A deeper look at our crayfish crisis

Being able to go out fishing and come home with a crayfish or two for dinner is almost a birthright here in New Zealand. People reminisce about the days when parents could go out into relatively shallow water and just scoop them up.

Unfortunately, those days are long gone. It is rare to see crays outside marine reserves anymore.

Crayfish – known to scientists as spiny lobster, or Jasus edwardsii – have historically supported the most lucrative inshore fishery in New Zealand. They are also important players in coastal ecosystems, maintaining kelp forests by munching on kina. But northeastern New Zealand has a crayfish crisis.

For the past two decades, crayfish numbers have been in decline. This decline has affected commercial cray fishermen, who, despite their ability to carry 50 or more cray pots and deploy them daily, are not meeting their quotas. No-take marine reserves, such as the Cape Rodney-Okakari Point (CROP) Marine Reserve, were put in place in part to protect ecologically and commercially valuable species, like crays, from fishing. Ideally, healthy, robust, populations inside reserves would help bolster the adjacent fisheries.

Instead, scientists have observed alarming declines in crayfish numbers within reserves, as well.

University of Auckland scientists Dr Nick Shears and Dr Craig Radford and I believe that crayfish declines inside marine reserves may be connected to how crayfish move and use different kinds of habitats. Over the next few years, we will explore cray movements within the CROP Marine Reserve by tracking individual animals through time, and working out when and how they are using rocky reef and sandy bottom habitats, both inside and outside the reserve.

We already know that crayfish use near-shore rocky reef habitats during moulting and mating, and then travel offshore to sandy habitats to search for food. Research performed in the 1990s suggested that these offshore movements may take them beyond the boundaries of the marine reserve, where they are vulnerable to fishing. Now, 20 years later, we have technology that enables us to answer questions that early researchers could not: How many animals travel across the marine reserve boundary while feeding? How often do they do so? How long do they stay?

Our plan is to ‘tag’ 30 male and 30 female crays of different sizes. The tags are a little smaller than an AA battery, and sit snugly on the back of a crayfish’s shell. They generate a ‘ping’ every two minutes: a series of beeps out of the range of human hearing that signal which animal the tag is attached to. A grid of ‘receivers’, attached to the sea floor throughout the reserve, ‘listen’ for these pings. If at least three receivers ‘hear’ a ping, they can triangulate and store the lobster’s position. Our receivers can record the movements of our 60 lobsters for at least a year.

We deployed our grid of acoustic receivers in mid-January, and are currently capturing, tagging and releasing crayfish. As soon as our first tagged animal was returned to the water, the grid began collecting data on its movements. We expect to have our first batch of numbers in about a month.

When the data comes through, it will provide valuable information that will improve our understanding of crayfish biology, ecology, behaviour and conservation. Once we can quantify where crayfish go, when, and for how long, we will be able to help managers develop new guidelines for marine reserve design and sustainable fishing practices. This may help marine reserves like the one at Cape Rodney-Okakari Point to function as they were originally intended – as safe areas for thriving adult populations of crays.

Our data may also shed new light on the secret lives of crayfish. Already, early tracking data held surprises; adult crays were supposed to stay in one place, but it turned out they could travel up to a kilometre offshore!

Just because an animal is hidden by water doesn’t mean it doesn’t move, explore, and interact. I am excited to see what other surprising behaviours our data might uncover, and to share those discoveries with the public. Crayfish are complicated, animated, and intelligent creatures, and I want people to be as familiar with crays in the wild as they are with crays on their dinner plates. People only strive to protect what they love, and it is impossible to love the unknown.

Diana LaScala-Gruenewald is a Postdoctoral Research Fellow at the University of Auckland’s Department of Marine Science.

This article reflects the opinion of the author and not the views of the University of Auckland. 

Used with permission from Newsroom, A deeper look at our crayfish crisis published on 13 March 2018.