Mr Benn Hanns
I completed my MSc at the University of Auckland's Leigh Marine Laboratory, working with Nick Shears. This research aimed to: 1) quantify, characterise, and explain morphological variation in the kelp species Ecklonia radiata across North-eastern New Zealand, 2) quantify and explain biomass accumulation and erosion in E. radiata across Hauraki Gulf sites characterised by different E. radiata morphologies and environmental conditions, 3) examine the trophic importance of E. radiata particulate within reef suspension feeder communities.
Research | Current
Understanding fishery-marine reserve interactions in the spiny lobster Jasus edwardsii
Marine reserve effectiveness can be defined as a reserve’s ability to provide resistance to, and refuge from the extractive effects of fishing. In theory a marine reserve should maintain stable populations of harvested species independent of the state of the surrounding fishery. However, due to continuous unrestricted movement of individuals across marine reserve boundaries, this is unrealistic for some species. Continued degradation of fisheries, lower certainties of catch success or the perception of higher chances of success has seen fishers across the globe disproportionately focusing fishing effort on marine reserve boundaries. This behaviour can result in increased fishing yields, including greater catches of larger individuals; but, may also restrict the ability of the marine reserve to meet its conservation objectives. Understanding how boundary fishing affects protected populations is fundamental to determining a marine reserves effectiveness. Here, “Effectiveness” will be dependent on the species in question, its mobility, and the size of reserve. Ultimately, whether a reserve is effective or not at protecting a species is a balance between the size of the marine reserve and the movement of that species.
It is hypothesized that in reserves that incorporate a species offshore limits, densities of said species will increase rapidly with distance from the longshore boundaries. Additionally, in response to the size selectivity of fishing, and the indirect effects of fishing on the health of released individuals, individual sizes and metrics of health or condition can also be expected to increase. New Zealand is home to a number of established coastal marine reserves of varying size and design. Surveying multiple marine reserves of differing levels of expected effectiveness provides an opportunity to examine these hypotheses.
The spiny lobster Jasus edwardsii is a highly valued species that supports an intensive commercial fishery and is known to respond positively to protection. J. edwardsii are mobile, with reproductively active lobster seasonally moving offshore from the rocky reef, to deeper soft-sediment habitats. How J. edwardsii responds to protection is predicted to reflect how effectively a reserve incorporates the offshore limits of its movement range and whether or not J. edwardsii are being fished on the reserves offshore boundary.
Selected publications and creative works (Research Outputs)
- Hanns, B. J. (2014). The trophic implications of morphological plasticity in Northeastern New Zealand Ecklonia radiata forests The University of Auckland. ResearchSpace@Auckland.