Building Coral Trout Management

This guest post is by Jordan Matley, a PhD Candidate at James Cook University who has worked on various subjects ranging from the foraging ecology of seals, beluga whales and narwhals in the Arctic to the movement of fish on coral reefs in Tropical Australia.  At the recent Australian Society of Fish Biology conference we were talking about all things fishy but his work on coral trout was one of the highlights for me. Hence (when he had his guard down at the bar) I asked him to give us a run down on some of his coral trout behaviour work.

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Building Coral Trout Management

By Jordan Matley

A tagged leopard coralgrouper (Plectropomus leopardus) ready for release.

Imagine you were opening a new hotel from scratch. Because you are in a rush (and without any prior experience) you decide to put an ad online – “Tradespeople needed to build hotel. First 100 qualified applicants will be hired on the spot”. True to your word, you hire the first century of people who have a diploma related to Trades and Services. See the problem with that? Well, chances are the workforce will consist of those with the most common experience, likely general labourers. However, to build a hotel, you need a plethora of highly skilled workers: electricians, builders, decorators, plumbers, and the list goes on. But you did not select for that, you just grouped all tradespeople together and the more abundant profession filled the ranks. Foolish? I’d say so.

Let’s put that kind of thinking into context of fisheries management, and surprisingly a similar process happens regularly. Often when there are similar fish species in the same geographic area, they are managed or treated as a group (tradespeople in my above example). There are several reasons for this grouping, mainly it can be difficult to differentiate between species (can you tell TAFE students apart?- Editor: That is something like a trades college for our international readers), and because there are so many species caught, species-specific data collection is a lot of work (that is why you hired the first 100 applicants instead of going through applications rigorously). But just like tradespeople, fishes are different despite their similarities. Growth, longevity, reproduction, maturation, diet, distribution, and habitat can all vary among closely related species. These differences can have significant influences on how productive and sustainable a fishery is. They also highlight that different species commonly have unique ecological roles in their environment (just like tradespeople).

Jordan releasing one of his tagged “general labourers” the leopard coralgrouper.

The problem with the hotel was assuming every tradesperson does the same thing, or more precisely, can do everything. Now, let’s consider a specific example – coral trout. Within the Great Barrier Reef (and other Indo-pacific reef areas), coral trout are highly sought after, both recreationally and commercially, because they are relatively abundant and well…delicious. But did you know coral trout is a generic term for at least seven different species? The issue is that the majority of information (scientific and fishery) about coral trout is from the more abundant species – leopard coralgrouper (re. general labourer). As a result, there is concern that trends of other, less common species are going unnoticed. Just as worrisome is that we do not know the functional role each species has in the reef ecosystem. For example, coral trout are top predators on the reef feeding on a wide range of fish species. Changes in their diet could have substantial influences on the population of species lower down in the food web. Similarly, the extent of movement patterns can have a large impact on the utility of marine protected areas (no-fishing zones). Like tradespeople, is it erroneous to assume all coral trout species do the same thing?
My research focuses on how species of coral trout differ behaviourally to determine the need for species-specific regulatory initiatives. I use two main approaches, acoustic telemetry (tracking the movement of coral trout tagged with transmitters) and stable isotopes (indicates if coral trout prey are similar or different). We sampled three different coral trout species at 5 different reefs and found that movement and diet patterns vary among species. For example, at offshore reefs blue-spot trout use more space than leopard coralgrouper (Fig 1), and they consume distinct prey (Fig 2).

Fig 1: Comparison of space use between two species of coral trout (Plectropomus leopardus and P. laevis). The reef distance is measured as a linear representation of Helix Reef. Contour plots indicate where most of the time (detection period indicated) was spent (50% and 95% level). These individual plots demonstrate that blue-spot trout move more than the leopard coralgrouper.

Fig 2: Stable isotope (δ15N and δ13C) bi-plot. The overall separation between species indicates different prey selection patterns.

Overall, these patterns demonstrate that each species has a specific role on the reef (e.g., structuring the food web) and will likely react differently to environmental or human disturbances. Consequently, management decisions should take into account these differences. If we only focus on the ecology or population trends of the more abundant leopard coralgrouper, we will miss what is happening to other coral trout. Just because a species is not abundant does not mean that it is not a critical part of an ecosystem. Would you build a hotel without an architect?
Jordan Matley

Mail: Jordan.matley@my.jcu.edu.au

Twitter: @JK_Matley

Website: www.jordanmatley.com

Related readings:
Currey LM, Williams AJ, Mapstone BD, Davies CR, Carlos G, Welch DJ, Simpfendorfer CA, Ballagh AC, Penny AL, Grandcourt EM, Maplestone A, Wiebkin AS, Bean K (2013) Comparative biology of tropical Lethrinus species (Lethrinidae): challenges for multi-species management. Journal of Fish Biology 82:764-788. DOI: 10.1111/jfb.3495

Matley JK, Heupel MR, Simpfendorfer CA (2015) Depth and space use of leopard coralgrouper Plectropomus leopardus using passive acoustic tracking. Marine Ecology Progress Series 521:201–216. DOI: 10.3354/meps11122

Matley JK, Fisk AT, Tobin AJ, Heupel MR, Simpfendorfer CA (In press) Diet-tissue discrimination factors and turnover of carbon and nitrogen stable isotopes in tissues of an adult predatory coral reef fish, Plectropomus leopardus. Rapid Communications in Mass Spectrometry.