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BA
CH
EL
OR
THESIS
Naturvård och Artmångfald, 180 hp
FISHERY RELATED INJURIES TO CETACEANSOFF THE NORWEGIAN COAST
Aino Ruusuvuori
Biologi, 15 hp
Halmstad 2017-09-13
1
FISHERY RELATED INJURIES TO CETACEANS OFF THE
NORWEGIAN COAST
Aino Ruusuvuori - Naturvård och artmångfald 2017.
Supervisor: Lars-Erik Widahl. External contact: Tiu Similä and Eve Jourdain.
Abstract
The fishing industry is a very important source of food and will be also used in the future.
Therefore it is essential to study the fisheries impact on marine mammals. Whales
(cetaceans) interact with fishing vessels because the catch is easy prey for them. Cetaceans
are caught everyday as bycatch and often get entangled in fishing gear. The result could be
starvation, drowning or infection of the cetacean. This study focused on injuries on dorsal
fins on orcas occurring in Norwegian waters. In Norway, Tiu Similä, Sanna Kuningas and
Norwegian Orca Survey have taken pictures and matched these to an ID-catalogue of orcas.
This ID-catalogue was used in this study. 842 pictures of individuals were categorized by the
size of the injury on the dorsal fin and the location of the nicks. Percent of total amount of
injured males and females/subadults was estimated. Females and subadults were grouped
together because of the difficulties of distinguishing the subadults from the females. 34% of
the females/subadults and 54% of the males had nicks on their dorsal fins. The amount of
damaged fins was 2% in females/subadults and 4% in males. This result was expected as my
theory was that orca males swim closer to fishing boats, than females/subadults do. The most
common location of the nicks was the upper hind part. It might be because that is the thinnest
part of the dorsal fin.
Sammanfattning
Fiskeriet är en viktig näringskälla som kommer fortsätta brukas även i framtiden och därför är
det viktigt att forska kring dess påverkan på marina mammalier. Fiskeriet påverkar arter
genom bifångst, ljud från fartygen samt minskning av arternas föda. Många valarter påverkas
negativt av fiskerinäringen, bland annat genom att de trasslar in sig i fiskenät. Valar har
anpassat sitt födosöksbeteende på grund av att fisk som faller ur när näten dras upp är enkelt
byte. Detta beteende kallas depredation. På grund av detta simmar valarna närmare fartygen
och löper större risk att få skador från dem. I Norge har Tiu Similä, Sanna Kuningas och
Norwegian Orca Survey tagit bilder av späckhuggare och matchat dessa till en ID-katalog
som användes som data i denna studie. 842 bilder har analyserats genom att placering och
storlek på skador på dorsala fenorna har undersökts. Antal skador på honor/subadulter och
hanar jämfördes. Honor och subadulter tillhörde samma grupp på grund av svårigheter att se
skillnad på dessa. Resultatet visade att 34% av honorna/subadulterna och 54% av hanarna
hade jack i sina dorsala fenor. Andel individer som hade förstörda fenor var 2% av
honorna/subadulterna och 4% av hanarna. Detta förstärkte min teori om att hanar interagerar
med fiskebåtar oftare än vad honor eller subadulter gör. Övre bakkanten av fenan var det
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ställe som var mest utsatt för jack i fenorna, gällande både honor och hanar. Det kan
diskuteras huruvida denna sektion är den mest utsatta eftersom fenan är smalast och tunnast
här.
Introduction
There are several anthropogenic caused problems that affect marine mammals today, for
instance the global warming, noise- and chemical pollution (Horsman, 2005, IWC, 2016,
Moore et al., 2006, Read, 2008). According to Halpern et al. (2008) over 40% of the world’s
oceans are considered to be medium highly to very highly affected by anthropogenic factors.
High impact areas are those near continental shelves and seas like the North and Norwegian
seas, North American eastern seaboard and the Mediterranean. Lowest anthropogenic impact
was in the Arctic and Antarctic, however the study did not count the pollution or illegal
fishing rates, which could be great in these locations (Halpern et al., 2008).
Noise from vessels disturb the communication of the cetaceans and their ability to detect
prey. PCB (polychlorinated biphenyl) accumulates through the food web and therefor the
cetaceans, and especially killer whales (Orcinus orca) (hereafter orca), have large amounts of
these pollutants in their bodies (Ford et al., 2000). Fisheries are becoming a major problem
for marine mammals and the risk of entanglement is increasing (Lewison et al., 2004a, Luque
et al., 2006). If the entanglement damages the whale too much it may lead to death and cause
the whale to flush up on the beach. In January 2016, an orca was found dead because of
entanglement in creel rope. This orca was stranded on Tiree, Scotland, and contained large
amounts of PCB - almost 100 times higher concentrations than the threshold amount for
marine mammals. High amounts of environmental toxins may lead to infertility or cancer.
This Tiree orca was 20 years old but had not given birth to any calves (Scotland’s rural
college, 2017). Orca females are usually between 12-14 years old when giving birth to their
first calf (Olesiuk et al., 2005).
Facts of toothed whales, baleen whales and the orca
Cetaceans are divided into two parvorders: Odontoceti (toothed whales) and Mysticeti (baleen
whales) depending on if they have teeth or not (Horsman, 2005).
Odontoceti hunt their prey and have between 2 and 200 teeth which are determined by
the type of prey. Echolocation a.k.a. sonar system means that whales give off sounds that
bounces from the object back to the whale. Whales use echolocation for scanning their
surroundings and communicating with other group members. Emitted sounds may be
clicking, whistling or calls. This tool has evolved further in the toothed whales than in baleen
whales and is very useable to detect e.g. fishing nets. (Ford et al., 2000).
Mysticeti have a filtering mechanism i.e. they gulp large amounts of prey and force
the water out through their mouths and baleens, which are keratinous plates with only 1-2 cm
between them. The other type of feeding mechanism is swimming with their mouths open
and filtering the prey continually (Horsman, 2005, Perrin et al., 2008).
3
The orca belongs to the parvorder odontoceti and is an apex predator, e.g. it lacks natural
enemies. It is listed as data deficient (DD) in the IUCN red list, because there is not yet
evidence if the orca should be listed as one or several species. If there was more than one
species in the taxon, some of these would probably be threatened due to human activities
(Ford et al., 2000, Hauser et al., 2007, Perrin et al., 2008, Taylor et al., 2013). Orcas are
easily recognized due to their black and white colour pattern and their dorsal fin which can
measure up to one meter. Orcas can grow up to 8.5-9.8 m in length and the males can weigh
up to 10000 kg. They live everywhere in the seas, but prefer cold temperature and subpolar
waters (Jefferson et al., 1994, Luque et al., 2006). Orcas live in matrilineal groups called
pods, which means that an older female, her offspring and the offspring of her daughters live
together (Bigg et al., 1990, Hauser et al., 2007, Hoelzel et al., 2007, Kuningas et al., 2013).
Males are either nomadic, meaning that they change pods occasionally, or more often they
occur in pods with the same female their whole life (Bisther & Vongraven, 1995). Luque et
al. (2006) observed the pod sizes to range from 3 - 40 individuals. In Norway orcas live in
groups of approximately 15 individuals according to a study made by Bisther and Vongraven
(1995). In 2003 the population of orcas off Norwegian coast was estimated to be 700
individuals (Kuningas et al., 2013). At this moment (2017) there are 862 individuals
identified (Norwegian Orca Survey, 2017).
Feeding behaviour of the orca
Orcas are omnivores that forage on herring (Clupea harrengus), salmon (Salmo salar) and
seals, amongst others (De Bruyn et al., 2012, Foote et al., 2009, Luque et al., 2006). In
northern Norway the orca usually feed on small shoals of spring spawning herring in ground
water (Similä, 2005). Orcas are either resident, which usually feed on fish, or transient, which
prefer marine mammals (Bigg et al., 1990, De Bruyn et al., 2012, Jefferson et al., 1994). Near
Marion island (located in the Southern Indian ocean) the orcas were most often very close to
the shore, over 50% of the observed orcas were closer than 5 metres. This is probably due to
great amounts of prey in these areas (Keith et al., 2001).
In a study done in Eastern North Pacific they found that the genetic diversity between orcas is
very small. Between transient and resident populations the difference was 1%. The variety
suggests that orcas breed only in their pods and that the difference in foraging behaviour
prevent these two groups from mating (Hoelzel et al., 1998). Orcas cooperate when
predating, to make the localization and predation more efficient (Hoelzel et al., 2007,
Horsman, 2005, Similä, 2005). They use tail slaps towards patches of herring to make the
herring unconscious and easier to prey upon. Groups of orcas can encircle shoals of herring
and force them towards the surface in a ball formation. This behaviour is called carousel
feeding and was increasing in 1995-1999 in Norway, probably due to the herring changed
their wintering regions from Tysfjord and Ofotfjord to Vestfjord. This location has fewer
underwater elevations which enhance the behaviour of carousel feeding (Domenici et al.,
2000, Similä, 2005).
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Interactions between fishery and cetaceans
In the beginning of 1900 the fishing catches in Europe was approximately 2 million tons and
started rising to 5.6 million tons in 1938. After the two world wars, the catch rates rose to 12
million tons in the 1960s (Sahrhage & Lundbeck, 1992). Around year 1990 the amount of
nicks on dorsal fins on orcas off Norway increased, which was probably due to the orcas
interacted more with fisheries than they do today (Kuningas et al., 2013). The fishing
industry in Norway is one of the greatest in Europe (FAO, 2016). The herring catches in
Norway were 3.2 million tons in 1965, but went a rapid decline in early 1970s, when the
catches dropped to around 900,000 tons, because of overexploitation. Because the herring
was at low levels the fishing industry changed its target to other species, e.g. mackerel
(Scomber scombrus) and the catch rates of all pelagic species in Norway became 6 million
tons in 1976 (Sahrhage & Lundbeck, 1993). Today the total fishing rates in Norway are
approximately 2 million tons, which is a decrease of 12 per cent since 2016 (Eurostat, 2017).
In Norway the fishing for spring spawning herring is done with ‘purse seine’ which is a net
that encircles the herring and have a line at the bottom of the net, that can be tightened in a
way where the net forms a bag (Lewison et al., 2004a, Sahrhage & Lundbeck, 1992, Schmidt,
no date). The only species that is known to be bycaught in these fisheries is saithe (Pollachius
virens) (The Norwegian Ministry of Trade, Industry and Fisheries, 2013).
When the fishing activity got more intense the interactions between fishery and cetaceans
increased. Entanglement in fishing gear and bycatch became a problem. Also interactions
with the boats and propellers started being dangerous for the animals. The dropping fish
when nets are dragged in are easy prey for cetaceans (Similä, 2005). The behaviour of
predating on fish from fishing nets is called depredation (Horsman, 2005, Read, 2008, Wells
et al., 2008).
Right whales (Eubalaena, Mysticeti) swim with their mouths open when feeding and this
forms a hydrostatic force, which sucks the prey into the throat of the whale and
simultaneously push the water out. Because of this the right whale can pull a lot of fishing
lines into its filtering system. Many populations of mysticeti are threatened and have
difficulties to increase in number due to entanglement (Cassoff, et al. 2011, Perrin et al.,
2008).
In New Zealand waters orcas caught school sharks (Gaelorhinus galeus) and bluenose
(Hyperoglyphe antarchia) from long-lines and dahn-lines. These nets consists of hooks,
sinkers and floats. When feeding the orcas pulled carefully the shark by its tail until it popped
off the line (Visser, 2000). In Norway the foraging strategies of orcas changed to sites where
catching of herring occurred. In 2000-2001 evidence showed that orcas followed ships in
evenings and nights when the catch was dragged in. In these cases there was a noticeable loss
of catch (Luque et al., 2006, Read, 2008, Similä, 2005). In a study done by Visser (2000)
fishermen indicated a loss of 5-10% of the catch per each line, when orcas were present.
5
Injuries from interactions with fishing gear or - vessels could affect the whale in several
ways. Previous studies have categorized injured whales after “serious injury” and “non-
serious injury”. For this categorization to be applied there have to be visible gear or hooks or
fractures on the whales. For an injury to be serious, it should lead to death or disturb the
reproduction. Disfigurement or missing of a dorsal fin could be a serious injury, depending
on the case. Bottlenose dolphins usually survive cuts in the dorsal fins and there are no
evidence that orcas would die from these either (NMFS, 2012, Wells et al., 2008).
Entanglement, bycatch and ingestion of fishing gear
Entanglement in fishing lines is the biggest threat to cetaceans today. Around 300,000
cetaceans perish each year because of entanglement (IWC, 2016, Moore & Van der Hoop,
2012, Moore et al., 2006, Read, 2008). Typical causes of death when entangled are drowning,
infections and starving (Cassoff et al., 2011, Moore & Van der Hoop, 2012). Marine
mammals have been observed to get entangled in fishing lines and nets and also ingesting
hooks (Wells et al., 2008). Salmon (Salmonidae), cod (Gadidae) and monkfish (Lophius) are
caught by gill nets, which are large nets that form a wall from the open water mass to the
bottom of the sea. These are the nets that cetaceans entangle most often in (Brown, 2016,
Marsh et al., 2002, Read et al., 2006). Cetaceans may get entangled by any part of their body,
but the most common part is the mouth. According to Cassoff et al. (2011) 67% of the
studied baleen whales were entangled in their mouths and starving was the most common
cause of death in these whales. Drowning is usually acute and the cetaceans that most often
experience this are juveniles, probably because they are not strong enough to disentangle
themselves (Cassoff et al., 2011).
Some mammals die because of entanglement, but the process is not always fast. When
entanglement damages the muscles of the cetacean, the muscles may heal but the
development of new muscle tissue and skin is very slow (Moore et al., 2006, Wells et al.,
2008). The period from being entangled to actually dead can last months. The average
duration before a right whale dies due to entanglement is 5.6 months. A North Atlantic right
whale (Eubalaena glacialis) was entangled for 320 days before it died due to starvation
(Cassoff et al., 2011, Moore et al., 2006, Wells et al., 2008).
Entanglement is also very energy requiring and affects the movement of the cetacean. Van
der Hoop et al. (2016) showed that when a right whale was entangled it spent as much energy
as a cetacean would need for feeding, migration or for carrying her calf. Two right whales
were studied when they were diving entangled versus non-entangled. One of the whales
swam slower both when descending and ascending, when it dragged gear. The other one
descended faster when entangled, but had the same speed when it ascended. If the whale was
forced to drag the gear for months it compensated the locomotion, which could later lead to
disfigurements in the muscles or skeleton (Van der Hoop et al., 2017).
6
Bycatch has lead to a decrease in many marine mammal species like the vaquita (Phocoena
sinus), the Mediterranean striped dolphins (Stenella coeruleoalba) and North Atlantic
harbour porpoises (Phocoena phocoena) (Lewison et al., 2004a). There is no agreed
definition of the word bycatch, but according to Alverson et al. (1994) bycatch means; 1)
species that are caught and later sold, 2) species that are discarded and 3) species that are
non-target but are sold or discarded. The term can be diffuse because sometimes fishermen
have no target species or do not report their bycatch (Alverson et al., 1994 Read et al., 2006).
Approximately 27 million tons of non target species are discarded globally every year.
Between 1990-1999 the amount of cetaceans as bycatch was around 3000 annually in US
waters (Alverson et al., 1994, Read et al., 2006). The Hawaii and American Samoa longline
fisheries were considered (2016) to be responsible for injuries on 89 out of 101 mammals that
interacted with fisheries in these locations (Bradford & Forney, 2016).
Ingestion of fishing gear is often lethal for the mammal because it can damage the interior
organs. In a study of bottlenose dolphins (Tursiops truncatus) seven out of twelve ingestion
cases lead to death of the animal. Four out of five dolphins died because of that the gear was
embedded in tissue. The dolphins that had embedded gear lost up to 27% of their weight in a
couple of weeks (Wells et al., 2008).
The aim of this study
The interactions between fishery and cetaceans is a very important topic at this moment,
because of the decline in many species (Lewison et al., 2004a, Read, 2008). There are very
few articles in the subject of estimating sizes and amount of nicks on the dorsal fins of
cetaceans worldwide. Baird and Gorgone (2005) studied false killer whales (Pseudorca
crassidens) interacting with longline fisheries and Visser (1998) wrote a report of orcas that
had scarring on their bodies or bent dorsal fins. This study area is very important because the
impact of the fishery on marine mammals has not been getting enough attention. To estimate
strategies for protecting the orca, there should be information about how orcas are affected of
fisheries. At this moment studies with solutions to the interactions between fisheries and
whales, are limited (Jefferson & Curry, 1996). The aim of this study is to estimate the amount
of dorsal fins that are injured and the size of these injuries, on orcas occurring off the islands
of Vesterålen, Norway. It is also relevant to find out if orca males get more often injured
because they tend to swim closer to the fishing boats. This study will be a good approach for
continuing the studies about fishery related injuries on cetaceans off the Norwegian coast.
Materials and methods
Tiu Similä started producing an ID-catalogue of orcas occurring off the coast of Norway in
the 1980s. In 2007 Sanna Kuningas and later the Norwegian Orca Survey have continued and
updated Similä’s work (Norwegian Orca Survey, 2016). Looking at nicks on the dorsal fins,
buckles on the bodies and scratches on the saddle patches on the back of the whales, a
matching of pictures with identities could be made.
7
For the analysis of the fins, sharp pictures, where the whale was parallel to the photographer,
were prioritized from the ID-catalogue. The dorsal fins in the 842 pictures were analyzed and
categorized as 1) Smooth fins, 2) Nicked fins and 3) Damaged fins (figure 1). Only pictures
with clear visual nicks were included in the “Nicked fins” category for the importance of
being consistent. A fin that was estimated to be >10% damaged or contained 7 nicks or more,
were categorized as “Damaged fins”. Each fin was divided into 6 sections; 1) refers to the
anterior apical section, 2) the anterior central section, 3) the anterior proximal section, 4) the
posterior apical section, 5) the posterior central section and 6) the posterior proximal section
(figure 2). The orcas in the catalogue were divided into males or females/subadults, because
of the difficulties of distinguishing the subadults from the females, due to same-sized dorsal
fins. Juveniles were excluded from the study because of the absence of permanent marks on
their bodies and fins.
Figure 1. Categorization; 1) Smooth fin, 2) Nicked fin and 3) Damaged fin. Picture: Norwegian Orca
Survey.
Figure 2. Division of a dorsal fin into sections (1-3 front, 4-6 back).
8
A comparison of amount of injured males and females/subadults was made. In the “Nicked
fins” category the location of the nick was noted and an average amount of nicks per dorsal
fin was counted.
Results
Fins of 370 females/subadults and 472 males were studied and categorized. 34% of the
females/subadults and 54% of the males had nicks on their dorsal fins. 2% of the
females/subadults and 4% of the males had damaged fins (figure 3).
The average amount of nicks on fins of females/subadults was 1.4 ± 0.6 nicks. On males the
average number of nicks were 2 ± 1.2 per individual. The most common location of the nicks
was the upper hind part of the fin on both females/subadults and males (figure 4). Of the 9
females/subadults that had damaged fins, one had a bent fin and of the 18 males, 5 had bent
fins.
Figure 3. Number of individuals in each category. Black = females/subadults, grey = males.
Figure 4. The amount of nicks (in percent) located to the different fin sections.
9
Discussion
This research suggests that the males get more nicks and damage than the females/subadults
do. Males could get injuries from interactions with fishing boats, because they supposingly
swim closer to these than the females/subadults do, or from intrasexual competition. If the
damage is extensive on the dorsal fin it can affect the balance of the orca when swimming
fast, but is usually not life threatening (Fish, 2002).
4% of the males and 2% of the females had major damage on their dorsal fins which could
not be caused by other orcas and is probably from interactions with the propellers from the
boats or entanglement in the fishing gear. 34% of the females/subadults and 54% of the males
had nicks on their dorsal fins, which could be caused by either other orcas or fishery. This
shows that there are not many orcas in the population off the islands of Vesterålen, that have
serious injury on their dorsal fins. This means that the interactions with fisheries are not yet a
major problem. The section that was most exposed to damage was the upper hind part of the
fin. It might be because of it is the uppermost and thinnest part of the fin. According to
Kuningas et al. (2013) orca males have higher mortality rates than females, which could be
because they approach fishing boats more often.
Orcas and other cetaceans have been observed to collide with vessels and that could lead to
damage or even death of the mammal (Horsman, 2005, Lusseau et al., 2009). In a New
Zealand population two out of 117 orcas had scars from propellers. These two had healed
despite large wounds on their backs. A third juvenile orca had collided with a boat and its
injuries were too extensive for it to survive (Visser, 1999). George et al. (1994) found that
only 1% of the bowhead whale (Balaena mysticetus) population of the Bering-Chukchi-
Beaufort seas had marks from collisions with vessels. In this study there could not be drawn a
conclusion that any of the orcas had collided with vessels, due to excluding analysis of the
body of the orca.
According to Keith et al. (2001) only 58% of the orcas had features that helped with
identification (for instance injuries on the dorsal fins). In this study the amount of injured fins
was 36% and 58% of females/subadult and males respectively, but other attributes were not
taken into account (e.g. marks on the body). Fishermen usually do not report when orcas are
being caught into the purse seiner nets, these reports are almost exclusively made when there
are observers present on the boats (Lewison et al., 2004b, Kuningas et al., 2013). In the Strait
of Gibraltar orcas were seen interacting with fishing gear 99% of the time, when vessels were
nearby the orca population (Esteban et al., 2016).
Studies of other species than orcas, having entanglement damages are also limited. According
to Moore et al. (2006) 75% of the Northern Atlantic right whale population had wounds from
entanglement. Baird and Gorgone (2005) studied the amount of wounds or damage caused by
fisheries on the false killer whale (Pseudorca crassidens) off Hawaii. 3.75% of the study
group had major damage which meant that the dorsal fin was completely missing, completely
10
bent or partly bent (Baird & Gorgone 2005). In 1999 22.3% of male orcas had collapsing,
collapsed or bent fins in New Zealand waters. Similä had commented that this percentage
was 0.57% off the coast of Norway (Visser, 1998). In this study group 0.27% of the
females/subadults and 1.9% of the males have bent fins.
Because of the lack of data from orcas being bycaught, the estimation of how many orcas
actually are affected by fisheries is impossible to make. The result of the amount of injured
orcas could be misleading because of the uncertainty if the damages and nicks are from
fishery interactions. Injuries could be from other orcas, from stress or the damages could be
natural. However, according to Bisther and Vongraven (1995) aggressive competition has not
been observed between orca males. Orcas have difficulties to bite deep on large items
because their jaws do not open wide enough (McCann, 1974). In a study done by Visser
(1998) there were two out of 125 orcas that had scarred bodies and these marks were
probably from intrasexual competition.
Apart from direct contact or accidental collisions that has led to injuries, fishing vessels may
cause other problems to marine mammals, such as they have been observed to affect the
foraging behavior of orca pods on the west coast of Washington. When boats were up to 400
m from the orcas their foraging decreased (Lusseau et al., 2009). Fisheries may also lead to a
decrease of the prey of the mammal. This is the most typical kind of competitive interaction
between fisheries and marine mammals (DeMaster et al., 2001).
There have been several attempts to solve the problem where marine mammals interact with
nets, but not many are proven useable (NOAA, 2001, Visser, 2000, Jefferson & Curry, 1996).
It is assumed that marine mammals cannot see the nets and therefore this study area is very
important (Jefferson & Curry, 1996). In Norway there are no documented measures for
reducing or completely remove the interactions between fishery and cetaceans. There are
records of shooting those marine mammals that come near the fishing boats, or for preventing
interactions. Shooting has not been proven to prevent interactions and is now illegal
(Jefferson & Curry, 1996, Pemberton & Shaughnessy, 1993, Visser, 2000). Another drastic
method is sealbombs which are explosives that give off a loud noise and a flash of light when
dropped in water. These bombs are used to scare off mainly seals but also other species that
could reduce the catch. These can injure both the mammals and the users if they are used in
an incorrect way (Jefferson & Curry, 1996, Pemberton & Shaughnessy, 1993, Visser, 2000).
To scare off cetaceans, acoustic alarms or “pingers” have been used. These are attached to
gillnets and give out a high frequency noise (Cox et al., 2003, Jefferson & Curry, 1996). Cox
et al. (2003) studied the rate of bycatch of bottlenose dolphins (Tursiops truncatus) in
presence of active pingers versus without active pingers. They observed a reduction of
interactions with the gillnets when the pingers were active. However the marine mammals
could adapt to the sound or even link the sound to fish, therefore this method is not yet
proved to work (Cox et al., 2003, Jefferson & Curry, 1996). Marine mammals often react to
boat noises and Pemberton and Shaughnessy (1993) confirmed that seals attacked fishing
11
farms more seldom when chased by boats to keep their distance, than when they were shot at
(Jefferson & Curry, 1996, Pemberton & Shaughnessy, 1993). Orcas however, may associate
the sound of fishing vessels with food and therefore get too close to the vessels. In ethology
this is a behaviour usually called associative learning (Reece et al., 2011). In Alaska there has
been attempts to make the fishing more quiet by using bubble screens or rubber pads to lower
the noise from the engine. These methods are still under investigation (Jefferson & Curry,
1996). Some fishing gear have been made thinner for cetaceans to be able to disentangle
quicker (Moore et al., 2006).
There have been some attempts to disentangle whales (Moore, 2010, NOAA, 2001). Sedation
doses were given to some right whale individuals that probably would have died if not
disentangled. This selection of individuals was made because there were no studies done
before to ensure that the method would not kill the whale. When the whale was sedated the
study group cut the fishing gear and afterwards the whale swam faster and its respiration got
better (Moore, 2010).
In contrast to the orcas occurring off the coast of Norway, depredation may be vital for some
cetacean species, especially the ones with few individuals left (Read, 2008). Because of the
importance of depredation for those species, further studies should be made before doing
drastical decisions about keeping the whales completely isolated from interactions with
fisheries.
There are not much data from pelagic cetaceans and this makes it difficult to estimate the
impact of the fishery on these mammals (DeMaster et al., 2001). For the future it would be
important to be able to distinguish the difference between injuries made from natural causes
versus from fishery interactions. Further studies concerning close encounters between
cetaceans and fishing vessels should be made before excluding their injuries as results from
contacts with fishing vessels and fishing gear. Observers that report bycatch or entanglements
are necessary to estimate the amount of interactions (Lewison et al., 2004b). These studies
could help in backing up the decision that fishery should go through a major change. The
manufacturing of fishing gear should develop to avoid disappearance of other marine
mammal species (Moore et al., 2006).
Conclusions
The fishing industry provides the living of 56.6 million (2014) people worldwide and is very
important for a lot of people (FAO, 2016). In opposition to Norway, a majority of fishermen
are underprivileged and therefore do not have the possibility to modify their fishing strategies
to suit the conservation of cetaceans. Fishermen overall are not eager to report bycatch which
leads to a conflict between them and ecology conservationists (Lewison et al., 2004b). This
study field is important for maintaining the biodiversity in the seas. All links in the ecosystem
plays significant roles and if one organism disappears it could lead to great disruptions.
12
There are only a few other studies that have researched injured orcas (Visser, 1999), therefore
further investigations should be done before making any permanent conclusions about how
threatened orcas actually are. Studying this area is uncommon and therefore this research is a
great start for continuing the investigations of the impact of fishery on cetaceans. The injuries
on dorsal fins in this study could be from fishing gear, collisions with fishing vessels or from
intrasexual competition. However the conclusion could be drawn that larger damages on the
fins are from vessels or fishing gear. Orcas cannot open their mouths wide and they are not
aggressive to their pod members, therefore larger injuries from intrasexual competition are
not likely (Bisther & Vongraven, 1995, McCann, 1974). Because the males in this study had
more injuries on their dorsal fins than the females/subadults, I conclude that male orcas injure
orcas of the same sex more often and interact more often with fisheries. The small amount of
orcas that had majorly damaged fins shows that the population off the islands of Vesterålen
are not acute threatened by fisheries in these waters.
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