Southern Biscay Canyon System IMMA

Criterion A – Species or Population Vulnerability

This IMMA provides good habitat for sperm whales (Physeter macrocephalus), which are listed as vulnerable on the IUCN Red List (Taylor et al. 2019).

It also provides hosts fin whales (Balaenoptera physalus), which are listed as vulnerable on the IUCN Red List of Threatened Species (Cooke, 2018a).

Sei whales (Balaenoptera borealis) are also found in this area, and are listed as endangered on the Red List (Cooke, 2018b).

Criterion B: Distribution and Abundance

Sub-criterion B2: Aggregations

Consistent sightings of beaked whales, particularly Cuvier’s beaked whales (Ziphius cavirostris), have been recorded throughout the Torrelavega Canyon, Santander Canyon and Cap Breton Canyon (ORCA, 2019, Laran et al. 2017, MacLeod et al. 2011, Smith, 2010), with habitat modelling studies predicting very high beaked whale densities in these canyons (Virgili et al. 2022).

A large aerial survey SAMM (Suivi Aérien de la Mégafaune Marine, Aerial Census of Marine Megafauna) was conducted over the Bay of Biscay and English Channel in winter 2011–2012 and summer 2012. Using conventional distance sampling, the relative density of beaked whales within a stratum that included the slope waters of the Bay of Biscay and the coast of Spain (including this IMMA) was estimated to be 0.006 individuals/km² (CV=50-70% for both winter and summer seasons (Laran et al. 2017a), which is high and for example consistent with those estimated for the Mozambique Channel in the Indian Ocean (Laran et al, 2017b).

High densities of beaked whales in the south-eastern Bay of Biscay are also well described by various large scale surveys such as SCANS-II (Small Cetaceans in European Atlantic waters and the North Sea), CODA (Cetacean Offshore Distribution and Abundance) and SCANS-III (Lacey et al. 2022).

Long-term citizen-science data collected from ferry-based platforms of opportunity surveys from March through October between 2006 and 2018 suggested that beaked whales were present year-round, with increased encounter rates in summer (Robbins et al. 2022).

The Cuvier’s beaked whale is the most abundant ziphiid in the Bay of Biscay, with encounter rates 12 to 16 times higher than those for northern bottlenose whales (Hyperoodon ampullatus) and Sowerby’s beaked whales (Mesoplodon bidens) (Virgili et al. 2022). The Santander, Torrelavega and Cap Breton canyons support particularly high densities of Cuvier’s beaked whales, with one study reporting an encounter rate of 1.2 per 100 nautical mile (nmi) in the southern Bay of Biscay, particularly around the Santander canyon, compared to 0.09 per 100 nmi in the northern part of the bay (Kiszka et al. 2007). The highest corrected density estimate of Cuvier’s beaked whales was 0.132 animals/km² in 2006 in the Torrelavega Canyon. This density is higher than any other published estimates for this species anywhere (MacLeod et al. 2011). Citizen-science data from POP surveys in this region include 329 sightings of Cuvier’s beaked whales from 2007 to 2022, with 683 individual animals (uncorrected for resightings) sighted (including 13 calves), with group sizes of 1-7 indivdiuals.

Sperm whales are regularly sighted throughout the area, but show a preference for deep oceanic waters in the southern Bay of Biscay (Hobbs et al. 2007, Kiszka et al. 2007, Waggitt et al., 2020). Encounter rates are higher in the southern Bay of Biscay (0.8 per 100 nmi), especially in the proximity of the Santander Canyon, than in the northern Bay (0.09 per 100 nmi), indicating this area to be an important area of aggregation for sperm whales (Kiszka et al. 2007). From the large scale seasonal aerial survey SAMM conducted in winter 2011–2012 and summer 2012, sperm whale density was estimated as 0.005 individual/km² (CV=69%, corrected for availability bias) in summer and decreased in winter from the same slope stratum of the Bay of Biscay, including the eastern part of the Spanish coast, as described for Cuvier’s beaked whales (Laran et al. 2017).

Long-term citizen-science platform of opportunity surveys (2006-2022) recorded sperm whales throughout the Torrelavega Canyon during every month of data collection (March to October), suggesting that they are present year-round (ORCA, unpublished data). Analyses of the combined data from SCANS-II and CODA predicted highest densities of sperm whales in the deep-water areas northwest of Spain and in the southeastern Bay of Biscay, an area which includes the Santander Canyon (Rogan et al. 2017).

Criterion D: Special Attributes

Sub-criterion D2: Diversity

This   IMMA contains habitat that supports a diversity of cetacean species. The varied topography in a relatively small space renders this a critical habitat that supports multiple species with distinct habitat preferences (Kiszka et al. 2007).

At least 19 species of cetaceans occur regularly in or around these canyons, ranging from small dolphin species such as common (Delphinus delphis) and striped dolphins (Stenella coeruleoalba) to large baleen whales such as fin and minke whales (Balaenoptera acutorostrata) (Matear et al. 2019). Of particular interest are the frequently encountered Cuvier’s beaked whales and sperm whales which are recorded in this area year-round, as well as other beaked whales, such as the northern bottlenose whales, Sowerby’s beaked whales, True’s beaked whales (Mesoplodon mirus), Blainville’s beaked whale (Mesoplodon densirostris) and Gervais’ beaked whales (Mesoplodon europaeus) (Robbins et al. 2022, Pelagis, 2021, Rogan et al. 2017, Kiszka et al. 2007).

A 10-year citizen-science platform of opportunity study reported species richness to be highest in the southern-most areas of the Bay of Biscay near Santander Canyon (Matear et al. 2019). Larborde (2008) also reported that a higher species richness was evident over the submarine canyons, based on CODA data.

In addition to the well documented deep divers, baleen whales were also frequently documented during dedicated boat-based and aerial surveys such as SCANS III and IV (Hammond et al. 2021, Lacey et al. 2022, Gilles et al., 2023), SAMM (Laran et al, 2017a, 2022). These species are also reported through citizen-science data collection from ferries (ORCA, 2019) or compilation of multiple data sets (Waggitt et al., 2020). Fin whales (Balaenoptera physalus) are sighted frequently in the southern Bay of Biscay in waters >2,000 m deep, with a clearly oceanic distribution in the summer (Laran et al. 2017, Hammond et al. 2021, Lacey et al. 2022).