Clutters de dominaci´ o amb poques hiperarestes o sobre un conjunt de pocs

to 2003 (Appendix C, Figure 2)�* The anchovy fishery is currently healthy, but sardines have subsequently declined, and there has been an eastward shift in their distribution (van der Lingen et al. 2006, Coetzee et al. 2008)� Although not yet fully understood, this shift has been partly attributed to an abrupt change in envi- ronmental forces influencing the relative favorability of eastern and western spawning locations (Roy et al. 2007)� Because fish-processing facilities are located on the west coast of South Africa, this has had a negative impact on fishery stakeholders (Coetzee et al. 2008) and dependent species�

Management

Historically, sardine and anchovy were managed sepa- rately in South Africa� However, since 1991, the South African anchovy fishery has been regulated using an Operational Management Procedure (OMP) approach (analogous to a Management Strategy Evaluation or MSE), which is an adaptive management system that is able to respond rapidly (without increasing risk) to major changes in resource abundance, as occurred around 2000 (de Moor et al. 2011)� The first joint sardine and anchovy OMP was implemented in 1994 (De Oliveira et al. 1998), with subsequent revisions (De Oliveira and Butterworth 2004, de Moor et al. 2011)� The neces- sity for joint management of sardine and anchovy is a result of the operational interaction between the two fisheries; it is not possible to catch anchovy without an accompanying bycatch of juvenile sardine (De Oliveira and Butterworth 2004), because juveniles of both

species can shoal together� Total allowable catches (TACs) are calculated based on abundance estimates from hydroacoustic surveys of recruitment each May and of spawning biomass each November (De Moor et al. 2008)� Recommendations for both target TAC and total allowable bycatch (TAB), respectively, are provided� An initial conservative anchovy TAC, associated with an initial sardine TAB, is specified at the start of the season based only on the results from the November spawning biomass survey (de Moor et al. 2011)� These limits may be increased later in the year based on results from the annual May recruitment survey�

The stability of South African pelagic yields has been attributed largely to effective and conservative manage- ment, with comparatively low catch rates (8 percent average for sardine; 30 percent average for anchovy) applied to the major forage species� In contrast, the collapse of sardine in the northern Benguela (Namibia) has been attributed to a) exploitation rates that were too high, b) underestimation of actual exploitation rates because of under-reporting of catches, c) growth over- fishing after a change from sardine to anchovy nets with smaller mesh size, and d) the interplay of unsustainable fishing levels under environmental change (Butterworth 1980, Boyer and Hampton 2001)� In South Africa and Namibia, an attempt at ecosystem-based management is also being made through the use of spatial closures to protect African penguins and other seabird foraging areas (see main text on the use of temporal and spatial management)� However no improvement is expected in Namibia until the sardine and anchovy stocks recover�

Ecosystem

The California Current is a temperate upwelling ecosys- tem spanning the coastal waters from the Baja California peninsula to British Columbia� It is characterized by a narrow shelf and steep slope that produce sharp offshore gradients in groundfish communities and also by distinct physical coastal features that are associated with unique biogeographic boundaries� The ecosystem consists of two major eco-regions, delimited at Point Conception, CA� Like many other upwelling ecosystems, the California Current is characterized by environmental variability at multiple scales (Huyer 1983, Checkley and Barth 2009)� Seasonally, the system is defined by the transition from net downwelling of coastal water from poleward winds in winter to net upwelling produced from equatorial winds in spring (Bograd et al. 2009)� Interannually, the ecosystem displays marked variation in the timing of the spring transition to upwelling (Barth et al. 2007)� Warm- and cold-phase El Niño-Southern Oscillation (ENSO) events have strong effects on the eco- system and food web, with predictable shifts in species composition associated with the warm-phase ENSO that brings subtropical or tropical species into the ecosystem (Bograd et al. 2009)� At longer time scales, decadal-scale shifts in ocean conditions (Pacific Decadal Oscillation, or PDO) are thought to underlie patterns of zooplankton diversity and forage fish productivity, affecting the entire food web (Francis et al. 1998)�

The California Current supports multiple species of for- age fish, chiefly Pacific sardine (Sardinops sagax), north- ern anchovy (Engraulus mordax), Pacific herring (Clupea pallasii), eulachon (Thaleichthys pacificus), whitebait smelt (Allosmerus elongates), and Pacific sand lance (Ammodytes hexapterus)� Euphausiids (Thysanoessa spinifera, Euphausia pacifica, Nyctiphanes simplex) are the key invertebrate forage species� Other species that may play similar ecological roles include juvenile hake (Merluccius productus) and salmon (Oncorhynchus spp�), Pacific (Scomber australasicus) and jack mackerel (Trachurus symmetricus), bonito (Sarda chiliensis line- olata), and market squid (Loligo opalescens) (Field and Francis 2006)� The abundances of many forage fish populations are not routinely estimated, but long-term records from scale deposition suggest that sardine and anchovy undergo oscillating patterns of abundance, with sardines exhibiting the most wide-ranging fluc- tuations (Baumgartner et al. 1992, but see Box 1�2 on variability)� Sardines are thought to be more productive during warm phases of the PDO, and anchovy productiv- ity is greater during cold phases (Chavez et al. 2003)� Several fish species of special concern, such as coho and Chinook salmon (Oncorhynchus kisutch and

Oncorhynchus tshawytscha), and some rockfish (Sebastes) species prey on forage fish but do not appear to

specialize on them� Forage fish are also consumed by commercially important marine fishes such as lingcod (Ophiodon elongatus), Pacific hake (Merluccius produc- tus), Pacific halibut (Hippoglossus stenolepis), and spiny

the california current:

supporting Multiple Forage Fish