Maya Srinivasan has her fins, scuba tank, surveyor tape and slate – and she’s jumping into the ocean for a fact-finding mission at beautiful Bowden Island off Mission Beach.

The small tropical island is in a green zone, so fishing and collecting isn’t allowed without a permit but snorkelling, swimming and boating are popular pastimes. Maya and her crew of marine biologists have recently added the waters around Bowden and nearby Smith Island to their list of 42 monitoring areas which extend from the Turtle Group of Islands off Cooktown in the north to Great Keppel Island near Yeppoon in the south.

“The further north you go, the greater diversity of fishes you see,’’ she says. “In some areas there are so many species you’re exhausted after every dive.”

The team from TropWATER at James Cook University have been surveying a collection of inshore island reefs, including the Palm Islands off Ingham, for more than two decades. They visit once a year and look at both green zones and areas where fishing is allowed, counting the numbers and estimating the sizes of fish species, recording the reefs’ animal and plant cover from hard and soft corals to algae, and noting any human disturbances including discarded fishing lines.

“From the data we collect, we can track changes in fish communities, measure the impact of disturbances on the reefs and follow their recovery,’’ she says.

“Inshore islands here are more influenced by what happens on the land than offshore reefs. They are subjected to more runoff from the land which brings sediments, nutrients and pollutants. The corals already have a background level of stress from dealing with runoff, which makes them more susceptible to coral bleaching. We’ve seen declines in both coral cover and fish species in response to coral bleaching, flooding and cyclones over the last 20 years.

“The reefs are also quite resilient. They can recover depending on how severe an event is and how much time there is between impacts, especially on the windward side of islands where there is more water movement to flush out the sediment. On average the trend has been downward. But there are still some amazing reefs.”

Maya says the monitoring shows green zones are working for popularly fished species like coral trout.

“Green or no-take zones consistently have higher numbers of targeted fish species and they’re larger on average than in fished areas. Another project has shown that higher numbers of larger fish, particularly larger females that spawn more offspring, are an important source of juveniles for fished areas.

“Roughly half of the juvenile fish in fished areas come from parents in green zones. The offspring spend the first four weeks of their life in the water column before settling onto a reef as a juvenile and usually ending up in a different area than their parents.

“Although only 30 per cent of the reef area is in green zones, our modelling shows that coral trouts spawned in green zones account for about 50 per cent of the coral trout caught in fished areas. Green zones are replenishing the populations in fished areas.”

The project complements the Australian Institute of Marine Science’s long-term monitoring program on the Great Barrier Reef.

“The in-shore islands we monitor are high use and high value locations for fishing and boating,’’ Maya says. “Our work can help manage these areas. For example, where coral cover was shown to be very high at one of the Keppel islands, boat moorings were added to a blue zone with recreational fishing so that it could continue without corals being damaged.”

This program is funded by the partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation.