Science Advisory Report 2019/028

Review of North Atlantic right whale occurrence and risk of entanglements in fishing gear and vessel strikes in Canadian waters

Summary

  • Surveillance and detection efforts for North Atlantic Right Whale (NARW) increased considerably in 2018 relative to 2017. NARW have been detected acoustically in Canadian waters year-round, although the number of detections is lower in the winter. The distribution of whales was generally similar in 2018 and 2017 with large aggregations of whales observed in the southwest Gulf of St. Lawrence (GSL) and smaller but persistent numbers observed in the northwestern Gulf. Only low numbers of whales were observed in the Critical Habitat areas of Roseway and Grand Manan Basins.
  • The general distribution of NARW in the southwestern Gulf of St. Lawrence was similar between 2017 and 2018, although on a finer scale, there were slight differences between the 2 years. The position of whales within their habitat varied on a short time scale. However, gaps in survey effort limit our ability to assess the seasonal and inter-annual variability.
  • The data presented here confirm that there was an increase in the presence of NARW in the Gulf of St. Lawrence beginning in 2015. This increase occurred following an earlier decline in abundance and change in distribution in the Bay of Fundy which began in 2010.
  • A number of factors influence the distribution of NARW. The primary driver of the presence of NARW is the density and availability of its main prey, the copepod (Calanus spp.). There have been significant changes in the abundance of Calanus in eastern Canadian waters since 2010. While there is interannual variability, biomass of Calanus in most areas has declined, with the greatest declines observed in the Gulf of Maine and on the Scotian Shelf.
  • A NARW bioenergetic foraging model identified persistent areas in Canadian waters where Calanus abundance and densities may be sufficient to meet the energetic needs of NARW.  However, there was considerable inter-annual variability in Calanus densities, with greater differences in habitat suitability observed before and after 2010. Many of the areas identified in the new analyses as potentially suitable NARW habitat were similar to those identified previously.
  • Species distribution models specific to the Scotian Shelf and the Bay of Fundy predicted suitable habitat for NARW based on physical, oceanographic, and biological factors used as proxies for prey. Although areas identified varied slightly between models, the Grand Manan Basin and Roseway Basin as well as areas in between, along with areas on the eastern Scotian Shelf and east of Cape Breton, were consistently identified as suitable habitat.
  • Diverse approaches consistently identified a number of areas that would benefit from new or increased survey effort, such as the northern Gulf of St. Lawrence, northeast of Anticosti Island, Cabot Strait, northeast Newfoundland, Emerald Channel (between Emerald Basin and the Shelf Break), Labrador Sea and potential migratory pathways.
  • Analysis of recent acoustic and visual survey data support the advice provided in 2017 on the timing of the movement of NARW into and out of the Gulf of St. Lawrence. Acoustic recorders indicate that NARW remained in the Gulf until late December 2017 and returned to the Gulf in late April 2018. Whales were first sighted in the Gulf in May 2018. Whales were still being detected acoustically in the Gulf as of the end of November 2018.
  • Preliminary photo-identification data indicate that at least 7 individually identified NARW were present in the Bay of Fundy and at least 135 in the southwestern Gulf of St. Lawrence in 2018. Aerial surveys estimated 190 NARW (95%CI: 52-692) in the southern Gulf of St. Lawrence although this is an under-estimate due to whales that were missed when diving. This represents a substantial (~50%) proportion of the known population.
  • Residency time of individual NARW in a given area can vary considerably. Based on the re-sightings of individual animals during one aerial survey program, residency time in the southwest Gulf of St. Lawrence in 2018 averaged 34 days although it was highly variable among individuals. Some of the whales were only seen on one day while others were seen over the full 69 days of aerial monitoring. Of the 51 individuals identified on the first airborne survey, 13 were re-sighted on the last survey. Previous research in Roseway Basin and the Bay of Fundy indicate that NARWs residence time averaged 136 and 75 days, respectively. 
  • The movement behaviour of individual NARW was highly variable. Some individuals did not move far between successive days while others moved considerable distances. Some whales in the southwestern Gulf of St. Lawrence were estimated to move as much as 50 km in a single day.
  • In Canadian waters, very few NARW have been detected in water depths less than 50 m. Also, Calanus were not abundant in waters less than 50m. While we cannot estimate the risk of entanglement of NARW in shallow waters due to the lack of adequate data on fishing activity in these areas, it is not zero.
  • The co-occurrence of NARW and fishing activities in the southern Gulf of St. Lawrence is high. A simulation study designed to estimate potential encounters between NARW and snow crab fishing gear during the years 2015 to 2017 in the southern Gulf of St. Lawrence indicated that the majority of the simulated potential encounters across all three years would have occurred in the 2018 fisheries static closure zone. 
  • The relative risk of a lethal vessel strike was estimated using a simulation model that incorporated data on vessel movements and speed with density and distribution of NARW in the Gulf of St. Lawrence in 2017. Risk was reduced within the mandatory speed restriction zone by 56% while in effect. However, relative risk increased northwest of Anticosti Island directly outside the bounds of the speed restriction zone due to increased vessel presence that coincided with the speed restriction in 2017.  There were other areas in the Gulf where the relative vessel strike threat was high although monitoring was limited.
  • In 2018, the presence of a single whale was used to trigger management actions in some areas. Alternative approaches using multiple whales to trigger management actions would require survey methods designed to assess the number of individuals and their persistence in a given area, as well as other operational requirements.
  • There are several potential options for monitoring NARW occurrence off eastern Canada, with strengths and limitations associated with each. All of the survey and monitoring methods used in 2018 provided relevant and complementary data for science and monitoring. The best methods to use depend on the management and science objectives and include a combination of tools. It is important to identify and prioritize the key questions and goals to develop the most effective monitoring program.

This Science Advisory Report is from the National Marine Peer Review Committee (NMMPRC) 2018 Meeting I: Review of North Atlantic right whale occurrence and risk of interactions with fishing gear and collision with vessels, held November 26-30, 2018, in Montreal, Quebec. 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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