The short- & long-term implications of marine reserves for fisheries on coral reefs

Hopf, Jessica Kay (2016) The short- & long-term implications of marine reserves for fisheries on coral reefs. PhD thesis, James Cook University.

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Abstract

Reserves are a popular tool in managing marine systems, and have wellestablished conservation benefits. However, since they are nearly always established in areas accessed by fishers, their impacts on fisheries are contentious. Reserve-fishery theory suggests that reserve implementation will often be a sub-optimal fisheries management action, while the observed level of biomass build-up within reserves is argued sufficient to compensate for the loss of fishable habitat. In this thesis, I have furthered our understanding of the impact of marine reserves on fisheries by addressing key knowledge gaps that have previously hampered our ability to link outcomes predicted from fishery-reserve theory with changes observed after reserve establishment.

Firstly, I examined the transient impacts of reserve establishment on fisheries and fished metapopulations. I considered a well-mixed larval pool model and a spatially explicit model based on coral trout (an important fishery species; Plectropomus spp.) metapopulation in the Great Barrier Reef Marine Park (GBRMP), Australia. I also symbolically explored a simplified, pseudo-spatial, age-unstructured model to elucidate the demographic mechanisms behind my results. When fishing pressure was reallocated relative to the area protected, yields decreased initially, then recovered, and ultimately exceeded pre-reserve levels. However, recovery time was on the order of several years to decades. If fishing pressure intensified to maintain pre-reserve yields, reserves were sometimes unable to support the increased mortality and the metapopulation collapsed. This was more likely when reserves were small, or located peripherally within the metapopulation. Overall, I found that reserves can achieve positive conservation and fishery benefits, but direct effort controls complementary to reserve implementation is essential.

Secondly, I tested a metapopulation model against observed fishery and population data for the coral trout in the GBRMP to evaluate how the combined increase in reserve area and reduction in fishing effort in 2004 influenced changes in fish stocks and the commercial fishery. I found that declines in catch, increases in catch rates, and increases in biomass observed since 2004 were substantially attributable to the integration of direct effort controls with the rezoning, rather than the rezoning alone. The combined management approach was estimated to have been more productive for fish and fisheries than if the rezoning had occurred alone, and comparable to what would have been obtained with effort controls alone. My sensitivity analyses also indicated that the direct effort controls prevented initial decreases in catch per unit effort that would have otherwise occurred with the rezoning. My findings demonstrate that, by concurrently restructuring the fishery, the conservation benefits of reserves were enhanced and the fishery cost of rezoning the reserve network was socialised, mitigating negative impacts on individual fishers.

Lastly, I evaluated the effects that reserves can have on fisheries subject to environmental disturbances. I found that they can be beneficial, reducing the magnitude of temporal fluctuations in yields and biomass, and extending the time to disturbancedriven collapse. This was true whether the fishery was heavily exploited and reserves increased average yields, or moderately exploited and reserves decreased average yields. Appling my model to a disturbed coral trout metapopulation across a small reserve network in the GBRMP, I find that protecting a mix of disturbed and non-disturbed reefs consistently provided stability for both fish populations and fishery catches, under a range of dispersal and reserve coverage scenarios. Furthermore, more centralised reserves were the most beneficial for reducing disturbance driven fluctuations in yields and biomass. This shows that, regardless of whether reserves increase or decrease time-averaged fishery yields, they can stabilize fisheries and fished populations, enhancing the sustainability and predictability of fishery dynamics, and ensuring the consistency of ecosystem functions provided by fished populations.

Research in this thesis provides theory that is directly relevant to currently established reserves and explicitly tests the efficacy of a major reserve network. My results show that minimising, or negating, the impacts of reserves on fisheries can be achieved by continuing to directly manage fisheries when reserves are established. This combined approach will also support the recovery of fish biomass, thereby preventing metapopulation (and fishery) collapse, reducing the return time on fishery benefits, and increasing the long-term productivity of the system. Even in cases where reserves reduce overall yields, they can provide stability to fisheries by reducing variations in catch due to natural disturbances.

Item ID: 46301
Item Type: Thesis (PhD)
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Additional Information:

Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2: Hopf, Jess K., Jones, Geoffrey P., Williamson, David H., and Connolly, Sean R. (2016) Fishery consequences of marine reserves: short-term pain for longer-term gain. Ecological Applications, 26 (3). pp. 818-829.

Chapter 3: Hopf, Jess K., Jones, Geoffrey P., Williamson, David H., and Connolly, Sean R. (2016) Synergistic Effects of Marine Reserves and Harvest Controls on the Abundance and Catch Dynamics of a Coral Reef Fishery. Current Biology, 26 (12). pp. 1543-1548.

Date Deposited: 10 Nov 2016 22:48
FoR Codes: 01 MATHEMATICAL SCIENCES > 0102 Applied Mathematics > 010202 Biological Mathematics @ 30%
05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050205 Environmental Management @ 50%
06 BIOLOGICAL SCIENCES > 0699 Other Biological Sciences > 069999 Biological Sciences not elsewhere classified @ 20%
SEO Codes: 83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8302 Fisheries - Wild Caught > 830201 Fisheries Recreational @ 40%
83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8302 Fisheries - Wild Caught > 830204 Wild Caught Fin Fish (excl. Tuna) @ 40%
96 ENVIRONMENT > 9699 Other Environment > 969999 Environment not elsewhere classified @ 20%
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