Orca

A comprehensive study published in the journal Marine Mammal Science analysed over 60 years of recorded interactions between Southern Resident killer whales (SRKW) and porpoises in the Salish Sea. This endangered population of orcas, known for their fish-based diet, particularly Chinook salmon, has been involved in numerous incidents of porpoise harassment, leading to the deaths of many porpoises.

Possible explanations

The study proposes three main reasons for this behaviour:

A study in the Marine Mammal Science journal examines the question of why Southern Resident orcas in the Pacific Northwest harass and sometimes kill porpoises without eating them.

Such behaviour has been passed down through the generations and across social groupings, and has been recorded as far back as 1962.

The question of why comes to mind.

Not on the menu

Certainly not to eat them. Southern Resident orcas do not harass the porpoises to consume them.

Scientists studying endangered southern resident orcas have noticed a steady increase of mysterious gray patches and gray targets (circular lesions which may appear on concentric rings – ed.) on the whales’ skin from 2004 to 2016. 

To date, researchers managed to identify six distinct types of lesions, with the two most common types being gray patches or targets. Some resemble tattooed skin.

They do not know the cause of the lesions and are worried that they could be due to underlying health problems in the struggling population.

The photo on top:  "A pod of Orcas off Point Reyes" by Gunn Shots ! is licensed under CC BY 2.0.

So far this year, dozens of orca attacks on vessels have been recorded on Spanish and Portuguese coasts. In most reported cases, orcas are biting, bending and breaking off the rudders of sailboats.

It turns out that raising sons takes a higher toll on southern resident orca mothers, when compared to raising daughters. So much so that the mother’s annual likelihood of successfully breeding is reduced by about half.

This is because the mothers share the fish they catch with their sons even after the latter become adults. The mothers would bite the fish they catch into two, consume one half and give the other half to their sons.

(In the case of their daughters, the mothers also share their food, but stop doing so when the daughters reach reproductive age.)

A scuba diver in British Columbia, Canada, has been fined a record 12,000 Canadian dollars ($9,250) for approaching a pod of orcas too closely.

In British Columbia, vessels must keep at least 200 meters away from orcas and in southern B.C. coastal waters between Campbell River and just north of Ucluelet, vessels must keep 400 meters away. Vessels must be at least 100 meters away from all other cetaceans.

In the pre-drone days, researchers relied on their observations of the orcas when they surfaced, and this was understandably limited.

“Until now, research on killer whale social networks has relied on seeing the whales when they surface, and recording which whales are together," said lead author Michael Weiss, of the University of Exeter.

"Looking down into the water from a drone allowed us to see details such as contact between individual whales," he added.

Focusing on nine of the most commonly found dolphin, whale and porpoise species in UK waters, the strategy has been developed by the Scottish Government, in collaboration with the UK Government, the Welsh Government and the Northern Ireland Executive.

Its objective is to ensure the effective management to achieve and maintain the current favourable status of the nine species. It highlights certain pressures where further research or extra management measures may help to improve the conservation of marine mammals.