NMML Harbor Porpoise Aerial Survey, Bristol Bay, Replicate 2, 1991

National Marine Mammal Laboratory

From 4 to 13 August 1991, as part of a larger study, Alaska harbor porpoise (Phocoena phocoena) abundance was investigated during an aerial survey throughout the coastal waters of Bristol Bay. A Twin Otter was used as the survey platform and was flown at an altitude of 152.2 m (500 ft) and at an airspeed of 185 km/h. The second of three identical sawtooth tracklines was flown along the south side of Bristol Bay. Line-transect methodology was used, and only those observations made during optimal conditions were analyzed. Density of harbor porpoises was calculated using line transect estimates based on perpendicular distances of sightings to the cruise track of the airplane. On average, porpoise group size and density for Bristol Bay was 1.17 (SE = 0.35) and 4.48 groups/100 km2 (SE = 1.38).

Although harbor porpoises, Phocoena phocoena, are known to occur throughout Alaska waters, few estimates of abundance exist. In 1991, the National Marine Mammal Laboratory initiated a 3 year study on Alaska harbor porpoises. The objectives of this program were to:
1) Obtain minimum population estimates in coastal waters using line transect methodology with a coefficient of variation for density estimates of less than 30% for each survey area, and
2) Establish a baseline for detecting changes in abundance through time, for analysis of trends.
During the present study, it was not fiscally possible to survey all areas of the state in any one year. Accordingly, we selected sections of the state to survey in consecutive years to maximize the likelihood of including all of the animals for a particular area surveyed while minimizing the likelihood of significant movement between areas among survey years.

This dataset and associated effort data were updated on September 8, 2005. Those who downloaded them before that date should renew them.

Overview

Attributes described below represent those in the original dataset provided by the provider.
Only minimum required attributes are visible and downloadable online. Other attributes may be obtained upon provider's permission.

Attributes in dataset

Attribute (table column)	Description
dataset
lineno
dupl
line
lleg
date
event
time
dtime
beaufort
cloudcov
portvis
starvis
pglar
sglar
airspd
alt
latdeg
latmin
dlat
londeg
lonmin
dlong
pobs
recorder
sobs
pilot
linenum
begwpt
endwpt
herdsize
spcode
common
tsn	Species ITIS TSN
scientific
group
angle
perpdis
observ
grpsiz
comments
excluded
oid	Unique ID number (generated by SEAMAP)