Assessing The Direct And Indirect Effects Of Marine Reserve Protection On Temperate Reef Fish Communities

Marine reserves are often effective in allowing the recovery of targeted species within their boundaries, which potentially have indirect effects on non-‐ target species. While the direct effects of protection on targeted species are fairly well understood, the indirect effects have been less well researched. In New Zealand’s oldest marine reserve at Leigh, the recovery of snapper Pagrus auratus and spiny lobster Jasus edwardsii populations has indirectly resulted in the increase of macroalgal habitats due to increased predation on sea urchins. Increased abundances of snapper and other targeted fish species may also affect other fish species via competition or predation. The main aim of this thesis was to investigate how these indirect effects, especially large-‐scale change in habitats, have affected reef fish species relative to the direct effects of protection. Reef fish abundances and sizes were estimated using habitat-‐ stratified underwater visual censuses inside and outside of the Leigh and Tawharanui marine reserves, which allowed for assessment of reef fish habitat associations. Based on these densities and the estimated extents of each habitat (from a drop-‐camera survey) the total population size of a number of key species was estimated for both reserves and surrounding coast. These estimates were then compared to historic population sizes in the Leigh Reserve that were estimated prior to habitat change. The main habitat change between 1978 and 2014 was the conversion of barrens into shallow kelp inside the Leigh reserve. In 2014 there were clear differences between reserve and fished sites at both locations, with virtually no urchin barrens and substantially more kelp habitat inside the reserves. Some species had clear habitat associations, with brown seaweed-‐associated species such as butterfish and silver drummer indirectly benefitting from increased kelp habitats in the Leigh Reserve. Overall changes in population sizes of most targeted species are most likely a direct response to protection. Some species (spotty and goatfish) were less abundant in the reserves, which may be due to increased competition or predation from snapper or other predators. In 2014 the majority of species showed a reserve effect, with greater abundance and/or average size in the reserves. However, aside from red moki, butterfish and silver drummer, which increased in abundance, and leatherjacket and banded wrasse, which showed no change, most species have declined in abundance inside the Leigh Reserve. These population declines may be a reflection of increased fishing pressure being placed on the surrounding coast, environmental change (e.g., sedimentation), or simply due to natural fluctuations in abundance. In summary, the patterns observed in this study, coupled with historic data, suggest that responses of most fish species to protection within northern New Zealand marine reserves are directly attributable to the absence of removal by fishing, with relatively few species showing indirect responses to large-‐scale habitat change or altered levels of competition or predation.

Marine reserves are established to protect marine ecosystems from fishing, allowing harvested fishes to recover: these are the "direct effects" of protection. However, changes may also occur among species not typically exposed to fishing mortality, via "indirect effects" . Most marine reserve studies have focused on direct effects, and the prevalence and relative importance of indirect effects is poorly understood. Understanding both direct and indirect effects is key to understanding how fishing affects wider fish assemblages. To investigate the direct and indirect effects of marine reserve protection on reef fish assemblages I examined monitoring data from four northeastern New Zealand marine reserves. This long-term analysis also provided a wider assessment of how reef fish have changed over the last 2-4 decades in this region. Across all reserves examined, the large predatory sparid Chrysophrys auratus responded strongly to protection. This response was hypothesised to drive indirect effects on other species, as a result of increased predation, competition, or predator-induced habitat changes. Long-term changes in reef fish assemblages in New Zealand's oldest marine reserve at Leigh suggested that along with direct effects on six targeted species, snapper recovery had indirect effects on three small-bodied non-target fishes and one herbivorous fish. Comparisons across three reserves revealed that the potential indirect effects identified in Leigh were not ubiquitous. While direct effects on target species like snapper and cheilodactylid Cheilodactylus spectabilis were largely predictable, potential indirect effects were more location-specific and difficult to differentiate from the effects of environmental gradients. At an offshore island marine reserve, with a more speciose temperate-subtropical fish fauna, potential indirect effects existed for just 3 wrasses, despite dramatic direct effects of protection on snapper. There was no evidence of tropicalisation of fish assemblages at this offshore island marine reserve over the last two decades. This study demonstrated that while protected fish assemblages are distinct, this is mostly driven by the recovery of harvested species. Potential indirect effects of long-term protection were identified, but were rarely consistent across multiple reserves. Trophic links between reef fishes appear weak, and the role of indirect effects is likely overwhelmed by the direct effects of fishing.

Marine protected areas (MPAs) are increasingly being implemented as a fisheries management tool. The continued decline of worldwide capture fisheries gives an impetus for studying how MPAs could sustain fisheries. Despite the growing MPA literature, many ecological effects have remained understudied. This doctoral thesis aimed to examine how MPAs can benefit small-scale fisheries, particularly in the French Mediterranean. Field experiments were conducted in the Cap Roux Fishery Reserve, Saint-Raphaël to determine the effects of protection on adult fish communities, recruitment and adjacent fisheries. Indirect effects of protection were detected, particularly on trophic interactions. Mortality of juvenile fish was higher inside the reserve compared to fished areas as seen from surveys of newly-settled Diplodus sargus in their nursery habitats and a caging experiment using recently-settled Symphodus ocellatus in artificial habitats. The mortality patterns were attributed to higher predation inside the reserve. Stable isotope analyses revealed that fish species with higher trophic levels were caught inside the reserve. Meanwhile, catch yields from experimental fishing were higher inside the reserve than in fished areas but decreased with distance from the center of the reserve. Spillover effect was not observed, which could be explained by several factors: poaching or fishing along the boundary which could offset any gains from protection, reserve size which could be incompatible with natural fish home ranges, and the age of the reserve which could still be young for full biomass recovery. These factors should be considered in the management of the Cap Roux Fishery Reserve.

The removal of apex predators is widely recognized to have broad ecological consequences for terrestrial and aquatic communities. In marine systems, the direct effects of fisheries exploitation include altering the community standing stock (biomass), species composition, and size-structure of the fish assemblage. Although the direct effects of fisheries exploitation are well documented, there is increasing evidence that the non-lethal effects of predation can also strongly influence the structure and function of ecological communities. In this dissertation I set out to increase our understanding of the effects of predators on coral reef fish assemblages by conducting a series of large-scale natural experiments across groups of Pacific islands spanning gradients of human population density and oceanographic productivity within four distinct geopolitical regions. My dissertation research reveals striking evidence for the effects of fisheries exploitation and oceanographic productivity on coral reef fish assemblages in three key areas. First, I found strong evidence that the effects of fisheries exploitation are not restricted to large-bodied species from higher-trophic levels but are realized throughout the entire fish assemblage and across multiple trophic groups. Importantly, I show that multiple forms of fisheries exploitation may be present on coral reefs, indicating the complex nature of coral reef fisheries. Second, I show strong evidence of biophysical coupling with gradients of oceanographic productivity and alterations in predatory fish abundance on the body condition, growth rates, maximum size, and longevity of coral reef fishes. I also observe a breakdown of natural coupling at inhabited islands, suggesting that local human impacts are capable of homogenizing life history traits of fishes even when strong environmental gradients are present. Third, I show that the trophic structure of coral reef fish assemblages are more tightly linked to changes in oceanographic productivity than to predatory fish abundance. I observed trophic channeling, a process by which different basal sources of energy entering the system can remain isolated on coral reefs forming distinct pathways up through the food web to top-level carnivores. In summary, my dissertation provides important insight into the mechanisms that structure marine communities and the direct and indirect effects of removing predators from marine ecosystems.

This topical and exciting textbook describes fisheries exploitation, biology, conservation and management, and reflects many recent and important changes in fisheries science. These include growing concerns about the environmental impacts of fisheries, the role of ecological interactions in determining population dynamics, and the incorporation of uncertainty and precautionary principles into management advice. The book draws upon examples from tropical, temperate and polar environments, and provides readers with a broad understanding of the biological, economic and social aspects of fisheries ecology and the interplay between them. As well as covering 'classical' fisheries science, the book focuses on contemporary issues such as industrial fishing, poverty and conflict in fishing communities, marine reserves, the effects of fishing on coral reefs and by-catches of mammals, seabirds and reptiles. The book is primarily written for students of fisheries science and marine ecology, but should also appeal to practicing fisheries scientists and those interested in conservation and the impacts of humans on the marine environment. particularly useful are the modelling chapters which explain the difficult maths involved in a user-friendly manner describes fisheries exploitation, conservation and management in tropical, temperate and polar environments broad coverage of 'clasical' fisheries science emphasis on new approaches to fisheries science and the ecosystem effects of fishing examples based on the latest research and drawn from authors' international experience comprehensively referenced throughout extensively illustrated with photographs and line drawings