Natural Sciences volunteer Darcie Hunt is developing a display of fish jaws to highlight differences in fish diets and feeding strategies. Here Darcie is preparing to remove the jaws from one of Tasmania’s top predators, an 86 kg Bluefin tuna (Thunnus maccoyi; Plate 1). It’s a gory process that will put you off your lunch, so it’s best to skip the next step and wait for the end product, which will appear later in the year.
So what can you expect to see, and what can it tell us about a fish’s diet?
Teeth tell us a lot about what a fish eats, how it catches its food, and how it feeds.
Fish such as tunas are fast swimmers that hunt in the pelagic zone (the open ocean, near the surface). They feed on smaller schooling fish including fast-swimming mackerels (Trachurus spp.) and Australia salmon (Arripis truttacea).
A tuna’s mouth is large and has many relatively small teeth that grasp its prey and stop it from escaping.
The fish is swallowed whole, so there is no need for sharp, slicing teeth. Similarly, deep-water fish like the orange roughy (Hoplostethus atlanticus; Plate 2) and the pomfret (Brama brama; Plate 3) have fine, needle-like teeth to grip their prey, to stop it wriggling or falling free.
Typically, these two species feed on smaller fish, squid and crabs or shrimp.
Sharks, on the other hand, can have a menacing set of teeth. These are the teeth of a mako (Isurus oxyrinchus; Plate 4), a top-order predator with a varied diet. It feeds on smaller animals like fish and squid, but can target larger animals like turtles, swordfish, dolphin and other small cetaceans. This last group of prey are fast and big — bigger than a mouthful. The mako has evolved teeth that are slender and pointed with a smooth edge. This allows them to grasp and hold their prey, as well as to tear it into bite-sized pieces.
Sharks also are able to replace teeth lost, damage or blunted during a struggle. Plate 5 shows the many rows of teeth in the lower jaw of a sevengill shark (Notorynchus cepedianus). Sharks continually produce and replace their teeth. The closeup of the sevengill shark teeth highlights how diverse shark dentition is (Plate 6). These high, short-based and comb-like teeth are used for slicing. The species feeds on other sharks, carrion and, in larger individuals, seals and small cetaceans just like the mako.
Not all sharks have ‘man-eater’ sets of teeth. The Port Jackson shark (Heterodontus portusjacksoni) is one of many species of bottom-dwelling sharks that have a very different diet to their larger, oceanic cousins. The Port Jackson shark feeds on seastars, urchins and shellfish. The mako’s sharp teeth do not suit this diet; instead this species has evolved small pointed teeth, set in rows, for crushing its food (Plate 7).
As an example that ‘one size does not fit all’, the eagle ray (Myliobatus australis), which has a similar diet to the Port Jackson shark, has also evolved teeth to crush its food, but these are plate-like (Plate 8).
So, teeth tell us a lot about an animal’s diet, how it hunts and how it deals with its food.
Over the next few months Darcie will be dissecting jaws from a range of Tasmanian marine fish species and de-fleshing them.This gory task will result in a stunning, educational display that will be displayed at the Queen Victoria Museum.
All photographs courtesy of David Maynard.
Last, PR and Stevens, JD 2009, Sharks and rays of Australia, CSIRO Publishing, Victoria.
Gommon, MF, Glover, JCM & Kuiter, RH 1994, The fishes of Australia’s south coast, State Print, Adelaide.
David Maynard, QVMAG Natural Sciences Curator