New Zealand Pāua – how low can they go?

Pāua are remarkably resilient creatures, thriving in New Zealand’s harsh coastal environment for the past 70 million years or so. During this time they’ve been through a lot, including earthquakes, tsunamis, sea temperature change, and more recently, predation by humans. One of the reasons pāua have thrived for so long might be their ability to occupy a range of ocean depths, from the warm intertidal zone to deeper, darker reefs.

What drives pāua depth distributions in our coastal waters, and how does fishing factor in?

Like many abalone species pāua are perfectly content across a range of depths, but are mostly oriented to shallow waters in 3-5 m where waves crash. Pāua love strong water movement, which enriches dissolved oxygen and optimises their physiology and growth. Crashing waves also break up seaweed, providing a reliable food supply (Fig. 1). This is why you’ll often find yourself getting pushed around by waves when diving on the best pāua beds.

Pāua can also live much deeper and have been found well past 15 m. These deeper-dwelling individuals are often some of the largest found, possibly because they’ve been overlooked by fishers (Fig. 2). However, the deeper pāua move the more competition they have with kina, which occupy similar rocky reefs and feed on the same seaweeds. Surveys have shown that pāua and kina are often stratified by depth, with pāua occupying shallow reef shelves, and kina preferring depths of 10-15 m (and as deep as 60 m or more). If pāua are removed from shallow areas completely, kina have an opportunity to move up and occupy that space, causing a loss of optimal habitat for pāua. For this reason, fishers should always aim to leave a good proportion of pāua in a patch so they can maintain their turf and deter encroachment by kina.

Fortunately for those who want to catch a feed without overworking their lungs, legal-sized pāua can also be found in very shallow intertidal habitats, sometimes even emerging from the water on spring low tides. This is especially the case in remote areas where there is little shore-based fishing. You may have noticed the effects of fishing on pāua depth distribution if you’ve ever been to a remote area such as the Chatham Islands, or seen a long term closed area. Here, large pāua can be found in great abundance at the water’s edge, illustrating their ability to live intertidally. Interestingly, after the 2016 Kaikōura earthquake lifted the seabed several meters, large pāua were thrust up into shallow tidal zones and remained there throughout the 5-year fishery closure, reaching huge sizes (Fig. 3). When the fishery was reopened in 2021, many fishers noted that they didn’t even have to get their feet wet to collect their limits. Unfortunately, this ‘wade-fishery’ didn’t last very long, and for the most part, fishers in the region now must don their wetsuits again.

So how does the depth distribution of pāua stack up against some of the other 55 species of abalone around the globe? One of the more interesting areas is the rocky, temperate coastline of California, USA, which is home to 8 species that once comprised one of the world’s great abalone fisheries. The shallowest dwelling of them all is the black abalone (Haliotis cracherodii), which lives predominantly on intertidal reef (Fig. 4). This highly heat-tolerant species was once a prime source of food for coastal hunter-gatherers dating back at least 9,000 years, who likely appreciated it’s easy harvestability. In contrast, California is also home to two of the deepest living abalone species. The white abalone (H. sorenseni) and pink abalone (H. corrugata), have been found at depths beyond 40 m. These abalone were so deep that, during the heyday of the California abalone boom, harvesters had to invent new diving technologies to access them. The extreme depth of these valuable abalone was the impetus for the development of assisted underwater breathing devices, such as SCUBA and ‘hookah’ gear.

Fortunately for the majority of Kiwi divers who can’t hold their breath very long, or prefer to avoid the dark abyss of the deep sea, the humble pāua lives at an agreeable depth. It seems there are several key drivers of their depth distribution, including temperature, dissolved oxygen, food availability, competitive interactions with other species, and, of course, humans.

We can only hope that by maintaining a healthy marine environment, and avoiding over-harvest, we can all have relatively easy access to pāua for years to come.