Fish facts: Aussie bonefish
BONEFISH are recognised as one of the most challenging species available to sport fishers all over the world. Their appeal arises from several factors. The tropical sand flat environments in which these fish are targeted are pleasant locations to visit, the bonefishing process requires finesse and skill, while the fish themselves are attractive and superbly adapted to life over shallow sand flat environments. With their supreme camouflage, keen eyesight, flighty disposition, selective feeding habits and a blistering turn of speed used to evade predators, they are indeed a complete light tackle sportfish.
Until relatively recently, scientists thought there were only two species of bonefish, Albula vulpes, the traditional “grey ghost of the Caribbean flats” which was thought to occur worldwide in tropical waters, and the morphologically distinct threadfin bonefish, A. nemoptera, which occurs only in the Atlantic Ocean. However, recent morphological and genetic studies have confirmed that A. vulpes is probably confined to the Atlantic Ocean as well, and that the bonefish occurring in the Indian and Pacific Oceans comprise at least 8 other species.
The existence of bonefish in Australia was probably first recognised when surf anglers fishing along the Queensland coast caught “oversized sand whiting” exceeding 2kg in weight. While superficially similar to sand whiting, bonefish are easy to tell apart in a variety of ways including only having one dorsal fin, a more robust body and a more underslung mouth. The species in question was the most widespread of the Indo-Pacific bonefishes, namely the roundjaw bonefish (Albula glossodonta), which occurs throughout the Indo-Pacific region from the Seychelles off eastern Africa, throughout Asia as far east as the Cook Islands, Kiribati and the Hawaiian Islands. A. glossodonta is a large bonefish, growing to at least 90 cm and over 8 kg. In Australia it has been recorded at Lord Howe Island and along the Queensland coast.
The other species of bonefish confirmed in Australia is the smallscaled bonefish Albula oligolepis, which occurs throughout the Indian Ocean including North Western Australia. This species differs morphologically from A. glossodonta by having relatively small scales, a pointed lower jaw, yellowish base of the pectoral fins, black nostrils and a black spot on the tip of the snout. The smallscaled bonefish was originally described from South Africa, where it seldom exceeds 2 kg in weight, but in Australia it grows to at least 6 kg and 80+ cm in places like Ningaloo Reef. This species was formerly considered to be Albula argenteus, until it was recognised that so named bonefish were in fact 3 different cryptic species, all possessing a pointed lower jaw and recently separated into A. argenteus, A. oligolepis and A. virgata, based on morphological and genetic studies. Genetic studies have also identified 4 other Indo-Pacific bonefish species including the shafted bonefish Albula pacifica from the Central America region of the eastern Pacific, A. koreana from Korea, and A. esuncula and A. gilberti from Baja California.
As for their diet, all species of bonefish are bottom foragers which use their underslung mouth to capture prey concealed within sandy substrates. Juvenile bonefish feed mainly on microscopic crustaceans called amphipods ("sand fleas"), which are a plentiful food source in sand and seagrass areas. Larger bonefish eat a wide range of food items, mainly crustaceans such as xanthid crabs and callianassids (yabbies or nippers), but also prawns, polychaetes, small bivalves and occasionally small fish. Bonefish move onto sand flats with the rising tide to feed, often into waters less than 10 cm deep, and return to deeper channels as the tide recedes. These daily movements with the tide are well known by anglers, but have also been confirmed by scientists using ultrasonic tags. Little is known about the growth rates of Indo-Pacific bonefish, but for A. vulpes in the Caribbean, a 50 cm bone is around four years old while a 70cm fish may be 10 years old or more with maximum age being around 20 years or so.
Bonefish have interesting spawning behaviours. Around 50% of male bonefish in the Florida Keys are mature by 42cm (age around 3-4 years old), while 50% of female bonefish mature by 48 cm (around 4 years old). Acoustic telemetry studies have confirmed that spawning in several species of bonefish occurs after adult fish migrate from their shallow sand flat feeding areas to specific aggregation sites in close proximity to deep water dropoffs near offshore reefs. Here spawning has been recorded around dusk during full moons, a timing that would help maximise tidal dispersal of the eggs and larvae into offshore waters.
Like their close relatives the tarpons, eels and giant herring, bonefish belong to a primitive group of fishes, called the Elopomorpha which possess a unique, transparent, leaf shaped larval stage called a leptocephalus larva. Unlike most other fish larvae, leptocephali spend many months in the plankton and can be transported many thousands of kilometers by oceanic currents. When bonefish finally metamorphose from the gelatinous larval stage into juveniles, it's a dramatic change which involves a 60 to 65% reduction in length (from about 7 cm to about 4 cm) and a 75% decrease in weight (due to dehydration). It is at this stage these small juvenile bonefish recruit to shallow sand flat and seagrass areas, forming schools that forage with the tide.
While Indo-Pacific bonefish populations have been subjected to overfishing in many parts of their range in the Pacific Islands by subsistence netting activities, it appears that their populations are most threatened in the long term by developments that interrupt spawning migrations or destroy seagrass nursery habitats. Throughout their range, its hoped that the massive value of bonefish as a recreational catch and release fishing target can be realised by governments so that the threats to their populations can be better managed. As their name implies, bonefish are full of bones and thus are virtually inedible, and the fish themselves are also small. Despite this, economic analysis of the sportfishery targeting bonefish in Florida found that it generated over one billion dollars per year to the Florida economy, from a fish population measured at a mere 300,000!
This amounts to a realised value of around $3500 per fish, per annum. But sportfishers in Florida release 99% of their bonefish – they are no good to eat and there are size limits and a strict bag limit of one fish anyway, so it’s essentially a catch and release fishery. Since bonefish live for up to 20 years, and survival of released bonefish is high (if they are handled correctly to minimise air exposure and are released away from predators), researchers in Florida consider these fish to be worth up to $70,000 each to the Florida economy over their lifetime. Given Florida bonefish average 3 kg or less, that’s over $23,000 per kg, making them arguably the most valuable sportsfish per kilo in the world. Lets hope that increased recognition of their economic value by Governments worldwide will bring with it the required protection of their habitats and management of their fisheries. After all, this is what is needed to encourage development of catch and release sportfisheries for bonefish which can generate much needed sustainable socio-economic benefits to coastal indigenous communities throughout the Indo-Pacific.