Is current management of the Antarctic krill fishery in the Atlantic sector of the Southern Ocean precautionary?

This paper explains the management of the Antarctic krill (Euphausia superba) fishery in the Atlantic sector of the Southern Ocean, and current knowledge about the state of the regional krill stock. In this region, krill fishing is permitted in an area of approximately 3.5 million km2 which is divided into four subareas (labelled Subareas 48.1 to 48.4) for management and reporting purposes. The effective regional catch limit (or ‘trigger level’), established in 1991, is 0.62 million tonnes year–1, equivalent to ~1% of the regional biomass estimated in 2000. Each subarea has also had its own catch limit, between 0.093 and 0.279 million tonnes year–1, since 2009. There is some evidence for a decline in the abundance of krill in the 1980s, but no evidence of a further decline in recent decades. Local-scale monitoring programs have been established in three of the subareas to monitor krill biomass in survey grids covering between 10 000 and 125 000 km2. Cautious extrapolation from these local monitoring programs provides conservative estimates of the regional biomass in recent years. This suggests that fishing at the trigger level would be equivalent to a long-term exploitation rate (annual catch divided by biomass) of <7%, which is below the 9.3% level considered appropriate to maintain the krill stock and support krill predators. Subarea catch limits exceed 9.3% of conservatively estimated subarea biomass in up to 20% of years due to high variability in krill biomass indices. The actual exploitation rate in each subarea has remained <3% because annual catches have been <50% of the trigger level since 1991. Comparison with the 9.3% reference exploitation rate suggests that current management is precautionary at the regional scale. The subarea catch limits help prevent excessive concentration of catch at the subarea scale. Finer-scale management might be necessary to manage the risk of adverse impacts which might occur as a result of concentrated fishing in sensitive areas or climate change. Frequent assessment of the krill stock will enhance CCAMLR’s ability to manage these risks. Continuing the local monitoring programs will provide valuable information on krill variability, but more information is required on how the monitored biomass relates to biomass at the subarea and regional scales

Standing stock of Antarctic krill (Euphausia superba Dana, 1850) (Euphausiacea) in the Southwest Atlantic sector of the Southern Ocean, 2018–19

Estimates of the distribution and density of Antarctic krill (Euphausia superba Dana, 1850) were derived from a large-scale survey conducted during the austral summer in the Southwest Atlantic sector of the Southern Ocean and across the Scotia Sea in 2018–19, the ‘2018–19 Area 48 Survey’. Survey vessels were provided by Norway, the Association of Responsible Krill harvesting companies and Aker BioMarine AS, the United Kingdom, Ukraine, Republic of Korea, and China. Survey design followed the transects of the Commission for the Conservation of Antarctic Marine Living Resources synoptic survey, carried out in 2000 and from regular national surveys performed in the South Atlantic sector by the U.S., China, Republic of Korea, Norway, and the U.K. The 2018–19 Area 48 Survey represents only the second large-scale survey performed in the area and this joint effort resulted in the largest ever total transect line (19,500 km) coverage carried out as one single exercise in the Southern Ocean. We delineated and integrated acoustic backscatter arising from krill swarms to produce distribution maps of krill areal biomass density and standing stock (biomass) estimates. Krill standing stock for the Area 48 was estimated to be 62.6 megatonnes (mean density of 30 g m–2 over 2 million km2) with a sampling coefficient variation of 13%. The highest mean krill densities were found in the South Orkney Islands stratum (93.2 g m–2) and the lowest in the South Georgia Island stratum (6.4 g m–2). The krill densities across the strata compared to those found during the previous survey indicate some regional differences in distribution and biomass. It is currently not possible to assign any such differences or lack of differences between the two survey datasets to longer term trends in the environment, krill stocks or fishing pressure

Prey selection of offshore killer whales Orcinus orca in the Northeast Atlantic in late summer : spatial associations with mackerel

The traditional perception of prey species preference of killer whales Orcinus orca L. in the Northeast Atlantic has, to a large extent, been linked to herring Clupea harengus L. Few studies have investigated the feeding ecology of killer whales from the offshore parts of this ecosystem. We conducted 2 summer-season ecosystem-based surveys in the Norwegian Sea, when it is most crucial for these animals to build up their energy reserves, using observational, acoustic, oceanographic, plankton net, and pelagic trawl haul data to quantify any spatial overlap between killer whales and the 3 most common and abundant pelagic fish species: herring, mackerel Scomber scombrus L., and blue whiting Micromesistius poutassou R. No spatial relationships were found between killer whales and herring or blue whiting. However, there was a significant relationship and spatial overlap between killer whales and mackerel. Feeding on this epipelagic schooling fish species during summer may incur lower migration costs and higher energetic gain than feeding on alternative prey. Killer whale group size was also correlated to the size of mackerel trawl catches, indicating active group size adjustment to available prey concentrations.Publisher PDFPeer reviewe

Prey selection of offshore killer whales Orcinus orca in the Northeast Atlantic in late summer:spatial associations with mackerel

The traditional perception of prey species preference of killer whales Orcinus orca L. in the Northeast Atlantic has, to a large extent, been linked to herring Clupea harengus L. Few studies have investigated the feeding ecology of killer whales from the offshore parts of this ecosystem. We conducted 2 summer-season ecosystem-based surveys in the Norwegian Sea, when it is most crucial for these animals to build up their energy reserves, using observational, acoustic, oceanographic, plankton net, and pelagic trawl haul data to quantify any spatial overlap between killer whales and the 3 most common and abundant pelagic fish species: herring, mackerel Scomber scombrus L., and blue whiting Micromesistius poutassou R. No spatial relationships were found between killer whales and herring or blue whiting. However, there was a significant relationship and spatial overlap between killer whales and mackerel. Feeding on this epipelagic schooling fish species during summer may incur lower migration costs and higher energetic gain than feeding on alternative prey. Killer whale group size was also correlated to the size of mackerel trawl catches, indicating active group size adjustment to available prey concentrations

Comparative analysis of Bricker versus Wallace ureteroenteric anastomosis and identification of predictors for postoperative ureteroenteric stricture

Purpose!#!Ureteroenteric anastomosis after cystectomy is usually performed using the Bricker or Wallace technique. Deterioration of renal function is the most common long-term complication of urinary diversion (UD). To improve surgical care and optimize long-term renal function, we compared the Bricker and Wallace anastomotic techniques and identified risk factors for ureteroenteric strictures (UES) in patients after cystectomy.!##!Material and methods!#!Retrospective, monocentric analysis of 135 patients who underwent cystectomy with urinary diversion at the University Hospital Essen between January 2015 and June 2019. Pre- and postoperative renal function, relevant comorbidities, prior chemo- or radiotherapy, pathological findings, urinary diversion, postoperative complications, and ureteroenteric strictures (UES) were analyzed.!##!Results!#!Of all 135 patients, 69 (51.1%) underwent Bricker anastomosis and 66 (48.9%) Wallace anastomosis. Bricker and Wallace groups included 134 and 132 renal units, respectively. At a median follow-up of 14 (6-58) months, 21 (15.5%) patients and 30 (11.27%) renal units developed UES. We observed 22 (16.6%) affected renal units in Wallace versus 8 (5.9%) in Bricker group (p &amp;lt; 0.001). A bilateral stricture was most common in Wallace group (69.2%) (p &amp;lt; 0.001). Previous chemotherapy and 90-day Clavien-Dindo grade ≥ III complications were independently associated with stricture formation, respectively (OR 9.74, 95% CI 2-46.2, p = 0.004; OR 4.01, 95% CI 1.36-11.82, p = 0.013).!##!Conclusion!#!The results of this study show no significant difference in ureteroenteric anastomotic techniques with respect to UES development regarding individual patients but suggest a higher risk of bilateral UES formation in patients undergoing Wallace anastomosis. This is reflected in the increased UES rate under consideration of the individual renal units

Feedback effects of chronic browsing on life-history traits of a large herbivore

1 Increasing ungulate populations are affecting vegetation negatively in many areas, but few studies have assessed the long-term effects of overbrowsing on individual life-history traits of ungulates. 2 Using an insular population of white-tailed deer (Odocoileus virginianus Zimmermann; Anticosti, Québec, Canada) introduced in 1896, and whose density has remained high since the first evidence of severe browsing in the 1930s, we investigated potential feedbacks of long-term and heavy browsing on deer life-history traits. 3 We assessed whether chronic browsing contributed to a decline of the quality of deer diet in early autumn during the last 25 years, and evaluated the impacts of reduced diet quality on deer body condition and reproduction. 4 Rumen nitrogen content declined 22% between two time periods, 1977–79 and 2002–04, indicating a reduction in diet quality. 5 After accounting for the effects of year within the time period, age and date of harvest in autumn, peak body mass of both sexes declined between the two time periods. At the end of November, males were on average 12% heavier and adult does 6% heavier in 1977–79 than in 2002–04. Hind foot length did not vary between time periods. 6 The probability of conception increased 15% between the two time periods, but litter size at ovulation declined 7%, resulting in a similar total number of ovulations in 2002–04 and in 1977–79. 7 Our results suggest that following a decline in diet quality, white-tailed deer females modified their life-history strategies to maintain reproduction at the expense of growth. 8 Deer appear to tolerate drastic reductions in diet quality by modifying their life history traits, such as body mass and reproduction, before a reduction in density is observed. Such modifications may contribute to maintain high population density of large herbivores following population irruption

Impact of climate change on Antarctic krill

Antarctic krill Euphausia superba (hereafter ‘krill’) occur in regions undergoing rapid environmental change, particularly loss of winter sea ice. During recent years, harvesting of krill has increased, possibly enhancing stress on krill and Antarctic ecosystems. Here we review the overall impact of climate change on krill and Antarctic ecosystems, discuss implications for an ecosystem-based fisheries management approach and identify critical knowledge gaps. Sea ice decline, ocean warming and other environmental stressors act in concert to modify the abundance, distribution and life cycle of krill. Although some of these changes can have positive effects on krill, their cumulative impact is most likely negative. Recruitment, driven largely by the winter survival of larval krill, is probably the population parameter most susceptible to climate change. Predicting changes to krill populations is urgent, because they will seriously impact Antarctic ecosystems. Such predictions, however, are complicated by an intense inter-annual variability in recruitment success and krill abundance. To improve the responsiveness of the ecosystem-based management approach adopted by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR),critical knowledge gaps need to be filled. In addition to a better understanding of the factors influencing recruitment, management will require a better understanding of the resilience and the genetic plasticity of krill life stages, and a quantitative understanding of under-ice and benthic habitat use. Current precautionary management measures of CCAMLR should be maintained until a better understanding of these processes has been achieved