Reproductive dynamics of an exploited serranid on the Great Barrier Reef

Samoilys, Melita Anne (2000) Reproductive dynamics of an exploited serranid on the Great Barrier Reef. PhD thesis, James Cook University.

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The reproductive output of exploited tropical reef fishes is intimately linked to factors such as mating patterns, sexual selection, sex ratios and reproductive success, because they affect an individual's fecundity and hence long term productivity. This information is critical to fisheries management, yet few studies have estimated annual fecundities and time schedules of egg production in exploited reef fishes. This study examines temporal and spatial patterns in egg production and spawning behaviour of an exploited serranid on the northern Great Barrier Reef.

Spatial patterns in the spawning behaviour of Plectropomus leopardus (coral trout) were examined by direct observations underwater at Scott and Elford Reefs for 3-4 years. A major (termed primary) spawning aggregation was located at each reef. These aggregations formed at the same sites each year, lasted for 5 days and formed around three consecutive new moons. Spawning occurred during a 33 min period spanning sunset. Maximum numbers of coral trout at these sites were 128 at Scott Reef, and 59 at Elford Reef. Smaller aggregations (termed secondary) were also located. Although their formation was inconsistent, their occurrence was also linked to the new moon phase.

The distribution and density of coral trout in a 6.5 km² area surrounding the primary site at Elford Reef was mapped using visual census surveys. Individuals were tagged within this area to estimate the catchment area of the aggregation site, and to track the movements of individuals to the site. The primary site was estimated to draw fish from a population of around 3,000 adults in an area of only 1.5 km², and it was estimated that around 14% of the population used the aggregation site to spawn. However, certain individuals showed high site fidelity, returning to the site on subsequent evenings within a new moon phase, on subsequent new moons within the season, and the following year.

Temporal patterns in egg production were determined from histological sections of gonads. Annual fecundity was estimated from counts of hydrated oocytes (batch fecundity) and from the proportion of females with post-ovulatory follicles (spawning frequency). The time schedule of hydrated oocytes was closely linked to lunar phase and time of day. Spawning occurred predominantly during the new moon and first quarter lunar phases at dusk. The average number of spawnings per female per year was estimated at 30, and annual fecundities of between 2.6 and 4.7 million eggs were obtained.

The results indicate that Plectropomus leopardus employs both aggregative and non-aggregative spawning. The high spawning frequency and range of mating mechanisms may maximise egg output. I suggest this flexibility in P. leopardus spawning strategies improves their resilience to exploitation.

Item ID: 27505
Item Type: Thesis (PhD)
Keywords: Plectropomus leopardus; spawning behaviour; site fidelity; spawning strategies; batch fecundity
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2: Samoilys, Melita A. (1997) Periodicity of spawning aggregations of coral trout Plectropomus leopardus (Pisces: Serranidae) on the northern Great Barrier Reef. Marine Ecology Progress Series, 160 . pp. 149-159.

Appendix I: Samoilys, Melita A. and Roelofs, Anthony, (2000) Defining the reproductive biology of a large serranid Plectropomus leopardus, CRC Reef Research Technical Report No. 31, CRC Reef Research Centre, Townsville, Qld.

Date Deposited: 20 Jun 2013 06:38
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 60%
05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050202 Conservation and Biodiversity @ 20%
05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050199 Ecological Applications not elsewhere classified @ 20%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 49%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 51%
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