Science Advisory Report 2018/003

Identification of habitats important to the blue whale in the western North Atlantic

Summary

• Commercial hunting in the North Atlantic between the late 1800’s and the 1960’s severely depleted blue whale populations, removing over 11,000 individuals, including approximately 1,500 individuals in eastern Canadian waters.
• Blue whales in the western North Atlantic and those in the eastern North Atlantic are currently managed as separate stocks.
• Population size and trend are unknown for blue whales in the Atlantic; however, blue whales in the western North Atlantic probably number in the low hundreds.
• Information on the current and historical seasonal distribution of blue whales comes from: 1) whaling catch records, 2) photo-identification studies, 3) land, aerial and ship-board surveys, 4) passive acoustic monitoring, 5) satellite and radio telemetry, 6) ice entrapment reports, 7) opportunistic sighting reports, and 8) species distribution modelling.
• Blue whales feed while in Canadian waters and their distribution is linked to aggregations of euphausiids (krill). Arctic krill (Thysanoessa spp.) and northern krill (Meganyctiphanes norvegica) are their main preys, but the species consumed likely varies seasonally, geographically, and among individuals. As a result, habitats important for blue whales were identified using information on blue whale distribution in combination with that on areas of observed or predicted prey (krill) aggregations.
• Evidence from blue whale diving behaviour, and from krill and blue whale distributions indicate that in the St. Lawrence Estuary (SLE) and northwestern Gulf of St. Lawrence (nwGSL), blue whales preferentially seek krill aggregations within 80-100 m from the surface, although they may feed at deeper depths in other areas. Krill aggregations are generally correlate with abrupt topography, including slopes, channel and canyon heads, vertical current, convergent surface currents, and to a lesser extent persistent phytoplankton concentrations.
• Whaling data indicate a historical distribution in the western North Atlantic extending from Davis Strait south to northern Florida. Whether the current range of blue whales in the western North Atlantic is smaller than that historically is unclear given the generally limited data available for most areas except the SLE and nwGSL. There are still occasional reports of blue whales throughout their historical range.
• In general, blue whale seasonal movements follow a north-south pattern where feeding occurs in productive waters at high-latitudes and breeding/calving likely takes place during winter in warmer, less productive waters at low latitudes. In the western North Atlantic, wintering areas of blue whales are poorly defined; satellite telemetry, passive acoustic monitoring, and whaling data suggest that it is relatively diffuse, and includes the Gulf of St. Lawrence (GSL), southwestern Newfoundland, and Scotian Shelf, as well as the mid-Atlantic Bight off the U.S. coast and warm and deep oceanic waters off this area. Whether breeding occurs in the latter region is unknown. There are also indications that part of the population remains in Canadian waters year-round.
• Multiple data sources indicate that a near-continuum of habitat suitable to foraging blue whales occur in the shelf, slope and deep waters of the Lower SLE and nwGSL between Tadoussac and Mingan along the north shore, and the Gaspé Peninsula along the south shore. It is estimated that 20 to 100 blue whales use areas within this region each year, with some using it year-round.
• Satellite telemetry and passive acoustic monitoring indicate that blue whales enter and leave the GSL through Cabot Strait, and access the nwGSL and SLE via the Honguedo Strait located between Anticosti and the Gaspé Peninsula.
• There is also evidence for a nearly year-round presence of blue whales in the waters off southwestern Newfoundland, and along the continental shelf edge south of Nova Scotia, Newfoundland and the Grand Banks.
• Southern Newfoundland, the nwGSL, Mecatina Trough, western Scotian Shelf and to a lesser extent Davis Strait were historically important areas of concentration for blue whales, based on reported harvests or sightings during whaling activities. An area located in the nwGSL to the northwest of Anticosti, where blue whales occurred regularly in the 1980s and early 1990s but are now seen only occasionally, is also considered an area of historical concentration. There are indications from observed or predicted krill aggregation areas and sightings data that several of these historically important areas remain suitable foraging habitat for blue whales. A possible exception is western Scotian Shelf. The current importance of Davis Strait for blue whales remains uncertain given the lack of data.
• Given the evidence provided above and using the bounding box approach, four areas were identified as important foraging (and potentially socializing) areas for blue whales: the lower SLE and nwGSL, the shelf waters south and southwest of Newfoundland, Mecatina Trough area, including the head of the Esquiman Channel, and the continental shelf edge of Nova Scotia, Newfoundland and the Grand Banks. Two areas were identified as transit corridors: the Honguedo and Cabot Straits (Figure 1).
• Important features and attributes of these areas include sufficient quantity and quality of prey, access to transit corridors, sufficient physical space to freely maneuver, water of sufficient quality as to not result in loss of habitat function, and an acoustic environment that does not interfere with communication or navigation, or impede use of important habitat by blue whales or their prey (Table 1).
• Anthropogenic activities that are likely to result in the loss of functions of these important habitats include those that would result in reduced prey availability or accessibility, acoustic disturbance, environmental contamination, and physical disturbance (Table 2).
• Based on new research, shipping noise is predicted to mask the main call types of blue whales and to reduce their potential communication space, with effects increasing with proximity to shipping lanes and density of traffic. Currently, most of the SLE and GSL is considered quiet for blue whales low-frequency communication band. However, several important habitats of blue whales occur in proximity to shipping lanes.
• There remain uncertainties about the diet of blue whales in areas other than the ESL and GSL, the relative proportion of the population occurring in Canadian waters in general or in specific regions, importance of deep oceanic waters and shelf break areas for blue whales, and location and extent of wintering areas. Further studies are needed to determine the characteristics that make an area attractive to blue whales, minimum energy requirements for successful reproduction, and amount of disturbance that blue whales can sustain before their body condition and fitness are affected.
• Climate change may also affect habitat functions by altering prey availability and physical properties of the ocean. Anthropogenic activities and their effects on habitat functions need to be managed in the context of this ongoing issue.
• It is unknown whether the important habitats identified in this report are sufficient to ensure the survival of the northwest Atlantic blue whales and to meet population recovery goals outlined in the Recovery Strategy. There is a need to expand research efforts outside of the summer period, and to offshore waters and other areas where blue whale sightings are limited but where significant krill aggregations suggest they may be important to blue whales.

This Science Advisory Report is from the February 23 to 26, 2016 National Marine Mammal Peer Review Committee (NMMPRC): Part II. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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