Australia relies heavily on commercial vessels for transportation of its imports and exports, with 99 per cent of Australian trade by volume carried by sea (AMSA 2016). With 85 per cent of the population living within 100 kilometres of the coast, recreational boating is a popular pastime for many Australians. There are very few areas in the Australian marine environment where international and domestic vessel activity does not occur (Figure MAR16).

In association with vessel activities, there is a risk of environmental damage from collision or grounding of vessels (NESMG 2014), and harm to marine animals by vessel strike from all types of vessels. Large, high-speed commercial vessels cause the death of whales worldwide (Jensen et al. 2004), and small recreational vessels regularly injure inshore species such as dugongs (Dugong dugon), turtles and dolphins (e.g. Thiele 2010).

Globally, commercial vessel activity has been increasing (Davis et al. 2016). Within Australian waters, commercial vessel activity has grown by approximately 4 per cent each year since the early 2000s (DIRD 2014, BITRE 2015; Figure MAR17). Much of this growth is within significant areas of marine mammal migration and/or breeding, such as the Great Barrier Reef. Use of port areas in regions used by turtles and dugongs is also increasing (e.g. Gladstone Harbour). At the same time, the size of recreational vessels has been increasing across most regions, and activity in remote areas is also increasing (Lyle et al. 2014, Giri & Hall 2015, Ryan et al. 2015, West et al. 2016).

Recently, vessel strike incidents by commercial vessels in Australian waters have predominantly involved humpback whales (Megaptera novaeangliae). Based on the behaviour and distribution of animals, the distribution of high-density commercial vessels, and overlaps between the two, mother–calf pairs of humpback whales have the potential to be particularly susceptible. Incidents with southern right whales (Eubalaena australis), sperm whales (Physeter macrocephalus) and pygmy blue whales (Balaenoptera musculus brevicauda) have also been reported.^a Given the speed and size of modern commercial vessels, collisions with whales have a high probability of being fatal (Vanderlaan & Taggart 2007). Vessel strike, particularly by recreational vessels, was identified more than a decade ago as being an issue for marine turtles in Queensland waters, mainly around Moreton Bay and Hervey Bay (EA 2003).

Quantification of historical impacts of vessel strike on marine animals is difficult, because the collation of records (from live, deceased and stranded animals) of vessel strike has not been consistent over time. It is also difficult to ascertain the specific contribution of vessels of varying sizes and types to the problem, because collisions of many animals, particularly with large vessels, will most likely go unnoticed and are therefore not reported (Laist et al. 2001). For example, in Australia, 109 incidents of vessel strike of whales have been reported through official reporting avenues since 1840 (DoEE 2016). However, in some regions, up to 10 per cent of all resident dolphins have been recorded as demonstrating evidence of vessel strike. The low number of official records of vessel strike from these regions suggests that most incidents of vessel strike remain unreported (Thiele 2010). As a result, the impacts of vessel strike on populations of marine animals remain unknown.

Management measures addressing vessel strike

The International Maritime Organization has adopted measures—including precautionary areas, areas to be avoided, re-routing measures and speed restrictions—aimed at minimising vessel strike of whales (Silber et al. 2012). In Australian waters, not enough is known about the spatial or temporal distribution of vessel strike risk or the scale of the issue to implement targeted management measures. Thus, no management frameworks directly addressing vessel strike are in place. However, zoning plans in a number of areas (e.g. Moreton Bay Marine Park) restrict the speed of vessels in an effort to minimise vessel strike of marine animals.

A national vessel strike strategy is being developed by the Australian Government Department of the Environment and Energy (DoEE 2016). The objectives of the strategy are to:

• collect data to understand the scale of vessel strike
• undertake risk assessment and analysis of existing databases
• develop efficient reporting procedures that can be assessed
• develop mitigation measures
• engage with industry regarding information gathering and mitigation.

At the same time, the National Environmental Science Programme Marine Biodiversity Hub is developing approaches to identify areas where there is overlap between the density of vessel activity and marine animal aggregation, as a potential indicator of risk of vessel strike. Such information will be essential for the development of risk management strategies focused on vessel strike.

Outlook

Commercial vessel activity is projected to continue to increase (DIRD 2014). Many populations of animals that are likely to interact with vessels are protected, with some recovering from past exploitation. Some, such as humpback whales, have increased notably (Noad et al. 2011). The combined growth of vessel activity and continuing recovery of populations of protected species such as whales are likely to increase the number of interactions between vessels and these populations. The impacts on marine animal populations associated with increased interactions will remain unquantified without effective reporting and mitigation schemes.

a Australian Transport Safety Bureau marine safety investigations and reports and Australian Marine Mammal Centre National Marine Mammal Database