Fact Sheet: Pink Snapper

Pink snapper

Chrysophrys auratus

© R.Swainston/www.animafish.com

Pink snapper are one of WA’s best-known and most sought-after fish, prized by commercial and recreational fishers alike, and seafood lovers for their excellent taste.

A large distribution

Pink snapper are found in coastal waters off China, Japan, Taiwan, the Philippines, New Zealand and Australia. In Australia snapper range from around Karratha in WA along the southern half of the continent to southern Queensland

In some locations, pink snapper gather seasonally to spawn in large schools called ‘aggregations’. The best known of these spawning aggregations occur in Shark Bay and in Cockburn and Warnbro sounds off the Perth metropolitan area.

Distribution of pink snapper in WA

Not actually snapper

Despite their name, pink snapper are actually members of the sea bream family (Sparidae) and are related to species such as black bream (Acanthopagrus butcheri) and tarwhine or silver bream (Rhabdosargus sarba), rather than the true snapper family (Lutjanidae).

Most prefer to stay close to home

While pink snapper has a large geographical range, they have isolated stocks with limited mixing between these populations. In WA, the population structure of pink snapper is complex. Three genetically related but biologically separate stocks have been identified within the inner gulfs of Shark Bay. In contrast, pink snapper in oceanic waters off the WA coast show lower levels of genetic differentiation over hundreds of kilometres as a result of more widespread dispersal of eggs and larvae.

Recent research has identified genetic discontinuities between pink snapper in the mid-west (Gascoyne coast to Lancelin), south-west (north Metro to Albany) and south-east (Esperance to western South Australia).

Tagging studies suggest that the majority of adult pink snapper are essentially resident to an area and undertake only localised movements associated with feeding and spawning, with a small number of older juveniles and adults found to move larger distances.

The tendency of adult pink snapper to reside in specific areas and have limited home ranges can make them vulnerable to high fishing pressure and localised stock depletion.

Pigments called ‘astaxanthins’ probably give snapper their pink colour – similar to what occurs with pink flamingos. In Japan, where snapper are farmed, the fish are fed krill oil to ensure the presence of these pigments.

Bottom-dwellers

Pink snapper are ‘demersal’ or bottom-dwelling but also spend some of their lives in the mid-to upper water levels.

Juveniles spend the first few years of life in bays, inlets and estuaries that provide important nursery areas, before moving offshore. Sub-adults and adults are found out to depths of several hundred metres along the continental shelf.

They have a broad-ranging diet and feed on small fish, crustaceans, worms, molluscs, jellyfish, echinoderms (such as sea stars and sea urchins) and algae. Although they are near the top of the marine food web, pink snapper may become prey to bigger species such as large estuary cod, dolphins and sharks.

Pink snapper are long-lived – they can live to 40 years. This long lifespan increases each snapper’s chance of reproducing successfully as natural variations in water temperature and/or food availability between years can influence spawning success and juvenile survival. Their longevity also makes them less able to quickly recover from overfishing and rapid environmental change than some other species.

Pink snapper have been caught weighing almost 20 kilograms and measuring over a metre long. These days it is rare to see pink snapper weighing more than 10 kilograms.

Serial spawners

In waters off Shark Bay, pink snapper reach maturity after 3-4 years on average, when they are around 40 centimetres long. In contrast, in the cooler waters off the lower west coast, snapper may be 5-6 years of age and around 60 centimetres in length by the time they reach maturity.

The timing of the spawning season for pink snapper also varies with location. Spawning peaks when the water temperature is around 19-21°C. This means that fish in Shark Bay spawn between mid-autumn and mid-spring (April – October) while further south, in the cooler waters of Cockburn Sound, spawning occurs between mid-spring and early summer (August – January).

During the spawning season, pink snapper in some locations form large aggregations. These can be made up of thousands of fish of both sexes and are often found in the same locations each year – so they can be easily located and targeted by fishers unless protected. Such large numbers of fish aggregating in the same place can give the impression that stocks are healthy, however these fish may have moved large distances to spawn.

Snapper in large spawning aggregations sometimes become so voracious they will bite a bare fish hook. It is thought they get so hungry because they expend lots of energy to produce eggs and sperm, and soon consume food sources at the aggregation site. The sinker in the photograph below is covered in bite marks from aggregating Shark Bay snapper and shows how easy it is for fishers to catch large numbers of pink snapper at these times. Perhaps these fish really do deserve to be called snappers!

Sinker with pink snapper bite marks

Spawning mostly occurs around the new and, to a lesser extent, full moon. During spawning, eggs and sperm are released into the water and fertilisation occurs externally. Females release millions of eggs in a series of batches over several weeks in an effort to increase reproductive success.

As they grow larger, females produce more eggs each year and become an increasingly valuable part of the breeding stock. Research has shown that a 40 centimetre female can release 100,000 eggs in a single spawning, while a larger fish of 70 centimetre can release 300,000 to 500,000 eggs at a time – which will add up to millions of eggs being produced over the entire season. However, most of these eggs and the larvae that result do not survive even long enough to become juveniles, due to a lack of food and predation (natural mortality).

Drifting with the currents

When spawning occurs in the open ocean, snapper eggs may be dispersed over large distances by the tide, currents and wind. In contrast, in sheltered waters such as Cockburn Sound and the inner gulfs of Shark Bay, the eggs are retained within well-defined areas.

About a day-and-a-half after fertilisation, the eggs hatch into tadpole-like larvae. The larvae cannot swim well so, like the eggs, they drift with the winds and currents. They stay near the ocean bottom in the daytime and as they grow, migrate up through the water column at night.

Over the next 3 weeks or so, the larvae transform into recognisable juvenile snapper before they settle in large numbers in the deeper waters over muddy or sandy bottoms.

When they are about 18 months old, juveniles leave their nursery areas and migrate offshore, where they typically associate with rocky reefs.

pink snapper fingerlings

Boom or bust?

Water temperature, salinity and food availability all play a role in the survival of pink snapper eggs, larvae and juveniles, as well as the growth of older fish.

Juvenile pink snapper, like many species of scalefish, have a very high natural mortality – in fact, more than 90 per cent die of natural causes in the first few weeks or months of life.

Successful recruitment depends on favourable environmental conditions. In most years, it is probable that there will be low recruitment, in that very few young fish will survive (‘bust’ years). In some years, when environmental conditions are more favourable, the survival rate can be much higher (‘boom’ years). These boom years may only happen a few times each decade and can lead to a snapper population being dominated by a small number of ‘year classes’ – that is, fish that were spawned in the same year. A fish population that has this sort of ‘age structure’ is highly vulnerable to sustained heavy fishing pressure.

A favourite of fishers

Pink snapper support important commercial fisheries and are very popular with recreational fishers in all the Australian mainland states. Management of fisheries seeks to control the overall catch and protect spawning fish.

Most of the commercial pink snapper catch in WA has historically come from oceanic waters off Shark Bay, Kalbarri and the Mid-west, where individuals grow faster but attain a smaller size than those in the lower west coast. The commercial pink snapper fishery in WA is relatively small compared to the commercial fishery in the more productive (nutrient -rich) waters of New Zealand, where thousands of tonnes are landed per year.

Recreational catches of pink snapper in WA are managed using daily bag, boat, possession, size and gear limits, as well as closed seasons to reduce fishing effort (and catches) and spawning closures to protect spawning aggregations.

Fishy science

Fisheries research scientists collect samples of pink snapper taken by commercial and recreational fishers. These fish are used to determine how fast pink snapper grow, spawning times and how old they are.

Researchers can determine the age of a fish by studying its ‘otoliths’ or ear bones. Thousands of these small bony structures are examined every year. The otoliths – used by fish to orientate themselves, balance and ‘hear’ underwater – lay down growth rings every year similar to those of trees. Researchers count the growth rings to build a picture of the abundance of each age class in the population and assess the health of the fishery.

The number of fish in each age class (same year of birth) when described across the lifespan of the species provides the age structure. Looking at the age structure of a fish population over several years, researchers can see the impact of successful recruitment and the effects of fishing.

section of pink snapper otolith

Hyperostosis

As they grow, pink snapper can develop bony humps on the forehead (see image above). This is called ‘hyperostosis’, or above-normal bone growth. Older males also grow fleshy bumps on the snout and it is thought that they use these bumps to nudge females at breeding time, as if to stimulate the release of eggs.

pink snapper with hyperostosis

Glossary

Abundance: Number or mass of fish in a stock or population.

Age structure: The number of fish of different ages within a population.

Aggregation: Large gathering of fish, usually occurring during spawning.

Catch rate: The amount of fish caught in relation to fishing effort.

Demersal: Bottom-dwelling, or living near the seabed.

Gonads: Organs producing eggs or sperm.

Hyperostosis: Above-normal bone growth.

Maturity: Stage at which a fish can reproduce or breed.

Mortality: Frequency of death.

Otolith: Fish ear bone.

Recruitment: Addition of fish to a stock or population as a result of reproduction.

Scalefish: Fish that have scales, unlike sharks and rays that have skin instead of scales.

Year class: Fish within a stock or population that were spawned in the same season (also called age class).

Fish illustrations © R.Swainston/www.animafish.com