In August, 1991, an entanglement event was observed in the High Seas Driftnet area in the North Pacific. This description of an entanglement of Lagenorhynchus obliquidens is the first such documented report of dolphins entangling while bowriding. One of the entangled dolphins was rescued from the driftnet

Hutchinson, C.

Mizroch, S. A.

English

Aquatic Commons

An Observed Entanglement of Lagenorhynchus obliquidens 
in the High Seas Driftnet Area in the North Pacific 
Introduction 
In 1978, the Japanese High Seas 
Squid Driftnet Fishery began in the 
S. A. Mizroch is with the National Marine Mam­
mal Laboratory and C. Hutchinson is with the 
Resource Ecology and Fisheries Management Di­
vision, both at the Alaska Fisheries Science Cen­
ter, NMFS, NOAA, 7600 Sand Point Way N.E., 
Bldg. 4, Seattle, WA 98115. 
ABSTRACT-In August, 1991, an en­
tanglement event was observed in the High 
Seas Driftnet area in the North Pacific. This 
description of an entanglement of Lagen­
orhynchus obliquidens is the first such docu­
mented report ofdolphins entangling while 
bowriding. One of the entangled dolphins 
was rescued from the driftnet. 
S. A. MIZROCH and C. HUTCHINSON 
North Pacific, and in 1979 and 1980, 
the Republic of Korea and Taiwan be­
gan their own driftnet fisheries in the 
same region (Yatsu et aI., 1993). The 
High Seas Squid Driftnet Fishery ex­
panded rapidly in the 1980's, and con­
cern grew that bycatch from this fish­
ery was having a large impact on popu­
lations of marine mammals, birds, and 
salmon (Hobbs and Jones (1993) pro­
vide an overview of the fishery). In 
1991, due to concern about bycatch, the 
United Nations General Assembly 
adopted a resolution which called for a 
ban on high-seas driftnet fishing effec­
tive 31 December 1992. 
In 1991, the National Marine Mam­
mal Laboratory of the NMFS Alaska 
Fisheries Science Center initiated a 
multidisciplinary research cruise to 
study the distribution and density of 
bycatch species taken in the High Seas 
Squid Driftnet Fisheries. A series of 
studies on oceanographic conditions, 
fish, seabirds, and marine mammals was 
undertaken on the RN Acania, a 126-ft 
(38.2 m) chartered vessel. The cruise 
consisted of three separate legs, begin­
ning in Homer, Alaska, on 7 July and 
ending in Honolulu, Hawaii, on 6 Sep­
tember. Major areas surveyed were be­
tween lat. 40°-45°N and long. 155°­
1700 W on Leg 1, and lat. 43°-45°N and 
long. 175°W-175°E on Legs 2 and 3. 
Line transect data on marine mam­
mal distribution were collected in con­
junction with fish, seabird, and oceano­
graphic studies. Gear used included an 
Isaacs-Kidd midwater trawl net, bongo 
net, Conductivity-Temperature-Depth 
Figure I.-Entangled Lagenorhynchus obliquidens lifting its head and blowhole above the water to breathe. Photographs taken 
by S. Mizroch, 15 August 1991, at lat. 44°21.3'N, long. 177°45.0'W. 
59(3),1997 41 
Marine Fisheries Review 42 
Figure 2.-(Facing pages) A series of pho­
tographs of a Lagenorhynchus obliquidens 
entangled in a driftnet. Note the cut on the 
trailing edge of the dorsal fin in the photo­
graph on the bottom right. Photographs 
taken by S. Mizroch, 15 August 1991, at 
lat. 44°21.3'N, long. 177°45.0'W. 
59(3),1997 43 
(CTD) probes, Expendable Bathyther­
mograph (XBT), and a sea surface tem­
perature recorder. Because the studies 
were conducted in the High Seas Drift­
net Fishery area during the fishing sea­
son, before setting our daily north-south 
transect lines, we would observe the 
nets being set on east-west lines the 
night before, and would layout north­
south transect lines to avoid crossing 
any net lines. 
Observations 
On 15 August 1991, at 0923 h, lat. 
44°21.3'N, long. 177°45.0'W, while on 
a standard line transect watch, a large 
mixed group ofLagenorhynchus obliqui­
dens and Lissodelphis borealis was spot­
ted at a distance of about 900 m. The 
group included about 200 L. obliquidens 
and 60 L. borealis. 
As the vessel's cruise track headed 
in the direction of the large group, small 
groups of L. obliquidens arrived at the 
bow on both sides of the vessel, with 
about four or five individuals bowriding 
at a time. Groups of two or three were 
approaching along the sides. At 0933 
h, while Hutchinson was on watch, the 
boat crossed a driftnet with about six L. 
obliquidens bowriding. As soon as the 
boat crossed the net, all but one bow­
riding dolphin dropped out of sight. It 
seemed possible at the time that some 
of the bowriding animals could have 
become entangled in the net. 
When the vessel turned and we ar­
rived at the location of the break in the 
net at 1000 h, we saw no free-swimming 
dolphins in the area, but we did see one 
entangled animal poke its head up to 
breathe (Fig. 1). The crew lifted the net 
with long poles that had hooks on one 
end. The plan was to bring the animal 
aboard to disentangle it. However, as the 
net was lifted, the animal was able to 
twist and tum and free itself. The entire 
disentanglement effort took less than 5 
minutes. There was some blood on the 
animal from net cuts (Fig. 2), but the 
animal seemed vigorous when freed 
from the net, and left with no netting 
attached. 
After the animal was released, we 
remained in the area of the break to see 
if any other animals were entangled and 
took above-water videotape of the 
driftnet on both sides of the break. We 
were unable to examine the entire net 
which was being actively fished at the 
time. 
Upon later review of the videotape 
taken while we searched for other en­
tangled dolphins, we noticed dips in the 
net's corkline that may have indicated 
as many as two other entangled dol­
phins, although there were no signs of 
movement in either of these areas. The 
dips could have also indicated some 
other nonmammal catch. 
Kasuya and Miyazaki (1976) report 
epimeletic behavior in L. obliquidens, 
when they observed a carcass that was 
held afloat through the actions of at least 
one, and perhaps two otherL. obliquidens. 
The animal remained by the carcass un­
til the carcass was hooked by the re­
search vessel, at which time the L. 
obliquidens swam away. Based on de­
composition of the carcass, they sur­
mised that the animal may have died the 
preceding day, but they did not know 
whether the carcass had been accom­
panied since death or was found by the 
other L. obliquidens after death. 
Weinrich (1996) observed an en­
tanglement of Lagenorhynchus acutus 
in the North Atlantic, and noted that the 
nonentangled dolphins left the area im­
mediately, with no attempt to aid the 
entangled one (i.e. no evidence at all of 
epimeletic behavior). 
It is unknown whether and how often 
Lagenorhynchus will exhibit epimeletic 
behavior during interactions with fishing 
gear. In the case described here and in 
Weinrich (1996), it appeared that the 
free-swimming accompanying dolphins 
did not remain in the area to provide 
aid to the animal that was entangled in 
the net. In Kasuya and Miyazaki (1976), 
the L. obliquidens that had been ob­
served accompanying the carcass left as 
soon as humans intervened. 
Acknowledgments 
The authors wish to thank R. Hobbs, 
Head Scientist, for his planning and lo­
gistical support during the cruise. We 
thank D. DeMaster, P. Gearin, M. 
Gosho, S. Hill, D. Rice, and B. Sinclair 
for their thoughtful review of this manu­
script. We also thank the captain and 
crew of the RN Acania, R. Harelstad, 
L. Lohse, G. Lohse, D. Carter, and S. 
Jones, and the scientific team on Leg 2, 
B. Ebberts, J. Gerwin, K. Sax, and A. 
Snyder. 
Literature Cited 
Hobbs, R. C., and L. L. Jones. 1993. Impacts of 
high seas driftnet fisheries on marine mam­
mal populations in the North Pacific. Int. N. 
Pac. Fish. Comm. Bull. 53:409-434. 
Kasuya, T., and N. Miyazaki. 1976. An observa­
tion of epimeletic behavior of Lagenorhynchus 
obliquidens. Sci. Rep. Whales Res. Inst. 
28:141-143. 
Yatsu, A., K. Hiramatsu, and S. Hayase. 1993. 
Outline of the Japanese squid driftnet fishery 
with notes on the by-catch. Int. N. Pac. Fish. 
Comm. Bull. 53:5-24. 
Weinrich, M. 1996. Abandonment of an en­
tangled conspecific by Atlantic white-sided 
dolphins (Lagenorhynchus acutus). Mar. 
Mamm. Sci. 12(2):293-296. 
Marine Fisheries Review 44 


An Observed Entanglement of Lagenorhynchus obliquidens in the High Seas Driftnet Area in the North Pacific

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An Observed Entanglement of Lagenorhynchus obliquidens in the High Seas Driftnet Area in the North Pacific

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