Late Settlers Research Articles

Variations in settlement and growth of 0-group plaice ( Pleuronectes platessa L.) in the dutch wadden sea as determined by otolith microstructure analysis

Larval growth, date of settlement, and subsequent growth of 0-group plaice were compared in the eastern (Dollard) and western (Texel) parts of the Dutch Wadden Sea in autumn 1988. Daily increment analysis in otoliths with SEM showed that specimens sampled in the Texel region, and at 2 Dollard stations, hatched early in the season, had a shorter larval period (50 to 61 d) with high growth rates, and early settlement. All specimens caught at the other 6 stations hatched later, had a long larval phase (62 to 82 d) and settled later in the season. Estimates of maximum growth based on optimal feeding conditions and the prevailing water temperatures in both tidal basins were compared to the growth rates observed in the field. According to previous studies, plaice in the Texel region have optimal growth. All late settlers in the Dollard and part of the early settlers also had optimal growth. However, some early settlers in the Dollard had significantly lower growth rates than the batch of synchronously settled specimens from the Texel region.

Growth of the anemonefish Amphiprion clarkii in temperate waters, with special reference to the influence of settling time on the growth of 0-year olds

The temperate population of the tropical anemonefish Amphiprion clarkii has a seasonality of reproduction, larval settlement and growth. There was a considerable difference in size (15–47 mm) among 0-year olds in December, after the season of larval settlement and growth. This difference could be attributed mainly to a difference in the duration of the first growing season spent after settlement and a social inhibition of growth of the subordinate late settlers by frequent attacks by the dominant early settlers. The growth equation which was used to describe the growth of tagged individuals estimated that an anemonefish would get an opportunity to spawn within four of five years after settlement. Breeding adult pairs occupied almost all sea anemones essential to breeding within a 50×50 m study area, and all 17 new adults that matured from non-breeding juveniles to breeding adults between June 1983 and August 1985 were found in the territories from which either or both of the mated adults had disappeared. The new adults were large juveniles who had resided near those vacant territories before. These results suggest that the onset of breeding by an individual is not only determined by his age, but also by his ranking in the dominance hierarchy. Therefore, the difference in size among 0-year olds in December might give rise to the difference in age of the earliest breeding and might be a factor in making a female apply more reproductive effort at the beginning of the season.

Polygyny and the breeding success of the great reed warbler Acrocephalus arundinaceus

SummarySettlement date, mating status, and breeding success of individually marked great reed warblers, Acrocephalus arundinaceus, were studied during the 1980–84 breeding seasons in Kahokugata, Ishikawa Prefecture, Japan. Twenty‐five per cent of the territorial males were polygynous, of which the majority were bigamous. The settling periods of both sexes were long, extending for 65 days in males and 49 days in females. About 80% of males and females settled in the first half of the settling period, and the settlement date of 28–54% males overlapped with that of females. Many of the late settlers were bachelors and the males which mated earlier tended to be polygynous. The timing of a male's settlement is important in acquiring mates. Fifty‐five per cent of eggs laid were lost before fledging, mainly due to predation. The mean number of fledglings was 3.19 per primary female, 2.41 per secondary female, and 2.80 per monogamous female. Comparison of the number of fledglings of females which mated during the same period showed that the presence of another female in the same territory did not adversely affect the breeding success of either of the polygynous females. Polygynous males have the advantage of decreasing the risk of breeding failure under high predation pressure.