Frequent encounters with the seafloor increase right whales’ risk of entanglement in fishing groundlines

Abstract

North Atlantic right whales Eubalaena glacialis utilize the entire water column and are frequently entangled in ropes from fishing gear. Data from telemetry tags have shown that right whales can swim/feed at or near the seafloor. Because those data are limited, some uncertainty remains regarding the frequency of dives to the seafloor and thus the likelihood of right whale encounters with fishing ropes there. The North Atlantic right whale photo-identification catalog was used to determine the number of sightings of right whales with seafloor sediment on their bodies and the relative frequency and geographic location of those seafloor encounters. Between 1980 and 2016, there were 2053 detections of right whales with 'mud' on their bodies, which represents 2.9% of all sightings (n = 70 593), or 58.2% of all cataloged whales (n = 730). Although muddy right whales were found throughout their range and in all months, 92.7% of all detections occurred in the Bay of Fundy in the summer where there was an average annual detection rate of 7.3%, with a maximum of 26% of sightings in 2010. Mud was found on whales of all age classes including calves of the year, and equally among males and females. These seafloor encounters suggest that any rope resting on, or floating above, the seafloor could pose an entanglement hazard. The use of sinking groundlines likely reduces the risk of entanglements for whales swimming near the seafloor, but may not eliminate the risk for whales making contact with the sediment.

Dive behavior of North Atlantic right whales on the calving ground in the Southeast USA: implications for conservation

“…For example, in Cape Cod Bay, USA, right whales have been documented to swim and feed just subsurface, where they are at increased risk of collisions with vessels (Mayo & Marx 1990, Parks et al 2012, Baumgartner et al 2017. In summer months, right whales often spend increased time at deeper depths while foraging, reducing the risk of vessel collisions, but potentially increasing risk of entanglement with bottom-associated fishing gear (Baumgartner & Mate 2003, Baumgartner et al 2017, Hamilton & Kraus 2019. Differences in dive behavior between mother−calf pairs and other age/sex classes have been documented on foraging grounds.…”

Body growth of North Atlantic right whales (Eubalaena glacialis) revisited

“…Improved estimates of body mass models contribute to the care and conservation of North Atlantic right whales. Ship strikes (Kite‐Powell, Knowlton & Brown, 2007; Vanderlaan & Taggart, 2007) and fishing gear entanglements (Caswell, Fujiwara, & Brault, 1999; Clapham, Young, & Brownell, 1999; Hamilton & Kraus, 2019; Johnson et al, 2005) are the leading causes of mortality for this endangered species. Consequently, accurate estimates of right whale mass are needed to help mitigate anthropogenic mortality.…”

Assessing Northeast Florida Offshore Blue Crab Fishing Effort within Florida’s State Waters

“…The ALWTRT is working with engineers and fishing industry members to develop cost-effective alternatives for reducing the number of vertical lines, such as ropeless gear (i.e., galvanic timed releases, timed line-cutting devices, and acoustic release buoys) or trawls (multiple pots per line; Myers et al 2019). However, trawls may not be a viable option in the calving areas due to the extra weight potential and additional groundline (Hamilton and Kraus 2019). Hamilton and Kraus (2019) suggested that any groundline fishery poses an increased risk of NARW entanglement because NARWs of all age-NORTHEAST FLORIDA OFFSHORE BLUE CRAB FISHERY classes will interact with the seafloor throughout their range.…”

“…However, trawls may not be a viable option in the calving areas due to the extra weight potential and additional groundline (Hamilton and Kraus 2019). Hamilton and Kraus (2019) suggested that any groundline fishery poses an increased risk of NARW entanglement because NARWs of all age-NORTHEAST FLORIDA OFFSHORE BLUE CRAB FISHERY classes will interact with the seafloor throughout their range. In 2021, the Atlantic Large Whale Take Reduction Plan generated additional regulations for fisheries.…”