A sense of porpoise

Harbour porpoise

I saw my first harbour porpoise standing on the back of a small boat anchored at the foot of a cliff off Anglesey in northwest Wales. I heard a distinctive puffing sound, a mixture of a snort with a breath drawn in simultaneously. When I followed the sound, I saw a small, dark and perfectly triangular dorsal fin on a bit of rounded black back rolling past the boat in a slow circular motion. Every time the porpoise came to the surface, he made this distinctive puffing sound, the reason why the Scottish call them “puffing pigs”.

Porpoises are small (less than two meters in length) and snub-nosed, and although they are the most abundant cetacean (collective term for whales, dolphins and porpoises) species in UK waters, are rarely seen, as they are shy and tend to avoid boats.

Pod of harbour porpoises. © Nicola Hodgins, WDC.

Harbour porpoises are found in coastal waters of the sub-Arctic, and cool temperate waters of the North Atlantic and North Pacific. They frequently visit shallow bays, estuaries, and tidal channels less than 200m in depth, and have been known to swim up rivers; the majority of sightings occur within 10km of land. In many areas harbour porpoises are present throughout the year but there also seem to be seasonal changes in distribution and sightings rates, with porpoises moving inshore in the summer and offshore in the winter, linked to prey availability and the location of suitable breeding and calving habitat. Female harbour porpoises disperse less than male harbour porpoises and this may indicate that female harbour porpoises show site fidelity for the places they calve and nurse their young, returning to preferred areas for these activities. There is also some evidence of north-south migrations.

Numbers of harbour porpoises in some areas have declined in the past few decades due to human activities and the global population is unknown although estimates have been suggested. The IUCN regards the species overall as of Least Concern (2008) although the subspecies found in the Black Sea is listed as Endangered and the population in the Baltic Sea is considered Critically Endangered. Historically, harbour porpoises were hunted in large numbers but the biggest current threat to harbour porpoises throughout their range is incidental capture in fishing nets with thousands of deaths each year. They are especially prone to get caught in bottom-set gillnets because they forage on the seabed. There is substantial research into mitigation measures for this threat including the use of ‘pingers’, an acoustic deterrent attached to the nets and intended to keep the porpoises away. This is crucially important work as bycatch causes horrible suffering and, in many areas annual bycatch rates may affect populations; i.e. – more porpoises are being caught than are being born. Additional threats to harbour porpoises include boat traffic, habitat loss, human disturbance and noise pollution and prey depletion. Chemical pollution has also recently been shown to adversely affect harbour porpoise health and reduce reproduction in the Northeast Atlantic – where they face all of these threats together.

Harbour porpoise commercial fishing bycatch. © Alexei Birkun Jr.

Harbour porpoises have been described as ‘living life in the fast lane’. Compared to other toothed whales, they mature at an earlier age, reproduce more frequently, and have a shorter lifespan. Living in cool or cold waters with a high metabolic rate means that the porpoises must feed continuously both day and night to provide the energy needed to survive, eating enough fish to replenish as much as 10% of their own body weight each day.

Porpoises, like other toothed whales and dolphins, use echolocation to find, track, and intercept individual prey, producing distinctive narrow, high-frequency click sequences to find food up to 30m away, but hear well in frequencies from 10 kHz upwards. Research reveals that porpoises have around a 90% success rate, consuming over 500 fish every hour. With their need to be continuously hunting, the findings also raise concerns about how even a small impact from human activities could have a potentially devastating impact on this species, making them vulnerable to threats such as disturbance from noise or habitat loss.

The European Union (EU) Habitats and Species Directive (also known for short as the Habitats Directive) recognises harbour porpoises as both a ‘species of community interest whose conservation requires the designation of special areas of conservation’ (SACs), and as a ‘species of community interest in need of strict protection’ wherever they are in European waters.

Harbour porpoise. © John Y Wang.

Because of this EU Directive, all European Member States had a duty to designate SACs for harbour porpoises by 2008. SACs of each country were then expected to form part of a coherent network of SACs, called Natura 2000, found throughout the territories and waters of EU Member States, to be put in place by 2012. Yet the development of the Natura 2000 network within the marine environment lagged significantly in comparison to terrestrial coverage. In 2012, the UK had put forward 33 marine SAC sites for consideration with the harbour porpoise listed as a ‘non-qualifying feature’ (grade D) in all of them. According to European guidance, a population is only ‘non-significant’ where the ‘species population is too small to be naturally viable, or where they occur only as vagrants’. The grade D listings meant that the harbour porpoise did not feature in the site management scheme, and was not taken into account in any subsequent Appropriate Assessment or the decision-making process (and protection) that flowed from it under Article 6 of the EU Habitats Directive. The UK had only one SAC designated with the harbour porpoise as a qualifying feature (grade C) in Northern Ireland which meant that this was the only site in UK waters where management measures for the conservation of porpoises were required. This meant that the UK was failing in its duty to designate SACs for harbour porpoises.

As a result of this, the EU commission issued the UK with a formal notice about the lack of harbour porpoise SACs in UK waters in June 2013, followed by a reasoned opinion on the lack of harbour porpoise SACs to the UK in October 2014. In February 2015, Defra announced that they would start a public consultation on eight big harbour porpoise SACs around the UK (England, Scotland, Northern Ireland and Wales) in the summer of 2015. This consultation was delayed until 2016 and in the end only consulted on five sites for harbour porpoises in England, Wales and Northern Ireland. In the meantime, Marine Scotland consulted on a site in the Hebrides and the Minches, on the west coast of Scotland. The European Commission sued the UK at the European Court of Justice (ECJ) for failure to allocate safe marine areas for harbour porpoises, as the process had stalled after the consultation had closed. Finally, in January 2017, the five harbour porpoise SACs consulted on in 2016 were given Ministerial clearance and were submitted to the European Commission for approval to designate. I am still waiting for the European Commission to accept the proposed SACs and management measures are at an early stage of discussion. The development of the UK Dolphin and Porpoise Conservation Strategy should help to provide the ‘strict’ protection throughout their range.

Harbour porpoise. © Nicola Hodgins, WDC.

Harbour porpoises seem to draw the short straw not only when it comes to adequate protection, they are also bullied and killed by bottlenose dolphins, and by grey seals. The cause of these incidents is not clear, but aggressive interactions could be due to high co-occurrence of bottlenose dolphins and porpoises which could result in competition over a shared food resource, occasionally leading to the death of the smaller species, although other theories have included practicing for infanticide, as a harbour porpoise has approximately the same size as a bottlenose dolphin calf. Grey seals seem to just have found their taste for mammal rather than fish.

So harbour porpoises have to contend with natural and human-introduced threats in their daily lives. When decisions about marine developments and industries occur, no consideration is given to each individual, but the population as a whole. When porpoises face so many pressures in their lives, it is difficult to do this well.

You can support Blue Planet Society’s cetacean bycatch campaign here.

Follow the hashtag #PorpoiseAugust on social media.

Pine Eisfeld-Pierantonio is a policy officer at WDC. Follow Pine on Twitter @Pindelinde.