Brad Hanson

Effects of vessels and noise on the subsurface behavior of endangered killer whales (Orcinus orca)

Prey availability and disturbance from vessels and noise are identified threats to endangered Southern Resident killer whales. Vessel noise can mask echolocation signals used for hunting and/or disrupt foraging with implications for energy acquisition in a likely prey-limited population. We utilized suction cup-attached digital acoustic recording tags (DTAGs), to measure received noise levels, understand killer whales’ use of sound, and determine effects of vessels/noise on subsurface behavior. During the 28 tag deployments, we collected vessel data concurrently along with opportunistic predation observations to validate feeding. Broadband received levels (dB re 1μPa) were significantly different across years. Of the vessel factors considered, both vessel count and speed were significant explanatory variables of received levels. Vessels emitting echosounder signals were commonly received by the DTAGs and overlapped with the echolocation frequencies use to hunt fish. Additionally, different phases of foraging were differentiated from the acoustic record, including the detection of crunching sounds after fish kills. Together with movement data analysis, these results allow the identification of different whale activities, including prey capture dives, to test hypotheses of vessel/noise effects on behavior. This work, along with a comparative investigation involving Northern Resident DTAG data, inform killer whale conservation and management measures.Prey availability and disturbance from vessels and noise are identified threats to endangered Southern Resident killer whales. Vessel noise can mask echolocation signals used for hunting and/or disrupt foraging with implications for energy acquisition in a likely prey-limited population. We utilized suction cup-attached digital acoustic recording tags (DTAGs), to measure received noise levels, understand killer whales’ use of sound, and determine effects of vessels/noise on subsurface behavior. During the 28 tag deployments, we collected vessel data concurrently along with opportunistic predation observations to validate feeding. Broadband received levels (dB re 1μPa) were significantly different across years. Of the vessel factors considered, both vessel count and speed were significant explanatory variables of received levels. Vessels emitting echosounder signals were commonly received by the DTAGs and overlapped with the echolocation frequencies use to hunt fish. Additionally, different phases of forag...

The relationship between vessel traffic and noise levels received by killer whales

Cetaceans that rely on their acoustic environment for key life history strategies are susceptible to noise effects from anthropogenic use such as ecotourism. Endangered Southern Resident killer whales (SRKW) are the primary target for vessel-based whale-watching in the Salish Sea. Vessel interactions and associated noise have been identified as potential stressors for SRKW. Previous research has indicated that both stressors negatively impact SRKW; however, there is a missing link between vessel characteristics/behavior and noise levels actually received by individual whales. To investigate this relationship, data were collected concurrently using mobile remote sensing survey equipment packages and digital acoustic recording tags. This allowed us to obtain precise geo-referenced vessel data and noise levels received by the whales. We used linear regression to summarize patterns in vessel characteristics and relate them to received noise levels. Received noise levels (RNL) were correlated with the number o...

Acoustic surveys of killer whales during winter along the Pacific Northwest Coast

An acoustic and visual survey was conducted along the outer coast of the Pacific Northwest (Washington to Central California) between 26 February and 14 March 2004 to determine the winter‐time distribution and behavior of the southern resident ecotype population of killer whales (SRKWs). SRKWs are vocally active with a vocal repertoire that is well documented. A towed hydrophone array was deployed on 17 of the 20‐day cruise resulting in an average of approximately 19 h of acoustic effort per day. Eleven of the 49 unique detections of marine mammal made were attributed to killer whales (22.5% of the total). Three of these killer whale detections occurred at night. Two of the three known SRKW pods (J, K, and L) were detected acoustically and positively identified as the J and L pods. Interestingly, the remaining nine unique acoustic encounters with killer whales were of either the offshore form or the transient form, considered to be vocally less active relative to the resident form. The hydrophone array su...