[MARMAM] New publication - Humpback whale group sizes in line transect ship surveys

Guilherme Augusto Bortolotto bortolotto.ga at gmail.com
Tue May 10 09:41:58 PDT 2016

Dear colleagues,

We are pleased to announce our recent publication:

Bortolotto G.A., Danilewicz D., Andriolo A. and Zerbini A.N. (2016).
Humpback whale *Megaptera novaeangliae* (Cetartiodactyla: Balaenopteridae)
group sizes in line transect ship surveys: An evaluation of observer
errors. *Zoologia (Curitiba)*, 33(2), e20150133.

In this *short communication* we describe a study were we aimed to evaluate
the potential errors in group size estimation during line transect ship
surveys to estimate abundances of the humpback whale.

ABSTRACT. Accurate estimates of group sizes through line transect sampling
methods are important to correctly ascertain the abundance of animals that
occur in groups. Since the average observed group size is a component of
the distance sampling formula, bias in these data leads to biased abundance
estimates. This study aimed to evaluate the potential errors in group size
estimation during line transect ship surveys to estimate abundances of the
humpback whale,* Megaptera novaeangliae* (Borowski 1781). In a research
cruise along the Brazilian coast, an experiment to collect group size
information was conducted from two different sighting platforms on the same
vessel. Group sizes were recorded by primary observers at first sighting (
*PO1*) and, in some cases, after some time (*PO2*). A tracker (*T*) was
located on a higher platform to estimate the sizes of groups detected by
the primary observers, but tracked one group at a time until it passed
abeam. Thus, the dedicated effort to obtain multiple group counts (i.e.
higher platform, more time and no responsibility for detecting new groups)
was expected to provide more accurate numbers. *PO2* estimates were
compared with *PO1* estimates, and *T* estimates were compared with both
*PO1* and *PO2*. Additionally, ratios between* T* and both *PO2* (*R1*) and
*PO1* (*R2*), and between *PO2 *and *PO1* (R3) were calculated. To
investigate a possible improvement in abundance estimates, a correction
factor (*CF*) was computed from the ratio of *T* and *PO2* means. Primary
observer self-correction (= 1.60, CV% = 70.3) was statistically similar to
the correction for the tracker (= 1.62, CV% = 84.1). *CF* resulted in 1 and
would not improve abundance estimates. This study supports that observers
conducting line transect surveys on large whales have the potential to
provide group size information that is as adequate as the correction
procedure adopted.

The paper is available online here:

With kind regards,

*Gui Bortolotto* *|* PhD Student
SMRU • CREEM • School of Biology
University of St Andrews
Mobile UK: (+44) 0 7884 398394
Email: gabdo at st-andrews.ac.uk

R3 Animal Association (http://en.r3animal.org/)
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