Bounty from the ocean

By Guest Author 14/01/2016


Looking for something tasty on your beach for dinner holiday this summer? NIWA scientists have the lowdown on some of the most mouth-watering fish and seafood that are yours for the taking.

Pāua

The scientific name for New Zealand’s iconic black-footed pāua captures its shape and iridescent hues perfectly: Haliotis iris means ”ear-shell rainbow”.

Paua in their shells
Paua in their shells

Pāua are a type of large edible sea snail of which there are about 55 species worldwide. The black-footed pāua is the most common of New Zealand’s three native pāua species. The others are the queen or yellow-footed pāua Haliotis australis and the virgin pāua Haliotis virginea.

Pāua could be considered shellfish royalty because their blood is blue. “The light blue tinge comes from the copper-based protein that carries oxygen in their blood,” says NIWA fisheries scientist Reyn Naylor. This contrasts with the iron-based oxygen-carrying protein (haemoglobin) in human blood, which gives it the red colour.

Pāua ‘breathe’ by extracting oxygen from seawater as it passes over their gills. The used water is expelled through the row of holes in their shell, along with waste products.

“Black-footed pāua are often found in large groups. They are found all around the New Zealand coastline, most commonly in shallow waters on rocky shores from low tide up to depths of 10 metres. They cling to rocks using their strong muscular ‘foot’, the part we eat.

“There is much variation in the size of pāua around the country – up north they don’t get that big. There seems to be a correlation between water temperature and size. This could be because their preferred algae food is more abundant in colder waters, but it could also be due to physiological factors,” says Mr Naylor.

The beautiful iridescent pāua shell – which changes colour when you look at it from different angles – is made up of very thin layers of calcium carbonate and protein. The calcium carbonate is a mixture of very thin, tile-like crystals, and it’s the diffraction of the light when it passes through these crystals that gives the stunning colours.

The seaweed they eat also seems to affect their colour, says Mr Naylor. In beds of giant kelp they have very deep blue colours inside the shell. Pāua in other areas seem to have lighter green to pink colours.

Cockles and pipi – fritter away your summer

Digging for cockles and pipi over summer is a great way to pass the time – and get dinner.
Both species are easy to find, free and plentiful.

Fresh cockles. Source: NIWA
Fresh cockles. Source: NIWA

Cockles have plump, round, hard, heart-shaped shells with ridges which run across and downwards.
Pipi can range in colour from white to a straw colour, they have an oblong shape shell with rounded ends, and a foot that they use to burrow. In fact, if you swim with your eyes open in the water, they can be seen moving through the water column – hovering or floating.

“The interesting thing about pipi is that they can make a mucus thread that makes them more buoyant and enables them to float in the water column. They stick out their mucus thread and off they go, travelling along with the current, – they can only go as fast as the water,” says NIWA marine ecologist Dr Vonda Cummings.
“You find pipi packed together in dense patches, in fast flowing water in estuaries,” says Dr Cummings.

They like exposed areas, for example, a sandbank in the middle of an estuary or near the estuary’s mouth. They can be found just below the surface on sandy flats, sometimes in such vast numbers that shells can be found forced into different shapes by the pressure of the shell beside it.

Baby pipi can be found further up in the estuaries.

In a spot that really suits them there can be over 1000 pipi per square metre.
They are closely related to tuatua and toheroa; they look similar, are a similar size. The way to distinguish them is by the hinge in the middle of their shell.

Pipi can be eaten raw; straight from the shell, tossed on an open fire or barbecue until their shells open. Fritters are fantastic.

The daily pipi limit is 150 per person and only larger pipi should be taken.

Cockles are a shallow-burrowing shellfish, preferring sediments that are predominantly sand, with little mud content. They are also common in eelgrass.

They burrow using their foot, and feed on plankton filtered from the surrounding water.

Because cockles filter large amounts of water they can accumulate toxins from phytoplankton or bacteria in the surrounding water. It is important that they be collected only from unpolluted sites, especially as they can be eaten raw. Unsafe areas are usually signposted.

Recreational fishers like relatively large cockles, and as a general guide 35mm is a reasonably sized adult. The South Island cockles grow even bigger.

The daily bag limit is 150 per person per day, except for Auckland and the Coromandel where it is 50 per person per day.

Kahawai – catch them if you can

Kahawai are an iconic species for recreational fishers. They are fantastic fighters that are found in most coastal waters, harbours, and estuaries around New Zealand.

Diner's treat - the Kahawai. Source: NIWA
Diner’s treat – the Kahawai. Source: NIWA

Some of the best catch rates are in the Bay of Plenty but kahawai are New Zealand’s second most commonly caught recreational species after snapper.

Keen to take bait, they are noticeable in the water with speckled grey-blue to blue-green upper bodies that are powerful and streamlined. They swim in small groups, and in schools of more than a million fish.
Kahawai can cover vast distances quickly because of their speed. They are fast growing, and are a very reproductively productive species compared to snapper.

They eat other fish, but mainly live on krill. The average size of a kahawai is 40–50 cm and 1–2 kg in weight. Females grow larger (up to 60 cm in length), and can weigh up to 3 kg, often half a kilo heavier than males.
The biggest kahawai ever caught was 79 cm. It was caught by a recreational fisher in the Waitangi Estuary, in Hawke Bay in August 1997.

Kahawai are an oily fish, have a thick fillet, and are delicious smoked. Anglers tend to bleed the fish as soon as they catch it, otherwise it can have an oily taste.

The recreational catch limit for kahawai is 20 fish.

Kahawai are usually aged using a method similar to how the age of a tree is determined. A thin cross section from the otolith, or ear bone, is made and the rings counted. The number of rings equals the age of the fish.

This summer NIWA recreational fisheries scientist Bruce Hartill is leading a project to find out more about the kahawai population. NIWA staff are spending weekends between January and April interviewing angles at 21 boat ramps between Mangonui in east Northland and Ohope in the Bay of Plenty.

“Fishing parties may be approached by an interviewer when they return to a boat ramp, and asked about their fishing trip. We will also ask them if we can measure their catch,” Mr Hartill said.

“If they land any kahawai, we will ask if we can cut the heads off the fish, so that we can remove the otolith ear bones in a lab at the end of the survey, Mr Hartill said.

The otoliths will then be examined to monitor changes in the structure of the kahawai population.
“It’s a voluntary survey and we really appreciate the public’s co-operation as they play a crucial part in monitoring the fishery and ensuring that there are plenty there for future generations.”