Juvenile Bonefish Habitats

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Like many marine fish species, bonefish have a complicated life cycle that makes conservation a challenge. Based on recent research, we know that adult bonefish have relatively small home ranges for much of the year, but that they are able to migrate long distances to spawning locations. Once at the spawning location, they move offshore at night in large schools where they spawn – they descend to around 200 feet deep to spawn, in water that is thousands of feet deep. And this is where it gets complicated. Bonefish spawn by ‘broadcast spawning’ – they eject eggs and sperm into the open water, where fertilization occurs. The adults then head home. The larvae that hatch from the eggs drift in the open ocean as plankton for 42 to 72 days (average = 53 days). At the end of their oceanic stage, the larvae enter coastal waters where they transform into miniature versions of their parents. Until recently, we didn’t know where to find juvenile bonefish. We funded scientists that found juvenile bonefish habitats (juvenile habitat are called nurseries) in the Bahamas. Now we’re trying to find the juveniles in the Florida Keys.

In the Bahamas, bonefish nurseries are protected bays with sand or silty bottom that are near deeper water. The thought is that the deeper water gives access to the incoming larvae. Juvenile bonefish are found mixed with schools of spotfish mojarra (in the Bahamas they call them shad), a small silver fish with mottled dark marks on their dorsal surface. Juvenile bonefish have similar markings, so fit in well. As they grow, the juvenile bonefish start to school together in these areas, and eventually move to adult habitats.

We used our knowledge of bonefish nurseries in the Bahamas to pinpoint likely nurseries in the Florida Keys. However, thus far we’ve caught very few juvenile bonefish in the Florida Keys. Is it because they use different nursery habitats in the Keys than in the Bahamas? Are there not enough larvae coming into the Keys to support a juvenile population? Is poor water quality or habitat degradation impacting juvenile bonefish survival? These are the questions we are addressing as we continue our search for juvenile bonefish in the Florida Keys.

Why is it so important to identify bonefish nurseries? If juvenile fish don’t have habitats where they can grow and be protected from predators, then not enough juveniles will survive to adulthood, and the fishery will decline. Nurseries are especially susceptible to habitat degradation because they tend to occur in shallow, coastal areas that are impacted by human activities.

Potential loss of nursery habitats is especially troubling because the impacts of this habitat loss may not be felt for many years. This is especially true for long-lived species like bonefish, which can live 20 years or more. As long-lived species age, their growth rate slows and fish of a wide age range may be of similar size. Thus, it is difficult to determine the age structure of the population – are there enough young fish to replace the aging fish each year? In a worst case scenario, if very few juveniles are surviving each year, the population decline won’t be seen until the older fish begin to die off without being replaced by enough juveniles. This means that by the time the problem is realized, it may be years too late.

Our search for juvenile bonefish in the Florida Keys continues. If you see juvenile bonefish (<3” long), please let us know at info@bonefishtarpontrust.org. (Juvenile bonefish found along sandy beaches are a different species, not the species – Albula vulpes – that supports the flats fishery. So sightings of bonefish not along sandy beaches are needed.)