Conclusions

From this analysis it is clear that dorsal and pectoral fin denticle characteristics can be used for the

discrimination of a number of shark species found in northern Australia, as nearly all species

showed discernable differences in crown morphology. As the species in this study are known to

have varied life history styles, differences in crown morphology are likely to be attributed to

modifications along differing functional lines of drag-reduction versus protective function.

Consequently, denticle crown characteristics appear to correspond to the functional requirements of

overall drag-reduction in denticles that have thicker crowns. As this study did not investigate the

quantitative effect of denticle patterning on hydrodynamic flow, future studies should consider this

to examine how flow effects differ between species.

Each individual fin showed large differences in denticle crown morphology at each area

investigated, likely to be due to the varied hydrodynamic forces that act on the fin during

swimming. Future studies of fin identification via denticles should incorporate these differences by

specifying the area of the fin that is investigated, or by using a combination of areas to maximise

the available characters for discrimination. Improvement of methods for identifying shark species,

particularly from removed fins, is imperative for adequate species management. The ability to

easily and reliably identify sharks to species, from both whole animals and shark parts, will enable

fisheries managers to quantify catch composition and fishing mortality. These are fundamental data

requirements for responsible fisheries management (see Chapters 1, and 5).

Despite the challenges of using this technique in the field, denticles can be considered a

useful tool for identifying species of sharks from fins in such situations as 1) where confiscated

catch is investigated in a lab, 2) when portable devices with high enough resolution to show

distinguishing features are used (e.g. a handheld digital microscope), and 3) when used in

conjunction with other characteristics such as fin shape and colour (discussed further in Chapter 4).

In the latter case, denticle morphology can be used as supporting evidence to make a positive final

identification from a list of possible species. Denticle morphology may particularly prove useful in

cases where the fin shape is not conserved, such as when fins are damaged or acutely desiccated

during processing.

Poor catch data collection in countries that target sharks and a failure to meet international

responsibilities to provide accurate and comprehensive catch and trade data to the Food and

Agriculture Organization (FAO) or to Regional Fisheries Management Organisations (RFMOs) is a

significant challenge to global shark management (Lack & Sant 2009). The importance of

particularly from fins alone, is vital in order to improve means of shark identification and improve

data quality. The aim of this study was to investigate the validity of using denticle features to

discriminate between common northern Australian shark species. As it was an investigative study,

the sample size and range of species used was not comprehensive enough to develop stand-alone

identification methods as yet, e.g. a binomial key. As denticle characteristic were found to be useful

for the aforementioned purpose, future studies should focus on comparing both a wider range of

4

4

Shark Fin Morphology: identifying shark

species using dorsal fins

4.1 Introduction

Species are the basic unit for the sustainable management and conservation of biodiversity (King

2007, Lindenmayer & Burgman 2005). Therefore, it is desirable that exploitation is monitored as

sharks are difficult to identify to species level, and a major hindrance to the management of shark

stocks has been the lack of species-specific catch data (Barker & Schluessel 2005, Castro, et al.

1999, Lack & Sant 2009, Shotton 1999a). This problem of identification is confounded when whole

sharks are reduced to severed fins for the shark fin trade. As fins represent one of the most traded

parts, quantification of shark mortality represented by fins may help to give a more accurate

representation of catch in the absence of more extensive and reliable species-specific statistics from

commercial fisheries. For example, Clarke et al. (2006) estimated the shark biomass represented by

the global fin trade is three to four timeshigher than shark catch figures reported in the FAO global

data base. Therefore, clear benefits exist in efficiently examining trade data. Although the

management priority for global shark fisheries is high, the resources available for the management

of these fisheries are low. Given the issues of under-reporting and the general lack of species-

specific data for global shark fisheries, a cost-effective tool is needed to collect species-specific

catch datausing shark fins.

Shark management in northern Australia illustrates this need. In recent years, northern

Australian waters have seen a large increase in the amount of illegal foreign fishing targeting shark

fin mainly by Indonesian fishers (Field, et al. 2009, Griffiths, et al. 2008, Salini, et al. 2007a,

Salini, et al. 2007b). This activity peaked dramatically in 2005-2006 with 368 vessel apprehensions,

and has steadily decreased to the present day (Griffiths, et al. 2008, Salini, et al. 2007c). Despite

reduced FFV numbers there is still illegal fishing activity in the region, and the past and current

impact of such fishing on shark stocks remains unknown. This is largely due to the inability to

identify shark species from isolated fins, which form a major component of the illegal shark catch.

As a result of this paucity of data, reliable risk assessments can not be made to effectively manage

the legal fisheries in these waters (Salini, et al. 2007b).

To date, the most common approach for identification of excised fins has been molecular-

methods not only provide accurate species identifications, but defensible evidence for prosecution

in the case of illegal fishing (Dawnay, et al. 2007). Molecular-based methods are particularly useful

in later stages of processing when morphological traits are not conserved, and visual identification

is not possible. Furthermore, they can potentially be used to identify stocks and trace the geographic

origin of fins (Chapman, et al. 2009). Despite these benefits and applications, there are drawbacks

to using molecular-based methods in catch quantification, including 1) analysis costs, 2) the time

lag between gaining a sample and the subsequent identification, inhibiting use in the field, and 3)

the inability to determine the size of the animal from which the fin was removed. As such,

molecular methods, although useful, cannot be solely relied upon to provide catch data using shark

fins.

Fewer studies have attempted to identify shark species from body parts using morphological

methods, such as denticle analysis (Marshall, et al. 2007, SEAFDEC 2006, Tanaka, et al. 2002,

Wagner 2001) and descriptive morphology (Hernandez, et al. 2009, Nakano & Kitamura 2000).

These studies have been largely qualitative and, in the case of general morphology, have only

compared a small number (> 11) of species. This is somewhat surprising, as morphological methods

are the preferred technique for identifying whole sharks, e.g. Last & Stevens (2009).

The current lag in morphological identification techniques for shark fins is due to a lack of

repeatable protocols, and techno-phile preference for molecular methods. In many cases, simpler

morphological methods would be more appropriate. The development of morphology-based

methods for identifying shark fins has potential advantages over molecular methods, such as 1) real-

time identifications of shark species in the field, 2) the estimation of shark size based on fin size,

and 3) cost-effectiveness, given the general lack of resources for the management of shark fisheries.

Effective identification protocols would enable the collection of species-specific catch data, which