Project: Resource use and multi-species interactions of large pelagic fishes at seamounts in the southern Gulf of California
Marine pelagic fishes are
migratory species that inhabit the open waters of the deep ocean. Rich
stocks of pelagic fishes are known to be associated with shallow
seamounts and offshore banks in the Gulf of California. Ocean currents
around these features are thought to impact local biological
productivity and plankton communities in a way that leads to an
abundance and diversity of pelagic fishes. Seasonally variable
oceanographic conditions in the Gulf of California result in dynamic
fish communities that change throughout the year. Understanding the
ecology of fish assemblages at fished sites will aid in preserving
populations and fisheries for the fishermen that utilize them.
We aim to determine how fish use resources at seamounts by looking at their feeding habits and residence patterns at two particular locations in the southern Gulf of California, El Bajo Espiritu Santo (ESS) and La Reina Seamount (LRS). We are conducting diet analyses using gut contents and stable isotopes to determine how several species coexisting in the same area use food resources. In addition, we are using fisheries catch data, underwater visual censuses, and electronic tagging studies to observe when species can be found at these seamounts.
Since 2001, over 1,000 gut samples from fifteen pelagic fish species have been collected and analyzed. Approximately 200 muscle samples for stable isotope analysis have also been collected. The fishing practices of artisanal fishermen have been observed since 2002, and fish camps have been mapped across seasons for two consecutive years. Recreational catch data has been collected from the four major fishing ports of southern Baja for the last 1-15 years. Understanding fishing practices and their impact on fish populations will permit outstanding fishing to continue in the Gulf for future generations.
Visual census has
delineated two unique seasonal fish assemblages at ESS, a winter
community associated with cooler water and a summer community that
migrates into the Gulf as the water warms. Two ultrasonic listening
stations (Vemco Ltd., VR1) including automated temperature loggers were
moored at ESS in September 2002. We tagged five planktivorous green
jacks, five predatory yellowtail, and two predatory hammerhead sharks
at ESS with coded, long-term ultrasonic tags (>2 yrs) in fall
2002. Twenty-three yellowfin tuna were similarly tagged in 1998 to
examine their residence patterns, and the results of the two-year study
have been published. With future research funds, we intend to increase
sample sizes and tag multiple species across trophic levels to
determine the residence patterns of these fishes at ESS and LRS.
John Richert, Ph.D.. (lead)
Peter Klimley, Ph.D.
Arturo Muhlia-Melo, Ph.D.
National Science Foundation
UC Pacific Rim Research Program
University of California, Davis