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Project Description

The National Marine Mammal Laboratory (NMML) has been conducting cetacean surveys throughout the inland waters of Southeast Alaska since 1991. The NOAA ship John N. Cobb has been used as the survey vessel. Between 1991 and 1993, line-transect methodology was used to obtain baseline information on harbor porpoise and Dall's porpoise abundance and distribution. Three surveys were carried out each year spanning spring, summer, and fall. Between 1994 and 2005 study objectives varied. Only two trips per year were conducted; one either in spring or summer and the other in fall. Photo-identification studies on killer whales and humpback whales were carried out during these years. Although line-transect methodology was not used, all cetaceans observed were recorded. Over the 15-year study period, observers reported fewer encounters for both species of porpoise. Although this raised concerns, our confidence in these data was low due to lack of quantification of effort, number of surveys per year varied, differences used in methodology, and other factors that could influence these counts (i.e., differences in mean group sizes by season or year, differences in survey coverage and duration, and focal studies on humpback whales or killer whales).

To fully assess population trends for Dall's porpoise and harbor porpoise, NMML, with the assistance of the Alaska Regional Office, conducted line-transect surveys in the study area in 2006 and 2007; one each in spring, summer, and fall (Note: Fall 2006 survey cancelled due to ship breakdown). Line-transect methods used in the 19991-1993 seasons were followed. Similar surveys are planned for the 2008 season. Detailed analysis, to include abundance estimates and population trends of Dall's porpoise and harbor porpoise will be completed by NMML researchers.

In 2008, one vessel survey (11-days) will be conducted within the inland waterways of Southeast Alaska to estimate the abundance of cetaceans and investigate population trends. A second survey will be added contingent upon receiving additional funding. In 2008, two methodologies will be used: line transect and mark/recapture studies. Abundance estimates for harbor porpoise and Dall's porpoise obtained during the line-transect surveys will be compared to those obtained during nine, line-transect surveys conducted in this same area during the 1991, 1992, and 1993 seasons (three surveys conducted each year) and the five surveys conducted in 2006 and 2007. Between 1994 and 2005, two surveys were conducted each year with an emphasis on photo-identification work with killer whales. Mark/recapture population estimates will use this long-term database, 1994 - 2007 and the 2008 survey data, to obtain killer whale abundance estimates.

Issues & Justification

NMML has conducted research on several species of cetaceans in Southeast Alaska, including humpback whales, killer whales, Dall's porpoise, and harbor porpoise for nearly two decades. Studies include: an assessment of cetacean population size and distribution, habitat characterization, genetic, dietary, and contaminant research. Estimates of cetacean abundance are required every 4-8 years to complete stock assessments for these species. We hope to dovetail upcoming assessment surveys with the Alaska Region's plans to observe certain commercial fisheries to ensure that there is both a population estimate and a fishery-related mortality estimate of marine mammals in the same season. Comparative studies between marine mammal populations in Southeast Alaska and western Alaska have provided important insights into factors that affect marine mammal populations. We have found that survey operations in protected waters such as Southeast Alaska to be cost-efficient for developing survey methodologies, allowing us to then apply lessons learned to more remote, operationally expensive regions. Herein, we propose to compare cetacean abundance estimates derived during the 1991-1993 ship surveys with those obtained during vessel surveys conducted in the 2006 - 2008 seasons. Trend analysis will be also completed.

Goals

  • Estimate abundance of Dall's porpoise & harbor porpoise in the inland waterways of Southeast Alaska.
  • Investigate Dall's porpoise & harbor porpoise population trends between 1991 and 2006 through 2008.
  • Examine harbor porpoise and Dall's porpoise distributional data and relate to environmental data.
  • Estimate abundance of killer whales through mark-recapture studies in Southeast Alaska

Methods

The NOAA R/V John N. Cobb will be used to complete both line-transect work and mark/recapture studies. This platform has been used for all previous survey work (36 cruises; 1991 through 2007). A three-observer system will be used (one port, one starboard, and one dedicated recorder). A team of 4 observers will be required to perform this research. The survey will be based out of Juneau, Alaska. All major waterways from Juneau to Ketchikan will be surveyed. Abundance is estimated using advanced distance analysis techniques.
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