A small team of seabird ecologists will use Leg 0 to carry out a survey and census of the seabirds observed on the journey between Vigo and Las Palmas.
Opportunities to observe seabirds out in the open ocean are quite rare, and iMirabilis2 provides an excellent opportunity to not only carry out a survey of these animals, but also to train seabird ecologists in survey and census techniques. This is done entirely through manual observation, involving many hours out on deck observing and counting seabirds using binoculars. No doubt marine mammals will also be spotted along the way, and recording our sightings of these creatures is also important for understanding the overall biodiversity of the region. Photographing the different species is a key part of this work, and we hope to share plenty of these beautiful images with you!
Our seabird ecology team on board iMirabilis2 are part of Projecto Vito – an initiative to protect and conserve biodiversity and natural resources in and around Cabo Verde.
It may seem an impossible task to get an accurate estimate of seabird abundance through visual observations in an environment as wide open and dynamic as the ocean, but there are established methods to achieve this. The method of seabird censusing used on iMirabilis2 will be mostly based on the article by Tasker et al. (1984), which is widely accepted as the standard method for seabird censusing at sea and it is also the basic method used to input to the European Seabirds At Sea (ESAS) Database. This methodology allows us to determine absolute seabird densities (birds/km2) as well as for other marine megafana. The method suffers from a number of potential biases, and therefore results must be used with caution, but it is currently considered the easiest and most rigorous method for this type of censuses during ship transits allowing to compare data across different areas and periods.
Our work on the journey from Vigo to Gran Canaria will be focused on oceanic birds, mainly petrels and shearwaters. Our survey method takes a distance sampling approach, which requires us to know some details about the ship in order to determine the bird position on survey transects:
- The eye height of the observer it is important for the sighting angle and it will affect how we calculate the position of survey bands. For the best visibility the recommended observation point is at highest place possible on the vessel with clear sight, usually at the bow.
- The survey transect width is 300m. Subdivision of survey transects allow us to make corrections. If we are able to precisely know the position or distance of an object using the ship’s radar, GPS or other positional methods this is a great help in calculating the subdivision of survey transects.
- We also need to know the vessel speed (the optimum is 10 knots, recommended between 4 and 10 knots), because this can modify the ‘snapshot’ of birds taken and the duration of the survey transect (1200m at 4 knots takes 10 min).
- The sea state is important too because it can affect our survey work. At a sea state of over 3 we will stop surveying.
- Whenever the ship changes course we have to start a new survey, so we need to know the ship’s course in advance so we can plan accordingly.
- At the start of new survey we will take lat-long coordinates. Survey time unity interval will be 10 min (regardless of ship’s speed).
Reference: Tasker M, Jones PH, Dixon T, Blake BF (1984) Counting seabirds at sea from ships: a review of methods employed and a suggestion for a standardized approach. Auk 101:567-577
Below: Short film from Projecto Vito of their Seabird Steering Committee visiting Ilheus Rombos in Cabo Verde – a site near the submarine volcano at Cadamosto, which is one of the sites under investigation during Leg 1 of the iMirabilis expedition