The structure of pelagic seabird assemblages in the African sector of the Southern Ocean

• Main Author: Abrams, Ronald Woolf
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Cape Town 1985
• Subjects: Zoology; Southern Ocean
• Online Access: http://hdl.handle.net/11427/7615; https://open.uct.ac.za/bitstream/11427/7615/1/thesis_sci_1985_abrams_rw.pdf

Includes bibliography. This study investigated the potential usefulness of aerial seabirds as indicators of the distribution of peculiar oceanic biotopes and prey populations in the African sector of the Southern ocean. The hypothesis examined was that the distribution and abundance of seabirds are non-random and predictable with respect to the availability of prey at the sea-surface. The distribution of seabirds was correlated with prey density, in cases where the appropriate information was available. More often than not, however, data on prey distributions were unavailable, so that seabird distribution was correlated with the abiotic indicators of hydrodynamic processes which order the distribution of potential prey. The distribution of seabirds was determined by means of shipboard observations. The trophic structure of seabird assemblages was assessed according to the diversity, biomass and abundance of 35 seabird species according to four principal diet-classes. The ecological structure of seabird populations was defined in terms of relationships between the trophic structure of seabird assemblages and Southern Ocean oceanography, meteorology and biogeography. The predictability of seabird distribution and abundance with respect to environmental variation was assessed using linear and nonlinear regression procedures. A deterministic model was developed in which analytical techniques are standardized and which can be applied to other ocean areas. There are predictable associations between the trophic structure of seabird assemblages and the structure of the surface of the sea. Assemblages of putative prey feature squid and fish in low latitudes, and plankton predominate in higher latitudes. The ecological structure of seabird populations reflects this trend on a macro-scale level. On a meso-scale level, the abundance of seabirds by diet-class correlates with the relative abundance of putative prey. Moreover, seabird abundance and biomass correlate positively with abiotic indicators of frontal zones and ...