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National Marine Mammal Laboratory

(Quarterly Report for July-Aug-Sept 2000)

Cooperative Research: Whale Survey off Brazil

Waters off the northeastern coast of Brazil were a major whaling ground during the 20th century until 1985.  After whaling ended, little information was available about the status and possible recovery of whale stocks there.  To determine the status of  the whale populations off the northeastern coast of Brazil, the Brazilian Environmental Agency (IBAMA), with support from the Brazilian Navy and the National Council for Science and Technology (CNPq), sponsored cetacean sighting cruises in the former whaling ground in 1998, 1999, and again in 2000.  This year a scientist from the National Marine Mammal Laboratory (NMML) participated in the 2000 cetacean survey, as the first step in establishing a long-term cooperative research project between the United States and Brazil.

The survey was conducted from 14 August to 5 September 2000 aboard the Brazilian Navy ship Almirante Graca Aranha and consisted of two 10-day legs, with a 3-day break between legs. The primary objective for the first leg was to conduct a line transect survey for Antarctic minke whales (Balaenoptera bonaerensis) in offshore waters of Brazil from approximately lat. 5°S to 10°S , offshore to approximately long. 33°W.  The primary objective for the second leg was to conduct a  line-transect survey for humpback whales (Megaptera novaeangliae) in shelf waters from approximately 5°S to 13°S.  All other cetacean species were recorded.

The Almirante Graca Aranha is a 74-m long vessel, and the survey was conducted from the 12- m high flying bridge with four observer stations while the ship was at a speed of approximately 9 kt.  One observer searched from the bow to 90° off the starboard side of the ship, while another searched from the bow to 90° off the port side. They searched mostly by naked eye with occasional sweeps with Fujinon 7x50 hand-held binoculars.  The other two observers searched the trackline from 0° to 10° (one to starboard and one to port), alternating every 5 minutes between naked eye and binoculars.  For every sighting, a distance measurement (using reticles in the binoculars) and an angle (using a pelorus) was recorded.  A data recorder recorded the beginning and end times of survey effort, environmental conditions, and sighting information. The observers rotated positions every half hour resulting in a 2.5-hour shift followed by a 2-hour rest period.  The survey was suspended during inclement weather and when light levels were too low for efficient observations.

A total of 1,071.1 nautical miles (nmi) were surveyed: training: 90 nmi; Leg 1: 490.9 nmi;  Leg 2: 490.2 nmi. Sightings included 209 cetacean groups.  The most frequent species were humpback whales (107 sightings), bottlenose dolphins (Tursiops truncatus) (35 sightings), pantropical spotted dolphins (Stenella attenuata) (11 sightings), and  Antarctic minke whales (9 sightings). Additional species sighted included clymene dolphins (Stenella clymene) (2 sightings), sei whales (Balaenoptera borealis) (2 sightings), tucuxi (Sotalia fluviatilis) (3 sightings), spinner dolphins (Stenella longirostris), (1 sighting, mixed with pantropical spotted dolphins), and 1 dwarf minke whale (Balaenoptera acutorostrata). Unusual sightings included 1 group of 8 false killer whales (Pseudorca crassidens), a pair of pygmy killer whales (Feresa attenuata) with bottlenose dolphins, a mother and calf Cuvier’s beaked whale (Ziphius cavirostris), a multispecies aggregation of 6 Antarctic minke whales, 10 shortfinned pilot whales (Globicephala macrorhynchus) and 40 bottlenose dolphins.

Results from this survey will be combined with previous years’ survey results to produce abundance estimates for minke and humpback whales and to report other new information about cetacean species in Brazilian waters.  The IBAMA plans to conduct three additional surveys from 2001 to 2003. The major goal is to expand the survey area and attain abundance estimates of minke whales from 5°S to 25°S. They also plan to collect biopsy samples from all cetacean species, whenever possible, and develop an acoustic project for large whales. A cooperative effort will continue with NOAA and Brazilian scientists.

By Janice Waite and Alexandre Zerbini (School of Aquatic and Fishery Sciences, University of Washington)

Aerial Surveys and Radio Tagging of Harbor Seals in Bristol Bay

Harbor seals (Phoca vitulina), were surveyed along the coast of Bristol Bay, Alaska, and adjacent waters from about Goodnews Bay in the north, to Unimak Pass in the south.  This region is one of five that are surveyed on a 5-year rotation to estimate the range-wide abundance of harbor seals in Alaska.  An additional survey was conducted along the southern Alaska Peninsula from Unimak Pass to Chignik, part of the very large Gulf of Alaska region, the remainder of which will be surveyed in 2001.  The surveys were conducted on 12-29 August by six observers flying in five chartered aircraft.  Observers flew daily survey routes to obtain counts (or photographs to be counted later) on as many as 9 days at each site where harbor seals hauled out.  These daily replicates provide information required to adjust for conditions such as date, time of day, tide height, and weather, which influence the proportion of seals ashore during the surveys.  This was the first systematic survey of harbor seals in southwestern Bristol Bay, which included Izembek Lagoon National Wildlife Refuge. Although seal numbers were expected, based on anecdotal reports, to be low in this area, we found the opposite to be true, with several groups of 300-500 seals observed daily on sandbars near breaks in the lagoon barrier.

To estimate the total abundance of harbor seals, the proportion of seals that were missed because they were not ashore during surveys must be obtained by other means, such as a mark-resight estimate.  In collaboration with the U.S. Fish and Wildlife Service (USFWS), harbor seals were tagged with radio transmitters during early August in Nanvak Bay in the Togiak National Wildlife Refuge.  This site in northwestern Bristol Bay was selected because seals are typically abundant there and because of the opportunity for logistical cooperation with the USFWS.  From 5 to 16 August 2000, three to six seals were captured daily at low tide with tangle nets in a procedure similar to one used for harbor seals hauled out on ice (AFSC Quarterly Report October-November-December 1999).  Thirty-two seals were captured, measured, weighed, tissue-sampled for genetic analysis, and tagged with single radio transmitters on a rear flipper so that the radio signal could be detected only if the seal was ashore.  During aerial survey flights in the Nanvak Bay area, the presence and location of radio-tagged seals were recorded.  Most tagged seals remained in Nanvak Bay, but on some days up to half were resighted outside the bay up to 50 km away.  These resighting data, along with other data obtained from a receiver and data-logger installed in the study area, will be used to derive a correction factor for the proportion of seals missed during the aerial surveys.

By John Jansen, Dave Withrow, and Peter Boveng.

Alaska Harbor Seal Comanagement Workshop

Four NMML scientists participated in a Harbor Seal Comanagement Workshop, held on 25-26 September 2000, in Juneau, Alaska.  The workshop brought together scientists, hunters, elders, and other technical experts in the areas of population monitoring, harvest management, and education, to provide perspectives on the current state of knowledge in those subject areas and to identify critical needs for information in support of harbor seal conservation. A half day was dedicated to a discussion on each subject area. Dave Withrow gave a presentation on the NMML research program for monitoring harbor seal populations.  Following the workshop, the Harbor Seal Comanagement Committee, composed of three members each from the Alaska Native Harbor Seal Commission (ANHSC) and NMFS, drafted its first action plan.  According to the Comanagement Agreement between the ANHSC and  NMFS, the action plan, which is to be updated annually, will be the guiding document for joint and separate management actions by the ANHSC and NMFS related to the conservation and management of subsistence use of harbor seals.

By John Bengtson and Peter Boveng.

Pinniped Population Studies at San Miguel Island

National Marine Mammal Laboratory scientists conducted pinniped population studies at San Miguel Island, California, from 18 May through 9 August 2000.  The primary focus of the studies was to continue the long-term study of survival, recruitment, natality, health, and population trends of California sea lions (Zalophus californianus), and northern fur seals (Callorhinus ursinus).  Research activities included observation of branded sea lions and tagged fur seals, pup mortality surveys, and live pup counts of both species.  During the mortality surveys at the end of July, scientists necropsied sea lion and fur seal pups to assess the incidence of hookworm infestation and to study the genetics of two different species of hookworms that affect these pinnipeds.

In general, California sea lion and northern fur seal pup production increased in 2000.  Sea lion pup production increased 3%, and northern fur seal pup production increased 52 % from 1999. California sea lion production appears to have recovered from the severe decline in 1998; however, northern fur seal production still remains 46% below the 1997 estimate, indicating that the 1997-98 El Niño event has had a long-term impact on northern fur seals at San Miguel Island.  Mortality surveys for California sea lion pups indicate an increase in pup mortality from 14% in 1999 to 19% in 2000, but northern fur seal pup mortality declined from 26% in 1999 to 10 % in 2000.  All 30 California sea lion pups and 20 northern fur seal pups sampled for hookworms had severe infestations, which probably caused their deaths. Long-term monitoring of the health of these two populations indicates that hookworm infestations have become a significant cause of mortality in the past decade.

The brand-resighting effort produced 7,300 sightings of 1,674 branded individual sea lions,  including 414 branded females with pups and 19 territorial males.  Increased effort to sight tagged northern fur seals produced sightings of 142 individuals.  These data will be used to generate age-specific survival and natality estimates for these species at San Miguel Island for use in age-structured population models.  The results of the 2000 field season show the importance of continued monitoring of the sea lions and fur seals at San Miguel Island.  Such data will provide a unique opportunity to identify the roles that disease and the environment play in the population dynamics of these two species.

By Sharon Melin.