Movement of an exploited coral reef teleost across multiple temporal and spatial scales

Currey, Leanne Margaret (2015) Movement of an exploited coral reef teleost across multiple temporal and spatial scales. PhD thesis, James Cook University.

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Ensuring the sustainability of teleost populations is essential to the nutrition and livelihoods of many people supported by coral reef fisheries worldwide. The distribution and abundance of fish populations is defined by the movement of individuals, which occur on a range of spatial and temporal scales. Species-specific biological and ecological knowledge of reef fish movement is useful for parameterising species assessments and designing effective management strategies for exploited fish populations. For example, understanding whether target species are sedentary or mobile as adults can indicate the likelihood of management approaches such as spatial closures (e.g. marine protected areas; MPAs) or temporal closures (during spawning seasons) as successful management tools. Since ecological information is fundamental to the effective management of coral reef fisheries, a model species Lethrinus miniatus, was selected for investigation of movement patterns at multiple spatial and temporal scales. Limited and contradictory ecological evidence is available despite the exploitation of this species in reef fisheries worldwide, therefore this research aimed to gain a better understanding of L. miniatus spatial ecology for future sustainability of populations.

Understanding the scales at which movements of adult fishes occur and the factors that influence movement patterns is essential for the knowledge of species-specific spatial ecology. Literature analysis suggested that while body size was a poor predictor of space use, fishes characterised by a mobile predatory feeding strategy that use spatially separate habitats for feeding are more likely to have large activity spaces and move greater distances. Likewise, broad-scale movement was observed for fishes with a broadcast spawning mode that migrate to reproduce, and larger home ranges (extent of activity space) were facilitated by contiguous habitat. In combination, habitat connectivity, feeding strategy and reproductive mode were important for predicting movement patterns of fish across the mosaic of reef habitats, and provides a context within which research can focus efforts to assist with the design and implementation of effective management strategies.

Ratios of oxygen and carbon isotopes (δ¹⁸O and δ¹³C) in L. miniatus otolith carbonate were analysed to elucidate the probability of broad-scale movement on the Great Barrier Reef (GBR). Otolith core and edge portions were compared between and within 120 individuals from the same cohort to determine whether isotopically different environments were inhabited by juveniles and adults from different latitudes. Comparisons between and within individuals revealed that ratios of δ¹⁸O and δ¹³C increased with latitude and were generally higher in edge than in core portions. No difference in δ¹⁸O between core and edge portions for some individuals potentially signify self-recruitment to the area, or occupation of areas of similar chemistry. The majority of individuals from 19-22°S and almost half of individuals from 18°S displayed juvenile δ¹⁸O signatures characteristic of a warmer environment, suggesting movement to cooler environments or potential southerly migration of early life stages to adult habitat. In contrast, almost half of adult individuals in the most northern latitude (18°S) appeared to originate from cooler environments, suggesting movement to warmer environments or potential northward migration with ontogeny. These results infer movement of individuals occurred across different isotopic environments with life stage and were related to latitude, which will be important for delineating management units for this commercially important species.

Reef-scale presence, horizontal and vertical activity space use and movement patterns of 26 L. miniatus were identified using an array of acoustic receivers in the southern GBR. Half of the individuals were recorded only in proximity of one receiver, half were detected at multiple receivers and used horizontal areas of approximately 4 km² , and one individual was recaptured ~160 km from the release location. Periods of non detection and lower detection frequency at night indicated individuals may move away from the monitored reef edge to adjacent sandy habitat, but most movements outside the array remain unknown. Variation in movement among adult L. miniatus indicates that while some individuals undergo broader-scale movement, spatial closures that cover individual reefs (> 4 km² ) could provide protection from fishing for the proportion of the population that displayed high site fidelity and moderate-sized activity spaces (over a period of up to 12 months).

Variation in dispersal and movement patterns of coral reef fishes are likely linked to changes in environmental conditions. Monitoring in situ environmental parameters in conjunction with the movements of the acoustically adult tagged L. miniatus revealed their daily presence on the reef slope was influenced by water temperature. Individuals occurred more often on the reef slope during cooler temperatures suggesting a thermal tolerance threshold may exist. Results indicate that individuals responded to elevated temperatures by moving away from the reef slope to deeper adjacent habitats, thus shifting their position in the water column to remain at a preferred temperature. With elevation of ocean temperature, L. miniatus will need to adapt to warmer waters or disperse into cooler habitats, by either shifting their distribution deeper or towards higher latitudes. Identifying key environmental drivers that affect the distribution of reef fishes is important, and may allow managers to predict the effect of these changes on exploited species.

Reef-scale movements of L. miniatus suggested that adult individuals may use reef slope habitat during the day, shifting to adjacent deeper sandy habitat a night. Using a closely-positioned acoustic telemetry system, movements of 11 L. miniatus were monitored among habitats from the reef crest, to reef slope and deeper adjacent sandy habitat over three months. Fine-scale movement patterns among these habitats were compared among day: dawn, day, dusk and night periods. Larger vertical core and space use extent were used during dawn, dusk and night compared to during the day. Area of activity space extent within the water column and proportional overlap among areas used during different periods of the day varied among weeks, and displayed a pattern consistent with full moon periods. Increased luminosity during these periods may cause L. miniatus to utilise a larger search area for foraging, yet further research is required to confirm this finding. This fine-scale approach identified patterns in nocturnal activity that can be examined in other important reef teleosts, and knowledge of these temporal and spatial differences in L. miniatus behaviour and movement are important to understanding how this species coexists within ecological niches.

The components of this thesis provide insight into the movement patterns of an exploited coral reef fish, for which little spatial ecology information was available. Using multiple methods, movement patterns were investigated at a variety of spatial and temporal scales, revealing individual variability within the sampled population. This highlights that no single management strategy (e.g. MPAs) can provide complete protection from fishing for L. miniatus throughout life, nor against the potential effects of a changing climate. Methods used in this research can be applied to other coral reef teleosts of fishery importance, to assist management in designing strategies to exploit populations sustainably.

Item ID: 41290
Item Type: Thesis (PhD)
Keywords: adaption; bony fishes; broad-scale movement; catch-and-release; coral reef fishes; fin fish; fish; fisheries; Great Barrier Reef; habitat; Heron Island; home range; Lethrinus miniatus; migration; movement; One Tree Island; One Tree Reef; ontogeny; osteichthyes; post-release; spatial ecology; stable isotope chemistry; stress physiology; Sykes Reef; teleosts; wild caught
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 4: Currey, Leanne M., Heupel, Michelle R., Simpfendorfer, Colin A., and Williams, Ashley J. (2014) Inferring movement patterns of a coral reef fish using oxygen and carbon isotopes in otolith carbonate. Journal of Experimental Marine Biology and Ecology, 456. pp. 18-25.

Chapter 5: Currey, Leanne M., Heupel, Michelle R., Simpfendorfer, Colin A., and Williams, Ashley J. (2014) Sedentary or mobile? Variability in space and depth use of an exploited coral reef fish. Marine Biology, 161 (9). pp. 2155-2166.

Appendix A: Currey, L.M., Heupel, M.R., Simpfendorfer, C.A., and Clark, T.D. (2013) Blood lactate loads of redthroat emperor Lethrinus miniatus associated with angling stress and exhaustive exercise. Journal of Fish Biology, 83 (5). pp. 1401-1406.

Date Deposited: 01 Dec 2015 06:00
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060207 Population Ecology @ 34%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 33%
05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050209 Natural Resource Management @ 33%
SEO Codes: 83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8302 Fisheries - Wild Caught > 830204 Wild Caught Fin Fish (excl. Tuna) @ 34%
96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 33%
97 EXPANDING KNOWLEDGE > 970105 Expanding Knowledge in the Environmental Sciences @ 33%
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