Climate change is a threat to marine ecosystems and the services they provide, and reducing fishing pressure is one option for mitigating the overall consequences for marine biota. We used a minimally realistic ecosystem model to examine how projected effects of ocean warming on the growth of Antarctic krill, Euphausia superba, might affect populations of krill and dependent predators (whales, penguins, seals, and fish) in the Scotia Sea. We also investigated the potential to mitigate depletion risk for predators by curtailing krill fishing at different points in the 21st century. The projected effects of ocean warming on krill biomass were strongest in the northern Scotia Sea, with a ≥ 40% decline in the mass of individual krill. Projections also suggest a 25% chance that krill biomass will fall below an established depletion threshold (75% of its unimpacted level), with consequent risks for some predator populations, especially penguins. Average penguin abundance declined by up to 30% of its unimpacted level, with up to a 50% chance of falling below the depletion threshold. Simulated krill fishing at currently permitted harvest rates further increased risks for depletion, and stopping fishing offset the increased risks associated with ocean warming in our model to some extent. These results varied by location and species group. Risk reductions at smaller spatial scales also differed from those at the regional level, which suggests that some predator populations may be more vulnerable than others to future changes in krill biomass. However, impacts on predators did not always map directly to those for krill. Our findings
indicate the importance of identifying vulnerable marine populations and targeting protection measures at appropriate spatial scales, and the potential for spatially-structured management to avoid aggravating risks associated with rising ocean temperatures. This may help balance tradeoffs among marine ecosystem services in an uncertain future.
We wish to draw the attention of Members to an online application of the R code published in the attached paper. The web-based app ‘photoR’ (https://jefferson.shinyapps.io/photor2) implements the methods of the paper and provides summary outputs for direct input to CEMP A6b and A9 eforms. The abstract of the paper follows:
Summary
1. Collecting spatially extensive data on phenology and reproductive success is important for seabird conservation and management, but can be logistically challenging in remote regions. Autonomous time-lapse camera systems offer an opportunity to provide such coverage.
2. We describe a method to estimate nest-level breeding phenology and reproductive success of colonial Pygoscelid penguins using photographs from time-lapse cameras. The method derives from stereotypical patterns of nest attendance, where predominantly two adults are present before and during egg laying, but switch to one adult during incubation. The switch approximates the date of clutch completion and is estimated by fitting a smoothing spline to daily nest attendance data, identifying candidate dates that switch from two adults to one, and selecting the date when the first derivative of the spline is minimized. Clutch initiation and hatch dates are then estimated from the mean, species-specific interval between egg laying (Pygoscelid penguins typically lay two eggs) and the duration of the incubation period. We estimated these intervals for each species from historical field data. The phenology is adjusted when photographs indicate egg or chick presence prior to their estimated lay or hatch dates. The number of chicks alive in each study nest on its crèche date determines reproductive success estimates. The method was validated with concurrent direct observations for each species and then applied to a camera network in the Antarctic Peninsula region to demonstrate its utility.
3. Mean egg lay and incubation intervals from direct observations were similar within species across sites. In the validation study, the mean clutch initiation, hatch, and crèche dates were generally equivalent between photographs and direct observations. Estimates of reproductive success were identical. Applying the method to a time-lapse network suggested relatively high reproductive success for all species across the region and corroborated general understanding of latitudinal trends and species-level plasticity in phenology.
4. The method accurately estimated phenology and reproductive success relative to direct observations and appears well-suited to operationalize regional time-lapse camera networks. The estimation method should be applicable for other seabirds with stereotypical nest attendance patterns from which breeding phenology could be estimated.
Sea ice is a major constraint of fishery performance in the Southern Ocean seasonal sea ice zone. We use sea ice concentration data from 2002-2017 that cover the wider Weddell Sea to establish statistical models of (i) accessibility, i.e. the probability that a particular area is navigable by fishery vessels at a given time, and of (ii) repeated accessibility, i.e. the probability that a particular area is navigable by fishery vessels at a given time and again within the following two years, as requested by CCAMLR research fishery regulations. Our findings indicate that under the actual sea ice conditions almost 50% of the entire WSMPA Planning Area is not suitable for fishery vessels at any time of the year, while there are high spatiotemporal variability in repeated accessibility in particular areas such as along the ice shelf of the eastern and south-eastern Weddell Sea. We consider our models to constitute valuable, riskreducing planning tools in the further development of fishery research as well as of ship-bound tourism in the wider Weddell Sea area.
