OPEN OCEAN AND DEEP SEA SYSTEMS

Prickly sharks are one of two species of shark known as bramble sharks in the family Echinorhinidae. They are named for the sharp, thorny dermal denticles or scales that leave their skin rough to touch. Few facts have been published about the basic biology of prickly sharks, as the majority of reports are based on descriptions of a small number of dead animals incidentally caught in fisheries. From the few animals that have been caught, we know that prickly sharks occur in temperate and tropical waters of the Pacific ocean, ranging in depth from 70–400 m. They reach a maximum length of 4.3 m and their diet appears to consist of small sharks, shark egg cases, octopus, squid, and some fishes.

For several years in the early 1990s, divers observed these sharks in aggregations of up to thirty animals at the head of the Monterey Canyon. These repeated observations led scientists from five different institutions to collaborate in 1999 on a preliminary study of prickly shark movements. Researchers from the University of California Sea Grant Extension Program, Moss Landing Marine Laboratories, the Monterey Bay Aquarium, Monterey Bay Aquarium Research Institute, and the Pfleger Institute of Environmental Research caught and placed sonic transmitters on eight prickly sharks to learn more about the basic aspects of shark biology. Our two primary study objectives were to determine if we could capture prickly sharks and to develop appropriate tagging and tracking techniques for use in future studies.

This year, prickly sharks were caught at the canyon head using a modified longline attached to a surface buoy. Once a shark was brought to the surface and secured to the side of the boat, an acoustic tag, which transmitted depth information, was attached to its dorsal musculature using medical grade plastic darts. The procedure lasted less than ten minutes from catch to release. Immediately after release, the sharks were tracked using two methods. The first method consisted of listening for tag transmissions with a directional hydrophone from a small skiff. This active tracking method allowed for the detection of sharks throughout the canyon, but was limited to daylight and good weather. The second method consisted of placing a subsurface listening station at the head of the Monterey Canyon. This passive listening station was able to gather data continuously, but could only record tag transmissions from sharks that were near the canyon head.

Prickly sharks moved more than we expected this year. Acoustic tags stayed on the sharks for the battery life of the tags—at least three months. During that time, sharks moved frequently during the study and ranged in depth from as little as 5 m of water near the canyon head to as deep as 375 m at a distance of 10 km offshore. Preliminary data analyses indicated four patterns of daily activity associated with prickly sharks: (1) present at the canyon head at night but in deep water during the day, (2) in deep water at night and at the canyon head during the day, (3) at the canyon head the entire day, and (4) completely absent from the canyon head.

Reasons for this wide variety of movements are as yet unknown. Do prickly sharks aggregate at the canyon head to mate, as indicated by the multiple scars on captured females? Or are they coming out of deep water for some other reason, such as to forage at the canyon head? As we work to answer questions such as these, we hope to learn more about the ecological relationship between prickly sharks and canyon heads.

Richard M. Starr1 and Jason Felton^{1, 2},
with Gregor M. Cailliet2, Heidi Dewar³,
John Heine2, Norm Maher⁴,
and John O'Sullivan⁵

1 University of California Sea Grant Extension Program
2 Moss Landing Marine Laboratories
3 Pfleger Institute of Environmental Research
4 Monterey Bay Aquarium Research Institute
5 Monterey Bay Aquarium

Scientists have just submitted a manuscript describing this ctenophore species.(George I. Matsumoto ©1999)

MBARI ecologists also published on mid-water mimicry. (Several species demonstrated curling behavior thought to mimic the outline of a jelly.) The authors used a novel format that incorporates the typical hard-copy scientific publication with an electronic publication (www.mbari.org/rd/midwater) that includes video clips demonstrating the described behavior. Scientists also determined that bioluminescence in one species of medusa originates from diet rather than an intrinsic source. Benthic ecologists are studying a new symbiont found in Monterey Bay tube worms that is very different from the typical sulfur oxidizing bacteria found in other tube worms.

This new species has been nicknamed 'bumpy' until a scientific name is published. (Kevin A. Raskoff ©1999 MBARI)

Oceanographers at Moss Landing Marine Laboratories and MBARI investigated the sources of iron in coastal ecosystems. Their results show that iron is added naturally to ocean waters from the continental shelf during coastal upwelling, a seasonal wind-driven process. These findings were particularly surprising because they suggest that coastal rivers are relatively unimportant as iron sources.

--George Matsumoto
Monterey Bay Aquarium Research Institute

While several CO2 disposal scenarios have been proposed at various ocean depths and in different forms (gas, liquid, solid, and hydrate), almost nothing is known about impacts on marine organisms. The few studies that directly considered the biological effects of ocean CO2 disposal have been toxicological models based on published values for mortality of shallow water animals (both fresh and marine) when exposed to low pH solutions. These models make two important assumptions: (1) the only important environmental impact is reduced pH and not increased carbon dioxide partial pressure (pCO2); and (2) only passively drifting or sessile organisms will be affected directly because mobile animals will avoid CO2 discharge sites. While this work is valuable in predicting the magnitude of potential losses, controlled experiments are needed both to examine the appropriate species that may be at risk in the various disposal scenarios and to test the model assumptions.

Using the remotely-operated vehicle (ROV) Ventana to conduct experiments at 625 m within Monterey Canyon, researchers from MBARI and the Monterey Bay National Marine Sanctuary have found that many species (both invertebrate and vertebrate) do not avoid rapidly dissolving CO2 hydrates when attracted by the scent of food. Further, the animals appeared to suffer from respiratory distress due to increased pCO2, and not decreased pH, when in close proximity to dissolving hydrates. One hagfish in particular swam very close to the CO2 hydrate and lost consciousness, sank to the bottom, and rolled over on its dorsal side.

After a few seconds it recovered and resumed tracking the odor plume back to its source. Twice more the same hagfish approached the hydrate, then lost consciousness. In all instances, the animal appeared to recover and resumed swimming only after it rolled down stream, away from the dissolving CO2 hydrate.

Oceans are clearly an integral component in global processes. However, we still do not understand completely all the complex physical, chemical, and biological factors that regulate marine systems and how they interact.

Any dramatic, large-scale changes made to these systems must therefore be done with great caution. While it is extremely unlikely that CO2 will ever be disposed of within Sanctuary boundaries, the work of local scientists and Sanctuary staff has contributed vital new insight to this important environmental issue.

--Mario Tamburri, Research Fellow
Monterey Bay Aquarium Research Institute
Monterey Bay National Marine Sanctuary
Monterey Bay Aquarium

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