Looking to the horizon
Vol.10. 30th June 2017
Guest post by Nadya Ramirez-Martinez
Nadya Ramirez-Martinez is a researcher at the Sea Mammal Research Unit (SMRU), University of St Andrews and is on board the RRS Discovery in a collaboration with Gisli Vikingsson at the Marine and Freshwater Research Institute in Reykjavik, Iceland. She is collaborating with Iceland, Norway and the Faroe Islands in a project to improve understanding of the environmental factors that influence the distribution and habitat use of a range of cetacean species in the central and northeast Atlantic over a period of three decades.
How do you ‘interview’ a dolphin?
Today, as I am writing, we have been three weeks on board the RRS Discovery and only have 4 days left of our visual and acoustic marine mammal surveys (see Blog vol.6.). For the visual surveys, we have a surveying effort ranging from optimal (unlimited visibility and calm seas) to very poor (fog and rough seas). To date, we can only mention preliminary observations as accounting for conditions during observation and the time spent in such conditions (as you can imagine) must be considered for analysis.
Striped Dolphin © Gui Bortolotto
As mentioned in a previous blog article (see Blog vol.5.), one of our goals is estimating abundance. Besides marine mammal abundance, we want to know more about where they occur; more precisely, what are their habitat preferences. If we were doing this same study on a group of people, the easiest approach would be performing interviews. Unfortunately, this is not possible with marine mammals, so instead we can combine data from different disciplines to approach this question. The lines of survey (transects) will be divided in small pieces of equal conditions (segments). Each segment will contain information about the abundance estimates, oceanographical variables (physical, chemical and biological) and topography. Using statistical tools (habitat modelling) we will be able to model how marine mammals use their habitat.
CTD (Conductivity Temperature Depth) Instrument © Nadya Ramirez-Martinez
A sight to behold: 12 different species of marine mammals!
What have we seen so far in our ‘Journey to the mid-Atlantic Ridge’? As of today, we are already in Canadian offshore waters; we have seen a total of 12 different species of marine mammals. The baleen whales (Mysticeti) seen have been: blue, fin, sei, humpback, and minke. The toothed whales (Odontoceti) are: sperm and pilot whales, and bottlenose, Risso’s, striped, short-beaked common, and Atlantic white-sided dolphins. Preliminarily, it seems that fin whales and short-beaked common dolphins were our most common sightings for each of the groups. Among the species mentioned above, there are deep divers such as sperm and pilot whales; these are known to feed upon prey found in deep waters. Most of the other species are believed to have mainly epipelagic (ranging from surface to 200 m depth) diets.
Pilot whales © Gui Bortolotto
Before analysis, it is difficult to know specifically how the marine mammal sightings (considering effort) are related to the oceanographical and topographical conditions. For example, we have had days of optimal effort conditions with high number of animal sightings but also the opposite, optimal conditions and not many sightings.
Feeding Fin whale © Claire Lacey
During the expedition, we have crossed over very productive areas (high chlorophyll a), sub-mesoscale and mesoscale eddies, sea mountains, frontal and fracture zones. This means that our trip included a wide range of oceanographic features that can affect or enhance primary productivity. Primary producers or phytoplankton is the base for the occurrence of higher trophic levels such as zooplankton, fish, sea birds, marine mammals. During our expedition, in-situ oceanographical data such as water profiles, nutrients and productivity is being collected. We look forward to be able to understand the habitat preference of marine mammals we have seen during this expedition taking a multidisciplinary approach in collaboration with other scientists on-board.
Follow the RSS Discovery's position on the National Oceanography Centre's 'Vessel Tracker'.