Complex temporal distribution of fin whales and sei whales in the Azores.

Abstract

In the last 10 years in São Miguel Island, Azores, we have sighted 6 different species of baleen whales (Suborder Mysticeti). Regarding fin whales and sei whales, most of the encounters have been recorded during spring (74.3%, 67.7%), but others have been seen in other seasons too (winter: 7.4%, 1.1%; summer: 15.4%, 22.9%; autumn 2.9%, 8.3%). This makes us think that the general baleen whale migration patterns for these species are overly simplified. The theory indicates that during winter time, baleen whales breed in low latitudes, while in summer they are usually found in higher latitudes, where food is abundant. We collected cetacean encounter data from a whale watching platform between 2008 and 2017 off São Miguel. Our results for fin whales show a clear preference for spring time. It is highly remarkable the high number of sightings in 2014, 2016 and 2017 compared to the other years. It is also notable that there was an increased number of records the last three summers (2015-2017), suggesting a delay in their timing. Regarding sei whales, preferences go for late spring to mid-summer. In 2017 most sightings occurred in autumn (41.3%), although they were sighted from late march every single month until December. Other studies in the north Atlantic had pointed out similar results, sightings out of the expected seasons. All those findings suggest that the temporal distribution of these whales species in the North Atlantic is more complex than previously thought. Hence, more research is needed in order to answer the questions arising from this study. Different whale stocks can choose different migration strategies. Maybe not all the fin/sei whales are travelling long distances every season, which could suggest different periodicity for individuals that are not yet sexually mature or reproductive or perhaps relate their journeys to the food availability.

Full text

Complex temporal distribution of fin whales
and sei whales in the Azores
Víctor Ojeda1, Cristina Montoya1, Miranda van der Linde1& Laura González1,2
1 Futurismo Azores Whale Watching, Ponta Delgada, Azores, Portugal.
2 Department of Applied Physics, Vigo University, Vigo, Spain.
DISCUSSION AND CONCLUSIONS
victor.ojma@gmail.com
RESULTS
AKNOWLEDGEMENTS.We would like to thank the Futurismo Azores Whale Watching team, biologists and guides who have collected data for this study, and especially, the
skippers and lookouts who have worked hard everyday with us. Also we would like to acknowledge the clients who choose this way to see the animals in their natural habitat.
REFERENCES. [1] Visser et al. (2011). Timing of migratory baleen whales at the Azores in relation to the North Atlantic spring bloom. Mar Ecol Prog Ser,440: 267-279. [2] Silva et al.(2013). North
Atlantic blue and fin whales suspend their spring migration to forage in middle latitudes: building up energy reserves for the journey? PLoS One,8(10): e76507. [3] Prieto et al.(2014). Sei whale movements
and behaviour in the North Atlantic inferred from satellite telemetry. Endang Species Res,26(2): 103-113. [4] Croll et al.(2002). Bioacoustics: Only male fin whales sing loud songs. Nature,417(6891), 809.
[5] Simon et al.(2010). Singing behavior of fin whales in the Davis Strait with implications for mating, migration and foraging. J. Acoust. Soc. Am.,128(5), 3200-3210.
Fig 1. Daily temporal distribution of fin whales from 2009 until 2017.Fig 2. Daily temporal distribution of sei whales from 2009 until 2017.
INTRODUCTION
In the Azores, most fin whales (Balaenoptera physalus)and sei whales
(Balaenoptera borealis) are usually recorded during spring [1-3]. This
supports the general migration theory: baleen whales spend summer in
high latitude feeding grounds and winter breeding in lower latitudes.
However, other studies suggest that shorter migrations or even longer
periods spent in the same area can occur, especially for fin whales [4,5].
Fig 1. Location of São Miguel, Azores
(adapted from: naturalearthdata.com and
hidrografico.pt)
OUR AIM: To analyse the temporal distribution of fin
whales and sei whales off São Miguel Island (Azores).
HD23
Cetacean data were collected from January 2009 to
December 2017 off São Miguel Island (Azores) (Fig 1
and 2), from whale watching tours with Futurismo
Azores Whale Watching. Whales were found by
lookouts with powerful binoculars working from
strategic points along the coast. Boats were directed
to the animals, and once there, specialised onboard
observers recorded encounter data.
METHODS
To analyse temporal distribution, we calculated the percentage of tours with fin or sei
whale sightings (Table 1 and 2). Trips in the north coast started in 2015.
Miranda van der Linde
Fin whale (Balaenoptera physalus)
Miranda van der Linde
Sei whale (Balaenoptera borealis)
•Long-term data series obtained from opportunistic sources like whale watching tours are highly valuable.
•Fin whales: mainly in spring [1-2]. But sightings outside of this period suggest that they could be breeding in winter around São Miguel
[4], and that while some of the individuals migrate others stay around for longer [5].
•Sei whales: mainly late spring to mid-summer [3]. They show a tendency to arrive later in the year over the study period,in particular
in 2017, which could be related to environmental factors (e.g. climate change) or species biology.
•The sightings outside of the main season and the increase of tours with fin/sei whales per year could indicate that different whales
choose different migration strategies, e.g. depending on their reproductive stage or on food availability.
Table 1. Monthly percentage of tours with fin whales each year. The highest values in red;
number of sightings in brackets.
Table 2. Monthly percentage of tours with sei whales each year. The highest values in red;
number of sightings in brackets.