Capensis Off Research Articles

Life-history parameters of adult females of Merluccius capensis (Gadidae) off the south coast of South Africa.

This study explores the life-history parameters of female Merluccius capensis off South Africa (N = 1819) during 2014-2016, including gonadosomatic index (GSI), length-at-maturity, length-weight relationships, and condition indices (relative condition [k] and Fulton's condition factor [K]). We detected weak indications of two peaks of spawning within the year, the first in austral autumn from March to May, whereas the other in austral spring around August. GSI was slightly higher in spring and autumn, though still low at all maturity stages (≤7%), though the opposite was true for the actively spawning stage (≥7%) as well as access to less such data during winter- and summertime. The length (L) at 50% maturity was around 38 cm (L50), though differences occurred between the two applied staging methods, histology and visual (macroscopic) classification, when L approached infinity. The latter method presented underestimated length at maturity values at the 75 and 95 percentiles (48 and 60 cm) compared to the corresponding percentiles given by histology (50 and 65 cm). There were trivial across-method differences in L50. However, we found a clear reduction in L50 in view of published information in prior years when this estimate was 48 (1985), 42 (2008), 53 (2011), and 24.8 (2015) cm. Overall, L explained 90% of the variation in whole body weight (W). As the bootstrapped, grand mean growth coefficient was b = 2.98, indicating a slight allometric growth function, there were no significant variations between years, though an isometric growth existed for 2016 with b = 3.0, whereas for 2014 and 2015 this b was 2.98 and 2.93, respectively. In terms of demography, females <60 cm generally showed isometric growth (b = 3) as opposed to allometric growth (b = 2.95) at >60 cm. The relative condition index (k = 1) exhibited higher values than Fulton's K, which was 0.80. Overall, the maternal stock of M. capensis along the south coast seems to be in good condition and likely spawns throughout the year, but we found that the macroscopic data tend to give biased maturity ogives.

Precautionary design of a marine protected area based on a habitat model

A basic principle of effective resource management is that decisions should be con- servative in the face of uncertainty. Due to limited data, there is often considerable uncertainty about species' habitat relationships and requirements. If the boundaries of a protected area are based on relationships estimated by a habitat model, effective management takes the uncertainty into account. The inclusion of uncertainty in the design of a hypothetical marine protected area is described for a coastal population of the long-beaked common dolphin Delphinus capensis off Baja California, Mexico. Line-transect and depth data were combined in a hierarchical Bayesian model. Two possible management goals were considered: protecting 100 000 animals or protect- ing 60% of the population. A precautionary approach was adopted, meaning that the manage- ment goal should be met with a high probability. The model estimated that a seaward boundary at 360 m would include 100 000 dolphins with a probability of 0.9. A conventional but less precau- tionary 'best estimate' boundary at 160 m would meet the management goal with a probability of 0.5. For the second goal of including 60% of the population, the precautionary and non-precau- tionary depths were 210 and 170 m, respectively. Habitat models are useful for management, but management decisions based on such models should consider the uncertainty inherent in estimat- ing parameters from data. Models which include the data observation process can improve infer- ence about habitat relationships.

Assessment and management of Cape horse mackerel Trachurus capensis off Namibia based on a fleet-disaggregated age-structured production model

The Cape horse mackerel stock off Namibia is assessed using a fleet-disaggregated age-structured production model including historical International Commission for the Southeast Atlantic Fisheries (ICSEAF) and current data. Data from acoustic biomass surveys, on commercial catch per unit effort and on commercial catch-at-age, were used to estimate current stock status over a range of model specifications. A management tool, the so-called management monitor graph, was introduced in order to track past management relative to stock status. Target, limit and precautionary reference points, decision rules and harvesting strategies, according to which the stock should be managed, are described and tested. The target reference point was set at maximum sustainable yield (MSY), the precautionary reference point at 80% of MSY and the limit reference point at 30% of MSY. Owing to some inconsistencies in the dataseries, evaluation of the current state of the resource is challenging, but estimates are that the resource is around the MSY level, somewhere between 250 000 and 300 000 t.

Estimating the probability of different levels of recruitment for Cape hakes Merluccius capensis off Namibia, using environmental indices

This paper describes the use of multinomial logistic regression analysis to calculate the probability of strong, average or weak recruitment of Cape hake ( Merluccius capensis). The model includes environmental indices, describing the extent of warm-water intrusion as well as the upwelling strength for different areas and periods over 2 years—from spawning until the fish are approximately 2 years of age. One of the warm-water indices as well as two of the upwelling indices have significant influences on the recruitment strength and these indices are included in the model. The rationale for using these indices is that if warm water is widespread during the spawning period (September–March) and the upwelling during the following May–September is reduced, the eggs spawned would be retained in favorable nursery areas which may result in potentially strong recruitment. If the upwelling during May–September of the following year produces sufficient food for the late juvenile hake, the chances of strong recruitment will be increased. The results indicate that the model accounts for 79% of the variance in recruitment.

Influence of Host Size and Sex on the Endohelminth Infracommunities of the Red Rockfish Sebastes capensis off Northern Chile

Influence of Host Size and Sex on the Endohelminth Infracommunities of the Red Rockfish Sebastes capensis off Northern Chile

Factors influencing growth of the African penguin colony at Boulders, South Africa, 1985–1999

This paper reports on growth of the Boulders colony of African penguins Spheniscus demersus from inception in 1985 to the present. More than 900 pairs now breed there. Growth of the colony slowed in 1995 and 1996 and reversed in 1998, coinciding with periods of low abundance of Cape anchovy Engraulis capensis off South Africa. In December 1996, penguins were excluded from a portion of land where they had formerly bred. They responded by increasing the density of their nests in other areas and expanding their area of breeding longshore. These patterns indicate that food and not space are currently controlling colony growth rate. Much of the colony growth probably results from immigration of first-time breeders from other colonies. Of immigrants, 70–80% may be from Dyer Island to the south-east, where numbers of penguins have decreased. Boulders also is frequently visited by penguins from other colonies, and by rehabilitated birds.

Influence of host size and sex on the endohelminth infracommunities of the red rockfish Sebastes capensis off Northern Chile.

The relationship between host size and sex and the abundance, prevalence, species richness, diversity, and total number of parasites in the infracommunities of Sebastes capensis was analyzed. Nine helminth species were obtained from 180 red rockfish captured off Coquimbo Bay, Northern Chile. These included the digeneans Pseudopecoelus sp., Diphtherostomum sp., Derogenes sp., Podocotyloides sp., and Lecithochirium sp., the acanthocephalan Corynosoma sp., and the nematodes Ascarophis sebastodis, Hysterothylacium sp., and Anisakis sp. The abundances of Pseudopecoelus sp. and Anisakis sp. were significantly and positively correlated with the size of S. capensis, while Corynosoma sp. correlated negatively with host size. Only prevalence of Anisakis sp. increased with host size. The number of parasite individuals increased significantly with size of S. capensis. However, species richness and diversity of the infracommunities was not affected by host size. These results suggest that red rockfish > 18 cm do not undergo significant ontogenetic changes in their diet. Host sex did not seem to affect abundance and prevalence of infections. The presence of Derogenes sp. and Podocotyloides sp. are new records of digeneans for S. capensis.

Metazoan Parasites of the Red Rockfish Sebastes capensis off Northern Chile

The parasites of the red rockfish Sebastes capensis off northern Chile are described quantitatively for the first time and compared with those of congeneric species of the Northern Hemisphere as well as of other Chilean marine fishes. Sixteen species were recorded, including 8 ectoparasites (2 copepods, 2 isopods, 1 turbellarian, and 3 monogeneans) and 8 endoparasites (2 acanthocephalans, 3 digeneans, and 3 nematodes). The ectoparasites Lepeophtheirus chilensis and Caligus cheilodactylus, and the endoparasites Pseudopecoelus sp. and Corynosoma sp. were predominant. Eighty percent of the fishes harbored 3-6 parasite species. Four parasite genera new to the genus Sebastes were found in S. capensis, which also shares several parasite genera with its congeneric species from other geographic areas. However, in contrast to its congeners, S. capensis exhibits a lower helminth species richness, although when all the metazoan fauna is considered the species number and diversity are similar. When compared with other demersal fishes of the Chilean coast, S. capensis shows a high number of species and high parasite abundance. Diphtherostomum sp. and Gnathia sp. are new generic records for the parasite fauna of Chilean coast fishes and the finding of Paramicrocotyle sp., Neobenedenia melleni, and Interniloculus chilensis in this study represents a new geographical record for these parasites.

Responses by four seabird species to a fluctuating availability of Cape Anchovy Engraulis capensis off South Africa

In recent years, Cape Anchovy Engraulis capensis has been the most important food for four seabirds breeding in South Africa–African Penguin Spheniscus demersus, Cape Gannet Morus capensis, Cape Cormorant Phalacrocorax capensis and Swift Tern Sterna bergii. Between 1984 and 1992, biomass of spawning anchovy fluctuated between about 0.5 and 1.75 million tons. Abundance of anchovy was significantly related to numbers of chicks fledged by African Penguins, occurrence of anchovy in the diet of Cape Gannets and numbers of Cape Cormorants and Swift Terns that attempted to breed. Numbers of African Penguins and Cape Gannets that attempted breeding probably also were influenced by abundance of anchovy. African Penguins and Cape Cormorants abandoned nests when anchovy were scarce and deferred breeding until anchovy became more plentiful. Survival of immature African Penguins in a period of anchovy scarcity was enhanced by availability of South African Sardine Sardinops sagax as an alternative food. When anchovy abundance was low, Cape Gannets fed on sardine.

"Predation" of anchovy by an Agulhas ring: a possible contributory cause of the very poor year-class of 1989

There was a marked decrease in abundance of anchovy Engraulis capensis off South Africa between November 1988 and November 1990 caused by formation of poor year-classes in 1989 and 1990. The percentage of anchovy in the diet of Cape gannets Morus capensis indicated that the most marked decrease in anchovy biomass was between June and July 1989. A filament from the Benguela upwelling front was in the process of being entrained by a passing ring of Agulhas Current water at that time. The ring extracted a large volume of frontal water over a period of 2–3 months, prevented its return to the shelf region and possibly removed anchovy larvae and pre-recruits from the Benguela system. It may have played a role in depressing the 1989 anchovy year-class, and hence the 1989 recruit biomass.

Top predators in the Benguela ecosystem — implications of their trophic position

Many top predators in the Benguela ecosystem feed on prey species targeted by commercial fisheries. Their roles as indicators of the state of exploited prey resources, as competitors with commercial fisheries for resources, and as susceptible to impact from commercial fishing on those resources are briefly considered. Trends in the occurrence of anchovy Engraulis capensis and pilchard Sardinops ocellatus in the diet of Cape gannets Morus capensis off South Africa's west coast are related significantly to survey estimates of the abundance of these fish species, and they provide useful confirmation of those estimates. In the 1980s, anchovy decreased in the diet of Cape gannets, but pilchard increased. In both the northern and southern portions of the Benguela system, groundfish were thought to eat most (66–73%) of the total quantity of cephalopods and vertebrates consumed by predators and man in the 1980s. South African fur seals Arctocephalus pusillus pusillus, predatory pelagic fish and man removed roughl...

Growth of Cape hakeMerluccius capensisoff Namibia determined by means of length frequency analysis and age/length data

Growth of Cape hake Merluccius capensis off Namibia is determined by means of length frequency analysis and age/length information. A time-series of length frequencies collected during 1987 was used for the analysis together with age data collected concomitantly. Estimated growth fluctuated seasonally, the minimum growth rate being in autumn. Application of age data in the analyses notably improved the fit of the growth curve. The results are similar to published estimates of Cape hake growth.

Anchovy distribution off Namibia deduced from acoustic surveys with an interpretation of migration by adults and recruits

Qualitative acoustic surveys of the anchovy Engraulis capensis off Namibia were undertaken between 1978/79 and 1985. Near-monthly maps of shoal distribution are presented for each year which covered the summer spawning and the winter feeding seasons. Distribution densities are ranked according to three selected grades. The data are discussed in relation to the oceanography of the region as well as to previously documented spawning and larval distributions. Conclusions are drawn which may help in understanding the migration patterns of anchovy off Namibia. Adults occupy winter feeding grounds in the north and move out to the spawning grounds between the Cunene River and Hollams Bird Island in summer. Post-larvae are transported passively to the nursery areas where they feed and develop. Juveniles move north in autumn to the preferred feeding grounds around Walvis Bay, where they enter the fishery as recruits in winter. At the end of winter, they join the adults in the north. The inferred pattern would be a...