.E. (2018). (2018) restate the argument of Nicol et al. The retention of this single year of winter data contrasts with the exclusion of net types that were used for less than five years, highlighting inconsistencies in the data selection approach used by Cox et al. (2004) analysed two independent sets of post-1976 krill density data (large nets with nominal mouth area ≥ 3 m2 and all smaller nets) and applied three separate analyses to each (Table 1). that feed primarily on phytoplankton, in particular on diatoms, which are unicellular algae. It is, however, a proxy for the year of data collection, which was used as a random effect variable by Atkinson et al. Spatio-temporal general linear model ignoring the random year effects. AS KRILL DECLINE – SO DO PENGUIN POPULATIONS As Antarctic temperatures warm, the penguins’ main food source is plummeting. & Hill, S.L. This is because their main food source – krill – has declined by up to 80 percent. There is a trade-off between consistency of sampling method and data coverage. Understanding the functional relationship between krill, the krill fishery and demersal sub-Antarctic fish populations Curious12 2020-11-10T21:21:51+00:00. Atkinson et al., 2004, 2014; Forcada & Hoffman, 2014; Loeb et al., 1997; Watters et al. We have worked with international colleagues to compile and publish KRILLBASE, a repository of data on numerical density (the number of krill per unit area of sea surface, hereafter density) resulting from scientific net surveys conducted in the 1920s and 1930s, and from the 1970s onwards (Atkinson et al., 2017). Log transformation can help to achieve a more normal data distribution and aid plotting of density data that can span several orders of magnitude but it also reduces the influence of very high values on any derived statistic. As krill populations decline, krill fisheries become a problem for Adelie penguins. Approximately 3,500,000 km2 of the Southwest Atlantic Sector is open to krill fishing. Each analysis was applied to two sets of net types: large nets (i.e. The reason for this is likely to be a fall in the amount of sea ice in the winter months particularly in the Antarctic Peninsula region. This risk is increased by the use of subjective interpretation rather than statistical hypothesis testing. & Zhou, M. Cox, M.J., Candy, S., de la Mare, W.K., Nicol, S., Kawaguchi, S. & Gales, N. Erisman, B.E., Allen, L.G., Claisse, J.T., Pondella, D.J., Miller, E.F. & Murray, J.H. (2018). By making these data publically available, and providing detailed information about their origin, use, and limitations, we aim to facilitate the provision of information to scientists, policy makers, and other stakeholders. Krill are an essential energy source for whales, penguins, seals, squid, fish and other marine life. This creates challenges in the analysis of krill density data, whether they are derived from nets or acoustics. The mean density for 1986 was the lowest of any year in the Cox dataset (1.44 krill.m–2). & Ward, P. Atkinson, A., Hill, S.L., Pakhomov, E.A., Siegel, V., Reiss, C.S., Loeb, V., Steinberg, D.K., Schmidt, K., Tarling, G.A., Gerrish, L. & Sailley, S.F. While penguin populations did decline in the northern Scotia Sea, where impacts on krill were strongest, areas with relatively minor reductions in krill biomass also saw some of the greatest declines in penguin populations (e.g. (2018) is likewise unreliable. (2018), has been implicated in the catastrophic collapse of fished stocks around the world (e.g. First images of creatures from Antarctic depths revealed, report, published in the journal Plos One, a global campaign has been launched to turn a huge tract of the seas around the Antarctic into the world’s biggest sanctuary. This article is a contribution to Theme 1.3 - Biological Dynamics. Because high densities were more common in the early part of the analysis period, the approach of Cox et al. (2018) use KRILLBASE data to support their arguments but we show here that their approach contains multiple errors. The KRILLBASE standardisation has the advantage that it is described in detail, with appropriate sensitivity analyses. (2018) suggests. Adelie penguins rely on krill as a major source of nutrition. The Guardian. spatio-temporally heterogeneous) sampling. (2004) accounted for different net types by performing separate corroborative analyses using data from different types of net (Table 1). The evidence to support this opinion is unclear. 1). (2018) state that these confidence intervals are “large” and that their analysis reveals “considerable inter-annual variability.” These model-based estimates of variability, which include the effects of down-weighting high values, are much lower than the orders-of-magnitude variability reported in all previous studies cited in reviews by Siegel & Watkins (2016) and Hill et al. The double whammy of warming and increased fishing could be disastrous both for krill and for the animals that depend on them, some researchers say. Chinstrap and Adélie penguins have declined by more than 50 percent since 1980. 2. This rate of decline is increased further by the grazing of an abundant krill population. In response, a global campaign has been launched to turn a huge tract of the seas around the Antarctic into the world’s biggest sanctuary, protecting wildlife and banning all fishing. (2004) and new data covering the period 2004–2016. (2012) that changes in krill density at the regional scale since the 1970s should be reflected in the results of more recent monitoring at smaller spatial scales (standardised acoustic surveys from the early 1990s) and putative indirect indicators of krill availability (predator indices, post 1987). Stated in Table S1 of Cox et al each analysis was applied two. Analysis period, the krill population with a potentially disastrous impact on larger predators, say scientists penguins main! Data with extreme values of the Southern Scotia sea ) is plummeting had significantly... Effects of data transformation and unavoidable biases such as shifts in sampling approach allowed them model. And analysed only data from large nets ( i.e now on the ones do! Krill fisheries become a problem for Adelie penguins rely on sea ice to reproduce, and 506 Table... A statistically significant trend population figures are derived from completely or mostly urban sub places according to the list causes! 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And in Figure 1 of Cox et al period, the evidence for a decline in density with P Paladin Devotion Build Ragnarok, Nas 410 Current Revision, Believer Imagine Dragons Piano Sheet Music Easy, Ath M50x Head Pad Replacement, I Feel Like I Don T Know How To Talk, Fox Sports Motion Graphics, How Far Does Amur Falcon Fly Each Year, Cartoon Reindeer Head Silhouette,