Trends in Fish Populations

This article is a brief synopsis of “Trends in Fisheries and Fishery Resources Associated with the Monterey Bay National Marine Sanctuary from 1981–2000” by R.M. Starr, J.M. Cope, and L.A. Kerr. Copies are available from the sanctuary or on the web at http://montereybay.nos.noaa.gov/research/techreports/fisherytrends.html.

Yellowtail rockfish. photo 2003 Richard Starr

The physical environment in the Monterey Bay region is dyn-amic and greatly influences the size of resident fish populations (see article, p. 20). In the past twenty years, the ocean environment has been favorable for pelagic species, but less so for many bottom-dwelling species. As populations of pelagic species increased, populations of groundfish decreased, partly due to intensive commercial and recreational fishing. In the late 1990s laws such as the federal Sustainable Fisheries Act and California’s Marine Life Management Act and Marine Life Protection Act were passed that mandated more conservative management of marine resources and established guidelines for rebuilding depleted populations.

Rockfishes, cabezon, greenling, and lingcod are commonly caught in nearshore rocky reef and kelp habitats. High catches in nearshore reef and kelp habitats in the 1990s appeared to have reduced abundance of some of these species in nearshore areas. There are now more restrictive regulations to protect fishes in these habitats. Because many of the nearshore species are shorter lived, they have the potential for faster recovery than deeper-dwelling species.

Nearshore soft-bottom habitats are home to many fishes and invertebrates. Population sizes of most of these fish species are unknown, but trends in fishery landings indicate that many of these populations are healthy in the Monterey Bay National Marine Sanctuary. The market squid, an important species living in nearshore soft-bottom habitats, dominates catches from these habitats. The population of market squid seems strong, but as commercial catches increase, so do concerns about squid conservation.

Semi-pelagic rockfish species such as bocaccio, chilipepper, widow, and yellowtail rockfish made up 98 percent of the total commercial catch from rocky deep shelf and slope habitats in the sanctuary. Scientific stock assessments indicate stable or increasing trends in abundance for chilipepper, shortbelly, and yellowtail rockfish. The biomass of bank rockfish has declined, but it is not known if a problem exists with this heavily fished species. Lingcod and the bocaccio, canary, cowcod, and widow rockfish stocks have been declared to be overfished and are now managed under stock rebuilding plans.

Low stock sizes of rockfish species have been attributed to poor recruitment and excessively high rates of fishing, caused by overly optimistic estimates of allowable catch in the 1980s. Most of these deep-water rockfishes are slow growing, long lived, and have experienced high exploitation rates. Managers are concerned about the capability of these species to recover from high harvest rates, especially because some are prone to long periods of poor recruitment. There is evidence that oceanographic conditions may be changing back to a cooler, more productive environment in this region. If that proves to be true, we may see more rapid rebuilding of cold-water stocks.

Species groups caught in soft-bottom, deep-shelf, and slope habitats include shrimp, prawns, rockfishes, thornyheads, sablefish, and flatfishes. Coast-wide, many species in these habitats are considered to be fully exploited but not overfished. Some of the rockfishes inhabiting soft-bottom habitats show signs of depletion in northern California, Oregon, and Washington waters, but the population status of most of the rockfishes in soft-bottom, deep-shelf, and slope habitats in the sanctuary is not well known.

Population abundances of most species in open water habitats are greatly determined by large-scale environmental phenomena that affect the success of spawning and recruitment. The population of one of these species, the Pacific sardine, has been extensively managed for thirty years and has dramatically increased in the past twenty years. In 1999 Pacific sardine biomass in U.S. waters was estimated to be about 1.7 billion kilograms (3.8 billion pounds). This is the highest level in recent history, but still much smaller than in the sardine heyday of the 1930s.

Another pelagic species, the chinook salmon, is one of the most important species in both commercial and recreational fisheries in the sanctuary. It has been intensively managed for more than thirty years, and population size is influenced by oceanic conditions and the quality of inland habitats. Most chinook salmon caught in the sanctuary originate in the Sacramento River or its tributaries. Recent landings have been dominated by the robust fall run, while spring and winter run populations of chinook salmon are considered severely depressed.

In summary, the population status of a great many species harvested in the sanctuary is unknown. Available data, however, indicate that populations in shallow rocky habitats declined in the 1990s. In shallow soft-bottom habitats in the sanctuary, populations of many species appear to be strong. Fisheries are closed in many deep, rocky habitats in the sanctuary in an effort to rebuild populations of a few overfished species, which may increase pressure on nearshore species. The species that have been studied in deep, soft-bottom habitats seem to be at sustainable levels. Open water habitats contain many short-lived, pelagic species that are greatly influenced by environmental conditions. Abundances of several of these species in the sanctuary are rapidly increasing.

Richard Starr(1), Jason Cope(2), and Lisa Kerr(3)
(1)University of California Sea Grant Extension Program
(2)University of Washington
(3)Moss Landing Marine Laboratories

The Monterey Bay Ocean Time-Series and Observatory (MOTO) Sheds Light on Multi-Decadal Basin-Scale Fluctuations of Anchovies and Sardines

To the lay world, Monterey Bay is famous as the setting for John Steinbeck’s stories of Cannery Row and its superabundant sardine fishery. To the oceanographic world, Monterey Bay is equally famous for the devastating collapse of this fishery following World War II.

When the Monterey Bay Ocean Time-Series and Observatory program (MOTO) was started by the Monterey Bay Aquarium Research Institute (MBARI) in the late 1980s, it was never envisioned that MOTO might shed light on the rise and fall of the sardines. MOTO is a field program that includes regular measurements from moorings, satellites, ships, and more recently autonomous underwater vehicles (AUVs).

In the early years, MOTO data described the seasonal and bay-wide spatial pattern of the physics, nutrient chemistry, and primary production in Monterey Bay, providing an observational foundation and basic understanding of ecosystem dynamics within the bay. During the 1990s MOTO data described El Niño and La Niña and their impacts on Monterey Bay, leading to the realization that global climate fluctuations cause dramatic changes in our local ecosystems. And finally, following the 1997-98 El Niño, MOTO data indicated that Monterey Bay had cooled – only slightly, but still enough to affect local ecosystem dynamics significantly.

This cooling was linked to a shift in the ‘Pacific Decadal Oscillation’ (PDO; Figure 1), a newly-described basin-scale climate cycle with cool and warm phases of about twenty-five years. Could this cycle explain the fluctuations in sardines? It appears so. Both sardine and anchovy stocks – not only in Monterey Bay but throughout the Pacific – appear to fluctuate in phase with the PDO.

We recently reviewed these fluctuations in Science magazine. The period from around 1925 to 1950 was warm and dominated by sardines. The twenty-five-year warm periods have been referred to as El Viejo (the old man, a play on El Niño). A cool period from about 1950 to 1975, where anchovies dominated, followed. Since 1975 the Pacific had been warm again until the recent cooling.

Figure 1. (A-C) Analysis of global sea level pattern observed from space. Satellite- derived sea surface height (SSH) has a characteristic spatial pattern globally (panel A) and for the California Current region (panel B). The coefficients on panel C indicate that SSH patterns for panels A and B change over time. Since late 1998 coefficients indicate lower SSH in the NE Pacific region. These changes are associated with cool surface temperatures (panel D) and high chlorophyll levels (panel E) observed as documented by MOTO in Monterey Bay. The changes indicate a change to cool conditions that may hold for twenty more years.

Oceanographers have referred to the periods of rapid change between these warm and cool periods as regime shifts. If the regime has shifted, then the next twenty years will be cooler than average and rainfall in central California will also be lower than average, perhaps leading to extended periods of drought. But of course the shadow of global warming looms over the horizon. Was the warming in the 1980s and 1990s just associated with El Viejo, or is there a global warming component? Given the prognosis for a prolonged cooling, the next decade should provide an answer. The sardine variations were first reported in the early 1980s, and it was a decade or more later that scientists discovered fluctuations in air temperatures, atmospheric circulation, and ocean temperatures that were remarkably similar in phase and duration to the biological records. As a result, it has been suggested that a regime or climate shift may even be best determined by monitoring marine organisms rather than climate.

MOTO data are used widely by students and scientists interested in Monterey Bay and U.S. West Coast oceanography. We hope that it has provided a foundation upon which to build better methods and systems for long-term ocean observing. These large-impact, long-term fluctuations demonstrate the need for such observing systems, which will be required to separate the changes resulting from the ever-increasing pressure that human populations are exerting over the ocean from natural variability. Clearly natural and human-induced impacts will need to be considered in the management of our planet.

Francisco P. Chavez, J. Timothy Pennington, Reiko Michisaki, and John P. Ryan Monterey Bay Aquarium Research Institute