Upwelling, offshore transport, and the availability of rockfish in central California

EXTRACT (SEE PDF FOR FULL ABSTRACT): We used the diet of a seabird, the common murre (Uria aalge), nesting on Southeast Farallon Island and feeding in the Gulf of the Farallones, California, as an index to abundance of juvenile rockfish, then related fish abundance to indices of turbulence and upwelling over an 18-year period, 1973-1990. Strong, persistent upwelling or downwelling led to reduced availability of fish in the study area, in contrast to great abundance when upwelling was mild or pulsed. ... On the basis of our study, one effect might be that fishes thought strong enough to resist Ekman transport could be transported out of normal areas of recruitment

A Summary of United States Research and Monitoring in Support of the Ross Sea Region Marine Protected Area

Due to the remarkable ecological value of the Ross Sea, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) adopted a large-scale Ross Sea region marine protected area (RSRMPA) in 2016. Since then, many CCAMLR Members have conducted research and monitoring in the region. In 2021, the U.S. Ross Sea science community convened a workshop to collate, synthesize, and coordinate U.S. research and monitoring in the RSRMPA. Here we present workshop results, including an extensive synthesis of the peer-reviewed literature related to the region during the period 2010&ndash;early 2021. From the synthesis, several things stand out. First, the quantity and breadth of U.S. Ross Sea research compares to a National Science Foundation Long Term Ecological Research project, especially involving McMurdo Sound. These studies are foundational in assessing effectiveness of the RSRMPA. Second, climate change and fishing remain the two factors most critical to changing ecosystem structure and function in the region. Third, studies that integrate ecological processes with physical oceanographic change continue to be needed, especially in a directed and coordinated research program, in order to effectively separate climate from fishing to explain trends among designated indicator species</div

New Technologies Aid Understanding of the Factors Affecting Adélie Penguin Foraging

The Ross Sea (Figure 1) is home to 33% of the world’s Adélie penguins (Pygoscelis adeliae), as well as substantial numbers of Emperor penguins (Aptenodytes forsteri), Weddell seals (Leptonychotes weddellii), and pelagic birds (Smith et al., 2014). Among these, the Commission for the Conservation of Antarctic Marine Resources (CCAMLR) has designated the Adélie penguin an “indicator species” for monitoring ecosystem structure and function in the newly designated Ross Sea Region Marine Protected Area (RSR-MPA). This penguin, among the best-known seabirds, has been studied for decades at multiple locations with investigations that have delved into its population history (both recent and through thousands of years), survival strategies, responses to environmental changes, and feeding ecology (summarized in Ainley, 2002, with numerous papers published thereafter)

Sex-based differences in Adélie Penguin (Pygoscelis adeliae) chick growth rates and diet

Sexually size-dimorphic species must show some difference between the sexes in growth rate and/or length of growing period. Such differences in growth parameters can cause the sexes to be impacted by environmental variability in different ways, and understanding these differences allows a better understanding of patterns in productivity between individuals and populations. We investigated differences in growth rate and diet between male and female Adélie Penguin ( Pygoscelis adeliae ) chicks during two breeding seasons at Cape Crozier, Ross Island, Antarctica. Adélie Penguins are a slightly dimorphic species, with adult males averaging larger than adult females in mass (~11%) as well as bill (~8%) and flipper length (~3%). We measured mass and length of flipper, bill, tibiotarsus, and foot at 5-day intervals for 45 male and 40 female individually-marked chicks. Chick sex was molecularly determined from feathers. We used linear mixed effects models to estimate daily growth rate as a function of chick sex, while controlling for hatching order, brood size, year, and potential variation in breeding quality between pairs of parents. Accounting for season and hatching order, male chicks gained mass an average of 15.6 g d -1 faster than females. Similarly, growth in bill length was faster for males, and the calculated bill size difference at fledging was similar to that observed in adults. There was no evidence for sex-based differences in growth of other morphological features. Adélie diet at Ross Island is composed almost entirely of two species--one krill ( Euphausia crystallorophias ) and one fish ( Pleuragramma antarctica ), with fish having a higher caloric value. Using isotopic analyses of feather samples, we also determined that male chicks were fed a higher proportion of fish than female chicks. The related differences in provisioning and growth rates of male and female offspring provides a greater understanding of the ways in which ecological factors may impact the two sexes differently

Slow recovery of previously depleted demersal fish at the South Shetland Islands, 1983-2010

Following seals and baleen whales prior to the 1970s, demersal fish stocks were depleted off the South Shetland Islands by intensive industrial fishing during the late 1970s to early 1980s. Little has been reported since about how these stocks have fared, after international agreement closed this fishery in 1990. We report changes in size and abundance of the commercially exploited Notothenia rossii and Gobionotothen gibberifrons relative to the ecologically similar but unexploited Notothenia coriiceps at Potter Cove, South Shetland Islands, over a 28-yr period, 1983?2010. N. rossii abundance declined from 1983 to 1991, and an increase in mean size during 1983?1984 is consistent with weak cohorts during preceding years. Modal age changed from 2?3 to 6?7 yr. Length data of G. gibberifrons, available from 1986, exhibited a similar pattern, showing a decrease until 1991?1992. After a period of relative stability (1992?1994), a sharp increase in length and a continued decline in relative abundance indicated low recruitment. The length?frequency distribution of unexploited N. coriiceps throughout the whole period showed no change in modal size or mean length of the fish. We relate these patterns to the fishery and suggest that a further two decades will lapse before these stocks recover. Using the South Shetland fisheries as an example, current management rules for Southern Ocean fisheries, deemed to be precautionary and disallowing depletion beyond which a stock can recover in 2?3 decades, may be unrealistic in an ocean profoundly altered by numerous stock depletions and rapid climate change.Fil: Marschoff, Enrique Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; ArgentinaFil: Barrera Oro, Esteban. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Alescio, Nadia Soledad. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ainley, David G.. No especifíca

The Ross Sea: In a Sea of Change

The Ross Sea, the most productive region in the Antarctic, reaches farther south than any body of water in the world. While its food web is relatively intact, its oceanography, biogeochemistry, and sea ice coverage have been changing dramatically, and likely will continue to do so in the future. Sea ice cover and persistence have been increasing, in contrast to the Amundsen-Bellingshausen sector, which has resulted in reduced open water duration for its biota. Models predict that as the ozone hole recovers, ice cover will begin to diminish. Currents on the continental shelf will likely change in the coming century, with a projected intensification of flow leading to altered deep ocean ventilation. Such changes in ice and circulation will lead to altered plankton distributions and composition, but it is difficult at present to predict the nature of these changes. Iron and irradiance play central roles in regulating phytoplankton production in the Ross Sea, but the impacts of oceanographic changes on the biogeochemistry of iron are unclear. Unlike other Southern Ocean regions, where continental shelves are very narrow and Antarctic krill dominates the herbivorous fauna, the broad shelf of the Ross Sea is dominated by crystal krill and silverfish, which are the major prey items for higher trophic levels. At present, the Ross Sea is considered to be one of the most species-rich areas of the Southern Ocean and a biodiversity hotspot due to its heterogeneous habitats. Despite being among the best-studied regions in the entire Southern Ocean, accurate predictions of the impacts of climate change on the oceanography and ecology of the Ross Sea remain fraught with uncertainty

Sea ice parameters near McMurdo Station, Antarctica from 1986 to 2013

Dataset: McMurdo Sound sea ice thicknessFast ice thickness and temperature data collected at the “sea ice runway” near McMurdo Station by the United States Antarctic Program (USAP) logistic support contractors and provided by the Ice Surveyor (J Scanniello). Fast ice measurements were taken at a suite of 16 stations along a 3000 m distance, and five stations across an orthogonal 1000 m distance. At each station, small holes were drilled through the fast ice and the thickness measured using a meter tape with a lever-arm that held the zero-point against the bottom of the fast ice. Thickness was measured for solid ice and did not include underlying platelet ice, nor overlying snow. Fast ice temperature was measured at 15 cm depth beneath the ice surface. Note that the sea ice runway area is routinely cleared of excess snow, which may affect the fast ice thickness and temperature measurements. For a complete list of measurements, refer to the supplemental document 'Field_names.pdf', and a full dataset description is included in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: http://www.bco-dmo.org/dataset/675187NSF Division of Polar Programs (NSF PLR) PLR-0944747, NSF Division of Polar Programs (NSF PLR) PLR-0944511, NSF Division of Polar Programs (NSF PLR) PLR-094469

Chlorophyll data from McMurdo Sound, Antarctica from 2012 to 2015 (McMurdo Predator Prey project)

Dataset: McMurdo Sound chlorophyllDiscrete chlorophyll a data were collected as part of an ecosystem study in McMurdo Sound, which is located at the southern extent of the Ross Sea in the Southern Ocean. The major goal of this multi-disciplinary project was to assess the influence of top−down forcing (predation) on pelagic zooplankton and fish. Samples were collected using Niskin water bottles deployed through the fast ice (sea ice attached to land) during two spring/summer seasons: 3 November 2012 – 21 January 2013 and17 November 2014 – 1 January 2015. Water samples were collected at the surface and in the chlorophyll maximum, when present, as determined by a fluorescence sensor during a CTD cast. During 2012/2013, stations were located along a transect in the middle of McMurdo Sound, perpendicular to the fast ice edge. During 2014/2015, stations were located along the fast ice edge, and along three transects into the fast ice along the eastern side of the McMurdo Sound (Ross Island), in the middle of the Sound, and on the western side of the Sound. For a complete list of measurements, refer to the supplemental document 'Field_names.pdf', and a full dataset description is included in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: http://www.bco-dmo.org/dataset/679685NSF Division of Polar Programs (NSF PLR) PLR-094451

CTD data from McMurdo Sound, Antarctica from 2012 to 2015 (McMurdo Predator Prey project)

Dataset: McMurdo Sound CTDsCTD data were collected as part of an ecosystem study in McMurdo Sound, which is located at the southern extent of the Ross Sea in the Southern Ocean. The major goal of this multi-disciplinary project was to assess the influence of top−down forcing (predation) on pelagic zooplankton and fish. During the first year (3 November 2012 – 21 January 2013), the CTD was deployed through ice core holes in the fast ice (sea ice attached to land), sampling from near surface to depths between 97 and 175 m. Stations were located along a transect in the middle of McMurdo Sound, perpendicular to the fast ice edge. In the second year (17 November 2014 – 1 January 2015), CTD casts were deployed between 100 and 254 m in depth, at stations along the fast ice edge, and along three transects into the fast ice along the eastern side of McMurdo Sound (Ross Island), in the middle of the Sound, and on the western side of the Sound. Chlorophyll fluorescence sensor measurements on the CTD casts were only made during the 2014/2015 field expedition. For a complete list of measurements, refer to the supplemental document 'Field_names.pdf', and a full dataset description is included in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: http://www.bco-dmo.org/dataset/680929NSF Division of Polar Programs (NSF PLR) PLR-094451