Pilot Whale

Pilot whale and squid information

Notes compiled by Pamela Mace
Chief Scientist
Ministry of Fisheries
16 August 2010

Introduction

These notes have been put together in response to the TV3 60 Minutes segment entitled “Deep Trouble” that aired on 4 August 2010. This programme only investigated one hypothesis to explain why pilot whales strand; namely, beached whales have empty and ulcerated stomachs, therefore they must be dying of starvation, and they’re starving because the fishing industry is catching all their food.
I am a scientist and I believe in the “scientific method”. Applying the scientific method would mean developing and testing alternative hypotheses to explain why pilot whales beach and why they have empty and ulcerated stomachs. For the most part, scientific hypotheses can only be disproven, not proven. However, the “weight of evidence” might lead to one or more hypotheses being favoured and/or further investigated.
My main conclusion after reading the available literature and holding discussions with knowledgeable colleagues is that there are numerous reasons why pilot whales strand, and there are only a handful of case studies that have been able to link cause and effect with any degree of certainty. Examination of stomach contents alone is totally inadequate to eliminate alternative explanations.
I also conclude that many of the statements made in “Deep Trouble” are unfounded.
You don’t have to be a scientist to use the scientific method. Before believing anything that you see, hear, or read, apply the scientific method. This includes questioning media articles and, indeed, the information presented in this document.

Pilot whales

Pilot whales have been known to strand on beaches for centuries (as evidenced by old paintings and stories). They are among the most common species of whale to be involved in mass strandings. I am unaware that there is strong evidence that such strandings are more prevalent now than they were in the past. It is possible that such strandings are reported/recorded more frequently nowadays, but this is possibly related to the expansion of the human population and increased public concern about such strandings.
Even though they may be depleted in some areas, pilot whales are not considered to be threatened or endangered (2010 NZ Threat Classification, Department of Conservation). There are likely to be almost a million long-finned pilot whales (Globicephala melas, the species found in New Zealand) and 200,000 short-finned pilot whales worldwide (American Cetacean Society factsheet). Except for possible isolated incidents in the 19th century during the peak whaling period, southern populations have not been significantly exploited (Reeves et al. 2003).
All whales eventually die, but the very young and the old are the most susceptible. Being top predators, healthy whales are generally not subject to predation. Most whales die, or become susceptible to predation, due to natural causes such as parasitism and viral or bacterial diseases or other illnesses. Encounters with fishing gear are also a problem in some areas. The carcasses may be scavenged by sharks and other marine life, but most soon fall to the bottom of the sea where they form “whale falls”, or “mini-ecosystems”, that enrich marine food chains and may serve as biological stepping stones for a host of exotic deep-sea animals. Some that die close to shore may eventually end up on beaches. These tend to wash up individually rather than in mass numbers.
Mass strandings mostly occur in highly social whales – such as pilot whales – that may follow a distressed or diseased member of their pod inshore into dangerously shallow waters and then be unable to re-float themselves. This has been speculated to be the result of a persistence to keep the group together. Even when they are re-floated, they may be unable to remain off the beach if other (dead or dying) pod members remain, due to a secondary social or “caring” response. [1]
The preferred diet of pilot whales is cephalopods (squid, octopus and cuttlefish). They also eat a range of fish species, especially when cephalopods are unavailable. Pilot whales can cover large distances and are known to move in response to changes in the distribution of their preferred prey. Schools of pilot whales are found up to 1,000 nautical miles offshore.
Ulcerated stomachs in pilot whales in New Zealand and other parts of the world are most likely caused by a nematode (roundworm) by the name of Anisakis simplex that is transmitted to the whales in their food. The main commercially-exploited species of squid in New Zealand (Nototodarus sloanii and Nototodarus gouldi) and many fish species are intermediate hosts of Anisakis. In other words, this parasite is transmitted to pilot whales via squid and fish.
Anisakis causes stomach wall ulceration and sometimes castration of both its squid and cetacean (whale and dolphin) hosts. A large number of other parasites can also cause stomach ulcers. Regardless of the cause, it is not uncommon to find parasites and ulcers in the stomachs of marine mammals.
The ulcers can be acute and haemorrhagic, or chronic with healing by fibrosis and granulation. In severe infections, perforation of the stomach wall can occur, causing peritonitis and death.
Anisakis can also be transmitted to humans through eating raw or undercooked seafood. It causes anisakiasis, the usual symptom being violent abdominal pain. However, humans are a dead-end host. The larvae can’t survive in humans and eventually die.
While Anisakis is likely to deprive its whale host of nutrition and negatively affect its general well-being, it is generally not believed to be life threatening to otherwise healthy individuals. If, as claimed in “Deep Trouble”, the “entire stomach lining is ulcerated”, then it is likely that some other factor has caused the whale to become ill, and this in turn has allowed Anisakis to infest the stomach lining at unusually high rates. Severe ulceration would likely result in the whale losing appetite, and ultimately losing weight and condition (as happens in humans and other animals).
However, there are other reasons for empty stomachs. Squid beaks do not pass through the intestinal system in the usual way, but tend to accumulate in the stomachs. But they certainly don’t accumulate over the entire lifespan of an individual, or else whales would end up with completely clogged stomachs and be destined to die from malnutrition.
The way whales avoid this situation is to regurgitate the squid beaks periodically. Whales that are distressed – e.g. those that find themselves stranding or stranded on beaches – also tend to regurgitate. One possible reason for stranded pilot whales having empty stomachs is that they regurgitate near or on the beach. The vomit may well then be washed away by the tides.
There are numerous other reasons why pilot whales die. The following is a non-exhaustive list of known or suspected causes:

Tapeworms (cestodes); [2] – these hook themselves onto the wall of the intestine. The host whale can become malnourished;
Flukes (trematodes) – these can infect the brain, heart, lungs, intestines, liver and other organs. They also secrete a toxin that damages tissues;
Lungworms (nematodes) – at least four species attack the lungs of whales, dolphins and other marine mammals and can cause severe complications including pneumonia. Heavy infestations can cause blockage to the airways along with inflammation that could create abscesses and eventually death. Infestations are generally caused by consuming squid or fish that are infected. Beached whales often have lungworms. Both lungworms and sinus flukes are life-threatening whale parasites;
Other nematodes (roundworms) – a key genus is Crassicauda that attacks the kidneys of whales and ultimately causes kidney failure and death. It is also known to attack the cranial sinuses of toothed whales (e.g. pilot whales), which alters brain function, and may produce lesions in the skull. Whales afflicted with this parasite tend to beach themselves;
Bacteria and viruses that cause a large number of diseases including influenza and pneumonia – viruses in the morbillivirus family (causing pneumonia) [3] and the influenza A family have been implicated in the deaths of many marine mammals;
Other parasitic infections that interfere with the whales’ hearing or receiving faculties (e.g. those in the middle ear cavities and nasal sinuses), or that cause other neurological disorders;
Fungi;
Protozoan parasites;
Ectoparasites (those on the skin (outside) of the host) – e.g. barnacles and lice, that probably rarely cause death in a healthy whale host unless they migrate into the anus or breathing holes;
Weakness due to old age or infection;
Difficulty giving birth;
Hunting too close to shore;
Navigation errors when following prey or when travelling;
“Follow me” strandings;
Rough weather;
Changes in the earth’s magnetic field just prior to earthquakes and in the general area of earthquakes;
Navy sonar tests; [4] or seismic tests used to locate hydrocarbons beneath the seabed (that can cause haemorrhaging or a form of decompression sickness);
Organochlorines and other toxic pollutants originating from human activities;
Heavy metals, such as cadmium and mercury, mostly originating from human activities;
Red tides;
Accidental capture in fishing operations;
Entanglement in abandoned fishing gear.

In order to have any chance of determining the actual cause of death in a beached pilot whale, a Rapid Response Team approach coordinated by a qualified marine mammal pathologist is essential. Teeth should be extracted to determine the age of the whale. Their state of health should be measured by taking a set of standard measurements as well as blubber and tissue samples to conduct fatty acid and other analyses (e.g. tests for heavy metals, organochlorines and other toxic pollutants). Blubber thickness should be determined at pre-specified locations on the body. Other organs – especially the brain, lungs and sinus cavities – should be sampled for the presence of pathogens, parasites, or other potential causes of death. Examination of stomachs alone is inadequate as this cannot rule out most of the above-listed causes.

Squid

According to an article written by Steve O’Shea, there are 119 known species of cephalopods (octopus, squid and cuttlefish) in New Zealand. The New Zealand fishing industry only targets two of these (Nototodarus sloanii and Nototodarus gouldi), albeit probably the two most abundant ones.
These two arrow squid species occur over the continental shelf in waters up to 500 metres depth, although they are most prevalent in waters less than 300 metres depth.
The main spawning season is in winter, but there is evidence of spawning throughout the year. In general, N. sloanii hatches in July and August, with spawning occurring in June and July. N. gouldi may generally spawn one-two months before N. sloanii.
The main fishing season is summer and autumn. Recruitment in squid fisheries throughout the world tends to be highly variable. The 2009/10 year was a poor one in New Zealand for Nototodarus.
The most common methods of squid fishing are mid-water trawling and bottom trawling. Jigging was common in the past, but accounts for only a small proportion of the catch nowadays due to a decline in the number of squid jigging vessels in New Zealand waters, probably because of economic factors. In more northerly areas where the subject pilot whales stranded, fishing pressure has been low since the mid-1990s due primarily to the substantial reduction in jig fishing effort (with catches declining from a high of 50,000 tonnes in the late 1980s to 1,000-2,000 tonnes in recent years). The fisheries are mostly active over the January-April period with smaller amounts of fishing in December and May/June in some years.
Contrary to the claim in “Deep Trouble” that the fishery generally targets spawning squid, the squid fishery generally does not target spawning squid for an obvious reason. Nototodarus species live for about a year, spawn and die. For most of that time, they feed voraciously in order to increase energy supplies and grow in size and muscle mass as a result. For the last few weeks or months of their lives, they redirect growth and muscle mass accumulation towards spawning products (eggs and sperms). At the time of spawning (shortly before they die) they have transferred most of their body mass to eggs and sperm to ensure the next generation. As a result, their bodies are emaciated and therefore non-marketable.
In addition, it is not known where these two species of arrow squid spawn, but it is unlikely to be on the main fishing grounds. There is some evidence that they go inshore to spawn, in waters less than 50 metres depth. As far as I am aware, the only confirmed sighting of free-floating arrow squid egg masses has been for N. gouldi off the Poor Knights Islands (O’Shea et al. 2004).
Observer records indicate only a few isolated instances of spent (spawned) squid captured in the main (Snares and Auckland Islands) arrow squid fishery. In the 2008 season, only 0.2% of the squid sampled by observers were spent, and only 1.3% were mature. By far the majority were immature, preparatory or maturing – 55%, 34%, 10%, respectively (data supplied by R. Hurst, pers. comm.).
Given the paucity of fishing activity on mature or spawning squid, it is unlikely that trawl gear has a significant impact on breaking up squid egg masses.

Information relevant to other statements made in “Deep Trouble”

“According to the Ministry, of the 117 fish stocks it manages, 79 are considered near or above sustainable level. Thirty-eight stocks are in trouble –

The 38 stocks are simply below their management targets. This does not mean they are being managed unsustainably, and they are certainly not “in trouble”. Fish stocks are expected to fluctuate around their targets. Of greater importance is the number of stocks that are below biomass limits such as the soft limit (a biomass level where the stock is deemed to be “overfished” and needs to be actively rebuilt), or the hard limit (a biomass level where fishery closures should be considered in order to rebuild stocks at the fastest possible rate). Nineteen percent of stocks of known status are below the soft limit. These all have active rebuilding plans in place. Six percent of stocks of known status are below the hard limit. Fisheries on these have either been closed or have had substantial reductions in catch limits imposed.

“Prior to the mid 60s orange roughy was the staple food for sperm whales. When they were fished from the ocean decade after decade, ton after ton, the whales' diet switched to squid, not dissimilar to the fishing industry”–

This is highly unlikely. Sperm whales migrate over huge distances and orange roughy only occupy a relatively small part of the sperm whales’ range. Also, the scientific literature indicates that the preferred prey of sperm whales is giant squid and cuttlefish. Sperm whales are capable of diving to 3000 metres to pursue their preferred prey. They may well feed opportunistically on orange roughy when they encounter them (depth range mostly 800-1200 metres).

Note also that orange roughy and squid fisheries developed in parallel, with both beginning in the late 1970s; it is therefore incorrect to say that orange roughy were fished out and then the fishing industry switched to squid.

“Whales are in a shocking state of health because their teeth are worn and broken, likely to be from an inappropriate diet.”–

Pilot whales only have one set of teeth to last their entire lives. As with other mammals (including humans who don’t go to dentists), these tend to wear down and even break over the course of a lifetime. Fortunately for pilot whales, they can survive even so, given that their preferred diet is cephalopods that can be “gummed”, rather than fish that require sharp teeth to catch.

If Joe or Jane Blogs who sits in the office all week can go out fishing on a weekend and bait a thin fishing line with a small piece of bait and have a reasonable chance of at least getting a few nibbles, is it reasonable to think that pilot whales that live in the marine environment 24/7 and range over thousands of miles can’t find enough to eat? Squid and other cephalopods also occur over vast areas of the oceans, but if they are scarce in a particular area, pilot whales can and do eat many other small to medium-sized marine fish species.

[1] This social response was however used successfully to keep a pod of long-finned pilot whales from repeated strandings by researchers in New Zealand. Because the "distress calls" of the beached young of the pod appeared to evoke a stranding response from the older whales, the younger whales were towed offshore and moored to buoys, an action which lured the older animals back out to sea (Bernard and Reilly, 1999 and refs. therein).

[2] Curiosity item: the longest tapeworm ever measured was 120 feet (36.6 metres), found in the gut of a sperm whale.

[3] An outbreak of a lethal morbillivirus infection of long-finned pilot whales occurred in the Mediterranean Sea from the end of October 2006 through April 2007. There was also an unusually high number of strandings during that period. However, there was inadequate evidence to determine cause and effect.

[4] A mass stranding of 16 whales in the Bahamas in March 2000 was caused by U.S. Navy tests in which intense underwater sounds were generated for 16 hours, according to a government report compiled by civilian and military scientists. The report's conclusions marked the first time that underwater noise other than from an explosion was shown to cause fatal trauma in marine mammals. The military acknowledged responsibility. X-ray studies showed bleeding around the inner ears, along with trauma to the auditory system and parts of the brain and throat sensitive to intense pressures. In one animal, the ligament that holds an eardrum-like membrane taut had ruptured.