• Adverse impacts
• Effects
• Human related threats

Human activities may affect marine wildlife in many ways. Such effects are caused by specific impacts or a combination of impacts. When assessing the possible consequences of human activities to marine organisms and developing management measures, it is important to identify impacts, effects and human related threats. These terms are used throughout this report and are defined as follows:

Adverse impacts

An adverse impact is an action or event that has an unfavourable influence (or effect) on an individual or a population.

Human activities on land and at sea can cause several different types of impacts on marine species. Impacts may directly affect the species. Impacts range in geographic scope from localised, affecting species in a small area, to global, affecting the species around the world. The duration of a particular impact may be short-term, ceasing within minutes or hours of the causal event or activity, or long-term, persisting for months or years. Effects may be short-term, long-term or permanent (e.g. death or permanent injury).

The susceptibility of marine wildlife to impacts varies according to the species and the nature of the impacts. For example, species or populations with few individuals, or that are confined to limited geographic areas, are generally more vulnerable than those that are common or cosmopolitan in distribution. In addition, species may be more vulnerable at certain times in their life cycle (for example when they are very young), at certain times of the year such as during breeding seasons, or when they are engaged in particular behaviours such as feeding. Species may also be more vulnerable to certain impacts because of physiological, behavioural, or other factors, such as breeding aggregations.

Furthermore, exposure to some impacts may lead to habituation, so that the effect of an impact on the animal declines with time as the animal becomes ‘accustomed’ to the impact. However, habituation does not always occur and is difficult to measure.

Whilst impacts that affect one or a few individuals are of concern, particular attention should be directed at impacts that affect many individuals, thereby threatening entire populations or genetic stocks and possibly risking species extinction.

Not all activities can be regulated by the Great Barrier Reef Marine Park Authority (GBRMPA). Some activities that may threaten species within the Great Barrier Reef World Heritage Area (GBRWHA) occur outside its boundary and direct responsibility for managing the impact of those activities rests with State or local governments. For example, land-use practices affecting catchments that flow into the GBRWHA are generally regulated by either Queensland Environmental Protection Agency, Department of Natural Resources, Mines and Energy or through local government plans (Wachenfeld 1998). Alternatively, some issues are global in nature (e.g. climate change) and require international co-operation. Global-level impacts are no less serious than those operating at a smaller scale and, indeed they may be more so. However, the primary intent of this paper is to provide a basis for the Species Conservation Program of the GBRMPA for managing human activities that will, or are likely to, affect species occurring in and around the World Heritage Area.

Many impacts may operate at once and it is difficult to assess the extent to which a particular impact will affect, or is affecting, individual species or a population. The main categories of impacts within the GBRWHA are, alphabetically:

• Accidental ingestion of and entrapment in marine debris
• Capture
• Deliberate or reckless killing and injuring
• Disease
• Explosions
• Harassment
• Incidental catch in fishing gear
• Noise
• Physical displacement
• Physical habitat degradation or destruction (e.g. downstream effects of land-use)
• Pollution
• Predation by feral animals
• Prey depletion
• Vessel strikes

Effects

An effect is the result of an adverse impact on an individual or a population.

Possible effects of impacts include mortality, injury or disease, reduced reproductive success, and behavioural modification. Many human activities can cause an animal to change its behaviour. Possible behavioural modifications include:

• changing swimming speed or direction (for example to approach or avoid a boat);
• changing dive depths or duration;
• changing breathing rates;
• changing nesting location;
• ceasing particular activities (e.g. feeding, breeding, nesting); and
• leaving an area.

These kinds of behavioural changes may not be significant if they occur infrequently, but may become a serious threat to the animals if they are frequent or persistent. For example, regular interruptions of feeding and other activities could threaten the survival of individual animals and ultimately of populations. Similarly, if human activities cause animals to leave key habitats such as sheltered bays used for foraging (i.e. if the animals neither habituate to nor tolerate the impacts), this could have serious consequences for a population.

Also, it is important to consider not only the potential impacts of individual activities, but also the potential cumulative impact of activities that are likely to affect the populations, over both the short and long terms. This is especially true for long-lived slow breeding species that may be under pressure from a variety of impacts.

Taking into account the wide variety of impacts and effects, and in accordance with the precautionary principle, as defined under the GBRMP Act, reasonable actions should be taken to avoid or minimise potentially serious or irreversible effects. Management decisions must take into account reasonable predictions of likely effects of human activities on species, despite a lack of supporting scientific evidence. Regular evaluation of the effects of human activities on marine animals, as well as determination and monitoring of the conservation status of the various populations, are essential to allow early detection of problems and allow the development, evaluation and modification of management measures.

Human-related Threats

A threat is an action or event, or the cumulative collection of adverse impacts that effect an individual or population to such an extent that it is faced, respectively with death or extirpation.

The effect of an impact may or may not pose a threat to an animal or a population. For example, a dolphin may be startled by the noise of a vessel. The noise (impact) causes the startle reaction (effect), but this may not pose a threat to the survival or well being of the animal. If the noise occurs repeatedly and continues to cause a startle reaction, the animal’s behaviour may be disrupted sufficiently to threaten its survival. If a sufficient number of animals in a population are threatened, then the population itself may be threatened.

Appendix 1 is a list of threats to species that was adopted by the World Conservation Union (IUCN)in February 2000. These threats apply mainly to the terrestrial environment and are difficult to extrapolate to species within the GBRWHA.

The main categories of human related activities that may threaten species within the GBRWHA are, alphabetically:

• Aircraft movement
• Aquaculture
• The movement of boats, ships and other motorised watercraft
• Coastal development and land-based practices that discharge to marine waters
• Conduct of defence exercises in marine environments
• Declining marine water quality
• Fishing
• Hunting and collecting
• Introduction of marine pests
• Marine dredging and construction
• Marine research and monitoring
• Marine based tourism and recreation
• Shark control programs

Generally, management should strive to eliminate or minimise adverse impacts in order to eliminate or minimise consequent effects and human related threats. It should be noted however that not all impacts or effects are necessarily adverse. 

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