Enrique Marschoff

Interannual study of Chinstrap penguin’s diet and reproductive success at Laurie Island, South Orkney Islands, Antarctica

Inter-annual variability in the diet of Chinstrap penguins (Pygoscelis antarctica) at Laurie Island, South Orkney Islands was examined based on stomach contents of adults coming ashore during the 1997/1998–2001/2002 breeding seasons. Krill (Euphausia superba) dominated the diet either as frequency of occurrence (in 100% of samples), number (>99%), and percentage contribution in weight (>99.5%). Other prey items were minor but did vary between years. The contribution in weight of fish, amphipods and cephalopods ranged between 0.01–0.5, <0.01–0.14 and 0–0.03, respectively. Although minor components varied slightly along the years, the weight of stomach contents was significantly different. It was found that for a given weight the maximum observed percentage of undigested krill resulted negatively correlated with the stomach contents total weight. The proportion of whole krill observed in individual penguins, expressed as a fraction of the maximum corresponding to its weight was used to characterize the prevailing conditions in each season.

Inter-annual variability in Chinstrap penguin diet at South Shetland and South Orkneys Islands

Inter-annual variability in the diet of Chinstrap penguins (Pygoscelis antarctica) at Laurie Island (South Orkney Islands) and 25 de Mayo/King George and Nelson Islands (South Shetland) was examined based on stomach contents of adults during the 2002/2003–2006/2007 and 2002/2003–2004/2005 breeding seasons, respectively. Krill (Euphausia superba) dominated the diet as frequency of occurrence (in 100% of samples), number (>99%), and percentage contribution in weight (>94.8%). Other prey items were minor and varied between years. The weight of stomach contents was significantly different. The percentage in weight of whole krill was used to compare the feeding conditions across seasons. It differed significantly at the three sites studied. Distribution of krill size varied among years and localities, showing different krill availability for penguins.

Vertical distribution of two substages of stage Calyptopis I of Euphausia superba Dana, in South Orkneys Area

SummarySamples of Euphausia superba larvae at the Calyptopis I stage, taken in the upper 200 m near South Orkney Islands, have been analyzed discriminating early and advanced substages on the basis of the presence or absence of pleon segmentation, evidenced through the actual cuticle. A significant difference in pleon length between these forms is demonstrated, suggesting growth between them. Results show no difference between these in relation to their vertical distribution; supporting the view that developmental ascent has been already completed in the area. In both substages, a significant difference between night and day catches existed, but no evidence of diel migration was found in their vertical distributions.

Changing status of three notothenioid fish at the South Shetland Islands (1983–2016) after impacts of the 1970–80s commercial fishery

Owing to commercial fishing during the late 1970s/early 1980s, targeted notothenioid species had become depleted around the South Shetland Islands. Herein we report subsequent changes in the prevalence of three species, Notothenia rossii, Gobionotothen gibberifrons and Notothenia coriiceps in Potter Cove, King George Islands/Isla 25 de Mayo, in a 33-year effort to monitor recovery. N. rossii and G. gibberifrons had been severely impacted by industrial fishing but in offshore waters N. coriiceps had never been commercially fished; however, all three species exhibit similar nearshore habitats and life history. We examined composition in trammel net catches during 2012–2016, augmenting a time series started in 1983. Our inshore results were consistent with those from offshore bottom trawl sampling in 2007 and 2012 around the South Shetland Islands: (1) continued increase in the abundance of N. rossii; (2) further decline in G. gibberifrons recruitment evidenced by low proportions of juvenile fish; and (3) a high abundance of N. coriiceps. Reasons for lack of recovery in G. gibberifrons remain obscure but seemingly relate to the dramatically changing ecosystem of the region due in part to climate as well as recovery among previously depleted upper trophic level species. Our results are also consistent with trends reported in seabirds that feed on juveniles of these notothenioids: decrease in the areas commercially fished. Under the regulation of CCAMLR, commercial fishing for finfish in the South Shetland Islands region (FAO Subarea 48.1) remains prohibited since 1991; results indicate that it cannot be reinstated.

The uropod as a proxy for total length distribution in Antarctic krill: an assessment of different models

The properties of the regression of standard length on the length of the exopodit of the uropod of Euphausia superba as a method to estimate the distribution of the standard length from penguin stomach contents samples are explored. The distance between the estimated and observed distributions was measured with the Kolmogorov–Smirnov statistic. Sample variability was determined using resampling techniques. The ability of linear functions (Models I and II), allometric and non-parametric methods to recover the observed distributions was evaluated within samples and exchanging parameters between samples. Linear and allometric models proved inadequate to recover the distribution, while the differences obtained with non-parametric methods fall within the bounds of sample variability, suggesting that a linear equation does not capture the relation between total and exopodit length. The use of a non-parametric regression is recommended to increase the sample size when estimating the distributions of prey lengths in the stomach contents of Antarctic penguins.

Profile analysis of Euphausia superba larvae vertical distribution in the Scotia Sea, related to time factor

SummaryThe vertical distribution of Euphausia superba larvae caught during the January–February 1981 cruise of BIP Dr Eduardo L Holmberg to the Scotia Sea, was studied by means of the multivariate linear model. The profile analysis technique was applied to vertical distribution of different stages, using a variable composed by counts at each one of the four sampling depths. After the logarithmic transformation of data, this technique showed significantly larger numbers of larvae by night than by daytime in the upper 100 m. No significant differenc was found between 100 to 200 m, which was the lowest level sampled. No vertical migration was observed.Younger larvae distributions suggest that ascending larvae were not present in significant quantities in the whole area. Net avoidance is proposed as the simplest explanation for night — day differences, in view that a supposed migration out of sampling limits in light hours, has no support in present or literature data.

A method for measuring the size of early euphausiid larvae

A simple method to measure early euphausiid larvae is tested on 35 specimens of Euphausia superba obtained in the Weddell-Scotia Confluence region (ranging from Calyptopes I to Furcilia III) against the measures obtained on the same specimens with a graduated eyepiece. The arrangement of the test includes two observers, four magnifications (from 7.5× to 62.5×) whenever feasible and two replications of each measurement. A total of 953 measurements were analyzed in an incomplete random blocks ANOVA design not finding significant differences between magnifications, methods, observers and their interactions. It was found that the relative differences between methods were of the same magnitude as the differences between replications (approximately 5%). The proposed method is less demanding on laboratory work, thus allowing the measurement of the large number of specimens needed to estimate size frequency distributions.