Effects of Marine Reserve Protection on Adjacent Non-protected Populations in New Zealand
Authors:   , Díaz-Guisado Daniela 
Published: November 2021

<p>Marine reserves (MRs) have been established in many parts of the globe for a variety of reasons and there is an increasing body of evidence that indicates they provide a wide range of benefits that can extend beyond their boundaries. In the present study, the biological effects of protection provided by MRs in New Zealand were evaluated, particularly focusing on the potential impacts of reserves on non-protected areas in terms of export of biomass. First, the biological response of two exploited species to MR protection in New Zealand was quantified by comparing meta-analysis results based on response ratio (RR) analysis and Hedges’ g statistics. Then, effect of MR size and age on those biological responses was determined. Most MRs supported a greater density of larger individuals than unprotected areas. Results indicated that the benefits provided by MRs scale with reserve size. Also, MR age explained a significant amount of the variation in the density and length of both species. Comparison of the performance of RRs with Hedges’ g revealed that RR analysis is an appropriate alternative to Hedges’ g statistic for meta-analyses of MR effectiveness because of its ease of use and interpretation. Then, a 14-year time series of fish density data was analyzed to determine early changes in a multi-species fish assemblage inside the Taputeranga Marine Reserve (TMR) compared to adjacent fishing grounds using a Before and After Control-Impact Paired Series (BACIPS) design. This analysis was performed in order to detect changes in fish density due to protection. Commercial, recreational and traditional fisheries are important in this region and the biomasses of several exploited species have been substantially depleted as a result of fishing. The exclusion of fishing from the area should enable at least some species to recover inside the reserve, as has happened in other reserves in New Zealand. The faster growing, more productive species, and those that have been heavily exploited are expected to recover within a few years. Early changes in density were evident in the area protected by the TMR for most of the species surveyed in terms of the effect size analysis. However, most of the changes were too small to be detected with the statistical analyses that were performed. To determine the most appropriate methodology to be used in a later survey in the study area, two Baited Underwater Video (BUV) methodologies (Horizontal versus Vertical set-up) were compared in terms of their ability to record the density and size of reef fish. Results indicated that both the horizontal and vertical BUV techniques are able to detect both conspicuous and cryptic species and both techniques were effective in the detection of carnivorous species, especially large predatory species such as blue cod, but also effective in the detection of fish species that have been overestimated in terms of abundance by other methodologies. The horizontal BUV technique seems to be a better technique for evaluating reef fish size, especially when measuring large fish that exhibit highly aggressive behaviour. The horizontal BUV technique was later used in conjunction with the Underwater Visual Census (UVC) technique to assess the effects of the protection provided by the TMR. A multispecies analysis was carried out to detect any differences in density and length of fish between reserve and fished areas and to detect gradients of fish density across reserve boundaries that could be related to the occurrence of spillover from the reserve to adjacent fished areas. Density gradients provide indirect evidence of spillover, defined as the movement of adult individuals from reserve to adjacent non-protected areas. Little evidence consistent with a positive effect of reserve protection in the TMR was found. Also, little evidence of spillover was found, with theexception of two target species (blue cod and blue moki). In contrast with the findings of previous studies, density gradients were found for both sedentary and vagile species. These results are consistent with the occurrence of density independent spillover that is expected to occur as soon as the density inside reserve areas is higher compared to fished areas. To further understand the patterns of fish movement relative to the effect of protection provided by MRs, spatial differences in density, length and survival of blue cod inside the TMR and adjacent fishing grounds and the movement patterns of the species across the boundaries of the reserve through a capture-mark-recapture (CMR) analysis were examined. CMR studies can provide direct evidence of spillover. Evidence of a positive effect of reserve protection in the TMR for blue cod in terms of increased density, length and survival in reserve areas was found. Also, evidence of high site fidelity of blue cod in both reserve and fished areas, with the majority of individual moving only short distances was found. However, the potential for this species to also travel long distances (>100 km) was confirmed, suggesting the possibility for spillover of the species from reserved to fished areas. Overall, the results of my thesis indicate that New Zealand MRs, consistent with a large body of earlier evidence, are having positive effects on the abundance and size of the species that afford protection to. These results also highlight that both MR age and area are important factors determining the response to protection both in terms of the effects within reserves and on adjacent non-protected areas. Finally, my results highlight the fact that the greater benefits in terms of increased abundance and size, and also movement across reserve boundaries, are obtained for highly exploited species that can potentially move between areas.</p>