Project Description
The purpose of this project is to obtain the field data (survey counts of harbor seals) that are necessary to support abundance estimates and MMPA stock assessments. Periodic surveys of harbor seal populations are fundamental to estimation of seal abundance, distribution, and trends, which in turn are essential for conservation and management. The most feasible approach to determining harbor seal distribution and abundance is to use aircraft to count seals when they haul out of the water and are visible. Harbor seals in Alaska occupy a geographically extensive range from approximately 172A§E to 130A§W (over 3500 km east to west) and from 51A§N to 61A§N (over 1000 km north to south). Previously, Alaska has been divided into five survey regions and only one of those regions is surveyed each year. This approach allowed us to survey the entire coastline for a region, but because regions were only surveyed once every five years, information on population trends was limited. In FY08 we plan to utilize a new approach that will allow us to survey harbor seals across the entire Alaska region. We will focus on surveying large sites every year and surveying smaller sites every few years. This should provide us the data necessary to estimate harbor seal population and trends on an annual basis.
Issues & Justification
The 1994 amendments to the Marine Mammal Protection Act require that NMFS produce a Stock Assessment Report (SAR) on the status of each species under its jurisdiction. Certain key population parameters are required to describe the status of the stock, including population size. Minimum population estimates are also needed for the calculation of a Potential Biological Removal (PBR) level, also required in the SARs. Since 1991 the NMFS National Marine Mammal Laboratory, in cooperation with ADF&G, has conducted yearly censuses of harbor seals in Alaska to provide baseline population information and for purposes of calculating a minimum population estimate for the SARs.
Goals
- Develop and implement a distributed survey strategy for harbor seals in the Alaska region.
- Conduct aerial surveys to determine abundance and distribution of harbor seals in the Alaska region.
- Generate counts for each site and date surveyed, by counting seals in digital images
Methods
In FY08 we plan to utilize a new approach that will allow us to survey harbor seals across the entire Alaska region. We will focus on surveying large sites every year and surveying smaller sites every few years. This should provide us the data necessary to estimate harbor seal population and trends on an annual basis. However, this approach will likely require more complex logistical arrangements and planning. Fixed-wing aircraft will be used to photograph harbor seals hauled out during the molt season in August. As many as 13 separate aircraft working simultaneously may be required to survey the region. Aerial surveys are flown between 100 and 300m altitude at 90 knots, within 2 hours on either side of low tide. The entire coastline is surveyed several times initially to identify haul-out sites. Then observers fly from site to site including all previously known sites. Four to six repetitive counts on separate days are planned for each haul-out site within each study area over the 10-day survey period. With a few exceptions, all seals are photographed with a digital camera equipped with a 70-210 mm lens. The seals are later counted from the digital images and the counts are entered into an SQL database.