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Geographic, seasonal, and diurnal surface behavior of harbor porpoises
Author(s) -
Teilmann Jonas,
Christiansen Casper T.,
Kjellerup Sanne,
Dietz Rune,
Nachman Gösta
Publication year - 2013
Publication title -
marine mammal science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.723
H-Index - 78
eISSN - 1748-7692
pISSN - 0824-0469
DOI - 10.1111/j.1748-7692.2012.00597.x
Subject(s) - phocoena , seasonality , range (aeronautics) , abundance (ecology) , geography , population , environmental science , predation , aerial survey , oceanography , home range , fishery , ecology , biology , physical geography , porpoise , habitat , remote sensing , geology , harbour , demography , materials science , sociology , computer science , composite material , programming language
Abstract During ship surveys harbor porpoises are only visible when breaking the sea surface to breathe, while during aerial surveys they may be seen down to 2 m below the surface. The fractions of time spent at these two depths can be used for correcting visual surveys to actual population estimates, which are essential information on the status and management of the species. Thirty‐five free‐ranging harbor porpoises ( Phocoena phocoena ) were tracked in the region between the Baltic and the North Sea for 25–349 d using Argos satellite transmitters. No differences were found in surface behavior between geographical areas or the size of the animals. Slight differences were found between the two sexes and time of day. Surface time peaked in April, where 6% was spent with the transmitter above surface and 61.5% between 0 and 2 m depth, while the minimum values occurred in February (3.4% and 42.5%, respectively). The analyses reveal that individual variation among porpoises is the most important factor in explaining variation in surface rates. However, the large number of animals documented in the present study covering a wide range of age and sex groups justifies the use of the seasonal average surface times for correcting abundance surveys.