Reproductive biology, seasonality and distribution of Tenagomysis macropsis W. Tattersall, 1923 ( Crustacea, Mysidacea) in a New Zealand estuary

Size at maturity averaged 6.4-8.7 mm (TL) for males, 6.6-8.8 mm (TL) for females, and varied seasonally showing strong inverse correlation with temperature. Mean number of stage I young per brood was 11 (max. 25), the number and size of these being correlated with female body-size and therefore varying seasonally also. During winter the population contained a maximum percentage of large females producing maximum numbers of large embryos. Brood mortality approximates 20%. The sampled population was found in salinities averaging 4-30per mille with maximum numbers (64/m) in waters of 19per mille. Tolerance tests confirmed a salinity optimum in the vicinity of 20per mille but demonstrated broad euryhalinity. Population numbers were lowest during summer and early autumn, highest during late winter/spring. Data did not demonstrate a consistent seasonal population cycle, and it is suggested this was related to differing salinity regimes, recruitment rates, breeding aggregation and migration. There was a relatively up-estuary shift in distribution in spring, especially of adult females and to a less extent of juveniles. This may be part of a broader inshore- offshore migration pattern. Large sexually differentiated individuals dominated (90%) the winter population, the first sexually mature individuals having appeared in late autumn. Reproductive activity resulted in new recruitment by late winter which continued through summer and autumn. The population was dominated by juveniles during summer, by which time the overwintering adult cohort was lost. Females dominated the population, probably producing >1 brood per year, and having a longevity of one year. Early post-mating mortality of males is indicated. -from Author