Title

Development and distribution of Nematalosa Vlaminghi (Perth herring) eggs and larvae within an estuary

Date of Award

2015

Degree Type

Thesis

Degree Name

Master of Science (Environmental Management)

School

School of Natural Sciences

Faculty

Faculty of Health, Engineering and Science

First Advisor

Associate Professor Glenn Hyndes

Second Advisor

Dr Kim Smith

Abstract

Nematalosa vlaminghi (Perth herring) is an endemic, semi-anadromous fish species in estuaries on the lower west coast of Australia. It is known to spawn in the upper reaches of estuaries, which are prone to changing salinity profiles, stratification levels and water temperature, that are being altered through human disturbances and climate change. The aim of this study was to describe the development of eggs and larvae of N. vlaminghi and determine their distributions in the Upper Swan Estuary in relation to salinity, temperature and salinity stratification during January-February 2013 and December 2013-January 2014. Throughout both sampling periods, 240 samples from 40 sites were collected from within the Upper Swan Estuary, an area of ~16 km, 31 km upstream from the estuary mouth.

N. vlaminghi eggs are pelagic, spherical, 0.98-1.58 mm in diameter, semi-opaque to transparent, with a moderate yolk and one to three indistinct oil globules. Egg development stages identified included eggs at fertilisation, gastrulation, neuralation and late organogenesis. The early stage N. vlaminghi larvae (1.78-3.87 mm) are very elongate with a large residual yolksac, possess unpigmented embryonic eyes and lack a functional mouth. Early N. vlaminghi larvae rapidly developed pigmented embryonic eyes and a functional mouth. A. caudavittata eggs are pelagic spherical, 0.56-0.86 mm in diameter, transparent, with moderate yolk and a moderate distinct oil globule. A. caudavittata eggs were only found at embryogenesis milestones. Early stage A. caudavittata larvae (1.46-2.49 mm) are elongate with a moderate residual yolksac, possessing slightly pigmented eyes and a partially-formed functional mouth.

Diel and depth differences in the distributions of eggs suggested that eggs were released in sub-surface waters at night and then floated to the surface before sinking to sub-surface waters prior to hatching during the day. Larvae were found mainly in sub-surface waters. Eggs and larvae were collected from ~36 to ~46 km from the estuary mouth, which was linked with salinities between ~8-19 PSU and a stratification index less than 1.5. The abundances of N. vlaminghi eggs and larvae were positively correlated with salinity and negatively correlated with stratification. The distribution of eggs was more restricted than that of the larvae, which was attributed to the development and morphology of the larvae. Historically, the downstream limit of N. vlaminghi larvae was 26 compared to 36 km from the estuary mouth. The 10 km reduction of the distribution range in the current study is likely to be attributed to changes to the riverine flow [9.4 x 108 m3 (1999) vs. 1.15 x 108 m3 (2006)] and salinity levels in the Upper Swan Estuary. This may increase egg and larval densities in the region, which could increase in mortality levels of these early life history stages and reduce recruitment of N. vlaminghi into the adult population.

LCSH Subject Headings

Nematalosa vlaminghi.

Amniataba caudavittata.

Estuarine ecology -- Western Australia -- Swan River Estuary.

Fishes -- Eggs -- Western Australia -- Swan River Estuary -- Geographical distribution.

Fishes -- Larvae -- Western Australia -- Swan River Estuary -- Geographical distribution.

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