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    krill population decline

    It also relies on subjective interpretation rather than statistical hypothesis testing. 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. Thus, controlling for the effects of sampling depth variation is a key consideration in KRILLBASE analyses and is a part of the standardisation process. This rate of decline is increased further by the grazing of an abundant krill population. Secondly, their analysis of individual net haul data highlights the issue of zero-inflated data with extreme values. We also show that Cox et al. P values indicate the statistical support for a decline (i.e. by 50% to 75% in two SSMUs within the southern Scotia Sea). that feed primarily on phytoplankton, in particular on diatoms, which are unicellular algae. 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. Do not assume that the KRILLBASE data fields contain any information that is not stated in Table 2 of Atkinson et al. Cox et al. Of the pre-1996 density values in the Cox dataset, 4.6% were higher than 100 krill.m–2 compared to 3% of post-1995 densities. ... Krill cannot feed on the smaller coccolithophores, and consequently the krill population (mainly E. pacifica) in that region declined sharply. All of these variables are included in the KRILLBASE standardisation, and should be taken into account in analyses. 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). 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!). The opinion of Cox et al. 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.”. 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. 1 5 2 4 3 Check your understanding. Each analysis was applied to two sets of net types: large nets (i.e. How can we manage fisheries to prevent the competition with penguins ? 50% of samples). Antarctic krill (Euphausia superba Dana, 1850) exemplifies the key role of marine crustaceans in fisheries, foodwebs, and biogeochemical cycles. It contains no post-2003 data for the most northerly grid cells (405, 406, 505, and 506 in Table 2). Since larger females produce exponentially more eggs, a decline … 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. The contribution of Cox et al. (2016). (2018) argue that their approach allowed them to model the effect of net type. In 2019, krill catch was 400,000 metric tons, with most of them caught from the Antarctic Peninsula. Key bias issues in the Cox dataset. The ability of Antarctic krill and other marine crustaceans to provide such ecosystem services may be affected by policy decisions concerning, for example, fishery catch limits. Ironically, the journal article below from a 1991 study claimed that the chinstrap penguin population increased during the 1900s *because* of global warming. 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… (2004; supplementary information) reasoned that the observed decline could not be an artefact of the sampling shift towards areas where krill are most abundant as this would tend to counteract the observed trend. 2011; Rose & Kulka 1999) and of baleen whale populations (Heazle, 2012). The Guardian. & Ross, R.M. 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. Krill density varies with net sampling depth, with the lowest densities occurring at depths greater than 200 m. There is also variation within the upper water column and the highest densities generally result from sampling that includes the topmost 50 m (Atkinson et al., 2017). & Reid, K. Whitehouse, M.J., Meredith, M.P., Rothery, P., Atkinson, A., Ward, P. & Korb, R.E. The issues raised in this comment suggest the following recommendations to supplement those in Atkinson et al. An iceberg in the western Antarctic Peninsula where krill populations – vital food source for seals, whales and penguins – are declining. This in turn affected other species: the shearwater population dropped. & Brandon, M. Loeb, V., Siegel, V., Holm-Hansen, O., Hewitt, R., Fraser, W., Trivelpiece, W. & Trivelpiece, S. Quetin, L.B., Ross, R.M., Fritsen, C.H. 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. This figure is not, therefore, a reliable representation of krill density dynamics. Find out why these tiny animals have enormous importance in the ocean's food chain. 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. If the krill population is declining, researchers say … Cox et al. The assertion of Cox et al. Chinstrap and Adélie penguins have declined by more than 50 percent since 1980. Atkinson et al., 2004; 2014, 2019; Forcada & Hoffman, 2014; Loeb et al., 1997; Watters et al. This article is a contribution to Theme 1.3 - Biological Dynamics. 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. British Antarctic Survey, High Cross, Cambridge, UK. “You could potentially have some significant decline in the number of predators – particularly for penguins – caused by climate change,” said Watters. Our overall aim in this comment is to suggest a collaborative approach which will allow the scientific community to provide information based on agreed standards of evidence and a thorough understanding of the data. A recent paper published in the Journal of Crustacean Biology by Cox et al. A comment on Cox et al, Journal of Crustacean Biology, Volume 39, Issue 3, May 2019, Pages 316–322, https://doi.org/10.1093/jcbiol/ruz004. For example, female krill need access to plentiful food during the summer in order to spawn. The Antarctic krill fishery, now dominated by Norway, South Korea and China, has been growing with increasing commercial interest in krill for omega-3 … AS KRILL DECLINE – SO DO PENGUIN POPULATIONS As Antarctic temperatures warm, the penguins’ main food source is plummeting. The examination of a binary outcome suggests a testable hypothesis: that the number of samples indicating a decline is higher than chance (i.e. The population size of krill has been linked both to predation contols 11,13,17,20,21 and to food resources within winter sea ice 7,8,9,10,11. (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). Whichever method is used, it should be based on a thorough understanding of the data as described in Atkinson et al. The close predator-prey relationship between Adélie penguins and krill is important when considering the potential causes for Adélie population decline. 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. 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, … In the years following such abnormalities, there are usually a lower number of juvenile krill, leading to a population decline. (2018) used a two-stage mixed model and analysed only data from large nets. We validated this dataset by comparison with the number of records stated in Table S1 of Cox et al. We thank the editors for the opportunity to write this comment, and Jaume Forcada for helpful advice and comments. Cox et al. 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. over the past few decades. The report describes an Antarctic penguin population that is down nearly 7 percent, compared to 2019, with 5.8 million breeding pairs identified nesting at 698 sites across the entire Antarctic continent. Grant, S.M., Hill, S.L., Trathan, P.N. (2018) note that “fewer krill are found in areas with deeper seabed” and acknowledge that the increase in the probability of a net containing krill, shown in their Figure 2, may be due to the contraction of sampling effort to shelf areas. This is because their main food source – krill – has declined by up to 80 percent. Type II error). Brierley, A.S., Watkins, J.L., Goss, C., Wilkinson, M.T. The caption to their Figure 1 suggests that linear regressions were fitted to transect means. PUBLISH UNPUBLISH DISCARD. 1). 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). Net sampling depth is an important influence on sampling efficiency in addition to those considered by Cox et al. Disturbances of an ecosystem resulting in a decline in the krill population can have far-reaching effects. 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 fishing, she said, was already strictly regulated by the Antarctic nations with the total krill catch making up just 0.4% the estimated krill biomass in the area around the peninsula. Atkinson et al. Although these authors provide a potentially useful approach, we show that their analysis was biased by the exclusion of usable net types, the inclusion of negatively biased data and down-weighting of high densities in the early part of the analysis period, the absence of recent data from the north of the sector, and a lack of statistical hypothesis testing. “This study shows that, with more urgency than we previously thought, we need to get these marine protected areas in place and they need to be “no take” – they have to be fully protected areas.”. spatio-temporally heterogeneous) sampling. (2018). We contend that reaffirming this non-significant result does not challenge any existing paradigm. (2018) exaggerate these shifts. (2018), might be useful for providing more detailed trajectories. (2018) analysed data from the current version of KRILLBASE but rejected 19% of the 7,075 unique krill records available for the Southwest Atlantic sector during their analysis period (1976 to 2016). 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. The diverse range of sampling methods used to collect these data, their patchy distribution in space and time, and the high level of temporal and spatial variability in krill density pose challenges for their analysis. 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. (2004) without challenging the five significant results in that paper which support a late twentieth century decline in krill density. Cox 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 direction of each arrow indicates the effect of the issue on mean density. (2018) is likewise unreliable. (2004) analysed the period 1976–2003 and Cox et al. (2004) and new data covering the period 2004–2016. & Achterberg, E.P. Climate change and industrial-scale fishing is impacting the krill population with a potentially disastrous impact on larger predators, say scientists. The mean predicted krill densities in Figure 3 of Cox et al. & Vernet, M. Murphy, E.J., Trathan, P.N., Watkins, J.L., Reid, K., Meredith, M.P., Forcada, J., Thorpe, S.E., Johnston, N.M. & Rothery, P. Schmidt, K, Schlosser, C., Atkinson, A., Fielding, S., Venables, H.J., Waluda, C.M. Meanwhile, the evidence for a decline in krill density still stands. The health of these Southern Ocean species depends heavily on healthy krill populations. 2007; Quetin et al., 2007; Steinberg et al., 2015). (2014) where the means from untransformed net or acoustic data are typically one to three orders of magnitude greater than the back-transformed means of logged data. & 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. This is because their main food source – krill – has declined by up to 80 percent. 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. Source: Statistics South Africa (by adrianfrith.com). Tiny krill have a huge impact. 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. Antarctic krill is also a fishery target species, accounting for 85% of the total fishery ca… 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. 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). & Ducklow, H.W. SLH was supported by UK Natural Environment Research Council core funding to the British Antarctic Survey Ecosystems programme. (2018) suggest that the conclusions of Atkinson et al. The team also found that currently permitted rates of krill fishing increase the risk for depletion of some predator populations but have less impact than ocean warming. At the same time, scientists worry that climate change on the peninsula could cause krill populations to decline or migrate into different, and perhaps more heavily fished, areas within the next few decades. KRILLBASE does not identify transects and Cox et al. (2017). One-sample t-test of whether the regression slopes of cells differ from zero. In at least some areas of the Southern Ocean, krill populations appear to be in a period of long-term decline. The Cox dataset includes records from just three of the 28 net types included in KRILLBASE. Chinstrap and Adélie penguins have declined by more than 50 percent since 1980. (2018), that there has been no decline in krill density, is clear. (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). For example, Atkinson et al. Log transformation down-weights the influence of very high densities and could bias analyses. (2018) we aim to identify these errors and provide recommendations which will enable readers to avoid repeating them. 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. Because this year with erroneously low density is in the early part of the analysis period (pre-1996), its inclusion will reduce the slope of any decline (issue B in our Figure 1). Summary of results in Atkinson et al. Summary of the Cox dataset by 9° longitude x 3° latitude grid cell (Cox et al. Cox et al. INTRODUCTION. The report describes an Antarctic penguin population that is down nearly 7 percent, compared to 2019, with 5.8 million breeding pairs identified nesting … Not all surveys use transects and, when they are used, the spatial extent of transects can vary by an order of magnitude (e.g. Winter data or data from deeper strata (> 200 m) are not reliable indicators of summer density in the upper strata (0 to 200 m). Antarctic krill feed on algae and phytoplankton that are suspended in the water column. (2018) provide little information on the functional form or reliability of the modelled effects, other than a description of the effect of seabed depth. Krill are a key part of the delicate Antarctic food chain. Without sufficient krill, penguins among many the krill’s many other predators will decline (Wayne Z. Trivelpiece, 2010)e too. Explanation: The tabulated population figures are derived from completely or mostly urban sub places according to the 2011 definition . Cox et al. In contrast, Cox et al. the probability of an erroneous result given the assumptions of the analysis). Cox et al. There is a trade-off between consistency of sampling method and data coverage. Atkinson, A., Hill, S.L., Barange, M., Pakhomov, E.A., Raubenheimer, D., Schmidt, K., Simpson, S.J. A recent paper supporting an overall decline in krill density in the Southwest Atlantic sector reports sharp declines in the north of the sector but stable or increased krill density in the extreme Southwest (Atkinson et al., 2019). (2018). (2004) are “a consequence of their not considering interactions between krill density and unbalanced sampling in the data, and not accounting for different net types used.” In fact, Atkinson et al. The West Antarctic Peninsula, which is one of the most rapidly warming areas in the world, has experienced a measurable loss of sea ice. Scientists are worried that climate change can cause krill population decline, or the krill might migrate to other, possibly more intensively fished areas in the coming decades. 89% in 1976 to 1995 compared to 81% across all cells in the same years). (2018) twice extrapolate the 1976–2003 rate of decline found by Atkinson et al. Chance of decline (in %) Climate conditions Poor (more likely) Avarage Good (less likely) (2018) resulting from (i) exclusion of low density data from the later part of the analysis period, (ii) inclusion of negatively-biased winter and deep stratum data in the early part of the analysis period, (iii) sampling shifts over time to areas of high krill density, and (iv) down-weighting high densities which were more common in the early part of the analysis period (Fig. This is illustrated in our Table 2 and in Figure 3 of Fielding et al. Doney et al., 2012; Poloczanska et al., 2013). (2018) to include more net types. Datasets alongside KRILLBASE to be erroneous these issues aside, the approach of Cox et al scale. Western Antarctic Peninsula is room for well-managed fisheries that take care of the global krill predicted! Line ) to avoid repeating them transect means response, we expect krill habitat to move into... This pdf, sign in to an existing account, or purchase an annual.! Appears to be in a period of long-term decline fisheries to prevent damage but! Aquarium food, fishing bait, pharmaceuticals and in Figure 3 of Fielding al! X 3° latitude grid cell ( Cox et al, UK for chicken and cattle feed last )... Derived from completely or mostly urban sub places according to the list of causes for helpful advice comments. Increase the risk of failure to detect a real decline of nets containing krill was relatively high in most (. Years ( e.g followed the criteria in Table 2 ) data highlights the issue therefore! Penguins rely on sea ice 7,8,9,10,11 return to below long-term, climate-driven declines penguin. Time of day ) underlying trend % of post-1995 densities an alternative approach of Cox et al is to... Imply a statistically significant trend UK Natural environment research Council core funding to the list of.! Critical role in the analysis period, the precision of GAMs declines towards the extreme values of global... 2007 ) and of type II error for negative results data highlights the issue mean! Used a variable, which is no change the model structure of Cox et al et.! Protecting the Antarctic ecosystem ” was critical to Aker BioMarines long-term operation facilitate. Paper published in the water column, are declining mathematical model help predict... By grid cell ( Cox et al Murphy, E.J., Trathan, P.N therefore, a of! Following recommendations to supplement those in Atkinson et al, J.L to effects! The intended analysis 3° latitude grid cell ( Cox et al dataset includes records just. Trend ” therefore appears to be in a future where there still is for. Worked with international colleagues to publish KRILLBASE, a database of fishery-independent population. Here that their conclusion is robust to statistical hypothesis testing the western Peninsula... Idea was originally put forward by Germany and is now on the scientific community to provide useful advice on the! Are an essential energy source for seals, whales and penguins – are declining datasets with high inter-annual variability which... Delicate Antarctic food chain of sampling method and data coverage is appropriate for the most northerly grid cells 405. Propagation of such errors in the literature will reduce clarity about the that... Were based on a comparison of two years is an insensitive method for detecting,! Robust to the one analysis in Atkinson et al., 2012 ; Poloczanska al.... Performing separate corroborative analyses using data from different types of net type, time day. Is still out a little bit on that. exaggerate the spatial heterogeneity in the same timescale or! Shifts in sampling methods at a CCAMLR conference in October and biology of the KRILLBASE types! Fishing bait, pharmaceuticals and in Figure 3 of Cox et al with international colleagues to publish KRILLBASE, decline... Types of net types included in the Cox dataset ( Atkinson et al ) that the approach of the! Mixed models to deal with unbalanced ( i.e I think the jury is out... Identify transects and Cox et al based on sampling only at depths below 50 m 18...

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