New Zealand Sea lions/ Pakake/ Whakahao (Phocarctos hookeri) breed in dune systems in the South Island of New Zealand. Recolonization occurred on the Otago Peninsula in 1994 after sea lions were extirpated approximately 150 years ago because of human hunting. Sea lion breeding is steadily increasing, however, due to a high level of philopatry (an organisms return, often yearly to its place of birth to breed) recolonization of the beaches of the southern South Island has not been rapid. A second recolonization event in the Catlin’s in 2006 has meant there is a greater spread of sea lions in southern New Zealand. Again, breeding amongst this population has been slow. Both of these populations are descended from singular matriarchal lines.

Active dune systems contain a patchy vegetation cover, migrating sand dunes and an irregular topography. These coasts are usually wind-dominated. New Zealand active dune systems have been substantially reduced in number and area. Reduction coincides with the decline of the dune colonizer pīkao (Ficinia spiralis). It also coincides with the global trend towards reduction of dynamic coastlines.

Marram (Ammophila arenaria) foredunes have become the dominant foredune type in southern coastal New Zealand resulting in widespread stabilization. What were once topographically varied active dune systems are now prograded, accreted and topographically uniform foredunes.

This research is aimed at understanding the impact that marram foredunes have on sea lion movement through the foredune zone. This is a key process, because females move through the foredune zone to raise their young in the shelter and safety of the dune hinterland. Any barrier to movement will limit breeding success. This study specifically focuses on sea lion movement through the foredune zone; and whether or not changes in the morphology of foredunes, related to marram invasion, might be limiting sea lion movement.

This study combined a variety of remote sensing and field surveying techniques to address each objective. The objectives for this study were as follows; (1) To determine the characteristic of pre-marram coastlines in Southern New Zealand, and what is the v evidence of sea lion occurrence in this pre-marram landscape; (2) Determine whether marram-dominated foredunes impede sea lion access to the hinterland; (3) Identify and explore the potential for sea lion habitat restoration. The combination of these techniques allows for a wider understanding of the transformation of sea lion foredune habitat.

Firstly, this research assessed current and present sea lion distributions and the transformation of sea lion habitat. These were assessed using archaeological records, current sea lion pupping distributions, LIDAR, and historic aerial photography. This chapter developed an understanding of sea lion habitat change based on where sea lions were historically and where they recolonised. Sea lions have recolonised and pupped in the areas where there is archaeological evidence of occupation. This then allowed for analysis of the coastal transformation at the study sites at Allan’s and Victory Beach, and Cannibal and Surat Bay.

Foredune transformation was most accurately observed at Surat and Cannibal Bay. Marram colonised this system extensively from 1948 onwards. After which marram formed a continuous and dense vegetation cover. The area was transformed from a sparsely vegetated tombolo to a densely vegetated hinterland. Widespread progradation at both Cannibal (up to 119m +/- 2m in places) and Surat Bay (up to 60m +/-2m) occurred during this period. The height of the foredune exceeds 10m in many areas.

Secondly, this research examined where sea lions’ movement through the foredune zone occurred on important pupping beaches. Assessment of these areas was conducted using handheld GPS and UAV (Unmanned Aerial Vehicle), RTK (Real Time Kinematic) and total station surveying. From this surveying a finer scale understanding of preferred sea lion foredune morphology could be assessed. Sea lions were observed, at Surat Bay specifically, being able to move through a considerably large marram foredune barrier. However, these foredune form a barrier to sea lions when scarped; and became inaccessible to sea lions after minor scarping events (0.5-1m high).

Long term ecosystem restoration is recommended. Restoration of this nature would be based on the west coast Rakiura model in which marram is removed from the system. Once marram is removed the foredune erodes and returns to the original active and topographically complex nature, which usually includes multiple conduits that allow sea vi lion access. Restoration could be attempted through the administration of herbicide to kill marram or with an excavator to destabilize the dunes and remove marram. Surat Bay is the recommended site for restorations. This is because of its remote nature and significance to sea lions. For short term restoration dune notching is advised.