Abstract:
The dynamics and individual movement patterns of snapper Pagrus auratus in the Leigh Marine Reserve (LMR), northeastern New Zealand, were investigated. Seasonal fluctuation in relative abundance was studied using Baited Underwater Video (BUV) at intermediate (six monthly for five years) and fine (two monthly for two years) temporal scales. Automated ultrasonic tracking was used to monitor the residency and movement patterns of 38 legal-size (> 25 cm fork length), mature snapper over a two year period in the LMR. A rapid increase in snapper relative abundance occurred during summer periods, with a slow but constant decline during winter. This seasonal fluctuation was strongly correlated with, but lagged behind, Sea Surface Temperature (SST). Relative abundance and size was highest throughout the central part of the reserve with a clear reduction in abundance and size close to the reserve boundary. As a methodology, BUV may be influenced by the behaviour of the species, yet it still proves to be a very useful tool to study the population dynamics of snapper. Long-term residency in the area of the reserve was observed in the majority of snapper (66%). However, the remaining individuals, showed an unexpected heterogeneity in their behaviour, with some fish leaving the array permanently while others returned after up to 221 days of continuous absence. Nearly all snapper showed some level of site fidelity/residency for varying periods of the time they were tracked. A distinct seasonality with summer time maxima was found for presence, activity rates and home range size. In addition, vertical movement records revealed a large proportion of time spent in the shallow depths (< 8 m) and a characteristic spawning behaviour. The strong seasonality of relative abundance has implications for the design of monitoring programmes and is important in interpreting the effectiveness and wider ecosystem benefits of this marine reserve. High site fidelity, small and relatively stable home ranges, and evidence of local spawning demonstrate the conservation value of the LMR. Still, a significant proportion snapper spend time outside the boundaries and most likely contribute to adult spillover. The observed range of movement patterns suggests that it may be vital to establish substantially larger marine reserves, or networks of marine reserves, not only to protect species with different life history traits but also single species that show a range of mobility patterns.