Sperm and northern bottlenose whale interactions with deep-water trawlers in the western North Atlantic

Abstract

Commercial fisheries have increased in all the world's oceans with diverse unintended impacts on marine ecosystems. As a result of resource overlap, interactions between cetaceans and fisheries are a common occurrence and, in many cases, can give rise to significant conservation issues. Research on the distribution and types of such interactions is important for efficient management. In this study, we describe the behaviors of two whale species: sperm whales (Physeter macrocephalus) and northern bottlenose whales (Hyperoodon ampullatus), interacting with benthic trawlers fishing off the eastern Grand Banks of the western North Atlantic in 2007. Whale interactions were only observed when vessels were targeting Greenland halibut (Reinhardtius hippoglossoides) in deep-water fishing areas and were most common during net hauling. Sperm whales and northern bottlenose whales appeared to engage in feeding behavior close to the surface during hauling, especially during the latter stages, suggesting they targeted fish escapees rather than discards. Using photo-identification methods, seven individual sperm whales were identified with multiple resights of six individuals being recorded over an almost two month period. The maximum distance between two resights was 234 km, suggesting individual sperm whales were repeatedly targeting and even following fishing vessels over multiple days and between fishing areas. By contrast, there were no photographic resights of individual northern bottlenose whales within this study, or with substantial photo-identification catalogues from other adjacent high density areas, suggesting that individuals of this species may be less likely to follow vessels or move between areas. This study documents the earliest confirmed records of northern bottlenose whales in this remote region. These interactions and high encounter rates may indicate that adjacent populations are recovering from the previous century of commercial whaling. Our study provides new insights and details on whale-fisheries interactions, which can inform future research and help managers understand the real and perceived impacts of depredation behaviour on fisheries and whales.

Fig 1. Map of the NAFO convention area, showing NAFO divisions, fishing areas named by fishermen and the Gully marine protected area (MPA).

Maps were created using R [16]. The bathymetric data was obtained from the Open Government Licence–Canada [17].

Fig 2. Sequence showing a sperm whale turning his body to the right.

First picture shows blowhole and dorsal fin, second turning to the right, dorsal fin and part of the side is observed, in the last four pictures the fluke is going to the right. In the last picture the sperm whale is almost upside down. We associated this pattern of observations with surface feeding close to the surface.

Fig 3

Sperm whale (A) and northern bottlenose whale (B) breaching. Northern bottlenose whales close to the boat at the end of hauling (C-D).

Fig 4. Examples of whale behaviors.

(A) and (B) Sperm and northern bottlenose whales seen together. (C) Five sperm whales following the trawler at the end of hauling with the mouth of the net visible at the surface behind the yellow buoys. Red stars and black arrows indicate sperm whales and yellow stars indicate northern bottlenose whales.

Fig 5. Location of hauling and shooting effort in relation to sightings of sperm whales and northern bottlenose whales.

Maps were created using R [16]. The bathymetric data was obtained from the Open Government Licence–Canada [17].

Fig 6. The occurrence of the different whale behaviours versus fishing area and trawler activity.

(A) Sperm whales (B) Northern bottlenose whales’ behavior per trawling activity. Mean whale encounter rates per (C) trawling activity and (D) fishing area. Six behaviors were scored: (1) swimming parallel to the vessel, (2) following the trawler at a constant speed and near constant distance astern, (3) swimming in the? opposite direction?? from the trawler (normally within 50 m), (4) fluke, (5) surface feeding, and (6) breaching/lobtailing.

Fig 7

Examples of distinct marks used for (A) bottlenose whale identification, including notches and large fin scars and (B) for sperm whale identification. Neboa, with characteristic scars at both sides of the dorsal fin; Scratchy had a large lateral scratch; Breixo, had many scars in the front part of his head; and Faneca, had a lateral scar visible only from the left side, but was easy to identify.