The
Blue-footed
as an indicator of anchovy availability
in the northern coast of Peru
Blue-footed boobies (Sula nebouxi) only breed at two islands in northern Peru: Lobos de
Tierra (6o25’S) and Lobos de Afuera (6o45’S).
The former is by far the largest and supports ten of thousands birds that
breed almost year around. Lobos
de Tierra lies near the southern limit of the Blue-footed booby southern
distribution and in the boundaries of the northern limit of the Humboldt
Current. Studies on their behavior, breeding biology and foraging ecology have
been carried in the coast of Mexico and in the Galapagos Archipelago, but
information for Peru is still scarce. Thus, Lobos de Tierra Island offers countless opportunities
to examine possible geographical variations their breeding and foraging
performance.
The
focus of this research is to examine
the foraging behavior
of the blue-footed booby, which feeds primarily on Peruvian anchovy (Engraulis ringens). I am
interested in determining how Blue-footed boobies adjust their foraging
performance according to changes in marine productivity and anchovy
availability. Because the
Blue-footed boobies exhibit sexual size dimorphism,
with females 30% heavier than males, I am also interested in examining possible
at-sea resource partitioning between sexes. For testing such hypothesis, I will
determine the diet composition and total food ingestion during a feeding trip.
This information will be compared to the total number of diving plunges per trip, duration of feeding trips, feeding
areas and maximum foraging distance in order to estimate an index of capture per unit effort (CPUE).
Diving behavior, feeding areas and routes will be determined by using bird-borne
data loggers equipped with flight sensors, depth meters and compass.
These devices are provided by Dr. Benvenuti from the University of Pisa,
Italy. Independent data on marine
productivity and anchovy availability is provided by the Peruvian Marine
Research Institute (IMARPE) through satellite images of chlorophyll-a
concentration, CPUE and anchovy sizes from the commercial fleet around the
islands, biomass and patchy distribution of anchovies from hydroacoustic
surveys, and location of fishing areas using satellite transmitters set up on
fishing vessels. All the parameters above described will allow to the
identification of areas where Blue-footed boobies and commercial vessels
overlap. These maps will be generated by using GIS analysis.
Foraging
characteristics and reproductive success of Blue-footed boobies are closely
matched with the availability of anchovy which varies both seasonal and annually
with upwelling conditions. During an El Niño Southern Oscillation (ENSO) event, low marine
primary productivity leads to horizontal dispersion, vertical migration or
mortality of anchovies. In other
years, strong cold-water upwelling promotes high anchovy productivity. Seabirds are known to respond to these variations with increased
fecundity, higher fledgling weights of their young and less foraging effort.
For this reason, Blue-footed boobies will be studied under different conditions
during the winter (July) 2002 and summer (January-March) 2003 .
In
Peru, the fisheries industry also is dependent on anchovy abundance, but needs
to avoid overharvesting, especially in years of poor productivity, to maintain a
sustainable yield. Knowledge on the
relative abundance of anchovy as provided by seabird foraging patterns and
breeding performance may provide an early warning to the Peruvian fisheries
industry for controlling harvesting during years of poor marine productivity.
Blue-footed boobies (Sula nebouxi) only breed at two islands in northern Peru: Lobos de
Tierra (6o25’S) and Lobos de Afuera (6o45’S).
The former is by far the largest and supports ten of thousands birds that
breed almost year around. Lobos
de Tierra lies near the southern limit of the Blue-footed booby southern
distribution and in the boundaries of the northern limit of the Humboldt
Current. Studies on their behavior, breeding biology and foraging ecology have
been carried in the coast of Mexico and in the Galapagos Archipelago, but
information for Peru is still scarce. Thus, Lobos de Tierra Island offers countless opportunities
to examine possible geographical variations their breeding and foraging
performance.