Gray Whales in the North Pacific: History, biology, and current research

Transcription

1 Gray Whales in the North Pacific: History, biology, and current research Aimée Lang Marine Mammal and Turtle Division Southwest Fisheries Science Center 13 October 2015 San Diego Natural History Museum Whalers Photo courtesy of W. Perryman

2 Photo credit: Wayne Perryman, SWFSC Overview: Taxonomic history Physical description Gray whale biology and life history How we study gray whales and what we ve learned!

3 Taxonomic history: First described based on subfossil remains from the coast of Sweden (Lilljeborg 1861) Eschrichtius named after a Danish zoologist (Dr. Daniel Eschricht) who was the first to suggest the remains might be from a new genus and family robustus Latin for strong

4 Relationship to other baleen whales: Fossil record is generally sparse but suggests higher diversity in the past Today the gray whale is the only living species in its genus and family Although traditionally considered morphologically distinct from the rorqual whales, molecular analyses indicate that gray whales are closely related to balaenopterid whales Sasaki et al. 2005, mitogenome analysis

5 Physical characteristics: Heart-shaped blow Mottled gray and white coloration Dorsal hump followed by series of 6 to 12 knuckles Yellowish white baleen Fewest baleen plates of any mysticete ( plates on each side of mouth) 2-5 throat grooves

6 Size: Adult body 11 to 15 m and weigh 45,000 kg Females are larger than males Calves 4.6 to 4.9 m at birth and weigh kg

7 Gray whale barnacles (Cryptolepas rhachianecti): Considered obligate commensals Attach to whales as larvae Filter-feeders Rely on whale s movements through water to find plankton A single whale typically carries 100s of lbs of barnacles Generally thought to be hostspecific But have been found on captive belugas and bottlenose dolphins in San Diego Bay One record of this barnacle on a stranded killer whale

8 Whale lice Crustaceans of the family Cyamidae Not host-specific (found on other whale species, especially those that tend to inhabit shallower water) Three species found on gray whales Parasitic - eat skin and dead tissue Found on healthy whales but may be much more abundant on whales in poor health

9 Gray Whale Feeding and Diet: Gray whales often feed in the mud on the seafloor Benthic feeding

10 Gray Whale Feeding and Diet: In the Arctic, the primary prey are benthic amphipods ~ 3 cm long!

11 Gray Whale Feeding and Diet: But gray whales are flexible foragers: They feed both in benthos and in water column They eat a variety of species, including benthic and mobile amphipods, cumaceans, mysids, crab larvae and herring eggs Mysid Cumacean

12 Gray Whale Reproduction: Sexual maturity between 6 to 12 years of age Mean date of conception mid- December Gestation period 13 months Mean calving date mid-january Healthy females can reproduce at intervals of two years Calves weaned at 6-8 months (about mid-august in the Arctic feeding area)

13 Gray Whale Migration Migrate annually 15,000-20,000 km round trip Takes about 2 months each way Southward migration begins mid-november and is segregated by age, sex and reproductive condition: (a) Pregnant females about to have their calves (b) Non-pregnant females and mature males (c) immature whales of both sexes Northward migration begins about mid-february and occurs in two phases: Phase I = (a) adult males and females without calves, (b) immature whales Phase II = mothers with calves

14 Gray Whale Distribution: Gray whales went extinct in North Atlantic in 1700s Currently gray whales are found only in the North Pacific, where two populations are recognized Eastern population Western population

15 Distribution of the Eastern population: Most of the eastern gray whales feed during summer and fall in Arctic A small number of whales show fidelity to southern feeding ground between Northern CA and southeastern AK Overwinter in the lagoons and coastal waters of Baja Mexico during winter/spring This is where most of the calves are born ~19,000 animals ~200 animals Pacific Coast Feeding Group

16 Abundance Status of the Eastern population: Commercial whaling on the eastern population was prohibited in the 1940s The population currently contains ~19,000 animals In 1994 the eastern population was removed from the List of Endangered and Threatened Wildlife as it was no longer considered endangered or threatened under the ESA Year Durban et al. (accepted)

17 Status of the Western population: Most of what is known is derived from long-term studies of whales feeding off Sakhalin Island, Russia The western population was probably always smaller than the eastern population Sakhalin Island, Russia ~19,000 animals ~200 animals But commercial whaling on the western population continued through at least the 1960s At one point, some scientists thought that the western population was extinct??? We now know it exists but in small numbers (~150 animals today) The western population was listed as Critically Endangered in 2000 by the International Union for the Conservation of Nature

18 Gray Whale Threats Entanglements in fishing gear Environmental degradation, exposure to contaminants Noise (e.g. seismic surveys) related to offshore oil and gas Ship strikes and associated disturbance Arctic environmental changes warming water and loss of sea ice?

19 How do we study gray whales? 1. Counts 2. Satellite tags 3. Photographs 4. Genetic sampling

20 Counts to monitor calf production (northbound migration) Piedras Blancas, CA

21 Calf production: Wayne Perryman Southwest Fisheries Science Center Conducted from the Piedras Blancas Light House station since 1994 (21 st anniversary this past year!) Counts of northbound whales Mothers with calves pass very close to shore and after adult and juvenile phase

22 Calf Estimate Calf production: Unofficial 2015 estimate ~1420 calves 1800 Estimates of Northbound Calves Survey Year

23 Correlation with sea ice in Arctic: LOTS OF ICE IN SPRING MEANS FEWER CALVES THE FOLLOWING YEAR! Ice Cover Calf Est

24 Mechanism: Ice extent in spring of previous year Ice Extent Low Ice Extent High High # of calves the following spring! Low # of calves the following spring!

25 But.. The pattern may be changing???? Ice Cover Calf Est Low Low # of # of calves the the following spring! In the spring of 2012, the sea ice extent was the greatest it had been during our time series. However, the number of calves that were counted going past PB was relatively high.

26 Learning about predation on gray whales using satellite tags (on killer whales!): John Durban Southwest Fisheries Science Center

27 Predation on gray whales by killer whales: Subadult male Bigg s killer whale attacking a juvenile gray whale; Most of the predation is on calves with some small juveniles taken

28 Satellite tag on a killer whale:

29 Killer whale tracks: Estimated ~150 transient killer whales are waiting on gray whale mothers and calves as they cross into the Bering Sea on northward migration May return to finish carcass later Most killer whales remain at entrance to Bering Sea but some follow the mother-calf pairs further north Can be a significant impact on calf production

30 Photo-Identification and Biopsy Sampling off Sakhalin Island, Russia ID 055

31 Photo-identification of gray whales:

32 What have we learned about the gray whales off Sakhalin from photos? Dave Weller SWFSC Small population size (~150 animals) Most animals return year after year, including some animals first identified as calves Very few reproductive females Relatively slow rate of population increase Relatively low calf survival

33 Biopsy sampling: Photo collected under SWFSC Permit #14097

34 What have we learned from genetics? There are genetic differences between gray whales that feed off Sakhalin and eastern gray whales Many of the whales that feed off Sakhalin learn to use the feeding ground from their mothers First hint that some whales that feed off Sakhalin travel to the coast of North America during winter

35 Distribution: ~19,000 animals ~200 animals ~150 animals??? Two animals sampled off Sakhalin Island were genetically identical to two animals that were sampled while migrating north in the Santa Barbara Channel in 1995 N=2

36 Satellite tagging studies (Mate et al. 2015) SI OdL Varvara: 22,511 km roundtrip!!! Varvara SE Varvara NW Calving area CSL Flex: 10 Dec Feb 2011 Varvara SE: 24 Nov Feb 2012 Varvara NW: 2 Feb May2012 Agent: 25 Nov Dec 2011

37 Distribution: ~19,000 animals ~200 animals ~150 animals N=6??? We now know that at least 22 of the ~150 gray whales off Sakhalin have traveled to the west coast of North America! N=2 N=14

38 But some gray whales remain in the western Pacific year-round: 22 records of gray whales off Japan since 1990 At least two of these records were photographs of whales that were first identified as calves off of Sakhalin Pacific coast of Japan - January 2007 Pacific coast of China - November records of gray whales off China since 1996

39 Conservation implications: Some whales ( true western gray whales) do remain in the western North Pacific year-round But this number may be very small We need to know more about where gray whales are during winter and spring in the western North Pacific (e.g. Japan, China)

40 What s next? A large whale survey (CLaWS) is currently being conducted between northern CA and Kodiak Island, AK Objectives: 1) Collect photo-id data and genetic samples from the Pacific Coast Feeding Groupof gray whales, especially in areas where we have little information 2) Search for right whales in the Gulf of Alaska 3) Collect photo-id data and biopsy samples from other species of large whales (e.g., fin whales, sperm whales, blue whales, etc.) Collaborative Large Whale Survey: 9 July 9 November, 2015 Dave Weller, Chief Scientist

41 Highlights so far.. All photos collected under SWFSC permit #14097

42 Thank you!

43 Extra slides

44 Understanding population structure in a changing environment Many marine mammals depend on the Arctic marine ecosystem The Arctic marine ecosystem is rapidly changing, including: Dramatic loss of sea ice Rising sea temperatures Ocean acidification These changes will not affect all areas in the same way Understanding the population structure is critical to evaluate potential impacts of these changes Jeffries et al. 2013

45 Case Study #1: Gray whales a sentinel species for monitoring Arctic environmental changes? Calving rates positively correlated with early-season icefree conditions Shift in distribution on Bering Sea feeding grounds and in timing of southbound migration Recordings of gray whales in the Arctic during winter months Movements of gray whales into the Atlantic. Photo courtesy of W. Perryman

46 Counts to estimate abundance (southward migration) Count whales from shore at Granite Canyon late December to mid-february Migration is about 2-3 km offshore along the central California coastline Counts have been conducted since 1968 Wayne Perryman Southwest Fisheries Science Center

47 Counts to estimate abundance: Use binoculars and eyes to find groups Count number of whales in each group

48 Abundance:

49 Mortality Event Angliss, R.P. and Allen, B.M. 2007

50 Abundance: 19, years of data on the abundance of ENP gray whales!!

51 Shift in migratory timing: Approx one week shift in migratory timing since 1980s Thought triggered by photo-period But suggests environmental factors May be related to oceanographic regime shift in late 1970s may have changed distribution of prey and thus of whales Could relate to increased population, meaning that whales have to disperse more to find food. ~6 km/hour southward migration rate.

52 Graphic shows where gray whale tracks intersect with shipping lanes in Southern California. Credit: Lauren Saez, NOAA SWFSC.

53 From Whalewatcher Estimated that 100+ transient killer whales are waiting for gray whales each spring as they cross into Bering Sea Take mostly calves and some small juveniles; must be able to separate calf from mother Prize the lips and tongues; usually eat only part of carcass then allow it to sink and come back to it later Typically try to drown the gray whale Gray whales typically try to retreat to shallow water to avoid drowning; killer whales do not follow because need to be able to attack from underneath Estimated that take ~100 calves and 20 juveniles a year; can be significant part of calf production, which is usually 1-8% of population. Estimate 5-50% of production lost due to killer whale predation Some leave after gray whales pass into Bering Sea, but others follow the whales further north

54

55 Assessment of Body Condition Wayne Perryman Southwest Fisheries Science Center The relationship between environmental conditions in the Arctic, especially the spatial and temporal distribution of sea ice, and gray whale physical condition is poorly understood. Photographs of southbound gray whales taken from aerial platforms can allow for an assessment of body condition post-feeding.

56 Does This Picture Make Me Look Fat? Southbound Southbound Pregnant Condition Index Data From Flights max width / length

57 So far Aerial photogrammetric sampling of southbound gray whales from , 2013 Reproductive condition in gray whales can be detected from measurements of length and width in vertical aerial photographs Northbound adults and juveniles were found to be significantly thinner relative to their length than southbound whales (about days interval) Next question: Can vertical aerial photographs be used as a primary data source for tracking population level changes in gray whale condition?

58 Piedras Blancas Light House Station:

59 Piltun Field Camp

60 Most days..

61 But on the good days

62 Potential threats: Entanglement in fishing gear Between 2005 and 2007, four female gray whales entrapped and killed in set nets off Japan Disturbance from offshore oil and gas activities Rapidly expanding oil and gas industry off Sakhalin

63 Western North Pacific gray whales: The population of gray whales in the WNP was probably never as large as that in the ENP Commercial whaling for WNP gray whales continued through at least 1966 At least some scientists believed that WNP gray whales were extinct in the 1970s, but their continued existence was later confirmed by sightings and catch records Little was known about the current status of WNP gray whales until 1995

64 Anthropogenic Threats: 19% of whales off Sakhalin show signs of entanglement in fishing gear 2% show signs of surviving at least one vessel collision Bradford et al.

65 Killer whale predation: 44% of whales demonstrate evidence of attacks by killer whales (Weller et al. 2008)

66 Body Condition: Skinny whales Bradford et al.

67 Distribution: ~19,000 animals ~130 animals? ~200 animals N=6??? N=1 14 records of gray whales off Japan since 1990 Most records concentrated between Mar May One animal linked to Sakhalin (Weller et al. 2008) 2 records of gray whales off China since 1996 N=2 N=14

68 Arctic sea ice extent for September 16, 2012 was 3.41m sq km. The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole. Photograph: National Snow and Ice Data Center In Sept 2012, Arctic sea ice shrank 18% compared to previous low record (2007)

69 Photo-identification of gray whales:

70 Fossil Record: Tsai and Boessinger 2015

71 Fossil Record: Tsai and Boessinger 2015

72 Taxonomic history: First described based on subfossil remains from the coast of Sweden (Lilljeborg 1861) Named after a Danish zoologist (Dr. Daniel Eschricht) who was the first to suggest the remains might be from a new genus and family Formally described as distinct by John Edward Gray, head of the Zoology Department at the British Museum of Natural History Gray named the genus Eschrichtius in honor of Dr. Eschricht Some confusion over whether the common name derives from the coloration or from the man who first formally recognized the genus as distinct