Reproduction in Euphausiacea

In the group Euphausiacea, females either retain mature eggs in a brood pouch until they hatch, or release the eggs directly into the water column. All the species currently being commercially harvested, however, are broadcast spawners (Nicol & Endo, 1997). The focus of our discussion of the reproduction patterns and strategies of euphausiids is on those species that are of commercial interest, e.g. Thysanoessa inermis, T. raschii, M eganyctiphanes norvegica, Euphausia pacifica, E. nan a and E. superba. However, we assume that certain reproductive characteristics are common to the entire taxonomic group. Our understanding of the reproductive cycle will be enhanced by including studies of non-harvested species, e.g. E. lucens, Nyctiphanes australis, N. couchii and four additional Antarctic species, E. crystallorophias, T. macrura, E. frigida and E. triacantha. The emphasis in this chapter is on reproductive patterns and population fecundity in euphausiids. Both are critical to our understanding of the pattern and level of fishing effort a population can withstand over the long term. Reproductive patterns include topics such as age and size at first spawning, initiation and duration of the spawning season, and the distribution of spawning populations. Oocyte maturation and the use of sexual development stages to identify seasonal patterns of ovarian development are emphasised. We address also the topics of mUltiple spawning, batch size, and embryo size. The implications of these reproductive characteristics and strategies for fisheries management are briefly discussed.