CCAMLR

We investigate the influence of krill (principally Euphausia superba) patchiness on the foraging distributions of seabirds to understand how variation in krill influences patch dynamics between krill and birds. At sea surveys were conducted near Elephant Island, Antarctica for three years (2004-2006) during the annual U.S. Antarctic Marine Living Resources (AMLR) program. Standardized strip-transect surveys were used to map seabirds, and a combination of acoustic and net surveys was used to map krill. We measured patch size of krill and seabirds and elucidated how krill patch dynamics influence foraging seabirds. The spatial association between krill and predators was influenced by the size and arrangement of krill patches. We found a negative relationship between abundance and patchiness of krill and predators, indicating that when krill is less abundant, krill and its predators are less abundant and concentrated. We conclude that annual patch dynamics of krill strongly influences the local abundance and distribution of seabirds. Such information should be used to interpret potential interactions between seabirds and krill fisheries operating near Elephant Island.

1. Implementing an ecosystem approach to fisheries management requires an effective ecosystem monitoring programme, the utility of which depends upon its ability (measured by the statistical power) to detect effects that trigger management action. 2. Using data from a long-term ecosystem monitoring programme of the predators of Antarctic krill Euphausia superba at South Georgia together with a krill population model to simulate natural and fisheries induced variability in krill abundance, the power to detect the effects of different levels of fishing was examined. 3. The power to detect the effects of fishing using either the krill population or a combined predator response index was low (20–40% power after 20 years with the probability of a type I error (α) = 0.05). The power increased to >50% when α was increased to 0.2 when the ability to detect change was greater with the predator response index than using the krill population itself. 4. The results indicate that although this monitoring programme has a proven ability to detect the effects of natural variability in krill abundance, its ability to detect the effects of fishing may be limited if there is a requirement for statistical significance at the 95% level. A situation where changing α produces a marked increase in statistical power, and the difference in the relative ecological costs of making type I and type II errors is likely to be high, may require a more flexible approach to choosing significance levels required to trigger management action. 5. Although long-term monitoring provides a wealth of basic ecological information it is essential to evaluate, the ability to detect specific changes in order that management action is not delayed because of an inability to detect an effect rather than the lack of an effect of the fishery.

The horizontal and vertical distribution and population structure of euphausiids in the Ross Sea and its adjacent waters were investigated during the summers of 2004/2005 using stratified towed samples. Nine species of euphausiids occurred in the survey area. Among them, Euphausia triacantha was dominant in biomass north of the southern boundary of the Antarctic circumpolar current (SB). Thysanoessa spp. was widely distributed north of the continental slope, while E. superba was distributed from the SB to the slope, where it showed the highest biomass. Juvenile E. superba was distributed offshore near the SB and remained at the surface, but gravid females were dominant in the slope and mainly occurred in the middle layers (400–600 m). Adult and juvenile E. crystallorophias were found at 200–300 m in the colder water of the continental shelf. In general, the peak biomass of euphausiids was found in the mid layers of the Ross Sea area. The life span and the number of spawns for major species are also discussed.

Small black spots have been noticed on the cephalothorax of Antarctic krill, Euphausia superba, since January, 2001. To study the nature of the black spots, the krill were sampled in the winter of 2003, 2006, and 2007 in the South Georgia region, the Antarctic Ocean. Histological observations revealed that the black spots were melanized nodules that were composed of hemocytes surrounding either bacteria or amorphous material. In the 2007 samples, 42% of the krill had melanized nodules. Most of the nodules had an opening on the body surface of the krill. A single melanized nodule often contained more than one type of morphologically distinct bacterial cell. Three bacteria were isolated from these black spots, and classified into either Psychrobacter or Pseudoalteromonas based on the sequences of 16S rRNA genes. More than three bacterial species or strains were also confirmed by in situ hybridization for 16S rRNA. The melanized nodules were almost always accompanied by a mass of atypical, large heteromorphic cells, which were not observed in apparently healthy krill. Unidentified parasites were observed in some of the krill that had melanized nodules. These parasites were directly surrounded by the large heteromorphic cells. Histological observations suggested that these heteromorphic cells were attacking the parasites. These results suggest the possibility that the krill had been initially affected by parasite infections, and the parasitized spots were secondary infected by environmental bacteria after the parasites had escaped from the host body.

A major mid-1980s shift in ecological structure of significant portions of the Southern Ocean was partially due to the serial depletion of fish by intensive industrial fishing, rather than solely to climate factors as previously hypothesised. Over a brief period (1969-1973), several finfish stocks were on average reduced to <50%, and finally (mid-1980s) to <20%, of original size. Despite management actions, few stocks have recovered and some are still declining. Most affected species exhibit K-selected life-history patterns, and before exploitation presumably fluctuated in accordance with infrequent strong year classes, as is true of such fish elsewhere. A climate regime, the Southern Annular Mode, once oscillated between two states, but has remained in its “positive mode” since the time of the fish extraction. This may have increased finfish vulnerability to exploitation. As breeding stocks decreased, we hypothesize that availability of annually-produced juvenile fish fed upon by upper-level predators remained low. Correlations between predator populations and fish biomass in predator foraging areas indicate that southern elephant seal Mirounga leonina, Antarctic fur seal Arctocephalus gazella, gentoo penguin Pygoscelis papua, macaroni penguin Eudyptes chrysolphus and “imperial” shag Phalacrocorax spp. — all feeding extensively on these fish, and monitored at Marion, Crozet, Kerguelen, Heard, South Georgia, South Orkney and South Shetland islands, where fishing was concentrated — declined simultaneously during the two periods of heavy fishing. These patterns indicate the past importance of demersal fish as prey in Antarctic marine systems, but determining these interactions’ ecological mechanisms may now be impossible.

The Southern Ocean is a major component within the global ocean and climate system and potentially the location where the most rapid climate change is most likely to happen, particularly in the high-latitude polar regions. In these regions, even small temperature changes can potentially lead to major environmental perturbations. Climate change is likely to be regional and may be expressed in various ways, including alterations to climate and weather patterns across a variety of time-scales that include changes to the long interdecadal background signals such as the development of the El Niño–Southern Oscillation (ENSO). Oscillating climate signals such as ENSO potentially provide a unique opportunity to explore how biological communities respond to change. This approach is based on the premise that biological responses to shorter-term sub-decadal climate variability signals are potentially the best predictor of biological responses over longer time-scales. Around the Southern Ocean, marine predator populations show periodicity in breeding performance and productivity, with relationships with the environment driven by physical forcing from the ENSO region in the Pacific. Wherever examined, these relationships are congruent with mid-trophic-level processes that are also correlated with environmental variability. The short-term changes to ecosystem structure and function observed during ENSO events herald potential long-term changes that may ensue following regional climate change. For example, in the South Atlantic, failure of Antarctic krill recruitment will inevitably foreshadow recruitment failures in a range of higher trophic-level marine predators. Where predator species are not able to accommodate by switching to other prey species, population-level changes will follow. The Southern Ocean, though oceanographically interconnected, is not a single ecosystem and different areas are dominated by different food webs. Where species occupy different positions in different regional food webs, there is the potential to make predictions about future change scenarios.

The consequences of warming for Antarctic long-lived organisms depend on their ability to survive changing patterns of climate and environmental variation. Among birds and mammals of different Antarctic regions, including emperor penguins, snow petrels, southern fulmars, Antarctic fur seals and Weddell seals, we found strong support for selection of life history traits that reduce interannual variation in fitness. These species maximise fitness by keeping a low inter-annual variance in the survival of adults and in their propensity to breed annually, which are the vital rates that influence most the variability in population growth rate (λ). All these species have been able to buffer these rates against the effects of recent climate-driven habitat changes except for Antarctic fur seals, in the Southwest Atlantic. In this region of the Southern Ocean, the rapid increase in ecosystem fluctuation, associated with climate variability observed since 1990, has limited and rendered less predictable the main fur seal food supply, Antarctic krill. This has increased the fitness costs of breeding for females, causing significant short-term changes in population structure through mortality and low breeding output. Changes occur now with a frequency higher than the mean female fur seal generation time, and therefore are likely to limit their adaptive response. Fur seals are more likely to rely on phenotypic plasticity to cope with short-term changes in order to maximize individual fitness. With more frequent extreme climatic events driving more frequent ecosystem fluctuation, the repercussions for life histories in many Antarctic birds and mammals are likely to increase, particularly at regional scales. In species with less flexible life histories that are more constrained by fluctuation in their critical habitats, like sea-ice, this may cause demographic changes, population compensation and changes in distribution, as already observed in penguin species living in the Antarctic Peninsula and adjacent islands.