Euphausiids, or krill, are relatively
small (two to four centimeters)
shrimp-like crustaceans that are
broadly distributed throughout the
worldfs oceans and are particularly abundant
in the productive waters of temperate and polar regions. The majority of the eighty or so krill species feed predominantly on phytoplankton | small unicellular organisms capable of photosynthesis. In addition, most krill migrate diurnally, spending daylight hours clustered in aggregations at depth (up to several hundred meters) and rising to the surface at night to feed.
Within the coastal upwelling systems of the Northeast Pacific, krill are key players in pelagic food webs. In particular, they are important forage for a number of commercially valuable species (market squid, salmon, rockfishes, hake, and sardine) as well as several species of seabirds (Cassinfs Auklet, Sooty Shearwater, and Common Murre) and marine mammals (humpback, fin, and blue whales). Krill are relatively large compared to other grazing zooplankton, which makes them directly accessible to these
predators. Indeed, the blue whale | the largest animal to have ever lived | feeds almost exclusively on krill.
|Figure 1. Mean (+ se) annual zooplankton biovolume (top panel) and krill abundance (bottom panel) collected in net samples taken within the Monterey Bay region between 1997 and 2004
Several species of krill may be found within the waters of the Monterey Bay National Marine Sanctuary, but two species | Euphausia pacifica and Thysanoessa spinifera | are typically the most abundant. E. pacifica is found in deeper waters associated with the continental slope and open ocean regions, while T. spinifera is more common in waters associated with the outer
continental shelf and continental slope. Both undergo strongly seasonal patterns of reproduction and growth within sanctuary waters. Peak larval production occurs in the spring and early
summer, when phytoplankton abundance is typically highest.
The newly hatched larvae occupy the surface waters (<100 meters) and drift with the prevailing currents as they rapidly grow. Individuals typically develop to the juvenile stage within two months of hatching, and adult status can be attained in as
little as four to five months. In years when upwelling persists into late summer, this new generation may reproduce in the early fall, but usually, the surviving adults overwinter and complete
the cycle the following spring.
Efforts to Prohibit Krill Harvesting
Due to the critical role krill play in the sanctuaryfs eco-
system, the Monterey Bay National Marine Sanctuary
convened a working group in January 2003, as part of its
management plan review, to address the threat of krill
harvesting. The State of California and commercial fishermen have also recognized the threat krill harvesting poses to the ecosystem and the statefs fisheries.
California was the first state to prohibit a targeted krill fishery in 2000, and Oregon and Washington have since followed suit. However, the threat of a fishery remains, as the most dense aggregations of krill often occur beyond the statesf three-mile jurisdictions. The working group therefore identified strategies to pursue a complementary ban in federal waters.
In June 2004 the three central coast sanctuaries submitted a request to the Pacific Fishery Management Council to prohibit krill fishing within their waters. They requested that the council take this action pursuant to its own authority under the Magnuson-Stevens Fishery Conservation and Management Act. The proposal was met with broad support from fishermen, environmentalists, and fishery managers, who all saw this as an opportunity to act preemptively to protect the marine ecosystem. As a result, after presenting this request to the council and its advisory bodies in June 2004, there was broad-based consensus that such a prohibition should not just be limited to sanctuary waters but rather should apply to all federal waters along the West Coast.
The council agreed to move forward and is currently pursuing a prohibition by including krill in the Coastal Pelagic Fishery Management Plan and then setting the total allowable catch to zero. Amending this fishery management plan can be expected to take some time, and a prohibition may not be fully implemented until late 2005.
Monterey Bay National Marine Sanctuary
Krill distributions within the sanctuary also appear to have a seasonal pattern. During the spring and early summer, strong coastal upwelling results in the offshore advection (movement)
of nutrient-rich water. This results in a broad zone of high phytoplankton abundance and krill, particularly larvae and juveniles.
As upwelling-favorable winds subside in the late summer and fall,
this productive zone collapses coastward, until by winter it
is restricted to a relatively narrow band. Adults,
owing to their deeper day time distributions
and superior swimming capability, may
not be subject to the same forcing
mechanisms, and their abundance is consistently higher in the nearshore (<40 kilometers) region.
Krill populations within the sanctuary also appear to fluctuate on interannual | and even longer | time scales. We have been monitoring total zooplankton and krill abundance within the Monterey Bay region since 1997. This period has included both the large 1997-98 El Nino as well as the 1998-99 La Nina, both of which disrupted the normal seasonal cycle of productivity within the sanctuary. Specifically, during the summer of 1998, krill were essentially restricted to a narrow (approximately twenty kilometers) coastal band, which greatly restricted the forage habitat for krill predators. This resulted in a disproportionately high number of baleen whale sightings during our research cruises, including the usual blues and humpbacks as well as fin whales, which typically forage in waters further offshore.
Many oceanographers believe that the recent La Nina event corresponded in time with a shift in the Pacific Decadal Oscillation (PDO) from a warm to a cool phase, though this is by no means accepted as certain. The PDO is a low-frequency climatic phenomenon, in contrast to the more dramatic, higher-frequency phenomena such as El Ninos/La Ninas. It may nevertheless have profound impacts on the structure of the pelagic ecosystem. Indeed, a shift
in the PDO from a warm to cool phase in the 1940s was implicated
in the decline of the California sardine fishery. Unfortunately, while the impacts of acute interannual events such as El Ninos/La Ninas may be assessed through research and monitoring in a relatively timely manner, the ramifications of longer-term phenomena such
as the PDO require more extensive datasets and the benefit of increased hindsight.
Nevertheless, our data have suggested some interesting trends. Zooplankton biovolume dramatically and significantly increased following the 1999 La Nina event. (See Figure 1, previous page.) Preliminary analysis suggests that this was due to an increase
in gelatinous plankton such as hydromedusa (small jellyfish), ctenophores (comb jellies), and pelagic tunicates (salps and doliolids). In contrast, no such pattern was evident in krill abundance, which remained statistically unchanged over the study
While the data are far from conclusive, these results stress the importance of krill as a key forage species for both commercially valuable and endangered species within the sanctuaryfs waters. Further, they highlight the uncertainty of how shifts in marine
climate may impact krill population dynamics and regional distribution within the California coastal environment.
Insitute of Marine Sciences, University of California Santa Cruz
While the open ocean forms the largest component of the Monterey Bay National Marine Sanctuary, it is also one of its least understood. The surface area is vast and hides the inhabitants as they move through a water column that is also ever-changing. These qualities have made following large, open-sea predators such as whales, tunas, sea turtles, and sharks in their ecosystem a daunting task throughout history. Today, advances in microelectronics and satellite technology offer scientists unprecedented access to the world of these oceanic travelers and their journeys.
|Elephant seals are among the many species that will offer TOPP scientists an "organismfs view" of their environment. Photo courtesy of Dan Costa, UCSC and TOPP
Launched in late 2000, the Tagging of Pacific Pelagics (TOPP) program is a pilot project of the Census of Marine Life | a global network of researchers engaged in a ten-year initiative to assess and explain the diversity, distribution, and abundance of life in the ocean. A collaboration among Stanford University, University of California Santa Cruz, the National Oceanic and Atmospheric Administrationfs (NOAA) Pacific Fisheries Environmental Lab, and the Monterey Bay Aquarium, TOPP seeks to discover and describe the highways and "hot spots" (areas of high activity) of ocean life by using a variety of pelagic animal species as sensors. Twenty-two species of marine predator | including pinnipeds, whales, tunas, turtles, seabirds, and large squid | will offer TOPP scientists an "organismfs view" of their environment as they migrate, feed, and breed.
During the first three years of the TOPP program, more than fifty scientists from eight countries worked together to tag nineteen different species of open-ocean animals in the North Pacific with more than 1,500 data-collecting electronic tags. TOPP scientists tested the effectiveness of existing electronic tags, and their experience has driven design improvements and innovations to these small but powerful devices. Some of the animals carry archival tags, which record data to be retrieved later in the journey, while frequently-surfacing animals like sharks or whales carry devices that regularly uplink to satellites, providing a near-real-time record of the animalsf movements across the Pacific.
While TOPP scientists continue to improve the tags and build software tools that integrate and visualize tracking and environmental information, the data returning from the tagged animals
are building a complex picture of activity in the eastern Pacific. Scientists have observed tunas that undertake trans-oceanic
journeys to and from the coast of Mexico to the Sea of Japan,
and they have followed salmon sharks for more than two years on migrations from the Gulf of Alaska to Hawaii and back. In the course of their journeys, the animals collect valuable environmental information, recording ocean temperature, salinity, light level, and depth preferences en route.
Working with oceanographers, the biologists hope to model how TOPP predators use the North Pacific ecosystem. A Live Access Server (a near-real-time data repository) will allow scientists to access and analyze tag data in the context of simultaneously gathered oceanographic information from weather satellites, buoys,
and research vessels. This cross-disciplinary approach helps TOPP scientists understand what factors influence migratory behavior.
Equally valuable to scientists and resource management officials are the larger patterns revealed through multi-species tagging. Finding areas where whole communities of open ocean animals
converge, "ocean hot spots" that are analogous to the watering holes and fertile valleys on land, is an important goal of the TOPP project. Locating areas where animals at the top of the oceanic food web congregate helps scientists reconstruct the larger ecosystem in which these "apex predators" move in conjunction with their prey.
TOPP information will not only advance our understanding of the open ocean and its inhabitants but will help policy makers develop ecosystem-based management strategies to ensure a future in which these magnificent animals maintain healthy populations.
To learn more about the TOPP project, visit www.toppcensus.org.
For a real-time look at TOPP data, visit http://las.pfeg.noaa.gov/ TOPP_recent/index.html.
Monterey Bay Aquarium