Spatio-temporal persistence of top predator hotspots near the Antarctic Peninsula

Abstract

We quantified species richness and abundance of seabirds and marine mammals in order to identify marine areas that are persistently attractive to top predators. Shipboard surveys across a 150 000 km 2 grid off the Antarctic Peninsula were conducted once or twice each year from 2003 to 2011 during which the distribution and abundance of top predators were mapped. We hypothesized that spatial organization of species richness and abundance hotspots reflect persistent habitat use and are regionalized according to distance from land and oceanographic boundaries. To test this, we used a new hotspot variance metric based on the percentage of time that the species richness or abundance estimate at any one location is greater than 1 standard deviation above the long term means for the entire survey grid. Species richness hotspots were based on all species sighted, while abundance hotspots were based on concentrations of 16 species: 13 seabirds (penguins, petrels and albatrosses), 1 pinniped and 2 baleen whales. Species abundance hotspots reflected 2 major groupings -those with oceanic and coastal origins. We identified 15 richness hotspots, 9 of which were in proximity to the southern Antarctic Circumpolar Current front; the 6 others were associated with major breeding colonies and the location of 2 submarine canyon systems. Our approach integrates temporal and spatial variances over 14 individual surveys and provides useful reference points for identifying ecologically important areas, refining food web models and developing spatial management of and conservation strategies for marine ecosystems.

Horizontal niche partitioning of humpback and fin whales around the West Antarctic Peninsula: evidence from a concurrent whale and krill survey

“…For example, recurrent and tidally predictable availability of krill occurrence has been shown to make areas highly attractive for whales (Cotté and Simard 2005). There are reoccurring hot spots for krill predator occurrence independent of changes in both the physical environment and prey distribution Santora and Veit 2013). Probably, thresholds of minimum krill density rather than interactions along gradients are more likely to describe the relationship between whales and their prey.…”

Persistence of hotspots and variability of seabird species richness and abundance in the southern California Current

“…This was accomplished using the create fishnet command in ArcView to project the individual 3km sampling points onto a grid with cells size of 0.78 3 0.78 (;4500 km 2 ). The size of cells was chosen to account for total trackline effort ( We standardized sampling effort by assessing the number of times the ship visited a cell and the amount of survey effort collected within that cell, relative to all cells in a given season over the entire length of the time series (Santora and Veit 2013). To determine a threshold to use as a cut off, we calculated the mean 6 SD of cell visits and effort per season, then omitted all effort less than 1 SD below the mean.…”

“…The assessment of seabird populations at sea is dependent on the size of an area surveyed and the consistency and repeatability of surveys across many years (Nur et al 2011, Lascelles et al 2012, Santora and Veit 2013. Seabirds tend to concentrate in suitable foraging habitat; some species concentrate near the coast, whereas others are more oceanic and found 500þkm offshore (Hyrenbach and Veit 2003).…”

“…Many seabird species exhibit long-distance migrations among disparate marine ecosystems and hemispheres to feed on seasonally abundant forage species (Veit et al 1996, Shaffer et al 2006, and therefore may affect marine food webs regionally and globally. Quantifying interannual spatial variability of seabirds at sea also provides valuable indicators of ecosystem health and habitat quality (e.g., pollution), as well as information on key scales of variability concern-ing trophic interactions in pelagic ecosystems (Ainley et al 2009, Sigler et al 2012, Santora and Veit 2013. Quantifying the persistence of seabird hotspots (i.e., the reoccurrence of locales of high abundance and/or diversity) may reduce uncertainty about seabird habitat requirements (e.g., marine Important Bird Areas; Lascelles et al 2012), and facilitate future investigations of seabird-forage interactions needed for improving ecosystem-based fishery management (Santora et al 2014), yet is rarely accomplished.…”

“…Therefore, deriving simple means or total counts of seabirds over a large survey area such as CalCOFI (Sydeman et al 2015) without adjusting for variability in spatially referenced survey effort can lead to an increase in uncertainty about trends in species populations. Here, we focus on the spatio-temporal variability of seabirds and conduct an assessment of their inter-annual and seasonal dynamics, and apply an application for the identification and location of persistent seabird species richness and abundance hotspots (i.e., reoccurring areas of high abundance and species; Suryan et al 2012, Santora andVeit 2013). With more than double the length (26 years; 1987-2012) of previously published time series on individual species (Hyrenbach and Veit 2003) we apply a spatial standardization (e.g., grid-based approach) to investigate the hypothesis that seabird densities have declined in the southern CCE (Veit et al 1997, Sydeman et al 2015.…”