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Map of South Africa showing the location of places mentioned in the text, the continental shelf (the 200-m isobath is shown) and the Agulhas and Benguela Currents. The west coast system is defined as extending from Cape Agulhas west and north, and the Agulhas Bank system as the area east of Cape Agulhas.
Source publication
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...
Contexts in source publication
Context 1
... Agulhas Bank (van der Lingen et al ., 2005). These include local depletion of fish stocks on the west coast and WAB following higher levels of exploitation in the west than in the east, environmentally induced changes in the distribution of sardine spawners, and the fact that the successful south coast spawning and recruit survivorship contributed disproportionately more towards the recruitment, with progeny spawned in that region now dominat- ing the population and exhibiting natal homing. The aim of this work is to evaluate the first of these hypotheses, which is related to fishing effort and local depletion, and to discuss the management implications of the sardine shift in distribution. Additionally, certain elements of the third hypothesis, which are linked to the first in terms of substock structure, and which may arise as a consequence of local depletion, are discussed. Two acoustic surveys have been conducted annually since 1984 to estimate the biomass and determine the distribution of small pelagic fish species off South Africa. The total biomass between Hondeklip Bay and Port Alfred is estimated in November each year, and recruitment is estimated in May between the Orange River and Cape Infanta, although recent surveys also extend to Port Alfred (Figure 1). Since 2000, survey effort towards the east has increased substantially during both surveys, as a result of a more easterly distribution of sardine and anchovy spawners. The surveys are conducted along a series of pre-stratified, randomly spaced, parallel transects, designed to obtain unbiased estimates of stock size and sampling variance (Jolly and Hampton, 1990; Barange et al ., 1999). Trawl samples, conducted to determine fish size and species composition, were pooled per stratum to obtain size compositions of the entire populations surveyed. Individual trawl length distributions were weighted according to the acoustically estimated biomass near the trawl. Weighted size frequencies were computed for all strata, then summed to produce a species size frequency for the area west and east of Cape Agulhas. These length frequencies were transformed into numbers-at-age through the use of a von Bertalanffy growth curve calculated from a combination of November survey and commercial landings data (D. Durholtz, MCM, pers. comm.). Data on the location, mass, and species composition of landed catches are collected by fisheries inspectors or monitors, or both, at designated landing points along the coast. Commercial catches are sampled at field stations next to the factories where most of the catch is landed for processing: data on species and size composition and biological characteristics have been collected routinely since 1953. Biological data collected include measure- ments of standard length, mass, sex, gonad mass, and macroscopic gonad maturity stage (Fairweather et al ., 2006). Individual landings are assigned a length frequency using the nearest (in space and time) sample length frequency, and catch length frequencies are raised according to their relative contribution to total catch to generate monthly and annual raised length frequency (RLF) tables. As for the survey data, RLF data were converted to numbers-at-age. Suggestions that sardine spawning is divided between two recruitment systems, with the west coast and WAB part of a west coast system and the remaining spawning areas part of an Agulhas Bank system (Lett et al ., 2006; Miller et al ., 2006), imply that a divi- sion of the continental shelf at Cape Agulhas to aid east–west comparisons is plausible (Figure 1). In this context, spatial stat- istics relating to survey distribution patterns, catch distributions, and biological indicators have been compared between the west coast and Agulhas Bank systems, respectively. To evaluate the extent of mixing between the two areas, a spatial overlap index (SOI) between the west coast and Agulhas Bank systems at different levels of sardine biomass was computed in a rectangle stretching along the shelf 120 nautical miles from 20 to 22 8 E (Cape Agulhas to Mossel Bay; Figure 1) and extending from the coast to the edge of the continental shelf. For each November survey, the proportion of positive elementary sampling distance units ( 10 nautical miles long), where the density of sardine was greater than zero and which were within this area, was calculated and plotted against the total population size in November. The surface area occupied by the sardine population during each survey was computed by projecting the contoured density surface onto a plane, then calculating the positive area of the projection in square nautical miles. The total biomass of sardine increased gradually from , 50 000 t in 1984 to some 2.5 million tonnes in 2000 (Figure 2), and although consecutive years of very good recruitment pushed the total biomass up to record levels above 4 million tonnes in 2002, a recent period of prolonged poor recruitment led to a decline in the adult biomass to , 500 000 t in 2007. Composite maps showing the distribution and relative abundance of sardine during periods of different biomass levels (low 1⁄4 0 –33.3 percentile; medium 1⁄4 33.3 –66.6 percentile; high 1⁄4 66.6 –100 percentile) are presented in Figure 3. The importance of the area west of Cape Agulhas, particularly the WAB but at times also farther up the west coast, as a preferred habitat during periods of low biomass is clear, with only low- density areas farther east (Figure 3a). At medium biomass levels, the WAB area remains the preferred area for sardine (Figure 3b), and the distribution there is expanded slightly north and south from that observed during periods of low biomass. The area occupied east of Cape Agulhas is also expanded significantly compared with that at low levels of biomass. At high biomass, the WAB remains important, but the area east of Cape Agulhas now sup- ports most of the sardine biomass (Figure 3c). A consistent separation is also evident (Figure 3) between sardine found west and east of Cape Agulhas, with overlap in the area (Cape Agulhas to Mossel Bay) between the two parts of the population only at very high levels of biomass. This is confirmed by the SOI (Figure 4), which shows an increasing presence of sardine in the overlap area between Cape Agulhas and Mossel Bay at higher levels of biomass. The increase in the total area occupied by sardine at higher biomass is also confirmed when calculating the area occupied by sardine as a function of biomass (Figure 5). Whereas the rate of increase was higher at low biomass ( , 1 million tonnes) than at high biomass, more variability in the area occupied at high biomass was evident than at low biomass. Further investigation into the changes in area occupied by the western and eastern parts of the population in relation to the biomass east and west of Agulhas revealed that the relationship between area and biomass was mostly driven by a rapid expansion of the area occupied by the eastern part of the population (Figure 6). Expansion of the area occupied by sardine in the western area was much slower in comparison, and the relationship between area occupied and biomass not as strong as for the area east of Cape Agulhas. ( r 2 1⁄4 0.48 and 0.83, respectively). Comparing the biomass east and west of Cape Agulhas (Figure 7), it is evident that the contribution of the biomass west of Cape Agulhas to total biomass was larger than that of the biomass east of Cape Agulhas before 1998. In 1999, a large increase in the biomass east of Cape Agulhas relative to that west of Cape Agulhas caused a shift in the relative distribution of sardine to the central and eastern Agulhas Bank. Further increases in the biomass of sardine east of Cape Agulhas after 1999 were mainly the result of the influx of a large number of 1-year-old sardine in 2001 and 2002, emanating from very successful west coast recruitment then. The distribution of fishing effort over the same period as the survey data reveals that as the biomass of sardine and hence the TAC increased, larger catches were taken mostly from the area west of Cape Agulhas (Figure 8). The quantity of sardine caught east of Cape Agulhas only increased from 2001, although remaining small compared with landings made to the west of Cape Agulhas until 2005, when for the first time since the start of the fishery, catches east of Cape Agulhas exceeded those made west of it. The relative exploitation level, i.e. the annual total catch as a proportion of biomass from the November survey in the previous year, ...
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... Agulhas Bank (van der Lingen et al ., 2005). These include local depletion of fish stocks on the west coast and WAB following higher levels of exploitation in the west than in the east, environmentally induced changes in the distribution of sardine spawners, and the fact that the successful south coast spawning and recruit survivorship contributed disproportionately more towards the recruitment, with progeny spawned in that region now dominat- ing the population and exhibiting natal homing. The aim of this work is to evaluate the first of these hypotheses, which is related to fishing effort and local depletion, and to discuss the management implications of the sardine shift in distribution. Additionally, certain elements of the third hypothesis, which are linked to the first in terms of substock structure, and which may arise as a consequence of local depletion, are discussed. Two acoustic surveys have been conducted annually since 1984 to estimate the biomass and determine the distribution of small pelagic fish species off South Africa. The total biomass between Hondeklip Bay and Port Alfred is estimated in November each year, and recruitment is estimated in May between the Orange River and Cape Infanta, although recent surveys also extend to Port Alfred (Figure 1). Since 2000, survey effort towards the east has increased substantially during both surveys, as a result of a more easterly distribution of sardine and anchovy spawners. The surveys are conducted along a series of pre-stratified, randomly spaced, parallel transects, designed to obtain unbiased estimates of stock size and sampling variance (Jolly and Hampton, 1990; Barange et al ., 1999). Trawl samples, conducted to determine fish size and species composition, were pooled per stratum to obtain size compositions of the entire populations surveyed. Individual trawl length distributions were weighted according to the acoustically estimated biomass near the trawl. Weighted size frequencies were computed for all strata, then summed to produce a species size frequency for the area west and east of Cape Agulhas. These length frequencies were transformed into numbers-at-age through the use of a von Bertalanffy growth curve calculated from a combination of November survey and commercial landings data (D. Durholtz, MCM, pers. comm.). Data on the location, mass, and species composition of landed catches are collected by fisheries inspectors or monitors, or both, at designated landing points along the coast. Commercial catches are sampled at field stations next to the factories where most of the catch is landed for processing: data on species and size composition and biological characteristics have been collected routinely since 1953. Biological data collected include measure- ments of standard length, mass, sex, gonad mass, and macroscopic gonad maturity stage (Fairweather et al ., 2006). Individual landings are assigned a length frequency using the nearest (in space and time) sample length frequency, and catch length frequencies are raised according to their relative contribution to total catch to generate monthly and annual raised length frequency (RLF) tables. As for the survey data, RLF data were converted to numbers-at-age. Suggestions that sardine spawning is divided between two recruitment systems, with the west coast and WAB part of a west coast system and the remaining spawning areas part of an Agulhas Bank system (Lett et al ., 2006; Miller et al ., 2006), imply that a divi- sion of the continental shelf at Cape Agulhas to aid east–west comparisons is plausible (Figure 1). In this context, spatial stat- istics relating to survey distribution patterns, catch distributions, and biological indicators have been compared between the west coast and Agulhas Bank systems, respectively. To evaluate the extent of mixing between the two areas, a spatial overlap index (SOI) between the west coast and Agulhas Bank systems at different levels of sardine biomass was computed in a rectangle stretching along the shelf 120 nautical miles from 20 to 22 8 E (Cape Agulhas to Mossel Bay; Figure 1) and extending from the coast to the edge of the continental shelf. For each November survey, the proportion of positive elementary sampling distance units ( 10 nautical miles long), where the density of sardine was greater than zero and which were within this area, was calculated and plotted against the total population size in November. The surface area occupied by the sardine population during each survey was computed by projecting the contoured density surface onto a plane, then calculating the positive area of the projection in square nautical miles. The total biomass of sardine increased gradually from , 50 000 t in 1984 to some 2.5 million tonnes in 2000 (Figure 2), and although consecutive years of very good recruitment pushed the total biomass up to record levels above 4 million tonnes in 2002, a recent period of prolonged poor recruitment led to a decline in the adult biomass to , 500 000 t in 2007. Composite maps showing the distribution and relative abundance of sardine during periods of different biomass levels (low 1⁄4 0 –33.3 percentile; medium 1⁄4 33.3 –66.6 percentile; high 1⁄4 66.6 –100 percentile) are presented in Figure 3. The importance of the area west of Cape Agulhas, particularly the WAB but at times also farther up the west coast, as a preferred habitat during periods of low biomass is clear, with only low- density areas farther east (Figure 3a). At medium biomass levels, the WAB area remains the preferred area for sardine (Figure 3b), and the distribution there is expanded slightly north and south from that observed during periods of low biomass. The area occupied east of Cape Agulhas is also expanded significantly compared with that at low levels of biomass. At high biomass, the WAB remains important, but the area east of Cape Agulhas now sup- ports most of the sardine biomass (Figure 3c). A consistent separation is also evident (Figure 3) between sardine found west and east of Cape Agulhas, with overlap in the area (Cape Agulhas to Mossel Bay) between the two parts of the population only at very high levels of biomass. This is confirmed by the SOI (Figure 4), which shows an increasing presence of ...
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... Agulhas Bank (van der Lingen et al ., 2005). These include local depletion of fish stocks on the west coast and WAB following higher levels of exploitation in the west than in the east, environmentally induced changes in the distribution of sardine spawners, and the fact that the successful south coast spawning and recruit survivorship contributed disproportionately more towards the recruitment, with progeny spawned in that region now dominat- ing the population and exhibiting natal homing. The aim of this work is to evaluate the first of these hypotheses, which is related to fishing effort and local depletion, and to discuss the management implications of the sardine shift in distribution. Additionally, certain elements of the third hypothesis, which are linked to the first in terms of substock structure, and which may arise as a consequence of local depletion, are discussed. Two acoustic surveys have been conducted annually since 1984 to estimate the biomass and determine the distribution of small pelagic fish species off South Africa. The total biomass between Hondeklip Bay and Port Alfred is estimated in November each year, and recruitment is estimated in May between the Orange River and Cape Infanta, although recent surveys also extend to Port Alfred (Figure 1). Since 2000, survey effort towards the east has increased substantially during both surveys, as a result of a more easterly distribution of sardine and anchovy spawners. The surveys are conducted along a series of pre-stratified, randomly spaced, parallel transects, designed to obtain unbiased estimates of stock size and sampling variance (Jolly and Hampton, 1990; Barange et al ., 1999). Trawl samples, conducted to determine fish size and species composition, were pooled per stratum to obtain size compositions of the entire populations surveyed. Individual trawl length distributions were weighted according to the acoustically estimated biomass near the trawl. Weighted size frequencies were computed for all strata, then summed to produce a species size frequency for the area west and east of Cape Agulhas. These length frequencies were transformed into numbers-at-age through the use of a von Bertalanffy growth curve calculated from a combination of November survey and commercial landings data (D. Durholtz, MCM, pers. comm.). Data on the location, mass, and species composition of landed catches are collected by fisheries inspectors or monitors, or both, at designated landing points along the coast. Commercial catches are sampled at field stations next to the factories where most of the catch is landed for processing: data on species and size composition and biological characteristics have been collected routinely since 1953. Biological data collected include measure- ments of standard length, mass, sex, gonad mass, and macroscopic gonad maturity stage (Fairweather et al ., 2006). Individual landings are assigned a length frequency using the nearest (in space and time) sample length frequency, and catch length frequencies are raised according to their relative contribution to total catch to generate monthly and annual raised length frequency (RLF) tables. As for the survey data, RLF data were converted to numbers-at-age. Suggestions that sardine spawning is divided between two recruitment systems, with the west coast and WAB part of a west coast system and the remaining spawning areas part of an Agulhas Bank system (Lett et al ., 2006; Miller et al ., 2006), imply that a divi- sion of the continental shelf at Cape Agulhas to aid east–west comparisons is plausible (Figure 1). In this context, spatial stat- istics relating to survey distribution patterns, catch distributions, and biological indicators have been compared between the west coast and Agulhas Bank systems, respectively. To evaluate the extent of mixing between the two areas, a spatial overlap index (SOI) between the west coast and Agulhas Bank systems at different levels of sardine biomass was computed in a rectangle stretching along the shelf 120 nautical miles from 20 to 22 8 E (Cape Agulhas to Mossel Bay; Figure 1) and extending from the coast to the edge of the continental shelf. For each November survey, the proportion of positive elementary sampling distance units ( 10 nautical miles long), where the density of sardine was greater than zero and which were within this area, was calculated and plotted against the total population size in November. The surface area occupied by the sardine population during each survey was computed by projecting the contoured density surface onto a plane, then calculating the positive area of the projection in square nautical miles. The total biomass of sardine increased gradually from , 50 000 t in 1984 to some 2.5 million tonnes in 2000 (Figure 2), and although consecutive years of very good recruitment pushed the total biomass up to record levels above 4 million tonnes in 2002, a recent period of prolonged poor recruitment led to a decline in the adult biomass to , 500 000 t in 2007. Composite maps showing the distribution and relative abundance of sardine during periods of different biomass levels (low 1⁄4 0 –33.3 percentile; medium 1⁄4 33.3 –66.6 percentile; high 1⁄4 66.6 –100 percentile) are presented in Figure 3. The importance of the area west of Cape Agulhas, particularly the WAB but at times also farther up the west coast, as a preferred habitat during periods of low biomass is clear, with only low- density areas farther east (Figure 3a). At medium biomass levels, the WAB area remains the preferred area for sardine (Figure 3b), and the distribution there is expanded slightly north and south from that observed during periods of low biomass. The area occupied east of Cape Agulhas is also expanded significantly compared with that at low levels of biomass. At high biomass, the WAB remains important, but the area east of Cape Agulhas now sup- ports most of the sardine biomass (Figure 3c). A consistent separation is also evident (Figure 3) between sardine found west and east of Cape Agulhas, with overlap in the area (Cape Agulhas to Mossel Bay) between the two parts of the population only at very high levels of biomass. This is confirmed by the SOI (Figure 4), which shows an increasing presence of sardine in the overlap area between Cape Agulhas and Mossel Bay at higher levels of biomass. The increase in the total area occupied by sardine at higher biomass is also confirmed when calculating the area occupied by sardine as a function of biomass (Figure 5). Whereas the rate of increase was higher at low biomass ( , 1 million tonnes) than at high biomass, more variability in the area occupied at high biomass was evident than at low biomass. Further investigation into the changes in area occupied by the western and eastern parts of the population in relation to the biomass east and west of Agulhas revealed that the relationship between area and biomass was mostly driven by a rapid expansion of the area occupied by the eastern part of the population (Figure 6). Expansion of the area occupied by sardine in the western area was much slower in comparison, and the relationship between area occupied and biomass not as strong as for the area east of Cape Agulhas. ( r 2 1⁄4 0.48 and 0.83, respectively). Comparing the biomass east and west of Cape Agulhas (Figure 7), it is evident that the contribution of the biomass west of Cape Agulhas to total biomass was larger than that of the biomass east of Cape Agulhas before 1998. In 1999, a large increase in the biomass east of Cape Agulhas relative to that west of Cape Agulhas caused a shift in the relative distribution of sardine to the central and eastern Agulhas Bank. Further increases in the biomass of sardine east of Cape Agulhas after 1999 were mainly the result of the influx of a large number of 1-year-old sardine in 2001 and 2002, emanating from very successful west coast recruitment then. The distribution of fishing effort over the same period as the survey data reveals that as the biomass of sardine and hence the TAC increased, larger catches were taken mostly from the area west of Cape Agulhas (Figure 8). The quantity of sardine caught east of Cape Agulhas only increased from 2001, although remaining small compared with landings made to the west of Cape Agulhas until 2005, when for the first time since the start of the fishery, catches east of Cape Agulhas exceeded those made west of it. The relative exploitation level, i.e. the annual total catch as a proportion of biomass from the November survey in the previous year, east and west of Cape Agulhas shows a striking difference between the two areas (Figure 9). Although the overall exploitation rate for the total population averaged 11% of the biomass during the period 1987– 2007, the exploitation level west of Cape Agulhas increased substantially, particularly after 1999, and reached 44% in 2006. The exploitation level has only recently increased east of Cape Agulhas. Investigation of the age structure of the western and eastern part of the population from November data for ...
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... sardine ( Sardinops sagax ) is a major component of a valuable commercial, pelagic, purse-seine fishery that has been in operation since the 1940s off South Africa’s west coast (Figure 1; Crawford, 1980; Crawford et al ., 1987). Intensive exploitation during the first years of the fishery led to rapidly increasing annual catches through the 1950s, peaking at around 400 000 t in 1962. This high level of exploitation was unsustainable and preceded a massive decline in catches and the eventual collapse of the fishery by the late 1960s. Catches of sardine remained low during most of the 1970s, averaging 80 000 t annually, then decreased even further during the 1980s to some 40 000 t annually. However, following the initiation in 1983 of a fishery-independent programme of acoustic surveys to estimate pelagic fish abundance (Hampton, 1987, 1992; Barange et al ., 1999), a stock-rebuilding strategy, which included the setting and enforcement of an annual total allowable catch (TAC) based on the results of the surveys, was implemented during the mid-1980s. Subsequent recovery of the sardine stock to levels similar to those estimated before exploitation has been attributed in part to this conservative management policy (Cochrane et al ., 1998). Catches of sardine averaged . 200 000 t between 2001 and 2005 following a period of exceptional recruitment from 2001 to 2003. A prolonged period of poor recruitment since 2004 has led, however, to a rapid decline in sardine biomass and reduced catches since ...
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... distribution and migrations of South African sardine at different life stages is not well understood, but has been assumed to be similar to that of anchovy, for which patterns have been well established (Crawford, 1980; Crawford et al ., 1980; Shelton, 1986; Hampton, 1987; Hutchings et al ., 1998). Therefore, the spatial dynamics of sardine are assumed to be influenced by the same environmental and oceanographic drivers that influence the spatial dynamics of anchovy. The range of the South African sardine extends from southern Namibia, where the existence of an intense perennial upwelling cell off L ̈deritz forms a thermal barrier to exchange with the Namibian sardine population (Lett et al . 2007), to Richard’s Bay on South Africa’s northeast coast (Beckley and van der Lingen, 1999). Most of the adult biomass has been confined to the southern west coast and Agulhas Bank, as far east as Port Alfred ( Figure 1), during much of the period for which there are acoustic-survey results. However, whereas adult sardine have been concentrated mainly on the western Agulhas Bank (WAB) during their major spawning season in spring and late summer (Crawford, 1980; Crawford et al ., 1980; Shelton, 1986; Armstrong et al ., 1987, 1991; Hampton, 1992; van der Lingen and Huggett, 2003), shifts between predominantly west coast spawning and predominantly south coast spawning have been fre- quent in the past (van der Lingen et al ., 2001, 2006). This ability to spawn in both areas is because sardine are relatively unspecific in the selection of their spawning habitat (van der Lingen et al ., 2001; Twatwa et al ., 2005). Ichthyoplankton is transported west and north towards the west coast nursery ground by a jet current (Figure 1) associated with a strong thermal front between cold upwelled water and warmer oceanic water flowing north along the shelf edge of the Cape coast (Shelton and Hutchings, 1982; Nelson and Hutchings, 1987; Fowler and Boyd, 1998; Miller et al ., 2006). There is then a return migration of juveniles south along the west coast during late summer / early autumn, with recruitment to the adult population on the Agulhas Bank during autumn and winter (Hutchings, 1992; Hutchings et al ., 1998, 2002; Barange et al ., 1999). Although a significant number of sardine recruits have been observed at times on the south coast during annual recruitment surveys conducted in winter (Barange et al ., 1999; Beckley and van der Lingen, 1999), west coast recruitment remains dominant. A mechanism for south coast recruitment, which relies on local retention of eggs and larvae rather than transport to the west coast nursery ground, has recently been hypothesized (Lett et al ., 2006; Miller et al ., 2006), and it suggests that sardine may be able to optimize their reproductive strategy by spawning in either area, or sometimes in both (van der Lingen et al ., 2001; Miller et al ., 2006). Adult sardine are generally targeted for canning, although some juveniles are caught as bycatch in the anchovy recruitment fishery on the west coast. During the early years of the fishery, most fishing effort was concentrated on the west coast (Crawford, 1980; Barange et al ., 1999), where sardine were then abundant for most of the year, resulting in intensive development of infra- structure related to fish processing centred on the harbour at St Helena Bay (Figure 1). During the 1960s and 1970s, however, the fishing grounds for sardine expanded south and east as far as Cape Agulhas on the WAB (Crawford, 1980, 1981; Crawford et al ., 1987). More recently, there has been an increase in fishing effort farther east (van der Lingen et al ., 2005; Fairweather et al ., 2006), particularly near Mossel Bay, following a shift in the distribution of sardine eastwards. The area west of Cape Agulhas, which incorporates the west coast, the southwest coast, and the WAB, contained the bulk of the sardine biomass during the 1980s and early 1990s (Barange et al ., 1999). Although a gradual increase in the proportion of sardine biomass east of Cape Agulhas has been noted since 1995, most of the sardine were located on the WAB up to 1999, when for the first time since the acoustic surveys started, sardine biomass east of Cape Agulhas exceeded that to the west. This distribution pattern has persisted ever since and has had severe cost and logistical implications for the fishery and management of the stock, because of the mismatch between the locations of sardine schools and fish-processing facilities, as well as between fish abundance and fishing effort. Several hypotheses have been suggested to explain the change in the distribution of sardine from the WAB to the central ...
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... distribution and migrations of South African sardine at different life stages is not well understood, but has been assumed to be similar to that of anchovy, for which patterns have been well established (Crawford, 1980; Crawford et al ., 1980; Shelton, 1986; Hampton, 1987; Hutchings et al ., 1998). Therefore, the spatial dynamics of sardine are assumed to be influenced by the same environmental and oceanographic drivers that influence the spatial dynamics of anchovy. The range of the South African sardine extends from southern Namibia, where the existence of an intense perennial upwelling cell off L ̈deritz forms a thermal barrier to exchange with the Namibian sardine population (Lett et al . 2007), to Richard’s Bay on South Africa’s northeast coast (Beckley and van der Lingen, 1999). Most of the adult biomass has been confined to the southern west coast and Agulhas Bank, as far east as Port Alfred ( Figure 1), during much of the period for which there are acoustic-survey results. However, whereas adult sardine have been concentrated mainly on the western Agulhas Bank (WAB) during their major spawning season in spring and late summer (Crawford, 1980; Crawford et al ., 1980; Shelton, 1986; Armstrong et al ., 1987, 1991; Hampton, 1992; van der Lingen and Huggett, 2003), shifts between predominantly west coast spawning and predominantly south coast spawning have been fre- quent in the past (van der Lingen et al ., 2001, 2006). This ability to spawn in both areas is because sardine are relatively unspecific in the selection of their spawning habitat (van der Lingen et al ., 2001; Twatwa et al ., 2005). Ichthyoplankton is transported west and north towards the west coast nursery ground by a jet current (Figure 1) associated with a strong thermal front between cold upwelled water and warmer oceanic water flowing north along the shelf edge of the Cape coast (Shelton and Hutchings, 1982; Nelson and Hutchings, 1987; Fowler and Boyd, 1998; Miller et al ., 2006). There is then a return migration of juveniles south along the west coast during late summer / early autumn, with recruitment to the adult population on the Agulhas Bank during autumn and winter (Hutchings, 1992; Hutchings et al ., 1998, 2002; Barange et al ., 1999). Although a significant number of sardine recruits have been observed at times on the south coast during annual recruitment surveys conducted in winter (Barange et al ., 1999; Beckley and van der Lingen, 1999), west coast recruitment remains dominant. A mechanism for south coast recruitment, which relies on local retention of eggs and larvae rather than transport to the west coast nursery ground, has recently been hypothesized (Lett et al ., 2006; Miller et al ., 2006), and it suggests that sardine may be able to optimize their reproductive strategy by spawning in either area, or sometimes in both (van der Lingen et al ., 2001; Miller et al ., 2006). Adult sardine are generally targeted for canning, although some juveniles are caught as bycatch in the anchovy recruitment fishery on the west coast. During the early years of the fishery, most fishing effort was concentrated on the west coast (Crawford, 1980; Barange et al ., 1999), where sardine were then abundant for most of the year, resulting in intensive development of infra- structure related to fish processing centred on the harbour at St Helena Bay (Figure 1). During the 1960s and 1970s, however, the fishing grounds for sardine expanded south and east as far as Cape Agulhas on the WAB (Crawford, 1980, 1981; Crawford et al ., 1987). More recently, there has been an increase in fishing effort farther east (van der Lingen et al ., 2005; Fairweather et al ., 2006), particularly near Mossel Bay, following a shift in the distribution of sardine eastwards. The area west of Cape Agulhas, which incorporates the west coast, the southwest coast, and the WAB, contained the bulk of the sardine biomass during the 1980s and early 1990s (Barange et al ., 1999). Although a gradual increase in the proportion of sardine biomass east of Cape Agulhas has been noted since 1995, most of the sardine were located on the WAB up to 1999, when for the first time since the acoustic surveys started, sardine biomass east of Cape Agulhas exceeded that to the west. This distribution pattern has persisted ever since and has had severe cost and logistical implications for the fishery and management of the stock, because of the mismatch between the locations of sardine schools and fish-processing facilities, as well as between fish abundance and fishing effort. Several hypotheses have been suggested to explain the change in the distribution of sardine from the WAB to the central ...
Context 7
... distribution and migrations of South African sardine at different life stages is not well understood, but has been assumed to be similar to that of anchovy, for which patterns have been well established (Crawford, 1980; Crawford et al ., 1980; Shelton, 1986; Hampton, 1987; Hutchings et al ., 1998). Therefore, the spatial dynamics of sardine are assumed to be influenced by the same environmental and oceanographic drivers that influence the spatial dynamics of anchovy. The range of the South African sardine extends from southern Namibia, where the existence of an intense perennial upwelling cell off L ̈deritz forms a thermal barrier to exchange with the Namibian sardine population (Lett et al . 2007), to Richard’s Bay on South Africa’s northeast coast (Beckley and van der Lingen, 1999). Most of the adult biomass has been confined to the southern west coast and Agulhas Bank, as far east as Port Alfred ( Figure 1), during much of the period for which there are acoustic-survey results. However, whereas adult sardine have been concentrated mainly on the western Agulhas Bank (WAB) during their major spawning season in spring and late summer (Crawford, 1980; Crawford et al ., 1980; Shelton, 1986; Armstrong et al ., 1987, 1991; Hampton, 1992; van der Lingen and Huggett, 2003), shifts between predominantly west coast spawning and predominantly south coast spawning have been fre- quent in the past (van der Lingen et al ., 2001, 2006). This ability to spawn in both areas is because sardine are relatively unspecific in the selection of their spawning habitat (van der Lingen et al ., 2001; Twatwa et al ., 2005). Ichthyoplankton is transported west and north towards the west coast nursery ground by a jet current (Figure 1) associated with a strong thermal front between cold upwelled water and warmer oceanic water flowing north along the shelf edge of the Cape coast (Shelton and Hutchings, 1982; Nelson and Hutchings, 1987; Fowler and Boyd, 1998; Miller et al ., 2006). There is then a return migration of juveniles south along the west coast during late summer / early autumn, with recruitment to the adult population on the Agulhas Bank during autumn and winter (Hutchings, 1992; Hutchings et al ., 1998, 2002; Barange et al ., 1999). Although a significant number of sardine recruits have been observed at times on the south coast during annual recruitment surveys conducted in winter (Barange et al ., 1999; Beckley and van der Lingen, 1999), west coast recruitment remains dominant. A mechanism for south coast recruitment, which relies on local retention of eggs and larvae rather than transport to the west coast nursery ground, has recently been hypothesized (Lett et al ., 2006; Miller et al ., 2006), and it suggests that sardine may be able to optimize their reproductive strategy by spawning in either area, or sometimes in both (van der Lingen et al ., 2001; Miller et al ., 2006). Adult sardine are generally targeted for canning, although some juveniles are caught as bycatch in the anchovy recruitment fishery on the west coast. During the early years of the fishery, most fishing effort was concentrated on the west coast (Crawford, 1980; Barange et al ., 1999), where sardine were then abundant for most of the year, resulting in intensive development of infra- structure related to fish processing centred on the harbour at St Helena Bay (Figure 1). During the 1960s and 1970s, however, the fishing grounds for sardine expanded south and east as far as Cape Agulhas on the WAB (Crawford, 1980, 1981; Crawford et al ., 1987). More recently, there has been an increase in fishing effort farther east (van der Lingen et al ., 2005; Fairweather et al ., 2006), particularly near Mossel Bay, following a shift in the distribution of sardine eastwards. The area west of Cape Agulhas, which incorporates the west coast, the southwest coast, and the WAB, contained the bulk of the sardine biomass during the 1980s and early 1990s (Barange et al ., 1999). Although a gradual increase in the proportion of sardine biomass east of Cape Agulhas has been noted since 1995, most of the sardine were located on the WAB up to 1999, when for the first time since the acoustic surveys started, sardine biomass east of Cape Agulhas exceeded that to the west. This distribution pattern has persisted ever since and has had severe cost and logistical implications for the fishery and management of the stock, because of the mismatch between the locations of sardine schools and fish-processing facilities, as well as between fish abundance and fishing effort. Several hypotheses have been suggested to explain the change in the distribution of sardine from the WAB to the central ...
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Citations
... A large population that initially supported high catches collapsed in the early 1960s, recovered in the 1990s, increased again at a maximum in the early 2000s before declining rapidly once again thereafter in the mid-2000s such that the sardine population has remained low and depleted (Beckley and van der Lingen 1999;van der Lingen 2021). The significant decrease in sardine biomass in both the western and eastern segments of the population since [2004][2005] has been caused by an extended period of low recruitment and a sudden rise in adult mortality that cannot be attributed to fishing activities (Coetzee et al. 2008). Moreover, changes to sardine life history parameters, namely, length at 50% sexual maturity (L50), condition factor (CF) and standardised gonad mass (SGM), have occurred since the 1950s (Beckley and van der Lingen 1999). ...
... The study area ( Figure 1) was located within the southern Benguela and extends southwards from Orange River mouth on the west coast to the Agulhas Bank off the southwest coast of South Africa. The Cape Agulhas (20° E) ( Figure 1) is considered the boundary between the two stocks, and the movement of sardines of all ages is assumed to be exclusively from west to south coast (Coetzee et al. 2008). However, some eggs spawned on the south coast may be transported to the west coast nursery area and thus contribute to recruitment to the west coast (Coetzee et al. 2008). ...
... The Cape Agulhas (20° E) ( Figure 1) is considered the boundary between the two stocks, and the movement of sardines of all ages is assumed to be exclusively from west to south coast (Coetzee et al. 2008). However, some eggs spawned on the south coast may be transported to the west coast nursery area and thus contribute to recruitment to the west coast (Coetzee et al. 2008). ...
Sardine ( Sardinops sagax ) in the southern Benguela has shown substantial changes in population size over the past 70 years. Heavy fishing pressure in the 1950s to early 1970s caused the collapse of sardine stocks in South Africa. A fishery collapse happens because of significant alterations in the marine community, hindering the recovery of valuable commercial species and leading to cascading effects across multiple trophic levels in marine food webs. In this study, a robust 58‐year biochronology (1962–2019) was developed using archived sardine otoliths from the West of Cape Agulhas in South Africa. Sequential t ‐test analysis of regime shifts (STARS) performed on the biochronology of fish growth indicated four regimes with three alteration points in 1986, 2006 and 2015 that correspond with periods of low, high, average and low biomass, respectively; that is, high growth rates occurred during the high biomass period and vice versa. A series of mixed effects models was developed to determine increment width response to selected environmental, prey availability and sardine biomass factors based on the assumption that otolith increment growth is a proxy for somatic growth. Predicted sardine growth positively correlated with sardine biomass, sea surface temperature and copepod abundance estimates. This observation suggests that sardine population dynamics exhibit a depensation mechanism, potentially destabilizing populations after the fishery collapse. Sea surface temperature and copepod abundance have been primary factors influencing sardine growth, partly because of depensatory population dynamics. Furthermore, the study improves understanding of how different factors have affected sardine growth following the collapse of the sardine fishery.
... A key driver of the decline in the number of African penguins is regionally poor prey availability; there has been a substantial decrease in the regional biomass of sardine, which has remained low since 2007 (Coetzee et al. 2022a ) and has been recognized as a significant factor influencing African penguin survival (Robinson et al. 2015, Crawford et al. 2022 ). In addition, a spatial redistribution of sardine and to a lesser extent anchovy biomass, likely due to environmental changes in wind and upwelling patterns and disproportionate fishing pressure (Roy et al. 2007, Coetzee et al. 2008, occurred in the late 1990s and has persisted in recent years (Coetzee et al. 2022b ). In this context, competition for anchovy and sardine from the commercial purse-seine fishery (Sherley et al. 2018, Sydeman et al. 2021, which is the largest fishery by volume in South Africa (Hutchings et al. 2009 ), contributes to the overall lack of available food at crucial times during the penguin's lifecycle (Crawford et al. 2022 ). ...
The African penguin population has declined precipitously in recent decades, and if current rates of decline persist, this species could become extinct in the wild by 2035. Resource extraction of small pelagic fish prey by the purse-seine fishery around African penguin breeding colonies has been identified as a demographically meaningful threat to African penguins. Consequently, long-term, effective no-take zones around breeding colonies have been endorsed by an expert panel of scientists constituted by the South African government. Here, we consider the six largest South African penguin colonies that currently hold 76% of the global population. We evaluate the adequacy of different no-take zone options using a trade-off mechanism recommended by the expert panel. For all six colonies except Bird Island, Algoa Bay, which is subject to the least fishing pressure, the current no-take zone delineations are assessed as having little benefit to the African penguin and little to no cost to the purse-seine fishery. Four of the six current no-take zones include ≤50% of the African penguins' core foraging areas. Alternative no-take zones that approximate a more balanced trade-off offer more impactful alternatives to the current fisheries restrictions. Given the urgent need to implement evidence-based conservation interventions for the endangered African penguin, we recommend the substitution of the current no-take zones with those proposed herein.
... This limits the capacity to effectively evaluate whether the current management strategies, including spatial and temporal restrictions on both recreational and commercial fishing, are adequate and reflect the true spatial scale of the exploited stock(s) Smart et al., 2022;Elsdon and Gillanders, 2006). The misalignment of population dynamics and static management boundaries are recognised in other fish species and question the effectiveness of current management strategies (Reiss et al., 2009;Coetzee et al., 2008). Implementing a multi-marker approach may inform on population connectivity and therefore the appropriate management scale, enable improved stock assessment, help reduce estimation biases, and support development of strategies to better align management units with biological stocks (Berger et al., 2021;Kerr et al., 2017;Reiss et al., 2009). ...
... A key driver of the decline in the number of African penguins is regionally poor prey availability; there has been a substantial decrease in the regional biomass of sardine, which has remained low since 2007 (Coetzee et al. 2022a ) and has been recognized as a significant factor influencing African penguin survival (Robinson et al. 2015, Crawford et al. 2022 ). In addition, a spatial redistribution of sardine and to a lesser extent anchovy biomass, likely due to environmental changes in wind and upwelling patterns and disproportionate fishing pressure (Roy et al. 2007, Coetzee et al. 2008, occurred in the late 1990s and has persisted in recent years (Coetzee et al. 2022b ). In this context, competition for anchovy and sardine from the commercial purse-seine fishery (Sherley et al. 2018, Sydeman et al. 2021, which is the largest fishery by volume in South Africa (Hutchings et al. 2009 ), contributes to the overall lack of available food at crucial times during the penguin's lifecycle (Crawford et al. 2022 ). ...
The African penguin population has declined precipitously in recent decades, and if current rates of decline persist, this species could become extinct in the wild by 2035. Resource extraction of small pelagic fish prey by the purse-seine fishery around African penguin breeding colonies has been identified as a demographically meaningful threat to African penguins. Consequently, long-term, effective no-take zones around breeding colonies have been endorsed by an expert panel of scientists constituted by the South African govern- ment. Here, we consider the six largest South African penguin colonies that currently hold 76% of the global population. We evaluate the adequacy of different no-take zone options using a trade-off mechanism recommended by the expert panel. For all six colonies ex- cept Bird Island, Algoa Bay, which is subject to the least fishing pressure, the current no-take zone delineations are assessed as having little benefit to the African penguin and little to no cost to the purse-seine fishery. Four of the six current no-take zones include ≤50% of the African penguins’ core foraging areas. Alternative no-take zones that approximate a more balanced trade-off offer more impactful alternatives to the current fisheries restrictions. Given the urgent need to implement evidence-based conservation interventions for the endangered African penguin, we recommend the substitution of the current no-take zones with those proposed herein.
... While Roy et al. (2007) linked the shift in anchovy distribution to environmental variability, specifically to a decrease in temperature on the Agulhas Bank, van der Lingen (2021) noted the shift may not be linked to climate change, but rather to multi-decadal variability in wind. Coetzee et al. (2008) linked the sardine distribution shift to an increase in fishing pressure and a change in environmental conditions. Sub-stock and spatial structure of this sardine population (i.e. two sardine components, primarily separated by coast, with movement between them) further complicates our understanding of the mechanisms underlying the distributional shift (de Moor et al., 2017;Teske et al., 2021). ...
This study investigates the movement of sardine and anchovy between areas around South Africa, and its possible relationship with key environmental drivers using a Model of Intermediate Complexity for Ecosystems (MICE). This model includes biomass-based, age-and area-structured population dynamics for sardine and anchovy to account for these species' major life history migrations and links between environmental variables and fish movement. In addition to movement, the model accounts for growth, recruitment, natural and fishing mortality. The environment-linked models use sea surface temperature (SST) and an upwelling index for the southern Benguela and Agulhas Bank as drivers. SST and upwelling were selected because these have consistently been identified as potential drivers of the movement of anchovy and sardine in South Africa. Eight models were developed in this study, and models with and without links to environmental variables are compared. The model parameters were estimated by fitting to the hydro-acoustic survey recruit and total biomass data, daily egg production method estimates of anchovy spawning biomass, and sea surface temperature and primary production data from 1987 to 2014. These spatially disaggregated models adequately reproduced the historical anchovy and sardine recruit and adult biomass. The results found that the relationships estimated between anchovy movement and environmental variables were relatively stronger than those for sardine, especially for upwelling. However, none of the environment-linked models, which estimated a greater variability in the movement residuals, substantially improved the representation of the dynamics of these species in the southern Benguela and the fit to the survey indices of abundance. These MICE are intended for strategic purposes and inclusion of a link between the sardine and anchovy dynamics and environmental indices could be used as the basis for evaluating the impact of future climate changes on these populations under alternative fishing scenarios.
... Fishing activities have played a significant role in declines and/or spatial changes in several fish stocks, alongside changes in the physical environment on various scales (Hutchings et al. 2012, Blamey et al. 2015, Jarre et al. 2015b, Shannon et al. 2020. Specifically, the centre of catches of rock lobsters (Tarr et al. 1996, Blamey et al. 2012 ) and small pelagic fish species (van der Lingen et al. 2002, Fairweather et al. 2006, Coetzee et al. 2008 ) have shifted south-and eastward along the west and south coast of South Africa since the mid-1990s, coinciding with increased upwelling and increased productivity in the Agulhas Bank subsystem (as distinct from the Agulhas LME; Fig. 1 Scoping an Integrated Ecosystem Assessment for the southern Benguela: fisheries still biggest risk 3 introduction of management changes, including the enforcement of minimum mesh size and species quotas in 1972, the declaration of the 200 nautical mile EEZ in 1977, and more recently, the establishment and expansion of marine protected areas and the adoption of ecosystem-based approaches, has shaped the dynamics of fishing activities and their ecosystem impacts (NBA 2018, Cochrane et al. 2020, DFFE 2020. However, as for other marine ecosystems, disentangling the combined effects of climate and anthropogenic drivers is complex, necessitating interdisciplinary efforts (Shannon et al. 2008, Jarre et al. 2013, 2018. ...
... These intervals encompass critical periods of significant ecosystem change in the southern Benguela (Howard et al. 2007, Blamey et al. 2012, Shannon et al. 2020, despite relatively large inter-annual and decadal-scale variability (Hutchings et al. 2012, Lamont et al. 2018. Notably, two ecosystem regime shifts have been identified, the first arising from the collapse of the sardine stock and heavy depletion of hake stocks during the early to mid-1960s, attributed to increased catch efficiency by the fishing fleet (Howard et al. 2007, Jarre et al. 2013, and the second involving an eastward shift in species distributions in the mid-1990s to early 2000s, thought to be triggered by environmental changes with a potential interaction with fishing impacts (van der Lingen et al. 2002, Coetzee et al. 2008, Blamey et al. 2012, Jarre et al. 2015a ). Additionally, national regulations/acts pertaining to South African marine ecosystems have changed during this period, with more recent measures being more stringent and more focused on an ecosystem-wide approach to fisheries management ( Table 2 ). ...
... Note that ecosystem regime shifts occurred in the southern Benguela in the late 1950s/early 1960s (fishery-induced) and in the late 1990s/early 2000s (environmental induced but aggravated by fishing) (Howard et al. 2007, Coetzee et al. 2008, Blamey et al. 2012 ). ...
The southern Benguela ecosystem faces complex pressures from anthropogenic activities and climate change, leading to structural and functional changes. To counter ecosystem service losses, intergovernmental marine science organizations propose integrated management. However, predictions to evaluate alternative strategies are challenging due to multifaceted sector interactions affecting ecological components. Scoping phases of Integrated Ecosystem Assessments (IEA), such as the Options for Delivering Ecosystem-Based Marine Management (ODEMM), identify priority sectors and pressures for management using linkage chains and impact risk scores. This study expands a South African-wide ODEMM assessment to investigate dependent sectors in the southern Benguela. Fishing emerged as the primary sector, exhibiting high connectance and impact risk on ecological components. Disaggregation of the fishing sector into sub-sectors and over three 21-year time periods revealed the demersal trawl and mixed species inshore trawl sectors to still have the greatest impact despite recent mitigation efforts, driven by species extraction, bycatch, and ‘incidental loss’. Research gaps, such as the effects of recreational fisheries and underwater noise, were identified and need to be addressed to improve future ecosystem assessments. Additionally, the effects of climate on long-term, ecosystem-scale variability and change need more attention in IEAs and should be incorporated into frameworks such as ODEMM.
... Environmental changes on a broader landscape scale also potentially affect piscivorous waterbird abundances in the WLC. These include increases in the number and area of artificial wetlands, such as farm dams, which may provide new feeding and breeding opportunities (Froneman et al. 2001), as do the eastward displacement in the southern coastal waters of South Africa of some marine pelagic fish preyed upon by marine feeding cormorants (Coetzee et al. 2008;Roy et al. 2007). ...
... The increasing proportion of Cape Cormorants breeding on the South African south coast compared with the western coastline of southern Africa has been well-documented (Crawford et al. 2015 and follows the eastward displacement of their main prey species anchovy Engraulis encrasicolus and sardine Sardinops sagax (Coetzee et al. 2008(Coetzee et al. :1680Crawford et al. 2014:115;Roy et al. 2007:316). Cape Cormorant do not breed in significant numbers in close proximity to the WLC, and increases in abundances within these waterbodies occurs in winter months (mostly from June to September) and most likely consist of migratory nonbreeding individuals who use the lakes for fishing and resting. ...
... Van Deventer et al. 2019) and estuaries (eds. Van Niekerk et al. 2019) including the overutilisation of fish, changing pelagic fish stocks (Coetzee et al. 2008;Roy et al. 2007) and disturbances in remaining wetlands and breeding sites, requiring urgent attention at a regional and national scale. On a local scale http://www.koedoe.co.za ...
Estuarine waterbodies typically support diverse and abundant waterbird communities. However, global environmental degradation as a result of anthropogenic activities is leading to species level changes in biodiversity, with top predators such as piscivorous waterbirds being particularly vulnerable to ecosystem changes. The study aimed to document long-term spatial and temporal patterns of abundance of piscivorous and scavenging waterbirds in the Wilderness Lakes Complex (WLC) in the Garden Route National Park, South Africa, and where possible identify potential causes for observed trends. The abundance of waterbirds on these wetlands was determined biannually from 1992 to 2019, with counts conducted from a boat following a standardised route. Historical waterbird abundance data from the 1980s were also used to describe long-term abundance changes. Eight of the species exhibited seasonal variability in abundance with most, excluding Common Tern Sterna hirundo, being more abundant in winter. Substantial changes occurred in the abundance of several species over the four-decade study period, notably increases in Cape Cormorant Phalacrocorax capensis and Great Crested Grebe Podiceps cristatus, and decreases in Common Tern and Black-necked Grebe Podiceps nigricollis. Long-term abundance trends indicate a combination of declining, increasing, and stable populations. Although some species have undergone contrasting abundance changes on different waterbodies in the WLC the dominant pattern was a similar direction of change on most or all waterbodies and in different seasons. Local reasons for changes probably include loss of sandbanks, changing prey availability, and the absence of recreational disturbance on some waterbodies.Conservation implications: Drivers of changes in the abundances of piscivores are likely to be multifaceted, functioning on multiple spatial and temporal scales, and affecting different species in different ways. Recommended local corrective actions include managing emergent macrophyte encroachment on sandbanks, reducing recreational disturbance, managing processes affecting indigenous fish stocks, and protecting nesting sites.
... Cape gannets mainly feed on sardines (Sardinops sagax) and anchovies (Engraulis capensis; Batchelor and Ross 1984;Adams and Klages 1999). In the southern Benguela upwelling system, the spatial distribution of these two small pelagic fish species has shifted since the early 1990s while their stock dwindled as a result of climate change and overfishing (Coetzee et al. 2008). This has led to a spatiotemporal mismatch between the traditional feeding areas of Cape gannets breeding on the west coast of South Africa and their eastward-shifting prey base, with detrimental effects for adult body condition, chick growth rates, individual fitness and ultimately population dynamics (Cohen et al. 2014;Grémillet et al. 2016). ...
Senescence is the irreversible decline in physiological functioning and survival with age. While this phenomenon has been studied in a range of different taxa, including seabirds, it has seldom been assessed for both sexes of monomorphic species, and in conservation contexts. Here, we studied the effect of age and sex on the foraging trip characteristics and energetics of the monomorphic Cape gannet (Morus capensis). Between 2017 and 2020, we used GPS recorders and miniaturised three-dimensional accelerometers to obtain data on the foraging trip characteristics and energy expenditure of 39 Cape gannets rearing chicks on Malgas Island, South Africa. This sample included 11 females and 28 males between the ages of 4 and 23 years. No difference in foraging trip characteristics was apparent between sexes or individuals of different ages. The energy expenditure of aging females (> 17 years) was higher than that of aging males. Aging females spent both more energy flying and less energy resting than males, despite similar foraging trip durations and distances. Males spent more energy diving and taking off from the water than females. The age-related sexual differences in energy expenditure presented in our study might reflect niche and/or risk partitioning strategies to ensure adequate provisioning to the chick, or a possible earlier onset of senescence in females relative to males. The higher energy expenditure of aging females, which presumably requires a concomitantly higher energy intake, likely reduces their resilience to environmental change.
... While much is now known about C. agulhensis, there is scant information on the other copepod taxa that contribute to the Agulhas Bank community, including their distribution and abundance, and whether these have changed over time. Several studies have highlighted marked environmental or ecosystem changes on the Agulhas Bank over the past few decades, including the so-called 'eastward shift' of pelagic fish in 1996, with severe implications for top predators such as seabirds (Roy et al., 2007;Coetzee et al., 2008b;Crawford et al. 2008Crawford et al. , 2016Blamey et al., 2015;van der Lingen and Hampton, 2018). The question of whether there have been parallel changes in the lower trophic levels, in particular the zooplankton community, remains to be addressed. ...
... Since 1996, however, the bulk of anchovy spawners have been located east of Cape Agulhas, on the CAB and EAB (van der Lingen et al., 2006, 2006van der Lingen and Hampton, 2018. A more gradual, but similar, change was observed in sardine, with an increasing proportion of biomass observed east of Cape Agulhas since 1999 (Coetzee et al., 2008b). The eastward shift in sardine distribution has had significant ramifications for the ecosystem in general, and in particular for seabirds such as Cape gannets and African penguins that depend on sardine for prey (Blamey et al., 2015). ...
... Such changes are observed in many small pelagic stocks, such as the Cape anchovy (E. encrasicolus, Engraulidae), which abruptly shifted its distribution eastward in 1996 (Roy et al., 2007), or the South African sardine (S. sagax) that experienced a persistent shift in its distribution since 2001, increasing the distance between the fishing grounds and the processing facilities (Coetzee et al., 2008). These changes brought severe costs and logistical implications for the fisheries and management of the stocks. ...
We present a novel adaptation of the classic discrete delay‐difference model, a continuous delay‐differential model (cDDM), which can adequately represent population dynamics of stocks that turn over rapidly and continuously over time (e.g., small pelagic fish, small tunas, and shrimps). We used the Northern‐Central Peruvian anchoveta stock ( Engraulis ringens , Engraulidae) as a case study for implementing the cDDM and conducted a management strategy evaluation (MSE) through stochastic optimization in policy space (SOPS). Our results showed that cDDM integrated with SOPS efficiently searches optimum and near‐optimum harvest control rules (HCR) and is an alternative to pre‐setting arbitrary HCRs as in traditional MSE. The cDDM showed comparable stock biomass and recruitment estimate reconstructions to more complex stock assessment models described for anchoveta. We concluded that the anchoveta stock is sustainably managed and is an example of adaptive fisheries management under high ocean‐climate variability and uncertainty. Contrary to fishery textbooks, the anchoveta's collapse was not entirely due to the 1972 El Niño (EN) but a recruitment failure preceding EN. Our reconstructions revealed that low recruitment (or recruitment failure) could still occur at high stock biomass. Anchoveta's stock biomass is larger than pre‐collapse, likely due to favourable environmental conditions (a cooling trend) and management, despite more frequent and stronger EN events. SOPS quickly revealed that harvest strategies with large base biomass (>5 mmt) lead to higher interannual stock variability and would not produce substantial increases in long‐term yield. Alternative HCRs with lower base biomass, while adjusting for productivity regimes, have similar long‐term yields without affecting the long‐term average stock.
