José G. Pajuelo

Life history of the red porgy Pagrus pagrus (Teleostei: Sparidae) off the Canary Islands, central east Atlantic

Abstract Red porgy Pagrus pagrus (N = 1858) caught off the Canary Islands between May 1985 and April 1986 and between January 1991 and September 1993 were studied. Total length was in the range 4.7–57.2 cm. Females predominated at the smaller sizes and males at the larger sizes. Protogynous hermaphroditism was found. The overall ratio of males to females was 1:3.29. The reproductive period extended from December to May, with most gonadal activity between February and March. Fifty per cent maturity was reached at 22.6 cm total length by females and 26.7 cm by males. The length-weight relationship for all fish was described by the following parameters: a = 0.017947, b = 2.9583. Fish aged 0–14 years old were present in the samples. The von Bertalanffy growth parameters for all fish were L∞ = 63.96 cm, and k = 0.144 year−1. Mortality rates for all fish, estimated from a length-converted catch curve, were Z = 0.56 year−1, F = 0.24 year−1 with M = 0.32 year−1 derived from Paulys empirical formula. The exploitation rate was E = 0.43. Total length at first capture was 15.2 cm.

Life History of Black Seabream, Spondyliosoma cantharus, off the Canary Islands, Central-east Atlantic

Black seabream, Spondyliosoma cantharus, caught off the Canary Islands is characterized by a protogynous hermaphroditism. The size range of the catches is between 8 and 40 cm, with a main distribution between 16 and 24 cm. The mean length of the individuals shows an increase with increasing depth. Males:females ratio is unbalanced in favour of females (1:2.18). The reproductive season extends from late autumn to mid spring, with a peak in spawning activity in January–February. A dichromatism is found between males and females during the spawning season. Males reach maturity at a larger total length, 22.7 cm (3 years old), than females, 17.3 cm (2 years old). Morphometric relationship between length and mass for the whole population is described by the parameters: a=0.00732, and b=3.24747. Otoliths age readings indicate that the exploited population consists of eleven age groups (0–X years), including a very high proportion of individuals between 2 and 3 years old. The von Bertalanffy growth parameters for the whole population are: L∞=43.35 cm, k=0.24 year−1, and t0=−0.11 year. The rates of total, natural and fishing mortality are 1.36, 0.52 and 0.84 year−1, respectively. The length at first capture is 16.8 cm. The exploitation rate indicates that the stock is overfished.

On the Population Ecology of the Zebra Seabream Diplodus cervinus cervinus (Lowe 1838) from the Coasts of the Canarian archipelago, North West Africa

Zebra seabream, Diplodus cervinus cervinus, caught off the Canary Islands is characterized by protogynous hermaphroditism. The male : female ratio is in favour of females (1 : 2.16). The reproductive season extends from spring to summer, with a peak in spawning activity in May–June. Males reach maturity at a larger total length, 327 mm (5 years old) than females 273 mm (4 years old). Recruitment occurs from late October to January in shallow waters of 0.5–8 m depth along the coastal line. The recruits are located over rocky substrates with an important algae vegetation forming schools lower than 2 m2. During the spawning season, schools of adults from 3 to 8 fish are observed. The schools are formed by one large individual and a few moderate size individuals. Mating takes place in small groups formed by one dominant male and a group of several females (polygamy). Moderate size individuals are often observed mixed in large schools (up to 30 individuals) of Diplodus sargus cadenati. Subadults form groups of a few fish (<5 individuals) or more commonly mixed groups (>15 individuals) with individuals of species of similar size. Otoliths age readings indicate that the population consists of 18 age groups, including a very high proportion of individuals between 2 and 4 years old. The von Bertalanffy growth parameters for the whole population are: L∞ = 603 mm, k = 0.149 year−1, and t0 = −0.22 year. The mean rates of total, natural and fishing mortality are 0.551, 0.215 and 0.336 year−1, respectively. The length at first capture is 183 mm. The exploitation rate indicates that the stock is overfished. The direct effects of fishing on the population result in changes in the abundance, with a reduction to 85% of the unexploited equilibrium level. The length at first capture by the commercial fishery is less than the length at maturity. With 58% of the total catch below this length there is a danger of recruitment overfishing.

Aspects of the life history of the salema, Sarpa salpa (Pisces, Sparidae), off the Canarian Archipelago (central-east Atlantic)

Life history of the salema, Sarpa salpa, off the Canarian archipelago was studied from samples collected between January 1998 and December 1999. Fish ranged from 119 to 452 mm in total length and from 24.9 to 1491.7 g in weight. The species was characterized by a protandric hermaphroditism. The overall sex ratio was unbalanced in favour of males (1 : 0.41). The reproductive season extends from September to March, with a peak in spawning activity in December–January. Males reached maturity at a smaller length (226 mm, 2 years old) than females (294 mm, 3 years old). Males, females and all fish showed an isometric growth. The morphometric relationship between length and mass for the whole population was described by the parameters: a = 0.0000134 and b = 3.01. A concentric pattern of opaque and translucent zones was readily distinguishable on the otoliths. Two rings, one opaque and one translucent, were laid down each year on the otoliths; the opaque zone was formed during the summer months, and the translucent zone during the winter months. Individuals aged 0 to 11 years were found. The parameters of the von Bertalanffy growth equation for all individuals were: L∞ = 479 mm, k = 0.212 year−1, and t0 = −1.08 year.

Biology of the Sand Smelt, Atherina presbyter (Teleostei: Atherinidae), Off the Canary Islands (central-east Atlantic)

Atherina presbyter is a common fish off the Canary Islands. Age, growth, reproduction, and mortality of the species are studied based on sampling carried out from July 1995 to June 1996. The parameters of the total length–total weight relationship are: a=0.004521, and b=3.0771. Otoliths age readings indicate that the sampled population consists of four age groups (0–III years). The von Bertalanffy growth parameters for all individuals are: L∞=122 mm total length, k=0.79 year−1, and t0=−0.21 years. Individuals grow quickly in their immature first year, attaining approximately 60% of their maximum length. After the first year, the annual growth rate drops rapidly, because the energy is probably diverted to reproduction. It is a gonochoristic species with no evidence of sexual dimorphism. The gonad is present as a single diffuse testis in males and as a single discrete ovary in females. The overall ratio of males to females is not significantly different from 1:1. The reproductive period of the species is protacted (February to June). The peak of the reproductive effort occurs in April–May. The size at first maturity is 68 mm. The population is being heavily exploited.

Reproductive characteristics of the sand sole Pegusa lascaris (Soleidae), from the eastern-central Atlantic

The reproductive biology of 1318 sand sole, Pegusa lascaris, was investigated. This species is a gonochoristic species with no evidence of sexual dimorphism. The overall sex-ratio was i male to 0.92 females. Females predominate in the larger size intervals, with a significant difference in mean standard length and range between sexes. Size at first maturity for males and females is attained at 17.2 and 17.7 cm standard length, respectively. Vitellogenesis does not begin synchronously for all females, as a consequence the spawning season appears to be continuous. In each female spawning takes place in two batches which are spawned mainly in spring and autumn, indicating that fish are serial synchronous spawners.

Ovarian maturity, egg development, and offspring generation of the deep-water shrimp Plesionika edwardsii (Decapoda, Pandalidae) from three isolated populations in the eastern North Atlantic

ABSTRACT Ovarian maturity, egg development and brood size were analysed for three isolated populations (Madeira, the Canary Islands and Cape Verde Islands) of Plesionika edwardsii (Decapoda, Pandalidae) in the eastern Atlantic. Multiple colour patterns were observed at the same ovarian maturity stage, which was verified histologically, invalidating the extensive use of ovarian colour as a maturity stage criterion. The physiological size at sexual maturity, based on the maturity of the ovaries, was higher in Madeira (carapace length of 19.73 mm) and decreased to the Cape Verdes (16.39 mm). Synchronic ovarian maturation was observed during the embryo incubation process, and ovigerous females bearing embryos at the final stage of development were found throughout the year. Females are multiple spawners during the reproductive season, after which the reproductive process ends and a rest period begins. The absence of females larger than the size at sexual maturity with ovaries in Stage 1, the incubation of embryos in the final developmental stages, suggests that the resting period begins with a process that reabsorbs the energy located in the ovaries and that the resting period occurs asynchronously in females in each of the studied populations. Embryo size was independent of female body size in the three populations studied, but increased with the developmental stage. A power equation was used to describe the relationship between brood size and female body size in the three areas studied. The mean number of external Stage I embryos carried by females decreased from Madeira (n = 7868) to the Cape Verdes (n = 3781), where less energy, in terms of the number of embryos and the size of the eggs, was invested in reproduction. Although female size decreases from north to south, the egg number was higher in Madeira than in the Cape Verdes for the same size range.

Biological parameters of the roudi escolar Promethichthys prometheus (Pisces: Gempylidae) off the Canary Islands

Abstract Roudi escolar Promethichthys prometheus ( N = 221) caught off the Canary Islands from August 1992 to July 1993 were studied. The total length ranged between 42.1 and 78.9 cm. The overall ratio between males and females was 1:1.48. The spawning period extended from April to August, with a peak in July. Fifty per cent maturity was reached at 51.1 cm total length. The length-weight relationship was described for all the individuals by the following parameters: a = 0.004509, and b = 2.9705. Fish aged 3–10 years were present in the samples. The parameters of the Von Bertalanffy growth equation were: L ∞ = 84.32 cm, k = 0.20 year −1 , and t 0 = −0.51.

Perception of faunal circadian rhythms depends on sampling technique

Ecologists aim at disentangling how species vary in abundance through spatial and temporal scales, using a range of sampling techniques. Here, we investigated the circadian rhythm of seagrass-associated decapod crustaceans through three sampling techniques. Specifically, we compared the abundance, biomass and structure of seagrass-associated decapod assemblages between the day and night using a hand net, an airlift pump and baited traps. At night, the hand-net consistently collected a larger total abundance and biomass of decapods, what resulted in significant diel differences, which were detected for the total biomass, but not for the total abundance, when decapods were sampled through an airlift pump. Traps, however, collected a larger total abundance, but not total biomass, of decapods during the night. In summary, our perception of faunal diel rhythms is notably influence by the way organisms are sampled.