Long-Term Changes in Coral Trout Numbers on the Far North GBR

We carried out coral trout counts on lots of reefs in the Far North Section of the Great Barrier Reef in 1984 for the Great Barrier Reef Marine Park Authority. This was before any zoning restrictions applied and the entire area was open slather for trawlers and fishers. We surveyed coral trout on some of these reefs again in November 2017 and have been able to compare present coral trout abundance on protected reefs and reefs open to fishing in the Far North with the numbers we recorded in 1984. We divided surveys into inner and outer reefs from both surveys because there are often large differences in fish abundance between these two groups of reefs.

It was intriguing that coral trout abundance in 1984 was equal to or higher on these reefs than in 2017 when the 'green' reefs had supposedly been protected from fishing for 30 years. There are several possible explanations for this. The Far North is a remote area and fishing levels may have been very low prior to marine park zoning and not having a measurable effect on coral trout numbers. This is unlikely to have been the case as at that time the reef fishery was based on filleted, frozen product and many commercial vessels operated in the Far North for at least part of the year. Alternatively, because of the remoteness of the area, present zoning may not be enforced regularly and fishing may presently occur on green reefs as well as on the blue reefs. I was surprised to see small outboard-powered vessels fishing on the outer barrier around Lagoon Reef during this trip and this suggests fishing pressure is relatively high in spite of the remoteness of the region.

It is extremely important that we have large areas of the Great Barrier Reef that are securely protected from fishing so that we can build up a pristine stock of large, reproductively active fishes that can seed fished areas with plenty of fish larvae. Studies have shown that a disproportionately large percentage of the fish larvae that settle on fished reefs have come from protected reefs.

Blue reefs are open to fishing and green reefs are theoretically protected. All reefs open to fishing in 1984.

New Fish and Echinoderm Records

In November/December 2017 we took part in a fantastic trip with GBR Legacy to the Far-North section of the Great Barrier Reef. This includes the remote reefs up north of Princess Charlotte Bay that are rarely visited and poorly known. 

We have been fortunate enough to make extended trips to this area on two previous occasions but it was great to get back in the Far-North and explore some more reefs. During this trip a number of fishes were photographed that we had not seen before on the GBR. We also photographed a remarkable sea cucumber or holothurian that was not like any we'd seen before. 

After enquiring with the experts in these fields we have confirmed that several of these animals have never been recorded from Australia before. One fish was a new record for the GBR and two other fishes had only been seen on the GBR on one previous occasion!

The new records for Australia are the candycane sea cucumber Thelenota rubralineata and the spaghetti garden eel Gorgasia maculata. The ambon emperor Lethrinus amboinensis was a new record for the GBR. The goldback damselfish Pomacentrus nigromanus and the strange-looking squarenose unicornfish Naso mcdadei had both only been seen once before on the GBR. I've included some pictures of these animals below.

Spaghetti Garden Eel

This strange eel, Gorgasia maculata, was at 35m depth on Lagoon Reef.

Candycane Sea Cucumber

Thelenota rubralineata as this is known was seen at 30m depth on the north end of Tijou Reef off Lockhart River.

Ambon Emperor

Known as Lethrinus amboinensis this fish was photographed on the front of an outer reef at the tip of Cape York.

Squarenose Unicornfish

Naso mcdadei was also seen on the front of an outer reef off the tip of Cape York.

Goldback Damselfish

Pomacentrus nigromanus was seen in the sheltered lagoon of Great Detached Reef at 20m depth.

Cyclone Devastation of Reefs

Almost exactly a year ago Tropical Cyclone Debbie crossed over our house in the northern Whitsunday region. This huge category 4 storm was moving at a walking pace and we had destructive winds for about 24 hours. These winds destroyed our house, which has now been repaired and is stronger than before, but they also destroyed our local reefs.

Our favourite shallow fringing reefs around nearby islands have been completely devastated. Most of the more fragile Acropora and Montipora coral has been torn off, broken up and deposited in a huge rubble bank on the reef flat. Larger corals have been damaged and partially broken.  Huge boulder corals, some of them over eight metres across, have been dislodged and turned on their side. The power of the waves kicked up by the 300+ km/hr wind gusts packed by this cyclone was almost unbelievable. It will take many years for the reefs to recover.

On some reefs fast growing algae has seized the opportunity to grow and cover the bare bottom and this will probably slow down recovery. Although some corals have survived, especially in the deeper parts of the reef, all have suffered damage to varying degrees. 

We have before and after photographs of many of these reefs and I will post some here to show the scale of the reef devastation.

Huge Coral

Before the cyclone this huge Porites coral at Rattray Island, 10m across and 5m high, was upright and healthy.

Toppled Coral

The same huge Porites coral has been turned on its side by the cyclone.

Coral Garden

Before the cyclone lush coral gardens covered the bottom at Rattray Island.

Cyclone Damage

After the cyclone very little coral remained where the gardens had been.

Healthy Corals

Healthy Montipora corals on Rattray Island before the cyclone.

Devastation

Damaged and toppled Porites in a barren landscape.

Lush Reef Flat

On Saddleback Island before the cyclone healthy corals covered the reef flat.

Rich Coral

Closeup of the rich coral on Saddleback Island before the cyclone.

Rubble Bank

After the cyclone the rich coral on Saddleback had been heaped in a metre high dead rubble bank.

Before Debbie

Paddling over the rich Saddleback reef before Cyclone Debbie.

After Debbie

After the cyclone almost nothing is left alive.

Super Rich Coral

Before the cyclone Gumbrell Island had an amazing coral garden.

Rubble

After the cyclone the shallow reef slope at Gumbrell had been turned into a rubble bank.

Coral Whorls

Before Debbie extensive stands of Montipora corals covered the shallow reef slope at Gumbrell.

Nothing Left

After Debbie most of the shallow reef had been stripped bare.

Algae

Dense forest of algae (seaweed) growing on the bare reef slope after the cyclone.

Staghorn Coral

The Gumbrell Island reef slope had dense staghorn coral thickets before the cyclone.

Rubble Bank

After the cyclone most of the staghorn coral had been broken and thrown up in a huge rubble bank.

Mackay Fringing Reefs

During January we revisited the fringing reefs in the Mackay Region that we have been monitoring for over a decade. We were working for North Queensland Bulk Ports, who run the Ports of Mackay and Hay Point, via TropWater at JCU in Townsville. Although Mackay had missed most of the wet season rain we had storms around us during this work and got rained on regularly.

We were lucky with the water conditions and underwater visibility was about 5 metres which made the diving easy. The reefs were healing following the damage from Cyclone Debbie in March 2017 and most corals were healthy. There was no evidence of bleaching from the 2018 summer period. As usual we saw some amazing sights on these fringing reefs and I'll post a few pictures below.

Staghorn Thicket

Healthy staghorn Acropora thicket on the sheltered face of St Bees Island.

Ornate Rocklobster

At some sites we often see crayfish or rocklobsters, usually in the same favourite holes.

Tasselled Wobbegong

Young wobbegongs often rest in the bowl of a Turbinaria coral.

Wobbegong Shark

This young wobbegong is well camouflaged and lying in wait.

Healthy Coral

These corals are competing for space, a slow but desperate process.

Anemone and Friends

This anemone has a few clown fish and lots of tiny transparent cleaner shrimps in residence.

Cleaner Shrimps

The cleaner shrimps come out to clean my fingers when I hold still.

Amazing Sea Cucumber

Colourful stars-and-stripes sea cucumber, an unusual filter feeder.