Seabird consumption and production in the Benguela and Western Agulhas ecosystems

Factors determining the number of seabirds impacted by oil spills and the success of their rehabilitation: Lessons learned from Namibia and South Africa

The coastal waters of Namibia and South Africa have an extensive history of oil spills, with 71 recorded up to 2021. Thirty-nine spills reportedly affected 83,224 seabirds, with African penguins (Spheniscus demersus; 91.0 %) and Cape gannets (Morus capensis; 8.5 %) most affected. Spills affecting seabirds were caused by unknown sources (46 %), bulk/cargo carriers (43 %), tankers (38 %) and ship-to-ship transfers (14 %). The number of penguins oiled was predicted by the breeding population size within 25 to 75 km, but not the volume of oiled spilled, the month or the year. Rehabilitation records from penguins oiled in spills since 2001 reveal that the day of admission (relative to the start of the spill) was predictive of packed cell volume, body mass, and plasma total solids, with the latter two being predictive of rehabilitation success. Our results highlight the importance of rapid monitoring at colonies to locate oiled birds in the event of spills.

The economic tradeoffs and ecological impacts associated with a potential mesopelagic fishery in the California Current

The ocean's mesopelagic zone (200-1000 m) remains one of the most understudied parts of the ocean despite knowledge that mesopelagic fishes are highly abundant. Apex predators from the surface waters are known to consume these fishes, constituting an important ecological interaction. Some countries have begun exploring the potential harvest of mesopelagic fishes to supply fishmeal and fish oil markets due to the high fish abundance in the mesopelagic zone compared with overfished surface waters. This study explored the economic and ecological implications of a moratorium on the harvest of mesopelagic fishes such as lanternfish off the US West Coast, one of the few areas where such resources are managed. We adapted a bioeconomic decision model to examine the tradeoffs between the values gained from a hypothetical mesopelagic fishery with the potential values lost from declines in predators of mesopelagic fishes facing a reduced prey resource. The economic rationale for a moratorium on harvesting mesopelagics was sensitive both to ecological relationships and the scale of the nonmarket values attributed to noncommercial predators. Using a California Current-based ecological simulation model, we found that most modeled predators of mesopelagic fishes increased in biomass even under high mesopelagic harvest rates, but the changes (either increases or decreases) were small, with relatively few predators responding with more than a 10% change in their biomass. While the ecological simulations implied that a commercial mesopelagic fishery might not have large biomass impacts for many species in the California Current system, there is still a need to further explore the various roles of the mesopelagic zone in the ocean.

Contrasting impacts of environmental variability on the breeding biology of two sympatric small procellariiform seabirds in south-eastern Australia

Seabirds play a vital role in marine ecosystems and the long-term study of their responses to environmental variations can be used to monitor the effects of climate change on marine fauna. However, slight differences in similar seabird species result in a range of responses which complicates our understanding of the effects of environmental changes to marine ecosystems. The present study investigated inter-annual differences in the breeding biology (breeding phenology, chick growth rates and breeding success) and environmental conditions (seasonal sea surface temperatures) of important foraging areas in two sympatric small Procellariiform species, the fairy prion (Pachyptila turtur) and the common diving petrel (Pelecanoides urinatrix), over four reproductive seasons (2017–2020) in Bass Strait, south-eastern Australia. Marine heatwaves occurred during the years of 2018/19 and 2019/20 and coincided with years of delayed laying dates, slower chick growth and reduced breeding success, in both species. While fairy prions maintained a relatively high breeding success and broadly constant breeding phenology, common diving petrels delayed the start of the breeding season by up to 50 days and experienced dramatic collapses in breeding success in years of high marine heat wave occurrence. The difference in foraging ecology and physiological capacity (largely in the production of stomach oils and fasting abilities of adults and chicks) between both species are likely to influence the variability and phenology in the observed breeding seasons.

Feeding ecology and microplastic ingestion in Chelon richardsonii (Mugilidae) associated with surf diatom Anaulus australis accumulations in a warm temperate South African surf zone

The study aimed to explore ontogenetic dietary changes and microplastic ingestion in Chelon richardsonii associated with diatom Anaulus australis accumulations in a warm temperate South African surf zone. This species is commercially important and forms an important trophic link in southern African coastal waters. Postflexion larvae, juveniles and adults are dominant in surf zones and were used for comparison. Index of Relative Importance (%IRI) results showed an ontogenetic dietary shift, with postflexion larvae ingesting mostly copepods (%IRI = 52.0) and microplastic fibres (%IRI = 30.7); while older developmental stages fed predominantly on diatoms (%IRI ranging from 53.9 to 65.6) and sand (%IRI ranging from 34.2 to 46.0). Microplastic fibres were found in 40% of fish sampled, microplastic fragments in 5%, and both types were recorded across all developmental stages assessed. This study provides the first record of microplastics in C. richardsonii, adding to growing microplastic research in fishes.

A non-invasive approach to estimate the energetic requirements of an increasing seabird population in a perturbed marine ecosystem

There is a growing desire to integrate the food requirements of predators living in marine ecosystems impacted by humans into sustainable fisheries management. We used non-invasive video-recording, photography and focal observations to build time-energy budget models and to directly estimate the fish mass delivered to chicks by adult greater crested terns Thalasseus bergii breeding in the Benguela ecosystem. Mean modelled adult daily food intake increased from 140.9 g·d⁻¹ of anchovy Engraulis capensis during incubation to 171.7 g·d⁻¹ and 189.2 g·d⁻¹ when provisioning small and large chicks, respectively. Modelled prey intake expected to be returned to chicks was 58.3 g·d⁻¹ (95% credible intervals: 44.9–75.8 g·d⁻¹) over the entire growth period. Based on our observations, chicks were fed 19.9 g·d⁻¹ (17.2–23.0 g·d⁻¹) to 45.1 g·d⁻¹ (34.6–58.7 g·d⁻¹) of anchovy during early and late provisioning, respectively. Greater crested terns have lower energetic requirements at the individual (range: 15–34%) and population level (range: 1–7%) than the other Benguela endemic seabirds that feed on forage fish. These modest requirements – based on a small body size and low flight costs – coupled with foraging plasticity have allowed greater crested terns to cope with changing prey availability, unlike the other seabirds species using the same exploited prey base.