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.
Highlights
The bowhead whale (Balaena mysticetus) is a large, slowswimming baleen whale that spends its entire life associated with high-latitude seas
For readers wishing to interpret these results within a hypothesis-testing framework, we have provided the p-values for explanatory variables included in the models with the smallest Akaike’s Information Criterion (AIC) value for each scar type
Of the 904 bowhead records we examined, 521 included information on scarring, while 514 had all the information required for this analysis
Summary
The bowhead whale (Balaena mysticetus) is a large, slowswimming baleen whale that spends its entire life associated with high-latitude seas. The return fall migration occurs as the whales travel westward into the Chukchi Sea, along the northeast coast of the Chukotka peninsula, through the Bering Strait, and into the northern Bering Sea (Moore and Reeves, 1993; Quakenbush et al, 2010). Their range includes the transboundary waters of the United States (Bering, Chukchi, and Beaufort Seas), the Russian Federation (Bering and Chukchi Seas), and Canada (Beaufort Sea) (Fig. 1). Close examination of landed whales during spring and fall hunts allows for the collection of invaluable “health-assessment” data from organismal to tissue level and allows close-up examinations of scars that are often not as apparent in aerial photos (e.g., Philo et al, 1993)
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