[MARMAM] New paper - Refining estimates of availability bias to improve assessments of the conservation status of an endangered dolphin

Federico Sucunza fsucunza at gmail.com
Thu Mar 22 10:02:07 PDT 2018

 Dear colleagues,

My co-authors and I are pleased to announce our new publication:

Sucunza F, Danilewicz D, Cremer M, Andriolo A, Zerbini AN (2018) Refining
estimates of
availability bias to improve assessments of the conservation status of an
endangered dolphin.

Abstract: Estimation of visibility bias is critical to accurately compute
abundance of wild populations. The franciscana, Pontoporia blainvillei, is
considered the most threatened small cetacean in the southwestern Atlantic
Ocean. Aerial surveys are considered the most effective method to estimate
abundance of this species, but many existing estimates have been
considered unreliable because they lack proper estimation of correction
factors for visibility bias. In this study, helicopter surveys were
conducted to determine surfacing-diving intervals of franciscanas and to
estimate availability for aerial platforms. Fifteen hours were flown and
101 groups of 1 to 7 franciscanas were monitored, resulting in a sample of
248 surface-dive cycles. The mean surfacing interval and diving interval
times were 16.10 seconds (SE=9.74) and 39.77 seconds (SE=29.06),
respectively. Availability was estimated at 0.39 (SE=0.01), a value 16–46%
greater than estimates computed from diving parameters obtained from boats
or from land. Generalized mixed-effects models were used to investigate
the influence of biological and environmental predictors on the proportion
of time franciscana groups are visually available to be seen from an aerial
platform. These models revealed that group size was the main factor
influencing the proportion at surface. The use of negatively biased
estimates of availability results in overestimation of abundance, leads to
overly optimistic assessments of extinction probabilities and to
potentially ineffective management actions. This study demonstrates that
estimates of availability must be computed from suitable platforms to
ensure proper conservation decisions are implemented to protect threatened
species such as the franciscana.

The paper is available here:

Best regards,
Federico Sucunza
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