Similar to the two types, offshore groups have been found to be matriarchal, but have a high degree of social fluidity. Offshore killer whales often travel in large groups of 50 to more than individuals.
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The activities of killer whales can be grouped into four major categories: foraging looking for food , resting, socializing, and travelling. All of these activities appear to occur during the day and night. Foraging is the most common activity, comprising a majority of their daily activity. When resting, the whales slow down, group tightly together, become mainly silent, and dive and surface synchronously for three to five minutes or longer.
Resting periods can last anywhere from less than an hour to over two hours. Socializing involves physical activity between individuals. Spy-hopping, breaching, tail-slapping, and pectoral-slapping are common during socializing. During periods of social activity, northern resident killer whales will spend a considerable amount of time rubbing their bodies on sloped, pebble beaches, particularly in the Robson Bight Michael Bigg Ecological Reserve in Johnstone Strait. Bigg's engage in conspicuous activities like breaching and playing at the surface less frequently than residents to avoid being detected by their prey.
The amount of time offshore killer whales spend foraging, resting, socializing, and travelling is unknown. Around the world, killer whales feed on prey ranging in size from herring to blue whales. They eat kg of food per day and are known to take mackerel, salmon, tuna, squid, sea turtles, stingrays, sharks, seals, sea lions, porpoises, dolphins, grey whales, minke whales, and many other species.
However, killer whales in the Northeast Pacific Ocean have very specialized diets and do not feed on all prey that are available to them.
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Furthermore, their food preferences are learned from family members and shared by other members of their population. Northern and southern resident killer whales only eat fish, and are salmon specialists. Three-quarters of their annual diet is Chinook salmon. Residents forage cooperatively and prey is often shared between individuals, particularly between mature females and juveniles. Offshore killer whales are also fish-eaters, but their diet is dominated by sharks, including the Pacific sleeper shark and Pacific spiny dogfish.
Both resident and offshore killer whales use echolocation to detect their prey. Killer whales communicate with each other through a variety of whistles, squeals, squawks, and screams that they produce in the nasal passages beneath the blowhole. Many of these sounds are distinct and produced repeatedly by a given group of killer whales as a set of discrete calls.
Killer whales learn their calls from their mothers and other family members. Resident killer whales are very vocal. They exchange calls and whistles to maintain contact with each other while travelling and foraging. Resident killer whales use sounds as a kind of family badge. Marine mammals have far better underwater hearing than most fish and are better at escaping when they detect a predator. To be successful at hunting marine mammals, Bigg's have to be quiet while foraging but they do produce calls during the final stages of an attack or while feeding.
Transients: Mammal-Hunting Killer Whales of B.C., Washington State, and Southeast Alaska
Much like residents, offshore killer whales are very vocal and produce a number of calls and echolocation clicks while travelling and foraging. Field studies in British Columbia suggest that males live to a maximum of 60 years while females may reach years of age. Average life expectancy is estimated at about 30 years for males and 50 years for females. Killer whales are mammals and give birth to live young.
Some females give birth to their first calf at age 12, but more commonly around 14 or 15 years of age. Usually single young are born; but there is one documented case of twins in British Columbia. The length of pregnancy gestation period is months and the maximum calving rate is one calf every three years. In , a young female, J50, was found to be in very poor condition. NMFS and other organizations put together a plan to give her antibiotics and to try to supplement her diet.
Antibiotics were administered and she was presented with live Chinook salmon, although it could not be ascertained whether she ate any of them. Unfortunately, her condition did not improve and she was last seen on September 7th. She is now presumed to be dead. The sizes, trends in numbers, and demographic patterns have differed among the three pods.
The dynamics of the largest pod, L Pod, have largely driven the population trends described above. The pod increased to a maximum of whales in the mids, declined to 34 in , and has been steady at 35 whales through In contrast, the next largest pod, J Pod, increased slowly in size from 16 whales in to 28 in , fluctuated between 25 and 30 whales through , but then suffered eight deaths through September ; there are now 22 whales in the pod.
It is this pod that has been responsible for the recent decline in the total population size. The smallest pod, K Pod, has shown only a very slight numerical increase from whales from the late 70s through the early 80s, to whales since , a growth rate of approximately two percent per year.
A healthy population would grow substantially faster. For example, the Alaska Resident killer whale population has been increasing in recent years at a rate of 3. While there have been 27 known births in J and L pods in the last 10 years, only one calf, born in , has been seen in K Pod during that period.
In addition, the three pods have different distributions off the West Coast and show different movements during the year, typically tied to the movements of different runs of Chinook and other salmon. This pattern has been breaking down in recent years, with the whales spending significantly less time in inland waters in , , and In early fall, J pod regularly includes the waters of Puget Sound within their foraging range. From late fall through spring, all three pods apparently spend the bulk of their time on the outer coast, ranging from San Francisco to Southeast Alaska.
J and K pods, but rarely L pod, make short excursions to inland waters during this period. Although relatively little is known about their distribution during this time, recent evidence suggest that they are spending time near the mouths of major rivers and estuaries, presumably to take advantage of salmon runs taking place in those seasons. Scientists are uncertain about how many Southern Resident killer whales can currently be supported by the environment.
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Like the other fish-eating killer whale populations in the North Pacific, the Southern Residents are dietary specialists on fish, and particularly Chinook salmon. Recent scientific findings suggest that the reproductive and mortality rates of resident killer whales are related to the abundance of Chinook salmon, which has declined significantly from before the era of intense commercial fishing and widespread habitat destruction.
Modeling studies suggest the modern carrying capacity is roughly 90 whales, which suggests that the decline since the mids is not due primarily to prey-related, density-dependent factors. The Marine Mammal Commission has long been concerned about the fate of Southern Resident killer whales, hosting the first workshop focusing on killer whales in Seattle in April The Commission has consulted with and assessed each of the steps taken by the National Marine Fisheries Service NMFS to promote the recovery of the population, and has provided recommendations to NMFS for improvements to their efforts.
In May , the Commission held its annual meeting in Seattle , and Southern Resident killer whales were a primary focus of the meeting.
Click here for a report of what was discussed at the Annual Meeting regarding Southern Resident killer whales. Since the s, as the abundance of Chinook salmon has declined, the whales have been moving about more to find the hundreds of thousands of salmon they require each year.
Declines in the abundance of many stocks of Chinook salmon, their preferred prey, could be limiting growth and reproduction. Greater numbers of deaths and fewer birth have been correlated with lower availability of Chinook salmon. Several whales who have died recently were observed be in poor body condition, perhaps related to poor nutritional status.
Southern Residents spend much of their lives in inland waters near numerous sources of pollutants that accumulate in the fish they consume. Some researchers have argued that calf and juvenile deaths, delayed breeding, and now a skewed sex-ratio in calves, may be related to the effects of persistent organic pollutants POPs that have accumulated in the fatty tissues of the whales. Most POPs are retained and accumulate in their fatty tissues, increasingly affecting their health over time. When killer whales give birth they offload a substantial proportion of the POPs they have accumulated to their calf.
A female giving birth for the first time is likely to deliver a much larger load than females who have already given birth. A disproportionately high number of first calves die early in life. The authors of the study concluded that limited availability of Chinook salmon was the primary cause, while the release of POPs as the mother metabolizes her fat may have been a contributing factor.
However, Transient killer whales have even higher levels of POPs in their tissues and are doing well, which suggests that reduced prey availability and other factors are likely more responsible, perhaps cumulatively, for the decline of Southern Residents. The Salish Sea is busy with boat traffic traveling to and from Vancouver, Seattle and Tacoma, and many smaller ports. That traffic could increase substantially in the future with the construction of a new oil pipeline in British Columbia, which is predicted to result in a roughly seven-time increase in the number of oil tankers passing through key habitat in the San Juan Islands.
Coast Guard, alleging that they failed to consult with NMFS regarding its traffic-separation scheme for the Strait of Juan de Fuca, and its potential impact on the Southern Resident killer whale population.
Haro Strait is part of, and adjacent to, critical foraging habitat for Southern Resident Killer Whales. Dozens of shipping and cruise companies complied with the request. Analyses showing the effect of the slowdown on noise levels in killer whale habitat will be published in Preliminary results showed the greatest noise reductions by the fastest and largest ships.
West Coast Bigg’s (Transient) Killer Whales • Georgia Strait AllianceGeorgia Strait Alliance
However, it is not likely that large vessels represent the greatest vessel threat to Southern Resident killer whales. Sounds emitted from certain vessels may exacerbate that disturbance, by possibly masking communications of the whales with each other. However, any effect of sound depends on whether the whales can hear the sounds e. Larger vessels transiting Southern Resident killer whale habitat in the Salish sea emit sounds at frequencies below the hearing sensitivity of killer whales or at source levels lower than or the distance is too great generally affect them.
These vessels may be using echosounders for navigation which the whales might be able to hear, but these higher frequency sounds do not propagate far and, therefore, to have an impact, the whales must be very close to the vessels. Smaller vessels, especially the commercial and private vessels engaged in whale watching, are more likely to be emitting sounds that the whales can hear within their hearing sensitivity and at a source level or within a distance that would make them audible , and are more likely to be in closer proximity to the whales.
In addition, vessels may contribute to an increase in stress hormones when prey is limited. However, these studies have not been able to ascribe the responses specifically to the presence of the vessels or the sounds they generate. Canada wanted to know whether the whale population could sustain the removal of 10 to 15 animals per year for the marine park industry. Bigg's work showed that the overall population was very small and could not endure such losses, but he discovered much more than just their numbers. He began to notice that in addition to the "normal" orcas residents that travel in large pods, there were occasional small groups transiting through, usually only 3 or 4 to a group, traveling erratically close to the rocky shores.
He assumed these animals had been rejected by their pods, like the nomadic lions of the Serengeti. So Bigg called them transients. As the first person to systematically observe these whales, Bigg could not have known that the Pacific Northwest is blessed to provide habitat to two drastically different forms of killer whales, now recognized as living in separate and distinct cultures. In the thirty-plus years since Bigg began orca studies, no migration by either sex from either type into the other has been recorded.
Membership in each begins at birth and cultural bonds and identity continue throughout life. Residents and transients differ in diet, vocal traditions, habitat range, morphology shape of dorsal fin, etc. Though they cross paths routinely throughout the inland waters of BC and Washington State, the two forms are becoming, or by some accounts are already, separate species.
DNA work indicates that they have not interbred for at minimum one hundred thousand years. Each orca population worldwide seems to follow its own rules to guide their diets, associations patters, behaviors and vocalizations, rather than simply show similarities with either residents or transients. Some researchers have suggested that residents should really be called "fish-eaters" and transients "mammal-eaters. Among the differences between residents and transients are that while resident orcas of both sexes stay within shouting distance of their mothers their entire lives, only first-born male transients maintain such intense fidelity to their mothers.
Optimum pod size for transients is three, so whenever a third offspring is born, one of the siblings often leaves. The rule seems to be that the eldest son can stay, but all but one of the others may have to go. After departing their mother's company, roving males may join up with other groups from time to time. Females are more likely to join up with other transients, at least for a time. It isn't known if the hosts are relatives. Departing offspring, whether male or female, tend to leave their mother at 5 to 12 years of age.
Orcas have no predators and are capable of ingesting virtually any bite-sized living thing found in the ocean, but residents select only fish mainly Chinook salmon and squid to dine upon, while transients never touch a fish or squid, but prey exclusively on seals, sea lions, porpoises, dolphins, and other large whales.
Orcas everywhere appear to specialize on certain prey. This way they divide up the available food in the marine ecosystem and avoid competition. Salmon, resident orcas' preferred delicacy, are widely dispersed, so residents are able to travel in large groups across wide expanses. Transients tend to move in their small groups silently, usually around seal haulouts. They silently stalk and outwit their wary food, zig-zaging in unpredictable patterns. The optimum number of orcas in a hunting party is three, since three can most easily detect and surround mammalian prey. In one transient family, the second-born male offspring M3 left his mom M2 at about age 7 when a third offspring M4 , a female, was born.