Frequency of Injuries from Line Entanglements, Killer Whales, and Ship Strikes on Bering-Chukchi-Beaufort Seas Bowhead Whales

Abstract

We analyzed scarring data for Bering-Chukchi-Beaufort (BCB) Seas bowhead whales (Balaena mysticetus) harvested by Alaska Native hunters to quantify the frequency of line entanglement, ship strikes, and killer whale-inflicted injuries. We had 904 records in our database for whales landed between 1990 and 2012, and after data quality screening, we found 521 records containing information on scarring. Logistic regression was used to evaluate different combinations of explanatory variables (i.e., body length, sex, year, year-group) to develop a prediction model for each scar type. We also list bowhead whales that were harvested, found dead, or observed alive entangled in commercial line/fishing gear. Our findings suggest that about 12% of harvested bowheads show entanglement scars. Their frequency is highly correlated with body length and sex: about 50% of very large bowheads (> 17 m) show such scars, while whales under 9 m rarely do, and males show a significantly higher rate than females. Scars associated with ship strikes are infrequent and occur on ~2% of all harvested whales; body length, sex, and year were not significant factors. Scarring from attempted killer whale predation was evident on ~8% of landed whales. As with entanglement injuries, the frequency of killer whale scars was much higher (> 40%) on whales more than 16 m in length and statistically more frequent in the second half of the study (2002 – 12). Increased killer whale injuries in the recent decade are consistent with studies conducted on bowheads of the Eastern Canada-West Greenland population. The findings presented here reflect the most thorough analysis of injury rates from entanglement, ships, and killer whales for the BCB bowheads conducted to date. They indicate that (1) entanglement rates primarily from pot fishing gear (crab or cod or both) are relatively high for very large and presumably older bowheads, (2) collisions with ships are infrequent at present, and (3) scarring from killer whales is frequent on very large adult whales (> 17 m). Considering that bowhead habitat is changing rapidly (e.g., sea ice reduction), industrial ship traffic in the Arctic is increasing, and commercial fishing operations are expanding to the north, we strongly recommend that monitoring of scarring and injuries on harvested bowheads continue into the future as a means of documenting change.

Entanglement‐scar acquisition rates and scar frequency for Bering‐Chukchi‐Beaufort Seas bowhead whales using aerial photography

“…) were assigned to the scar data set for landed whales (George et al . ) we found that about 49% (11 of 33) of the whales over 50 yr old carried entanglement scars.…”

“…Our scar acquisition rate estimate therefore applies mainly to adult whales, based on an average length‐at‐maturity for both sexes whose range is approximately 12–13.7 m (Koski , George et al . ). When estimated ages (Wetzel et al .…”

“…George et al . () found that about 50% of large harvested whales (~17 m) carried entanglement scars. The whales used for the interyear comparisons tended to be larger scarred animals averaging 14.2 m in body length when recaptured.…”

“…In previous studies on landed whales, George et al . (, ) provided evidence that line‐wrap marks on the caudal peduncle, notches at the fluke‐insertion point, scarring along the fluke leading edge, and tissue damage in the peduncle region are primarily inflicted by commercial fishing operations.…”

“…George et al . () reported 12.2% of carefully examined bowhead whales harvested by Alaska Native hunters between 1990 and 2012 showed evidence of entanglement scarring, but there was no statistically significant increase in injuries through that period. Here we expand previous studies of bowhead entanglement in order to better understand the magnitude of the problem, provide a baseline for future assessments, and help guide management efforts in the U.S. arctic region.…”