Tag Archives: Baja California

Seabird diets provide early warning of fishery declines

Gulf of California Study finds that the proportions of sardines and anchovies in the diet of pelicans, gulls and terns in spring, can signal the need to reduce fishing efforts in the ensuing season to prevent a fisheries collapse.

Small pelagic fisheries show wide fluctuations, generally attributed to oceanographic anomalies. Most data on these fisheries come from landings, often reporting sustained catches-per-unit-effort (CPUEs) until a decline occurs. It would be useful to be able to predict the decline in advance, and thus avoid it. Research published in Scientific Reports shows significant relationships between fishing effort and seabird diet.

As sardine availability for seabirds declines, CPUEs remain high until the fishery falls, one or two seasons later. A declining proportion of sardines in the seabirds’ diet, combined with the status El Niño, give a reliable forecast of diminishing CPUEs and signals the need to reduce fishing efforts in the ensuing season.

In upwelling regions, such as the California, Humboldt, and Benguela current systems, fishing industries capture the same fish species that seabirds and other marine species feed upon. These small pelagic fishes (known as “forage fish”) constitute around 37% of the world’s commercial landings and often show wide fluctuations, generally attributed to oceanographic-anomalies. Key components of the coastal pelagic marine ecosystem6, their fisheries have been difficult to manage sustainably, and regional economies have been shaken by their collapses. Forage fish transfer energy from microscopic plankton to larger predators and constitute a fundamental food source for marine mammals, seabirds and larger fish species, many of which are also commercially important.

In the Gulf of California (also known as the Sea of Cortez) there are no robust fishery-independent stock assessments available for small pelagic fisheries. Seabirds, however, face similar challenges as does the fishing fleet to find available prey and harvest it.

The relationship between the proportion of sardine in the seabird diets and sardine CPUE shows that sardine catchability decreases faster for seabirds than it does for the fleet, which can maintain high CPUEs even when seabirds have shifted entirely away in search of other fish species, mostly anchovies. Thus, even when CPUEs are high and there is no evidence of decreasing catchability in the fishery itself, other ecosystem components, such as seabirds, may be confronting a decline in available sardine. Availability may further decline during El Niño anomalies, when a deeper thermocline may prevent seabirds from reaching their prey. Thus, the El Niño anomaly and the relative abundance of sardine in the seabirds’ diets can jointly predict the sardine CPUE by the commercial fleet.

Elegant Terns and Heermann’s Gulls feed on juvenile pelagic fish, while Brown Pelicans feed mostly on the same adult fish that are taken by the fleet. This very likely explains why tern and gull diets are statistically more related to CPUEs in the following fishing season, while Brown Pelican diets are more related to CPUEs during the same season.

Sardine catchability is much higher for the fleet than it is for seabirds (and possibly for other ecosystem components). The increased sensitivity of the seabird diets relative to CPUE suggests that the seabirds are more diversified in their prey base and able to switch to other prey species when sardine availability starts to decline. Observed reductions in the proportion of sardines in seabirds’ diets in the Gulf of California Midriff before the beginning of the fishing season may provide a useful way of monitoring the fishery and forecasting the success of the fishing fleet.

Map credit: Map of the Midriff Islands, Gulf of California, Mexico, indicating the location of Isla Rasa and other islands (drawn by Cathy Moser Marlett)

Further Reading:
Enriqueta Velarde, Exequiel Ezcurra &, Daniel W. Anderson, Seabird diets provide early warning of sardine fishery declines in the Gulf of California. Scientific Reports 3, Article number: 1332 doi:10.1038/srep01332 (2013).

World’s Most Robust Marine Reserve is at Baja California

A thriving undersea wildlife park tucked away near the southern tip of Mexico’s Baja peninsula has proven to be the most robust marine reserve in the world, according to a new study led by researchers at Scripps Institution of Oceanography at UC San Diego.

Results of a 10-year analysis of Cabo Pulmo National Park (CPNP), published in the Public Library of Science (PLoS) ONE journal, revealed that the total amount of fish in the reserve ecosystem (the “biomass”) boomed more than 460 percent from 1999 to 2009. People living around Cabo Pulmo, previously depleted by fishing, established the park in 1995 and have strictly enforced its “no take” restrictions.

“The study’s results are surprising in several ways,” said Octavio Aburto-Oropeza, a Scripps postdoctoral researcher, World Wildlife Fund Kathryn Fuller fellow and lead author of the study. “A biomass increase of 463 percent in a reserve as large as Cabo Pulmo (71 square kilometers) represents tons of new fish produced every year. No other marine reserve in the world has shown such a fish recovery.”

The paper notes that factors such as the protection of spawning areas for large predators have been key to the reserve’s robustness. Most importantly, local enforcement, led by the determined action of a few families, has been a major factor in the park’s success. Boat captains, dive masters and other locals work to enforce the park’s regulations and share surveillance, fauna protection and ocean cleanliness efforts.

Strictly enforced marine reserves have been proven to help reduce local poverty and increase economic benefits, the researchers say. Cabo Pulmo’s marine life recovery has spawned eco-tourism businesses, including coral reef diving and kayaking, making it a model for areas depleted by fishing in the Gulf of California and elsewhere.

“The reefs are full of hard corals and sea fans, creating an amazing habitat for lobsters, octopuses, rays and small fish,” said Brad Erisman, a Scripps postdoctoral researcher and co-author of the article. “During some seasons thousands of mobula rays congregate inside the park and swim above the reef in a magnificent way.”

The scientists have been combining efforts to monitor the Gulf of California’s rocky reefs every year for more than a decade, sampling more than 30 islands and peninsula locations along Baja California, stretching from Puerto Refugio on the northern tip of Angel de la Guarda to Cabo San Lucas and Cabo Pulmo south of the Bahia de La Paz.

In the ten years studied, the researchers found that Cabo Pulmo’s fish species richness blossomed into a biodiversity “hot spot.” Animals such as tiger sharks, bull sharks and black tip reef sharks increased significantly. Scientists continue to find evidence that such top predators keep coral reefs healthy. Other large fish at Cabo Pulmo include gulf groupers, dog snappers and leopard groupers.

Sea of Cortez Threatened

Life in the Sea of Cortez is endangered by destructive new fishing methods.

Ten years ago graduate students Octavio Aburto-Oropeza and Gustavo Paredes surveyed the marine life of the Sea of Cortez (also known as the Gulf of California). In 2009 they went back and were shocked at how things had declined. Sixty percent of the surveyed sites showed signs of degradation, according to Aburto-Oropeza, and many are now missing the top predators normally present in healthy, functioning ecosystems.

“Ten years later we can actually measure the effects of not putting conservation measures in place,” Paredes told Explorations Magazine. “Some of us had been conducting surveys in certain sites every year, but until this year we didn’t know the whole story of what was going on.”

The changes have occurred because of fishing. Traditional hook-and-line fisherman have been put out of business by vastly more damaging gill net fishing and “hookah” diving. Hookah fishermen use surface-supplied air through piping that allows them to walk along the seafloor for long periods of time. The technique is typically conducted at night when fish are resting, allowing the hookah fishermen to spear or grab large numbers of vulnerable fish and invertebrates.

In the most dramatic example of fishing impacts observed on the 2009 expedition a survey of San Esteban Island in the north revealed reefs devoid of fish and instead covered by mats of cyanobacteria.

There are areas which have flourished, though. One example is Cabo Pulmo near the southern tip of the Baja peninsula. Fishing restrictions there since 1995 have ensured that Cabo Pulmo retains a mix of sea life and flourishing fish populations. Other successes include Coronado Island inside the Loreto marine park and Los Islotes inside Espiritu Santo marine park.

Using compressed air has been banned in Mexico for sports fishermen for 40 years, but since commercial fishermen weren’t named specifically they had been allowed to use compressed air to clean the reef. In May 2009 this changed: the use of hookahs have now been outlawed for any type of fishing. Illegal fishing still goes on though, and environmental organisation Sea Watch is asking people to report any that they encounter at http://seawatch.org/en/Resource-Library/359/report-illegal-fishing

Further Reading:
Scripps Institution of Oceanography