SMRU sperm whale distribution around the Balearic Islands 2003-2008

Luke Rendell and Enrico Pirotta, Sea Mammal Research Unit (SMRU)

Sperm whale Physeter macrocephalus habitat preferences are still poorly understood in the Mediterranean, despite the population being classified as ‘Endangered’ by the IUCN. Techniques to make the best use of multiple data sources are important in improving this situation. This work provides
a detailed evaluation of sperm whale distribution and habitat use around the Balearic Islands using a novel analytical framework that combines transect and follow data while accounting for any autocorrelation present. During dedicated research cruises (2003 to 2008), sperm whales were
located by listening at regular intervals along a search track and subsequently followed acoustically. Sperm whales were encountered 56 times and followed for periods ranging from a few hours to 3 d. Logistic Generalized Additive Models were used to model the probability of whale presence across
the study area as a function of environmental variables, and Generalized Estimating Equations were used to account for autocorrelation. The results suggest that sperm whales do not use the region uniformly and that topography plays a key role in shaping their distribution. Moreover, solitary individuals
were found to use the habitat differently from groups. This segregation appeared to be driven by water temperature and might reflect different needs or intraspecific competition. By shedding light on sperm whale habitat preference in such a critical area, this study represents an important step
towards the implementation of conservation measures for this population.

In this study we develop a novel analytical framework that can make use of combined acoustic and tracking data and account for autocorrelation in such data. We use a multi-scale approach to investigate the pattern of sperm whale distribution around the Balearic archipelago, and the potential differences in habitat selection by single individuals versus groups.

Exact numbers for the presence of groups were not available, so an abundance of "2" was used as a conservative estimate. The sequences of consecutive presence points do not represent new animals being encountered, but follows of the same animals.

Overview

This section explains attributes included in the original dataset. OBIS-SEAMAP restricts the attributes available to the public to date/time, lat/lon and species names/counts only. Should you need other attributes described here, you are encouraged to contact the data provider.

Attributes described below represent those in the original dataset provided by the provider.
Only minimum required attributes are visible and downloadable online. Other attributes may be obtained upon provider's permission.

Attributes in dataset

Attribute (table column)	Description
oid	Unique ID number (generated by SEAMAP)
recnum	Record number (generated by SEAMAP)
obs_date	Observed date
obs_time	Observed time
latitude	Latitude of observation
longitude	Longitude of observation
pres	Acoustic contact: presence or absence (1 or 0)
grouping	Group or single
sp_obs	Species observed
sp_tsn	Species ITIS TSN
obs_count	Observed count (1 for single, 2 for groups)
notes	Exact group size was not available, and an abundance of "2" was used as a conservative estimate. The sequences of consecutive presence points do not represent new animals being encountered, but follows of the same animals.