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Fish population variability and fisheries activities are closely linked to weather and climate dynamics. While weather at sea directly affects fishing, environmental variability determines the distribution, migration, and abundance of fish. Fishery science grew up during the last century by integrating knowledge from oceanography, fish biology, marine ecology, and fish population dynamics, largely focused on the great Northern Hemisphere fisheries. During this period, understanding and explaining interannual fish recruitment variability became a major focus for fisheries oceanographers. Yet, the close link between climate and fisheries is best illustrated by the effect of “unexpected” events—that is, nonseasonal, and sometimes catastrophic—on fish exploitation, such as those associated with the El Niño–Southern Oscillation (ENSO). The observation that fish populations fluctuate at decadal time scales and show patterns of synchrony while being geographically separated drew attention to oceanographic processes driven by low-frequency signals, as reflected by indices tracking large-scale climate patterns such as the Pacific decadal oscillation (PDO) and the North Atlantic Oscillation (NAO). This low-frequency variability was first observed in catch fluctuations of small pelagic fish (anchovies and sardines), but similar effects soon emerged for larger fish such as salmon, various groundfish species, and some tuna species. Today, the availability of long time series of observations combined with major scientific advances in sampling and modeling the oceans’ ecosystems allows fisheries science to investigate processes generating variability in abundance, distribution, and dynamics of fish species at daily, decadal, and even centennial scales. These studies are central to the research program of Global Ocean Ecosystems Dynamics (GLOBEC). This review presents examples of relationships between climate variability and fisheries at these different time scales for species covering various marine ecosystems ranging from equatorial to subarctic regions. Some of the known mechanisms linking climate variability and exploited fish populations are described, as well as some leading hypotheses, and their implications for their management and for the modeling of their dynamics. It is concluded with recommendations for collaborative work between climatologists, oceanographers, and fisheries scientists to resolve some of the outstanding problems in the development of sustainable fisheries.

Summary 1.Remote-sensing measurements of marine primary productivity are widely used to predict the distribution and movements of marine top predators, despite the fact that predators do not feed directly on phytoplankton but several trophic levels higher up the food chain. 2. To test for potential links between primary productivity and top-predator feeding hotspots, we assessed spatial match-mismatch across four trophic levels of the Benguela upwelling zone (south-east Atlantic). The food chain studied consisted of phytoplankton, zooplankton (copepods), pelagic fish (anchovies and sardines) and two top predators (Cape gannets Morus capensis and human fisheries). 3. Remote-sensing data of sea-surface temperature (SST) and chlorophyll_a concentration were used as indices of phytoplankton abundance throughout the study area. Copepod biomass and pelagic fish density were determined during at-sea surveys in the South African section of the Benguela using net tows and hydro-acoustics, respectively. Seabird (Cape gannet) home ranges and foraging zones were assessed from two Namibian breeding colonies (Mercury and Ichaboe) and two South African colonies (Lambert's Bay and Malgas) using global positioning system (GPS) tracking. Industrial fishing for anchovies and sardines was investigated using South African landing statistics and logbooks. 4. Our spatial analyses revealed a strong match of seabird at-sea habitat and zones of high primary productivity throughout the southern Benguela. Conversely, there was a marked spatial mismatch between copepods and pelagic fish, as well as between pelagic fish, seabirds and human fisheries: copepods were present in the southern Benguela but pelagic fish usually feeding upon them were located further east (Indian Ocean), outside of the Benguela sensu stricto . Consequently, the majority of these pelagic fish were out of reach for seabirds and fisheries confined to the southern Benguela. 5. Synthesis and applications . Our study demonstrates the impact of an ecosystem shift across one of the world's most productive marine ecosystems and highlights the limitations of using remotesensed patterns of primary productivity to interpret the foraging behaviour of marine top predators. These findings underline the importance of a better knowledge of food web spatial dynamics to support ecosystem-based fisheries management and the conservation of marine top predators.

Coetzee, J. C., van der Lingen, C. D., Hutchings, L., and Fairweather, T. P. 2008. Has the fishery contributed to a major shift in the distribution of South African sardine? – ICES Journal of Marine Science, 65: 1676–1688. A major shift in the distribution of South African sardine (Sardinops sagax) has resulted in a significant spatial mismatch in fishing effort vs. fish abundance in recent years. The sardine fishery started on the west coast during the 1940s, and processing capacity there increased rapidly. This trend together with increases in annual landings continued up to the early 1960s, but then the fishery collapsed as a consequence of overfishing. The population then recovered steadily during the 1980s and 1990s, coincident with, but perhaps not entirely attributable to, the inception of conservative management practices, to support catches similar to pre-collapse levels. Since 2001, however, most of the sardine population has been situated on South Africa’s south coast, far from processing facilities. Fishing effort has increased concomitantly on that coast, particularly during the past three years, reflecting the continued decline in the abundance of sardine on the west coast. Three hypotheses explaining the change in the distribution of sardine have been proposed: (i) intensely localized (i.e. west coast) fishing pressure depleted that part (or functionally distinct unit) of the population; (ii) the shift was environmentally induced; and (iii) successful spawning and recruit survival on the south coast contributed disproportionately more towards the bulk of recruitment, and progeny spawned there now dominate the population and exhibit natal homing. The first of these hypotheses is evaluated, and management implications of the shift discussed.

Spatio-temporal variability of the diet of sardine Sardina pilchardus off Portugal was examined through analysis of the stomach contents of fish collected every 14 d from the west and south of Portugal during 2003Portugal during /2004. Dietary composition of the modal sardine length class was assessed by determining the frequency of occurrence and carbon content of identified prey, and these 2 parameters were combined to estimate a modified index of relative importance of prey (mIRI). The most important prey for sardines were zooplankton, comprising crustacean eggs, copepods, decapods, cirripedes and fish eggs, dinoflagellates and diatoms (particularly the toxin-producer genus Pseudo-nitzschia), which together accounted for > 90% of the estimated dietary carbon. Dietary seasonality was similar for both areas, except that the contribution of phytoplankton was higher for fish from the west Portuguese coast, where upwelling events are stronger and recurrent during spring and summer months. The predominance of prey < 750 μm in sardine diet suggests that filter feeding is the dominant feeding mode used in the wild. Feeding intensity was similar for both sexes and for fish of different length classes and was higher on the west coast than in the south, which is probably related to the higher productivity of the west coast. Although there was high inter-annual variability in feeding intensity, this parameter was highest for both areas during spring and winter months. Temporal variability in satellite-derived chlorophyll a matched the temporal variability in the dietary contribution by phytoplankton and of sardine feeding intensity, suggesting further investigation of the potential use of satellite-derived chlorophyll a data as a proxy for sardine feeding intensity. KEY WORDS: Sardina pilchardus · Stomach analysis · Feeding intensity · SeaWIFSResale or republication not permitted without written consent of the publisher