Surveys

Abstract

Surveys are used to address many different marine mammal research questions, including distribution, abundance, trends, and habitat associations. Equipment and methodology vary depending on the species of interest, financial resources, availability of research platforms, and survey objective. Marine mammals at sea are most commonly surveyed aboard ships or large boats, or from fixed-wing aircraft. Small boats, helicopters, airships, and land-based viewing stations are also used when appropriate. Line-transect methods are often the most effective for estimating the abundance of marine mammals at sea, although other survey techniques are also used. Marine mammals on or near land, such as pinnipeds, sea otters, or walruses, are more commonly counted from land-based viewing points or using aerial photography. Large oceanographic research vessels are the most versatile platform for at-sea surveys of marine mammals. They can carry a dozen or more researchers and remain at sea for weeks at a time, providing the ability to cover extensive marine areas. The main advantages of aerial surveys are the ability to cover large areas quickly and the lower cost of aircraft compared to large ships. They are particularly useful for rapid assessments and preliminary studies to determine the relative distribution and abundance of species in a particular region. Using strip or line-transect methods, aerial survey can be used to estimate abundance and monitor trends. A typical aerial survey observer team consists of two observers searching through the two side windows, one data recorder, and, if possible, a belly observer. Aircraft can also be outfitted with downward viewing instrumentation to measure ocean surface properties, such as sea surface temperature and ocean color, to provide habitat information during surveys. Detectability of marine mammals is a key factor in deciding what type of survey platform to use. There is increasing recognition that marine mammal surveys are most effectively interpreted in the context of the habitat conditions at the time of the survey. Marine ecosystems are very dynamic, and the concurrent collection of real-time ecosystem data during surveys provides an ecological context for the observed patterns in marine mammal distribution and abundance.