Mission Statement:

The Pelagic Fish Research Group (PFRG) is a collaborative group of researchers from the U.S. and Mexico committed to the study of seamount ecosystems in the southern Gulf of California. Our projects collect oceanographic and ecological data that further our understanding of pelagic fishes and their environment. We aim to provide information that will improve management and sustain the stocks of pelagic fishes in the Gulf so that these resources can be enjoyed for generations to come.

 

What is a pelagic fish?

The “pelagic zone” refers to the open waters of the ocean. Fish that live in pelagic zones are typically mobile and migratory species that are not closely associated with permanent structures such as coral reefs. This behavior makes pelagic fish difficult to study and understand because it is often impossible to observe them using Scuba gear typically employed by marine biologists. Therefore, it is useful to combine a variety of methods, including the vast knowledge of experienced fishermen, to learn about these important oceanic fish.

Some of the largest and most commercially important species are pelagic fishes, including billfish, tunas, dorado, and many sharks. Most of the favorite sport fish in the Gulf of California are pelagic fishes, including:

Billfish	Tuna	Jacks	Dolphinfish
Striped marlin Blue marlin Black marlin Sailfish	Yellowfin Skipjack Bonito	Yellowtail Amberjack	Dorado

 

Fisheries in the Gulf of California

Pelagic fishes are important resources in the Gulf of California. Wide ranging commercial fisheries as well as more localized artesanal and recreational fisheries target these species. Certain fishing practices, such as gill nets and longlines, extract astounding numbers of target species as well as unwanted bycatch. These harmful fishing practices have threatened fisheries throughout the Gulf. The decline in many fish populations, particularly sharks and manta rays, has led to an attempt to reduce fishing in certain areas of the Gulf. However, these efforts are handicapped because of the absence of critical information about the ecology and distribution of pelagic species.

Marine protected areas (MPAs) are an increasingly popular tool among fisheries management and have been proposed in the Gulf of California. Obviously, reserves limiting fishing will help conserve fish populations, but they also impact a fisherman's way of life and recreation. At the PFRG, we seek to understand fish populations and recommend management that not only conserves biodiversity but also enhances fisheries to the satisfaction of most resource users.

 

How can you help?

Are you a fishermen or diver interested in helping with PFRG research projects? We could use your help in a variety of ways. Browse the projects below, and look for the "Help Wanted" icon for detailed needs. Click the icon to learn more about how you can help. Thanks!

 

PFRG Background

For the past decade, we have been involved in this collaborative effort to examine pelagic fishes and seamount ecosystems in the southern Gulf of California. Our work has examined Gulf waters surrounding El Bajo Espiritu Santo near La Paz, Cerralvo Island, the East Cape, and Gorda Banks near Cabo San Lucas. Studies have been conducted by U.S. and Mexican scientists to describe:

- the oceanographic currents around seamounts and the potential impacts on fish populations
- the abundance and diversity of plankton that form the base of pelagic food webs
- the seasonal residency of large pelagic fish

 

Current Projects

Seasonal Residence

We use underwater visual census, fisheries observation, and ultrasonic tagging to determine how fish communities change with oceanographic conditions. We have been conducting seasonal visual censuses of fish communities at El Bajo for four years to detect the presence of fish species in the community. Visual census has delineated two unique seasonal fish assemblages, a winter community associated with cooler water and a summer community that migrates into the Gulf as the water warms. Fish communities are compared with environmental variability, including fluctuations in sea temperature and primary productivity.

You can help by providing:
- boat time for making census dives

 

 

 

Feeding Habits and Food Webs

Useful food web descriptions and multi-species diet analyses necessary to understand fish populations are fundamentally lacking for pelagic fish communities. We are analyzing the feeding habits of pelagic fishes by examining their stomach contents. Samples of fish stomachs as well as muscle tissue are collected over each season of the year from sport fishermen at specific locations.

Prey items found in the stomach are carefully identified and given a value of importance. We use specific ecological indices to determine the specialization of an individual species’ diet, the similarity of diets between species, and differences between size classes and seasons of the same species. Diet analyses will also allow comparison of species feeding habits in different areas.

Stable isotope methods are used to clarify food web interactions among fish communities. An fish’s isotopic composition represents assimilated food on larger spatial and temporal scales (you are what you eat). The ratio of nitrogen (15N/14N; d15) stable isotopes can help define trophic levels of organisms because the heavy isotope 15N is typically enriched by 3-4‰ from prey to predator. Stable isotopes of nitrogen (d15N) will be used to define the trophic levels and improve understanding of trophic relationships between species. Trophic position of predators as well as food chain length will be compared between seamounts and open-ocean areas using this useful technique.

You can help by providing:
- boat time for catching fish
- biological samples from the fish you catch
- funds for stable isotope analyses (small donations yield great amounts of data!)

 

Fisheries Impacts

Fisheries catch data in the region coarsely parallels water temperatures and is used to track seasonal migrations of the fishes into the southern Gulf. Recreational catch data is obtained from major sport fishing ports of southern Baja, including La Paz, East Cape, and Cabo San Lucas. These records continue to be collected and trends in fish abundance are currently being analyzed. Mexican students are beginning to monitor the catch of artisanal fishermen during weekly trips to fish camps in the region.

 

You can help by providing:
- catch data from the fish you catch

 

 

Fish Residence and Migration – Tag-A-Pelagic (TAP)

Ultrasonic tagging provides a method for determining fish residence patterns at specific locations without the difficulties and biases inherent to census techniques and fisheries catch data. Application of an ultrasonic tagging study produces a continuous record of tagged fish presence and absence. Two acoustic listening stations were moored at El Bajo in September 2002. In a continuing effort to investigate the residence of multiple species in a pelagic fish community, five green jacks, five yellowtail, and two hammerhead sharks were tagged at El Bajo with coded, long-term ultrasonic tags (>2 yrs) in September-November 2002. Records of these fish species have shown short-term residence patterns that are currently being analyzed.

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 seamounts. Ideally, >20 tags would be affixed to all species in this study. The residence of twenty-three yellowfin tuna at El Bajo was analyzed in a previous study. The tagging procedure includes catching the fish by rod and reel, measuring the fish, inserting the tags inside the body cavity, and releasing the fish in less than two minutes. Billfish are tagged externally with a tethered tag because their size and mobility prevents bringing this species aboard.

You can help by providing:
- funds for tags ($300 each) and listening stations at seamounts ($1,000 each)
- boat time for catching and tagging fish

 

We thank the following supporters of the PFRG and ask that you consider their services during your next trip to Baja: