Coherent patterns of abundance and size of a tropical snapper in dynamic estuary systems

• Published in: Wetlands ecology and management Vol. 9; no. 5; pp. 429 - 439
• Main Authors: Sheaves, Marcus, Molony, Brett
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Nature B.V 01.10.2001
• Subjects: Aquatic reptiles; Brackish; Cattle; Creeks; Creeks & streams; Estuaries; Lutjanus russelli; Marine; Mortality; Rainy season
• ISSN: 0923-4861; 1572-9834
• DOI: 10.1023/A:1012066107807

Although tropical estuaries are important juvenile habitats for the snapper, Lutjanus russelli, the extent of this utilisation, and relationships to physical variation are unknown. We used fish trapsto investigate spatial and temporal patterns of distribution, abundance and size of L. russelli within and between three tropical estuaries (Cattle, Barramundi and Alligator Creeks) over a two year period. L. russelli showed no indication of spatial segregation by size along the lengths of the estauries. The probability of capturing L. russelli was similar throughout Barramundi Creek and the seaward parts of Cattle Creek. However, the probability of capture fell markedly in upstream regions of Cattle Creek. These areas where characterised by depressed salinity levels due to seasonal flooding. High probabilities of capture of L. russelli during the wet and post-wet seasons in the whole of Barramundi Creek correlated with the time of smallest modal sizes. Thisreflected the entry of large numbers of small recruits into the trappable population. Temporal patterns in mean length were consistent for both years. The major feature of the size data was a clear pattern of seasonal change in the mean fork length of L. russelli, with largest mean sizes occurring in the pre-wet and the smallest mean sizes in the wet and post-wet seasons. This pattern probably reflected the interaction of four processes; the entry of new recruits into the trappable population, growth and mortality during residence in the estuarine nursery habitats, and migration of large fish away from the estuaries. The three creeks studied provided L. russelli with a harsh and extremely variable environment. Over the three creeks, salinities ranged from extremely hyposaline (0[per thousand]) to very hypersaline (55.5[per thousand]) and varied up to 39[per thousand] within a location. However, despite the substantial physical differences and the spatial separation of the three estuaries, the patterns of temporal change were clear and consistent. Overall, the annual pattern of change insize seemed to relate more to biological processes of recruitment, mortality and migration than to responses to physical variability.[PUBLICATION ABSTRACT]