NOAA Technical Memorandum NMFS-AFSC-108

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Alaska Fisheries Science Center

November 1999

by

P. S. Hill, J. L. Laake, and E. Mitchell

Results of a Pilot Program to Document

Interactions Between Sperm Whales and

Longline Vessels in Alaska Waters
NOAA Technical Memorandum NMFS

The National Marine Fisheries Service's Alaska Fisheries Science Center

uses the NOAA Technical Memorandum series to issue informal scientific and

technical publications when complete formal review and editorial processing

are not appropriate or feasible. Documents within this series reflect sound

professional work and may be referenced in the formal scientific and technical

literature.

The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries

Science Center continues the NMFS-F/NWC series established in 1970 by the

Northwest Fisheries Center. The new NMFS-NWFSC series will be used by

the Northwest Fisheries Science Center.

This document should be cited as follows:

Hill, P. S., J. L. Laake, and E. Mitchell. 1999. Results of a pilot

program to document interactions between sperm whales and longline

vessels in Alaska waters. U.S. Dep. Commer., NOAA Tech. Memo.

NMFS-AFSC-108, 42 p.

 

Reference in this document to trade names does not imply endorsement by

the National Marine Fisheries Service, NOAA.
November 1999

NOAA Technical Memorandum NMFS-AFSC-108

by

P. S. Hill, J. L. Laake, and E. Mitchell

Results of a Pilot Program to Document

Interactions Between Sperm Whales and

Longline Vessels in Alaska Waters

National Marine Mammal Laboratory

Alaska Fisheries Science Center

7600 Sand Point Way N.E., BIN C-15700

Seattle, WA 98115-0070

P.O. Box 933

Eugene, OR 97440

U.S. DEPARTMENT OF COMMERCE

William M. Daley, Secretary

National Oceanic and Atmospheric Administration

D. James Baker, Under Secretary and Administrator

National Marine Fisheries Service

Penelope D. Dalton, Assistant Administrator for Fisheries

1 2

2

1

1
This document is available to the public through:

National Technical Information Service

U.S. Department of Commerce

5285 Port Royal Road

Springfield, VA 22161

www.ntis.gov
Notice to Users of this Document

In the process of converting the original printed document into Adobe Acrobat .PDF format, slight

differences in formatting can occur; page numbers in the .PDF may not match the original printed

document; and some characters or symbols may not translate. 

This document is being made available in .PDF format for the convenience of users; however, the

accuracy and correctness of the document can only be certified as was presented in the original hard

copy format.
iii

ABSTRACT

Interactions between sperm whales (Physeter macrocephalus) and longline fisheries have

been well-documented in the Southern Ocean, but in Alaska waters only anecdotal reports of

sperm whales interacting with longline operations have been available. In 1996, NMFS received

reports from observers on commercial fishing vessels that sperm whales were preying on sablefish

(Anoplopoma fimbria) targeted by longline vessels in the Gulf of Alaska. As a result, a pilot

project was initiated to characterize the nature and extent of the interactions between sperm

whales and the commercial longline fishery in Alaska. Between 17 May and 14 December 1997,

fishery observers aboard 16 different vessels monitored 557 longline sets and recorded

observations and behavior of sperm whales and any damage to fish brought aboard. Likewise,

between 31 March and 14 November 1998, fishery observers aboard 41 different vessels 

monitored 1,060 longline sets. Sperm whales were not present during any of the 1,075 sets in the

Bering Sea. Whereas, sperm whales were present in 28.5% of the 562 sets in the Gulf of Alaska

and observers recorded fish damage in 46.2% of the sets in which sperm whales were present. 

However, few damaged fish (n = 65, x) = 3.45, SE = 0.28) were landed during sets in which

depredation was reported. There was no evidence that mortality or serious injury to sperm whales

was occurring as a result of this interaction. An initial exploration of the catch data suggested that

average standardized catch (metric tons/1,000 hooks) depended on the fish species caught, the

North Pacific Fishery Management Council (NPFMC) statistical area fished, and the bottom

depth. The presence of sperm whales appeared to be related to bottom depth and NPFMC

statistical area. To control for these factors, we computed the average standardized catch for

trips that had at least three sets when both sperm whales were absent and present and which met

the following criteria: 1) predominant fish species was sablefish; 2) sets were conducted within

NPFMC statistical areas 630 through 680; and, 3) bottom depth was greater than 200 fm. This

data selection provided 12 trips with 285 sets (113 without sperm whales present and 72 with

sperm whales present) for the comparison. The Wilcoxson signed rank test of a difference in

catch associated with sperm whale presence (V = 62, n = 12) was not significant (P = 0.08). The

average difference in catch between sets with sperm whales present and absent was -0.095 t (SE =
iv

0.057). At an average weight of 3.5 kg , 27 fish per set were lost to account for the 0.095 t

estimated difference in catch between sets in which sperm whales were present and absent. Our

finding of no significant difference does not mean that there was no loss. Sperm whale

interactions clearly reduced the catch because some fish were damaged (and were therefore

worthless) and other fish were presumably removed from the line. However, at present, the

difference in catch was too small to estimate precisely with the current sample size and high

variability in catch per set. 
v

CONTENTS

Abstract ................................................................. iii

Introduction ............................................................... 1

Methods .................................................................. 3

Results ................................................................... 4

Discussion ................................................................. 8

Conclusion ............................................................... 11

Acknowledgments .......................................................... 11

Citations ................................................................. 13

Appendix 1 - Ancillary data ................................................... 15

Appendix B - Photo-identification data .......................................... 17

Figures .................................................................. 24
INTRODUCTION

Sperm whales (Physeter macrocephalus) are widely distributed in the North Pacific, where

in the winter they are typically encountered south of latitude 40/N (Gosho et al. 1984). Females

and young sperm whales usually remain in tropical and temperate waters year-round (Rice 1978),

while males are thought to move north in the summer to feed in the Gulf of Alaska, Bering Sea,

and waters around the Aleutian Islands. However, movement patterns of sperm whales into

Alaska waters are unclear because commercial whaling data (i.e., Discovery Tags) revealed

substantial east-west movement between Alaska waters and the western North Pacific (Japan and

the Bonin Islands), with little evidence of north-south movement into Alaska waters (B. Taylor,

pers. comm., Southwest Fisheries Science Center, P.O. Box 271, La Jolla CA 92038) 

Due to the residual impacts of commercial whaling, sperm whales are listed as

“endangered” under the Endangered Species Act of 1973. There are no reliable estimates for the

number of sperm whales inhabiting the North Pacific (Hill and DeMaster 1998). Though believed

to be upwardly biased, preliminary abundance estimates indicate that 102,112 (CV=0.155) sperm

whales inhabit the western North Pacific (Kato and Miyashita 1998). Barlow and Taylor (1998)

estimate that there are 39,200 (CV=0.60) sperm whales in the eastern temperate North Pacific. 

There is no abundance estimate for sperm whales in Alaska waters (Hill and DeMaster 1998).

 Interactions between sperm whales and longline fisheries have been well-documented in

the Southern Ocean; in particular off South Georgia, the Kerguelen Islands, and Southern Chile. 

Such interactions include entanglement in gear (Anonymous 1994, Ashford et al. 1996), following

vessels for periods of days (Ashford et al. 1996, Capdeville 1997), and observed feeding off gear

(Crespo et al. 1997, Anonymous 1994). This evidence, combined with anecdotal reports,

suggests that interactions between sperm whales and longline operations may be widespread in

Southern Ocean waters. In Alaska waters, aside from scattered anecdotal reports (Dahlheim

1988, Rice 1989, NMML unpubl. data), few data are available regarding sperm whale behavior in

relation to commercial longline operations.

The National Marine Fisheries Service (NMFS) is charged with monitoring groundfish

fisheries in the U.S. Exclusive Economic Zone (EEZ) off Alaska. Commercial fishing for

sablefish occurs annually from 15 March to 15 November on the upper continental slope at depths
3

Includes the value of the fish and the value of dressing the fish at sea, but not the value of

any further processing at-sea or ashore.

4The 1996 fishery statistics were compiled from vessel, landings, and fishery Observer

Program data provided by the Alaska Fisheries Science Center, Alaska Region Office, and the

Pacific States Marine Fisheries Commission.

5Observer coverage in Alaska groundfish fisheries is assigned according to vessel length;

where vessels greater then 38 m have 100% coverage, vessels 18-38 m have 30% coverage, and

vessels less than 18 m are not required to carry observers.

2

averaging 250-350 fm. An individual fishing quota (IFQ) for sablefish was implemented in 1995,

with over 1,000 individuals receiving quota shares. In 1996, 639 longline vessels targeting

sablefish landed over 17,000 metric tons (t) in Alaska waters worth an estimated $73.1 million.3,4

Vessels targeting sablefish tend to be small (78% less than 18 m; 21% between 18-38 m in length)

and usually fish two or three sets of gear concurrently, alternating between sets (i.e., hauling in

the gear, deploying the gear and then moving on to the next set). It is estimated that these vessels

fished 48.2 million hooks in 1996.4 Each set of the longline gear averaged 9 km in length with

circle hooks spaced at approximately 1.2 m intervals. 

In 1996, NMFS received reports from observers on commercial fishing vessels that sperm

whales were preying on sablefish (Anoplopoma fimbria) targeted by longline vessels in the Gulf of

Alaska. Some observers suggested the whales were removing fish directly from the longline gear

while others believed the whales were feeding on the discarded offal. Anecdotal reports from

commercial fishers on vessels without observers corroborated this information.5 As a result, a

pilot project was initiated to characterize the nature and extent of the interactions between sperm

whales and the commercial longline fishery in Alaska. This paper reports on the results of the

pilot study for 1997 and 1998.
3

METHODS

Fishery observers aboard longline vessels fishing in Alaska waters are required to collect

data used to manage the fishery (e.g., species targeted, tons landed, area fished), assess the

resource (e.g., measure fish lengths and weights), record the level of bycatch (e.g., number of

non-target or prohibited species landed), and record interactions between the fishery and

protected species (e.g., mortalities and deterrences of marine mammals and seabirds). Observers

are also asked to record opportunistic sightings of marine mammals using a standard sighting

form.

In addition to their regular duties, fishery observers participating in the pilot program were

asked to collect detailed sighting and behavioral information on sperm whales. During each

longline set in which sperm whales were present, observers were instructed to complete a sperm

whale interaction form along with the standard sighting form. Prior to departing on an assignment

each observer was briefed via phone or in person about proper form completion, the types of

interactions and behaviors that might be encountered, and the importance of detailed observations

to ensure there was ample evidence to support any interaction that could occur. Assignments

occurred when observer positions on longline vessels became available. 

Upon completion of an assignment, observers were debriefed through the NMFS

Groundfish Observer Program managed by the Resource Ecology and Fisheries Management

(REFM) Division (Alaska Fisheries Science Center, Seattle, WA). All pilot project participants

who observed sperm whale interactions (depredation of longline-caught fish) met with the

Principal Investigator (S. Hill) to discuss what was observed and to address any data ambiguities. 

All data collected during pilot project cruises were then provided either as original data or in an

edited format from the NORPAC database (which is managed by REFM and contains data related

to each observed longline set). 

We examined both direct and indirect measures of sperm whale depredation on

standardized fish catch (t/1,000 hooks) from the longline. The only direct measure of depredation

by sperm whales was the number of damaged fish per set. However, that ignores the possibility

that the entire fish was removed from the hook. Therefore, we also examined indirect measures
4

of depredation by comparing standardized catches when sperm whales were present and absent. 

We used the Mann-Whitney test (Zar 1996) to compare the distributions of catches. However, in

doing so, we assumed that the only difference between the sets was the presence and absence of

sperm whales. The possibility existed that the factors affecting sperm whale presence also

affected longline catch and any association with sperm whale presence was largely spurious. 

Therefore, we explored various factors that might affect catch and for a series of trips with

comparable conditions we used the paired Wilcoxson signed rank test to compare the average

catch when sperm whales were absent to the average catch when sperm whales were present

during the same trip.

RESULTS

During 1997, 12 fishery observers participated in the sperm whale/longline interaction

pilot project aboard 16 different vessels. Observers monitored 557 longline sets (Fig. 1) between

17 May and 14 December 1997. Longline fishing effort was not uniformly distributed over time

on the fishing grounds. Vessels conducted more sets (n = 462) in the Bering Sea than the Gulf of

Alaska (n = 115). Most sets in the Gulf of Alaska occurred prior to September, with none

occurring after October (Fig. 2). Fishing effort was concentrated in the Bering Sea during the

latter part of the year (Sept.-Dec.). Sperm whales were not seen during any of the 462 longline

sets conducted during 1997 in the Bering Sea.

During 1998, 22 fishery observers participated in the sperm whale/longline interaction

project aboard 41 different vessels. Observers monitored 1,060 longline sets (Fig. 3) between 31

March and 14 November 1998. Vessels conducted more sets (n = 613) in the Bering Sea than the

Gulf of Alaska (n = 447). Monitored sets were more evenly distributed within the Bering Sea and

Gulf of Alaska than in 1997, with sets occurring in both regions from April through November

(Fig. 4). A majority of the sets in the Bering Sea occurred during April and May where as a

majority of sets in the Gulf of Alaska occurred from May through July. As in 1997, sperm whales

were not observed during any of the longline sets conducted during 1998 in the Bering Sea.
5

In 1997, sperm whale sightings were recorded during 50 of the 115 (43.5%) longline sets

within the Gulf of Alaska. Interactions (incidents where observers believed sperm whales were

feeding on longline-caught fish) were reported during 34 sets, or 68.0% of the sets in which

sperm whales were sighted. Interactions occurred within 110 nautical miles (nmi) of Middleton

Island in the northern Gulf of Alaska, either slightly to the southwest (referred to hereafter as SW

of Middleton) or almost due east of the Island near a bathymetric feature called Pamplona Spur

(southwest of Icy Bay; Fig. 5). The only exception was a single interaction which occurred

approximately 10 nmi off Kruzof Island in southeastern Alaska. All interactions during May (n =

19) and August (n = 6) occurred SW of Middleton while all interactions during July (n = 8)

occurred near Pamplona Spur. The remaining three interactions were recorded SW of Middleton,

near Pamplona Spur, and off Kruzof Island, respectively, within a 6-day period during a

September trip. Few sightings and no interactions were recorded in North Pacific Fishery

Management Council (NPFMC) statistical areas 610 and 620, to the southwest of Kodiak Island

(Fig. 5).

In 1998, sperm whale sightings were recorded during 110 of the 447 (24.6%) longline sets

within the Gulf of Alaska. Few sightings and no interactions were recorded in NPFMC statistical

areas 610 and 620, to the southwest of Kodiak Island (Fig. 6). Interactions were reported during

40 sets, or 36.4% of the sets in which sperm whales were sighted. Interactions occurred, as in

1997, in the northern Gulf of Alaska, SW of Middleton Island and near Pamplona Spur

(southwest of Icy Bay; Fig. 6). The increased coverage in Southeast Alaska during 1998 also

documented interactions off Yakutat and along the coast to as far south as the southern tip of

Baranof Island. The two interactions during April occurred near Yakutat. Interactions during

May (n = 21), June (n = 8), July (n = 6), and August (n = 3) occurred in both the northern Gulf of

Alaska (SW of Middleton and Pamplona Spur) and off Southeast Alaska, simultaneously at times. 

For example, interactions were recorded off the southern tip of Baranof Island and Pamplona

Spur on the same day in May, and off Kruzof Island and SW of Middleton one day apart in June. 

When whales were present and suspected depredation of hooked fish occurred, observers

reported the nature and magnitude of damage to caught fish, sometimes providing photographs

(Fig. 7). Damage to fish included lack of tails, only heads or lips left on the hook (some of which
6

were smashed or flattened), large gashes along the sides, and stomachs torn out. Fish recorded as

damaged were primarily sablefish, except during seven cruises in which damaged grenadiers

(Coryphaenoides spp.) were also noted. Several observers believed that depredation had

occurred while the line was being hauled because severely damaged fish were still alive. Some

observers reported incidents where the depth sounder clearly showed whales around the gear;

lower catch rates when whales were diving as compared to when they were at the surface; many

hooks were clean of bait and straightened (note: this damage could occur if the gear was caught

on the bottom); and a whale was seen approaching the gear underwater and pausing in the vicinity

of the fishing gear.

Observers recorded fish depredation (interaction) in 74 of the 160 sets (46.2%) in which

sperm whales were present during both years. However, few damaged fish (n = 65, x) = 3.45, SE

= 0.28) were landed during sets in which depredation was reported (Fig. 8). Pod sizes ranging

from one to twenty-two whales (n = 74, x) = 4.29, SE = 0.36) were observed during sets where

depredation was recorded. Whales would typically remain near the vessel during the entire set,

often following the vessel from its previous set or arriving as soon as haul back of the gear was

initiated. During several cruises, the same group of whales followed the vessels for consecutive

days (individual whales were re-identified by unique characteristics such as scar patterns). 

Observers noted that the whales did not exhibit any behaviors that would suggest they were

disturbed by or aggressive towards the vessel. However, one observer reported tangled gear on

every set during which depredation of the catch occurred. Groups of whales typically remained

25-100 m off the stern or starboard quarter of the vessel (gear is hauled on the starboard side) and

alternated between resting at the surface and diving. At times individual whales were within 2 m

of the vessel. 

When we examined the distribution of standardized catch for each set when sperm whales

were absent and present (Fig. 9), we found that the catch was lower for sets when sperm whales

were present (Wilcoxson rank sum test Z = 5.29, P < 0.0001). The mean catch was 0.83 t/1,000

hooks (n = 160, SE = 0.04) when sperm whales were present and 0.99 t/1,000 hooks (n = 402,

SE=0.03) when they were absent. However, the observed difference was not necessarily the

result of depredation by sperm whales.
7

An initial exploration of the data suggested that many different variables potentially

affected both fish catch and sperm whale presence during the set. The average catch was lower

(Z = 6.5, P < 0.001) for sets when the predominant species was sablefish (n = 478 sets, x) = 0.94,

SE = 0.02) than for sets catching predominantly non-sablefish (n = 68, x) = 1.80, SE = 0.13),

which was primarily halibut (Fig. 10). The average catch for sablefish sets was greater (Z = 3.5, P

< 0.001) in NPFMC statistical areas 610 and 620 (n = 92 sets, x) = 1.12, SE = 0.06) than the

average catch in statistical areas 630 through 680 (n = 368 sets, x) = 0.90, SE = 0.02) (Fig. 10). 

Sets on sablefish occurred primarily where the bottom depth exceeded 200 fm and non-sablefish

sets were primarily in shallower water (Fig. 11). The average catch decreased with bottom depth

(Fig. 12) which could be partially explained by the target species. Likewise, the presence of

sperm whales appeared to be related to bottom depth and fishing region. The observed

proportion of sets with sperm whales present increased with bottom depth (Fig. 12), and sperm

whales were more often present and more likely to interact with sets (i.e., damage fish) in

NPFMC statistical areas 630 through 680 than in statistical areas 610 and 620 (Fig. 13).

We used this initial exploration to restrict the data to a set that would eliminate most of

the variables that could create a spurious relationship. We computed the average standardized

catch for trips that had at least three sets when both sperm whales were absent and present and

which met the following criteria: 1) predominant fish species was sablefish; 2) sets were

conducted within NPFMC statistical areas 630 through 680; and, 3) bottom depth was greater

than 200 fm. This data selection provided 12 trips (Table 1) with 285 sets (113 without sperm

whales present and 72 with sperm whales present) for the comparison. The paired comparison

within trip controlled for year, vessel, and target species. It also largely controlled for time of

year, fishing region, and bottom depth. When the target catch was sablefish, there was no

significant effect of sperm whale presence on catch (Wilcoxson signed rank: V = 62, n = 12,

P=0.08). The average difference in catch between sets with sperm whales present and absent was

-0.095 t (SE = 0.057). 
8

Table 1. Number of sets and average catch categorized by sperm whale

presence for the 12 trips of the paired analysis. All trips were from 

different vessels except trips 15 and 40, which were from the same vessel.

Sets without sperm

whales

Sets with sperm whales 

present

Trip n Mean catch n Mean catch Difference

12 37 21 1.250 0.968 -0.283

13 8 7 0.585 0.569 -0.015

15 9 3 0.799 0.730 -0.069

21 3 4 1.029 0.918 -0.111

24 4 4 0.774 0.736 -0.037

25 14 7 1.212 1.170 -0.042

26 3 4 1.019 0.894 -0.124

29 11 6 0.512 0.462 -0.049

36 5 4 0.722 0.971 0.249

37 4 5 1.145 0.883 -0.262

38 4 4 1.647 1.122 -0.525

40 11 3 0.853 0.977 0.124

DISCUSSION

In general, pilot program coverage (Figs. 1 and 3) gave a reasonable representation of

overall observer coverage in the Alaska longline fishery during 1997 and 1998 (Figs. 14 and 15). 

While effort in the observed segment of the fleet may not precisely reflect effort in the unobserved

portion of the fleet (e.g., if observer presence contributed to decisions regarding where and when

a vessel fished), the lack of reported interactions in the Bering Sea by the pilot program and

ancillary data sources (see Appendix 1) suggests that sperm whale depredation of longline-caught

fish is not occurring outside the Gulf of Alaska. This is also supported by: 1) the paucity of sperm

whale sightings from observers aboard longline vessels operating in the Bering Sea and along the
9

Aleutian archipelago; 2) the lack of any indication of sperm whale interactions from ancillary data

sources from that region; and, 3) the small number of sperm whale sightings in the Bering Sea

dating back to 1958 in the National Marine Mammal Laboratory’s Platforms of Opportunity

database (Fig. 16).

Due to the opportunistic nature of the ancillary data (i.e., sightings data are provided on a

not-to-interfere basis with other duties), those data are not readily comparable with the pilot

program data. However, the ancillary data supports certain trends seen in the pilot program data

such as interactions tending to occur in predominantly the same locations (Figs. 5, 6, 17 and 18). 

Although sperm whales were sighted by longline vessels operating to the west of Kodiak Island,

longline depredation seems to be restricted to the Gulf of Alaska waters east of Kodiak. Gear

depredation off southeastern Alaska may be more widespread than the pilot program and ancillary

data indicated because most longline vessels operating in that region are less than 18 m in length

and did not have fishery observers on board. Anecdotal reports from these vessels and from the

Alaska Department of Fish and Game indicated that longline vessels operating off southeastern

Alaska were commonly visited by sperm whales. 

Sperm whale depredation on longlines may be a learned behavior that begins when the

whales associate fishing operations with a feeding opportunity. Yano and Dahlheim (1995) made

a similar assumption when documenting longline depredation by specific killer whale (Orcinus

orca) pods in Alaska waters. In the present study, gear depredation was relatively localized

spatially and temporally. It is possible that instead of a being a widespread behavioral

phenomenon only several groups of sperm whales have learned to exploit longline-caught fish. 

This theory is supported by: 1) the timing and location of depredation occurrences in the pilot

program and ancillary data; 2) the documented reports of groups of whales (believed to be the

same whales, as determined by characteristic features) following a particular vessel between sets

for a period of days; and, 3) individually identifiable whales photographed across areas and years

(see Appendix 2). Anecdotal reports from longline fishermen in the Gulf of Alaska indicate that

sperm whale sightings in the past were uncommon while fishing, whereas sperm whales now tend

to remain in the vicinity of their vessels while fishing. This suggests the number of whales

learning the behavior and the overall impact of this behavior on the fishery may rise in the future.
10

The changes in the Alaska sablefish longline fishery from derby-style (in which many

vessels raced to maximize catch during the short fishery openings) to IFQs (in which fishermen

can choose when and where to fish over a 7-8 month season) may have fostered learning the

behavior of feeding from the gear and increased the potential for the whales to impact the fishery. 

The prolonged season allows groups of whales to follow longliners around and prey off the

discards, drop-offs, or directly from the gear. Having a pod of whales accompany a vessel during

an entire trip could have a significant impact on the catch, thereby causing longer trips and

increasing the costs. 

Unlike killer whales, which tend to strip nearly all of the fish from large sections of the

gear, depredation by sperm whales is much less obvious. Some observers were convinced the

whales were not feeding on the gear but were eating discarded fish and drop-offs until they

observed severely damaged live fish being landed. The numbers of damaged fish used as evidence

for sperm whale depredation on the catch was small. Although no other marine mammals were

sighted during instances of depredation, it is impossible with the available evidence to determine if

damaged fish were caused by the sperm whales or some other predator. However, observers

stated that the types of injuries seen on the fish only occurred when sperm whales were present. 

As there are numerous reasons why a hook could be empty (e.g., bait falls off, bait taken

without catching the fish, fish falling off, or fish taken off), it is not possible for observers to

estimate the number of fish actually taken by the whales by the number of empty hooks. Although

average catch was lower when sperm whales were present, the difference was not statistically

significant. Our finding of no significant difference does not mean that there was no loss. Sperm

whale interactions clearly reduced the catch because some fish were damaged (and were therefore

worthless) and other fish were presumably removed from the line. However, our result does

mean that the difference in catch is too small to estimate precisely with the current sample size

and high variability in catch per set. Factors that may lead to the high variability include spacing

between hooks on the longline, time of day, weather, and actual fish density. Therefore, the total

take of longline-caught fish by sperm whales is unknown, as is the associated total impact on the

fishery. 
11

During recent years the average weight of sablefish caught during NMFS longline cruises

in Alaska was 3.5 kg (Sigler et al. 1998). It would take 27 fish of this weight to account for the

0.095 t estimated difference in catch between sets in which sperm whales were present and absent. 

An average of 3.45 damaged fish per set were reported by observers during depredation events,

representing approximately 13% of the estimated loss. It is quite reasonable that the remaining

estimated loss of fish (23 per set) were completely removed from the hooks. 

CONCLUSION

In 1997 and 1998, sperm whale depredation of longline-caught fish was recorded in the

Gulf of Alaska. Within the Gulf of Alaska, the sperm whale/longline interaction pilot program

demonstrated a high percentage of sets during which sperm whales were observed. Whales were

present during 28.5% of the 562 sets monitored over the two years. Depredation was recorded

during 46.2% of the 160 sets in which sperm whales were present over that same period. The

whales clearly affect the longline fishery, although at this time it is not possible to assess the level

of impact. 

There was no evidence that mortality or serious injury to sperm whales was occurring as a

result of this interaction. However, in longline fisheries off South America, entanglements of

sperm whales in longline gear has been recorded. The first and only documented sperm whale

entanglement in Alaska’s longline fishery occurred in 1997 (the animal was not considered

seriously injured according to the NMFS definition; Angliss and DeMaster, 1998), providing

further impetus to continue research on the nature and magnitude of this interaction. 

ACKNOWLEDGMENTS

This project could not have been completed without the dedication of the fishery

observers who participated in the pilot program: H. Bergerund, M. Chambrone, J. Chaszar, K.
12

Clark, S. Davis, S. Evavold, G. Fadler, S. Gray, J. Hackney, E. Herr, A. Kendall, A. Kittel, M.

Kuhn, G. Larsen, R. La Torra, C. Leedy, C. Obert, J. Majewski, T. Mauer, E. Mitchell, K.

Moore, M. Piazza, J. Quenette, B. Ronco, E. Soderlund, M. Stoughton, A. Swagler, M. Todd, A.

Vanderhoeven, and M. Vechter. M. Loefflad and B. Chambers helped with obtaining access to

the NORPAC database. Ancillary data were provided by M. Sigler, T. Rutecki, M. Jackson, D.

Harris, and the International Pacific Halibut Commission. Discussions with S. Mizroch, D.

DeMaster, M. Dahlheim, and K. Teig aided in initiating the pilot program. K. Laidre, G. Duker,

and M. Perez provided technical assistance with the figures and intricacies of the NORPAC

database, respectively. This manuscript was improved with insight from M. Sigler and thoughtful

reviews provided by K. Shelden, M. Dahlheim, D. Rice, D. DeMaster, and two anonymous

reviewers. Special thanks to A. Lopez for completing final edits, formatting, and following this

document through the publication process.
13

CITATIONS

Anonymous. 1994. Report of the ad-hoc working group on incidental mortality arising from

longline fishing, p. 401-440. In Report of the Thirteenth Meeting of the Scientific

Committee (SC-CAMLR-XIII), Annex 8. Hobart, Australia. 

Angliss, R. P., and D. P. DeMaster. 1998. Differentiating serious and non-serious injury of

marine mammals taken incidental to commercial fishing operations: Report of the serious

injury workshop 1-2 April 1997, Silver Spring, Maryland. U.S. Dep. Commer., NOAA

Tech. Memo. NMFS-OPR-13, 48 p.

Ashford, J. R., P. S. Rubilar, and A. S. Martin. 1996. Interactions between cetaceans and

longline fishery operations around South Georgia. Mar. Mammal Sci. 12(3):452-457.

Barlow, J., and B. L. Taylor. 1998. Preliminary abundance of sperm whales in the northeastern

temperate Pacific estimated from a combined visual and acoustic survey. Paper

SC/50/CAWS/20 presented to the IWC Scientific Committee, Muscat, Oman. 19 p.

Capdeville, D. 1997. Interaction of marine mammals with the longline fishery around the

Kerguelen Islands (Division 58.5.1) during the 1995/96 cruise. CCAMLR Sci. 4:171-174.

Crespo, E. A., S. N. Pedraza, S. L. Dans, M. K. Alonso, L. M. Reyes, N. A. Garcia, M.

Coscarella, and A. C. M. Schiavini. 1997. Direct and indirect effects of the highseas

fisheries on the marine mammal populations in the northern and central Patagonian Coast. 

J. Northw. Atl. Fish. Sci. 22:189-207.

Dahlheim, M. E. 1988. Killer whale (Orcinus orca) depredation on longline catches of sablefish

(Anoplopoma fimbria) in Alaskan waters. U. S. Dep. Commer., NWAFC Processed Rep.

88-14, 31 p.

Gosho, M. E., D. W. Rice, and J. M. Breiwick. 1984. The sperm whale, Physeter macrocephalus. 

Mar. Fish. Rev. 46(4):54-64.

Hill, P. S., and D. P. DeMaster. 1998. Alaska marine mammal stock assessments, 1998. U.S.

Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-97, 166 p.

Kato, H., and T. Miyashita. 1998. Current status of North Pacific sperm whales and its

preliminary abundance estimates. Paper SC/50/CAWS/2 presented to the IWC Scientific

Committee, Muscat, Oman. 6 p.
14

Rice, D. W. 1978. Sperm whales, p. 82-87. In D. Haley (editor), Marine mammals of the eastern

North Pacific and Arctic waters. Pac. Search Press, Seattle, WA. 

Rice, D. W. 1989. Sperm whale, Physeter macrocephalus Linnaeus, 1758, p. 177-233. In S. H.

Ridgway and R. Harrison (editors), Handbook of marine mammals, Vol. 4, River dolphins

and larger toothed whales. Academic Press, London. 

Sigler, M. F., J. T. Fujioka, and S. A. Lowe. 1998. Sablefish, p. 219-278. In Stock assessment

and fishery evaluation report for the groundfish resources of the Gulf of Alaska as

projected for 1999. Available from North Pacific Fishery Management Council, 605 West

4

th Ave., Suite 306, Anchorage, AK, 99501.

Yano, K., and M. E. Dahlheim. 1995. Killer whale, Orcinus orca, depredation on longline

catches of bottomfish in the southeastern Bering Sea and adjacent waters. Fish. Bull.,

U.S. 93:355-372.

Zar, J. H. 1996. Biostatistical analysis. Prentice Hall. 918 p.
15

APPENDIX 1

Ancillary data
16

During 1997 and 1998 there were several other sources of data concerning sperm

whale/longline interactions in Alaska waters. The largest source in both years was the

opportunistic sighting data collected by fishery observers aboard commercial fishing vessels. In

1997 and 1998, fishery observers monitored 15,186 and 16,265 longline sets in Alaska waters,

respectively (Figs. 13 and 14). This data set includes data from all observers aboard longliners

other than those who participated in the pilot program. Observers aboard longline vessels in

Alaska waters recorded 65 sightings of sperm whales between 21 March and 4 October 1997,

including 13 instances of depredation (Fig. 19). Between 12 March and 4 November 1998,

fishery observers recorded 66 sightings of sperm whales, including 12 instances of depredation

(Fig. 19). 

Aside from fishery observer information, data were collected during an International

Halibut Commission longline survey (1997), National Marine Fisheries Service sablefish longline

surveys (1997-98), and interested commercial fishermen (1997-98). These other sources

provided 15 sightings with 8 interactions in 1997 and 24 sightings with 14 interactions in 1998

(Fig. 19). 

The positions of the sightings and interactions from all ancillary data sources for 1997 and

1998 are shown in Figures 17 and 18, respectively. In both years, there were several sightings

(with no interactions) in the Bering Sea. However, most sperm whale sightings occurred in the

Gulf of Alaska to the east of Kodiak Island even though there was substantial longline effort in

waters to the west. Descriptions of whale behavior were consistent with behaviors noted in the

pilot program data (i.e., position of whales in relation to the vessel, number of whales present,

reports of damaged fish, and whale groups following the vessel from set to set). Of note in the

ancillary data were the following observations: 1) one set in which damaged skates (Raja spp.)

were landed; 2) one set in which damaged Greenland turbot (Reinhardtius hippoglossoides) were

landed; 3) one set in which damaged halibut were landed; and, 4) the suggestion that the whales

are feeding at 40-80 fm by being able pick up and follow whales’ echo returns on the echosounder. 
17

APPENDIX 2

Photo-identification data
18

Another aspect of the pilot program included taking photographs of sperm whales which

were associated with the longline vessels while fishing. Individuals can be identified by unique

markings on the flukes or dorsal area. During 1997 and 1998, 46 photos were taken by observers

and fishermen. An additional 18 photos were provided by E. Mitchell, which were taken while

participating as a fishery observer during 1995. From these 64 photos, twenty-six individuals

have been identified. Five individuals have been photographed during different years and three

individuals have been photographed in different areas (i.e., off Southeast Alaska during one year

and near Middleton Island during another year). Increasing the sample size will enable a better

estimate of the minimum number of whales involved in predation events and the frequency of

individual whales’ predatory behavior. A sample of the interesting matches follows:
19

1a. Dorsal Fluke

12 June 1995 59° 8.3NΝ 147° 27.0NW 

1b. Dorsal Fluke

6 May 1998 59° 4.2NN 141° 27.0NW
20

 

2a. Right Dorsal 2b. Right Dorsal 

11 June 1995 59° 8.3NN 147° 27.0NW 4 June 1998 58° 39.0NN 148° 22.0NW

2c. Right Dorsal

12 June 1995 59° 8.0NN 147° 27.0NW

2d. Dorsal Fluke

11 June 1995 59° 8.5NN 147° 29.6NW
21

3a. Dorsal Fluke

11 June 1995 59° 8.5NN 147°29.6NW

3b. Ventral Fluke

3 July 1997 58°55.0NN 148° 4.0NW
22

4a. Ventral Fluke

3 July 1997 58°55.0NN 148° 4.0NW

4b. Ventral Fluke

27 May 1998 59°16.4NN 142° 5.5NW
23

 

5a. Head scars 5b. Head scars

3 July 1997 58°55.0NN 148° 4.0NW 10 May 1998 56°18.4NN 135°36.6NW 

 

5c. Ventral Fluke

3 July 1997 58°55.0NN 148° 4.0NW
Figure 1. -- Locations (black triangles) of the 557 longline sets conducted during the 1997 sperm whale/longline interaction pilot

program. Many triangles overlap because vessels tended to fish relatively small areas during a particular cruise.
25

0

50

100

150

200

250

May Jun Jul Aug Sep Oct Nov Dec

Month (1997)

Number of longline sets

Gulf of Alaska

Bering Sea

Figure 2. -- 1997 pilot program longline sets by month and region.
Figure 3. -- Locations (black triangles) of the 1,060 longline sets conducted during the 1998 sperm whale/longline interaction

pilot program. Many triangles overlap because vessels tended to fish relatively small areas during a particular cruise.
27

0

50

100

150

200

250

Mar Apr May Jun Jul Aug Sep Oct Nov

Month (1998) 

Number of longline sets

Gulf of Alaska

Bering Sea

Figure 4. -- 1998 pilot program longline sets by month and region.
Figure 5. -- Locations of the 50 sperm whale sightings recorded during longline operations in the Gulf of Alaska during 1997.

Positions of sightings (open triangles) and interactions (black triangles) are shown for North Pacific Fishery

Management Council Statistical Areas.
Figure 6. -- Locations of the 110 sperm whale sightings recorded during longline operations in the Gulf of Alaska during 1998.

Positions of sightings (open triangles) and interactions (black triangles) are shown for North Pacific Fishery

Management Council Statistical Areas.
30

Figure 7.-- Longline-caught sablefish which have been damaged by sperm whales

(photo courtesy of T. Mauer, NMFS Observer Program). Scale represents 70 cm.
31

0

2

4

6

8

10

12

14

16

18

1 2 3 4 5 6 7 8 9 10 11

Number of damaged fish

Frequency

Figure 8. -- Number of damaged fish landed during sets in which depredation on the

longline occurred. For 9 of the 74 sets where depredation occurred, the

number of damaged fish was not recorded. 
32

0 1 2 3 4 5 6

Absent Present

Sperm whales

Standardized catch (tons/1000 hooks)

Figure 9. -- Distribution of standardized catch per set (tons per 1,000 hooks) when sperm

whales were absent and present. Rectangular shaded box is the inter-quartile range

and notched area is the 95% confidence interval for the median. The brackets

represent twice the inter-quartile range and values outside are shown as individual

lines.
33

0.5

1

1.5

2

2.5

3

610-620 630-680 All

Fishing region

Tons/per 1,000 hooks

sablefish others

n= 27

n= 41

n= 68

n= 92

n= 386 n= 478

Figure 10. -- Mean catch and 95% confidence interval for sets which predominantly caught sablefish

and other species grouped by North pacific Fishery Management Council Statistical

Areas. For 16 of the 562 sets, the fish were not sampled so the 

 predominant species was unknown. 
34

0

50

100

150

200

250

300

0-100 101-200 201-300 301-400 >400

Bottom Depth (fathoms)

Number of sets

Others

Sablefish

Figure 11. -- Number of longline sets categorized by bottom depth and predominant fish

species caught.
35

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0-100 101-200 201-300 301-400 >400

Bottom depth (fathoms)

Proportion of sets with sperm whale presence

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Standardized fish catch (t/1000 hooks)

Presence

Catch

Figure 12. -- Association between bottom depth and sperm whale presence and standardized fish

catch.
36

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

610-

620

630-

680

All 610-

620

630-

680

All

Proportion of sets

Presence Interaction

Figure 13. -- Proportion of longline sets with sperm whales present and with a sperm whale 

interaction (i.e., damaged fish) grouped by North Pacific Fishery Management

Statistical Areas. The 95% confidence intervals were constructed based on a

normal approximation.

Figure 15. -- Locations (black circles) of the 16,265 longline sets monitored by fishery observers in Alaska waters during 1998.
Figure 16. -- Locations of sperm whale sightings (black circles) in Alaska waters during the period from 1958 to 1995. (Unpubl.

data from the National Marine Mammal Laboratory’s Platforms of Opportunity database).
Figure 17. -- Locations of the 80 sperm whale sightings recorded by ancillary data sources operating in Alaska waters during 1997

(see Appendix 1). Positions of fishey observer sightings (open triangles), fishery observer interactions (black

triangles), other data source sightings (open dots), and other data source interactions (black dots) are shown.
Figure 18.-- Locations of the 90 sperm whale sightings recorded by ancillary data sources operating in Alaska waters during 1998

(see Appendix 1). Positions of fishey observer sightings (open triangles), fishery observer iuteractions (black

triangles), other data source sightings (open dots), and other data source interactions (black dots) are shown.
42

53.3%

18.1%

58.3% 

 20.0%

0

10

20

30

40

50

60

70

1997 Observer 1997 Other 1998 Observer 1998 Other

Data source

Number of sightings/interactions

Interactions

Sightings

Figure 19. -- Number of sightings and interactions from ancillary data sources during 1997

and 1998. Percentages shown refer to the percentage interactions related to the

number of sightings provided by a given data source.
RECENT TECHNICAL MEMORANDUMS

Copies of this and other NOAA Technical Memorandums are available from the

National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22167

(web site: www.ntis.gov). Paper and microfiche copies vary in price. 

AFSC107 MOORE, S. E., M. E. DAHLHEIM, K. M. STAFFORD, C. G. FOX, H. W. BRAHAM, M. A. MCDONALD,

and J. THOMASON. 1999. Acoustic and visual detection of large whales in the eastern north Pacific

Ocean, 27 p. NTIS No. PB2000-101119.

106 SINCLAIR, E.H., and B. W. ROBSON. (editors). 1999. Fur seal investigations, 1997, 111 p. NTIS No.

PB2000-100223.

105 MURPHY, J. M., A.L. J. BRASE,andJ. A. ORSI. 1999. Survey of juvenile Pacific salmon in the northern

region of southeastern Alaska, May-October 1997, 40 p. NTIS No. PB99-175630.

104 SMITH, K. R., and R. A. MCCONNAUGHEY. 1999. Surficial sediments of the eastern Bering Sea

continental shelf: EBSSED database documentation, 41 p. NTIS No. PB2000-100938.

103 RUGH, D. J., M. M. MUTO, S. E. MOORE, and D. P. DEMASTER. 1999. Status review of the eastern

north Pacific stock of gray whales, 93 p. NTIS No. PB99-172678.

102 BUCKLEY, T. W., G. E. TYLER, D. M. SMITH, and P. A. LIVINGSTON. 1999. Food habits of some

commercially important groundfish off the coasts of California, Oregon, Washington, and British

Columbia, 173 p. NTIS No. PB99-166563.

101 MCELDERRY, H., W. A. KARP, J. TWOMEY, M. MERKLEIN, V. CORNISH,and M. SAUNDERS. 1999.

Proceedings of the first biennial Canada/U.S. observer program workshop, 113 p. NTIS No. PB99-

146482. 

100 SEASE, J. L., and T. R. LOUGHLIN. 1999. Aerial and land-based surveys of Steller sea lions

(Eumetopias jubatus) in Alaska, June and July 1997 and 1998, 61 p. NTIS No. PB99-140618.

99 SEASE, J. L., J. M. STRICK, R. L. MERRICK, and J. P. LEWIS. 1999. Aerial and land-based surveys

of Steller sea lions (Eumetopias jubatus) in Alaska, June and July 1996, 43 p. NTIS No. PB99-134462.

98 LAUTH, R. R. 1999. The 1997 Pacific West Coast upper continental slope trawl survey of groundfish

resources off Washington, Oregon, and California: Estimates of distribution, abundance, and length

composition, 284 p. NTIS No. PB99-133043.

97 HILL, P. S.,and D. P. DEMASTER.1998. Alaska marine mammal stock assessments, 1998, 166 p. NTIS

No. PB99-130791.

96 WING, B. L., M. M. MASUDA, C. M. GUTHRIE III, and J. H. HELLE. 1998. Some size relationships and

genetic variability of Atlantic salmon (Salmo salar) escapees capturedin Alaskafisheries, 1990-95, 32 p.

NTIS No. PB99-118697.

95 ORR, J. W., M. A. BROWN,and D. C. BAKER. 1998. Guide to rockfishes (Scorpaenidae) of the genera

Sebastes, Sebastolobus, and Adelosebastes of the northeast Pacific Ocean, 46 p. NTIS No. PB99-

114217.

94 THROWER, F., R. MARTIN, and R. HEINTZ. 1998. Effect of seawater entry date on 24-hour plasma

sodium concentrationandsurvivalofjuvenilespringchinook salmon(Oncorhynchus tshawytscha) reared

in marine net-pens, 18 p. NTIS No. PB98-173545.